Session 2

Question 1

what are the 4 stages of carbohydrate metabolism?

Answer 1

stage 1
- breakdown of building block moeclules for absorption

• occurs in the GI tract (extracellular)

stage 2
- breakdown to metabolic intermediates
- oxidative: releases reducing power (NADPH)
- in cytoplasm

stage 3
- TCA/Krebs cycle
- oxidative: released reducing power
- in mitochndria

stage 4
- oxidative phosphorylation
- ATP
- in mitochondria

Question 2

what are carbohydrates?

Answer 2

general formula: (CH20)n

if they have aldehyde group: aldose

if they have ketone group: ketose

Question 3

what are the 3 main dietary monosaccharides?

Answer 3

• glucose, fructose, galactose

— they are structurally similar and only differ in some chiral carbons

Question 4

which cells have an absolute requirement of glucose?

Answer 4

1. RBC
2. Neutrophils
3. innermost cells of kidney medulla
4. CNS

Question 5

why do RBC and lens fiber cells only metabolise glucose?

Answer 5

they have no mitochondria: cannot undergo oxidative phosphorylation

Question 6

why can neutrophils only use glucose?

Answer 6

they’re in an environment where ox phosphorylation cannot happen

• or their mitochondria is being used for something else

Question 7

how’s much glucose does the CNS use?

Answer 7

140g/24 hours

Question 8

why can’t humans digest cellulose?

Answer 8

no enzymes are produced to breakdown the beta 1-4 linkages

enzyme = glycosidase that recognises beta structure

Question 9

what is the difference between alpha and beta glucose?

Answer 9

alpha = more flexible, can be forced and stored compactly

beta = more linear and rigid for structure

Question 10

what is lactose?

Answer 10

a disaccharide broken down by lactase in stage 1 of glycolysis

Question 11

what is the normal phenotype of lactase?

Answer 11

1. during gestation and in newborn babies the levels of lactase are high
2. by age 5-7 lactase levels drop to 10% of the original
3. normal phenotype = lactose deficiency as adult
4. some populations have lactose persistence in adulthood whom can consume lactate products —> not normal

Question 12

what is lactose intolerance?

Answer 12

lactase deficiency

Question 13

what are the 3 types of lactose intolerance?

Answer 13

1. primary lactase deficiency
2. secondary lactase deficiency
3. congenital lactase deficiency

Question 14

what is primary lactose?

Answer 14

adult lactase deficiency (cannot digest lactose)

• they don’t have lactose persistence allele
• age related: declines
• only in adults

Question 15

what are the symptoms of lactose intolerance?

Answer 15

• bloating
• flatulence
• diarrhoea
• vomiting

—> build up of undigested lactose is metabolised by bacteria in colon which releases CO2 and methane
- leads to dehydration as water drawn into tissues

Question 16

what is secondary lactase deficiency?

Answer 16

caused by injury to small intestine —> inflammation to small intestine

• lactase levels drops
• reversible
• e.g gastroenteritis

Question 17

what is congenital lactase deficiency?

Answer 17

autosomal recessive defect in lactase gene

• extremely rare

Question 18

what is the treatment of lactose intolerance?

Answer 18

remove lactose from diet

Question 19

how is glucose and galactose absorbed?

Answer 19

actively transports into the intestinal epithelial cells by SGLT1

• depends on sodium potassium pump
• then passively diffuses from epithelial cells to blood via GLUT -2

Question 20

how is fructose absorbed?

Answer 20

passively transported into epithelial cells via GLUT -5

• then passively transported into the blood via GLUT -2

Question 21

how do target tissues receive glucose, fructose and galactose?

Answer 21

facilitated diffusion using transport proteins (GLUT -1 to GLUT -5)

• different tissues have different glucose transports

Question 22

what are the symptoms of hyper and hypoglycaemia?

Answer 22

hyperglycaemia
- caused by diabetes
- nerve and blood vessel damage due to inflammation

hypoglycaemia
- fainting
- seizures
- cognitive impairments
—> due to brain not getting glucose

Question 23

what is stage 1 of carbohydrate metabolism?

Answer 23

enzymes such as amylase break down starch into maltose in the saliva

• disaccharidases attached to border membrane of epithelial cells secreted to hydrolyse maltose into glucose