Download Proteins Hwk KEY

IB Bio Year 1 / IHS
PROTEINS Homework, Neil 9e KEY
Directions: after reading 5.4, answer the following questions in your journal. Please rephrase the questions in the
answers.
1.
Draw a “generalized” amino acid (this means using “R” to stand for its side
chain).
(Image credit: education-portal.com)
Remember, the amino and carboxyl groups do ionize under certain conditions.
2.
Explain how the 20 different amino acids found in living things are separated into 3 groups.
They are separated by the fundamental “personalities” (chemical properties) of their side chains or R groups:
 9 have nonpolar side chains (making them hydrophobic)
 6 have polar side chains (making them hydrophilic)
 5 have side chains that ionize (acquire electrical charges), making them really hydrophilic). Of these 5, 2 of
them are acidic (acquire negative charges when they lose H), and 3 are basic (acquire positive charges when
they gain H).
3.
State the functions of these 8 proteins: cellulase, collagen, hemoglobin, immunoglobulin, insulin, rhodopsin,
rubisco, and silk. (Use the index!)
Proteins
cellulase
collagen
hemoglobin
immunoglobulin
insulin
rhodopsin
rubisco
silk
4.
Functions
Secreted by bacteria and fungi to hydrolyze cellulose molecules so the component glucose
molecules can be absorbed for energy
Structural component of connective tissue and bone
Reversibly binds oxygen so it can be delivered to the tissues from the lungs; found inside red
blood cells
Also known as antibodies, these proteins bind to and inactivate antigens (molecules on germs)
Hormone secreted by the pancreas that promotes the uptake of glucose and the synthesis of
glycogen
A “hybrid” molecule consisting of a protein (opsin) and a second molecule (retinal) within the
cells of your retina; absorbs light and sets into motion the biochemical processes that result in
vision.
Short for Ribulose Bisphosphate Carboxylase, this enzyme participates in one of the sugarmaking reactions of photosynthesis
Spiders use this stretchy, strong protein to build their webs (among other things)
For each level of protein structure, list the bonds that stabilize the protein. (Hint: use the Exploring figure 5.20)
Level of structure
Primary structure
Secondary structure
Tertiary structure
Bonds that stabilize that level
Covalent peptide bonds
Hydrogen bonds between the O and H atoms of the polypeptide’s backbone
R group interactions: hydrogen bonds, ionic bonds (+/-) and charge repulsions (+/+
and -/-), disulfide bridges, hydrophobic interactions/van der Waals
Quaternary structure
5.
Same as for tertiary structure
Why does a denatured protein lose its function?
Every protein has a “job” (function) because of its shape. For instance, immunoglobulins bind (grab onto) parts of
germs, hemoglobin binds oxygen, enzymes grab substrates, and so on. If a protein is exposed to high heat or
abnormal pH or salt conditions that interfere with the bonds holding it in secondary, tertiary, or quaternary
structure, its shape is lost – and its function as well.