MEH 3 - Energy Production

Question 1

What is stage 1 of catabolism?

Answer 1

Breakdown to building blocks

Question 2

Where/how is stage 1 of catabolism carried out in the body?

Answer 2

• SALIVA contains amylase
• the PANCREAS contains amylase
• SMALL INTESTINE contains disaccharidases

Question 3

What are the three types of lactase deficiency?

Answer 3

• primary lactase deficiency (absence of lactase persistence allele)
• secondary lactase deficiency (caused by injury to small intestine)
• congenital lactase deficiency (autosomal recessive defect in lactase gene)

Question 4

What are the symptoms of lactose intolerance?

Answer 4

• bloating/cramps
• flatulence
• diarrhoea
• vomiting
• ‘rumbling’ stomach

Question 5

How are monosaccharides absorbed into the blood?

Answer 5

• active transport by sodium dependent glucose transporter (SGLT1)
• facilitated diffusion via GLUT2 transport proteins into blood supply

Question 6

Where are GLUT2 and GLUT4 proteins found?

Answer 6

• GLUT2 - kidney, liver, pancreatic beta cells, small intestine
• GLUT4 - adipose tissue, striated muscle

Question 7

Which cells have an absolute requirement for glucose as a food?

Answer 7

• red blood cells
• neutrophils
• innermost cells of kidney medulla
• lens of the eye
• brains prefers glucose but can use ketone bodies

Question 8

What is stage two of catabolism?

Answer 8

• breakdown to metabolic intermediates

- release of reducing power and energy

Question 9

What are the functions of glycolysis?

Answer 9

• oxidation of glucose
• NADH production
• synthesis of ATP from ADP
• production of C6 and C3 intermediates

Question 10

Can glycolysis occur anaerobically?

Answer 10

Yes - with the addition of an enzyme (PDH) it is the only pathway that can operate anaerobically.

Question 11

How much ATP and NADH is produced in glycolysis?

Answer 11

• 2 ATP produced per glucose

- 2 NADH produced per glucose

Question 12

Which enzyme converts glucose into glucose-6-P?

Answer 12

Hexokinase (or glucokinase in the liver)

Question 13

Which enzyme converts fructose-6-P into fructose 1,6-bis-P?

Answer 13

Phosphofructokinase-1

Question 14

Which enzyme converts phosphoenolpyruvate into pyruvate?

Answer 14

Pyruvate kinase

Question 15

Why is glucose phosphorylated?

Answer 15

It makes glucose negatively charged so it cant pass back through the plasma membrane. It also increases reactivity to permit subsequent steps.

Question 16

How many steps are there in glycolysis?

Answer 16

10

Question 17

Which steps of glycolysis use ATP?

Answer 17

1 and 3

Question 18

Which steps of glycolysis form ATP?

Answer 18

7 and 10, which occur twice per glucose

Question 19

Why is reaction 10 (conversion of phosphoenolpyruvate to pyruvate) irreversible?

Answer 19

Large -ve delta G

Question 20

How is glycolysis regulated?

Answer 20

• Phosphofructokinase is the main regulator.
• allosteric regulation in muscle
• hormonal regulation in liver
• hexokinase product inhibition
• metabolic regulation
• pyruvate kinase regulation

Question 21

How do hormonal and allosteric regulation take place?

Answer 21

Allosteric:

• inhibited by high ATP
• stimulated by high AMP

Hormonal:

• stimulated by insulin
• inhibited by glucagon

Question 22

What is glycerol phosphate?

Answer 22

• byproduct of step 4 and 5 of glycolysis

- important to triglyceride and phospholipid synthesis

Question 23

What is 2,3-bisphosphoglycerate?

Answer 23

• 1,3-bisphopsphoglycerate (glycolysis intermediate) can be converted into this
• produced in red blood cells
• regulator of haemoglobin O2 affinity

Question 24

What is lactate dehydrogenase used for?

Answer 24

It converts NAD+ to NADH and vice versa, allowing continued aerobic respiration in tissues, the heart and the liver and kidney

Question 25

What is lactic acidosis?

Answer 25

Occurs when plasma lactate rises above 5 mM, and blood pH is lowered

Question 26

What is hyperlactaemia?

Answer 26

A less severe form of lactic acidosis when plasma lactate reaches 2-5mM, but there is no change in blood pH due to its buffering capacity

Question 27

What is normal plasma lactate concentration?

Answer 27

Less than 1 mM

Question 28

How is the galactose from milk digested?

Answer 28

• milk splits into glucose and galactose
• galactose turned into galactose-1P by galactokinase
• galactose-1P converted into glucose-1P by uridyl transferase, then converted into glucose-6P and undergoes glycolysis
• galactose-1P can also be converted into UDP-galactose by UDP-galactose epimerase
• it is then converted into UDP-glucose, which forms glycogen

Question 29

Describe fructose metabolism

Answer 29

• using ATP, converted into fructose-1P by fructokinase
• aldolase converts into glyceraldehyde and DHAP
• triose kinase (uses ATP) and TPI convert these into 2 x glyceraldehyde-3-P
• these undergo glycolysis

Question 30

What is the difference between essential fructosuria and fructose intolerance?

Answer 30

Essential fructosuria is fructose in urine due to missing fructokinase.
Fructose intolerance is fructose-1P accumulating in liver due to missing aldolase.

Question 31

What does the pentose phosphate pathway start with?

Answer 31

Glucose-6-phosphate

Question 32

The pentose phosphate pathway is an important source of NADPH. What is this required for?

Answer 32

• reducing power for biosynthesis
• maintenance of GSH levels
• detoxification reactions

Question 33

The pentose phosphate pathway produces C5-sugar ribose. What is this required for?

Answer 33

Synthesis of nucleotides, DNA and RNA.

Question 34

What is the rate limiting enzyme in the pentose phosphate pathway?

Answer 34

Glucose-6-phosphate dehydrogenase

Question 35

True or false - both ATP and CO2 are produced in the pentose phosphate pathway?

Answer 35

False - only CO2 is produced