Energy Production 1

Question 1

What is the purpose of amylase

Answer 1

Breaks down carbs such as glycogen to dextrins in saliva and pancreatic amylase to monosaccharides in duodenum

Question 2

Disaccharides attach to what in the GI tract

Answer 2

Brush border of of membrane of epithelial cells

Question 3

What enzymes breakdown disaccharides

Answer 3

Lactase
Sucrose
Pancreatic amylase
Isomaltase

Question 4

What are the three types of lactose intolerance

Answer 4

Primary- absence of lactase persistence allele occurring in adults with northwest Europe prevalence

Secondary- damage to small int. gastroenteritis, coeliac, chrohn’s, ulcerative colitis. Affects all ages and reversible

Congenital lactase deficiency- extremely rare autosomal recessive defect in lactase gene. Cannot digest breast milk

Question 5

What are the symptoms of lactose intolerance

Answer 5

Bloating and cramps, flatulence, diarrhoea, vomiting, rumbling stomach

Question 6

How are monosaccharides absorbed by the gut epithelia

Answer 6

Active transport by the sodium dependent glucose transporter 1 (SGLT1) then GLUT2 into blood

Question 7

How is glucose uptaken by cells from the blood

Answer 7

GLUT1 (foetal, erythrocytes, blood brain)
GLUT2 (kidney, liver, beta cells, small int.)
GLUT3 (neurones, placenta)
GLUT4 (adipose, striated musc INSULIN REG)
GLUT5 (sperm intestine)

2 and 4 most important to know

Question 8

What does the term absolute requirement mean and which cells have one for glucose

Answer 8

Only can metabolise glucose

RBC, Neutrophils, Innermost cells of kidney medulla, Lens of eye (no vessels so no oxygen)

Question 9

What are the two phases of gylcolysis

Answer 9

Investment (uses 2 ATP) and payback (producing 4 ATP, 2 NADH per glucose). Net gain 2 ATP

Question 10

What are the features of glycolysis

Answer 10

Central pathway for carb catabolism, occurs in all tissues cytoplasm, is exergonic and oxidative, 6C to 2 3C, pyruvate dehydrogenase produces lactase and regenerates NAD+

Question 11

What are the main enzymes of glycolysis

Answer 11

Hexokinase (glucokinase in liver) which phosphorylase glucose to glucose-6-P

Phosphofructokinase- key control enzyme

Both irreversible

Pyruvate kinase

Question 12

Why is glycolysis composed of so many steps

Answer 12

Chemistry easier, efficient energy conservation, versatility (pathways intermediates reverse), control

Question 13

Why is glucose phosphorylated

Answer 13

Gives -ve charge to prevent backpassage across plasmalemma

Increases reactivity for subsequent steps

Question 14

Why is step 3 (fructose 6P to fructose 1,6bisP) called the committing step

Answer 14

Like step one is irreversible due to large -ve delta G and commits to glycolysis pathway

Question 15

Outline phase 2 of glycolysis

Answer 15

Cleavage of 6C to two 3C

Captures reducing power (NAD+ to NADH)

SUBSTRATE LEVEL PHOSPHORYLATION

Question 16

How many irreversible steps are there in glycolysis

Answer 16

3 due to large -ve delta G. Converting pyruvate to glucose (gluconeogenesis) but bypass these

Question 17

How many times higher is the rate of glycolysis in cancer and how is it measured

Answer 17

Up to 200 times. Use radiactive modified hexokinase substrate eg FDG) imaged with a PET scan

Question 18

How is phospofructokinase PFK regulated

Answer 18

Allosterically (muscle)- inhibited by high ATP, stim by high AMP

Hormonal (liver)- inhibited by glucagon, stim by insulin

Question 19

True or false, hexokinase exhibits product inhibition

Answer 19

True glucose6P inhibits hexokinase but not glucokinase

Question 20

How else is glycolysis regulated in the body

Answer 20

Product inhibition

Metabolic regulation by NAD concentrations inhibiting step 6

Pyruvate Kinase by high insulin:glucagon ratio.

Question 21

What are some important intermediates of glycolysis

Answer 21

Dihydroacetone-P which is converted to glycerol phosphate by GLYCEROL 3-PHOSPHATE DEHYDROGENASE for fat sythesis

1-3bisphosphoglycerate which is converted to 2,3-bisphosphoglycerate (2,3BPG) by BISPHOSPHOGLYCERATE MUTASE for regulation of haemoglobin O2 affinity promoting release

Question 22

What is the purpose of lactate dehydrogenase

Answer 22

To convert pyruvate from glycolysis to lactate to resupply the cell with NAD+ from NADH produced prior

Question 23

How is lactate metabolised

Answer 23

Sent through blood to the heart or liver where it is converted back to pyruvate for aerobic respiration by the same LDH enzmyme or for gluconeogenesis

Question 24

Why might plasma lactate increase and outline hyperlactaemia and lactic acidosis

Answer 24

Depends on production rate, utilisation by liver heart muscles and disposal by kidneys

Normal conc in 1mM.

2-5mM is hyperlactaemia no change in blood pH due to buffering capacity

Lactic acidosis above 5 mM as above renal threshold so blood pH lowered

Question 25

How may galactosaemia occur

Answer 25

Deficiencies in enzymes such as GALACTOKINASE, UDP-GALACTOSE EPIMERASE, URIDYL TRANSFERASE

Question 26

What is essential fructosuria and fructose intolerance

Answer 26

EF by FRUCTOKINASE missing so fructose in urine wth no clinical signs

FI by ALDOLASE missing. Fructose1P accumulates in liver leading to liver damage treatment is removing fructose from diet

Question 27

What is the purpose of the pentose phosphate pathway

Answer 27

Producing Ribose5P which is required for nucleotides, DNA, RNA and Coenymes

To also produced NADPH

Question 28

What is NADPH used for in the body

Answer 28

Fatty acid and steroid synthesis as well as GSH regeneration, reducing power, detoxification reactions

Question 29

Where does the pentose phosphate pathway occur

Answer 29

In the cytosol of cells

Question 30

What enzyme converts G6P to the first molecule of the pentose phosphate pathway and what is its purpose

Answer 30

G6PDH initiates reaction pathways so is the rate limiting enzyme. Pathway produces no ATP but does produce CO2