Energy Releasing Pathways:
Cellular Respiration and Glycolysis
Biology 1010 -Chapter 8
Introduction
A. Unity of Life
1. all organisms use energy
2. byproducts of metabolism
a. carbon dioxide
b. water
c. heat
3. at the biochemical level, all life is united
Process of ATP Synthesis
A. Comparison of Pathways
1. ATP is the energy currency of all cells
2. glycolysis
a. common to all pathways
b. splitting of glucose forms ATP
c. occurs in the cytoplasm of the cell
2. Fermentation and anaerobic electron
transport
a. occur in the absence of oxygen
b. release small amounts of ATP
3. Aerobic respiration
a. main pathway for converting
CHO to ATP
b. occurs in the mitochondria
c. requires oxygen
d. efficient
4. chemical formula
H2O +C6H12O6 + O2 = CO2 + H2O
5. similarities to photosynthesis
Glycolysis
A. First stage of all energy-releasing pathways
1. occurs in the cytoplasm of the cell
2. does not require oxygen
3. evolutionary considerations
B. Stages
1. energy investment phase
a. glucose is phosphorylated by
2 ATP molecules
2. energy releasing phase
a. glucose is split to form 4 ATP
and 2 pyruvate molecules.
b. electrons captured by NAD+ to
form NADH (to ETS)
c. ATP is produced by substratelevel phosphorylation.
C. Inputs and Outputs
1. Inputs
a. glucose
b. NAD+
c. ADP
2. Outputs
a. 2 pyruvate
b. 2 NADH
c. 2 ATP (net)
Krebs Cycle: Aerobic Respiration
A. General
1. occurs in the mitochondria (inner
membrane space)
2. requires oxygen
3. input is the pyruvate (3-C)from
glycolysis, which is modified to form
acetyl-CoA
4. carbon leaves the cycle as CO2
B. Stages
1. pyruvate is converted to acetyl-CoA
2. oxygen is used to break C-C bonds
3. broken bonds release energy and
electrons.
4. energy is used to form ATP by
oxidative phosphorylation
5. electrons captured by NAD+
and FAD+ to form NADH and
FADH2 (to ETS)
6. carbon leaves as CO2
7. cyclic pathway - intermediates are
recycled
8. 1 glucose = 2 pyruvate. Two complete
turns of the pathway per glucose
molecule
9. 2 ATP produced per glucose
C. Inputs and Outputs
1. Inputs
a. pyruvate
b. NAD+ and
FAD+
c. ADP
d. O2
2. Outputs (per
glucose)
a. CO2
b. NADH and
FADH2
c. 2 ATP
Electron Transport System (ETS)
A. General
1. inputs are the NADH and FADH2 from
glycolysis and the Krebs cycle
a. processes electrons, not carbon
2. located on the inner membrane of the
mitochondria (integral proteins)
3. uses oxygen as a terminal electron
receptor
4. ATP is produced by chemiosmosis or
electron-level phosphorylation
B. Stages of chemiosmosis
1. NADH and FADH2 transfer electrons to
integral proteins on the inner membrane
a. electrons are high energy
2. passage of energy between proteins
pumps H+ ions out of the inner space
a. generates an electrical gradient
3. channels are opened, allowing the H+
ions to reenter, generating ATP.
4. oxygen is used to gather the spent
electrons, generating water
5. high amounts of ATP are produced,
typically 32 ATP per glucose.
6. NAD+ and FAD+ are recycled
C. Inputs and Outputs
1. Inputs
a NADH and
FADH2
b. ADP
c. O2
2. Outputs (per
glucose)
a. H2O
b. NAD+ and
FAD+
c. 32 ATP
Summary of Energy Harvest
A. ATP per glucose
1. glycolysis 2 ATP
2. Krebs 2 ATP
3. ETS 32 ATP
B. Variations
1. yield per glucose
may be 32-38 ATP
depending on cell type
ATP Yields
2
2
Glyco
Kreb
ETS
32
Anaerobic Respiration
A. General
1. occur in the absence of oxygen or
oxygen-poor environments
2. after glycolysis, pyruvate is converted to
other molecules than acetyl-CoA.
3. many bacteria are completely anaerobic
B. Fermentation Pathways
1. Lactate fermentation
a. pyruvate is converted to lactate
b. process regenerates NAD+
c. occurs in bacteria and muscle
cells
2. Alcohol fermentation
a. pyruvate is converted to
acetaldehyde and then alcohol
b. NAD+ is regenerated
C. Anaerobic electron transport
1. some bacteria have modified
electron transport systems.
2. types
a. convert SO4 to H2S
b. convert NO3 to NO2
3. evolutionary significance