MCBG (mostly topic 6 carbohydrates)

Question 1

which pathways are activated when ATP conc high

Answer 1

anabolic

Question 2

which pathways are activated when ATP conc LOW

Answer 2

catabolic

Question 3

List HIGH energy signals, activate which pathways?

Answer 3

ATP
NADH
NADPH
FAD2H
activate anabolic

Question 4

List LOW energy signals, activate which pathways?

Answer 4

NAD+
FAD
NADP+
ADP/AMP
activate catabolic

Question 5

clinical relevance of Creatine Kinase

Answer 5

marker for MI

Question 6

Role of Creatine Kinase

Answer 6

converts creatine into phosphocreatine.
Requires ATP, produces ADP
Reversible reaction, can provide ATP when low in cell.

Question 7

What can be used as marker for urine dilation?

Answer 7

Creatine excretion

Question 8

Describe the 4 stages of catabolism

Answer 8

stage 1- complex molecules to building blocks e.g. carbohydrates to monosaccharides.
stage 2- building blocks to simpler (fewer) molecules e.g. monosaccharides to pyruvate.
oxidative (require coenzymes NAD+) some ATP produced.
stage 3- mitochondrial. TCA cycle. oxidative.
stage 4- mitochondrial. Electron transport and ATP synthesis (large yield). Oxygen required. NADH and FAD2H reoxidised.

Question 9

Describe the absorption of monosaccharides into epithelial cell and uptake into target cells

Answer 9

uses SGLT1 (sodium glucose transporter) into epithelial cell. 
Glucose uptake into cells via facilitated diffusion using transport proteins (GLUT1-5)
GLUT 1-5 all have different affinities and tissue distribution.

Question 10

Describe glycolysis

Answer 10

Glucose C6 oxidation. Requires 2x ATP.
Reduction of 2x NAD+ –> NADH
4x ADP –> ATP
pyruvate C3 (Two produced)

yield = 2x ATP per glucose

Question 11

which enzymes are important in glycolysis.

Answer 11

hexokinase (glucokinase in liver): glucose –> glucose 6P

Phosphofructokinase 1: Fructose 6P –> fructose bisphosphate.

Pyruvate kinase: phospoenolpyruvate –> pyruvate.

Question 12

why so many steps in glycolysis?

Answer 12

• chemistry easier in smaller steps
• efficient energy conversion
• allows interconnections with other pathways
• can be controlled

Question 13

List some important intermediates in glycolysis

Answer 13

1,3 bisphosphoglycerate feeds out pathway to 2,3 BPG which is produced in RBC, regulator of Hb O2 affinity (promotes release of O2)

glycerol phosphate -important to triglyceride and phospholipid biosynthesis. produced from DHAP in adipose tissue and liver

Question 14

Which glucose transporter is regulated by insulin

Answer 14

GLUT4

Question 15

describe what each glucose transporters main role is

Answer 15

GLUT1- in erythrocytes and also in endothelial cells of the blood–brain barrier. Required to sustain respiration

GLUT2- liver allowing the hepatocytes to export glucose made by gluconeogenesis into the blood. primary glucose transporter in pancreatic beta cells.

GLUT3-main transporter in brain. high affinity isoform for times of low glucose plasma conc.

GLUT4-insulin-regulated glucose transporter expressed by skeletal muscle and adipose tissue

Question 16

Which enzyme is crucial for the regeneration of NAD+ from NADH in red blood cells?

Answer 16

Lactate dehydrogenase.
No mitochondria so no normal regeneration in stage 4 (electron transport chain). regenerate NAD+ by converting pyruvate to lactate.
Lactate is transported to the liver and converted back to pyruvate and used in gluconeogenesis to produce glucose.

Question 17

monomers of maltose

Answer 17

2x glucose

Question 18

monomers of lactose

Answer 18

glucose and galactose

Question 19

monomers of sucrose

Answer 19

fructose and glucose

Question 20

how does glycogen differ from cellulose

Answer 20

Glycogen- alpha glucose 1,4 and 1,6
Branched chains
made/used in humans
fuel reserve

cellulose- beta glucose 1,4
linear chains
made by plants
structural role

Question 21

what are the possible fates of lactate?

Answer 21

• converted back into pyruvate via LDH in liver
• converted into acetyl-coA in heart muscle to feed into TCA cyle
• converted into glucose via glucneogenesis in liver
• converted to acetyl-coA for lipid biosynthesis in liver.

Question 22

why may lactic acidosis occur

Answer 22

heavy eating
vigorous exercise
shock
congestive heart disease

Question 23

role of pyruvate dehydrogenase. when is this enzyme activated?

Answer 23

converts pyruvate into acetyl-coA. feed into TCA cycle.

activated when there’s high conc of glucose to be catabolised. (insulin activates)
ADP activates

Question 24

symptoms of lactase deficiency, why do these happen?

Answer 24

stomach cramping
diarrhoea

unhydrolyzed lactose is fermented by gut bacteria.irritates GI tract.

Question 25

how does liver disease/alcohol affect the conversion of lactate?

Answer 25

lactate --> pyruvate via LDH inhibited/impaired as no NAD to use. As alcohol converts NAD+ into NADH

Question 26

how does Glucose-6-phosphate dehydrogenase deficiency effect RBCs?

Answer 26

``` dec NADPH disulphide bonds form aggregated proteins Heinz bodies (RBCs with denatured Hb) haemolysis (breakdown RBC as unable to transport O2) ```

Question 27

How does dinitrophenol (DNP) affect oxidative phosphorylation?

Answer 27

uncoupler of oxidative phosphorylation. protonophore- allows protons to leak across the inner mitochondrial membrane. Bypass ATP synthase. Temp inc as energy is released as heat.

Question 28

cyanide effect on electron transport chain?

Answer 28

Inhibits enzyme (cytochrome oxidase) complex so no longer able to facilitate acceptance of e- by O2. prevents flow of e- through the e- transport chain. no p.m.f generated. ATP production stops.

Question 29

how are dietary carbohydrates are digested? which enzymes

Answer 29

Starch, glycogen, cellulose, lactose, sucrose. - salivary amylase. Pancreatic amylase. polysaccharide into disaccharide. Release glucose and maltose, leave smaller polysaccharides. - Glycosidases (membrane bound) break disaccharides into monosaccharides. - enzymes: sucrase, glycoamylase, lactase

Question 30

enzyme that converts galactose to galacticol

Answer 30

aldose reductase

Question 31

why is the pentose phosphate pathway an important metabolic pathway in some tissues.

Answer 31

produces NADPH. Biosynthetic reducing power, lipid biosynthesis > high activity in liver/adipose tissue. produce C5 nucleotides for nucleic acid synthesis > high activity in bone marrow

Question 32

compare oxidative phosphorylation with substrate level phosphorylation

Answer 32

Oxidative: - requires membrane associated complexes - energy uncoupling occurs indirectly through use of proton gradient (pmf) - REQUIRES O2 - major ATP synthesis process Substrate level: - requires soluble enzymes - energy uncoupling occurs directly through formation of high energy of hydrolysis bond - can occur to some extent w/o O2 - minor ATP synthesis process

Question 33

Describe how uncoupling occurs in brown adipose tissue

Answer 33

thermogenic (UCP)- uncoupling protein. response to cold: - noradrenalin activates lipase, releases fatty acids to be oxidised and activate UCP - produces NADH/FADH2 for electron transport - UCP transports H+ into mitochondria bypassing ATP synthase. > energy released as heat