energy I

Question 1

what are the 2 categories of metabolic processes

Answer 1

Catabolic processes - the breakdown of complex molecules to release energy
Anabolic processes - synthesis of new molecules from less complex components

Question 2

what is glycolysis

Answer 2

Glucose is metabolised to pyruvate

Question 3

when is glycogen broken down?

Answer 3

when circulating glucose concentrations are low.

Question 4

in catabolic processes, what are large molecules broken down into

Answer 4

c02 and heat and ATP.

Question 5

what links the 2 metabolic processes

Answer 5

ATP, NADP and NADPH.

Question 6

How is energy utilised from atp

Answer 6

• ATP contains a high energy phosphate bond, and when its broken it yields energy which can be used for many processes. Biosynthesis, detoxification, contraction, ion transport, thermogenesis.

Question 7

what is the total amount of energy available from the hydrolysis of ATP ?

Answer 7

65kj/mole

Question 8

How much ATP do we use at rest

Answer 8

40Kg/24hour

Question 9

How much ATP do we use during exercise ?

Answer 9

0.5Kg/minute

Question 10

How does the body meet the demands of atp

Answer 10

it must re-synthesise ATP from ADP.

Question 11

what are the cofactors central to metabolism?

Answer 11

• NAD and FAD are activated carriers of electrons used for oxidation/reduction reactions.
• NAD = nicotinamide adenine dinucleotide
• FAD= flavin adenine dinucleotide
• reactions theyre primarily involved in oxidised to reduced form

Question 12

what are the major oxidative pathways

Answer 12

• Glycolysis
• Citric acid cycle
• Electron transport coupled to oxidative phosphorylation
• Fatty acid oxidation

Question 13

outline the steps of glycolysis

Answer 13

1. • Glucose is phosphorylated to form glucose-6-phosphate (G-6-P). This requires energy and results in the hydrolysis of ATP .
   • The formation of G-6-P has two functions. First, it maintains the glucose gradient. The concentration of glucose within the cell is kept relatively low compared to the outside. Second, it traps the glucose within the cell. The g-6-p is unable to be transported out of the cell.
   • This step is largely an irreversible step.

2.
• The G-6-P is converted to fructose-6-phosphate.
• The fructose-6-phosphate is further phosphorylated, using a molecule of ATP to form fructose 1,6 bisphosphate (C6)

3. • Fructose 1,6 bisphosphate is then split into 2 3C units:
   • Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
   • These two molecules are in equilibrium, and the equilibrium in this reaction lies more towards glyceraldehyde 3 phosphate.
4. • The glyceraldehyde 3 phosphate then undergoes a series of reactions forming phosphoenol pyruvate.
   • NADH and one molecule of ATP is formed.
5. • Phosphoenol pyruvate is then coverted to form pyruvate.
   • One ATP molecule is formed.

Question 14

what are the reactants of glycolysis

Answer 14

• One molecule of glucose
• 2 molecules of ATP
• 2 molecules of NAD
• 2 molecules of ADP and pi.

Question 15

what are the products of glycolysis

Answer 15

• 2 pyruvate molecules
• 2 NADH molecules
• 2 ATP molecules

Question 16

what regulates glycolysis

Answer 16

Enzymes catalysing irreversible reactions are potential sites
for regulation
Activity of such enzymes can be regulated by:

• reversible binding of allosteric effectors – rapid
• covalent modification
• Transcription – quantity of an enzyme can be increased or decreased depending on gene expression.

Question 17

what are the 3 enzymes that regulate glycolysis

Answer 17

• Hexokinase regulates the first step in glycolysis; the conversion of glucose to G-6-P in an energy requiring step.
• The second step, which is the conversion of fructose 6 phosphate to fructose 1,6 bisphosphate, is regulated by phosphofructokinase. ATP is hydrolysed.
• The third point is the conversion of phosphoenol pyruvate to pyruvate. It is regulated by pyruvate kinase. This enzyme exists in several different forms which are distributed in different tissues.

Question 18

How are the enzymes in the glycolysis pathway regulated ?

Answer 18

• by the need for ATP
• Hexokinase is regulated by the product of the reaction. G-6-P will inhibit the further conversion of glucose to G-6-P. this prevents too much glucose from being formed when it is not required.
• phosphofructokinase. It is negatively regulated by ATP, citrate and H+. The reason why these molecules regulate phosphofructokinase is because they are the end products of glycolysis or pathways that follow on from it.
• ATP – there is no need for glycolysis to take place if there is ATP.
• Citrate, the first product of the TCA cycle which feeds into the ETC. It results in the synthesis of ATP.
• H+ ions are important in skeletal muscle cells as it prevents the skeletal muscles from being damaged by low pH of continued glycolysis.
• These are all negative regulators.
• A positive regulator of glycolysis is AMP. AMP is a good indicator of the energetic state of the state of the cell.
• Pyruvate kinase, in the liver, is negatively allosterically regulated by ATP.

Question 19

WHY IS PYRUVATE KINASE only regulated in the liver and not other tissues.

Answer 19

in the liver pyruvate kinase does have allosteric sites.

• whereas other tissues dont and so cannot be regulated by pyruvate kinase

Question 20

How is glycolysis regulated in muscles ?

Answer 20

• pfk is the most important control point.
• high concentrations of ATP inhibit pfk by lowering the affinity for fructose-6-phosphate.
• it is also inhibited by low ph.
• inhibition of pfk leads to inhibition of hexokinase because if its inhibited it will lead to an increase in g-6-p
• high levels of AMP activate pfk

Question 21

why is regulation important in muscles

Answer 21

Important for muscle to protect them from excessive lactate production during anaerobic respiration

Question 22

why is AMP a good indicator of the energetic state and not adp.

Answer 22

ATP can be made from ADP by adenylate kinase 2ADP gives ATP + AMP therefore AMP is a better indicator of energy state

Question 23

which enzyme catalyses the reaction of the formation of ATP from ADP

Answer 23

adenylate kinase

Question 24

describe the regulation of glycolysis in the liver

Answer 24

• the liver has more functions so the regulation i smore complex.
• High concentrations of ATP inhibit PFK
• PFK is inhibited by citrate.
• The liver uses glucose and glycolysis as a source of carbon skeletons. Glycolysis in the liver is inhibited by citrate. High levels of citrate indicate the precursors of biosynthesis are abundant.
• • Pfk is stimulated indirectly by a build up of F6P
• • Hexokinase is inhibited by G6P, but the liver has glucokinase which is not inhibited by G6P. This means that there is a differential regulation of glycolysis in liver cells compared to other non-hepatic cells.
• • Regulation of PFK by ATP is the same as the muscle. Low pH is not a problem as the liver does not normally produce lactate.
• the liver is responsible for storing excess glucose, so when glucose levels are high, glucokinase increases the rate of glycolysis.

Question 25

describe the metabolism of galactose and fructose

Answer 25

• They feed into the glycolytic pathway at different levels.
• Galactose is first converted to glucose which can then enter then glycolytic pathway.
• Fructose in adipose tissue can be converted to fructose-6-phosphate which can then enter the glycolytic pathway.
• Fructose in the liver can be converted to DHAP and GAP which can then enter the second part of glycolysis.

Question 26

deacribe glycolysis in excercising myscles.

Answer 26

the limitations of the muscle to generate ATP is dependent on the availability of NADH.

• muscle overcomes this limitation by synthesising lactate from pyruvate, using NADH generating NAD+
• the lactate is sent to the liver to be converted to glucose so the build up of acid doesnt inhibit pfk and put is then put back into the cycle.
• Nad+ is used in the coversion of GALP to phosphoenol pyruvate until NAD+ is the limiting factor, allowing the second part of glycolyisis to continue.

Question 27

what is the limitation of the glycolysis in excercising muscles ?

Answer 27

• The limitation of this is that lactate is acidic. Under these conditions the build-up of acid will lead to a reduction in pH, which has an adverse effect on the activity of phosphofructokinase, inhibiting its activity.

Question 28

what is the difference in glycolysis between aerobic and anerobic conditions

Answer 28

• In aerobic conditions, the muscle converts the pyruvate to acetyl coA which will then undergo oxidative phosphorylation.

Question 29

how do tumours grow ?

Answer 29

As the size of the tumour increases, the need for blood supply is also increasing. The tumour will often produce angiogenic factors which will stimulate the endothelial cells of a nearby vessel to proliferate and migrate. This will lead to the formation of a vascular network.
However, the rate at which a tumour grows often exceeds the ability of the newly formed vessels to deliver sufficient oxygen to that tissue.

– Low oxygen will stimulate the activity of a transcription factor called HIF-1 alpha
- HIF-1 alpha has a number of effects both on stimulating blood vessel growth and metabolic pathways involved in glycolysis, allowing the tumour tissue to thrive even in low oxygen concentrations and where oxidated phosphorylation cannot take place to any great extent.
-

Question 30

what is a similarity between excercising skeletal muscle and tumour cells

Answer 30

energy needs are met through anerobic respiration

Question 31

what are the differences between tumors and muscles?

Answer 31

→A rapidly growing tumor does not have sufficient blood supply to have enough oxygen so it respires anaerobically.

→Tumors are not susceptible to low pH like muscles are.

Question 32

what is the difference between hexokinase and glucokinase

Answer 32

→Hexokinase is found in all cells in the body
glucokinase is found in the liver and is not inhibited by G6P.

→Glucokinase has a higher Km.

Question 33

How is glycolysis in the liver activated indirectly?

Answer 33

ndirect activation by F6P which is converted to Fructose 2,6 bisphosphate when blood glucose is high – example of feed forward regulation.