Download Bio1A Unit 1-6 Cell Resp Notes File

Cellular Respiration: Harvesting Chemical Energy
• Aerobic respiration consumes organic molecules and O2 and yields ATP
• Fermentation is a partial degradation of sugars that occurs without O2
• Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O 2
Cell respiration Overall
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
ΔG° = - 686 kcal/mole released
But broken down into more controlled release
Stepwise oxidation of carbon
Each step releases significant energy
Hallmarks of Oxidation (C loses H and/or C gains an O)
 releases energy
NAD+, NADP+
Nicotinamide adenine dinucleotide (NAD+)
Electron shuttling
NAD+ + 2H+ + 2e-  NADH + H+
Dehydrogenases - Enzymes perform redox reactions using NAD+/NADH as substrate
The Stages of Cellular Respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Citric
acid
cycle
Pyruvate
oxidation
Oxidative
phosphorylation:
electron transport
& chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
I. Glycolysis
Location: Cytosol
•Simplest metabolic pathway
•Most cells do it
•Considered most primitive biochemical process
•10 steps  10 enzymes
Glycolysis: Phase I - Energy Investment Phase
ATP is used to convert glucose into G3P
Glycolysis: Phase II - Payoff Phase
G3P is oxidized releasing energy captured by NAD+
Released energy also used for substrate level phosphorylation
Investment Phase
4 ADP & 2 NAD+
2 ATP
Glucose
2 G3P
2 ADP
Overall for glycolysis:
Payoff phase
2Pyruvate
4 ATP
2 NADH + H+
(C3)
3-carbon
molecule
Glucose + 2ADP + 2Pi + 2NAD+  2pyruvate + 2ATP + 2 NADH + 2H+
Transported into
mitochondrial matrix
Substrate level phosphorylation
Transfer of a phosphate from substrate to ADP to generate ATP
R-P + ADP  R + ATP
• A smaller amount of ATP is formed in glycolysis and the citric acid cycle
by substrate-level phosphorylation
• Oxidative phosphorylation accounts for almost 90% of the ATP
generated by cellular respiration
Fermentation
• Result of anaerobic conditions (for organisms with a mitochondria)
always for bacter
• Removes buildup of NADH & resupplies NAD+, NAD+ is needed for glycolysis
• Removes pyruvate
• Prevents the overall glycolytic pathway from reaching equilibrium
• Many other forms including production of methane and hydrogen gas
Obligate Anaerobes
• organisms that produce ATP using fermentation
• sometimes killed by O2 (no SOD)
• Some bacteria
Facultative anaerobes
• Fermentation in absence of O2
• Respiration in presence of O2
Obligate aerobes
• can only do respiration (humans)
Intermembrane space
Outer membrane
Free ribosomes
Inner membrane
Cristae
Matrix
II. Pyruvate decarboxylation & The Citric Acid Cycle
•
•
•
•
Location: Mitochondrial Matrix
Complete the oxidation of carbon to
Generate more NADH & FADH2
More substrate-level phosphorylation
Pyruvate decarboxylation
•
•
•
•
Pyruvate pumped into matrix
Generation / release of CO2
Oxidation step  NADH + H+
Remaining 2-carbon molecule delivered
to citric acid cycle by CoenzymeA
Citric acid cycle
• Carbons are further oxidized, until fully oxidized and released as CO2
• Each of the 2 pyruvates from glycolysis generate:
1 ATP
3 NADH + H+
1 FADH2 (similar to NADH but less energetic)
III. Oxidative Phosphorylation
• Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the
energy extracted from food (Oxidation products)
• These two electron carriers donate electrons to the electron transport chain, which
powers ATP synthesis via oxidative phosphorylation
Electron Transport
• Location: Mitochondria cristae
• Most of the chain’s components are proteins, which exist in multiprotein complexes
Fe3+  Fe2+
• The carriers alternate reduced and oxidized states as they accept and donate electrons
• Electrons drop in free energy as they go down the chain and are finally passed to O 2,
forming H2O
• Release energy is used to power H+-pumps that are the protein complexes that the
cytochromes are part of
• This builds a high H+ gradient within the limited space of the mitochondrial
intermembrane space.
• Ultimately electrons are used to reduce O2, which combines with H+ to generate H2O.
Remember this ultimately began with NADH + H+  NAD+ + 2e- + 2H+
• All steps are coupled together, meaning: if O2 is not available then none of these reactions
can occur
Chemiosmosis / ATP synthesis
• Location: Intermembrane space, cristae and matrix
• Use of the H+-gradient is chemiosmosis
• This potential energy drives the enzyme ATP
synthetase
• Called proton-motive force
• Gycolysis and the citric acid cycle are major intersections to
various catabolic and anabolic pathways
• Catabolic pathways funnel electrons from many kinds of
organic molecules into cellular respiration
• Glycolysis accepts a wide range of carbohydrates
• Proteins must be digested to amino acids; amino groups can
feed glycolysis or the citric acid cycle