Biology Junction Team - BIOLOGY JUNCTION

Protein Degradation

Information for the Public
Nobel Prize in Chemistry
6 October 2004

Discovery of Ubiquitin-Mediated Protein Degradation

A human cell contains some hundred thousand different proteins. These have numerous important functions: as accelerators of chemical reactions in the form of enzymes, as signal substances in the form of hormones, as important actors in the immune defense and by being responsible for the cell’s form and structure. This year’s Nobel Laureates in chemistry, Aaron Ciechanover, Avram Hershko and Irwin Rose, have contributed ground-breaking chemical knowledge of how the cell can regulate the presence of a certain protein by marking unwanted proteins with a label consisting of the polypeptide ubiquitin. Proteins so labeled are then broken down – degraded – rapidly in cellular “waste disposers” called proteasomes.

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Through their discovery of this protein-regulating system Aaron Ciechanover, Avram Hershko and Irwin Rose have made it possible to understand at molecular level how the cell controls a number of very important biochemical processes such as the cell cycle, DNA repair, gene transcription and quality control of newly-produced proteins. New knowledge of this form of controlled protein death has also contributed to explaining how the immune defense functions. Defects in the system can lead to various diseases including some types of cancer.

Proteins labeled for destruction

Degradation needs no energy – or does it?

While great attention and much research have been spent on understanding how the cell controls the synthesis of a certain protein – at least five Nobel Prizes have been awarded in this area – the reverse, the degradation of proteins, has long been considered less important. A number of simple protein-degrading enzymes were already known. One example is trypsin, which in the small intestine breaks down proteins in our food to amino acids. Likewise, a type of cell organelle, the lysosome, in which proteins absorbed from outside are broken down, had long been studied. Common to these processes is that they do not require energy in order to function.

Experiments as long ago as the 1950s showed, however, that the breakdown of the cell’s own proteins does require energy. This long puzzled researchers, and it is precisely this paradox that underlies this year’s Nobel Prize in Chemistry: that the breakdown of proteins within the cell requires energy while other protein degradation takes place without added energy. A first step towards an explanation of this energy-dependent protein degradation was taken by Goldberg and his co-workers who in 1977 produced a cell-free extract from immature red blood cells, reticulocytes, which catalyze the breakdown of abnormal proteins in an ATP-dependent manner (ATP = adenosine triphosphate – the cell’s energy currency).

Using such an extract Aaron Ciechanover, Avram Hershko and Irwin Rose, in a series of epoch-making biochemical studies in the late 1970s and early 1980s, succeeded in showing that protein degradation in cells takes place in a series of step-wise reactions that result in the proteins to be destroyed being labeled with the polypeptide ubiquitin. This process enables the cell to break down unwanted proteins with high specificity, and it is this regulation that requires energy. As distinct from reversible protein modifications such as phosphorylation (Nobel Prize in Physiology or Medicine 1992), regulation through polyubiquitination is often irreversible since the target protein is destroyed. Much of the work was done during a series of sabbatical leaves that Avram Hershko and Aaron Ciechanover of the Technion (Israel Institute of Technology) spent with Irwin Rose at the Fox Chase Cancer Center in Philadelphia, USA.

The label is ubiquitin

The molecule that would later prove to be the label that marks out a protein for degradation was isolated as early as 1975. This 76-amino-acid-long polypeptide was isolated from calf sweetbread and was assumed to participate in the maturation of white blood cells. Since the molecule was subsequently found in numerous different tissues and organisms – but not in bacteria – it was given the name ubiquitin (from Latin ubique, “everywhere”) (fig. 1).

Fig 1. Ubiquitin – a common polypeptide that represents the “kiss of death”.

The discovery of ubiquitin-mediated protein degradation

After taking his doctorate, Avram Hershko had studied energy-dependent protein degradation in liver cells, but decided in 1977 to transfer to the reticulocyte extract described above. This extract contained large quantities of hemoglobin, which upset the experiments. In their attempts to remove the hemoglobin using chromatography, Aaron Ciechanover and Avram Hershko discovered that the extract could be divided into two fractions, each inactive on its own. But it turned out that as soon as the two fractions were recombined, the ATP-dependent protein degradation restarted. In 1978 the researchers reported that the active component of one fraction was a heat-stable polypeptide with a molecular weight of only 9000 which they termed APF-1 (active principle in fraction 1). This protein later proved to be ubiquitin.

The decisive breakthrough in the research was reported in two works that Ciechanover, Hershko and Rose published in 1980. Until that time the function of APF-1 was entirely unknown. In the first work it was shown that APF-1 was bound covalently, i.e. with a very stable chemical bond, to various proteins in the extract.

In the second work it was further shown that many APF-1 molecules could be bound to the same target protein; the latter phenomenon was termed polyubiquitination. We now know that this polyubiquitination of substrate proteins is the triggering signal that leads to degradation of the protein in the proteasome. It is this reaction that constitutes the actual labeling, the “kiss of death” if you will.

At a stroke, these entirely unanticipated discoveries changed the conditions for future work: it now became possible to concentrate on identifying the enzyme system that binds ubiquitin to its target proteins. Since ubiquitin occurs so generally in various tissues and organisms, it was quickly realized that ubiquitin-mediated protein degradation must be of general significance for the cell. In addition, the researchers guessed that the energy requirement in the form of ATP enabled the cell to control the specificity of the process.

The field was now open and between 1981 and 1983 Ciechanover, Hershko, Rose and their post docs and students developed “the multistep ubiquitin-tagging hypothesis” based on three newly-discovered enzyme activities they termed E1, E2 and E3 (fig. 2). We now know that a typical mammalian cell contains one or a few different E1 enzymes, some tens of E2 enzymes and several hundred different E3 enzymes. It is the specificity of the E3 enzyme that determines which proteins in the cell are to be marked for destruction in the proteasomes.

Fig 2. Ubiquitin-mediated protein degradation

The E1 enzyme activates the ubiquitin molecule. This reaction requires energy in the form of ATP.
The ubiquitin molecule is transferred to a different enzyme, E2.
The E3 enzyme can recognize the protein target which is to be destroyed. The E2-ubiquitin complex binds so near to the protein target that the actual ubiquitin label can be transferred from E2 to the target.
The E3 enzyme now releases the ubiquitin-labeled protein.
This last step is repeated until the protein has a short chain of ubiquitin molecules attached to itself.
This ubiquitin chain is recognized in the opening of the proteasome. The ubiquitin label is disconnected and the protein is admitted and chopped into small pieces.

All the studies up to this point had been done in cell-free systems. To be able to study the physiological function of ubiquitin-mediated protein degradation as well, Avram Hershko and his co-workers developed an immunochemical method. By using antibodies to ubiquitin, ubiquitin-protein-conjugate could be isolated from cells where the cell proteins had been pulse-labeled with a radioactive amino acid not present in ubiquitin. The results showed that cells really break down faulty proteins using the ubiquitin system, and we now know that up to 30% of the newly-synthesized proteins in a cell are broken down via the proteasomes since they do not pass the cell’s rigorous quality control.

The proteasome – the cell’s waste disposer

What is a proteasome? A human cell contains about 30,000 proteasomes: these barrel-formed structures can break down practically all proteins to 7-9-amino-acid-long peptides. The active surface of the proteasome is within the barrel where it is shielded from the rest of the cell. The only way in to the active surface is via the “lock”, which recognizes polyubiquitinated proteins, denatures them with ATP energy and admits them to the barrel for disassembly once the ubiquitin label has been removed. The peptides formed are released from the other end of the proteasome. Thus the proteasome itself cannot choose proteins; it is chiefly the E3 enzyme that does this by ubiquitin-labeling the right protein for breakdown (fig. 3).

Fig 3. The cell’s waste disposer, the proteasome. The black spots indicate active, protein-degrading surfaces.

More recent research

While the biochemical mechanisms underlying ubiquitin-labeled protein degradation were laid bare around 1983 its physiological significance had not yet been fully understood. That it is of importance in destroying defective intracellular proteins was known but, to proceed, a mutated cell was needed in the ubiquitin system. By studying in detail how the mutated cell differs from a normal cell under various growth conditions, it was hoped to gain a better idea of what reactions in the cell depend on the ubiquitin system.

A mutated mouse cell had been isolated in 1980 by a research group in Tokyo. Their mouse-cell mutant contained a protein that, because of the mutation, was sensitive to temperature. At lower temperatures the protein functioned as it should, but not at higher. Cells cultured at the higher temperature stopped growing. In addition, they showed defective DNA synthesis and other erroneous functions at the higher temperature. Researchers in Boston quickly showed that the heat-sensitive protein in the mutant mouse cell was the ubiquitin-activating enzyme E1. Obviously, ubiquitin activation was necessary for the cell to function and reproduce itself at all. Controlled protein breakdown was not only important for degrading incorrect proteins in the cell but it probably also took part in control of the cell cycle, DNA replication and chromosome structure.

Since the late 1980s a number of physiologically important substrates for ubiquitin-mediated protein breakdown have been identified. Only a few of the most important will be mentioned here.

Prevention of self-pollination in plants

Most plants are bisexual, hermaphroditic. Self-pollination leads to a gradual decline in genetic diversity which in the long run can cause the whole species to die out. To prevent this, plants use ubiquitin-mediated degradation to reject “own” pollen. The exact mechanism has not yet been clarified but the E3 enzyme has been encountered and when proteasome inhibitors have been introduced, the rejection has been impaired.

Regulation of the cell cycle

When a cell is to make a copy of itself, many chemical reactions are involved. In a human being, six thousand million base pairs must be duplicated in DNA. These are gathered in 23 chromosome pairs that must be copied. Ordinary cell division, mitosis, and the formation of sex cells, meiosis, have many points of contact with the subjects of this year’s Nobel Prize. The E3 enzyme responsible, a protein complex termed the “anaphase-promoting complex” (APC) checks that the cell goes out of mitosis. This enzyme complex has also proved to play an important role in the separation of the chromosomes during mitosis and meiosis. A different protein complex acts like a rope around the chromosome pair, holding it together. At a given signal, the APC labels an inhibitor of a certain protein-degrading enzyme, whereupon the inhibitor is carried to the proteasome and destroyed. The enzyme is released, is activated and cuts the rope around the chromosome pair. Once the rope is gone, the chromosome pair can be separated. Incorrect chromosome division during meiosis is the commonest cause of spontaneous miscarriage during pregnancy, and an extra chromosome 21 in humans leads to Down’s syndrome. Most malignant tumors have cells with changed numbers of chromosomes as a result of incorrect chromosome division during mitosis.

DNA repair, cancer and programmed cell death

Protein p53 has been dubbed “the guardian of the genome” and it is a tumor-suppressor gene. This means that as long as a cell can produce p53 the development of cancer is hampered. Sure enough, the protein is mutated in at least 50% of all human cancer. The amount of protein p53 in a normal cell is low in consequence of continual production and breakdown. The breakdown is regulated through ubiquitination and the E3 enzyme responsible forms a complex with protein p53. Following DNA injury, protein p53 is phosphorylated and can no longer bind to its E3 enzyme. The breakdown stops and the quantity of p53 in the cell rises rapidly. Protein p53 acts as a transcription factor, i.e. a protein that controls the expression of a certain gene. Protein p53 binds to and controls genes that regulate DNA repair and programmed cell death. Raised levels of protein p53 lead first to interruption of the cell cycle to allow time for repair of DNA damage. If the damage is too extensive the cell triggers programmed cell death and “commits suicide”.

Infection with human papilloma virus correlates strongly to the occurrence of cervical cancer. The virus avoids the protein p53 control function through one of its proteins activating and changing the recognition pattern of a certain cellular E3 enzyme, E6-AP, which is tricked into ubiquitinating the protein p53, which is totally destroyed. In consequence of this the infected cell can no longer repair DNA damage in a normal manner or trigger programmed cell death. The DNA mutations increase in number and this can ultimately lead to the development of cancer.

Immune and inflammatory reactions

A certain transcription factor regulates many of the genes in the cell that are important for immune defense and inflammatory reactions. This protein, the transcription factor, occurs bound to an inhibitor protein in the cytoplasm of the cell, and the bound form of the transcription factor lacks activity. When cells are exposed to bacteria or various signal substances, the inhibitor protein is phosphorylated, and this results in its being ubiquitinated and broken down in the proteasome. The released transcription factor is transported to the cell nucleus where it binds to, and activates the expression of, specific genes.

The ubiquitin-proteasome system also produces the peptides that are presented by the immune defense on the surface of a virus-infected cell by breaking down virus proteins to suitable sizes. T lymphocytes recognize these peptides and attack the cell as an important part of our defense against virus infections.

Cystic fibrosis (CF)

The hereditary disease cystic fibrosis, CF, is caused by a non-functioning plasma membrane chloride channel called CFTR, the “cystic fibrosis transmembrane conductance regulator”. Most CF patients have one and the same genetic damage, loss of the amino acid phenylalanine in the CFTR protein. The mutation causes faulty folding of the protein and this in turn leads to the protein being retained in the cell’s control system for protein quality. This system ensures that the incorrectly folded protein is destroyed through ubiquitin-mediated protein breakdown instead of being transported out to the cell wall. A cell with no functioning chloride channel can no longer transport chloride ions through its wall. This affects secretion in, among other organs, the lungs and leads to the accretion of thick phlegm in the lungs which impairs their function, greatly increasing the risk of infection.

The ubiquitin system has become an interesting area of research for medicines against various diseases. Such preparations can be aimed at components of the ubiquitin-mediated breakdown system to prevent the degradation of specific proteins. They can also be designed to cause the system to destroy unwanted proteins. A medicine already being tested clinically is the proteasome inhibitor Velcade (PS341) which is used against multiple myeloma, a cancer disease that affects the body’s antigen-producing cells.

This year’s Laureates have explained the molecular background to a protein regulation system of great importance for all higher cells. New cell functions controlled by ubiquitin-mediated protein degradation are being discovered all the time and this research is being conducted in numerous laboratories all over the world.

The Laureates

Aaron Ciechanover

Technion (Israel Institute of
Technology)
Rappaport Institute
1 Efron Street
P.O. Box 9697
Haifa 31096
Israel

Israeli citizen. Born 1947 (57 years) in Haifa, Israel. Doctor’s degree in medicine in 1975 at Hebrew University of Jerusalem, and in biology in 1982 at the Technion (Israel Institute of Technology), Haifa. Distinguished Professor at the Center for Cancer and Vascular Biology, the Rappaport Faculty of Medicine and Research Institute at the Technion, Haifa, Israel.

Avram Hershko

Technion (Israel Institute of Technology)
Rappaport Institute
1 Efron Street
P.O. Box 9697
Haifa 31096
Israel

Israeli citizen. Born 1937 (67 years) in Karcag, Hungary. Doctor’s degree in medicine in 1969 at the Hadassah and the Hebrew University Medical School, Jerusalem. Distinguished Professor at the Rappaport Family Institute for Research in Medical Sciences at the Technion, Haifa, Israel.

Irwin Rose

Dept. of Physiology and Biophysics
College of Medicine
University of California, Irvine
Irvine, CA 92697
USA

American citizen. Born 1926 (78 years) in New York, USA. Doctor’s degree in in 1952 at the University of Chicago, USA. Specialist at the Department of Physiology and Biophysics, College of Medicine, University of California, Irvine, USA.

Illustrations: Typoform

Source: http://nobelprize.org/nobel_prizes/chemistry/laureates/2004/press.html

Preap Fungi Study Guide

Fungi Review

1. Fungi Differ from plants in important ways: Fungi Lack _______________________ and are Not _______________________________. Fungi Never Reproduce by _____________________. The cell walls of fungi are made of ___________________, not __________________________, as are the cell walls of Plants.

2. _____________________, a tough, flexible material, also makes up the hard outer skeleton of insets.

3. Fungi have FOUR Characteristics in common:

A.___________________________________________________________________
B.___________________________________________________________________
C.___________________________________________________________________
D.___________________________________________________________________

4. All fungi are ______________________________, obtaining their nutrition from other organisms.

5. Most fungi are ______________________________ and obtain their nutrients by digesting and absorbing nutrients from _______________________ organisms.

6. Some fungi are _______________________ and obtain their nutrients from living host. A few fungi are actually _____________________, able to trap and kill prey.

7. Fungi include _____________________ and __________________ organisms. Yeast is a typical ___________________________ fungi.

8. Most fungi are ____________________________ organisms. The body of a fungus consists of tiny filaments called ______________________________.

9. _________________________ are tiny tubes filed with __________________ and _____________________ that form the body of a fungus. Hyphae are the __________________, _________________ parts of _______________________ fungi.

10. Hyphae are divided into segments by walls called _____________________. The _________________ have ________________ which cytoplasm and organelles can move from segment to segment.

11. The mass of tangled, interwoven hyphae that form the body of a fungus is called a _________________________.

12. An organism that digest dead organisms and absorbs their nutrients is called a _____________________________________________.

13. Tiny tubes filled with cytoplasm and nuclei that form the body of a fungus are called _________________________________.

14. Septa are the cross-walls that divide __________________________________.

15. Hyphae tangle and interweave to form a mass know as a _____________________.

16. Asexual reproduction, which produces offspring that are __________________ ___________________ to the parent, is most common when ____________________ and _____________________ are ____________________.

17. Sexual reproduction occurs in fungi mostly when _______________________ or ________________________ become __________________.

18. __________________ are the means by which fungi are dispersed. Each spore contains a ______________________ and dehydrated __________________ surrounded by a _____________________ ____________________.

19. The reproductive structures of fungi that produce spores are ___________________ ___________________.

20. A fruiting body consists of a _____________________ and a _______________ in which spores are produced. In a Mushroom, the ________________ contains thousands of ____________________ ____________________.

21. All the spores released by fungi are ___________________________ (1n).

22. Spores cannot move themselves, but can be dispersed by _______________, ___________________, ________________, or ____________________.

23. There are NO ________________ or ________________ Fungi. Instead, the TWO mating types are called the ___________________ and the ______________________.

24. Fungi are grouped in one of Three Phyla: _____________________, common molds; _______________________, club fungi; _________________________, sac fungi; and a group called _______________________ or imperfect fungi.

25. Common molds have No ____________ in their hyphae.

26. The part of hyphae that anchor a fungus to its source of nutrients are called ________________________. _____________________ resemble the _____________ of plants but lack the specialized tissues of true roots.

27. ___________________ are the hyphae that connect groups of rhizoids. ________________ transport the nutrients absorbed by ________________ throughout the ____________________.

28. The study of fungi is called _______________________________.

29. Hyphae whose cells are divided by septa are called ________________________ ________________________.

30. ___________________________ is a special Asexual process. __________________ is the formation of a small, bud-like cell from a larger cell.

31. The one characteristic shared by all imperfect fungi is an absence of ________________________________ ________________________________.

32. A ____________________ is a symbiotic association between a _______________________ and a ___________________________ organism.

33. ____________________________ are mutualistic associations between a __________________ and the _________________ of a plant.

34. The process in which a smaller cell breaks away from a larger cell in some yeasts is called __________________________.

35. Fungi help return nutrients to the ecosystem by acting as _________________________.

36. Mycorrhizae are mutualistic associations between a fungus and what? _______________________________________________

37. A lichen is a symbiotic association between a fungus and what type of organism? ____________________________________________.

38. Hyphae that do not have septa are called _________________________________.

39. The ability to change from Multicellular to Unicellular is called ___________________________________.

40. Cells containing two nuclei are called __________________________.

41. Cells containing one nucleus are called _________________________________.

42. A plant can benefit from a fungus because the fungus _____________________________
_________________________________________________________________________.

43. The species of Mushrooms that is poisonous is ________________________________.

44. The Edible species is known as __________________________________.

47. A Mycelium is an interwoven mat of ____________________________________.

48. All asexual reproductive spores in fungi are composed of only _______________ ___________________.

49. Fungi cause disease in humans through _______________________________, _____________________________ and _______________________________.

50. Unlike animals, fungi ____________________ their food before ________________________________ it.

51. Visible, cup-like sexual reproductive structures are called ______________________________________.

52. The association between a fungus and plant roots is called ______________________________________.

53. Fused gametangia is called __________________________________.

54. A tangled mass of hyphae describes what type of fungus? _______________________________________.

55. An association between a fungus and a green algae is called _________________________________________.

56. The cells walls of fungi are composed of ___________________________.

57. All fungi reproduce ___________________________ some only reproduce ________________________________.

58. Fungi imperfect reproduce only _____________________________________.

59. A unicellular fungi that resembles bacteria is a ____________________________.

60. Fungi evolve from __________________________ through ___________________________________.

61. Mycorrhizae and lichens are both ________________________ _____________________________ associations.

DIRECTIONS: Answer the questions below as completely and as thoroughly as possible. Answer the question in essay form (not outline form), using complete sentences. You may use diagrams to supplement your answers, but a diagram alone without appropriate discussion is inadequate.

1. Describe Three different kinds of Asexual Reproduction found in fungi.

2. Explain why lichens are important to the environment.

3. How does gametangium differ from a Zygosporangia?

4. Explain how fungi obtain their nutrients?

5. What are mycorrhizae, AND what is their ecological role?

6. Identify ONE Way in which fungi differ from organisms in Each of the Other KINGDOMS of Eukaryotic Organisms.

7. What Characteristic makes fungi an important resource recycler?

8. Explain why being able to reproduce Both Sexually and Asexually is an adaptive advantage.

9. Explain how fungi cause disease in humans and Which fungi causes athlete’s foot and vaginal yeast infection?

10. Compare an Ascocarp with a Basidiocarp.

11. Describe the reproduction of Ascomycetes.

12. Describe the reproduction of Zygomycetes.

13. Describe the reproduction of Basidomycetes.

14. Explain the benefits plants and fungi derive from a mycorrhizal relationship.

Preap Chemistry Study Guide

Chemistry Review

1. Everything in the universe is made of __________________________________.

2. The measurement of the amount of matter in an object is called ___________________.

3. What are the Three States of matter?
A.____________________________________
B.____________________________________
C.____________________________________

4. Charged particles that move around an atom’s nucleus are called ________________________.

5. Chemical bonds are broken, atoms are rearranged, and new bonds are formed during _______________________________ ______________________________.

6. Atoms with filled outermost energy levels tend _____________ to participate in chemical reactions.

7. A pure substance that cannot be broken down is called an _____________________.

8. The simplest part of an element is an ____________________.

9. The central core of an atom is called the _____________________________.

10. In an ionic bond, __________ atoms of ________________ charge are held together by _________________________ attraction.

11. The part of an atom that has a neutral charge is a _______________________.

12. Most of the mass of an atom is found in the _____________________.

13. A pure substance made up of atoms of one or more elements is called a ____________________________.

14. Most atoms tend to undergo ____________________ _________________, combining in ways that cause their atoms to become more ____________________.

15.When two atoms share one or more electrons, it is called ____________________________ ______________________.

16. A bond formed by electrical attraction between two opposite charged ions is called ______________________ ____________________.

17. The ability to do work or cause change is _____________________.

18. A redox reaction involves the _____________________ of ___________________ between atoms.

19. The amount of energy needed to start a chemical reaction is the reaction’s _________________________ ___________________.

20. A substance that neutralizes small amounts of acids or bases added to a solution is a _______________________.

21. A chemical reaction that can proceed forward or backward is a ______________________ ______________________.

22. Sodium chloride (table salt) is an example of a compound formed by ______________ _________________.

23.The positive charge part of an atom is called a ___________________________.

24. A particle composed of one or more atoms is a ________________________.

25. Chemical reactions that release free energy are called ____________________________ ____________________________.

26. Chemical reactions that absorb free energy are called ____________________________ _______________________________.

27. The loss of one or more electrons is called ______________________.

28. The gaining of one or more electrons is called _______________________.

29. The breaking apart of water molecules into two ions of opposite charge is called ___________________________________.

30. An atom has six electrons, what is it atomic number? ____________ Name?___________ It is a stable or unstable atom? _________________.

DIRECTIONS: Read Chapter 2, Chemistry, and Answer the questions below as completely and as thoroughly as possible. Answer the question in essay form (not outline form), using complete sentences. You may use diagrams or pictures to supplement your answers, but a diagram or picture alone without appropriate discussion is inadequate.

1. Describe the dissociation of water.

2. Define acid and base. What is a buffer?

3. List TWO characteristics of Acids and TWO Characteristics of Bases.

4. Describe the relationship between the solute, the solvent, and the concentration of a solution.

5. How does an ionic bond differ from a covalent bond?

6. Why is it necessary for oxidation and reduction reactions to occur in pairs?

7. Define the Three States of Matter?

8. State the difference between endergonic and exergonic reactions.

9. What is the role of enzymes in chemical reactions occurring in living things? Explain how a catalyst affects a reaction.
10. What is the pH Scale, and what does its range of values mean?
11. Draw and Label a model of a Chlorine (Cl) atom. Is this atom stable? Why or Why not?
12. Describe the difference between an oxidation and reduction reaction.

13. An oxygen atom has six electrons in its outermost energy level. Explain why two oxygen atoms must share four electrons when they form a covalent bond.

Preap Cellular Respiration Study Guide

Cellular Respiration Review

1. Most eukaryotic cells produce only about ___________ ATP Molecules per Glucose Molecule.

2. What is the process by which glucose is converted to pyruvic acid? ________________________________________

3. At the beginning of aerobic respiration, pyruvic acid bonds to a molecule called ______________________________________ to form Acetyl CoA.

4. The breakdown of pyruvic acid in the presence of oxygen is called ______________________________ _______________________.

5. With every completion of the Krebs Cycle, how many ATP Molecules are made? ________________

6. What is the waste product of the Krebs Cycle? _____________________________________________.

7. The conversion of pyruvic acid to carbon dioxide and ethanol is called ___________________________________ _____________________________________________.

8. The release of energy from food molecules in the absence of oxygen is ______________________________________ _________________________________________________________.

9. What is the byproduct of the electron transport Chain?_______________________________________________.

10. How efficient is Anaerobic Respiration? __________% Aerobic Respiration? ____________%

11. What is the first pathway of cellular respiration called? ________________________________________________

12.What is the location of Glycolysis? _______________________________________________________

13. What is the scientific unit of Energy? ________________________________________________

14. What do you call cellular respiration in the presence of oxygen? _______________________________________ _________________________________________________________.

15. Yeast produces ______________________________ and _______________________________ in the process known as ____________________________________ ___________________________________________.

16. In cellular respiration, glycolysis proceeds the _______________________________ ___________________________.

17. In cellular respiration, more energy is transferred in the ___________________________ ________________________ _________________________________ than in any other step.

18. Glucose molecules are converted into _______________________________ _______________________ molecules in the process of glycolysis.

19. What is the location of the electron transport chain in prokaryotes? ________________ _______________________.

20. The processes of glycolysis and the anaerobic pathways is called ___________________________________.

21. What is the product of acetyl CoA and oxaloacetic acid? _________________ ___________________

22. What molecule is the electron acceptor of glycolysis? _________________________________________

23. The breakdown of organic compounds to produce ATP is known as ____________________________________ ________________________-_______________________________.

24. Glycolysis begins with glucose and produces ______________________________ _________________________.

25. An important molecule generated by both lactic acid and alcoholic fermentation is ______________________________.

26. In the first step of aerobic respiration, pyruvic acid from glycolysis produces CO2, NADH, H+, and _________________________________ _____________________________________.

27. The electron transport chain is driven by two products of the Krebs Cycle – ______________________ and ___________________________.

28. What happens to electrons as they are transported along the electron transport chain? _________________________________________________________________

29. The energy efficiency of aerobic respiration (including glycolysis) is approximately ______________ __________________________________________________.

30. Where in the mitochondria do the reactions of the Krebs cycle occur? _____________________________ ___________________________________________________________

31. Where in the mitochondria is the electron transport chain located? _____________________________ __________________________________________________

32. In alcoholic fermentation, ethyl alcohol is produced from _______________________________ ______________________________________.

33. ____________________________________, and _______________________________ supply electrons and protons to the electron transport chain.

34. Cellular respiration takes place in Two Stages: _______________________________________, then ________________________________________ ________________________________.

35. Water is an end product in the ________________________________________________________________
___________________________________________________________________.

36. In cellular respiration, a two-carbon molecule combines with a four-carbon molecule to form citric acid as part of the _____________________________________________________________________________________.

37. When glycolysis occurs, a molecule of glucose is ___________________________________________.

38. The name of the process that takes place when organic compounds are broken down in the absence of oxygen is _____________________________________________ or _______________________________________.

39. Energetic electrons that provide the energy for the production of most of a cell’s ATP are carried to the electron transport chain by _______________________________ and __________________________________________.

40. _______________________________________ is a biochemical pathway of cellular respiration that is anaerobic.

41. Glucose is split into smaller molecules during the biochemical pathway called __________________________________.

42. In the absence of oxygen, instead of oxidative respiration following glycolysis, glycolysis is followed by ______________________________________________________.

43. During fermentation, either ethyl alcohol and carbon dioxide or _______________________________________ is formed.

DIRECTIONS: Answer the questions below as completely and as thoroughly as possible. Answer the question in essay form (not outline form), using complete sentences. You may use diagrams to supplement your answers, but a diagram alone without appropriate discussion is inadequate.

1. How does aerobic respiration ultimately depend on photosynthesis?

2. Explain the role of oxaloacetic acid with respect to the cyclical nature of the Krebs cycle.

3. Glycolysis produces only 3.5% of the energy that would be produced if an equal quantity of glucose were completely oxidized. What has happened to the remaining energy in the glucose?

4. Why do most cells produce fewer than 38 ATP molecules for every glucose molecule that is oxidized through aerobic respiration?

5. What happens to electrons that accumulate at the end of the electron transport chain?

6. What role does chemiosmosis play in aerobic respiration?

7. What condition must exist in a cell for the cell to engage in fermentation?

8. How is the synthesis of ATP in the electron transport chain of mitochondria similar to the synthesis of ATP in chloroplasts?

9. The fourth step of glycolysis yields four ATP molecules, but the net yield is only two ATP molecules. Explain this discrepancy.

10. Under what conditions would cells in your body undergo lactic-acid fermentation?

11. What role does oxygen play in aerobic respiration? What molecule does oxygen become a part of as a result of aerobic respiration?

12. Where in the mitochondrion do protons accumulate, and what is the source of the protons?

Preap Cell Study Guide

Cell Structure & Function Review

1. The first Person to describe microscopic organisms and living cells was
________________________________.

2. The maximum size to which a cell may grow is limited mainly by the cell’s ___________________________ ____________________________.

3. Short, hair-like organelles that can move and may cover a unicellular organism or line the respiratory tract are called ______________________________________.

4. Some Ribosomes are free in the cytoplasm, while others line the membrane of the
_________________ __________________ __________________________.

5. Everything between the cell membrane and the nucleus, is the cell’s
____________________________________.

6. All cells, from all organisms, are surrounded by a _______________ _____________________.

7. Membranes are _______________________ and have the consistency of vegetable oil.

8. The organelle that stores DNA and synthesizes RNA _________________________.

9. The organelle that processes and packages substances produced by the cell ______________________ _________________________.

10. The ____________________________ is the control center of the cell.

11. The DNA in the form of a long strand is called ______________________________.

12. Cytoplasm consists of two main components: ____________________________ and
______________________________.

13. The cell membrane functions like a ______________________, controlling what
__________________ and _______________________ the cell.

14. A lipid is a simple form of ________________________________.

15. There are many kinds of ______________________ in cell membranes; they help to move material into and out of the cell.

16. Scientist call the modern view of the cell membrane structure the
______________________________ ____________________ _________________.

17. The nucleus is surrounded by a double layer membrane called the
__________________________ _________________________________.

18. During cell division, _________________________ strands coil and condense into thick structures called _____________________________________.

19. The nucleoli make ___________________________. Which in turn build proteins.

20. Membranes are made mostly of ___________________ and ______________________.

21. The _________________ is the smallest unit that can carry out all of the processes of life. The basic unit of life.

22. The maximum size to which a cell may grow is limited mainly by the cell’s ___________________ ____________________.

23. The discovery of cells is linked most directly the development of the __________________________.

24. Organisms whose cells never contain a membrane bound nucleus are called _____________________________________.

24. Suspended in the cell’s cytosol are tiny ___________________________________.

25. Cell membranes consist of two phospholipid layers called a ___________________.

26. The chromosomes in the nucleus contain coded _____________________ that control all cellular activity.

27. When a cell prepares to reproduce the _______________________ disappears.

28. Cytosol is a jelylike mixture that consists mostly of _____________________.

29. The nucleus is one ______________________________.

30. In Eukaryotic cells, most organelles are surrounded by a _____________________.

31. Organisms whose cells always or usually contain a nucleus or nuclei are called
____________________________________.

32. ________________________ are structures that carry out specific functions in the cell.

33. Most cells have a single ______________________; some cells have more than one.

34. Unicellular organisms such as bacteria and their relatives are ___________________________.

35. The Fluid Mosaic Model presents the modern view of a
__________________ ___________________________.

36. The “Blueprints” in a Cell that controls all its activity are the ___________________.

37. Where are poisons and waste detoxified in a cell? _________________________ _________________________________.

38. A cell synthesizes protein by using organelles called _______________________________.

39. The Mitochondria of a cell contain an inner membrane called _____________________________.

40. What are the membrane-bound sacs that package and secrete cell products?
___________________________ ___________________________.

41. Unlike animal cells, plant cells have ______________ ________________.

42. A Chloroplast can convert _________________, __________________________, and ____________________________ into ________________________.

43. What are Flagella? ___________________________________________________.

44. In animal cells, the Cytoskeleton maintains three-dimensional structure and helps the cell ___________________________.

45. The organelle that digest molecules, old organelles, and foreign substances in the cell _______________________________________.

46. A pigment that absorbs energy in sunlight ________________________________.

47. The organelle that prepares proteins for export and synthesizes steroids is ________________________ ________________________.

48. Ribosomes differ from most organelles because they have no ___________________________.

49. What type of cells would you expect to find large numbers of mitochondria? _______________________ _________________.

50. The “Powerhouse” of the cell _______________________________.

51. Short, hairlike organelles that can move and may cover a unicellular organism or line the respiratory tract are called _______________________________.

52. The first cells on Earth were likely _______________________ that did __________ make their own _________________.

53. Microfilaments and microtubules function in cell _______________________ and ____________________________.

54. What is the correct order of structures in living things, from simplest to the most complex? ______________________, __________________________, ______________________________, ______________________________.

55. The is the organelle that transfers energy in ATP _______________________________.

56. What word means “Water Fearing”? ____________________________.

57. What word means “Water Loving”? _____________________________.

58. What is cell specialization? Give an example.
59. Distinguish between the structure of rough ER and that of smooth ER.

60. Explain how ribosomes, endoplasmic reticulum, Golgi apparatus function together in protein synthesis.

61. Explain the difference between a tissue and an organ.

62. Why is the cell membrane said to be selectively permeable?

63. If a cell has a high energy requirement, would you expect it to have many or few mitochondria? Explain your answer.

64. Describe TWO differences between prokaryotic cells and eukaryotic cells.

65. How can you determine whether a unicellular organism is a prokaryote or a eukaryote?

66. Plant cells have cell walls, but animal cells do not. Why do you think that is so?

67. What are the THREE Parts of the Cell Theory?

68. Describe three differences between plant and animal cells.

69. Name the TWO different kinds of animal cells, and describe how their shape is related to their function.

70. What is the difference between chromatin and chromosomes?

71. What are the major roles of the nucleus, and what parts of the nucleus carry out these roles?

72. What is a colonial organism, and what does it have in common with multicellular organisms?

Information for the Public Nobel Prize in Chemistry 6 October 2004

Proteins labeled for destruction

Degradation needs no energy – or does it?

Information for the Public
Nobel Prize in Chemistry
6 October 2004