carbs 2

Question 1

metabolic regulation of glycolysis

Answer 1

high NADH concentration= high energy levels
causes product inhibit of step 6
inhibits glycolysis

Question 2

step 6 of glycolysis

Answer 2

2 moles of NADH produced per mole of glucose so the pathway needs NAD+. this is regenerated from nada in stage 4 of metabolism. however in cells that lack mitochondria or have an adequate absence of oxygen NADH is converted back to NAD+ via the lactate dehydrogenase reaction.
NADH + H+ +pyruvate NAD+ + lactate

Question 3

hyperlactaemia

Answer 3

2-5 mM of plasma lactate
below renal threshold
no change in blood pH

Question 4

lactic acidosis

Answer 4

above 5 mM of plasma lactate
above renal threshold
blood pH lowered

Question 5

how can enzymes be regulated

Answer 5

1) allosteric- activator/inhibitor binds at ‘another’ site.

2) covalent modification- phosphorylation/dephosphorylation

Question 6

regulation of phosphofructokinase (PFK)

Answer 6

allosteric regulation(muscle)- inhibited by high ATP. stimulated by high AMP.
hormonal regulation(liver)- stimulated by insulin. stimulated by glucagon.

Question 7

describe fructose metabolism

Answer 7

metabolised in liver
fructose becomes fructose-1P via fructokinase
fructose-1P becomes glyceraldehyde/DHAP via aldolase
becomes glyceraldehyde-3-P

Question 8

what is essential fructosuria

Answer 8

fructokinase missing
fructose in urine
no clinical sign

Question 9

what is fructose intolerance

Answer 9

aldolase missing so fructose-1-P accumulates in liver leading to liver damage.

Question 10

what are the enzymes involved in galactose metabolism

Answer 10

galactokinase
galactose-1-P urdidyl transferase
UDP- galactose 4’-epimerase

Question 11

cause of galactosaemia

Answer 11

individuals can’t utilise galactose obtained from diet because of lack of kinase(galactose accumulates)/transferase(galactose & galactose-1-P accumulate) enzyme
transferase deficiency is more common

Question 12

issues associated with galactosaemia

Answer 12

accumulation of galactose leads to its reduction into galactitol by the activity of the enzyme aldose reductase
this reaction requires NADPH so depletes tissues from it.
prevents maintenance of free sulphydryl groups on proteins
inappropriate disulphide bond formation
loss of structural and functional integrity of some proteins that depend on free -SH groups

Question 13

effects of galactosaemia on eyes

Answer 13

in the eye the lens is structure is damaged(cross linking of lens proteins by -S-S bond formation) causing cataracts.
there also might be non-enzymatic glycosylation of the lens protein due to the accumulation of galactose also contributing to cataract formation.
accumulation of galactitol and galactose may lead to glaucoma which could lead to blindness.

Question 14

why is the pentose phosphate pathway used

Answer 14

if energy levels, glycolysis is inhibited so levels of G-6-P will rise and feed out into the pentose phosphate pathway.

Question 15

what does the pentose phosphate pathway do

Answer 15

converts G-6-P from glycolysis to 5C sugar phosphates, providing NADPH.
requires Glucose-6-Phosphate dehydrogenase.

Question 16

what is the importance of NADPH provided by pentose phosphate pathway

Answer 16

helps the antioxidant molecule glutathione (GSH) to remain in its active state.
GSH prevents damage caused by ROS.
Glutathione reduces disulphide bonds formed within cytoplasmic proteins to cysteines by serving as an electron donor. In the process, glutathione is converted to its oxidized form, glutathione disulphide (GSSG). To be converted back to GSH, NADPH is required as an electron donor.
GlSH helps to maintain proteins in their correct structure by keeping the SH groups in their reduced state.

Question 17

what happens in G-6-P dehydrogenase deficiency

Answer 17

reduced NADPH production
inappropriate disulphide bonds can form causing proteins to aggregate.
e.g damage of reactive oxygen species in red blood cells causes Heinz bodies(denatured haemoglobin)——–> haemolysis

Question 18

what are the 5C-sugar ribose made in the pentose phosphate pathway required for?

Answer 18

synthesis of nucleotides

DNA & RNA