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MCAT Biochemistry > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

Glucokinase

A

present in the pancreatic beta-islet cells as part of the glucose sensor and is responsive to insulin in the liver

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2
Q

Hexokinase

A

traps glucose

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3
Q

Phosphofructokinase-1 (PFK 1)

A

rate limiting step

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4
Q

Phosphofructokinase-2 (PFK 2)

A

produces F2,6-BP, which activakes PFK-1

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5
Q

Glyceraldehyde-3-phosphate dehydrogenase

A

produces NADH

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6
Q

3-phosphoglycerate kinase and Pyruvate Kinase

A

perform substrate level phosphorylation

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7
Q

Irreversible reactions catalyzed by

A

Glucokinase, PFK-1, pyruvate Kinase

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8
Q

Aerobic Oxidation of NADH

A

occurs via electron transport chain

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9
Q

Anaerobic Oxidation of NADH

A

occurs via cytoplasmic lactate dehydrogenase

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10
Q

Pyruvate Dehydrogensare

A

converts pyruvate to acetyl-CoA and is stimulated by insulin and inhibited by acetyl-CoA

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11
Q

Citric Acid Cycle Main Substrates

A 
Pyruvate 
Citrate
Isocitrate
Ketogluterate
Succinyl-CoA
Succinate
Fumarate
Malate
Oxaloacetate
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12
Q

Location of CAC

A

mitochondrial matrix

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13
Q

Main Goal of CAC

A

to oxidize acetyl-CoA to CO2 and generate NADH, FADH and GTP

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14
Q

Location of ETC

A

matrix facing surface of the inner mitochondrial membrane

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15
Q

General Steps of ETC

A

NADH donates electrons to the chain, which are passed from one complex to the next. Reduction potentials increase down the chain until the electrons end up on oxygen, which has the highest reduction potential

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16
Q

How does NADH cross the inner mitochondrial membrane?

A

2 shuttle mechanisms
glycerol 3-phosphate shuttle
malate-aspartate shuttle

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17
Q

Proton-Motive Force

A

The electrochemical gradient generated by the ETC across the inner mitochondrial membrane. The intermembrane space has a higher concentration of protons than the matrix; this gradient stores energy, which can be used to form ATP vie chemiosmotic coupling.

18
Q

ATP Synthase

A

enzyme responsible for generating ATP from ADP and an inorganic phosphate (Pi)

19
Q

Summary of the Energy Yield of Metabolic Processes:
Glycolysis:
Pyruvate Dehydrogenase:
CAC:

A

2 NADH and 2 ATP
1 NADH
3 NADH, 1 FADH2, 1 GTP

20
Q

NADH Produces:

A

2.5 ATP

21
Q

FADH Produces:

A

1.5 ATP

22
Q

GTP Produces:

A

1 ATP

23
Q

Total Energy Yield from 1 Glucose

A

30-32

2 ATP from glycolysis + 2 ATP (GTP) from CAC + 25 ATP from NADH + 3 ATP from FADH2

24
Q

Glycogenesis

A

the building of glycogen using glycogen synthase and branching enzyme

25
Q

Glycogen Synthase

A

Creates alpha-1,4-glycosidic links between glucose molecules.
Activated by insulin in liver and muscles.

26
Q

Branching Enzyme

A

Moves a block of oligoglucose from one chain and connects it as a branch using an alpha-1,6-glycosidic link

27
Q

Glycogenolysis

A

The breakdown of glycogen using glycogen phosphorylase and debranching enzyme

28
Q

Glycogen Phosphorylase

A

removes single glucose 1-phosphate molecules by breaking alpha-1,4 glycosidic links.
In the liver is is activated by glucagon to prevent low blood sugar
In exercising skeletal muscle it is activated by epinephrnie and AMP to provide glucose fo the muscle itself

29
Q

Debranching Enzyme

A

moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link

30
Q

Gluconeogenesis

A

Occurs in the cytoplasm and the mitochondria, of primarily the liver. Mostly the reverse of glycolysis with the same enzymes but some exceptions.

31
Q

Three Irreversible Steps of Glycolysis Needed Different Enzymes in Gluconeogenesis

A

Pyruvate Carboxylase and PEP Carboxykinase bypass Pyruvate Kinase

Fructose-1,6-bisphosphatase bypasses phosphofructokinase-1 (PFK-1)

Glucose-6-phosphatase bypasses hexokinase/glucokinase

32
Q

Pentose Phosphate Pathway

A

Occurs in the cytoplasm and generates NADPH and sugars for biosynthesis.

33
Q

Rate Limiting Enzyme for Pentose Phosphate Pathway

A

glucose-6-phosphate dehydrogenase

activated by NADP+ and insulin
inhibited by NADPH

34
Q

Fermentation

A

occurs in the absence of oxygen, lactate dehydrogenase oxidizes NADH to NAD+ therefore replenishing the oxidized coenzyme for glyceraldehyde-3-phosphate dehydrogenase, reduces pyruvate to lactate

35
Q

Functions of NADPH

A

primarily acts as an electron donor, potent reducing agent for many functions

36
Q

Pathways that form acetyl-CoA

A 
Glycolysis
Fatty Acid Oxidation (beta-oxidation)
Amino Acid Catabolism
Ketones
Alcohol
37
Q

Complex 1 in ETC

A

NADH donates elections here

38
Q

Complex 2 in ETC

A

FADH2 donates electrons here

39
Q

Complex 3 in ETC

A

Q-cycle occurs, which is the main contributor to the proton motive force

40
Q

Complex 4 in ETC

A

final transfer of electrons to oxygen and water is formed

MCAT Biochemistry (12 decks)

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