OC3 - carbohydrate metabolism

Question 1

what is glycolysis (basic)?

Answer 1

breakdown of glucose

Question 2

what is gluconeogensis (basic)?

Answer 2

formation of glucose

Question 3

what is glycogenesis (basic)?

Answer 3

formation of glycogen

Question 4

what is glycogenolysis (basic)?

Answer 4

breakdown of glycogen

Question 5

what are the subunits in carbohydrate metabolism?

Answer 5

glycolysis
gluconeogenesis
glycogenesis
glycogenolysis
TCA cycle
pentose pathway
cori cycle

Question 6

what is carbohydrate metabolism?

Answer 6

carbohydrates are broken down through glycolysis to provide pyruvate and ATP
carbohydrates undergo glycogenesis to make glycogen as the storage substance for glucose
carbohydrates undergo the pentose pathway to produce DNA, RNA and various cofactors

Question 7

what is glycolysis?

Answer 7

oxidation of glucose to produce ATP
glycolysis is the first step of cellular respiration
substrate-level phosphorylation
1x glucose > 2x pyruvate
net gain: 2xATP and 2x NADH + H+

Question 8

what is pyruvate?

Answer 8

pyruvate is a key intersection in the network of metabolic pathways
the fate of pyruvate is dependent upon the availability of oxygen

Question 9

what is the fate of pyruvate in the presence of oxygen?

Answer 9

pyruvate enters the mitochondria and is converted into acetyl CoA, before entering the TCA cycle

Question 10

what is the fate of pyruvate in the absence of oxygen?

Answer 10

pyruvate is converted to lactate and undergoes the cori cycle
restores the NAD+ consumed in step 6 of glycolysis

Question 11

what are the three irreversible steps in glycolysis?

Answer 11

glycolysis is an irreversible anaerobic process, due to the 3 highly exergonic (-‘ve ΔG) reactions
step one
step three
step ten

Question 12

what is glycolysis step one?

Answer 12

hexokinase catalysed catabolism of glucose to glucose-6-phosphate
consumes 1 ATP molecule
exergonic - reverse reaction would require +16.7kJ of energy so will not proceed

Question 13

what is glycolysis step three?

Answer 13

phosphofructokinase catalysed catabolism of fructose-6-phosphate to fructose-1,6-bisphosphate
consumes 1 ATP molecule
key regulatory enzyme - first commited step, allosteric modification by ATP
exergonic - reverse reaction would require +14.2kJ of energy so will not proceed

Question 14

what is glycolysis step ten?

Answer 14

pyruvate kinase catalysed catabolism of phosphoenolpyruvate to pyruvate
synthesises 1 ATP molecule
exergonic - reverse reaction would require +31.4kJ of energy so will not proceed.

Question 15

what is the TCA cycle?

Answer 15

TCA cycle is the second stage of cellular respiration
occurs in the mitochondrial matrix
TCA cycle is amphibolic
intermediates from carbohydrates, fat and amino acid metabolism meet in the citric acid cycle to be completely oxidised to carbon dioxide and water
a large amount of chemical potential energy is released in a stepwise fashion
the oxidation-reduction reactions transfer chemical energy to NAD and FAD - 3x NAD & 1x FAD
pyruvate derivatives are oxidised - lose electrons
coenzymes are reduced - gain electrons

Question 16

what are the products of TCA cycle?

Answer 16

one molecule of GTP is produced - converted to ATP
TCA cycle = 3xNADH + FADH2 +3xH+ + GTP + 2xCO2
NADH and FADH2 - electron transport chain
no net gain of intermediates
TCA cycle is a rich source of intermediates for other biosynthetic pathways where needed

Question 17

what is the electron transport chain?

Answer 17

reduced coenzymes from the citric acid cycle travel to the inner mitochondrial membrane to the electron transport chain
ETC is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen.

Question 18

what is the process of the electron transport chain?

Answer 18

protons (H+) are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water
ATP synthase uses the proton (H+) gradient to form ATP from ADP + Pi
energy is gained by a difference in concentration of the protons (H+) across the inner membrane of the mitochondria - electrochemical gradient
net gain of 30-32 ATP

Question 19

what is the pentose pathway?

Answer 19

makes pentoses - a class of simple sugars including deoxyribose (DNA) and ribose (RNA)
makes NADPH - provides the electrons needed for reduction in anabolic reactions (reducing potential)

Question 20

what are the end products of the pentose pathway?

Answer 20

glyceraldehyde-3-phosphate and fructose-6-phosphate that link back to glycolysis
ribose-5-phosphate to make nucleotides
glucose-6-phosphate > 6x CO2 + 12x NADPH + 12x H+ + 6x ribose-5-phosphate

Question 21

what is the function of ribose-5-phosphate?

Answer 21

leads to nucleotide biosynthesis to make DNA, RNA and various cofactors (CoA, NAD+, NADP+)

Question 22

what is the function of the pentose pathway?

Answer 22

provides the release of reducing power needed for anabolic reactions

Question 23

what is gluconeogenesis?

Answer 23

the synthesis of glucose from pyruvate, lactate, glycerol and amino acids
occurs primarily in the liver as glycogen is stored in the liver
used when glycogen stores are low
requires the input of energy
occurs in the cytoplasm
important in liver control of blood glucose homeostasis

Question 24

what regulates gluconeogenesis?

Answer 24

reciprocally regulated with glycolysis by ATP levels
low ATP = glycolysis - produces ATP
high ATP = gluconeogenesis - uses ATP

Question 25

why is gluconeogenesis used?

Answer 25

the creation of glucose in cells cannot occur by reversing glycolysis due to the three irreversible steps (1,3&10) gluconeogenesis creates glucose using three reactions that bypass these irreversible reactions

Question 26

what is glucagon?

Answer 26

initiates gluconeogenesis raises concenetration of glucose produced by alpha cells in the pancreas

Question 27

what are the three steps of gluconeogenesis?

Answer 27

bypass I bypass II bypass III

Question 28

what is gluconeogensis bypass I?

Answer 28

converts pyruvate to phosphoenolpyruvate without using pyruvate kinase pyruvate travels to the mitochondrial matrix where pyruvate carboxylase converts it to oxaloacetate which is then converted to malate and the malate travels to the cytoplasm where it is converted back to oxaloaetate which produces phosphoenolpyruvate

Question 29

what is gluconeogenesis bypass II?

Answer 29

convert fructose-1,6-bisphosphate to fructose-6-phosphate without using phosphofructokinase fructose-1,6-bisphosphatase removes a phosphate group from fructose-1,6-bisphosphate to produce fructose-6-phosphate inhibited by AMP - low ATP - glycolysis activated by ATP - high ATP - gluconeogenesis

Question 30

what is gluconeogenesis bypass III?

Answer 30

convert glucose-6-phosphate to glucose avoiding hexokinase glucose-6-phosphatase removes a phosphate group from glucose-6-phosphate to produce glucose

Question 31

what is the cori cycle?

Answer 31

the conversion of glucose to pyruvate to lactate in muscle cells, this lactate travels through the bloodstream to the liver where it produces pyruvate which then undergoes gluconeogenesis to produce glucose which is then recycled through the blood stream back into muscle cells. PATHWAY

Question 32

why does the cori cycle take place in the liver?

Answer 32

the cori cycle takes place in the liver as muscle cells lack the glucose-6-phosphatase required for gluconeogenesis to occur.

Question 33

what is glycogenesis?

Answer 33

formation of glycogen from glucose. PATHWAY

Question 34

what are the enzymes used during glycogenesis?

Answer 34

glucokinase phosphoglucomutase UDP-glucosepyrophosphorylase glycogen synthase/ glycogen branching enzyme

Question 35

what is the key enzyme in glycogenesis?

Answer 35

glycogen synthase

Question 36

what is glycogenolysis?

Answer 36

breakdown of glycogen to form glucose

Question 37

what is the key enzyme in glycogenolysis?

Answer 37

glycogen phosphorylase

Question 38

how is the activity of glycogen phosphorylase controlled?

Answer 38

by phosphorylation and dephosphorylation phosphorylase a = active (phosphorylase kinase + 2ATP) phosphorylase b = inactive (phosphorylase phosphatase)

Question 39

what is the equation for glycogenolysis?

Answer 39

(glucose)n <> (glucose)n + glucose-1-phosphate