Chapter
5: Cell Structure and Function
The unfortunate truth of this chapter is that it is a lot of memorization. You have to learn all the components of the eukaryotic cell and their functions. There is no easy way to do, you just have to study them. I would suggest trying to draw them in place on the diagram, so that you get used to identifying them in location and basic representation. You should also list them and try to write out a little one sentence description of their functions.
The other key concept in this chapter is the differences and similarities between the eukaryotic and prokaryotic cells. Again, make lists of the similarities and lists of the difference. Be sure and check the lists against one another.
I. What are the basic features of cells?
A. Modern Cell Theory
1. Every living thing is composed of one or more cells.
2. The smallest living things are single celled organisms, and cells are the functional units of multicellular creatures.
3. All cells arise from preexisting cells.
B. All cells share some common features
1. The Plasma Membrane
2. All cells use DNA for heredity and contain cytoplasm
3. All cells obtain nutrients and energy from the environment
a. Essentially all energy on this planet comes from the sun.
b. Energy from the sun can be directly harnessed by some cells which in turn provide food and energy for other cells.
4. Cell function limits cell size
a. Diffusion is a major factor in transport in an out of the cells.
b. Diffusion is limited by the surface area of the plasma membrane.
c. Larger cells have less surface area than a group of smaller cells would have.
C. There are two types of cells: prokaryotic and eukaryotic
1. Prokaryotic – “before nucleus”
2. Eukaryotic – “true nucleus”
II. What are the major features of prokaryotic cells?
A. Prokaryotic cells are small and possess specialized surface structures
1. The exteriors of prokaryotic cells are highly specialized with a number of attendant structures.
a. Cell Wall – the exterior structure of bacteria is a rigid structure composed of a complex material called peptidoglycan.
b. Pili – structures that project out of the cell that allow for the transfer of DNA between bacteria.
c. Fimbriae – structures that project out of the cell that helps bacteria to adhere to surfaces.
d. Capsules and Slime Layers – thick coatings that bacteria produce outside their cell walls for a variety of protective purposes.
2. Prokaryotic cells have fewer specialized structures within their cytoplasm.
a. The DNA of a prokaryotic cell have singular, circular chromosomes, coiled and localized in a region called the nucleoid.
b. Small independent circular pieces of DNA called plasmids also reside in many bacteria.
c. There is very limited internal organization within prokaryotic cells, mostly a homogeneous mixture.
III. What are the major features of eukaryotic cells?
A. Eukaryotic cells contain organelles
1. Organelles are membrane – enclosed structures that perform specific functions within the cells.
2. The cell also contains a network of protein fibers, called the cytoskeleton, that give shape and organization to the cell.
3. Not all cells contain all possible organelles; the particular mix depends on the exact role of the cell.
B. The nucleus is the control center of the eukaryotic cell.
1. The nucleus is the organelle that contains the DNA of the cell.
2. The nucleus is separated from the remainder of the cell by a double membrane called the nuclear envelope.
3. The nuclear envelope allows for the selective exchange of materials.
a. Movement through the envelope is regulated by nuclear pores, protein holes through the membrane.
b. The movement of large molecules is regulated.
4. Chromatin contains DNA, which codes for the synthesis of proteins.
a. Chromatin is DNA associated with proteins.
b. The material self assembles into higher structures called chromosomes.
c. The DNA material is not used, but copied to working copies of RNA.
5. The nucleolus is the site of ribosome assembly
a. The nucleolus is the site of the ribosome assembly.
b. Ribosomes are the site of protein synthesis
C. Eukaryotic cells contain a complex system of membranes.
1. The cells have elaborate membrane systems that interconnect and recycle membrane material.
2. The plasma membrane both isolates the cell and allows selective interactions between the cells and its environment.
3. The endoplasmic reticulum (ER) forms membrane-enclosed channels within the cytoplasm.
a. The rough ER is ER studded with ribosomes and is the site of production for proteins that are membrane bound.
b. The smooth ER is used for the production of lipids and membranes.
c. Membrane vesicles containing proteins are constantly budding off the ER to transport materials to the Golgi Complex.
4. The Golgi Complex is a structure that sorts, chemically alters, and packages molecules in the cell.
5. Lysosomes are vesicles that contain digestive enzymes.
a. Lysosomes become fused to food vacuoles and aid it the processing and digesting of material.
b. Lysosomes also digest and recycle defective membranes and organelles.
6. Membranes are recycled and reused through out the cell.
D. Vacuoles serve many functions, including water regulation, support, and storage.
1. Vacuoles – fluid filled sacs formed by a single membrane.
2. Contractile Vacuoles – are specialized vacuoles in freshwater microorganisms that collect water absorbed due to osmosis and pump it back outside of the cell.
3. Central Vacuoles – specialized vacuoles that take up around three quarters of plant cells and are used for storage and water balance.
E. Mitochondria – double membrane bound organelles that convert the energy in sugar to ATP (the energy currency of the cell)
1. The mitochondria enable the use of oxygen to convert sugars through the aerobic metabolism.
2. Without mitochondria, aerobic metabolism can not occur and only anaerobic metabolism is accomplished.
F. Chloroplast – double membrane bound organelles that allow the conversion of sunlight into energy.
1. The process of converting sunlight into energy is called photosynthesis.
2. Photosynthesis is accomplished through structures called thylakoid membranes that contain the pigment chlorophyll.
G. Plastids – storage vesicles used by plants and photosynthetic protists for the storage of materials.
H. Cytoskeleton – a network of protein filaments that organize and give structure to the interior of the cell.
1. Three types of proteins are involved
a. Microfilaments
b. Intermediate Filaments
c. Microtubules
2. Functions
a. Cell shape
b. Cell movement
c. Organelle movement
d. Cell division
I. Cilia and Flagella move the cell through fluids or move the fluid past the cell.
1. Cilia – short numerous projections that allow for movement
2. Flagella – long, sparse filaments
3. Both structures are membrane-bound and filled with cytoplasm.
4. The structure of these units are controlled by a basal body composed of an organelle called a centriole.
IV. Endosymbiont Hypothesis