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BIOC 3560 Final exam 2024/2025 with questions and correct answers || grade A
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BIOC 3560 Final exam 2024/2025 with questionsand correct answers || grade A
The phosphofructokinase enzyme and the fructose 1,6 bisphosphate-1 phosphatase
catalyze the same reaction in opposite directions.
(a) What are the essential differences in the two reactions?
(b) What would be the result of both reactions acting simultaneously?
(c) What physiological benefit could be derived from (B)?
(d) What physiological harm (pathology) could arise from (B)? - CORRECT
ANSWER ; (a) PFK-1 catalyzes ATP-dependent phosphorylation
FBPase-1 catalyzes hydrolysis - without generation of ATP
(b) futile cycle, consumption of ATP, release of heat
(c) production of heat for warmth
(d) depletion of ATP (glycolysis is not being completed), decreased blood sugar
(gluconeogenesis is not being completed)
The bifunctional or tandem enzyme (phosphofructokinase-2/fructose1,6-
bisphosphatase-2), glycogen phosphorylase, and glycogen synthase are all:
,(a) Activated by serine phosphorylation
(b) Inactivated by serine phosphorylation
(c) Directly regulated by the same protein kinase
(d) Controlled through a cAMP-dependent serine kinase signalling pathway. -
CORRECT ANSWER ; (d) Controlled through a cAMP-dependent serine kinase
signalling pathway.
How does PKA contribute to the coordinated regulation of glycogen metabolism? -
CORRECT ANSWER ; PKA can phosphorylate glycogen synthase and inhibit its
activity. This decreases glycogen synthesis. PKA can also phosphorylate an
enzyme called glycogen phosphorylase kinase (GPK). Phosphorylation of GPK by
PKA activates GPK. GPK then phosphorylates glycogen phosphorylase, which
activates the latter. Active glycogen phosphorylase breaks down glycogen. Thus,
PKA activity reciprocally coordinates glycogen synthesis and breakdown.
During the first steps of gluconeogenesis, depletion of NADH from the cytosol is
avoided. How is this accomplished? - CORRECT ANSWER ; Pyruvate is
converted to malate in the mitochondria, consuming mitochondrial NADH.
Subsequently, malate is transferred to the cytosol (via oxoacetoacetate), and then
converted to PEP, which results in the production of cytosolic NADH.
What is the committed step in the β-oxidation of fatty acids? Name the integral
membrane protein that mediates this step. Identify the compound that is primarily
responsible for regulation of this step. - CORRECT ANSWER ; 1. Transport into
mitochondrion
2. Fatty-acyl-carnitine/carnitine transporter
,3. Malonyl-CoA inhibits carnitine acyltransferase I
What are the four major steps in the biosynthesis of fatty acids? Describe the
chemical event that happens at each enzymatic step. - CORRECT ANSWER ; 1.
Malonyl-CoA is attached to the activated acyl group (condensation)
2. b-keto group is changed to an alcohol (reduction)
3. H2O is eliminated to form C=C (dehydration)
4. C=C is changed to a saturated acyl group (reduction)
Metabolic control can be described to occur with three different speeds (fast, slow
and gradual). Over what time scale do these control mechanisms happen? Describe
how control occurs at the biochemical level. - CORRECT ANSWER ; Fast - s to
min; regulation of enzymes in the cell
Slow - min to h; hormonal regulation
Gradual - h to days; change in gene expression
What is the correct order of function of the following enzymes of β-oxidation?
1. b-Hydroxyacyl-CoA dehydrogenase
2. Thiolase
3. Enoyl-CoA hydratase
4. Acyl-CoA dehydrogenase - CORRECT ANSWER ; 4., 3., 1., 2.
, What is an amphipathic compound? Explain how such compounds contribute to
the structure of biological membranes. - CORRECT ANSWER ; An amphipathic
compound has one region or domain that is hydrophilic and another that is
hydrophobic. When added to water, amphipathic compounds tend to arrange in a
way that exposes their hydrophilic regions to the solvent and hide their
hydrophobic domains. One structure that accomplishes this is the lipid bilayer,
which forms spontaneously when phospholipid is added to water.
(a) List the major components of membranes. - CORRECT ANSWER ; (a)
Phospholipids, sterols, proteins (integral and peripheral)
(b) When a preparation of mitochondrial membranes was treated with high salt (0.5
M NaCl), it was observed that 40% of the total protein in this preparation was
solubilized. What kind of membrane proteins are in this soluble extract, and what
forces normally hold them to the membrane? - CORRECT ANSWER ; (b)
Peripheral membrane proteins, which are associated with the membrane through
ionic and hydrogen bonds between their charged and polar side chains and the
charged head groups of phospholipids
(c) What kind of proteins constitutes the insoluble 60%, and what forces hold these
proteins in the membrane? - CORRECT ANSWER ; (c) integral membrane
proteins, which are held to the membrane by hydrophobic interactions between
their nonpolar side chains and the hydrophobic fatty acyl chain of phospholipids,
and those peripheral membrane proteins that are held to the membrane by a
covalent lipid anchor.
(a) When relatively high concentrations of fatty acids are suspended in water, they
form structures known as ___________. - CORRECT ANSWER ; (a) Micelles
(b) When relatively high concentrations of membrane phospholipids are dissolved
in water, they form structures known as __________. - CORRECT ANSWER ;
(b) Bilayers or liposomes
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