Overall Metabolism

Question 1

What are the steps of glycogen synthesis? (5 total)

Answer 1

Step 1: Glucose Uptake and Activation
Step 2: Conversion to Glucose-1-Phosphate (G1P)
Step 3: Activation of Glucose-1-Phosphate
Step 4: Elongation of Glycogen Chain
Step 5: Branching of Glycogen

Question 2

What happens during each step of glycogen synthesis?

Answer 2

Step 1: Glucose is transported into the cell and phosphorylated to glucose-6-phosphate (G6P)
Step 2: G6P is isomerized to G1P
Step 3: G1P reacts with uridine triphosphate (UTP) to form UDP-glucose
Step 4: UDP-glucose donates glucose residues to the growing glycogen chain, forming α-1,4-glycosidic bonds
Step 5: The enzyme branching enzyme (glycosyl 4:6 transferase) creates branches by transferring a segment of the glycogen chain to form α-1,6-glycosidic bonds.

Question 3

What are the enzymes for each step of glycogen synthesis?

Answer 3

Step 1: Hexokinase (Glucokinase in liver)
Step 2: Phosphoglucomutase
Step 3: UDP-glucose pyrophosphorylase
Step 4: Glycogen synthase
Step 5: Branching enzyme

Question 4

What are the two stages of the Pentose Phosphate Pathway (PPP)?

Answer 4

The Oxidative stage: This stage generates NADPH and ribulose-5-phosphate.
The non-oxidative stage: This stage produces intermediates for nucleotide synthesis and glycolysis.

Question 5

How is the PPP related to glycolysis and gluconeogenesis?

Answer 5

Need for NADPH: When cells require NADPH glucose-6-phosphate enters the oxidative phase of PPP.
Need for Ribose-5-Phosphate: When ribose-5-phosphate is needed the non-oxidative stage predominates without NADPH production
Need for Energy: If energy is needed, intermediates from the non-oxidative stage of PPP re-enter glycolysis, fueling ATP production.

Question 6

What is the primary regulatory enzyme of the PPP?

Answer 6

Glucose-6-phosphate dehydrogenase (G6PD), (Activated by NADP⁺, Inhibited by NADPH)

Question 7

Where does Fatty acid degradation take place?

Answer 7

It occurs primarily in the mitochondrial matrix

Question 8

What are the steps of Fatty acid degradation?

Answer 8

1. Activation of Fatty Acids
2. Transport into the Mitochondria
3. β-Oxidation in the Mitochondrial Matrix

Question 9

What happens during each step of Fatty acid degradation?

Answer 9

1. Fatty acids are activated to acyl-CoA using ATP and acyl-CoA synthetase
2. Acyl-CoA is transferred to carnitine by carnitine acyltransferase I to form acyl-carnitine then shipped into the mitochondria where it then turned back into Acyl-CoA
3. Each cycle of β-oxidation removes a 2-carbon unit (as acetyl-CoA) from the fatty acid chain

Question 10

What is the role of ketone bodies in the body?

Answer 10

Ketone bodies are water-soluble molecules produced in the liver during periods of low glucose (They serve as an alternative energy source for tissues)

Question 11

Where are ketone bodies synthesized?

Answer 11

Ketone bodies are synthesized in the liver

Question 12

Where are fatty acids synthesized?

Answer 12

Fatty acid synthesis occurs in the cytoplasm of cells, primarily in liver cells and adipocytes.

Question 13

What are the steps of fatty acid synthesis?

Answer 13

1. Transport of Acetyl-CoA to the Cytoplasm
2. Formation of Malonyl-CoA (Committed Step)
3. Fatty Acid Chain Elongation
4. Release of Palmitate

Question 14

What is the key regulatory enzyme for fatty acid synthesis?

Answer 14

Acetyl-CoA Carboxylase (ACC) is the key regulatory enzyme (Activated by High levels of citrate and Dephosphorylation, Inhibited by High levels of palmitoyl-CoA)

Question 15

How do hormones regulate fatty acid synthesis?

Answer 15

-Insulin promotes fatty acid synthesis by activating ACC and stimulating glucose uptake.
-Glucagon and epinephrine inhibit ACC, reducing fatty acid synthesis during fasting.

Question 16

How does energy state regulate fatty acid synthesis?

Answer 16

High Energy State: Promotes fatty acid synthesis (high ATP and NADPH levels).
Low Energy State: Promotes fatty acid degradation (high AMP levels activate AMPK).

Question 17

How are triacylglycerol synthesis and phospholipid
synthesis related?

Answer 17

Triacylglycerol synthesis and phospholipid synthesis share common intermediates but diverge depending on cellular needs for storage or membrane formation.

Question 18

What are the regulatory steps in the control of cholesterol synthesis?

Answer 18

Cholesterol synthesis is tightly regulated at multiple levels, with HMG-CoA reductase as the central point of control, ensuring proper cholesterol levels in response to metabolic demands and external signals.