energy I Flashcards
(33 cards)
what are the 2 categories of metabolic processes
Catabolic processes - the breakdown of complex molecules to release energy
Anabolic processes - synthesis of new molecules from less complex components
what is glycolysis
Glucose is metabolised to pyruvate
when is glycogen broken down?
when circulating glucose concentrations are low.
in catabolic processes, what are large molecules broken down into
c02 and heat and ATP.
what links the 2 metabolic processes
ATP, NADP and NADPH.
How is energy utilised from atp
• 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.
what is the total amount of energy available from the hydrolysis of ATP ?
65kj/mole
How much ATP do we use at rest
40Kg/24hour
How much ATP do we use during exercise ?
0.5Kg/minute
How does the body meet the demands of atp
it must re-synthesise ATP from ADP.
what are the cofactors central to metabolism?
- 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
what are the major oxidative pathways
- Glycolysis
- Citric acid cycle
- Electron transport coupled to oxidative phosphorylation
- Fatty acid oxidation
outline the steps of glycolysis
- • 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)
- • 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. - • The glyceraldehyde 3 phosphate then undergoes a series of reactions forming phosphoenol pyruvate.
• NADH and one molecule of ATP is formed. - • Phosphoenol pyruvate is then coverted to form pyruvate.
• One ATP molecule is formed.
what are the reactants of glycolysis
- One molecule of glucose
- 2 molecules of ATP
- 2 molecules of NAD
- 2 molecules of ADP and pi.
what are the products of glycolysis
- 2 pyruvate molecules
- 2 NADH molecules
- 2 ATP molecules
what regulates glycolysis
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.
what are the 3 enzymes that regulate glycolysis
- 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.
How are the enzymes in the glycolysis pathway regulated ?
- 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.
WHY IS PYRUVATE KINASE only regulated in the liver and not other tissues.
in the liver pyruvate kinase does have allosteric sites.
- whereas other tissues dont and so cannot be regulated by pyruvate kinase
How is glycolysis regulated in muscles ?
- 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
why is regulation important in muscles
Important for muscle to protect them from excessive lactate production during anaerobic respiration
why is AMP a good indicator of the energetic state and not adp.
ATP can be made from ADP by adenylate kinase 2ADP gives ATP + AMP therefore AMP is a better indicator of energy state
which enzyme catalyses the reaction of the formation of ATP from ADP
adenylate kinase
describe the regulation of glycolysis in the liver
- 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.
