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Cellular Respiration
Chapter 9
CP Biology
Chemical Pathways

Energy
◦ food is source of E for cells
◦ calorie=the amount of E needed to raise the
temp of 1 gram water 1 degree Celsius
◦ cells don’t burn glucose
 gradually release E
Chemical Pathways

cellular respiration
◦ =process that releases E by breaking down
glucose and other food molecules
◦ aerobic =in the presence of oxygen
◦ anaerobic= oxygen is NOT present
◦ 602 + C6H1206  6CO2 + 6H20 + E
◦ 3 stages:
 1. glycolysis
 2. Krebs cycle (citric acid cycle)
 3. electron transport
Cellular Respiration~aerobic
Chemical Pathways

1. glycolysis
◦ 1 molecule of glucose (6-C) is broken in half
producing 2 molecules of pyruvic acid (3-C)
◦ CCCCCC  CCC CCC
◦ glucose
pyruvic acid
◦ cell gains 2 ATP
◦ e- carrier NAD accepts a pair of H-E e- 
NADH
Krebs cycle

2. Krebs cycle (citric acid cycle)
◦ aerobic
◦
◦
◦
◦
 glycolysis  Krebs cycle  e-TC
mitochondrion
pyruvic acid (CCC) broken down into CO2 in a series
of E extracting reactions
pyruvate CCC  mitochondrion  CO2 (released
in air)
other 2 CC  2 E carriers accept H-E e-s
NAD+  NADH and FAD  FADH2  carry E to
e-TC
3. Electron Transport
uses H-E e- from Krebs to convert ADP  ATP
 eukaryotes: series of proteins embedded in the inner
membrane of mitochondrion
 prokaryotes: same chain in cell membrane
 H-E e- move from 1 carrier protein to the next
 E is used to move H ions across membrane (ATP
synthase)
 every rotation of ATPase phosphate group is added to
A-P-P  A-P-P~P
 absence of oxygen  2 ATP (glycolysis)
 presence of oxygen  34 more ATP
 glycolysis + Krebs + e-TC  36 ATP per glucose

Chemical Pathways

fermentation (anerobic)
◦ = releases E from food molecules by producing ATP
◦ cells convert NADH back into the e-carrier (NAD+)
 needed for glycolysis
◦ 1. alcoholic
 yeasts and alcohols
 pyruvic acid + NADH  alcohol + CO2 + NAD+
◦
2. lactic acid
 builds in muscles during strenuous exercise
 pyruvic acid + NADH  lactic acid + NAD+
Chemical Pathways
Chemical Pathways
glycolysis
aerobic
Krebs cycle
e-TC
anaerobic
fermentation
alcoholic
lactic acid
totals

glycolysis produces 2 ATP molecules per glucose
 w/o O, that’s all the E a cell can extract from each glucose molecule)
 w/ O, Krebs cycle & e-TC enable the cell to produce 34 more ATP
molecules per glucose molecule, in addition to the 2 ATP obtained
from glycolysis
 18xs as much ATP can be generated from glucose in presence of O
◦ 36 ATP = 38% of the total E of glucose; other 62% lost as heat
 1 mole of glucose (~180 g) contains 686 Kcal of E)
 1Kcal = 1000 calories
◦ How much E does respiration yield from 1 mole glucose?
 686 Kcal x .38 = 261 kcal
◦ How much E is lost as heat?
 686 Kcal x .62 = 425 kcal
 OR
 686 kcal – 261 kcal = 425 kcal
Energy & Exercise
one glucose stores 90x as much E than ATP
 quick

◦ cells only contain small amounts of ATP (from glycolysis & CR)
◦ muscles contain only enough ATP for few seconds producing
ATP from LA (enough E to last ~ 90 seconds)
◦ LA is a byproduct  rid  oxygen pathway  oxygen debt=
using oxygen faster than you are taking it in

long term (longer than 90 seconds)
◦ CR is the only way to generate a continuous supply of ATP
◦ CR releases E more slowly that fermentation
◦ body stores E in muscles & other tissues in the form of glycogen
(carbohydrate)which usually lasts ~ 15 to 20 minutes
◦ after that, your body begins to break down other stored
molecules (fats, for E)
FYI…
quick, heavy weight lifting = 100% anaerobic
 running (marathon) = 99% aerobic
 soccer or basketball = 20% anaerobic 80% aerobic
 ATP production can be improved through training
 resistance vs endurance
 anaerobic

 springs & similar bursts of E
and tolerance of LA
 aerobic
 long runs can
level of glycogen in muscles