Week 3 - Releasing energy from food without oxygen

Question 1

How is glucose transported into a cell?

Answer 1

using glucose transporters

glucose uniporters - GLUT1 etc

sodium-glucose linked transporters

Question 2

What does a high K_m value indicate?

Answer 2

low affinity for glucose

a large amount of glucose (substrate) needs to be present for the transporter to be activated if it has a high K_m

Question 3

Where would you find GLUT1 transporters?

Answer 3

everywhere in the body

RBC’s and blood brain barrier rely exclusively on these transporters

Question 4

Where would you principally find GLUT2?

Answer 4

in hepatocytes

it is the priciple transporter for glucose between the liver and the blood

also found in pancreas, intestine and kidney

Question 5

Where are GLUT4 transporters found?

Answer 5

adipose tissue

striated muscle

insulin regulated transporters

Question 6

How is glucose moved into a cell using a sodium-glucose linked transporter (SGLT)?

Answer 6

• Na⁺/Ka⁺ ATPase pump moves 3 Na⁺ outward into the blood while 2x K⁺ moves in
• concentration gradient created
• SGLT protein uses energy from this Na⁺ gradient to transport glucose across the membrane

Question 7

What is hexokinase inhibited by?

Answer 7

glucose-6-phosphate (the product of the reaction)

Question 8

What is the liver isoform of hexokinase called?

Answer 8

glucokinase

requires a much higher glucose concentration for maximal activity - high K_m

most active after the consumption of a carbohydrate rich meal

Question 9

What is phosphofructokinase inhibited by?

Answer 9

ATP

if there is too much ATP in a RBC it would be unadvantageous to allow this step to continue if its primary aim is to yield more ATP from glycolysis

Question 10

What is produced by one turn of the Krebs cycle?

Answer 10

3x NADH

1x GTP

1x FADH₂

1x CO₂

Question 11

What is glycogenolysis?

Answer 11

breakdown of glycogen to glucose-1-phosphate

Question 12

Where does glycogenolysis predominantly take place?

Answer 12

in the liver and skeletal muscle

Question 13

What enzyme catalyses the first step of glycogenolysis?

Answer 13

glycogen phosphorylase

breaks alpha 1,4 glycosidic linkage

Question 14

Name two instances in which levels of lactic acid may increase

Answer 14

during intense exercise and COPD

Question 15

What enzyme reduces pyruvate to lactate?

Answer 15

lactate dehydrogenase

Question 16

How many molecules of pyruvic acid are produced for one molecule of glucose?

Answer 16

2

Question 17

Where are the enzymes of glycolysis located in a eukaryotic cell?

Answer 17

cytosol

Question 18

In which part of the cell does the activation of fatty acids take place?

Answer 18

outer mitochondrial membrane

Fatty acids are activated on the outer mitochondrial membrane and then oxidised in the mitochondrial matrix. The carnitine shuttle carries long chain activated fatty acids from the outer membrane into the matrix.