Lec14-16 - Metabolism, Glycolysis and the Citric Acid Cycle Flashcards
Name and define the two main classes of metabolic pathways
Catabolic (breakdown of complex molecules into simple ones to release energy) and Anabolic (build-up of complex molecules from simple ones)
What is the advantage of a multistep pathway rather than a single step one?
In a single step pathway, all the energy would be released at once, mostly in the form of heat, which would be quite inefficient. A multistep pathway (with one enzyme per step) allows the energy to be released in smaller units cells can use.
It also allows activation and inhibition of each step
What are the general characteristics of metabolic pathways?
Highly regulated (to allow response to environmental changes and avoid futile steps); often irreversible, no backing up (with a few exceptions)
Define feedback inhibition
When the product of a pathway controls its own synthesis by inhibiting an earlier step (usually the first “committed” step)
Define feed-forward activation
When a metabolite early in a pathway activates an enzyme further down the pathway
What is meant by “coupled reactions”?
Sometimes, enzyme-catalysed reactions can be the sum of two coupled reactions - one endergonic and the other exergonic, to give an overall negative delta-G
Describe the “interconversion” function of adenylate kinase
It interconverts adenine nucleotides at near equilibrium (ATP + AMP <-> 2ADP):
1. when ATP is hydrolysed rapidly in the cell, ADP levels increase; the eqb reaction will convert some ADP back into ATP
2. As the reaction moves to the left, AMP concentration increases
3. AMP acts as a metabolic signal to increase rate of some catabolic reactions
What do Nucleoside Diphosphate Kinases (NDKs) do?
They convert ATP to any other NTP (ATP + NDP <-> NTP + ADP)
How do enzymes respond to different NTPs (e.g., CTP, TTP, etc.)
They are non-specific, and work on all NTPs. NTPs participate in nucleic acid synthesis and several cellular phosphorylation reactions, and are energetically equivalent to ATP.
Free 5/5 :)
Cheers
State the net outcomes of glycolysis
(Per glucose molecule)
- TWO molecules of pyruvate produced
- TWO molecules of ATP produced
- TWO molecules of NAD+ reduced to NADH
- FOUR electrons transferred from glucose to two molecules of NAD+
Name the products/intermediates of each step of glycolysis
Glucose -> G-6-Phosphate -> Fructose-6-Phosphate -> Fructose-1,6-Bisphosphate -> Glyceraldehyde-3-Phosphate (2) -> 1,3-bisphosphoglycerate -> 3-phosphoglycerate -> 2-phosphoglycerate -> phosphoenolpyruvate -> PYRUVATE
Name the first two steps in glycolysis (reactants, products, enzymes, etc.)
- Glucose -> G-6-Phosphate (transfer of a phosphoryl group from ATP to glucose; HEXOKINASE< GLUCOKINASE)
- G-6-Phosphate -> Fructose-6-Phosphate (Isomerisation; PHOSPHOGLYCOSE ISOMERASE)
Name the third and fourth steps in glycolysis (reactants, products, enzymes, etc.) *after phosphorylation + isomerisation
- F-6-Phosphate -> F-1,6-Bisphosphate (transfer of a second phosphoryl group from ATP to F-6-P; PHOSPHOFRUCTOKINASE/PFK)
- F-1,6-Bisphosphate -> 2 Dihydroxyacetone phosphate//Glyceraldehyde-3-Phosphate (rapid interconversion of triose phosphates (FRUCTOSE 1,6-BISPHOSPHATE ALDOLASE, then TRIOSE PHOSPHATE ISOMERASE)
Name the fifth and sixth steps in glycolysis (reactants, products, enzymes, etc.) *after split + interconversion
- Glyceraldehyde-3-phosphate -> 1,3-bisphosphoglycerate (Oxidation and phosphorylation; GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE/GAPDH)
- 1,3-bisphosphate -> 3-phosphoglycerate (substrate-level phosphorylation; PHOSPHOGLYCERATE KINASE)
Final 3 steps of glycolysis (reactants, products, enzymes, etc.) *after S-L phosphorylation
- 3-phosphoglycerate -> 2-phosphoglycerate (PHOSPHOGLYCERATE MUTASE)
- 2-phosphoglycerate -> phosphoenolpyruvate (removal of water; ENOLASE)
- Phosphoenolpyruvate -> Pyruvate (substrate level phosphorylation; PYRUVATE KINASE)
Name all 10 steps of glycolysis (short version)
- ATP hydrolysis
- Isomerisation
- ATP hydrolysis
- Cleavage/split
- Rapid interconversion of triose phosphates
- Oxidation + Phosphorylation by NAD+ + Pi
- S-L phosphorylation
- Isomerisation
- Removal of H2O
- S-L phosphorylation
What are the three possibilities for further metabolism of pyruvate (and where/when do each of these occur)?
- Aerobic Conditions - Oxidised to Acetyl CoA (Link Reaction) then Citric Acid Cycle + ETC
- Anaerobic Conditions - converted to Ethanol (microorganisms; fermentation)
- Anaerobic Conditions - converted to Lactate (muscles, red blood cells)
Name the two steps of further metabolism of pyruvate in Yeasts (alcoholic fermentation)
- Pyruvate -> Acetaldehyde (PYRUVATE DECARBOXYLASE)
- Acetaldehyde -> Ethanol (ALCOHOL DEHYDROGENASE)
State the OVERALL reaction of respiration in yeasts, and state what this shows about net redox
Glucose + 2ADP + 2Pi + 2H+ -> 2Ethanol + 2ATP + 2CO2 + 2H2O
(no NAD+ or NADH appear in overall reaction - no net oxidation or reduction)
Describe the further metabolism of pyruvate in anaerobic conditions in cells of higher organisms
Pyruvate -> Lactate (dehydrogenation; LACTATE DEHYDROGENASE)
State the OVERALL reaction of anaerobic respiration in higher organisms, and state what this shows about net redox
Glucose + 2ADP + 2Pi -> 2Lactate + 2ATP + 2H2O
Name the three steps of glycolysis that involve a free energy change (number, reactants/products)
- Glucose + ATP -> Glucose-6-Phosphate + ADP (HEXOKINASE)
- Fructose-6-Phosphate + ATP -> Fructose-1,6-bisphosphate + ADP (PHOSPHOFRUCTOKINASE)
- Phosphoenolpyruvate + ADP -> Pyruvate + ATP (PYRUVATE KINASE)
What is the significant difference between the three steps of glycolysis that involve a free energy change, and the seven that do not
These 3 reactions are IRREVERSIBLE and their enzymes are REGULATED
