Cellular Respiration
- the aerobic (uses oxygen) harvesting of energy from food molecules by cells.
- Formula: C6H12O6 + 6O2 ---à 6CO2 + 6H20 + 38ATP
- glucose + oxygen à carbon dioxide + water + adenosine triphosphate
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- Note that typical cells can only convert about 40% of glucose taken in to ATP – the rest is converted to heat (laws of Thermodynamics)
ATP (adenosine triphosphate) – molecule which is main energy source for cellular work. Composed of 1) adenine – a nitrogenous base 2) ribose – a 5-carbon sugar 3) a chain of 3 phosphate groups. See ATP cycle in text p 221.
Cellular energy
- trapped in electron arrangement within chemical bonds of organic molecules
- released during respiration in a series of energy-releasing (exergonic) reactions when electrons (e-) move from molecules where they have more energy to a molecule where they have less energy
- small amounts of energy released (exergonic) as ADP and some energy stored (endergonic) as ATP
- rearrangement of H atoms allows for this energy transfer (H “lost” from glucose to leave behind CO2; H gained by O2 to form water)
- O2 is final electron acceptor in cellular respiration – the electrons from the H atoms end up in H2O by-product of cell respiration. O “pulls” the H because it needs its e- to gain stability, building the polar water molecules.
Redox reactions – Oxidation Reduction reactions- drive both cellular respiration and photosynthesis. These reactions always occur in pairs because an e- donor and an e- acceptor are required. e- moves when more attracted to another molecule. 2 parts to redox reactions:
- Oxidation – loss of e- (H atoms removed); oxidized
- Reduction – addition of e- (H atoms attached); reduced
Ex: Enzyme + NAD+(coenzyme) remove 2 H+ and 2 e- from donor--– donor is oxidized
Ex: NAD+ (coenzyme) picks up 1 H+ and 2 e- forming NADH+--- NAD is reduced (and remaining H+ is released into solution around the cell)
NADH+ is a electron carrier; it stores energy from the hydrogen it gets from donor (glucose or pyruvic acid – both compounds containing C, H, O)
Overview 3 Stages of Cellular Respiration:
I. Who: Glycolysis - “sugar breakdown”
What – glucose broken down into 2 molecules of pyruvic acid (-COOH acid group)
Where – cytoplasm of all cells (outside of any organelles)
Why – 2 ATP + supplies electrons for ETC
II. Who: Krebs (Citric Acid or TCA) cycle
What – Derivatives of 2 pyruvic acid molecules cycle to form 2CO2
Where – in mitochondrial matrix of eukaryotic cells
Why – 2 ATP + supplies electrons for ETC
III. Who: Electron Transport Chain
What – Coenzymes NADH + FADH2 release energy stored in ATP
Where – along mitochondrial membrane of eukaryotic cells
Why – 34 ATP produced!!!
Total ATP = 2 from glycolysis + 2 from Kreb’s cycle + 34 from ETC = 38 Total ATP
Note that your textbook has wrong ATP numbers on this on p. 231 – ignore paragraph 2 and 3 and study these notes!!!.