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Biochemistry > Metabolism 3 (Regulating glycolysis) > Flashcards

Metabolism 3 (Regulating glycolysis) Flashcards

1
Q

What are the 2 types of response to changing environmental conditions?

A

Rapid response
= regulation of enzyme activity

Long-term response
= changes in gene expression & protein synthesis

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2
Q

What are the 4 factors responsible for controlling fluxes through metabolic pathways?

A

> substrate availability
conc of enzymes
allosteric regulation
covalent modification

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3
Q

How is glucose taken up by cells?

A

Uptake of glucose into cells is regulated by GLUT transporter proteins
- work via conformational changes

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4
Q

How does the 1st step of glycolysis affect glucose?

How does it do this?

Why is this useful?

A

Traps glucose inside the cell

Glucose moves into cell via GLUT

  • > Hexokinase adds phosphate = G6P
  • > can no longer pass back out of cell

Glucose kept inside cell where it can be metabolised by glycolysis

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5
Q

Which reactions in glycolysis are the rate limiting steps?

What are the enzymes involved in these steps?

A

The irreversible reactions:

  1. Hexokinase
  2. Phosphofructokinase
  3. Pyruvate kinase
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6
Q

What are the mechanisms are used to control the rate of limiting steps?

A

Concs of key rate-limiting enzymes in glycolysis are regulated by hormones
- insulin + glucagon

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7
Q

Which enzymes does insulin affect + what affect does it have?

A

Upregulates expression of :
>hexokinase
>phosphofructokinase
>pyruvate kinase

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8
Q

Which enzymes does glucagon affect and what affect does it have?

A

Inhibits:
> hexokinase
> phosphofructokinase
> pyruvate kinase

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9
Q

Describe how insulin up regulates the expression of hexokinase

A
  1. insulin enters cell via insulin receptor
  2. activates transcriptional activator
  3. TF binds to promoter of genes
  4. increases expression of Hexokinase gene
  5. –> increases glycolysis
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10
Q

What is allosteric control?

A

Inhibition/activation of enzyme by a small regulatory molecule that interacts at an allosteric site other than active site
= ability of enzyme to catalyse a reaction is modified

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11
Q

Describe the process of product inhibition of hexokinase

A

Glucose converted to G6P via hexokinase
-> hexokinase is inhibited by G6P
(allosterically)

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12
Q

What is glucokinase?

What does it facilitate?

How does it differ from hexokinase?

A

(AKA Hexokinase IV)
Enzyme sequestered in the nucleus of liver cells by a regulatory protein

Phosphorylation of glucose to G6P

NOT inhibited by G6P

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13
Q

In terms of glucokinase, what happens when blood glucose is >5mM?

A

Glucokinase = active

localised in cytosol

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14
Q

In terms of glucokinase, what happens when blood glucose is <5mM?

Why is this important?

A

Glucokinase = inactive
(localised in nucleus)

Prevents liver from taking glucose that might be needed by other cells when glucose is scarce
- liver can carry out gluconeogenesis

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15
Q

What is the most important control site in the mammalian glycolytic pathway?

Why is this?

A

Phosphofructokinase (PFK)

It catalyses a unique step

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16
Q

What is PFK controlled by in muscle?

A

The energy state of the cell

ATP:AMP ratio

17
Q

How is glycolysis in resting muscles controlled through allosteric regulation?

A

Not as much glycolysis:

Hexokinase inhibited by
-ve feedback from G6P accumulation

PFK inhibited by high energy charge
= high ATP:low AMP

18
Q

How is glycolysis in contracting muscles controlled through allosteric regulation?

A

More glycolysis:

ATP used up

PFK stimulated by low energy charge
= low ATP:high AMP

19
Q

How is PFK controlled?

A

By citrate, fructose 2,6-bisphosphate + ATP

As citrate accumulates –> inhibits PFK

ATP inhibits PFK

2,6-bisphosphate comes from fructose 1,6 bisphosphate via alternative pathway

20
Q

How is pyruvate kinase regulated via allosteric control?

A

Upregulated: via feed forward mechanism mediated by fructose 1,6 bisphosphate

Downregulated: ATP + Acetyl CoA inhibits

21
Q

How is glycolysis controlled through covalent modification of pyruvate kinase?

A

Phosphorylated state of pyruvate kinase regulates catalytic activity

Phosphorylated = less active

De-phosphorylated = more active

22
Q

What are the 2 catalytic subunits of the bifunctional enzyme that synthesises fructose 2,6 bisphosphate?

A

Phosphofructokinase 1 (PFK1)

+ fructose 2,6 bisphosphate

23
Q

How is pyruvate kinase phosphorylated?

A

Via kinases + ATP

24
Q

How is pyruvate kinase dephosphorylated?

A

Via phosphotases

25
Q

Why are metabolic pathways formed from step-wise processes?

A

> cell gets greater control of reaction
gets rid of products that could lead to a reversible reaction
metabolic processes produce heat -> small amounts of heat protect cell

26
Q

How do GLUT transport glucose into cells?

A

T1 configuration = open to outside of cell
-> glucose binds
-> conformational change
T2 configuration = open to inside of cell
-> glucose release
-> conformational change
T1 configuration

27
Q

What are the 3 GLUTs?

A

GLUT1
GLUT2
GLUT4

28
Q

Where is GLUT1 found and what is its function?

A

Red blood cells

Controls basal glucose uptake

29
Q

Where is GLUT2 found and what is its function?

A

Liver cells
Pancreatic beta cells

Uptake glucose at rate proportional to amount of glucose
Remove excess glucose from blood

30
Q

Where is GLUT4 found and what is its function?

What is it regulated by?

A

Muscle cells
Adipocytes

Removes excess glucose from blood

Insulin

31
Q

Describe how insulin is stimulated to be released from pancreatic beta cells

A
  1. Blood glucose >5mM
  2. Glucose enters cell via GLUT2
  3. Glycolysis occurs to produce ATP + pyruvate
  4. Pyruvate undergoes oxidative phosphorylation in mitochondria -> produces lots of ATP
  5. ATP inhibits K+ exiting cell = cell is depolarised
  6. Ca2+ enters cell
  7. Insulin-containing vesicles fuse with plasma membrane + release insulin into blood
32
Q

Describe glucose uptake in muscle cells when blood glucose is >5mM

A
  1. High insulin in blood from beta cells
  2. Insulin binds to receptor on cell
  3. Cascade
  4. GLUT4 fuse with plasma membrane
  5. Glucose enters cell via GLUT4
33
Q

Describe how PFK is activated by fructose 2,6 bisphosphate

A

F6P is converted into F 2,6 BP by PFKII

F 2,6 BP activates PFKI

34
Q

What happens to fructose 2,6 bisphosphate when glucose levels drop?

A

F 2,6 BP is converted into F6P by F 2,6 BPase

F6P can then continue along the glycolytic pathway

35
Q

Why does citrate inhibit PFK?

A

As there’s lots of metabolites downstream

-> NO need to continue breaking down glucose

36
Q

What are the 3 things G6P can be used in?

A

Glycolysis
Forming glycogen
Pentose phosphate pathway

Biochemistry (14 decks)

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