B12- Respiration Flashcards
Respiration
Chemical potential energy from biological molecules into usable energy - ATP
Mitochondria
organelle that is responsible for aerobic respiration
Inner membrane: folded into cristae, less permeable, and is the site of the electron transport chain & ATP synthase (both used in oxidative phosphorylation)
Intermembrane space: has a high concentration of H+ ions (protons), so used to build a proton gradient (essential for ATP synthesis)
Matrix: contains ribosomes, enzymes and circular mtDNA
Phosphorylation:
Glucose (6C) is phosphorylated by 2 ATP molecules, to from fructose bisphosphate (6C) - Glucose + 2ATP → Fructose bisphosphate
Lysis
Fructose bisphosphate (6C) is unstable, and splits into two molecules of triose phosphate (3C) - Fructose bisphosphate → 2 Triose phosphate
Oxidation
Hydrogen is removed from each molecule of triose phosphate (3C), and transferred to coenzyme NAD → form 2 reduced NAD (NADH) - 4H + 2NAD → 2NADH + 2H+
Dephosphorylation
Phosphates are transferred from the intermediate substrate molecules, to form 4 ATP through substrate-linked phosphorylation - 4Pi + 4ADP → 4ATP
Production of Pyruvate
used in the next stage of respiration
2 Triose phosphate → 2 Pyruvate
Link Reaction
- Pyruvate is oxidised by enzymes → produced acetate (CH3CO(O)- and carbon dioxide (NAD is reduced here → NADH)
- Acetate combines with coenzyme A → forms acetyl coenzyme A (acetyl CoA)
What is NAD & FAD?
Both types of coenzymes
- Accept hydrogen ions & electrons
- Hydrogen atom & electrons removed - coenzyme has been oxidised (NAD / FAD)
- Hydrogen atom & electrons accepted - coenzyme has been reduced (NADH / FADH2)
Krebs cycle
The third stage of respiration
- Acetyl CoA (2C) enters from the link reaction
- Oxaloacetate (4C) accepts the 2C acetyl fragment (from acetyl CoA) → forms Citrate (6C) (CoA is released & reused)
- Citrate is converted back to oxaloacetate through many redox reactions…
Citrate is converted back to oxaloacetate through many redox reactions…
- Citrate is decarboxylated → CO2 released as waste gas
- Citrate is also oxidised (dehydrogenation)
- Released H atoms, that will reduce NAD & FAD
- 3 NAD and 1 FAD → 3NADH + H+ and 1 FADH2
- Substrate-linked phosphorylation
A phosphate group is transferred from one of the intermediates, to ADP → forms 1 ATP
Oxidative Phosphorylation & ATP Synthesis
Current model of this stage is the chemiosmotic theory, and is summarised below:
- Energy from electrons is passed through a chain of electron-carrying proteins
- The energy from this is used to pump protons (H+ ions) up a concentration gradient → into the intermembrane space
- These ions are pumped BACK into the matrix by facilitated diffusion, through ATP synthase channels → creates ATP
Ethanol Fermentation
- Pyruvate is decarboxylated to ethanal (+ produced CO2)
- Ethanal is reduced to ethanol (by alcohol dehydrogenase - enzyme)
Lactate Fermentation
- Reduced NAD transfers its hydrogens to pyruvate
- Pyruvate is reduced to lactate (by lactate dehydrogenase - enzyme)
Lactate can be oxidised back to pyruvate (requires oxygen)→ can be used in Krebs OR be converted into glycogen & stored in the liver
