biochemistry questions

1. For every molecule of glucose that enters
glycolysis, there is an initial investment of 2
molecules of ____ before the subsequent
generation of ____ .
• ATP, ATP

2. What is the purpose of glucagon?
• It slows down glycolysis when blood sugar
is low and stimulates the formation of
more glucose.

3. An enzyme that catalyzes the
phosphorylation of a molecule using ATP is
called ____
• Kinase

4. Name two molecules that carries electrons
from glycolysis and Krebs Cycle to the
electron transport system.
• NADH and FADH2

5. Phosphofructokinase-1 (PFK-1) is an enzyme in glycolysis.
It’s activity is controlled by a complex allosteric regulation.
What is the function of AMP in the PFK-1 regulation?
• AMP allosterically activates PFK-1

6. There are three irreversible reactions in the
glycolysis. What are the corresponding
enzymes that catalyze those reactions?
• Hexokinase or Glucokinase
• Phosphofructokinase 1 or PFK-1
• Pyruvate Kinase

7. Hexokinase is allosterically inhibited by its product Glucose
6 phosphate. The hexokinase in the liver is called
glucokinase. However, glucokinase is not subject to product
inhibition by glucose-6-phosphate. What the benefit of this
characteristics of glucokinase?
• Liver will take up & phosphorylate glucose
even when liver glucose-6-phosphate
concentration is high.

8. During the Cori cycle, _____ is transported
to the liver to regenerate glucose which is
returned to muscle tissue.
• Lactic acid or lactate

9. Insulin is produced when blood glucose is
high. How does insulin regulate the
transcription of the glycolysis enzyme in liver,
glucokinase?
• Insulin activates of transcription of
Glucokinase in liver.

10. In the liver, the most important coordinating modulator is fructose 2,6-
bisphophate (F2,6BP). It is formed from F6P by the enzyme domain,
phosphofructokinase-2 (PFK-2), and broken down by the same enzyme,
but at a different domain called fructose 2,6-bisphosphatase (FBPase-
2). How does the balance of PFK-2 to FBPase-2 activity controlled by
glucagon?
• Glucagon causes the enzyme phosphorylation.
Phosphorylation of the enzyme results in the
inactivation of the phosphofructokinase-2 activity
and activation of the fructose-2,6-
bisphosphatase activity.

11. The last product of glycolysis is ____ while
the first reactant of Krebs cycle is ____.
• Pyruvate, Acetyl Co-A

12. Briefly explain the Cori cycle which is a
linked metabolic pathways.
• The glucose can enter the blood and be
carried to muscles.
• Lactic acid is produced by anaerobic
glycolysis in the muscles
• The lactic acid is sent in the blood to the
liver which can convert it back to glucose
through gluconeogenesis.

13. What is epinephrine’s role in glycogen
and glucose metabolism?
• Epinephrine markedly stimulates glycogen
breakdown and glycolysis.

14. Palmitic acid, CH3(CH2)14COOH, can
maximally yield ____ acetyl-CoAs
through ____ cycles of beta-oxidation.
• Eight, seven

15. Why can acetone be detected on
breath of diabetic patients?
• Acetone breath in diabetics is caused by an
excess production of ketone bodies.
• Glucose is abundant in blood, but uptake by
cells in muscle, liver, and adipose cells is low.
Cells, metabolically starved, turn to
gluconeogenesis and fat/protein catabolism
• However, due to excess gluconeogenesis,
oxaloacetate is low, so acetyl-CoA from
fat/protein catabolism does not go to TCA, but
rather to ketone body production.

16. High cholesterol diet leads to ____
(promotion/repression) of LDL receptor synthesis.
• repression

17. Chylomicrons are vesicles found in the blood and lymphatic
fluid where they serve to transport lipid from the intestine to
the liver and to adipose tissue. Of what are the chylomicrons
composed? List at least 3 components.
• Triglycerides
• Cholesterols
• lipoproteins
• phospholipids
• Cholesteryl ester

18. What is the effect of epinephrine and
glucagon on triglyceride metabolism?
• Epinephrine and glucagon trigger the
mobilization of stored triglycerides

19. What is oxidative phosphorylation?
• Answer1: Oxidative phosphorylation
transfers energy from NADH to ATP. (via
chemiosmosis)
• Answer2: Oxidative phosphorylation is the
process of converting this high redox
potential into energy-rich ATP molecules.

20. Oxidative phosphorylation is accomplished
via two separate systems in the
mitochondrion. What are those two systems?
• Electron transport chain system and ATP
synthesis system.

21. ATP synthesis is driven by proton motive
force. What are the two types of gradient
associated with proton motive force?
• a proton gradient or pH gradient
• a electrical gradient or ion gradient

22. Metabolism of amino acids differs, but all of
them require the removal of amino groups.
What are the two types of reactions to
remove amino groups?
• Transamination
• Deamination

23. Disposal of ammonia from amino acid metabolism
as _____ in most tissues especially in the brain
and kidneys, as _____ in the liver, and as _____
in the skeletal muscles.
• Glutamine, urea, alanine

24. Based on the catabolic fates of carbon
skeleton of amino acids, the amino
acids can be classified as ____ or
_____.
• Glucogenic, ketogenic

25. Dietary nucleotides _____ (do/do not)
contribute energy as an energy source
material and _____ (are/are not)
incorporated into RNA or DNA.
• Do not, are not

26. The purine nucleotides are synthesized via
two pathways in the body. One is ____
synthesis pathway while the other is ____
pathway.
• De novo, salvage

27. The purine synthesis is _____ by PRPP,
_____ by IMP, _____ by AMP, and _____by
GMP. Fill the blank with activated or
inhibited.
• Activated, Inhibited,
Inhibited, Inhibited,

28. What are the carbohydrate and fat
metabolic events occurred in liver
during fasting?
• The liver first starts glycogen degradation,
then gluconeogenesis to maintain blood
glucose levels.
• The fatty acid oxidation and ketone body
production are increased.

29. Insulin promotes the translocation of
______ to the plasma membrane.
• GLUT or glucose transporter

30. Why do we say that DNA replication is
semiconservative?
• The new strands composed of one original
strand and one daughter strand

31. DNA polymerases cannot initiate synthesis of a
polynucleotide; they can only add nucleotides to
the 3’ end. Therefore, a short _____ is required to
initiate nucleotide synthesis.
• RNA primer

32. Eukaryotic chromosomal DNA molecules have
special nucleotide sequences at their ends called
______.
• telomeres

33. Why is DNA replication semi-discontinuous?
• DNA strands are antiparallel. And,
replication process obeys the principle that
DNA is synthesized from the 5´ end to the
3´end.
• Leading strand synthesized continuously
while lagging strand synthesized
discontinuously

34. List at least 3 differences between
replication and transcription.
replication transcription
template double strands single strand
substrate dNTP NTP
primer yes no
Enzyme DNA polymerase RNA polymerase
product dsDNA ssRNA
base pair A-T, G-C A-U, T-A, G-C
The whole genome of DNA needs to be replicated, but only small
portion of genome is transcribed

35. During transcription, one of the DNA strands
called ______ strand is the strand from which
the RNA is actually transcribed. The other
strand called _____ strand is the strand whose
base sequence specifies the amino acid
sequence of the encoded protein.
• Template, coding

36. What is asymmetric transcription?
• Only the template strand is used for the transcription, but
the coding strand is not.
• The transcription direction on different strands is
opposite.
5'
3'
3'
5'

37. The mRNA start codon is ___ in
most cases.
• AUG

38. Deoxyribonucleotides are formed from
their corresponding _____.
• ribonucleotides

39. Explain mRNA splicing
• During splicing, introns are removed from
the strand, and the exons that remain are
assembled into a finished strand of mRNA
that is ready for translation.

40. What is the consequence of
frameshift mutation?
• Frameshift mutations result in all
subsequent reading frames (codons)
being shifted by one or two nucleotides.
These shifted frames will code for different
amino acids than before, and will result in
the creation of a malfunctioning protein.

41. The GUU  GUA transition still codes for
Val and it therefore called to be ______
mutation.
• nonsense

42. The insertion or deletion of a nucleotide
into a gene results in a _____ mutation.
• frameshift

43. An incoming aminoacyl-tRNA enters
the ribosome at the ___ site.
• A

44. ____ are synthesized as inactive precursors
that require proteolysis for activation.
• zymogen or proenzyme

45. In the operon system, tryptophan acts
as a ____ by binding the trp repressor.
• Co-repressor