CELLULAR RESPIRATION

Overall Process

C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY

Purpose: Organisms routinely break down complex molecules in controlled steps and use energy released (in the form of ATP) from this catabolic process to do work.

ATP – adenosine triphosphate

Phosphate bonds• PO4 bonds are high energy bonds

– Require energy to make– Release energy when broken

Phosphorylation• Adding a phosphate group to any molecule

– Ex: ADP + Pi ATP

• Oxidative phosphorylation – phosphorylation results from redox reactions

• Substrate-level phosphorylation – phosphate group transfers from a molecule (“substrate”) instead of ADP + Pi ADP

How ATP Drives Cellular Work

Transport Work:ATP Phosphorylates Transport Proteins

Mechanical Work:ATP Phosphorylates Motor Proteins

Chemical Work:ATP Phosphorylates Key Reactants

Phosphate groups are removed and recycled as work is performed

ATP ADP + P

Cellular Respiration

• Divided into 3 parts:1. Glycolysis2. Krebs Cycle (aka Citric Acid Cycle) or Fermentation 3. Oxidative phosphorylation (ETC & Chemiosmosis)

1. Glycolysis• Breakdown of glucose into pyruvate in cytoplasm w/

or w/o presence of O2

• 2 phases:– Investment phase: use 2 ATP to break up glucose into 2

PGAL (C-C-C-p)– Payoff phase: each PGAL turns into pyruvate (C-C-C)

• Each PGAL pyruvate change makes 2 ATPs via substrate level phosphorylation and 1 NADH via redox

2. Krebs Cycle (aka citric acid cycle)

• Occurs in presence of O2

• Occurs in inner space or matrix of mitochondria• Complete oxidation of glucose to CO2 occurs here

1. Pyruvate is oxidized into Acetyl CoA reducing NAD+ into NADH on the way

• CO2 is formed

2. Acetyl CoA + oxaloacetic acid → citric acid

3. Citric acid is oxidized forming 2 CO2 as waste• This becomes oxaloacetic acid again @ end of cycle• This oxidation powers the reduction of 3 NAD+ 3

NADH and 1 FAD+ FADH2 as well as the phosphorylation of ADP ATP.

• Also get e-’s and protons (H+) for ETC/Chemiosomosis

ETC• Occurs in the inner membrane of mitochondrial

matrix• Energy released as e- travels down

ETC is used to establish a proton gradient

• Final electron acceptor is O2 • 2H+ (from FADH2 and NADH)

• 2e- (from FADH2 and NADH)

• ½ O2

H2O!

Key Points

• No ATP is generated during ETC; ATP comes from chemiosmosis!

• Source of e- = NADH and FADH2 reduction• Source of H+ = same as above!

Phosphorylation…1. Photophosphorylation – plants use energy from

sun to drive phosphorylation of ADP ATP2. Substrate-level phosphorylation – glycolysis

and Krebs cycle use proteins (substrates) to phosphorylate ADP ATP

3. Oxidative phosphorylation – in ETC, redox reactions drive production of ATP• This is where most of ATP generated from cell

respiration comes from!

Fermentation

• Process whereby cells produce ATP without O2

• Alcohol fermentation – pyruvate is converted to ethanol• CO2 released

• Lactic acid fermentation – pyruvate is reduced directly by NADH to form lactate • No CO2 released