(Dr. McLachlin) (Unit B) Topic Note 9

Question 1

What is the phosphorylated form of glucose?

Answer 1

Glucose-6-phosphate (G6P)

Question 2

How does glucose provide energy to the cell?

Answer 2

Oxidized in glycolysis

Question 3

Where is glycogen stored?

Answer 3

Liver and striated muscle

Question 4

How is glucose converted to glycogen?

Answer 4

1. G6P converted to G1P
2. G1P added to glycogen chain

Step 2 is a two step process, involves:
1. Net hydrolysis of UTP to UDP and Pi
2. Second step catalyzed by glycogen synthase

Question 5

How are glucose monomers removed from glycogen when glucose is required?

Answer 5

Removed as G1P
* By glycogen phosphorylase
* Phosphate comes from inorganic phosphate dissolved in the cytosol

Question 6

How does phosphorylation affect glycogen synthase?

Answer 6

• Phosphorylated = Less active
• Dephosphorylated = More active

Question 7

How does phosphorylation affect glycogen phosphorylase?

Answer 7

• Phosphorylated = More active
• Dephosphorylated = Less active

Question 8

How is the phosphorylated vs. dephosphorylated form concentrations of glycogen synthase/phosphorylase determined?

Answer 8

Hormone signals
* Insulin
* Glucagon

Question 9

How does insulin work?

Answer 9

Released by pancreas into the bloodstream when blood glucose levels are high

Question 10

How does glucagon work?

Answer 10

Stimulates glycogen breakdown in liver but not skeletal muscles
* Maintains blood glucose level

Question 11

What controls glucose levels in skeletal muscles?

Answer 11

Norepinephrine

Question 12

What is glycogen synthase allosterically activated by?

Answer 12

G6P

Question 13

What is glycogen phosphorylase allosterically regulated by in:
1. Skeletal muscles
2. Liver

Answer 13

1. Activated by AMP, Inhibited by ATP and G6P
2. Inhibited by glucose

Question 14

What is glycolysis?

Answer 14

Oxidative process that occurs in the cytoplasm

Question 15

What is the net reaction of glycolysis and how many steps are there?

Answer 15

10 Steps

Glucose + 2 ADP + 2 Pi + 2 NAD+
–>
2 pyruvate + 2 NADH + 2 ATP

Question 16

How many electrons are transferred from glucose to NAD+ molecules in glycolysis?

Answer 16

4 electron to 2 NAD+

Question 17

Which steps of glycolysis are considered irreversible? Why?

Answer 17

Steps 1, 3, 10
* Large, negative value for ΔG

Question 18

What are the enzymes are will control flux through glycolysis?

Answer 18

1. Hexokinase
2. Phosphofructokinase (PFK)
3. Pyruvate kinase

Question 19

Why does fermentation occur even though glycolysis doesn’t use oxygen?

Answer 19

Glycolysis produces NADH, which in the end gives its electrons to oxygen to become NAD+ (regenerating NAD+)

Without oxygen, we cannot regenerate NAD+

So we need another process to regenerate NAD+ in the absence of oxygen

Question 20

Where does Lactate Fermentation occur?

Answer 20

In many microorganisms, in higher organisms when little oxygen in available

Question 21

Formation of Lactate

Answer 21

Pyruvate + NADH
–>
Lactate + NAD+

Question 22

Fermentation of glucose to lactate

Answer 22

Glucose + 2 ADP + 2 PI
–>
2 lactate + 2 ATP

Question 23

Where does Ethanol Fermentation occur?

Answer 23

Yeast, and several other microorganisms

Question 24

Formation of ethanol

Answer 24

2 step process:

Step 1
Pyruvate + H+
–>
CO2 + Acetaldehyde

Step 2
Acetaldehyde + NADH
–>
Ethanol + NAD+

Question 25

Net reaction of fermentation to ethanol

Answer 25

Glucose + 2 ADP + 2 Pi
–>
2 Ethanol + 2 CO2 + 2 ATP

Question 26

Where do humans use ethanol fermentation?

Answer 26

Brewing and making bread

Question 27

Which cells can switch between fermentation of glucose and complete oxidation? Which cannot?

Answer 27

Muscles cells can

Strict aerobes such as brain cell cannot

Question 28

Gluconeogenesis

Answer 28

Synthesizing glucose when blood glucose levels and glycogen reserves are low

Question 29

What can be used as raw materials for gluconeogenesis?

Answer 29

• Pyruvate
• Glycerol
• Lactate
• Citric acid cycle intermediates
• Amino acids

Question 30

Where does gluconeogenesis occur?

Answer 30

Liver cells

Question 31

Explain:

Reversing Step 10 of Glycolysis for Gluconeogenesis

Answer 31

1. Cell makes oxaloacetate, consumes 1 ATP
2. Converts oxaloacetate to phosphoenolpyruvate, consumes 1 GTP

Question 32

True or False:

ATP is made during gluconeogenesis

Answer 32

False, no ATP is made in the gluconeogensis direction

Question 33

Net reaction of gluconeogenesis, using pyruvate

Answer 33

2 pyruvate + 4 ATP + 2 GTP + 2 NADH
–>
Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+

Question 34

How does insulin and glucagon affect gluconeogenesis?

Answer 34

• Insulin stimulates glycolysis
• Glucagon relieves inhibition of gluconeogensis

Question 35

What is fructose bisphosphatase inhibited by?

Answer 35

• Allosterically: AMP
• Competitively F2,6P

Question 36

What does AMP and F2,6P activate?

Answer 36

Phosphofructokinase (PFK)
* Enzyme for step 3 of glycolysis

Question 37

When is gluconeogenesis and glycolysis stimulated?

Answer 37

When starting materials are in abundance

Question 38

What is a major process used to generate NADPH?

Answer 38

Pentose phosphate pathway
* Oxidize G6P

Question 39

Net reaction for Pentose phosphate pathway

Answer 39

3 G6P + 6 NADP
–>
2 fructose-6-phosphate + glyceraldehyde phosphate + 6 NADPH + 3 CO2

Question 40

What intermediates in the pentose phosphate pathway can be used in glycolysis?

Answer 40

• Fructose-6-phosphate
• Glyceraldehyde phosphate

Question 41

What intermediates in the pentose phosphate pathway is required for nucleotide synthesis?

Answer 41

Ribose-5-phosphate

Question 42

Net reaction for ribose-5-phosphate production in the pentose phosphate pathway

Answer 42

G6P + 2 NADP+
–>
Ribose-5-phosphate + CO2 + 2 NADPH

Question 43

When is ribose-5-phosphate produce in the pentose phosphate pathway?

Answer 43

When nucleotide levels are low