C1.2 Cell Respiration

Cell respiration

C1.2.1. ATP

Currency of energy in cells. See 2).
Adenosine triphosphate; nucleotide serving as energy carrier
ribose, adenine, 3 phosphates - energy is stored in the P₂-P₃ bond.
Properties: soluble, sufficient energy, easily made/created, non-diffusable so no leaking, stable at neutral pH

C1.2.2. Cellular processes requiring ATP

1. Active transport across cell membranes

2. Anabolism (mono→macromolecules)

3. Movement of cell - motility (cilia/flagellum)

4. Movement of cell components (eg. chromosomes in mitosis/meiosis)

C1.2.3. ATP and ADP

Endlessly converting. ATP ←→ADP + Energy (sufficient for many tasks).
The → produces energy used in anabolism. →exergonic, hydrolysis

The ← reaction uses light energy, catabolism etcetc… ←endergonic, condensation

C1.2.4. Cell respiration forming ATP

Respiration: Carbon compounds oxidized to release ATP. Mainly glucose and fatty acids.

Ventilation: moving air in and out of lungs
Gas exchange: swap one gas for another

C1.2.5. Anaerobic vs aerobic respiration (in humans)

Aerobic: _{use O2. sugar/lipid. 30-36ATP. CO2+H2O Cytoplasm+mitochondria}

Anarobic: _{no O2. sugar 2ATP. Lactate Cytoplasm}

Aerobic: Glucose + Oxygen → Carbon Dioxide + Water + Energy

Anaerobic: Glucose → Lactate + Energy

C1.2.6. Factors rate of cell respiration

• T: optim = 20-30^oC

• CO₂ conc: increase [], decrease R

• O₂ conc: increase [], increase R

• Gluc conc: increase [], increase R

• Type of cell: more mitochonria; higher R rates

Respirometers: calculate R by measuring O₂ use or CO₂ production

C1.2.7. NAD

NAD (Nicotinamide adenine dinucleotide) acts as a hydrogen carrier; in cell respiration;

Oxidation occurs when hydrogen, along with its electron, is removed from a substrate (dehydrogenation);

Thereby oxidizing the substrate; NAD is reduced when it gains hydrogen;

NAD⁺ + H⁺ + 2e^- ←→ NADH (→red, ←ox)

Oxidation: -e, -H, +O
Reduction: +e, +H, -O

In resp; removing hydrogen from substrate = dehydrogenation

C1.2.8. Glycolysis

First step of respiration with glucose as substrate, in cytoplasm,
1. Phosphorelation: use 2 ATP→ C₆→C₆2p (fructose 1-6 biphosphate)
2. Lysis: F-1,6-B breaks into 2 triose (C₃p) phosphates

Another Phosphate added but not through ATP…
3. Oxidation: 2x NAD⁺→ NADH
Overall, triose phospates turned into G3P = glycerate-3-phosphate (2p3c)
4. Dephosphorelation: G3P → Pyruvate (C₃) + 2ATP

Overall: input 2ATP and glucose, output 4ATP and 2NADH_reduced and 2 pyruvate

C1.2.9. Anaerobic humans

Without oxygen, respiration ends here; can continue when ADP and NAD regenerated (by using up…) and supply of glucose is continuous

In humans; NAD is regenerated by adding hydrogen to pyruvate → lactate

In sprint; need very quick very short supply of ATP; use anaerobic; lactic acid produced; lower pH cytoplasm/blood ; hurts so you stop moving etc…

C1.2.10. Anaerobic yeast

Regenerate NAD aswell:
Pyruvate + NADH→ CO₂+ethanal(CH₃COH) → NAD + Ethanol

1. CO₂ is used in baking for rising (bubbles), less dense

2. Ethanol is used in brewing drinks; sugar but no oxygen in container, increase alc concentration

C1.2.11. Link Reaction

If there is oxygen available the pyruvate molecules have to go to the Krebs cycle, but the input in this is acetylCoA. So the pyruvate moves into mitochondria (matrix) So; series of steps:
Pyruvate → CO₂ +Acetate. (1)
Acetate + NAD → NADH+H⁺ + Acetate (2)
Acetate + CoA (Coenzyme) → Acetyl-CoA

Fatty acids can also do this, just cut off a C2 group and add CoA

C1.2.11 De- carbo,hydro,phospho

1. Decarboxylation: removing of CO₂ resulting in an C_n-1 molecule

   1. oxidative decarboxylation: the C_n-1 molecule loses electrons

2. Dehydrogenation: NAD+ → NADH + H⁺, oxidation of other group

3. Phosphorelation: ADP + P → ATP

C1.2.12. Krebs Cycle

Matrix of mitochondria

1. Acetyl CoA (C₂) + Oxaloacetate (C₄) → Citric acid (C₆), coA is released

2. Citrate is oxidatively decarboxilized → 1CO₂, 1NADH+H⁺ into C₅ compound

3. C₅ again→ 1CO₂ + 1NADH+H⁺ + 1ATP + C₄

4. C₄ is turned into oxaloacetate (C₄) → FADH₂ + NADH+H⁺

5. Oxaloacetate continues the cycle with the addition of an acetylCoA

C1.2.12. Yield of Krebs/Citric Cycle

1AcetylCoA → 2CO₂ +1ATP + 1FADH₂ + 3(NADH+H⁺)

C1.2.13 What next?

Electron Transport Chain: happens on inner membrane of mitochondria

From last few steps, we have 6ATP and 10NADH_red + 2FADH₂

Reduced NADH+H⁺+reduced FADH₂ go to ETC to produce ATP.

NADH: 3 ATP. FADH₂: 2ATP

C1.2.13 Phosphorelation

Substrate-level: phosphate released from an actual substance and added to ADP to form ATP (Glycolysis and Krebs)

Oxidative: use free energy from redox reaction (ETC)

C1.2.13 Splitting of NADH

The NADH+H⁺ (& FADH₂) sare in the matrix. They are split up:
NADH + H⁺ → NAD⁺ + 2e^- + 2H⁺
FADH₂→ FAD⁺ + 2e^- + 2H⁺

The electrons go into the ETC and the Hydrogen create proton gradient. The regenerated NAD goes back to be reused.

C1.2.13 ETC

The electrons released by the oxidation of NADH are transferred through electron carrier proteins (cytochromes) through the inner membrane of the mitochondria. They move and move, until they reach cytochrome oxidase; which releases the electrons back into the matrix, where oxygen; the terminal electron acceptor uses these for:
O₂ + 4e^- + 4H⁺ → 2H₂O

C1.2.14/15 Proton Gradient

As electrons pass along the chain from 1 carrier to the next, energy is released, used to pump proteins from matrix to intermembrane space. This area is small so a gradient is quickly established. A potential diffference/store of energy is created. This causes proteins to move to the proton channel: ATP Synthase; a motor like protein that uses the energy H⁺ gives off through passing when moving back to the matrix to oxidatively phosphorelate ADP into ATP. Process of energy releasing/requiring etc to pump H⁺ through membrane; chemiosmosis

C1.2.14 Gain of ETC

Every NADH gives 3 ATP, Every FADH₂ gives 2 ATP.
From glycolysis, link, krebs: 10NADH_red + 2FADH₂

10×3=30, 2×2=4. 34 ATP produced through ETC

C1.2.16 Terminal electron acceptor

Its important to note that although the electrons move through several carrier proteins, it moves out of the chance at some point and forms water. This reaction further contributes to proton gradient. Oxygens only role in cell resp. is as terminal electron acceptor at end of ETC. No O₂ means no regeneration of NAD, thus no respiration. H₂O is called metabolic water.

C1.2.16 Equation of respiration

2 ATP Krebs, 2 ATP Glycolysis, 34 ATP ETC:

C₆H₁₂O₆→ 6CO₂ + 6H₂O + 38ATP

C1.2.17 Respiratory substrates

Not just sugars, also lipids and proteins can be used for ATP production; lipids 9kcal/g, sugar/proteins 4kcal/g.

Lipids have more oxidizable C-H bonds and lower O-content. A 16C f.a. produces >100ATP, while 1 gluc=38…

Glycolysis only glucose. No oxygen=carbs only (anaerobic). Lipid is long term, carbs is rapid short term.

f.a. form acetyl-coA, and enter Krebs here