Cellular Metabolism Flashcards
What 6 types of metabolic reactions are present?
Oxidation-reduction Ligand requiring ATP cleavage Isomerization Group transfer Hydrolytic Addition or removal of functional groups
What are oxidation-reduction reactions?
Electron transfer
What are ligation reactions?
Formation of covalent bonds
What are isomerization reactions?
Rearrangement of atoms to form isomers
What are group transfer reactions?
Transfer of a functional group from one molecule to another
What are hydrolytic reactions?
Cleavage of a bond by the addition of water
What are the reduction reactions?
Addition of electrons or the addition of hydrogen
Removal of oxygen
What are oxidation reactions?
Addition of oxygen/removal of hydrogen
Name the hydrogen acceptors present within the electron transport chain:
Flavoprotein, coenzyme Q, cytochrome b,c,a
What is NAD?
Nicotinamide adenine dinucleotide. Coenzyme hydrogen acceptor.
Oxidised form is denoted as NAD+
What is FAD?
Flavin adenine dinucleotide
What is the first step of glycolysis?
Glucose is phosphorylated into glucose-6-phosphate by hexokinase (Phosphoryl transfer)
Which enzyme catalyses the initial phosphorylation of glucose?
Hexokinase-4
What is step 2 of glycolysis?
Glucose-6-phosphate undergoes isomerization reactions into fructose-6-phosphate, under the action of phosphoglucoisomerase (Aldose to ketose)
What enzyme catalyses the isomerization of glucose-6-phosphate –> Fructose-6-phosphate?
Phosphoglucoisomerase
What is step 3 of glycolysis?
Fructose-6-phosphate is phosphorylated by ATP into fructose-1,6-bisphosphate by phosphofructokinase (group transfer)
How is fructose-6-phosphate phosphorylated into fructose-1,6-bisphosphate?
Phosphofructokinase
What is step 4 of glycolysis?
Fructose-1,6-bisphosphate is hydrolyzed into two molecules of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate (hydrolytic cleavage)
What molecules is fructose-1,6-bisphosphate hydrolysed into?
Glyceraldehyde-3-phosphate
Dihydroxyacetone phosphate
What happens to dihydroxyacetone phosphate?
Undergoes isomerisation reaction into glyceraldehyde-3-phosphate via triosephosphate isomerase (TPI)
What is step 6 of glycolysis (Glyceraldehyde-3-phosphate –>)?
Dehydrogenated and phosphorylated by group transfer into 1,3-bisphosphoglycerate
NAD+ is the hydrogen carrier,oxidises the molecule resulting in reduced NAD
How is reduced NAD formed through the conversion of glyceraldehyde-3-phosphate into 1,3bisphosphoglycerate?
Dehydrogenation of glyceraldehyde-3-phosphate reduces NAD into reduced NAD
Oxidation-reduction reaction
What happens to 1,3-bisphosphoglycerate?
Under the action of phosphoglycerate kinase (group removal) into 3-phosphoglycerate (ADP is phosphorylated into ATP)
What enzyme catalyses the convention of 1,3bisphosphoglycerate into 3-phosphoglycerate?
Phosphoglycerate kinase
What is the destination of 3-phosphoglycerate?
3-Phosphoglycerate undergoes isomerization reaction into 2-phosphoglycerate by phosphoglycerate mutase
What enzyme isomerises 3-phosphoglycerate into 2-phosphoglycerate?
Phosphoglycerate mutase
What is the destination of 2-phosphoglycerate?
2-phosphoglycerate is converted into phosphoenolpyruvate by enolase (dehydration, water is removed)
What converts 2-phosphoglycerate into phosphoenolpyruvate?
Enolase
What type of reaction is the conversion of 2-phosphoglycerate into phosphoenolpyruvate?
Dehydration (water is removed)
What is the destination of phosphoenolpyruvate?
Phosphoenolpyruvate is converted into pyruvate by pyruvate kinase. ATP is formed
Where does glycolysis occur?
Cellular cytoplasm
What is glycolysis?
Substrate level phosphorylation of respiratory substrate glucose to synthesize pyruvate, ATP, and reduced NAD to generate ATP
Why is glucose phosphorylated?
Phosphorylation makes glucose more reactive, therefore unable to pass through cell membrane (negative charge)
Stored within cell
Regulated by phosphofructokinase
How many gross ATP molecules is produced via glycolysis?
4
2 via 1,3bisphosphoglycerate –> 3-bisphosphoglycerate
2 via phosphoenolpyruvate –> pyruvate
How many net ATP is produced?
2
What is the destination of the 2 NADH molecules under aerobic conditions?
Pass through the outer mitochondrial membrane into the electron transport chain
What is the destination of pyruvate under aerobic conditions?
Actively transported into the mitochondrial matrix, where it undergoes the link reaction
What is released from glucose phosphorylation into glucose-6-phosphate?
Proton
What ion is required to enable phosphorylation?
Magnesium ion
Why is magnesium required for the initial phosphorylation of glucose?
Positively charged ion shields negative ATP phosphate group.
What type of enzyme is phosphofructokinase?
Allosteric enzyme
Why is phosphofructokinase an allosteric enzyme?
The pace of glycolysis is dependent on enzyme activity, allosterically controlled by ATP.
ATP is an inhibitor
What effect does ATP have on phosphofructokinase?
Inhibition
Why is the symmetrical configuration of hexose-bisphosphate useful?
High energy compound
What is mutase?
An enzyme that catalyzes the intramolecular shift of a chemical group (phosphoryl)
What are the advantages of enol phosphates? (Phosphoenolpyruvate)
Dehydration elevates the group-transfer potential of the phosphoryl group.
High phosphoryl transfer potential, thereby making it easier for the conversion into pyruvate and the generation of ATP
What is the fate of pyruvate under anaerobic conditions?
When oxygen is unavailable to be the final hydrogen accept during oxidative phosphorylation.
Pyruvate is reduced to lactate by NADH to continue substrate-level phosphorylation via glycolysis
Lactate dehydrogenase is used
Reoxidises NADH to continue glycolytic pathway
What enzyme is used for the reduction of pyruvate into lactate?
Pyruvate dehydrogenase
What is the benefit of pyruvate –> lactate conversion?
Reoxidises NADH to continue glycolytic ATP synthesis
What is the overall reaction for anaerobic respiration?
Glucose +2pi + 2ADP –> 2 Lactate + 2ATP + 2H2O
What is the fate of pyruvate under aerobic conditions?
Actively transported to mitochondrial matrix
Link reaction
Dehydrogenated and decarboxylated to an acetate
Combines with Coenzyme-A (CoA) to form acetyl CoA
What enzymes convert pyruvate into acetyl-CoA?
Pyruvate dehydrogenase and pyruvate decarboxylase
What is the overall equation for the link reaction?
Pyruvate + NAD + CoA –> AcetylCoA + CO2 + NADH
What are the products of the link reaction per glucose molecule?
2 carbon dioxide
2 acetyl-CoA
2 NADH
What is the fate of pyruvate under anaerobic conditions in yeast?
Loses carbon dioxide –> Ethanal (Pyruvate decarboxylase)
Ethanal is reduced by NADH to ethanol
Alcoholic fermentation
What coenzyme assists with decarboxylation of pyruvate into ethanal?
Thiamine pyrophosphate
What is the neural response to lactate production?
Release of hydrogen ions enter into the blood, subsequently dropping blood pH
Detected by chemoreceptors within the carotid sinus and aortic arch
Triggers CNS to reduce muscle contraction, muscle have time to recover and return to aerobic respiration.
What happens to lactate in the blood plasma?
Transported to the liver, converted back to pyruvate
Where is lactate dehydrogenase predominantly located?
Heart, liver, kidneys, skeletal muscle, blood and lungs