Metabolic pathways and ATP I Flashcards
What are the three principle forms of food molecules used by the cells?
Polysaccharides –> simple sugars
Proteins –> amino acids
Fats –> glycerol and fatty acids
Describe the 3 main stages of cellular metabolism
- Glycolysis - oxidation of glucose within the cytosol of cells, generating ATP and NADH. Anaerobic process.
- TCA cycle/citric acid cycle - further oxidation of small molecules generated by glycolysis within the mitochondria of cells, generating ATP, NADH, FADH2 and waste products
- Oxidative Phosphorylation - generation of ATP within the mitochondria by the reduction of oxygen to water
List the 6 types of reactions that define metabolism
- Oxidation-reduction - electron transfer
- Ligation requiring ATP cleavage - formation of covalent bonds
- Isomerisation - rearrangement of atoms to form isomers
- Group transfer - transfer of a functional group from one molecule to another
- Hydrolytic - cleavage of bonds by the addition of water
- Addition or removal of functional groups - Addition of functional groups to double bonds or their removal to form double bonds
Describe the stages of glycolysis (first half)
- Glucose –> glucose-6-phosphate (by hexokinase, using hydrolysis of ATP to ADP)
- All kinases catalyse the transfer of a phosphate group from a donor such as ATP, onto a substrate
- An irreversible reaction and traps glucose inside the cell due to neg. charge - Glucose-6-phosphate –> fructose-6-phosphate (by phosphoglucose isomerase)
- The logic behind this reaction is that fructose can be split into equal halves when subsequently cleaved - Fructose-6-phosphate –> fructose-1,6-bisphosphate (by phosphofructokinase using ATP)
- Here a highly symmetrical, high energy compound is generated.
- Regulation of phosphofructokinase exquisitely controls the entry of sugars into the glycolysis pathway. - Fructose-1,6-bisphosphate –> glyceraldehyde 3-phosphate + dihydroxyacetone phosphate (by aldolase)
- An opening of the fructose ring to generate two high energy compounds, one of which, (dihydroxyacetone phosphate) subsequently undergoes isomerisation. - Dihydroxyacetone phosphate –> glyceraldehyde 3-phosphate (by triose phosphate isomerase (TPI))
Describe the stages of glycolysis (second half)
- Glyceraldehyde 3-phosphate –> 1,3-bisphosphoglycerate (by glyceraldehyde
3-phosphate dehydrogenase)
- NAD+ + Pi = NADH
- NADH is generated here which can be later used to generate yet more ATP within the mitochondria in a process known as oxidative phosphorylation - 1,3-bisphosphoglycerate –> 3-phosphoglycerate (by phosphoglycerate kinase, produces ATP)
- A phosphate group is transferred to an ADP molecule to give ATP. - 3-Phosphoglycerate –> 2-phosphoglycerate (by phosphoglycerate mutase)
- Shuffling of the phosphate group from the 3 to the 2 position. - 2-phosphoglycerate –> phosphoenolpyruvate + H2O (by enolase dehydration)
- Phosphoenolpyruvate –> pyruvate (using pyruvate kinase and producing ATP)
Transfer of the high energy phosphate group to ADP, generating one ATP molecule in the process.
Define substrate level phosphorylation and how this differs to other ways of producing ATP.
The formation of ATP in glycolysis is called substrate-level phosphorylation because ATP was produced by the direct transfer of a high-energy phosphate group from an intermediate source in the biochemical pathway to ADP
Contrasted to oxidative phosphorylation where ATP is produced using energy derived from the transfer of electrons
What happens to pyruvate in alcoholic fermentation
It can be turned into ethanol (anaerobic condition in yeasts)
- Pyruvate –> acetaldehyde (using pyruvate decarboxylase and producing CO2
- Acetaldehyde –> ethanol (using alcohol dehydrogenase and NADH + H+ = NAD+)
what happens to pyruvate in generation of lactate?
Can be turned into lactate (characteristic in anaerobic organisms and mammals during intensive exercise)
Pyruvate —> lactate (using lactate dehydrogenase and NADH + H+ = NAD+)
What is the importance of alcoholic fermentation and generation of lactate?
Regeneration of NAD+ is essential for glycolysis to continue, in conditions of oxygen deprivation.
Alcoholic fermentation and the generation of lactate serve the purpose of regenerating NAD+.
needed for the dehydrogenation of glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate, which is the first step in generating ATP for the body.
NAD+ + Pi—–> NADH
describe the process of pyruvate to acetyl coA
- Pyruvate + HS-CoA –> acetyl CoA + CO2
(using pyruvate dehydrogenase complex and NAD+ –> NADH)
Occurs in the mitochondria
Acetyl CoA formed is able to enter into the citric acid cycle and ultimately produce ATP by process of oxidative phosphorylation
Define the function of creatinine phosphate
- Creatine phosphate is a large reservoir of phosphate which can be used to phosphorylate ADP to ATP.
- Creatine kinase catalyses the reaction of:
creatine phosphate –> creatine + ATP
enzyme: creatine kinase
Function of thiamine pyrophosphate (TPP)
- derivative of vitamin B1
- Thiamine pyrophosphate (TPP) readily loses a proton and the resulting carbanion attacks that of pyruvate to make hydroxyethyl-TPP
- A deficiency of thiamine (vitamin B1) is a cause of Beri-Beri symptoms include:
- damage to the peripheral nervous system,
- weakness of the muscles and
- decreased cardiac output. The brain is particularly vulnerable too, as it relies heavily on glucose metabolism
Function of lipoamide
- Functional group undergoes oxidation and reduction.
- long arm allows dithiol group to swing from one active site to another.
- Arsenite and mercury have high affinity for neighbouring sulphydryl groups and will readily inhibit pyruvate dehydrogenase.
Function of FAD(Flavine Adenine Dinucleotide )
FAD accepts and donates two electrons with two protons:
FAD + 2e- + 2H+ —> FADH2
What charge does glucose-6-phosphate have and what is the consequence of this
Negative
Means it traps the glucose inside the cells.
