bsc 2010 - exam i lectures and text pages i. intro to biology (2-29) ii. chemistry of life –...
TRANSCRIPT
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
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respiration
in mitochondria
Organicmolecules
+ O2
ATP
powers most cellular work
Heatenergy
Figure 9.2
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 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)
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
Na + Cl Na+ + Cl–
becomes oxidized(loses electron)
becomes reduced(gains electron)
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
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
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.
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
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
(a) Uncontrolled reaction
Fre
e en
ergy
, G
H2O
Explosiverelease of
heat and lightenergy
Figure 9.5 A
H2 + 1/2 O2
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
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
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
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 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
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
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
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
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
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
– 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
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.
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.
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
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