4th Biochemistry Lecture Exam (Batch 2024) Flashcards
- TRUE about pyruvate dehydrogenase.
A. Oxidatively decarboxylates pyruvate into Acetyl-CoA.
B. Phosphorylates pyruvate into Acetyl-CoA.
C. Dehydrates pyruvate into Acetyl-CoA.
D. Deaminates pyruvate into Acetyl-CoA.
A. Oxidatively decarboxylates pyruvate into Acetyl-CoA.
- Areas of regulation in the glycolytic pathway EXCEPT.
A. Phosphofructokinase
B. Hexokinase
C. Aldolase
D. Pyruvate kinase
C. Aldolase
- What molecule is regenerated at the end of the citric acid cycle for gluconeogenesis?
A. Ketoglutarate
B. Citrate
C. Malate
D. Oxaloacetate
D. Oxaloacetate
- The reaction involving glucose-6-phosphate, catalysed by phosphohexose isomerase, produces the compound;
A. Fructose-6-phosphate
B. Fructose-1,6-biphosphate
C. Dihydroxyacetone phosphate
D. 1,3-biphosphoglycerate
A. Fructose-6-phosphate
Step 2
- What is an important compound at the junction of glycolysis, gluconeogenesis, and the pentose phosphate pathway?
A. Glyceraldehyde-3-phosphate
B. 1,3-biphosphoglycerate
C. Glucose-6-phosphate.
D. Fructose-6-phosphate
C. Glucose-6-phosphate.
Step 1 : G6P -> 6-phosphogluconolactone (6PGL)
Enzyme: Glucose 6 phosphate Dehydrogenase (G6PDH)
- Glycolysis in erythrocytes always terminates in this substrate.
A. Lactate
B. Pyruvate
C. Glucose
D. Acetyl-CoA
A. Lactate
Aerobic:
* G + 2 Pi + 2 ADP2 lactate + 2 ATP + 2 H2O;
* net of 2 ATP / G; At oxygen debt or lacking mitochondria, no net NADH+H consumption
- What comprises pyruvate dehydrogenase enzyme complex?
A. Thiamine diphosphate, CoA-SH, Riboflavin
B. Thiamine diphosphate, Lipoate, Riboflavin
C. Thiamine diphosphate, CoA-SH, Lipoate
D. Thiamine diphosphate, CoA-SH, CO2
B. Thiamine diphosphate, Lipoate, Riboflavin
E1: Pyruvate Dehydrogenase
Co-Enzyme : Thiamine Pyrophosphate (TPP)
E2: Dihydrolipoyl Transacetylase
Co-Enzyme : Lipoate, Coeynzyme A (Vitamin B5 : Pantothenic Acid)
E3: Dihydrolipoyl Dehydrogenase
Co-enzyme: NADH (Vitamin B3 : Niacin), FADH (Vitamin B2: Riboflavin)
- What inhibits pyruvate dehydrogenase?
A. Pyruvate
B. FADH
C. Acetyl-CoA.
D. Glucose
C. Acetyl-CoA.
- In glycolysis, how much ATP is produced via substrate level phosphorylation?
A. 4
B. 5
C. 6
D. 7
A. 4
Substate-level phosphorylation = 4 ATP
(7) Phosphoglycerate kinase (1,3-BPG -> 3-PG)
(10) Pyruvate Kinase (PEP->Pyruvate)
- How much energy is produced from the reduction of pyruvate to Acetyl-CoA?
A. 3 FADH
B. 2 NADH
C. 5 GTP
D. 4 ATP
B. 2 NADH
- What is the important substrate regenerated in the reaction catalysed by lactate dehydrogenase for the continuation of anaerobic glycolysis?
A. NADH
B. NAD+
C. Lactate
D. Pyruvate
B. NAD+
- Which catalyzes an irreversible reaction?
A. Phosphohexose isomerase
B. Pyruvate kinase
C. Aldolase
D. Enolase
B. Pyruvate kinase
Regulatory/ Irreversible Steps
(1) Hexokinase/ Glucokinase
(3) Phosphofructokinase-1 (Rate-limiting step)
(10) Pyruvate Kinase
- Which enzyme commits the glucose molecule to the cell and prevents it from leaving the cell’s plasma compartment?
A. Glycogen synthase
B. Glycogen phosphorylase
C. Glucose-6-phosphate
D. Phosphofructokinase
D. Phosphofructokinase
Regulatory/ Irreversible Steps
(1) Hexokinase/ Glucokinase
(3) Phosphofructokinase-1 (Rate-limiting step)
(10) Pyruvate Kinase
- Which enzyme is active when phosphorylated?
A. Glycogen synthase
B. Glycogen phosphorylase
C. Glucose-6-phosphate
D. Phosphofructokinase
B. Glycogen phosphorylase
- What is the rate limiting factor of glycolysis?
A. Glucose-6-phosphate
B. Phosphofructokinase-1
C. Pyruvate kinase
D. All of the above
B. Phosphofructokinase-1
- Which of the following reactions are considered as gluconeogenic reactions or pathways?
A. Glycogen → Glucose
B. Alanine → Pyruvate
C. Acetoacetate → Glucose
D. Pyruvate → Acetyl-CoA
B. Alanine → Pyruvate
Glycogen ➝ Glucose (Glycogenesis)
Alanine ➝ Pyruvate (GNG : Glucose-Alanine Cycle)
Acetoacetate ➝Glucose (Cholesterol synthesis)
Pyruvate ➝ Acetyl-CoA (Transition State)
- Which of the following is not a gluconeogenic enzyme?
A. Glucose-6-phosphatase
B. Glyceraldehyde-3-phosphate dehydrogenase
C. Phosphoglycerate kinase
D. Pyruvate kinase
D. Pyruvate kinase
- What is the role of the enzyme aldolase in gluconeogenesis?
A. It synthesizes 2 triose phosphates for gluconeogenesis
B. It condenses 2 triose phosphates to form a 6-carbon compound
C. It converts aldoses to ketoses
D. It delivers adenosine triphosphate to the cytosol as a source of energy for gluconeogenesis
B. It condenses 2 triose phosphates to form a 6-carbon compound
- Why is gluconeogenesis not possible in skeletal muscles?
A. Skeletal muscles do not have the enzyme lactate dehydrogenase to convert lactate to pyruvate
B. Skeletal muscles do not have mitochondria for oxaloacetate synthesis
C. Skeletal muscles do not have the enzyme glucose-6-phosphatase
D. Skeletal muscles are deficient in fructose-1,6-bisphosphatase, the rate-limiting enzyme of
Gluconeogenesis
C. Skeletal muscles do not have the enzyme glucose-6-phosphatase
- Which of the following can be used as a substrate for gluconeogenesis?
A. Acetyl-CoA
B. Lactate
C. Acetoacetate
D. Leucine
B. Lactate
GNG:
Synthesis of glucose from non-carb sources
* Lactate
* Pyruvate
* Glycerol
* Glucogenic AA (Alanine)
* Odd-chain FA (Propionate)
FUNCTION OF GNG
* maintains blood sugar concentration,
* uses lactate and glycerol (end products of glycolysis and glycerol),
* excretes excess protons by kidneys during metabolic acidosis,
* recycles C skeletons of deaminated AA
- Which glucose transporter is activated in the presence of insulin?
A. GLUT 1
B. GLUT 2
C. GLUT 4
D. SGLT 1
C. GLUT 4
- Which is the correct sequence of events for the secretion of insulin from the pancreas?
A. Increase glucose → increase glycolysis → increased ATP synthesis → depolarization of the beta cell → exocytosis of insulin.
B. Decreased serum glucose → increased pancreatic gluconeogenesis → increased glycolysis →
depolarization of the beta cell → insulin secretion
C. Increased glycolysis → elevation of pancreatic glucose → increased ATP synthesis → increased free
phosphate in pancreas → insulin exocytosis
D. Decrease of pancreatic glucose → cell depolarization → increased calcium influx to the cell → increased
glycolysis → insulin secretion
A. Increase glucose → increase glycolysis → increased ATP synthesis → depolarization of the beta cell → exocytosis of insulin.
- Which enzymes circumvent the glycolytic reaction catalysed by pyruvate kinase?
A. Pyruvate dehydrogenase and lactate dehydrogenase
B. Pyruvate carboxylase and PEP carboxykinase
C. Hexokinase and glucokinase
D. Fructose-6-phosphate and fructose-1,6-bisphosphate
B. Pyruvate carboxylase and PEP carboxykinase
- Which of the following substrates are decreased by glucagon?
A. Glucose
B. Fructose-2,6-bisphosphate
C. Fructose
D. Cyclic AMP
B. Fructose-2,6-bisphosphate