metabolism 3 and 4 Flashcards
(32 cards)
What is the difference between an endergonic and an exergonic reaction?
Endergonic reactions require an input of energy and have a positive ΔG (non-spontaneous). Exergonic reactions release energy and have a negative ΔG (spontaneous).
What is biochemical coupling?
Biochemical coupling is the process by which an exergonic reaction (like ATP hydrolysis) drives an endergonic reaction by transferring energy, often through phosphorylation.
What are the five types of biochemical reactions found in metabolism?
- Phosphorylation/Dephosphorylation
- Oxidation/Reduction (Redox)
- Isomerization
- Decarboxylation
- Hydrolysis/Dehydration
Where does glycolysis occur in the cell?
In the cytoplasm of the cell.
What are the main products of glycolysis?
- 2 pyruvate molecules
- 4 ATP total (2 net)
- 2 NADH
- 2 H₂O
What is the purpose of glycolysis?
To oxidize glucose (6C) into 2 pyruvate (3C), generating ATP and NADH as energy carriers.
Is ATP → ADP an endergonic or exergonic reaction? What type of reaction is it?
It’s an exergonic reaction (ΔG < 0), specifically a dephosphorylation reaction, releasing energy.
Which molecule has more free energy: glucose or glucose-6-phosphate?
The reaction:
Glucose + ATP → Glucose-6-phosphate + ADP
is exergonic, meaning it has a negative ΔG.
• That means glucose-6-phosphate is at a lower energy state than glucose plus ATP, and certainly lower than glucose alone in terms of free energy per molecule.
What type of reaction is involved in converting glucose-6-phosphate to fructose-6-phosphate?
It’s an isomerization reaction – a rearrangement of atoms without adding or removing atoms.
Why must fructose-6-phosphate be phosphorylated again?
It is unstable and can revert back; phosphorylation commits it to glycolysis.
Which molecule has more free energy: fructose-6-phosphate or fructose-1,6-bisphosphate?
Fructose-1,6-bisphosphate has more free energy due to the presence of two phosphate groups.
What type of reaction adds a phosphate group?
A phosphorylation reaction, which is endergonic and requires energy input.
Why is fructose-1,6-bisphosphate considered unstable?
It is unstable due to the repelling negative charges on its phosphate (P) groups, which create internal strain.
What two molecules does fructose-1,6-bisphosphate break down into?
- G3P (glyceraldehyde-3-phosphate)
- DHAP (dihydroxyacetone phosphate)
What happens to DHAP after the split?
DHAP undergoes an isomerization reaction and is converted into G3P.
What is the final product of this stage in glycolysis?
The process ends with 2 molecules of G3P, which continue through glycolysis.
Which reaction is endergonic and which is exergonic?
The oxidation of G3P is exergonic – it releases energy as electrons are transferred to NAD⁺, forming NADH. The formation of 1,3-bisphosphoglycerate (1,3-BPG) is endergonic – it requires energy to attach a high-energy phosphate group.
What types of reactions are taking place during the oxidation of G3P?
- Oxidation – G3P is oxidized as it loses electrons to NAD⁺, forming NADH.
- Reduction – NAD⁺ is reduced to NADH.
- Phosphorylation – An inorganic phosphate (Pi) is added to form 1,3-BPG.
Which molecule has more free energy: 1,3-bisphosphoglycerate or G3P?
1,3-bisphosphoglycerate (1,3-BPG) has more free energy than G3P.
What reaction occurs when converting 1,3-bisphosphoglycerate to 3-phosphoglycerate?
The conversion of 1,3-bisphosphoglycerate (1,3-BPG) to 3-phosphoglycerate is exergonic – it releases energy.
What is Substrate Phosphorylation?
When a phosphate group is transferred from a substrate to ADP to form ATP.
What type of reaction took place when moving the phosphate group from 3-phosphoglycerate to 2-phosphoglycerate?
This is an isomerization reaction, specifically a mutase reaction.
What type of reaction took place when 2-phosphoglycerate is converted to phosphoenolpyruvate?
This is a dehydration reaction.
Which molecule has more free energy: phosphoenolpyruvate or 2-phosphoglycerate?
Phosphoenolpyruvate (PEP) has more free energy than 2-phosphoglycerate.
