Glycolysis and glucose oxidation

Question 1

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

Answer 1

60%

Question 2

What is the molecular formula for glucose?

Answer 2

C6H12O6.

Question 3

Which hormones control glucose? Where are they made?

Answer 3

Insulin and glucagon

Made in Islets of langerhans

Question 4

How is glucose stored

Answer 4

Glycogen

Question 5

How is glucose trapped in the cell

Answer 5

Phosphate group is added to it

Question 6

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

Answer 6

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

Question 7

How an where can G6p be reformed

Answer 7

Gluconeogenesis

Reformed by pyruvate in the liver and kidneys

Question 8

Is the glucose cell membrane hydrophobic or

hydrphylic

Answer 8

hydrophobic

Question 9

Name of glucose transporters

Answer 9

GLUTS

Question 10

How do GLUTS work?

Answer 10

Facilitate transport
Down concentration gradient
No ATP needed

Question 11

Name the 3 main Glucose transporters

Answer 11

GLUT1
GLUT2
GLUT4

Question 12

Location and function of GLUT1

Answer 12

Found- In all cells

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

Question 13

Location and function of GLUT2

Answer 13

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

Question 14

Location and function of GLUT4

Answer 14

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

Question 15

How does insulin control GLUT4?

Answer 15

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

Question 16

Effect of Exercise on GLUT 4?

Answer 16

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

Question 17

Where is exercise good for diabetes?

Answer 17

Reduces glucose concentration in the blood as it stimulates increased uptake

Question 18

What is the main goal in glycolysis?

Answer 18

Conversion of glucose into pyruvate

Question 19

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

Answer 19

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

Question 20

Describe the first step if glycolysis

Answer 20

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

Question 21

Properties of Hexokinase

Answer 21

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

Question 22

What happens when glucose concentration in the cell is high

Answer 22

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

Question 23

Describe the alternative step 1- glucokinase

Answer 23

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

Question 24

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

Answer 24

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

Question 25

What are the differences between gluckinase and hexokinase?

Answer 25

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

Question 26

Describe step 2 of Glycolysis

Answer 26

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

Question 27

Describe step 3 of Glycolysis

Answer 27

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

Question 28

Describe step 4 of Glycolysis

Answer 28

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

Question 29

Name an alternative source of acetone and how it enters glycolysis

Answer 29

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)

Question 30

Describe step 6 of Glycolysis

Answer 30

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

Question 31

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

Answer 31

Generate NAD+ in crebs cycle | Lactic acid

Question 32

Describe step 7 of Glycolysis

Answer 32

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

Question 33

Describe step 8 of Glycolysis

Answer 33

Phosphate is shifted to middle carbon

Question 34

Describe step 9 of Glycolysis

Answer 34

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

Question 35

Describe step 10 of Glycolysis

Answer 35

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

Question 36

How does fructose feed into glycolysis?

Answer 36

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)

Question 37

Pentose phosphate pathway and glycolysis

Answer 37

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.