Metabolic regulation and glycolysis Flashcards

Question

What is triose phosphate isomerase? (TIM)

Answer 1

Great catalytic prowess, accelerates isomerisation by a factor of 10^10 compared to simple base catalysts Kinetically perfect enzyme, the rate limiting step is the diffusion-controlled encounter of substance and enzyme So 2 molecules of G-3-P almost simultaneously form from F 1,6 –bisP

Answer 2

Glucose enters the cell via specific transporters Phosphorylation of glucose traps it within the cell and begins the process of destabilisation The 6C molecule is isomerised from an aldose to a ketose sugar prior to further destabilisation by phosphorylation The destabilised 6C sugar then fragments into two interconvertible 3C sugars Stage 1 has utilised 2 ATP molecules

Answer 3

G 3-P is oxidised and phosphorylated by the enzyme G 3-P dehydrogenase Dehydrogenase transfer ‘high energy’ electrons from complex organic molecule to NAD+ to form NADH

Answer 4

The resulting intermediate 1,3-bisphosphoglycerate is an acyl phosphate (has a high-phosphoryl-transfer potential Sum of 2 process Oxidation of the aldehyde to a carboxylic acid by NAD+ Joining of orthophosphate to the carboxylix acid

Answer 5

Phosphoryl group on 3-Pglycerate shifts position, followed by dehydrogenation and formation of a C=C bond Increases transfer potential of phosphoryl group 3-Phosphoglycerate =(phosphoglycerate mutase)= 2-Phosphoglycerate =(enolase)= phosphenolpyruvate =(pyruvate kinase)= ATP + pyruvate

Answer 6

Irreversible transfer of phosphoryl group to form ATP Substrate level phosphorylation Regulatory enzyme activated by Fructose 1,6bisP and inhibited by ATP and alanine

Answer 7

Glucose + 2NAD+ + 2ADP + Pi - 2 pyruvate + 2NADH + 2 ATP + 2H+ + 2H2O Glycolysis would not proceed for long if the pyruvate was final metabolite as the redox balance of the cell would not be maintained Limited amounts of NAD+ in cells. Must be replaced.

Answer 8

During glycolysis NAD+ is converted to NADH Glycolysis cannot continue if NAD+ decreases Oxygen present – electrons on NADH transferred to oxygen (via electron transport chain) to produce H2O, ATP and NAD+ No oxygen present – electrons on NADH transferred to pyruvate to form lactate or ethanol and NAD+ (recycled for step 6 of glycolysis)

Answer 9

Ethanol formation: yeast and some other microorganisms Anaerobic process (no o2 required) Glucose + 2H+ + 2ADP + 2Pi – 2 ethanol + 2CO2 + 2ATP + 2H2O

Answer 10

Lactic acid formation: microorganisms also in higher organisms when oxygen is limited eg intense exercise Regeneration of NAD+ for step 6 of glycolysis

Answer 11

Lactic acid fermentation ensures a continuous supply of NAD+ under anaerobic conditions, allowing glycolysis to keep producing ATP, even without oxygen.

Answer 12

Under aerobic conditions much more energy can be extracted by means of the TCA cycle and OXPHOS Pyruvate enters mitochondria and is oxidised to acetyl coA NADH generated at step 6 of glycolysis cannot enter the mitochondria so NAD+ is regenerated indirectly by OXPHOS using specific shuttles

Answer 13

When cells breakdown glucose (in glycolysis), they produce NADH in the cytoplasm. But to make more ATP, NADH needs to pass its electrons into the mitochondria – to create energy in the ETC Problem – NADH itself cannot cross the mitochondrial membrane Solution – the malate/aspartate shuffle – sneaks electrons from NADH into the mitochondria using other molecules

Answer 14

In the cytoplasm: NADH gives its electrons to oxaloacetate, turning it into malate NAD+ is regenerated (so glycolysis can keep going) Malate can enter the mitochondria Inside the mitochondria: Malate gives the electrons back, becoming oxaloacetate again The electrons go to NAD+, turning it into NADH – now inside the mitochondria This NADH can enter the electron transport chain and help make ATP Recycling The oxaloacetate can’t leave the mitochondria directly So it is converted into aspartate, which can leave Outside the mitochondria, aspartate is converted back into oxaloacetate, ready to repeat the cycle

Answer 15

The glycerol 3-phosphate shuttle is another way cells move electrons from NADH (in the cytoplasm) into the mitochondria to help make ATP – especially in tissues like the brain and skeletal muscles Why its needed: Just like with the malate-aspartate shuttle, NADH can’t move across the mitochondrial membrane. But cells still need to transfer the electrons from NADH into the mitochondria for ATP production

Answer 16

In the cytoplasm: NADH donates its electrons to dihydroxyacetone phosphate (DHAP), turning into glycerol 3-phosphate This regenerates NAD+ so glycolysis can continue Glycerol 3-phosphate crosses into the mitochondrial membrane region, where it meets a special mitochondrial enzyme In the mitochondria Glycerol 3-phosphate donates its electrons to FAD, forming FADH2 (instead of NADH) FADH2 passes the electrons into the ETC, helping make ATP (but a bit less than NADH would)

Answer 17

Key difference vs malate-aspartate shuttle This shuttle gives electrons FAD – makes 1.5 ATP per pair of electrons Malate aspartate shuttle gives electrons to NAD+ - makes 2.5ATP per pair of electrons So glycerol 3-phosphate is faster but less efficient This is common in muscle and brain, where speed is important and efficiency can be sacrificed.

Metabolic regulation and glycolysis Flashcards

(45 cards)