Cellular RespirationChapter 7
• An overview of cellular respiration
Figure 6.8
High-energy electrons carried by NADH
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
MitochondrionCytoplasmic
fluid
• Details of glycolysis in the cytoplasm
Figure 6.9B
Steps – A fuelmolecule is energized,using ATP.
1 3
1
GlucosePREPARATORY
PHASE(energy investment)Step
2
3
4
Glucose-6-phosphate
Fructose-6-phosphate
Glyceraldehyde-3-phosphate (G3P)
Step A six-carbonintermediate splits into two three-carbon intermediates.
4
Step A redoxreaction generatesNADH.
55 ENERGY PAYOFF
PHASE1,3-Diphosphoglyceric acid(2 molecules)
6
Steps – ATPand pyruvic acidare produced.
6 9 3-Phosphoglyceric acid(2 molecules)7
2-Phosphoglyceric acid(2 molecules)8
2-Phosphoglyceric acid(2 molecules)
9
(2 moleculesper glucose molecule)
Pyruvic acid
Fructose-1,6-diphosphate
What happens if oxygen is not present?
• Fermentation– Occurs in the cytosol– Generate NAD+ for recycling to glycolysis– No ATP production– Lactic acid and alcoholic fermentation
Lactic acid fermentation and alcoholic fermentation
Efficiency of glycolysis and fermentation
• In the matrix of the mitochondria, each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle
When Oxygen is present : Pyruvic acid is chemically groomedfor the Krebs cycle which takes place in the mitochondria
Figure 6.10
Pyruvicacid
CO2
Acetyl CoA(acetyl coenzyme A)
• The Krebs cycle, in the matrix of the mitochondria, is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group
When Oxygen is present: The Krebs cycle completes the oxidation of organic fuel,
generating many NADH and FADH2 molecules
Figure 6.11A
Acetyl CoA
KREBSCYCLE
2CO2
Figure 6.11B
Oxaloaceticacid
Step Acetyl CoA stokesthe furnace
1
2 carbons enter cycle
Citric acid
Steps and NADH, ATP, and CO2 are generatedduring redox reactions.
2 3
CO2 leaves cycle
Alpha-ketoglutaric acid
CO2 leaves cycle
Succinicacid
KREBSCYCLE
Steps and Redox reactions generate FADH2
and NADH.
4 5
Malicacid
1
2
3
4
5
• The electrons from NADH and FADH2 travel down the electron transport chain to oxygen
• Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes
• In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP
Chemiosmosis powers most ATP production in the inner membrane
• Chemiosmosis in the mitochondrion inner membrane
Figure 6.12
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Proteincomplex
Electroncarrier
Electronflow
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Connection: Certain poisons interrupt critical events in cellular respiration
Figure 6.13
Rotenone Cyanide,carbon monoxide
Oligomycin
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
• For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules
Review: Each molecule of glucose yields many molecules of ATP
KREBSCYCLE
Electron shuttleacrossmembranes
Cytoplasmic fluid
GLYCOLYSIS
Glucose2
Pyruvicacid
2AcetylCoA
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
by substrate-levelphosphorylation
used for shuttling electronsfrom NADH made in glycolysis
by substrate-levelphosphorylation
by chemiosmoticphosphorylation
Maximum per glucose:Figure 6.14
• Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP – But a cell must have a way of replenishing
NAD+
Fermentation is an anaerobic alternative to aerobic respiration