Chapter 12: RespirationChapter 12: Respiration

Leaving Certificate BiologyLeaving Certificate Biology

Higher LevelHigher Level

RespirationRespiration• Internal versus external:

– Internal respiration is the enzyme-controlled release of energy from food

– External respiration is the exchange of gases with environment

• Aerobic versus anaerobic:– Aerobic respiration is the enzyme-controlled

release of energy from food using oxygen– Anaerobic respiration is the enzyme-controlled

release of energy from food without the use of oxygen

Aerobic RespirationAerobic Respiration

• Two stage process:1. Glycolysis

2. Krebs cycle & Electron Transport Chain

Stage 1: GlycolysisStage 1: Glycolysis• Oxygen-independent (can occur in presence

or absence of oxygen)• Occurs in cytosol• Glucose (a 6-carbon molecule) is changed into

two 3-carbon molecules (pyruvate)– This breaking down of glucose releases high energy

electrons – they are mopped up by NAD+ to become NADH

– NADH is an energy carrier but cannot release its energy to power metabolic reactions and so it needs to pass it on to ATP

– NADH powers the production of 3 ATP molecules– Glycolysis produces 2 molecules of ATP directlydirectly

Stage 1: GlycolysisStage 1: Glycolysis

GLUCOSEGLUCOSE

2ATP2ATP 2NADH2NADH

2ADP + 2P2ADP + 2P 2NAD2NAD++

2 PYRUVATE2 PYRUVATE

HH22OO Electron Transport

ChainMetabolism

Stage 2: Krebs CycleStage 2: Krebs Cycle• Oxygen-dependent (can only occur in the presence of O2)

• Occurs in the lumen of the mitochondrion (matrix)• Pyruvate enters mitochondrion and converted to 2-C

molecule (acetyl-coA) with release of NADH and CO2

• The acetyl-coA then joins with 4-C molecule from the previous Krebs cycle to form 6-C molecule

• The 6-C molecule is then broken down into 5-C molecule with release of CO2 and NADH

• The 5-C molecule is then broken down into 4-C molecule with release of ATP, CO2, 2NADH and 1FADH2

– The ATP goes to power metabolism

– The NADH and the FADH2 energy carriers go to the electron transport chain to pass their energy onto ATP molecules

– The 4-C molecule goes into the next Krebs cycle

Stage 2: Krebs CycleStage 2: Krebs CyclePYRUVATEPYRUVATE PYRUVATEPYRUVATE

Acetyl-CoA (2C)Acetyl-CoA (2C) Acetyl-CoA (2C)Acetyl-CoA (2C)

4C

2C +4C

6C

5C

4C

2C + 4C

6C

5C

CoA CoA

CO2

NADHCO2

2NADH

ATP CO2

NADHCO2

2NADH

ATP

CO2 NADH CO2 NADH

Metabolism Metabolism

Stage 2: Electron Transport ChainStage 2: Electron Transport Chain

• NADH molecules from glycolysis and Krebs cycle travel to the inner membrane (cristae) of mitochondrion

• The high-energy electrons release their energy slowly to power the production of ATP

• 3 ATP molecules are produced from each NADH

Stage 2: Electron Transport ChainStage 2: Electron Transport Chain

NADHNADH

NADNAD++

3ADP + 3P3ADP + 3P

3ATP

Inner mitochondrial membrane

Aerobic respiration Aerobic respiration produces a total of 38 produces a total of 38

ATP moleculesATP molecules

HH++ , 2e , 2e––

OO22 HH22OO

Metabolism

Anaerobic RespirationAnaerobic Respiration

• Anaerobic respiration occurs when no oxygen or limited oxygen is present

• Two stages:– Glycolysis– Lactic acid fermentation/Alcohol fermentation

Animals Animals and some and some bacteriabacteria

Plants, fungi, Plants, fungi, and some and some bacteriabacteria

Anaerobic RespirationAnaerobic RespirationGLUCOSEGLUCOSE

2ATP2ATP 2NADH2NADH

2ADP + 2P2ADP + 2P 2NAD2NAD++ + 4e + 4e-- + 2H + 2H++

2 x PYRUVATE2 x PYRUVATE

HH22OOElectron

Transport Chain

Metabolism

2 x Lactate2 x Lactate 2 x Ethanol2 x Ethanol

2CO2CO22NADH

NAD+

NADH

NAD+

SummarySummary

Mandatory Experiment: To produce and test for alcohol

• Set up the apparatus as shown• Leave for a number of days, or

until the carbon dioxide is no longer produced

• Test for alcohol by filtering and taking 3 ml of filtrate; then adding 3 ml potassium iodide solution followed by 5 ml sodium hypochlorite solution

• Heat gently and the production of pale yellow crystals indicates the presence of alcohol