Module 2

Question 1

Peptide bonds

Answer 1

display double bond characteristics:
shorter than single bonds but longer than double bonds
rigid and planar which prevents free rotation
link the alpha carboxyl gp with alpha amino gp

Question 2

Secondary Protein Structure

Answer 2

Alpha Helix:
side chains face outside while helix is composed of backbone
stabilized by H-bonding every 4 residues

Beta Sheets:
can be composed of one or more peptide chains
H bonds also stabilize

Beta Bends:
reverse the direction of the polypeptide chain helping it to form a globular shape
Gly is frequently found in this structure

Question 3

Tertiary Structure

Answer 3

Folding and final arrangement of polypeptide
core of a domain is built from combinations of super- secondary structures
Stabilized by:
disulfide bonds
hydrophobic interactions
ionic interactions
H-bonds

Question 4

Enzymes

Answer 4

Increase rate of rxn by lowering the activation energy (substrate –> transition state) without getting used up themselves
ES complex stabilizes the transition state which is how the activation energy gets lowered (catalytic gps in active site enhance the probability that the transition state will form)

Question 5

Michaelis-Menton Kinetics

Answer 5

Vmax = highest rate of rxn that can be achieved
enzymes following this have a hyperbolic curve
describes the relation btw rxn velocity and substrate concentration
Km = reflects affinity of the enzyme for the substrate (high Km means low affinity while low Km means high affinity)

Question 6

Lineweaver-Burke Plot

Answer 6

Plots 1/V0 on the y-axis against 1/[S] on the x-axis
x-intercept: -1/Km
y-intercept: 1/Vmax

Question 7

Enzyme Inhibition

Answer 7

Competitive: Inhibitor binds to active site of enzyme
-Causes an increase in Km/Decrease in ES affinity
while Vmax remains the same
Noncompetitive: Inhibitor binds to allosteric site
-Causes Vmax to decrease and Km to remain the
same

Question 8

Hemoglobin

Answer 8

tetramer
heme molecule bound that is stabilized by his residue
Relaxed - high O2 affinity 
taut - low O2 affinity
O2 is a positive effector (homotropic)
sigmoidal curve for O2

Question 9

Myoglobin

Answer 9

hyperbolic curve
binds O2 in muscle
very high O2 affinity

Question 10

bohr effect

Answer 10

decrease in pH = decrease in affinity of O2 (in tissues) (shifts curve to right)
increase in pH = increase in affinity of O2 (in lungs) (shifts to left)

Question 11

heterotrophic effectors of hemoglobin

Answer 11

pH, pCO2, (2,3-BPG) (all negative effectors)

Question 12

GLUT

Answer 12

GLUT 1 - most tissues (basal glucose uptake)
GLUT 2 - liver, kidney, pancreas (remove excess glucose from blood)
GLUT 3 - most tissues ( basal)
GLUT 4 - muscle and fat (removes excess glucose)
GLUT 5 - small intestine and testes (transport of fructose)

low Km (high affinity) GLUT 1 and 3
high Km (low affinity) GLUT 2 and 4

GLUT 4 is the only transporter that is insulin-sensitive (aka insulin dependent)

Question 13

Active transport of Glucose

Answer 13

in small intestine
glucose is present in high concentrations inside intestinal cells
must use active transport to get glucose through these cells
glucose/Na symporter - Na follows its concentration gradient while glucose goes against it

Question 14

Glycolysis

Answer 14

3 rate limiting steps:
glu -> g-6-p (glucokinase and hexokinase)
f-6-p -> f-1,6-bisp (phosphofructokinase 1) (COMMITS to glycolysis)
phosphoenolpyruvate -> pyruvate

Question 15

Fructose-2,6-bisphosphaste

Answer 15

postive allosteric effector
stimulates PFK-1
when high, glycolysis is ON
when low, gluconeogenesis is ON

2 domains:
kinase domain (PFK-2) 
    unphos= active
    phos = not active
phoshphatase domain (FBP-2)