bsc 2010 - exam i lectures and text pages i. intro to biology (2-29) ii. chemistry of life –...
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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)
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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)
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Energy ultimately comes from the Sun
• Energy
– Flows into an ecosystem as sunlight and leaves as heat Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respiration
in mitochondria
Organicmolecules
+ O2
ATP
powers most cellular work
Heatenergy
Figure 9.2
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Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is exergonic (releases energy)
• Catabolic pathways yield energy by oxidizing organic fuels
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Catabolic Pathways
• One catabolic process, fermentation
– Is a partial degradation of sugars that occurs without oxygen
– Involves Glycolysis
– Yields 2 ATP/Glucose molecule
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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
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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)
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Cellular RespirationRespiration 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)
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Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
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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
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Examples of redox reactions• Examples of redox reactions
Na + Cl Na+ + Cl–
becomes oxidized(loses electron)
becomes reduced(gains electron)
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Some redox reactions• Do not completely exchange electrons
• Change the degree of electron sharing in covalent bonds
CH4
H
H
HH
C O O O O OC
H H
Methane(reducingagent)
Oxygen(oxidizingagent)
Carbon dioxide Water
+ 2O2 CO2 + Energy + 2 H2O
becomes oxidized
becomes reduced
Reactants Products
Figure 9.3
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidation of Organic Fuel Molecules During Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
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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.
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Electrons from organic compounds• Are usually first transferred to NAD+, a
coenzyme
NAD+
H
O
O
O O–
O
O O–
O
O
O
P
P
CH2
CH2
HO OHH
HHO OH
HO
H
H
N+
C NH2
HN
H
NH2
N
N
Nicotinamide(oxidized form)
NH2+ 2[H]
(from food)
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NADH
OH H
N
C +
Nicotinamide(reduced form)
N
Figure 9.4
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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.
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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
(a) Uncontrolled reaction
Fre
e en
ergy
, G
H2O
Explosiverelease of
heat and lightenergy
Figure 9.5 A
H2 + 1/2 O2
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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
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Electron Transport Chain
2 H 1/2 O2
(from food via NADH)
2 H+ + 2 e–
2 H+
2 e–
H2O
1/2 O2
Controlled release of energy for synthesis of
ATP ATP
ATP
ATP
Electro
n tran
spo
rt chain
Fre
e en
ergy
, G
(b) Cellular respiration
+
Figure 9.5 B
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An overview of cellular respiration
Figure 9.6
Electronscarried
via NADH
GlycolsisGlucos
ePyruvate
ATP
Substrate-levelphosphorylation
Electrons carried via NADH and
FADH2
Citric acid cycle
Oxidativephosphorylation:
electron transport and
chemiosmosis
ATPATP
Substrate-levelphosphorylation
Oxidativephosphorylation
MitochondrionCytosol
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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)
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Stages of Cellular Respiration1. 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
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Stages of Cellular Respiration
3. Oxidative phosphorylation
– Is driven by the electron transport chain (receives electrons from NADH and FADH2)
– Generates 32 – 34 ATP
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An overview of cellular respiration
Figure 9.6
Electronscarried
via NADH
GlycolsisGlucos
ePyruvate
ATP
Substrate-levelphosphorylation
Electrons carried via NADH and
FADH2
Citric acid cycle
Oxidativephosphorylation:
electron transport and
chemiosmosis
ATPATP
Substrate-levelphosphorylation
Oxidativephosphorylation
MitochondrionCytosol
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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
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Both glycolysis and the citric acid cycle• Can generate ATP by substrate-level
phosphorylation
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
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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
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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
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Glycolysis
• Glycolysis consists of two major phases
– Energy investment phase
– Energy payoff phase
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
Glucose
2 ADP + 2 P
4 ADP + 4 P
2NAD+ + 4 e- + 4H + 2 NADH + 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2NAD+ + 4e– + 4H +2NADH + 2H+
Figure 9.8
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Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
HH
H
HH
OHOH
HO HO
CH2OHH H
H
HO H
OHHO
OH
P
CH2O P
H
OH
HO
HO
HHO
CH2OH
P O CH2O CH2 O P
HOH HO
HOH
OP CH2
C OCH2OH
HCCHOHCH2
O
O P
ATP
ADPHexokinase
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
ATP
ADP
Phosphoglucoisomerase
Phosphofructokinase
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Glycolysis
1
2
3
4
5
CH2OHOxidative
phosphorylation
Citricacidcycle
Figure 9.9 A
A closer look at the energy investment phase
Uses 2 ATP. Produces 2 Glyceraldehyde-3-phosphates to feed into energy payoff phase.
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2 NAD+
NADH2+ 2 H+
Triose phosphatedehydrogenase
2 P i
2P C
CHOH
O
P
O
CH2 O
2 O–
1, 3-Bisphosphoglycerate2 ADP
2 ATP
Phosphoglycerokinase
CH2 O P
2
C
CHOH
3-Phosphoglycerate
Phosphoglyceromutase
O–
C
C
CH2OH
H O P
2-Phosphoglycerate
2 H2O
2 O–
Enolase
C
C
O
PO
CH2
Phosphoenolpyruvate2 ADP
2 ATP
Pyruvate kinase
O–
C
C
O
O
CH3
2
6
8
7
9
10
Pyruvate
O
Figure 9.8 B
A closer look at the energy payoff phase
Produces 4 ATP, 2 NADH (for ETC), and 2 pyruvates to be converted to Acetyl-CoA and fed into Citric Acid Cycle.
So, net of glycolysis is 2 ATP, 2 NADH, and 2 pyruvate.
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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.
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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
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
Process yields 2 NADH (for ETC) from 2 pyruvate