Hormonal Regulation (Pentose Phosphate Pathway)

Question 1

Insulin is an example of a(n)______ hormone, whereas adrenaline is an example of a(n)_______ hormone.

(a) catecholamine; peptide
(b) peptide; eicosanoid
(c) endocrine; paracrine
(d) peptide; catecholamine
(e) steroid; endocrine

Answer 1

D

Question 2

When blood glucose is excessively high, the pancreas releases _____. In contrast, when blood glucose is excessively low, the pancreas releases _____

(a) adrenaline; insulin
(b) insulin; glucagon
(c) leptin; adrenaline
(d) inulin; glycogen
(e) cortisol; glucagon

Answer 2

B

Question 3

An elevated insulin level in the blood:

(a) inhibits glucose uptake by the liver.
(b) inhibits glycogen synthesis in the liver and muscle.
(c) results from a below-normal blood glucose level.
(d) stimulates glycogen breakdown in liver.
(e) stimulates synthesis of fatty acids and triacylglycerols in the liver

Answer 3

E

Question 4

Elevated adrenaline levels do not normally stimulate:

(a) fatty acid mobilization in adipose tissue.
(b) gluconeogenesis in liver.
(c) glycogen breakdown in muscle.
(d) glycogen synthesis in liver.
(e) lipolysis in adipocytes

Answer 4

D

Question 5

Adrenaline triggers an increased rate of glycolysis in muscle by:

(a) activation of hexokinase.
(b) activation of phosphofructokinase-1.
(c) conversion of glycogen phosphorylase a to glycogen phosphorylase b.
(d) inhibition of the Cori Cycle
(e) the Pasteur effect

Answer 5

B

Question 6

All of the following occur in the pancreatic β cell when blood glucose levels increase except

(a) Glucose enters the β cell through GLUT-2 transporters.
(b) Intracellular ATP levels increase.
(c) K+ channels close, altering the membrane potential.
(d) Ca 2+ channels open.
(e) Insulin is released by receptor-mediated endocytosis

Answer 6

E

Question 7

Which of the following does not happen following an increase in blood glucose levels?

(a) Liver cells automatically increase their glucose uptake through the action of glucokinase.
(b) Insulin stimulates translocation of glucose transporters to non-hepatic cell membranes.
(c) Intracellular cAMP levels increase and stimulate glycogen synthesis.
(d) Glycogen phosphorylase loses activity.
(e) Triacylglycerol synthesis increases in adipose tissue

Answer 7

C

Question 8

Aerobic activity in response to stress results in which of the following?

I. Glycolysis occurs in the muscle.
II. Glycolysis occurs in the liver.
III. Glycogenolysis occurs in the muscle.
IV. Glycogenolysis occurs in the liver.

(a) I, III, IV
(b) I, II, IV
(c) II, IV
(d) II, IV
(e) III, IV

Answer 8

A

Question 9

Protein kinase A, which stimulates glycogen degradation, is activated directly by:

(A) glucagon.
(B) insulin.
(C) epinephrine.
(D) cyclic AMP
(E) adrenergic receptors

Answer 9

D

Question 10

Which of the following is not correct?

(a) adrenalin causes muscle glycogen to be mobilised
(b) glucagon causes an increase in cAMP in liver cells
(c) glucagon is released when blood glucose levels fall
(d) insulin activates glycogen synthase
(e) insulin increases glucose uptake in liver cells

Answer 10

E

Question 11

The level of fructose 2,6-bisphosphate in liver cells decreases when:

(a) intracellular cAMP levels fall.
(b) intracellular ATP levels rise and AMP levels fall.
(c) glucagon activates phosphorylase and glycogen is mobilized
(d) intracellular cAMP levels are high
(e) intracellular fructose-6-phosphate levels fall and cAMP levels are high

Answer 11

D
Explanation: Fructose 2,6-bisphosphate in the liver decreases when:
* glucagon is secreted in response to low blood glucose, which triggers increased levels of cAMP (second messenger) to signal the phosphorylation of PFK2/F26BPase (PFK2 inactivated and F26BPase activated)
* F26BPase activated so fructose-2,6-bisphosphate is converted to fructose-6-phosphate (and its concentration increases)

Question 12

If cAMP levels are high

i. Glycogenolysis will occur in muscle cells but not liver cells.
ii. Glucose released from muscle glycogen will enter glycolysis.
iii. Glucose released from liver glycogen will exit liver cells via the GLUT4 transporter.
iv. Glucose will enter liver cells resulting in glycogen synthesis.

(a) i, ii, and iv
(b) i and ii
(c) ii, iii and iv
(d) ii only
(e) iii only

Answer 12

D

Question 13

Which of the following most closely describes the stoichiometry of the complete pentose phosphate pathway?

(a) Glucose 6P + NADP+ -> CO2 + Ribose 5P + NADPH
(b) Glucose 6P + 2 NADP+ -> CO2 + Ribulose 5P + 2 NADPH
(c) 2 Glucose 6P + 2 NADP+ -> 2 CO2 + Fructose 6P + glyceraldehyde 3P + 2 NADPH
(d) 3 Glucose 6P + 6 NADP+ -> 3 CO2 + 2 Fructose 6P + glyceraldehyde 3P + 6 NADPH
(e) none of the above

Answer 13

D

Question 14

The pentose phosphate pathway can produce each of the following EXCEPT:

(a) ribose 5-phosphate
(b) NADPH
(c) fructose 6-phosphate
(d) ATP
(e) glyceral-dehyde-3-phosphate

Answer 14

D

Question 15

The oxidative phase of the pentose phosphate cycle consists of:

(a) interconversion of pentose phosphates with fructose phosphate and triose phosphates catalysed by transketolase and transaldolase
(b) the production of ribose phosphate for nucleotide synthesis
(c) conversion of glucose phosphate to 1 pentose phosphate, 1 CO2 and 1 NADPH
(d) conversion of glucose phosphate to 1 pentose phosphate, 1 CO2 and 2 NADPH
(e) conversion of 6-phosphogluconate to ribose phosphate

Answer 15

D

Question 16

The pentose phosphate pathway has two primary products.
They are _____ and _____

(a) ATP; NADPH
(b) oxaloacetate; acetyl CoA
(c) sorbitol; fructose
(d) ribose 5-phosphate; NADPH
(e) glucose 6-phosphate; glyceraldehyde 3-phosphate

Answer 16

D

Question 17

Which of the following statements about the pentose phosphate pathway is correct?

(a) It generates 36 moles of ATP per mole of glucose consumed.
(b) It generates 6 moles of CO2 for each mole of glucose consumed
(c) It is a reductive pathway; it consumes NADH.
(d) It is present in plants, but not in animals.
(e) It provides precursors for the synthesis of nucleotides

Answer 17

E

Question 18

Which of the following statements about the pentose phosphate pathway is incorrect?

(a) It generates CO2 from C-1 of glucose.
(b) It involves the conversion of an aldohexose to an aldopentose.
(c) It is prominent in lactating mammary gland.
(d) It is principally directed toward the generation of NADPH.
(e) It requires the participation of molecular oxygen

Answer 18

E

Question 19

Which of the following tissues displays the lowest activity in the pentose-phosphate pathway?

(a) Adrenal gland
(b) Liver
(c) Adipose tissue
(d) Ovary
(e) Skeletal muscle

Answer 19

E (Unlike the other 4 tissue types, skeletal muscle displays low levels of lipid synthesis and, hence, less need for NADPH)

Question 20

The major regulatory step of the pentose phosphate pathway is catalysed by which enzyme?

(a) transaldolase
(b) phosphofructokinase-1
(c) glucose 6-phosphate dehydrogenase
(d) ribose 5-phosphate isomerase
(e) transketolase

Answer 20

C

Question 21

How do hormonal signalling cascades result in large amplifications of the original signal?

Answer 21

At each level a small quantity of the signal molecule activates a larger number of molecules at the next level. When this occurs over several levels this multiplicative effect can result in considerable amplification (~10 5 – 10 6 fold) of the original signal

Question 22

What metabolic changes occur during the early fasting state?

Answer 22

In the initial hours after a meal, the blood glucose levels start to decrease, the insulin levels decrease, and glucagon is secreted by the α–cells of the pancreas. Glucagon stimulates the liver to mobilise glycogen stores, blocks glycogen synthesis, and inhibits fatty acid synthesis. Glucagon also stimulates gluconeogenesis and blocks glycolysis. These processes make glucose available to the other tissues of the body

Question 23

Compare in general terms the effects of adrenaline (epinephrine), glucagon, and insulin on glucose metabolism

Answer 23

Adrenaline and glucagon cause an increase in the blood glucose level. Adrenaline acts when a higher than normal level of glucose is required; glucagon acts when the level is unusually low. Both stimulate gluconeogenesis and glycogen breakdown and decrease
glycolysis and glycogen synthesis. Insulin causes a decrease in blood glucose levels; it acts by increasing glycogen synthesis, glycolysis, and glucose uptake by cells as well as by decreasing glycogen breakdown

Question 24

Name three general classes of hormones and give an example of each

Answer 24

1) peptide hormones (e.g., insulin, glucagon);
(2) catecholamine hormones (e.g., adrenaline);
(3) steroid hormones (e.g., testosterone, progesterone);
(4) eicosanoids (e.g., prostaglandins, thromboxanes)

Question 25

Choose the correct answer from the list below. Not all of the answers will be used.
a) UDP-glucose
b) α-1,6-glycosidic
c) phosphorylase kinase
d) α-1,4-glycoside
e) glycogenin
f) phosphorylase a
g) glucose 6-phosphatase
h) UTP-glucose
i) calmodulin
j) phosphorolysis
k) epinephrine/adrenaline
l) glucagon

1. Most of the glucose residues in glycogen are linked by this type of bond.
2. This is the activated form of glucose that is required for glycogen synthesis.
3. This is the process by which a bond is cleaved by the addition of orthophosphate.
4. This type of bond is located at the branch points in glycogen.
5. This is the liver enzyme that cleaves the phosphate from
   glucose-6-phosphate.
6. This enzyme catalyses the phosphorylation of glycogen phosphorylase.
7. This protein is the δ subunit of phosphorylase kinase.
8. This hormone signifies the starved state.
9. This protein serves as the primer used by glycogen synthase.
10. This enzyme serves as the glucose “sensor” enzyme in liver cells.

Answer 25

1. Most of the glucose residues in glycogen are linked by this type of bond.
   Ans: d
2. This is the activated form of glucose that is required for glycogen synthesis.
   Ans: a
3. This is the process by which a bond is cleaved by the addition of orthophosphate.
   Ans: j
4. This type of bond is located at the branch points in glycogen.
   Ans: b
5. This is the liver enzyme that cleaves the phosphate from
   glucose-6-phosphate.
   Ans: g
6. This enzyme catalyses the phosphorylation of glycogen phosphorylase.
   Ans: c
7. This protein is the δ subunit of phosphorylase kinase.
   Ans: i
8. This hormone signifies the starved state.
   Ans: l
9. This protein serves as the primer used by glycogen synthase.
   Ans: e
10. This enzyme serves as the glucose “sensor” enzyme in liver cells.
    Ans: f

Question 26

Choose the correct answer from the list. Not all the answers will be used.
A) α-adrenergic receptor
B) β-adrenergic receptor
C) Cori cycle
D) urea cycle
E) leptin
F) phosphatase
G) liver
H) hormones
I) acetyl CoA
J) ketone bodies
K) urea
L) kidney
M) brain
N) pancreas

I. The activity of the enzyme glucokinase increases with high blood glucose.

II. and other waste products from the blood are excreted by the kidney.

III. The provides a pathway for the metabolic use of lactate for production of glucose.

IV. The endocrine glands secrete which result in numerous cellular responses.

V. Epinephrine binding to the causes an increase in intracellular [Ca 2+].

VI. Following prolonged starvation, are used as fuel by the brain.

VII. is the degradation product of glucose, fatty acids, and ketogenic amino acids.

VIII. During starvation the generate as much as 50% of the body’s glucose supply.

IX. The stores very little glycogen and therefore requires a steady supply of glucose from the blood.

X. Mice lacking the protein are genetically obese.

Answer 26

I. The activity of the enzyme glucokinase increases with high blood glucose.
Ans: G

II. and other waste products from the blood are excreted by the kidney.
Ans: K

III. The provides a pathway for the metabolic use of lactate for production of glucose.
Ans: C

IV. The endocrine glands secrete which result in numerous cellular responses.
Ans: H

V. Epinephrine binding to the causes an increase in intracellular [Ca 2+].
Ans: A

VI. Following prolonged starvation, are used as fuel by the brain.
Ans: J

VII. is the degradation product of glucose, fatty acids, and ketogenic amino acids.
Ans: I

VIII. During starvation the generate as much as 50% of the body’s glucose supply.
Ans: L

IX. The stores very little glycogen and therefore requires a steady supply of glucose from the blood.
Ans: M

X. Mice lacking the protein are genetically obese.
Ans: E

Question 27

How is the pentose phosphate pathway regulated?

Answer 27

The level of NADP + is very important in regulating the pathway. Low levels of NADP + inhibit the dehydrogenation of glucose-6-phosphate because NADP + is required as the electron acceptor, and NADPH competes with NADP + in the binding active site of the enzyme. The
nonoxidative phase of the pathway is primarily controlled by the availability of the substrates.

Question 28

What are the sources of glucose 6-phosphate in liver cells?

Answer 28

Glucose 6-phosphate is produced from free glucose after it enters the cell. Two other common sources of glucose 6-phosphate are from the breakdown of glycogen and from gluconeogenesis.

Question 29

Rat liver is able to metabolize glucose by both the glycolytic and the pentose phosphate pathways.
Indicate in the blanks if the following are properties of glycolytic (G), pentose phosphate (P), both (G + P), or neither (0):

NAD+ is involved.
CO 2 is liberated.
Phosphate esters are intermediates.
Glyceraldehyde 3-phosphate is an intermediate.
Fructose 6-phosphate is an intermediate

Answer 29

G, P, G +P, G+P, G+P