Cellular Processes 13 - BIOLOGY JUNCTION

Nucleic Acids & Protein Synthesis

Nucleic Acids and Protein Synthesis
All Materials © Cmassengale

Cell à Nucleus à Chromosomes à Genes à DNA

Proteins

Organic molecules (macromolecules) made by cells
Make up a large part of your body
Used for growth, repair, enzymes, etc.
Composed of long chains of small units called amino acids bonded together by peptide bonds
Twenty amino acids exist

DNA

Deoxyribonucleic acid is a coiled double helix carrying hereditary information of the cell

Contains the instructions for making proteins from 20 different amino acids
Appears as chromatin when cell not dividing

Structure discovered by Watson & Crick in 1953
Sides made of pentose (5-sided) sugars attached to phosphate groups by phosphodiester bonds
Pentose sugar called Deoxyribose

Steps or rungs of DNA made of 4 nitrogen-containing bases held together by weak hydrogen bonds
Purines (double carbon-nitrogen rings) include adenine (A) and guanine (G)
Pyrimidines (single carbon-nitrogen rings) include thymine (T) and cytosine (C)

Base pairing means a purine bonds to a pyrimidine (Example: A — T and C — G)
Coiled, double stranded molecule known as double helix
Make up chromosomes in the nucleus
Subunits of DNA called nucleotides
Nucleotides contain a phosphate, a Deoxyribose sugar, and one nitrogen base (A,T,C, or G)

Free nucleotides also exist in nucleus
Most DNA is coiled or twisted to the right
Left twisted DNA is called southpaw or Z-DNA
Hot spots which can result in mutations occur where right & left twisted DNA meet

History of DNA discovery

Freidrich Miescher (1868) found nuclear material to be ½ protein & ½ unknown substance
1890’s, unknown nuclear substance named DNA
Walter Sutton (1902) discovered DNA in chromosomes
Fredrick Griffith (1928) working with Streptococcus pneumoniae conducted transformation experiments of virulent & nonvirulent bacterial strains
Levene (1920’s) determined 3 parts of a nucleotide
Hershey & Chase (1952) used bacteriophages (viruses) to show that DNA, not protein, was the cell’s hereditary material
Rosalind Franklin (early 1950’s) used x-rays to photograph DNA crystals

Erwin Chargraff (1950’s) determined that the amount of A=T and amount of C=G in DNA; called Chargaff’s Rule
Watson & Crick discovered double helix shape of DNA & built the 1st model

Click for larger picture!

DNA Replication

Process by which DNA makes a copy of itself
Occurs during S phase of interphase before cell division
Extremely rapid and accurate (only 1 in a billion are incorrectly paired)
Requires many enzymes & ATP (energy)
Begins at special sites along DNA called origins of replication where 2 strands open & separate making a replication fork

Nucleotides added & new strand forms at replication forks
DNA helicase (enzyme) uncoils & breaks the weak hydrogen bonds between complementary bases (strands separate)
DNA polymerase adds new nucleotides to the exposed bases in the 5’ to 3’ direction

Leading strand (built toward replication fork) completed in one piece
Lagging strand (built moving away from the replication fork) is made in sections called Okazaki fragments

OKAZAKI FRAGMENTS

DNA ligase helps join Okazaki segments together

DNA polymerase proofreads the new DNA checking for errors & repairing them; called excision repair
Helicase recoils the two, new identical DNA molecules

RNA

Ribonucleic acid
Single stranded molecule

Found in nucleus & cytoplasm
Contains ribose sugar
Contains the nitrogen base uracil (U) instead of thymine so A pairs with U
Base pairings are A-U and C-G
Three types of RNA exist (mRNA, TRNA, & rRNA)

mRNA

Messenger RNA
Single, uncoiled, straight strand of nucleic acid
Found in the nucleus & cytoplasm
Copies DNA’s instructions & carries them to the ribosomes where proteins can be made
mRNA’s base sequence is translated into the amino acid sequence of a protein
Three consecutive bases on mRNA called a codon (e.g. UAA, CGC, AGU)
Reusable

tRNA

Transfer RNA
Single stranded molecule containing 80 nucleotides in the shape of a cloverleaf
Carries amino acids in the cytoplasm to ribosomes for protein assembly
Three bases on tRNA that are complementary to a codon on mRNA are called anticodons (e.g. codon- UUA; anticodon- AAU)
Amino Acid attachment site across from anticodon site on tRNA
Enters a ribosome & reads mRNA codons and links together correct sequence of amino acids to make a protein
Reusable

rRNA

Ribosomal RNA
Globular shape
Helps make up the structure of the ribosomes
rRNA & protein make up the large & small subunits of ribosomes
Ribosomes are the site of translation (making polypeptides)

Aids in moving ribosomes along the mRNA strand as amino acids are linked together to make a protein

Amino Acids

20 exist
Linked together in a process called protein synthesis in the cytoplasm to make polypeptides (subunits of proteins)
DNA contains the instructions for making proteins but is too large to leave the nucleus
Three consecutive bases on DNA called a triplet (e.g. TCG, ATG, ATT)
mRNA codon table tells what 3 bases on mRNA code for each amino acid (64 combinations of 3 bases)
Methionine (AUG) on mRNA is called the start codon because it triggers the linking of amino acids
UAA, UGA, & UAG on mRNA signal ribosomes to stop linking amino acids together

Genetic Code (RNA)

Amino Acid	3 Letter Abbreviation	Codons
Alanine	Ala	GCA GCC GCG GCU
Arginine	Arg	AGA AGG CGA CGC CGG CGU
Aspartic Acid	Asp	GAC GAU
Asparagine	Asn	AAC AAU
Cysteine	Cys	UGC UGU
Glutamic Acid	Glu	GAA GAG
Glutamine	Gln	CAA CAG
Glycine	Gly	GGA GGC GGG GGU
Histidine	His	CAC CAU
Isoleucine	Ile	AUA AUC AUU
Leucine	Leu	UUA UUG CUA CUC CUG CUU
Lysine	Lys	AAA AAG
Methionine	Met	AUG
Phenylalanine	Phe	UUC UUU
Proline	Pro	CCA CCC CCG CCU
Serine	Ser	AGC AGU UCA UCC UCG UCU
Threonine	Thr	ACA ACC ACG ACU
Tryptophan	Trp	UGG
Tyrosine	Tyr	UAC UAU
Valine	Val	GUA GUC GUG GUU
Start		AUG
Stop		UAA UAG UGA

Practice Table:

DNA Codon	mRNA Codon	tRNA Anticodon	Amino Acid
	GCU
TAC
		AUU
	UUU
TCA
		UCU
CTT
		ACU
	ACU

Protein Synthesis

Consists of 2 parts — Transcription & Translation
Begins in the nucleus with mRNA copying DNA’s instructions for proteins (transcription)
Completed in the cytoplasm when tRNA enters ribosomes to read mRNA codons and link together amino acids (translation)

Steps in Transcription

DNA helicase (enzyme) uncoils the DNA molecule
RNA polymerase (enzyme) binds to a region of DNA called the promoter which has the start codon TAC to code for the amino acid methionine
Promoters mark the beginning of a DNA chain in prokaryotes, but mark the beginning of 1 to several related genes in eukaryotes
The 2 DNA strands separate, but only one will serve as the template & be copied
Free nucleotides are joined to the template by RNA polymerase in the 5’ to 3’ direction to form the mRNA strand
mRNA sequence is built until the enzyme reaches an area on DNA called the termination signal
RNA polymerase breaks loose from DNA and the newly made mRNA
Eukaryotic mRNA is modified (unneeded sections snipped out by enzymes & rejoined) before leaving the nucleus through nuclear pores, but prokaryotic RNA isn’t
All 3 types of RNA called transcripts are produced by this method

Steps in Translation

mRNA brings the copied DNA code from the nucleus to the cytoplasm
mRNA attaches to one end of a ribosome; called initiation
tRNA’s attach the correct amino acid floating in the cytoplasm to themselves
tRNA with its attached amino acid have 2 binding sites where they join the ribosome
The tRNA anticodon “reads” & temporarily attaches to the mRNA codon in the ribosome
Two amino acids at a time are linked together by peptide bonds to make polypeptide -chains (protein subunits); called elongation
Ribosomes) move along the mRNA strand until they reach a stop codon (UAA, UGA, or UAG); called termination

tRNA’s break loose from amino acid, leave the ribosome, & return to cytoplasm to pick up another amino acid

Click here for an animation of Translation

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Mitosis Activity

Stages of Mitosis

Introduction

Mitosis, also called karyokinesis, is division of the nucleus and its chromosomes. It is followed by division of the cytoplasm known as cytokinesis. Both mitosis and cytokinesis are parts of the life of a cell called the Cell Cycle. Most of the life of a cell is spent in a non-dividing phase called Interphase. Interphase includes G1 stage in which the newly divided cells grow in size, S stage in which the number of chromosomes is doubled and appear as chromatin, and G2 stage where the cell makes the enzymes & other cellular materials needed for mitosis.

Mitosis has 4 major stages — Prophase, Metaphase, Anaphase, and Telophase. When a living organism needs new cells to repair damage, grow, or just maintain its condition, cells undergo mitosis.

During Prophase, the DNA and proteins start to condense. The two centrioles move toward the opposite end of the cell in animals or microtubules are assembled in plants to form a spindle. The nuclear envelope and nucleolus also start to break up.

Prophase

During Metaphase, the spindle apparatus attaches to sister chromatids of each chromosome. All the chromosomes are line up at the equator of the spindle. They are now in their most tightly condensed form.

Metaphase

During Anaphase, the spindle fibers attached to the two sister chromatids of each chromosome contract and separate chromosomes which move to opposite poles of the cell.

Anaphase

In Telophase, as the 2 new cells pinch in half (animal cells) or a cell plate forms (plant cells), the chromosomes become less condensed again and reappear as chromatin. New membrane forms nuclear envelopes and the nucleolus is reformed.

Telophase

Objective:

In this lab, you will determine the approximate time it takes for a cell to pass through each of the four stages of mitosis. You may use your textbook and class notes to help you identify the stages of mitosis as seen under the microscope.

Materials:

Microscope, prepared slide onion root tip or whitefish blastula, textbook, lab worksheet, pencil

Procedure:

Set up a compound light microscope and turn on the light.
Place a slide containing a stained preparation of the Allium (onion root tip) or Whitefish blastula.
Locate the meristematic or growth zone, which is just above the root cap at the very end of the tip or
Focus in on low power, and then switch to medium or high power. Below find micrographs of the four stages of mitosis. Use them to help you identify the stages on the microscope slide.

Prophase (onion)

Metaphase (onion)

Anaphase (onion)

Telophase (whitefish)

Now count the number of cells found in each stage of mitosis and place the data in the chart below.
Determine the percentage of time each cell will spend in each stage of mitosis. Divide the number of each cell by the total number of cells and multiply by 100 to determine the percentage. Place these values in the chart below.

Stage of Mitosis	Number of Cells	Percent of time in each stage = # of cells in stage X 100% Total # of Cell
Prophase		%
Metaphase		%
Anaphase		%
Telophase		%
Interphase (Not a Mitotic Stage)		%
Total # cells		100%

Line graph the data you have just collected. Be sure to label the X and Y axis & include the units of measurement.

Title: __________________________________________________

Graph Legend:

Questions:

1. Of the four stages of mitosis, which one takes the most time to complete?

2. Which is the shortest stage in duration?

3. What would happen if the process of mitosis skipped metaphase? telophase?

Further Study:

Normal Cell Division may be observed in onion root tips. Many of the processes are similar to those in animal cells. However, in plant cells, the cell plate between daughter cells forms from the Golgi.

Find all of the stages of mitosis and interphase in the above picture. Make a sketch of each stage and briefly describe what is occurring. Count and record the number of cells you see in each stage.

	Projects
	Notes

Mitosis and Meiosis

Mitosis and Meiosis

Introduction
All new cells come from previously existing cells. New cells are formed by the process of cell division which involves both replication of the cell’s nucleus (karyokinesis) and division of the cytoplasm( cytokinesis).

There are two types of nuclear division: mitosis and meiosis. Mitosis typically results in new somatic (body ) cells. Formation of an adult organism from a fertilized egg, asexual reproduction, regeneration, and maintenance or repair of body parts are accomplished through mitotic cell division. Meiosis results in the formation of either gametes (in animals) or spores ( in plants). These cells have half the chromosome number of the parent cell. You will study meiosis in Exercise 3B. Where does one find cells undergoing meiosis? Plants and animals differ in this respect. In higher plants the process of forming new cells is restricted to special growing regions called meristems. These regions usually occur at the tips of stems or roots. In animals, cell division occurs anywhere new cells are formed or as new cells replace old ones. However, some tissues in both plant and animals rarely divide once the organism is mature.

Exercise 3A.1: Observing Mitosis in Plant and Animal Cells Using Prepared Slides of the Onion Root Tip and Whitefish Blastula

Figure 3.1 Close up view of different stages of mitosis in an onion root tip:

Figure 3.2 Whitefish Blastula

Procedure:
Examine prepared slides of either onion root tips or whitefish blastula. Locate the meristematic region of the onion, or locate the blastula with 10X objective, and then use the 40X objective to study individual cells. Identify one cell which clearly represents each phase of mitosis. Sketch and label the cell in the box provided.

1. The non dividing cell is in a stage called interphase. The nucleus may have one or more dark-stained nucleoli and is filled with a fine network of threads, the chromatin. During interphase, DNA replication occurs.

Interphase

2. The first signs of cell division occurs in prophase. There is a thickening of the chromatin threads, which will continue until it is evident that the chromatin has condensed into chromosomes. With somewhat higher magnification you may be able to see the two chromatids held together by the centromere. As prophase continues , the chromatids continue to thicken and shorten. The nuclear envelope disappears and the beginnings of the spindle apparatus begin to appear.

Prophase

3. At metaphase, the chromosome pairs have moved to the center of the spindle. One particular part of each chromosome, the centromere, attaches to the spindle. The centromeres of all the chromosomes lie about the same level of the spindle called the metaphase plate.

Metaphase

4. At the beginning of anaphase, the centromere regions of each pair of chromatids separate and are moved by the spindle fibers toward opposite poles of the spindle, dragging the rest of the chromatid behind them. Once each chromatid is separate it is called a chromosome.

Anaphase

5. Telophase, the last stage of division, is marked by a pronounced condensation of the chromosomes, followed by the formation of a new nuclear envelope around each group of chromosomes. The chromosomes gradually uncoil into the fine threads of chromatin, and the nucleoli reappears. Cytokinesis may occur. This is the division of the cytoplasm into two new cells. In plants, a new cell wall is laid down between the daughter cells. In animal cells, the old cells will pinch off in the middle along a cleavage furrow to form two new daughter cells.

Telophase

Analysis Questions:
1. Why is it more accurate to call mitosis “nuclear replication” rather than “cellular division”?

_____________________________________________________________________

2. Explain why the whitefish blastula and onion root tip are selected for study of mitosis.

_____________________________________________________________________

Exercise 3A.2: Time for Cell Replication
Procedure:
It is hard to imagine that you can estimate how much time a cell spends in each phase of cell replication from a slide of dead cells. Yet this is precisely what you are going to do in this part of the lab. Since you are working with a prepared slide, you cannot get any information about how long it takes a cell to divide. What you can determine is how many cells are in each phase. From this, you can infer the percent of time each cell spends in each phase.

1. Observe every cell in one high power field of view and determine which phase of the cell cycle it is in. This is best done in pairs. The partner observing the slide calls out the phase of each cell while the other partner records. Then switch so the recorder becomes the observer and visa versa. Count at least two full fields of view. If you have not counted 200 cells, then count a third field of view.

2. Record your data in Table 3.1.

Table 3.1

	Number of Cells				Percent of Total Cells Counted	Time in Each Stage
	Field 1	Field 2	Field 3	Total
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total Cells Counted

3. Calculate the percentage of cells in each phase.

Consider it takes, on average, 24 hours (or 1,440 minutes) for onion root-tip cells to complete the cell cycle. You can calculate the amount of time spent in each phase of the cell cycle from the percent of cells in that stage.

Percent of cells in stage X 1,440 minutes = ___________ minutes of cell cycle spent in stage.

Questions:
1. If your observations had not been restricted to the area of the root tip that is actively dividing, how would your results have been different?

_____________________________________________________________________

2. Based on the data in Table 3.1, what can you infer about the relative length of time an onion root-tip cell spends in each stage of cell division?

_____________________________________________________________________

Mitosis PPT Questions

Cell Cycle and Mitosis
ppt Questions

Cell Cycle

1.Prokaryotic organisms include ___________, while plants and animals are ____________.

2. Describe prokaryotes.

3. How do bacteria asexually reproduce?

4. Name the 3 main steps of binary fission in bacteria.

5. Name a bacterial cell that reproduces by binary fission.

6. Describe eukaryotes.

7. How do eukaryotes asexually reproduce cells?

8. The stages in the growth and reproduction of a cell are called the __________ ___________.

9. List the 5 stages in the cell cycle.

10. What does G1 stage stand for?

11. Name two things that happen to a cell during G1?

12. What is the S stage of the cell cycle?

13. _________ instructions are copied in the S phase as ___________ are duplicated.

14. _______ stands for second growth stage.

15. G2 is the time between ____________ and ___________.

16. Cells continue to _________ during G2 and to make __________ that will be needed for mitosis or cell division.

17. Mitosis or cell division is known as the ________ stage.

18. How does a cell use its energy during the M phase?

19. Does a cell continue growing & making proteins in the M phase?

20. Mitosis is also called _______________ which means division of the ____________.

21. ____________ is called the resting stage and makes up the longest part of a cell’s life cycle.

22. What happens to cells during interphase?

23. Are chromosomes visible during interphase?

Mitosis

24. Name the 4 stages of mitosis.

25. Name 2 things that happen to a cell during prophase.

26. Can chromosomes be seen during prophase?

27. Sketch a eukaryotic chromosome and label the centromere and kinetochore fiber that attaches to it.

28. How many pairs of chromosomes are found in humans?

29. List 3 things that occur during metaphase.

30. Where are chromosomes located during metaphase of a cell?

31. What stage occurs after metaphase?

32. List 2 things that happen to cells during anaphase.

33. Sketch and label the mitotic spindle and attached chromosomes.

34. What is the last stage of mitosis?

35. Where are the two sets of chromosomes located at Telophase?

36. What two things reform during Telophase?

37. Chromosomes ___________ during Telophase so they are no longer visible.

38. In plants, what begins to form that will separate the two cells?

39. How are the two cells separated from each other in animals?

40. _____________ or division of the cytoplasm follows ___________, division of the nucleus, and forms ____________ daughter cells.

41. How do the two, new daughter cells compare to each other?

42. Label the following stages of mitosis.

Printable Copy

Meiosis Labeling

Meiosis

On each of the images, label the phase of meiosis

1. _______________	2. _______________	3. _______________
4. _______________	5. _______________	6. _______________
7. _______________	8._______________	9._______________
10. _______________	11. A cell with a diploid number of 20 undergoes meiosis. This will produce ________ daughter cells, each with ________ chromosomes. 12. Synapsis occurs during this phase: _______________________ 13 How many different possible combinations are there for a cell that has 10 chromosomes (5 pairs): _____________ 14. Tetrads line up along the equator during this phase: ______________ 15. At the end of meiosis I, ________ daughter cells are created. These daughter cells are [ diploid \| haploid ]. 16. Meiosis occurs in what type of cells: ____________________________

Now label the photographs.
17. _______________	18. _______________	19. _____________
20. _______________	21. _______________	22. _____________
23. _______________	24. _______________	24. _____________
25. _______________

History of DNA discovery

RNA

GCU