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Biochemistry > Glycolysis and glucose oxidation > Flashcards

Glycolysis and glucose oxidation Flashcards

1
Q

How much of the glucose in blood does the brain use?

A

60%

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2
Q

What is the molecular formula for glucose?

A

C6H12O6.

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3
Q

Which hormones control glucose? Where are they made?

A

Insulin and glucagon

Made in Islets of langerhans

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4
Q

How is glucose stored

A

Glycogen

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5
Q

How is glucose trapped in the cell

A

Phosphate group is added to it

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6
Q

In what form does glucose enter the body? What are its possible fates?

A 
Enters- G6P
Possible fates:
1. Stored as  glycogen
2. Used in pentose phosphate pathway to make nucleotides and steroid hormones 
3. Broken down to form pyruvate
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7
Q

How an where can G6p be reformed

A

Gluconeogenesis

Reformed by pyruvate in the liver and kidneys

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8
Q

Is the glucose cell membrane hydrophobic or

hydrphylic

A

hydrophobic

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9
Q

Name of glucose transporters

A

GLUTS

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10
Q

How do GLUTS work?

A

Facilitate transport
Down concentration gradient
No ATP needed

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11
Q

Name the 3 main Glucose transporters

A

GLUT1
GLUT2
GLUT4

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12
Q

Location and function of GLUT1

A

Found- In all cells

Has a low Km- so works at top speed even at low glucose concentrations

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13
Q

Location and function of GLUT2

A

Found- Liver an pancreas only
Low Km- works slow at low-normal glucose concentrations
Works fast as concentration increases

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14
Q

Location and function of GLUT4

A

Found- muscle and adipose
Has a low Km
Controlled by insulin

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15
Q

How does insulin control GLUT4?

A

In skeletal muscle, GLUT4 transporters are bound to vesicles inside the cell. So glucose can not enter.

Insulin activation causes vesicles to move and merge with cell membrane. This exposes the GLUT4 transporters and allows glucose uptake

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16
Q

Effect of Exercise on GLUT 4?

A

Causes glute 4 vesicles to merge with the cell membrane to increase glucose uptake into muscle. Glucose concentration is reduced in the blood

17
Q

Where is exercise good for diabetes?

A

Reduces glucose concentration in the blood as it stimulates increased uptake

18
Q

What is the main goal in glycolysis?

A

Conversion of glucose into pyruvate

19
Q

How many steps in glycolysis? What is special about the first and last 5 steps

A

10 steps
First 5- require ATP
Last 5- produce 4ATP, 2NADH,2 pyruvate

20
Q

Describe the first step if glycolysis

A

Phosphorylation of glucose into G6P
PO4 is added
Catalysed by hexokinase
Requires ATP

21
Q

Properties of Hexokinase

A

Found in all tissues
Phosphorylaes all 6 carbon molecules
G6P- negative feed back- High G6p= inhibited hexokinase

22
Q

What happens when glucose concentration in the cell is high

A

Decreased concentration gradient, further uptake of glucose blocked
Reduced glucose conversion to G6P

23
Q

Describe the alternative step 1- glucokinase

A

Converters ONLY glucose to G6P
Found in pancreas and liver
Has a high Km- responds quickly to increased glucose concentrations. Slow activity otherwise
No negative feed back

24
Q

Function of glucokinase in the pancrease? What is the mechanism?

A

Acts as a sensor for glucose
Signals for insulin and glycogen production/ secretion

Low glucose concentration glucokinase is kept bound to nucleus by GKRP (glucokinse regulatory protein)
High glucose concentrations- Glucokinase dissociates from GKRP and acts in the cytosol

25
Q

What are the differences between gluckinase and hexokinase?

A 
Glucokinase- 
High KM
Responds to changes in blood glucose
Phosphorylates only glucose
Acts as a glucose sensor
Found only in pancreas and liver
26
Q

Describe step 2 of Glycolysis

A

Isomerisation
G6P is converted into fructose-6-phosphate
from 6 carbon to a 5 carbon ring
Makes further reactions more energetically favourable

27
Q

Describe step 3 of Glycolysis

A

Phosphorylation of F-6-P to F1-6-bisphosphate
Enzyme-Phosphofructokinase
ATP used
Rate limiting step:
PFK1- allosterically inhibited by ATP to AMP ratio. High ATP switches off glycolysis. High AMP stimulates PFK1

Citrate inhibits PFK1

PFK1- covalently inhibited by production of fructose,2,6,phosphate. High F,2,6P stimulates PFK1

28
Q

Describe step 4 of Glycolysis

A

F1-6-bisphosphate is broken down to give 2 3 carbon chains
Enzyme-Aldose
First chain- Aldehyde-glyceraldehyde-3-phosphate
Second chain- Acetone-dihydroxyacetone-phosphate

Acetone converted into aldehyde as only aldehyde is used in glycolysis
Result- 2 Aldehyde-glyceraldehyde-3-phosphate

29
Q

Name an alternative source of acetone and how it enters glycolysis

A

Glycerol from fat can be broken down into acteone. This is then converted into aldehyde in glycolysis
Enzyme- Isomerase
Location- only the liver (has the enzyme)

30
Q

Describe step 6 of Glycolysis

A

Free inorganic phosphate is added to glyceraldehyde
Enzyme- Dehydrogenase
Product- Glycerate
By product- NADH

31
Q

Use of NADH produced from glycolysis? Name another source of NADH

A

Generate NAD+ in crebs cycle

Lactic acid

32
Q

Describe step 7 of Glycolysis

A

1,3,bisphosphate glycerate gives off 1 phosphate to produce ATP from ADP (substrate level phosphorylation)
Enzyme- Phosphoglycerate kinase

33
Q

Describe step 8 of Glycolysis

A

Phosphate is shifted to middle carbon

34
Q

Describe step 9 of Glycolysis

A

Hydrolysis
water molecule removed to produces PEP
PEP is also produced by gluconeogenesis.

35
Q

Describe step 10 of Glycolysis

A 
PEP is broken down to pyruvate 
Enzyme- pyruvate kinase.
pyruvate feeds into  Kreb’s cycle.
ATP is produced
substrate level phosphorylation
36
Q

How does fructose feed into glycolysis?

A

Fructose (diet) can be matabolised by hexokinase to form F-6-P (step 3)
Main path is fructokinase produced in liver which metabolises fructose ultimately producing Glyceraldehyde (step 4)

37
Q

Pentose phosphate pathway and glycolysis

A

Alternative pathway for G-6-P
makes nucleic acids, steroid hormones, fat
Important for NADPH production
The products from the pathway glyceraldehyde-3-phosphate and fructose-6-phosphate, can feed into glycolysis.

Biochemistry (7 decks)

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