cellular respiration

bio sac 2

Cellular respiration formula

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

glycolysis

occurs in cytosol

does not require oxygen

glucose is split into two pyruvate molecules

uses the energy from 2 ATP but produces 4 ATP - net gain of 2 ATP

NAD+ → NADPH, carrying electrons and protons

NADH & FADH₂

coenzymes loaded during glycolysis + krebs cycle

NAD⁺ + H ions and electrons → NADH; loaded in matrix and krebs cycle

FAD + H ions and electrons → FADH₂; only loaded in matrix

loaded forms transfer electrons and protons during electron transport chain

aerobic respiration

occurs in cytosol and mitochondria

energy released from glucose is used to turn ADP + P_i into ATP

3 stages; glycolysis, Krebs cycle, electron transport chain

Krebs cycle

occurs in mitochondrial matrix

• Acetyl CoA (from pyruvate) → CO₂

• NAD⁺ → NADH

• FAD → FADH₂

• 2ADP+P_i → 2ATP

electron transport chain

movement of protons (H+) and electrons across the inner mitochondrial membrane to generate ATP

oxygen is required- “acceptor”

oxygen gas combines with protons and electrons to form water; if oxygen wasn’t present the ETC could not be completed due to build-up of H+ ions and electrons

• O₂ → H₂O

• 26/28 ADP+P_i → 26/28 ATP

• NADH → NAD⁺

• FADH₂ → FAD

anaerobic fermentation

occurs in cytosol when there is not enough oxygen

→ ETC cannot be completed

→ NADH and FADH₂ cannot become NAD⁺ and FAD, so Krebs cycle cannot occur

lactic acid fermentation (animals)

glycolysis occurs, producing 2 ATP (net) and 2 pyruvate

pyruvate is converted into lactic acid using NADH, which becomes NAD⁺ again

NAD⁺ can be used for further glycolysis, but lactic acid build-up is toxic

ethanol fermentation (yeast)

glycolysis occurs, producing 2 ATP (net) and 2 pyruvate

pyruvate is converted into ethanol and CO₂ using NADH, which becomes NAD⁺

NAD⁺ can be used for further glycolysis, but ethanol build-up is toxic

bioethanol production

1. Breakdown of biomass into glucose by enzymatic hydrolysis

2. Production of ethanol via fermentation under anaerobic conditions

3. Bioethanol is dehydrated and purified

bioethanol advantages

•Reduced carbon emissions; decreases enhanced greenhouse effect

•Renewable; provide energy security

•Sourced locally; reduced transport requirements

•Can be used as an input to make biodiesel

bioethanol disadvantages

•Competes with land usage for food production and ecosystems

•More expensive to produce

•Reduced compatibility with existing vehicles compared to fossil fuels