MCB Lecture 13 Glycogenolysis and Glycogenesis, PDH, Citric acid cycle Flashcards Preview

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Flashcards in MCB Lecture 13 Glycogenolysis and Glycogenesis, PDH, Citric acid cycle Deck (31)
0

Differentiate between Glycogenesis, glycogenolysis, gluconeogenesis and glycolysis.

Glycogenesis: making glycogen from glucose monomers
Glycogenolysis: breaking down glycogen into glucose monomers
Gluconeogenesis : converting pyruvate back to glucose
Glycolysis: breaking glucose down into pyruvate

1

Describe the steps involved in glycogenolysis

1. Glycogen phosphorylase enzyme breaks off glucose-1-phosphate molecules from the non-reducing end

NB phosphate attached, phosphate cleaved the a-1,4 bond

2. Debranching enzyme has two functions:
a. transferring strings of glucose to the linear chain to isolate on glucose on the side branch
b. cleaving the a-1,6 bond of the glucose on the side chain

This creates a linear chain for further glycogen phosphorylase activity

3. Phosphoglucomutase enzyme move the phosphate from 1C to 6C

The serine residue on the phosphoglucomutase enzyme is phosphorylated. This phosphate group move to the 6-carbon position, then the phosphate on the 1-carbon is cleaved and ends up on the serine residue.

2

Outline the steps in Glycogenesis

1. UDP-glucose phosphorylase catalyses Glucose-1-phosphate molecules being added to UTP, making UDP-glucose, releasing pyrophosphate (PiPi)

2. Glycogen synthase transfers the glucose from the UDP-glucose onto the end of a glycogen chain

3. Glycogen branching enzyme transfers a group of glucose monomers in a linear chain onto the 6-carbon of another monomer, creating a branch.

4. Glycogenin is the primer for a glycogen molecule.

Glycogen synthase isn't able to start the molecule itself, a primer is required.
Glycogen in is both the primer and the enzyme making the primer

3

Describe the structure of glycogen

Branched chains of a-D-glucose monomers.
a-1,4 glycosidic bonds between the monomers in the linear chain
a-1,6 glycosidic bonds between the molecules at the branch points

It has a reducing and a non reducing end.

4

How is Citrate formed?
Anything else?

Acetyl-CoA + Oxaloacetate -> Citrate
Enzyme: citrate synthase

This is inhibited by ATP

5

Citrate -> ?
Enzymes?
Anything else?

Isocitrate
Aconitase

6

Isocitrate -> ?
Enzymes?
Anything else?

Alpha-ketogluterate
Isocitrate dehydrogenase
NADH produced

7

Alpha-ketogluterate -> ?
Enzymes?
Anything else?

Succinyl-CoA
Alpha-ketogluterate dehydrogenase complex
NADH produced
CO2 evolved

8

Succinyl CoA -> ?
Enzymes?
Anything else?

Succinate
Succinyl CoA synthetase
GTP evolved

9

Succinate -> ?
Enzymes?
Anything else?

Fumarate
Succinate dehydrogenase
FADH2 produced

10

Fumarate -> ?
Enzymes?
Anything else?

Malate
Fumarase

11

Malate -> ?
Enzymes?
Anything else?

Oxaloacetate
Malate dehydrogenase
NADH produced

12

At which points is GTP formed?

Succinyl-CoA -> Succinate

13

In which steps is NADH produced?

Isocitrate -> alpha-ketogluterate

Alpha-ketogluterate -> succinyl CoA

Malate -> Oxaloacetate

14

In which steps is FADH2 produced?

Succinate -> fumarate

15

Describe the function of the PDH complex

Converts pyruvate -> acetyl-CoA

3,4,5 reaction : 3 subunits of PDH
4-step reaction
5 cofactors

TPP, lipoate, NAD, FAD, CoA-SH

16

Which vitamins are especially important for metabolism?
Give some examples

These vitamins are cofactors for many important steps in cellular respiration

Niacin: NADH and NADPH
Riboflavin: FAD and FMN
Thiamin: TPP
Pantothenic acid: coenzyme A
Biotin: pyruvate carboxylase

17

Where is glycogen stored?

Mostly in muscle cells and liver cells as granules

18

What percentage of the total energy stored in a 70kg person is in the form of glycogen

Not much 1%

19

Which bonds are present in glycogen?

Alpha-1,4
Alpha-1,6

20

Where is the PDH complex?

In the mitochondria

21

What are the three irreversible steps of the citric acid cycle?

What is also important about these steps?

1. Pyruvate -> acetyl CoA
2. Isocitrate -> alpha ketogluterate
3. Alpha ketogluterate -> succinyl co-A
They are the control steps of the citric acid cycle

22

How many vitamin Bs are there?

8

23

What is the first point of control of the citric acid cycle?

The PDH complex
Pyruvate -> acetyl CoA

24

Describe the first control point of the citric acid cycle

1. The PDH complex

(+) ADP, pyruvate
(-) Acetyl-CoA, NADH, ATP

25

Describe the second control point of the citric acid cycle

2. Isocitrate -> alpha ketogluterate
Isocitrate dehydrogenase

(+) ADP
(-) NADH, ARP

26

Describe the third control point of the citric acid cycle

3. Alphaketogluterate dehydrogenase complex

(+) none
(-) NADH, ATP, succinyl-CoA

27

Which steps of glycolysis produce NADH?

i. Isocitrate -> alpha ketogluterate
ii. Alpha ketogluterate -> succinyl-CoA
iii. Malate -> oxaloacetate

28

Which steps of the citric acid cycle produce FADH2?

Succinate -> fumarate

29

Which steps of the citric acid cycle produce GTP?

Succinyl-CoA -> succinate

30

Which steps of the citric acid cycle evolve CO2?

Isocitrate -> alpha ketogluterate

Alpha ketogluterate -> succinyl-CoA

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