Carbohydrates And The Pentose Phosphate Pathway

Question 1

What enzyme in the saliva and the pancreas helps to break down carbohydrates?

Answer 1

Amylase

Question 2

What substances in the small intestine break down dissaccharides to monosaccharides? Give an example.

Answer 2

Dissacharidases.
Lactase breaks down lactose.
Sucrose breaks down sucrose.

Question 3

What is secondary lactose intolerance?

Answer 3

Injury to the small intestine following an illness e.g. Coeliac disease, Crohn’s disease - usually reversible.

Question 4

What are the three types of lactose tolerance?

Answer 4

Primary - lactase deficiency
Secondary - after injury
Congenital - very rare, autosomal recessive

Question 5

What are some symptoms of lactose intolerance?

Answer 5

Cramping, vomiting, bloating, diarrhoea.

Question 6

What two transporter pumps do monosaccharides have to pass through the meet the bloodstream? How do they work?

Answer 6

To pass through intestinal epithelium - Sodium Dependent Glucose Transporter 1 (SGLT1). 2 sodiums exchanged for 1 glucose. ACTIVE TRANSPORT.

To pass from epithelium to bloodstream - GLUT2 pump - uses transport proteins to pass through (GLU1-GLU5).

Question 7

Where are GLU2 proteins used?

Answer 7

In pancreatic beta cells.

Question 8

Where are GLU4 proteins used?

Answer 8

In adipose tissue, striated muscle - is insulin regulated.

Question 9

Name four areas/cells of the body where glucose is an absolute requirement.

Answer 9

RBC - no mitochondria
Neutrophils - Mitochondria is only used to destroy bacteria
Innermost cells of kidney medulla
Lens of eye - no capillaries, poor oxygen supply.

Question 10

What is the CNS’s preferred fuel?

Answer 10

Glucose.

Question 11

What is glycolysis?

Answer 11

The breakdown of glucose by enzymes, releasing energy and pyruvic acid.

Question 12

What is the net gain of ATP during glycolysis?

Answer 12

2

2 are invested for 2 return

Question 13

During glycolysis there is no loss of carbons, how are these carbons distributed by the end?

Answer 13

Glucose - 6 carbons

X2 Pyruvate - 3 carbons each

Question 14

Where does glycolysis occur?

Answer 14

In the cytosol of cells.

Question 15

How many NADH molecules are produced in glycolysis?

Answer 15

2 (2 per glucose molecule).

Question 16

In what two steps of glycolysis are ATPs invested?

Answer 16

Stage 1 (glucose to glucose-6-p) and stage 3 (Fructose-6-p and fructose 1,6-bids-p).

Question 17

What product represents the first ‘committing step’ of glycolysis, where the chain reaction is irreversible? Why is this?

Answer 17

Fructose 1,6-bis-p

Large negative Gibbs Free Energy - reaction cannot be turned.

Question 18

At what stage in glycolysis does the cleavage of the 6 glucose carbons to 3 pyruvate carbons occur?

Answer 18

Stage 4 - conversion from Fructose 1,6-bid-P to DHAP

Question 19

How many irreversible steps int the glycolysis pathway are there?

Answer 19

3

Question 20

What the name of the production of ATP is stages 7 and 10?

Answer 20

Substrate Level phosphorylation

Question 21

What is Glycerol Phosphate an important intermediate for?

Answer 21

Triglyceride and Phospholipid biosynthesis.

Question 22

What enzyme produces glycerol phosphate and what co-enzyme is used?

Answer 22

Enzyme - Glycerol 3-phosphate dehydrogenase

Co-enzyme - NADH (NAD+ to NADH)

Question 23

Where is glycerol phosphate produced?

Answer 23

In the liver and adipose tissue.

Question 24

Where is 2,3-bisphoglycerate found?

Answer 24

In the RBC

Question 25

What does 2,3-bisphosphoglycerate regulate?

Answer 25

Haemoglobin oxygen affinity

Question 26

What effect would an increase in 2,3-bids phosphoglycerate have on oxygen affinity? What effect would this have in the body?

Answer 26

It would decrease it. | High levels of 2,3-DPG at tissues - encourage oxygen release.

Question 27

The rate of glycolysis is X times more in cancer.

Answer 27

X = 200

Question 28

Key regulator phosphofructokinase (PFK) is present at which stage of glycolysis?

Answer 28

Stage 3 | From fructose-6-phosphate to fructose 1,6-bisphosphate

Question 29

Phosphofructokinase (PFK) is an allosteric muscle regulator. What effect does the varying levels of ATP have on its activity?

Answer 29

Inhibited by high levels of ATP Stimulated by low levels of AMP. This is because if ATP in the cell is high, there is no need to produce more, therefore glycolysis is unnecessary.

Question 30

PFK (phosphofructokinase) is also a hormonal tissue regulator. What effect do the levels of insulin and glucagon have on its activity?

Answer 30

Stimulated by insulin. Inhibited by glucagon. After a meal, there is lots of glucose in the body, so insulin is released, and PFK helps to break it down in glycolysis. Glucagon is released by the liver when the body has a low blood sugar level, so PFK is reduced to ensure glycolysis doesnt break down the little glucose there is in the body.

Question 31

How does Hexokinase help regulate step one of the glycolysis pathway (glucose to glucose-6-p)?

Answer 31

A high amount of product slows down the reaction. | So if there are high amounts of glucose-6-p, hexokinase is reduced to ensure no backlog of product.

Question 32

Would high levels of NADH is step 6 of the glycolysis pathway speed up or slow down the reaction?

Answer 32

Slow down NAD+ is converted to NADH here. If there are high levels of NADH (product), reaction needs to slow down to ensure there is no backlog. Equally, low amount of NAD+ stimulates the reaction.

Question 33

What is pyruvate kinase inhibited and stimulated by in the glycolysis pathway?

Answer 33

Stimulated by insulin (lots of glucose to break down). | Inhibited by glucagon (no glucose to breaks down).

Question 34

At what stage in the glycolysis pathway does lactate dehydrogenase (LDH) take place and why?

Answer 34

Stage 4. In aerobic conditions, NAD+ is regenerated from NADH and the pathway continually. However oxygen is needed to do this, so in anaerobic conditions (e.g. Exercising muscles), NAD+ regeneration is done via LDH.

Question 35

What is the equation of lactate dehydrogenase?

Answer 35

NADH + H+ + pyruvate = NAD+ + lactate

Question 36

In anaerobic conditions, pyruvate is converted to X instead of age 4 metabolism.

Answer 36

X = lactate

Question 37

What plasma concentration range of lactic acid is considered hyperlactaemia?

Answer 37

2-5 mM

Question 38

What plasma concentration range of lactic acid is considered lactic acidosis? Why is this so dangerous?

Answer 38

Above 5mM Low ph Kidneys cannot dispose of lactic acid in time.

Question 39

What is the average safe amount of lactic acid concentration in the body?

Answer 39

Under 1mM

Question 40

What food is galactose found in?

Answer 40

Milk

Question 41

What three enzyme deficiencies could result is galactosaemia?

Answer 41

Galactokinase Uridyl transferase UDP-galactose epimerase

Question 42

What do you call of galactose intolerance?

Answer 42

Galactosaemia

Question 43

Where is fructose metabolised?

Answer 43

In the liver

Question 44

What is fructosuria?

Answer 44

Where the enzyme fructokinase is missing in the body. | No symptoms - just high fructose level in urine.

Question 45

What enzyme is missing in patients with fructose intolerance and what can it lead to?

Answer 45

Missing aldokinase Leads to a build up of fructose-1p (no aldokinase to use it up) - can lead to liver damage. Treatment: no fruit