Carbohydrate Metabolism

Question 1

What are sources of ATP in the body? Describe

Answer 1

Creatinine phosphate - short term replacement, found in muscle
Anaerobic metabolism
Aerobic metabolism

Question 2

What is the source of creatinine phosphate? When is it used?

Answer 2

Short term replenishment, found in muscle, used for intense exercise

Question 3

List examples of polysaccharides in diet?

Answer 3

Starch

Cellulose

Question 4

List examples of disaccharides in diet?

Answer 4

maltose
sucrose
lactose

Question 5

List examples of monosaccharides in diet?

Answer 5

glucose

fructose

Question 6

how does alphaD glucose differ from BetaD glucose?

Answer 6

AlphaD = -OH group is below C atom
BetaD = -OH group is above C atom

Question 7

Why are dense starches slowly digested?

Answer 7

They have a smaller surface area for enzymes to work on

Question 8

What affect does a high glycemic index have on digestion time?

Answer 8

Food with a high glycemic index e.g. banana takes less time to digest (since mostly glucose)

Question 9

Since beans have a low glycemic index, what effect does this have on its digestion time?

Answer 9

Low glycemic index = longer digestion time

Question 10

Which body tissues/organs are dependant on a constant supply of glucose? Explain why

Answer 10

Brain: the blood brain barrier does not allow lipids to cross so must use carbohydrates to source their glucose. Brain can also only make neurotransmitters using glucose (so even if lipids could pass BBB, would still need glucose for NTs)

Erythrocytes: Don’t have mitochondria so no aerobic respiration. They need a constant glucose supply.

Question 11

What is the storage form of carbohydrates in humans?

Answer 11

Glycogen

Question 12

what is the normal range of plasma glucose concentration in fasting state?

Answer 12

4-5 mM

Question 13

what is the normal range of plasma glucose concentration after a meal?

Answer 13

8-12 mM

Question 14

What are the 2 main hormones involved in glucose homeostasis?

Answer 14

Insulin and glucagon

Question 15

Where can glucose be synthesised DE NOVO?

Answer 15

In the liver and in kidneys (only in extreme starvation mode)

Question 16

where in the body is glycogen stored and how do they differ?

Answer 16

In liver (stored during fasting state)
In muscle (glucose stored here as glycogen can only be used by THAT muscle)

Question 17

how does transportation using GLUT and SGLT1/2 transporters compare?

Answer 17

GLUT - involves passive diffusion

SGLT - involves active transport (cotransport of sodium)

Question 18

Where are SGLT1/2 transporters found? What do they transport?

Answer 18

Kidney tubules and intestinal mucosa

Co transports glucose/galactose along with sodium ions (NOT FRUCTOSE)

Question 19

Where are GLUT-1 transporters found? What do they transport?

Answer 19

Found in every tissue

Has a high affinity for glucose, transports glucose and galactose only.

Question 20

Where are GLUT-2 transporters found? What do they transport?

Answer 20

Liver, pancreatic beta cell, small intestine, kidney
Transports glucose, galactose and fructose.
It is a low affinity, high capacity glucose transporter.

Question 21

Where are GLUT-3 transporters found? What do they transport?

Answer 21

In brain, placenta, testes

transports glucose and galactose

Question 22

Where are GLUT-4 transporters found? What do they transport?

Answer 22

Skeletal and cardiac muscle, adipocytes

Has high affinity for glucose

Question 23

Where are GLUT-5 transporters found? What do they transport?

Answer 23

small intestine and sperm

transport ONLY FRUCTOSE

Question 24

which glut transporter is insulin sensitive?

Answer 24

GLUT 4

Question 25

how do GLUT4 transporters respond in the presence of insulin?

Answer 25

in presence of insulin, GLUT4 vesicles fuse with plasma membrane and GLUT4 allows glucose to move into cell.

Question 26

what is gluconeogenesis? Where does it occur?

Answer 26

Making glucose from other sources e.g. lipids and proteins. It occurs in the liver.

Question 27

what is the process of converting glucose to glycogen?

Answer 27

Glycogenesis

Question 28

What does the pentose phosphate pathway involve?

Answer 28

Synthesis of sugars for RNA/DNA

Question 29

What is the first step which all glucose pathways undergo in a cell? what effect does this have?

Answer 29

undergo phosphorylation to make glucose-6-phosphate. this traps it within the cell and kenos the glucose concentration low as it is immediately phosphorylated.

Question 30

What catalyses the phosphorylation of glucose?

Answer 30

hexokinase I-IV

Question 31

what is hexokinase IV also known as?

Answer 31

glucokinase

Question 32

which tissues express glucokinase ? Describe it glucose affinity.

Answer 32

Expressed by beta cels of pancreas and liver

It has a low affinity for glucose

Question 33

which tissues express hexokinase 1-3? Describe it glucose affinity.

Answer 33

expressed in all other tissues

It has a high affinity for glucose

Question 34

describe the pathway of converting glucose to fructose-1,6-bisphopshate

Answer 34

Glucose to Glucose-6-phosphate (using Hexo/glucokinase)
Glucose 6-phosphate to fructose-6-phosphate
Fructose-6-phosphate to Fructose-1,6-bisphosphate (using phosphofructokinase-1)

Question 35

How is phosphofructokinase regulated?

Answer 35

It is inhibited by ATP, citrate

Question 36

which enzyme converts pyruvate into acetyl-coA? and where does it occur?

Answer 36

pyruvate dehydrogenase

in the mitochondria

Question 37

What enzyme is involved in converting pyruvate to lactate?

Answer 37

Lactate dehydrogenase

Question 38

Where does the TCA cycle occur?

Answer 38

In mitochondria