Structure & Function of the Cells



All Materials © Cmassengale

I. All Organisms are Made of Cells


A. The cell is the basic unit of structure & function


B. The cell is the smallest unit that can still carry on all life processes

C. Both unicellular (one celled) and multicellular (many celled) organisms are composed of cells

D. Before the 17th century, no one knew cells existed

E. Most cells are too small to be seen with the unaided eye


F. In the early 17th century microscopes were invented & cells were seen for the 1st time

G. Anton Von Leeuwenhoek, a Dutchman, made the 1st hand-held microscope & viewed microscopic organisms in water & bacteria from his teeth


Leeuwenhoek’s microscope consisted simply of:

  • A) a screw for adjusting the height of the object being examined
  • B) a metal plate serving as the body
  • C) a skewer to impale the object and rotate it
  • D) the lens itself, which was spherical



H. In 1665, an English scientist named Robert Hooke made an improved microscope and viewed thin slices of cork viewing plant cell walls


I. Hooke named what he saw “cells”

J. In the 1830’s, Matthias Schleiden (botanist studying plants) & Theodore Schwann (zoologist studying animals) stated that all living things were made of cells


K. In 1855, Rudolf Virchow stated that cells only arise from pre-existing cells


L. Virchow’s idea contradicted the idea of spontaneous generation (idea that nonliving things could give rise to organisms)

M. The combined work of Schleiden, Schwann, & Virchow is known as the Cell Theory





II. Principles of the Cell Theory


A. All living things are made of one or more cells

B. Cells are the basic unit of structure & function in organisms

C. Cells come only from the reproduction of existing cells


III. Cell Diversity


A. Not all cells are alike

B. Cells differ in size, shape, and function


C. The female egg cell is the largest cell in the body & can be seen without a microscope

relative sizes of cells and their components

D. Bacterial cells are some of the smallest cells & are only visible with a microscope

E.coli Bacterial Cells

E. Cells need surface area of their cell membrane large enough to adequately exchange materials with the environment (wastes, gases such as O2 & CO2, and nutrients)


F. Cells are limited in size by the ratio between their outer surface area & their volume


G. Small cells have more surface area for their volume of cytoplasm than large cells

H. As cells grow, the amount of surface area becomes too small to allow materials to enter & leave the cell quickly enough

I. Cell size is also limited by the amount of cytoplasmic activity that the cell’s nucleus can control

J. Cells come in a variety of shapes, & the shape helps determine the function of the cell (e.g. Nerve cells are long to transmit messages in the body, while red blood cells are disk shaped to move through blood vessels)


IV. Prokaryotes


A. Prokaryotic cells are less complex

B. Unicellular

C. Do not have a nucleus & no membrane-bound organelles


D. Most have a cell wall surrounding the cell membrane & a single, looped chromosome (genetic material) in the cytoplasm


E. Include bacteria & blue-green bacteria


F. Found in the kingdom Monera



V. Eukaryotes


A. More complex cells

B. Includes both unicellular & multicellular organisms


C. Do have a true nucleus & membrane-bound organelles


D. Organelles are internal structures in cell’s that perform specific functions


a. Nucleusb. Chloroplastc. Golgid. Mitochondria


E. Organelles are surrounded by a single or double membrane


F. Entire eukaryotic cell surrounded by a thin cell membrane that controls what enters & leaves the cell

G. Nucleus is located in the center of the cell

H. The nucleus contains the genetic material (DNA) & controls the cell’s activities

I. Eukaryotes include plant cells, animal cells, fungi, algae, & protists

J. Prokaryotes or bacteria lack a nucleus

K. Found in the kingdoms Protista, Fungi, Plantae, & Animalia



VI. Cell Membrane


A. Separates the cytoplasm of the cell from its environment

B. Protects the cell & controls what enters and leaves


C. Cell membranes are selectively permeable only allowing certain materials to enter or leave

D. Composed of a lipid bilayer made of phospholipid molecules


E. The hydrophilic head of a phospholipid is polar & composed of a glycerol & phosphate group and points to the aqueous cytoplasm and external environment.

F. The two hydrophobic tails are nonpolar point toward each other in the center of the membrane & are composed of two fatty acids

G. When phospholipids are placed in water, they line up on the water’s surface with their heads sticking into the water & their tails pointing upward from the surface.

H. The inside of the cell or cytoplasm is an aqueous or watery environment & so is the outside of the cell. Phospholipid “heads” point toward the water.

I. Phospholipid “tails” are sandwiched inside the lipid bilayer.

J. The cell membrane is constantly breaking down & being reformed inside living cells.

K. Certain small molecules such as CO2, H2O, & O2 can easily pass through the phospholipids


VII. Membrane Proteins


A. A variety of protein molecules are embedded in the cell’s lipid bilayer.

B. Some proteins called peripheral proteins are attached to the external & internal surface of the cell membrane

C. Integral proteins or transmembrane proteins are embedded & extend across the entire cell membrane. These are exposed to both the inside of the cell & the exterior environment.

D. Other integral proteins extend only to the inside or only to the exterior surface.

E. Cell membrane proteins help move materials into & out of the cell.

F. Some integral proteins called channel proteins have holes or pores through them so certain substances can cross the cell membrane.

G. Channel proteins help move ions (charged particles) such as Na+, Ca+, & K+ across the cell membrane

H. Transmembrane proteins bind to a substance on one side of the membrane & carry it to the other side. e.g. glucose


I. Some embedded, integral proteins have carbohydrate chains attached to them to serve as chemical signals to help cells recognize each other or for hormones or viruses to attach



VIII. Fluid Mosaic Model


A. The phospholipids & proteins in a cell membrane can drift or move side to side making the membrane appear “fluid”.

B. The proteins embedded in the cell membrane form patterns or mosaics.

C. Because the membrane is fluid with a pattern or mosaic of proteins, the modern view of the cell membrane is called the fluid mosaic model.


IX. Internal Cell Structure & Organelles of Eukaryotes

A. Cytoplasm includes everything between the nucleus and cell membrane.


B. Cytoplasm is composed of organelles & cytosol (jellylike material consisting of mainly water along with proteins.


C. Eukaryotes have membrane-bound organelles; prokaryotes do not


D. Mitochondria are large organelles with double membranes where cellular respiration (breaking down glucose to get energy) occurs

1. Energy from glucose is used to make ATP or adenosine triphosphate


2. Cells use the ATP molecule for energy

3. More active cells like muscle cells have more mitochondria


4. Outer membrane is smooth, while inner membrane has long folds called cristae


5. Have their own DNA to make more mitochondria when needed

E. Ribosomes are not surrounded by a membrane & are where proteins are made in the cytoplasm (protein synthesis)


1. Most numerous organelle

2. May be free in the cytoplasm or attached to the rough ER (endoplasmic reticulum)

F. Endoplasmic reticulum are membranous tubules & sacs that transport molecules from one part of the cell to another

1. Rough ER has embedded ribosomes on its surfaces for making proteins

2. Smooth ER lacks ribosomes & helps break down poisons, wastes, & other toxic chemicals

3. Smooth ER also helps process carbohydrates & lipids (fats)

4. The ER network connects the nucleus with the cell membrane


G. Golgi Apparatus modifies, packages, & helps secrete cell products such as proteins and hormones

1. Consists of a stack of flattened sacs called cisternae


2. Receives products made by the ER


H. Lysosomes are small organelles containing hydrolytic enzymes to digest materials for the cell

1. Single membrane

2. Formed from the ends of Golgi that pinch off


3. Found in most cells except plant cells

I. Cytoskeleton consists of a network of long protein tubes & strands in the cytoplasm to give cells shape and helps move organelles


1. Composed of 2 protein structures — microtubules, intermediate filaments, & microfilaments


2. Microfilaments are ropelike structures made of 2 twisted strands of the protein actin capable of contracting to cause cellular movement (muscle cells have many microfilaments)

3. Microtubules are larger, hollow tubules of the protein called tubulin that maintain cell shape, serve as tracks for organelle movement, & help cells divide by forming spindle fibers that separate chromosome pairs


Cytoskeleton Element General Function
MicrotubulesMove materials within the cell
Move the cilia and flagella
Actin FilamentsMove the cell
Intermediate FilamentsProvides mechanical support



J. Cilia are short, more numerous hair like structures made of bundles of microtubules to help cells move


1. Line respiratory tract to remove dust & move paramecia

Cross section of Cilia & Flagella

K. Flagella are long whip like tails of microtubules bundles used for movement (usually 1-3 in number)

1. Help sperm cells swim to egg

L. Nucleus (nuclei) in the middle of the cell contains DNA (hereditary material of the cell) & acts as the control center


1. Most cells have 1 nucleolus, but some have several

2. Has a protein skeleton to keep its shape

3. Surrounded by a double layer called the nuclear envelope containing pores

4. Chromatin is the long strand of DNA in the nucleus, which coils during cell division to make chromosomes


5. Nucleolus (nucleoli) inside the nucleus makes ribosomes & disappears during cell division


M. Cell walls are nonliving, protective layers around the cell membrane in plants, bacteria, & fungi

1. Fungal cell walls are made of chitin, while plant cell walls are made of cellulose


2. Consist of a primary cell wall made first and a woody secondary cell wall in some plants


N. Vacuoles are the largest organelle in plants taking up most of the space

1. Serves as a storage area for proteins, ions, wastes, and cell products such as glucose


2. May contain poisons to keep animals from eating them

3. Animal vacuoles are smaller & used for digestion

O. Plastids in plants make or store food & contain pigments to trap sunlight

1. Chloroplast is a plastid that captures sunlight to make O2 and glucose during photosynthesis; contains chlorophyll

a. Double membrane organelle with an inner system of membranous sacs called thylakoids


b. Thylakoids made of stacks of grana containing chlorophyll

2. Other plastids contain red, orange, and yellow pigments

3. Found in plants, algae, & seaweed

X. Multicellular Organization


A. Cells are specialized to perform one or a few functions in multicellular organisms

B. Cells in multicellular organisms depend on each other


C. The levels of organization include:
Cells –> Tissues –> Organs –> Systems –> Organism

D. Tissues are groups of cells that performs a particular function (e.g. Muscle)


E. Organs are groups of tissues working together to do a job (e.g. heart, lungs, kidneys, brain)

F. Systems are made of several organs working together to carry out a life process (e.g. Respiratory system for breathing)

G. Plants have specialized tissues & organs different from animals

1. Dermal tissue forms the outer covering of plants

2. Ground tissue makes up roots & stems

3. Vascular tissue transports food & water

4. The four plant organs are the root, stem, leaf, & flower


H. Colonial organisms are made of cells living closely together in a connected group but without tissues & organs (e.g. Volvox)

Cell Analogy


Cell City Analogy
By Shannan Muskopf

In a far away city called Grant City, the main export and production product is the steel widget. Everyone in the town has something to do with steel widget making and the entire town is designed to build and export widgets. The town hall has the instructions for widget making, widgets come in all shapes and sizes and any sizes and any citizen of Grant can get the instructions and begin making their own widgets. Widgets are  generally produced in small shops around the city, these small shops can be built by the carpenter’s union (whose headquarters are in town hall).

After the widget is constructed, they are placed on special carts which can deliver the widget anywhere in the city. In order for a widget to be exported, the carts take the widget to the postal office, where the widgets are packaged and labeled for export. Sometimes widgets don’t turn out right, and the “rejects” are sent to the scrap yard where they are broken down for parts or destroyed altogether. The town powers the widget shops and carts from a hydraulic dam that is in the city. The entire city is enclosed by a large wooden fence, only the postal trucks (and citizens with proper passports) are allowed outside the city.


Match the parts of the city (underlined) with the parts of the cell.

1. Mitochondria_____________________________________________
2. Ribosomes_____________________________________________
3. Nucleus_____________________________________________
4. Endoplasmic Reticulum_____________________________________________
5. Golgi Apparatus_____________________________________________
6. Protein_____________________________________________
7. Cell Membrane_____________________________________________
8. Lysosomes____________________________________________________________
9. Nucleolus_____________________________________________

** Create your own analogy of the cell using a different model. Some ideas might be: a school, a house, a factory, or anything you can imagine**



Cell Death

Nobel Prize in Medicine 2002

Genetic Regulation of Organ Development and Programmed Cell Death

Sydney BrennerH. Robert HorvitzJohn E. Sulston
Sydney BrennerH. Robert HorvitzJohn E. Sulston


Sydney Brenner, Robert Horvitz and John Sulston’s discoveries concerning the genetic regulation of organ development and programmed cell death have truly opened new avenues for biological and medical research. We have all begun our lives in a seemingly modest way – as the fertilized egg cell, a tenth of a millimeter in size. From this small cell, the adult human being develops, with its hundred thousand billion cells, through cell division, cell differentiation and by formation of the various organs. To only make new cells is however not sufficient, certain cells must also die at specific time points as a natural part of the growth process. Think for example about how we for a short period during fetal life have web between our fingers and toes, and how this is removed by cell death.

The importance of cell differentiation and organ development was understood by many, but progress was slow. This was largely an effect of our complexity, with the large number of cells and many cell types – the forest could not be seen because of all the trees. Could the task to find the genetic principles be made simpler? Were there a species simpler than humans, but still sufficiently complex to allow for general principles to be deduced?

Sydney Brenner in Cambridge, UK, took on the challenge, and his choice was the nematode Caenorhabditis elegans. This may at first seem odd, a spool-shaped approximately 1 millimeter long worm with 959 cells that eats bacteria, but Brenner realized in the early 1960s that it was, what we today would call, “loaded with features”. It was genetically amenable and it was transparent, so that every cell division and differentiation could be directly followed in the worm under the microscope. Brenner demonstrated in 1974 that mutations could be introduced into many genes and visualized as distinct changes in organ formation. Through his visionary work, Brenner created an important research tool. The nematode had made into the inner circle of research.

John Sulston came to Brenner’s laboratory in 1969. He took advantage of that cell divisions could be followed under the microscope and assembled the cell lineage in the worm, showing which cells are siblings, first and second cousins. He found that cell divisions occurred with a very high degree of precision, the cell lineage was identical between different individuals. He also realized that certain cells in the lineage always died at a certain time point. This meant that programmed cell death was not a stochastic process, but rather occurred with a very high degree of precision. During the course of this work Sulston identified the first gene important for the cell death process: nuc-1.

Robert Horvitz came to work with Brenner and Sulston in 1974. Horvitz started a systematic search for genes controlling programmed cell death. He identified the key genes for the cell death process proper. The discovery of these central death genes, ced-3, ced-4 and ced-9, changed the view on programmed cell death from something rather obscure to a process with a strict genetic program. Horvitz also showed that there are human homologues to the death genes in the worm and that those have corresponding functions – the cell death machinery had deep evolutionary roots.

This year’s Nobel Prize celebrates the Joy of Worms. Brenner’s almost prophetic visions from the early 1960s of the advantages of this model organism have been fulfilled. It has given us new insights into the development of organs and tissues and why specific cells are destined to die. This knowledge has proven valuable, for instance, in understanding how certain viruses and bacteria attack our cells, and how cells die in heart attack and stroke.

Cell lineage – from egg to adult

All cells in our body are descendents from the fertilized egg cell. Their relationship can be referred to as a cellular pedigree or cell lineage. Cells differentiate and specialize to form various tissues and organs, for example muscle, blood, heart and the nervous system. The human body consists of several hundreds of cell types, and the cooperation between specialized cells makes the body function as an integrated unit. To maintain the appropriate number of cells in the tissues, a fine-tuned balance between cell division and cell death is required. Cells have to differentiate in a correct manner and at the right time during development in order to generate the correct cell type.

It is of considerable biological and medical importance to understand how these complicated processes are controlled. In unicellular model organisms, e.g. bacteria and yeast, organ development and the interplay between different cells cannot be studied. Mammals, on the other hand, are too complex for these basic studies, as they are composed of an enormous number of cells. The nematode C. elegans, being multi-cellular, yet relatively simple, was therefore chosen as the most appropriate model system, which has then led to characterization of these processes also in humans.

Programmed cell death

Normal life requires cell division to generate new cells but also the presence of cell death, so that a balance is maintained in our organs. In an adult human being, more than a thousand billion cells are created every day. At the same time, an equal number of cells die through a controlled “suicide process”, referred to as programmed cell death.

Developmental biologists first described programmed cell death. They noted that cell death was necessary for embryonic development, for example when tadpoles undergo metamorphosis to become adult frogs. In the human foetus, the interdigital mesoderm initially formed between fingers and toes is removed by programmed cell death. The vast excess of neuronal cells present during the early stages of brain development is also eliminated by the same mechanism.

The seminal breakthrough in our understanding of programmed cell death was made by this year’s Nobel Laureates. They discovered that specific genes control the cellular death program in the nematode C. elegans. Detailed studies in this simple model organism demonstrated that 131 of totally 1090 cells die reproducibly during development, and that this natural cell death is controlled by a unique set of genes.

The model organism C. elegans

Sydney Brenner realized, in the early 1960s, that fundamental questions regarding cell differentiation and organ development were hard to tackle in higher animals. Therefore, a genetically amenable and multicellular model organism simpler than mammals, was required. The ideal solution proved to be the nematode Caenorhabditis elegans. This worm, approximately 1 mm long, has a short generation time and is transparent, which made it possible to follow cell division directly under the microscope.

Brenner provided the basis in a publication from 1974, in which he broke new ground by demonstrating that specific gene mutations could be induced in the genome of C. elegans by the chemical compound EMS (ethyl methane sulphonate). Different mutations could be linked to specific genes and to specific effects on organ development. This combination of genetic analysis and visualization of cell divisions observed under the microscope initiated the discoveries that are awarded by this year’s Nobel Prize.

Mapping the cell lineage

John Sulston extended Brenner’s work with C. elegans and developed techniques to study all cell divisions in the nematode, from the fertilized egg to the 959 cells in the adult organism. In a publication from 1976, Sulston described the cell lineage for a part of the developing nervous system. He showed that the cell lineage is invariant, i.e. every nematode underwent exactly the same program of cell division and differentiation.

As a result of these findings Sulston made the seminal discovery that specific cells in the cell lineage always die through programmed cell death and that this could be monitored in the living organism. He described the visible steps in the cellular death process and demonstrated the first mutations of genes participating in programmed cell death, including the nuc-1 gene. Sulston also showed that the protein encoded by the nuc-1 gene is required for degradation of the DNA of the dead cell.

Identification of “death genes”

Robert Horvitz continued Brenner’s and Sulston’s work on the genetics and cell lineage of C. elegans. In a series of elegant experiments that started during the 1970s, Horvitz used C. elegans to investigate whether there was a genetic program controlling cell death. In a pioneering publication from 1986, he identified the first two bona fide “death genes”, ced-3 and ced-4. He showed that functional ced-3 and ced-4 genes were a prerequisite for cell death to be executed.

Later, Horvitz showed that another gene, ced-9, protects against cell death by interacting with ced-4 and ced-3. He also identified a number of genes that direct how the dead cell is eliminated. Horvitz showed that the human genome contains a ced-3-like gene. We now know that most genes that are involved in controlling cell death in C. elegans, have counterparts in humans.

Of importance for many research disciplines

The development of C. elegans as a novel experimental model system, the characterization of its invariant cell lineage, and the possibility to link this to genetic analysis have proven valuable for many research disciplines. For example, this is true for developmental biology and for analysis of the functions of various signaling pathways in a multicellular organism. The characterization of genes controlling programmed cell death in C. elegans soon made it possible to identify related genes with similar functions in humans. It is now clear that one of the signaling pathways in humans leading to cell death is evolutionarily well conserved. In this pathway ced-3-, ced-4- and ced-9-like molecules participate. Understanding perturbations in this and other signaling pathways controlling cell death are of prime importance for medicine.

Disease and programmed cell death

Knowledge of programmed cell death has helped us to understand the mechanisms by which some viruses and bacteria invade our cells. We also know that in AIDS, neurodegenerative diseases, stroke and myocardial infarction, cells are lost as a result of excessive cell death. Other diseases, like autoimmune conditions and cancer, are characterized by a reduction in cell death, leading to the survival of cells normally destined to die.

Research on programmed cell death is intense, including in the field of cancer. Many treatment strategies are based on stimulation of the cellular “suicide program”. This is, for the future, a most interesting and challenging task to further explore in order to reach a more refined manner to induce cell death in cancer cells.

Using the nematode C. elegans this year’s Nobel Laureates have demonstrated how organ development and programmed cell death are genetically regulated. They have identified key genes regulating programmed cell death and demonstrated that corresponding genes exist also in higher animals, including man. The figure schematically illustrates the cell lineage (top left) and the programmed cell death (below) in C. elegans. The fertilized egg cell undergoes a series of cell divisions leading to cell differentiation and cell specialization, eventually producing the adult organism (top right). In C. elegans, all cell divisions and differentiations are invariant, i.e. identical from individual to individual, which made it possible to construct a cell lineage for all cell divisions. During development, 1090 cells are generated, but precisely 131 of these cells are eliminated by programmed cell death. This results in an adult nematode (the hermaphrodite), composed of 959 somatic cells.



Cell Drawings HRWch4

Cell Drawings

Holt, Rinehart, Winston    Modern Biology

Draw on separate sheets of unlined paper, label drawing & each part, color, and tell the function of EACH LABELED PART (FUNCTION MUST BE WRITTEN NEXT TO THE LABEL) for the following cell drawings:

Page 72    Figure 4.4         Cell Shapes

Page 74    Figure 4.6         Animal Cell

Page 75    Figure 4.7         Bacterial cell (Prokaryote)

Page 76    Figure 4.9         Cell Organization

Page 77    Figure 4.10       Phospholipid

Page 78    Figure 4.11        Cell Membrane

Page 79    Figure 4.12        Nucleus & Nucleolus

Page 80    Figure 4.13        Mitochondria

Page 80    Figure 4.14        Ribosome

Page 81    Figure 4.15        Endoplasmic Reticulum

Page 82    Figure 4.16        Golgi

Page 84    Figure 4.18        Cytoskeleton

Page 85    Figure 4.19        Microtubule

Page 87    Figure 4.21        Plant Cell

Page 89    Figure 4.23        Chloroplast

When all drawings are complete — drawn, colored, labeled, and all functions written — then make a cover sheet with your name and a title and staple this to the top of your drawings. Number the pages in the lower right hand corner.