Download Key to Homework 2

1 A Describe the four possible levels of protein structure? What is meant by the term
“final conformation” and “denatured” with respect to proteins
Primary – the specific sequence of amino acids of a polypeptide
Secondary – the coiling or sheeting of the polypeptide due to hydrogen bonds between
different regions of the backbone
Tertiary – the folding of the polypeptide due to interaction of the R groups of different
amino acids
Quaternary – two or more polypeptides form the final functional protein
Final conformation refers to the final functional shape of a protein after it has attained all
the levels of structure.
Denatured refers to the loss of structure and as a result function of a protein
2 What are the three basic components of all nucleotides? What is the difference
between purines and pyrimidines? Which of each are found in DNA and which are found
in RNA?
A phosphate, a five carbon sugar, and a nitrogenous base
Both DNA and RNA have phosphates and the purines A and G.
They differ in that DNA has deoxyribose for it’s sugar while RNA has ribose and DNA
has C T for its pyrimidines while RNA has C & U.
3 Describe the major similarities and differences between prokaryote and eukaryote cells.
Both Prokaryotes and Eukaryotes have a cell membrane, cytoplasm, and genetic material
Prokaryotes lack a true nucleus and membranous organelles, eukaryotes have both these
features.
4 The surface area of a sphere is 4πr2, and the volume is 4/3πr3 (where π = 3.14, and r =
the radius). Calculate the surface area to volume ration for a sphere with a radius of:
• 1 microns = 9.44
• 10 microns = 0.944
• 100 microns = 0.094
5 A Explain the following types of transport across membranes
• Simple diffusion = the passive movement from high to low concentration directly
through the cell membrane
• Facilitated diffusion the passive movement from high to low concentration with the
assistance of a transport protein
Active transport = the actrive movement from low to high concentration directly with the
assistance of a transport protein and a net input of energy
B What is the difference between a channel protein and a carrier protein. Which would
be involved in active transport? A channel protein forms a tunnel through the membrane
that allows for the passage of small polar molecules while a carrier protein forms an
articulating pincher like structure that pulls material through the membrane. The latter
would be involved in active transport
6 What role does a recognition protein serve in a cell membrane? How about a receptor
protein? What feature do they have in common?
Recognition proteins act as an label that identifies what type of cell they are attached to.
Receptor proteins serve as switches that transmit chemical signals across the cell
membrane. They both have oligosaccharide chains attached to their outer surface.
7 A Describe the function for each of the following organelles
• nucleus containment of genetic material
• rough endoplasmic reticulum: internal cell transport, protein synthesis via the
attached ribosomes
• smooth endoplasmic reticulum: internal cell transport, lipid synthesis
• golgi body : receiving, shipping, storage, and processing of biological molecules
• vesicle: internal cell transport, endo/exocytosis
B What network are all these structures a part of? Endo or cytomembrane system
8 Describe how the mitochondrion and the chloroplast are structurally similar and
functionally different.
Both are membranous organelles that have a double membrane consisting of an outer
membrane and an inner membrane that is highly convoluted to increase its effective
surface area. They differ in that the mitochondrion is the principle site of aerobic
respiration while the chloroplast is the principle site of photosynthesis.
9 What is a ribosome? What is it made of? What function does it serve? Where would
you find it in 1) a prokaryotic cell and 2) an eukaryotic cell.
A ribosome is a work bench upon which polypeptides are assembled. It is made up of
ribosomal RNA. It would be found unattached in the cytoplasm of a prokaryote as well
as a eukaryote. In addition, it can be found attached to the rough endoplasmic reticulum
of eukaryotes
10 Describe two ways that a generalized plant cell differs from a generalized animal cell.
Plant cells photosynthesize, animal cells don’t
Plant cells have chloroplasts, animal cells don’t
Plant cells have cell walls, animal cells don’t
Plant cells have central vacuoles, animal cells don’t