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Physiology > Carbohydrate metabolism > Flashcards

Carbohydrate metabolism Flashcards

1
Q

What is the key common end product of metabolism?

A

Acetyl-CoA

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2
Q

How are carbohydrate used?

A

Carbs are used immediately as fuel, they are stored as glyocgen and fat

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3
Q

What cell has an absolute requirement for glucose?

A

Erythrocytes because they do not have mitochondria

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4
Q

What organ is the control point for glucose metabolism?

A

Liver

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5
Q

What happens after glucose absorption stops following a meal?

A

The liver returns stored glycogen to the blood as glucose to provide fuel. This is the “postabsorptive” phase of starvation and is short

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6
Q

How is glucose metabolized?

A

By glycolysis

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7
Q

Describe glucose obsorption

A

Glucose arrives in intenstinal lumen, is absorbed by intestinal mucousal cells via active transport, enters circulation and goes to liver & tissues

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8
Q

Where does glucose go first?

A

Liver

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9
Q

How is glucose absorbed by intestinal mucousal cells?

A

Sodium-GLucose transporter 1

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10
Q

What is SGLT1 dependent on?

A

Activity of Na+/K+-ATPase pump

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11
Q

Describe glucose uptake

A

Glucose is highly polar and cannot cross the cell membrane, so it is absorbed by the glucose transporter (GLUT)

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12
Q

What is GLUT?

A

A carrier-mediated glucose transport sysytem

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13
Q

Do all cells have at least 1 GLUT receptor?

A

Yes

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14
Q

Name GLUT receptors

A 
GLUT1 (Low Km, basal transporter)
GLUT2 (High Km)
GLUT3 (Low Km, Basal transporter)
GLUT4 (Insulin dependent, located in muscle and fat)
GLUT5 (high affinity for fructose)
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15
Q

How does GLUT receptors work?

A

GLUT1 sits on the basal membrane, glucose binds to it. Insulin binds to an insulin receptor on the cell which upregulates GLUT4 and more glucose is absorbed

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16
Q

What is the end product of glycolysis?

A

Pyruvate

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17
Q

Where does glycolysis occur?

A

Anaerobic, in cytoplasm

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18
Q

How much energy from glycolysis is captured as ATP?

A

42%

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19
Q

What is step 1 of glycolysis?

A

Glucose -> Glucose 6-phosphate

Enzyme: hexokinase, glucokinase

Irreversible but not committed step

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20
Q

What is the difference between hexokinase and glucokinase?

A

Hexokinase is inhibited by larger concentrations of glucose 6-phosphate and hexokinase has a higher affinity for glucose than glucokinase

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21
Q

What is the concentration of glucokinase after a meal?

A

15mM

22
Q

What is glucokinases major function?

A

Keep the brain supplied with glucose

23
Q

What is glucose trapping?

A

When glucose -> glucose 6-phosphate, the molecule cannot diffuse out of the cell. G6P is a substrate for multiple pathways

24
Q

WHat are the pathways of G6P?

A

Glycolysis, Glycogen synthesis, hexose monophosphate shunt (pentose shunt)

25
Q

What is the 2nd step of glycolysis?

A

G6P to fructose 6-phosphate

Phosphoglucose isomerase

Freely reversible

26
Q

What is the 3rd step of glycolysis?

A

F6P to Fructose 1,6-biphosphate

Phosphofructokinase 1

This is the committed step and rate limiting step of glycolysis

Irreversible

27
Q

What factors increase PFK activation?

A 
Upregulated by:
ADP, AMP
F6P
Epinephrine
Insulin
Ammonium (NH4+)
28
Q

What factors decrease PFK activation?

A 
Citrate
ATP
Phosphocreatine
Glucagon
H+
29
Q

What is step 4 of glycolysis?

A

F1,6BP -> Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3 phosphate (G3P)

Aldolase

Reversible

30
Q

What is step 5 of glycolysis?

A

DHAP -> G3P

Triosphosphate isomerase

Equilibrium favors G3P over DHAP

Reversible

31
Q

How many ATP are used in steps 1-5?

A

2

32
Q

What is step 6 of glycolysis?

A

G3P -> 1,3 biphosphoglycerate

Glyceraldehyde 3-phosphate dehydrogenase

Reversible, produces NADH+ when hydrogen is replaced by high energy phosphate link (NAD+ -> NADH+)

33
Q

What is step 7 of glycolysis?

A

1,3BPG -> 3-phosphoglycerate

Phosphoglycerate kinase

Reversible but makes ATP

34
Q

Whatis unique about step 7 of glycolysis?

A

Eve though an ATP is made, it is a reversible reaction

35
Q

How many ATP/NADH are made in steps 6 & 7?

A

2 ATP, 2 NADH+ because there are 2 G3P molecules

36
Q

What is step 8 of glycolysis?

A

3-phosphoglycerate to 2-phosphoglycerate

Phosphoglycerate mutase

Reversible

37
Q

What is step 9 of glycolysis?

A

2-phosphoglycerate to phosphoenolpyruvate (PEP)

Enolase

Reversible

Becomes a high energy compound from a low energy compound because of the double carbon bond that forms

38
Q

What is step 10 of glycolysis?

A

PEP -> pyruvate

Pryruvate kinase

Creates (2) ATP

Irreversible

39
Q

What are regulators of Pyruvate kinase?

A

Fructose 1,6 Biphosphate increases Pyruvate kinase in the liver

In the muscle, a drop in the ATP/ADP ratio will increase pyruvate kinase

High ATP will inhibit pyruvate kinase, phosphocreatine will inhibi pyruvate kinase

40
Q

How many ATP is NADH+ equal to?

A

2.5

41
Q

What is the net result of ATP from glycolysis?

A 
7 ATP (2 ATP, 2 NADH) 
Total yield is 9 ATP (4 ATP, 2 NADH)
42
Q

What makes glycolysis possible?

A

Energy coupling

43
Q

What is the purpose of the electron transport system?

A

Aerobic metabolism, mass production of ATP

44
Q

Where does 90% of the available metabolic energy in glucose remain?

A

In pyruvate

45
Q

Where can pyruvate go?

A

Lactate, Acetyl-CoA, other Carb, Fat & Protein metabolism

46
Q

What actions is lactate used for?

A

Anaerobic metabolism, sprinting

47
Q

How does lactate produce ATP?

A

Quickly, but low quantity

48
Q

What actions is Acetyl CoA used for?

A

Aerobic metabolism, endurance

49
Q

How does Acetyl Coa produce ATP?

A

Slow, but high quantity

50
Q

What organs rely heavily on anaerobic glycolysis?

A

Cornea, lens
Red blood cells
Cancer cells

51
Q

Why is glycolysis essential?

A

Quickest way to provide energy from rest to full flgiht

Less dependent on blood supply and vasculature (cornea)

Reduce need to have bulky mitochondria in cornea, lens and blood

Physiology (45 decks)

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