Biology - Cell Respiration

TOPIC 3.7 + 8.1: CELL RESPIRATION

3.7.1 Define cell respiration.

Cell respiration is the controlled release of energy from organic compounds in cells to form ATP (adenosine triphosphates).

3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP.

Glycolysis in cytoplasm: Glucose 2 pyruvates + small amount of ATP
(does not use oxygen)

3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.

Anaerobic cell respiration (no oxygen) in cytoplasm:

Humans: Pyruvate Lactate (lactic acid) + small amount of ATP

Yeast: Pyruvate Ethanol + carbon dioxide + small amount of ATP

3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.

Aerobic cell respiration (uses oxygen) in mitochondrion:

Pyruvate Water + carbon dioxide + large amount of ATP

8.1.1 State that oxidation involves the loss of electrons from an element, whereas reduction involves a gain of electrons; and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen.

Oxidation: gain oxygen / lose hydrogen / lose electrons
Reduction: lose oxygen / gain hydrogen / gain electrons

8.1.2 Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation.

Location: cytoplasm
Outline: oxidation of glucose to 2 pyruvates; reduction of ADP to ATP
4 stages: PLOA – phosphorylation, lysis, oxidation, ATP formation.

Summary of glycolysis: * 1 glucose 2 pyruvates * 2 ATP molecules used per glucose but 4 produced, hence net yield = 2 ATP * 2 NAD+ 2 NADH + H+

Hexose (glucose)
Two phosphate groups added to glucose to form hexose biphosphate phosphorylation. 2 ATP provide the phosphate groups.
Two phosphate groups added to glucose to form hexose biphosphate phosphorylation. 2 ATP provide the phosphate groups.

2 ATP

2 ADP
2 ATP

2 ADP
Phosphorylation
Phosphorylation

Hexose biphosphate
Hexose biphosphate split into 2 molecules of triose phosphate lysis
Hexose biphosphate split into 2 molecules of triose phosphate lysis

Lysis

Lysis

Oxidation: 2 atoms of hydrogen removed from each triose phosphate molecule. Energy released by oxidation is used to link on another phosphate group, producing a 3-carbon compound carrying 2 phosphate groups.

ATP formation: pyruvate formed by removing the 2 phosphate groups and passing them to ADP.
Oxidation: 2 atoms of hydrogen removed from each triose phosphate molecule. Energy released by oxidation is used to link on another phosphate group, producing a 3-carbon compound carrying 2 phosphate groups.

ATP formation: pyruvate formed by removing the 2 phosphate groups and passing them to ADP. 2 triose phosphate molecules
2 NAD+

2 NADH + H+
2 NAD+

2 NADH + H+

Oxidation

ATP formation

Oxidation

ATP formation

4 ADP

4 ATP
4 ADP

4 ATP

2 pyruvate molecules

8.1.3 Draw and label the structure of a mitochondrion as seen in electron micrographs.

* double membrane * cristae (folded inner membrane) * matrix (inner space between membranes; place to concentrate H+)

*Mitochondria only found in eukaryotic cells; location of aerobic respiration; pyruvate can be further oxidized here to release more energy.

8.1.4 Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain and the role of oxygen.

Stages in aerobic respiration: * link reaction * krebs cycle * ETC (electron transport chain)

NAD+ NADH + H+
NAD+ NADH + H+
Link reaction

CoA CO2 CoA CO2 Pyruvate acetyl CoA

* Pyruvate transported to matrix of mitochondria * CoA joins pyruvate * Pyruvate is decarboxylated one carbon removed as carbon dioxide * Remaining fragment is acetyl coA * NAD+ reduced to NADH + H+

Krebs cycle

Acetyl group transferred from acetyl CoA to 4-carbon compound (oxoaloacetate) to from 6-carbon compound (citrate), which is then converted back to oxoaloacetate.

* Decarboxylation: carbon dioxide (waste product) removed in 2 of the reactions. * Oxidation: hydrogen removed in 4 of the reactions, & accepted by NAD+ in 3 of the reactions / by FAD in the 4th reaction. * Substrate-level phosphorylation: ATP is produced in 1 of the reactions.

Electron transport chain

ETC is a series of electron carriers located in inner membrane of mitochondrion.
NADH supplies 2 electrons to first carrier in the chain (electrons come from oxidation reactions in earlier stages of cell respiration).
The electrons pass along ETC and give up energy each time they pass from one carrier to the next.
At 3 points along the chain enough energy is given up for ATP to be made by ATP synthase oxidative phosphorylation, since ATP production relies on energy released by oxidation.
FADH2 also feeds electrons into ETC but later than NADH. Only at 2 points is sufficient energy released for ATP production by electrons from FADH2.

Role of oxygen (terminal electron acceptor)

At the end of ETC, electrons are given to oxygen, which accepts hydrogen at the same time to form water. This happens on the surface of the inner membrane of the matrix, and is the ONLY stage at which oxygen is used in cell respiration.

If oxygen is unavailable, electron flow along ETC stops and NADH + H+ cannot be reconverted to NAD+, which runs out in the mitochondrion, hence link reaction and Krebs cycle cannot continue. Glycolysis can continue because conversion of pyruvate into lactate / ethanol + carbon dioxide produces as much NAD+ as is used in glycolysis.

Aerobic cell respiration = 30 ATP per glucose; glycolysis = 2 ATP per glucose. Oxygen greatly increases ATP yield.

8.1.5 Explain oxidative phosphorylation in terms of chemiosmosis.

* Energy released (as electrons pass along ETC) is used to pump protons (H+) across inner mitochondrial membrane into space between membranes. * A concentration gradient is formed. * ATP synthase transports protons back across membrane down the concentration gradient. * As protons pass across membrane, they release energy which is used by ATP synthase to produce ATP. * Coupling of ATP synthesis to electron transport via a concentration gradient of protons: chemiosmosis.

8.1.6 Explain the relationship between the structure of the mitochondrion and its function.

* Cristae folds: increase surface area for electron transfer / oxidative phosphorylation * Small space between inner and outer membranes: high proton concentration can be easily formed in chemiosmosis * Matrix: fluid containing enzymes for link reaction and Krebs cycle