D’YOUVILLE COLLEGE
BIOLOGY 102 - INTRODUCTORY BIOLOGY II
LECTURE # 15
CELLULAR RESPIRATION IV - OXID. PHOSPH./ALT. FUELS
5.
Oxidative Phosphorylation:
• electron transport (occurs in inner membrane of mitochondrion):
- series of electron-exchanging enzymes with cofactors including cytochromes
(iron-containing enzymes) (Fig. 9 – 13 & ppt. 1)
- accepts high-energy electrons of reduced NAD & lower energy electrons of
reduced FAD
- electrons pass to progressively lower energy states (increased electronegativity)
until accepted by oxygen (& hydrogen) to produce water
- energy released by electrons drives transport of H+ into intermembrane
space, creating electrochemical gradient for H+ (chemiosmosis) (fig. 9 – 15 & ppt. 2)
- energy stored in gradient drives phosphorylation of ADP to ATP (=
oxidative phosphorylation) (fig. 9 – 14)
- electrons from reduced NAD energize synthesis of 3 ATPs
- electrons from reduced FAD energize synthesis of 2 ATPs
• grand summary (fig. 9 – 16 & ppts. 3 & 4): glycolysis: 2 ATPs + 2 reduced
NADs
- pyruvate oxidation: 2 reduced NADs
- Krebs cycle: 2 ATPs + 6 reduced NADs + 2 reduced FADs
- oxidative phosphorylation: 32 – 34* ATPs from 10 reduced NADs & 2
reduced FADs; total of 36 - 38* ATPs
* depends on energy cost of shuttling reduced NAD from glycolysis (in cytosol)
into mitochondrion
Biology 102, lec 15 - Spring ‘13
page 2
6.
Oxidation of Fats & Proteins (fig. 9 – 19 & ppt. 5):
• triglycerides: hydrolysis yields fatty acids + glycerol
- glycerol converted to G3P (processed by second half of glycolysis)
- fatty acids oxidized via b-oxidation (aka fatty acid cycle - occurs in mitochondrial
matrix)
- each round of cycle produces acetyl-CoA; e.g. 20-carbon fatty acid
generates 10 acetyl CoAs
- large ATP payoff
- excess acetyl-CoA converted to ketone bodies (may cause acidosis)
•. proteins: hydrolysis yields amino acids
- amino acids oxidized & deaminated; yield: ammonia + various organic acids
(enter glycolysis or Krebs cycle at pyruvate, acetyl CoA, oxaloacetate, & a-ketoglutarate
stages); similar energy yield to carbohydrates
- ammonia converted to urea (via urea cycle in liver) for excretion
7.
Control of Cellular Respiration: (fig. 9 - 20 & ppt. 6)
• feedback inhibition: accumulation of excess ATP inhibits glycolysis, whereas
AMP (from ADP) stimulates glycolysis; also, citric acid inhibits glycolysis, which slows
down until more citrate is used up by the Krebs cycle; this has effect of making the rate
of glycolysis closely matched to the rate of the Krebs cycle.