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BSC 2010 - Exam I Lectures and Text Pages
• I. Intro to Biology (2-29)
• II. Chemistry of Life
–
Chemistry review (30-46)
–
Water (47-57)
–
Carbon (58-67)
–
Macromolecules (68-91)
• III. Cells and Membranes
–
Cell structure (92-123)
–
Membranes (124-140)
• IV. Introductory Biochemistry
–
Energy and Metabolism (141-159)
–
Cellular Respiration (160-180)
–
Photosynthesis (181-200)
Cellular Respiration
• ALL energy ultimately comes from the SUN
• Catabolic pathways  Yield energy by
oxidizing organic fuels
• All the primary organic molecules can be
consumed as fuel
• We’ll only examine the most common fuel =
sugar (C6H12O6)
• Exergonic rxn: ∆G = -686 kcal/mol of Glucose
(the energy will be used to generate ATP)
Energy ultimately comes from the Sun
• Energy
– Flows into an ecosystem as sunlight and
leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
Heat
energy
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic (releases energy)
• Catabolic pathways yield energy by oxidizing
organic fuels
Catabolic Pathways
• One catabolic process, fermentation
– Is a partial degradation of sugars that occurs
without oxygen
– Involves Glycolysis
– Yields 2 ATP/Glucose molecule
Catabolic Pathways
• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen and organic molecules
such as glucose
– Involves Glycolysis
– Yields up to 38 ATP/Glucose molecule
• To keep working
– Cells must regenerate ATP
Cellular Respiration
Redox rxns = oxidation-reduction rxns
• Transfer of electrons (e-) releases energy stored in
organic molecules  this energy is ultimately used to
generate ATP
• Oxidation = loss of e- from one substance
• Reduction = addition of e- to another substance
• Na + Cl  Na+ + Cl-
• Na is the reducing agent (donates an e- to CL)
• Cl is the oxidizing agent (removes an e- from Na)
Cellular Respiration
Respiration is a redox rxn:
• By oxidizing glucose, energy stored in glucose is
liberated to make ATP
– Happens in a series of enzyme-catalyzed steps
– Coenzyme (NAD+) acts as e- shuttle
• Electron transport chains (ETC) - breaks the
energetic fall of e- into several energy-releasing steps
(not one big explosive rxn), fig 9.5
– Consists of mostly proteins embedded in the inner
mitochondrial membrane
• Overview of Respiration: (fig 9.6)
Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to
another by oxidation and reduction
• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
Examples of redox reactions
• Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
Cl–
Some redox reactions
• Do not completely exchange electrons
• Change the degree of electron sharing in
covalent bonds
Products
Reactants
becomes oxidized
+
CH4
CO
2O2
+
Energy
2 H2O
becomes reduced
O
O
C
O
H
O
O
H
H
H
C
+
2
H
H
Methane
(reducing
agent)
Figure 9.3
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the
Electron Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
– Allows the cell to use the energy harvested
from sugar to power work rather than losing it
in one explosive reaction.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Electrons from organic compounds
• Are usually first transferred to NAD+, a
coenzyme
2 e– + 2 H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O–
O
O P
O
H
–
O P O HO
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
N
H
O
H
HO
N
H
OH
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
NH2
N
N
2 e– + H+
H
Figure 9.4
NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
NADH, the reduced form of NAD+
• Passes the electrons to the electron transport
chain
• So it is an electron shuttle and moves electrons
to the ETC from both glycolysis and from the
citric acid cycle.
If electron transfer is not stepwise
• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to
form water
Free energy, G
H2 + 1/2 O2
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
(a) Uncontrolled reaction
The electron transport chain (ETC)
• Passes electrons in a series of steps instead of
in one explosive reaction
• Uses the energy from the electron transfer to
form ATP
Electron Transport Chain
2H
1/
+
2
O2
1/
O2
(from food via NADH)
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Figure 9.5 B
(b) Cellular respiration
2
An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolsis
Pyruvate
Glucose
Cytosol
ATP
Figure 9.6
Substrate-level
phosphorylation
Citric
acid
cycle
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Three Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
– Glycolysis
– The citric acid cycle (Kreb’s Cycle)
– Oxidative phosphorylation (driven by the ETC)
Stages of Cellular Respiration
1. Glycolysis
– Breaks down glucose into two molecules of
pyruvate
– Produces net 2 ATP and 2 NADH
Conversion of pyruvate to acetyl CoA yields
2NADH
2. The citric acid cycle
– Completes the breakdown of glucose
– Produces net 2 ATP, 6 NADH and 2 FADH2
from 2 Acetyl CoA
Stages of Cellular Respiration
3. Oxidative phosphorylation
– Is driven by the electron transport chain
(receives electrons from NADH and FADH2)
– Generates 32 – 34 ATP
An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolsis
Pyruvate
Glucose
Cytosol
ATP
Figure 9.6
Substrate-level
phosphorylation
Citric
acid
cycle
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Cellular Respiration
• Glycolysis & Citric Acid Cycle = catabolic
pathways that breakdown glucose
• Glycolysis  pyruvate + coenzymes + ATP
• CAC  coenzymes + ATP
• ATP formed by substrate-level
phosphorylation (fig 9.7) = enzyme transfers
a phosphate group from an organic substrate
to ADP to make ATP
• Oxidative Phosphorylation = ATP synthesis
powered by ETC. Makes 90% of the 38 ATPs
Both glycolysis and the citric acid cycle
• Can generate ATP by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
Product
ATP
Glycolysis
•
Glycolysis harvests chemical E by oxidizing glucose to pyruvate
•
Glucose  Two 3-C sugars  oxidized & rearranged  Two pyruvates
•
Two Major Phases of Glycolysis
•
1. E-investment phase (fig 9.9)
•
Rearrange glucose + add phosphate groups (uses 2 ATP)
•
Split 6-C sugar  two 3-C sugar isomers
•
Glyceraldehyde-3-phosphate form  next phase
•
2. E-payoff phase (fig 9.9)
•
2 NAD+  2 NADH & a phosphate group added to each of 2 3-C sugars
•
4 ATP produced by substrate-level phosphorylation
•
Rearrangement of remaining phosphate group and the 3-C substrate
Final Products from 1 Glucose = 2 ATP + 2 pyruvate + 2NADH
Glycolysis
• Glycolysis harvests energy by oxidizing
glucose to pyruvate
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
Glycolysis
• Glycolysis consists of two major phases
– Energy investment phase
Glycolysis
– Energy payoff phase
ATP
Citric
acid
cycle
Oxidative
phosphorylation
ATP
ATP
Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
2NAD+ + 4 e- + 4H +
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
2NAD+ + 4e– + 4H +
2 Pyruvate + 2 H2O
2 ATP
2NADH
+ 2H+
A closer look at the energy investment phase
CH2OH
HH
H
HO H
HO
OH
H OH
Glycolysis
Citric
Oxidative
acid
cycle phosphorylation
Glucose
ATP
1
Hexokinase
ADP
CH2OH P
HH OH
OH H
HO
H OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O P
O CH2OH
H HO
HO
H
HO H
Fructose-6-phosphate
3
ATP
Phosphofructokinase
ADP
P O CH2 O CH2 O P
HO
H
OH
HO H
Fructose1, 6-bisphosphate
4
Aldolase
5
H
P O CH2 Isomerase
C O
C O
CHOH
CH2OH
CH2 O P
Figure 9.9 A
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Uses 2 ATP. Produces 2
Glyceraldehyde-3-phosphates to
feed into energy payoff phase.
A closer look at the energy payoff phase
6
Triose phosphate
dehydrogenase
2 NAD+
2 Pi
2 NADH
+ 2 H+
2
P
O C O
CHOH
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
O
H C O
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
Produces 4 ATP, 2 NADH
(for ETC), and 2
pyruvates to be
converted to Acetyl-CoA
and fed into Citric Acid
Cycle.
2
2
O–
C O
C O
P
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
O–
C O
C O
Figure 9.8 B
CH3
Pyruvate
So, net of glycolysis is 2
ATP, 2 NADH, and 2
pyruvate.
Citric acid cycle
• Citric acid cycle completes the E-yielding oxidation of
organic molecules
• Pyruvate enters mitochondrion via active transport 
converted to acetyl coenzyme A (acetyl CoA)
–
Happens in 3 rxns catalyzed by a multienzyme complex
• Citric acid cycle (also = Krebs cycle)
• Citrate (ionized form of citric acid) = 1st molecule produced
• Acetyl CoA brings two C atoms to cycle  recycles
oxaloacetate  C atoms leave cycle as CO2 (completely
oxidized)
• Ultimately get CO2, NADH, FADH2, and ATP from the CAC.
Before the citric acid cycle can begin
• Pyruvate must first be converted to acetyl CoA, which
links the citric acid cycle to glycolysis
• Happens in 3 rxns catalyzed by a multienzyme
complex.
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
Process yields 2
NADH (for ETC)
from 2 pyruvate
C
O
O
1
CH3
Pyruvate
Transport protein
Figure 9.10
3
CH3
Acetyle CoA
CO2
Coenzyme A