BIO 1140 Cell Energy Extraction/Generation

mainly about cellular respiration and photosynthesis

Stages of metabolism

1. Mouth & Gut - chewing, salivary and digestive enzymes, nutrient absorption into the blood

2. Cytosol - glycolysis (breakdown of glucose to pyruvate)

3. Mitochondria - pyruvate oxidation, citric acid cycle, oxidative phosphorylation —> ATP

Glycolysis

process of 10 reactions that makes

• 2 pyruvate

• 2 ATP (net)

• 2 NADH

Phase 1: invest 2 ATP to phosphorylate glucose

Phase 2: Split phosphorylated glucose into two 3-C molecules

Phase 3: Energy payoff - produce NADH & ATP

Pyruvate Oxidation

the process as it moves into the mitochondrial matrix

Pyruvate is transported into the matrix —> looses CO2, forms acetyl-CoA (2C) + NADH

Citric-Acid Cycle 

Happens in the mitochondrial matrix

Each acetyl-CoA —> 3 NADH, 1 FADH2, 1 GTP (ATP) + 2 Co2

Net per glucose: 2 acetyl-CoA —> 6 NADH, 2 FADH2, 2 GPT

Oxidative Phosphorylation 

Happens in the inner membrane

NADH/FADH2 donates electrons to —> complex 1 —> 3 —> 4 —> O2 (water)

Electron flow powers proton pumping from matrix —> matrix —> creates electrochemical gradient

ATP synthase uses returning protons (chemiosmosis) to convert ADP + Pi —> ATP

Approx 28 ATP from oxidative phosphorylation + 4 ATP from earlier steps

32 ATP per glucose

Exergonic and Endergonic

Exergonic: reactions release free energy

Endergonic: reactions require energ

Enzymes

Enzymes lower activation energy by:

• Providing a favourable micro-environment

• Straining bonds, alighting reactants

Fermentation

No Oxygen —> pyruvate stays in cytoplasm —> converted to lactate (muscle) or ethanol (yeast)

Regenerates NAD+ from NADH, allowing glycolysis to continue (2 ATP per glucose)

Without fermentation, NADH would accumulate, halting glycolysis

Photosynthesis

Occurs in the chloroplasts of plants and algae

Two stages

• Light dependent reactions need light/water and makes ATP/NADPH and Oxygen as byproduct

• Light independent reactions uses ATP/NADPH and converts them into sugars

Thylakoid membranes

Inside chloroplasts that are sites of light dependent reactions

Pigments

Pigments absorb visible light; chlorophyll absorbs red/blue, reflects green.

Carotenoids and anthocyanins are other pigments visible in the fall

Photosystems

Chlorophylls and proteins form photosystems

Photosystems have light harvesting complexes and a reaction center

Energy transferred between chlorophylls to reaction centre, where electrons are excited and transferred to electron carriers

ATP and NADPH production in photosynthesis

Photosystem 2: electrons from water —> electron transport chain —> ATP via proton gradient 

Photosystem 1: electrons boosted again —> reduce NADP* to NADPH
ATP and NADPH produced in stroma, used for Calvin cycle 

Proton gradient in photosynthesis

Proton gradient in thylakoid space formed by

• proton pumping by cytochrome b6f

• Water splitting adds protons to lumen

• Protons in stroma used up for NADPH formation, lowering stroma proton concentration

ATP synthase uses gradient to make ATP

Calvin Cycle

Occurs in stroma; uses ATP/NADPH to fix CO2 into sugars

Three phases: Carbon fixation, sugar formation, regeneration of acceptor molecule.

For each G3P produced: 3 CO2, 9 ATP, 6 NADPH needed

Phsophorylation

process of adding a phosphate group

Lysis

process of splitting a molecule

Decarboxylation

Remove a carboxyl (COOH) group releasing carbon dioxide