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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)
Citric Acid Cycle
• Citric acid cycle completes the energy-yielding
oxidation of organic molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
An overview of the citric acid cycle
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ H+ Acetyle CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
A closer look at the citric acid cycle
Glycolysis
Citric
Oxidative
acid phosphorylation
cycle
S
CoA
C
O
CH3
Acetyl CoA
CoA SH
O
NADH
+ H+
C COO–
COO–
1
CH2
COO–
NAD+
8 Oxaloacetate
HO C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
CH2
2
HC COO–
COO–
Malate
Figure
CH2
HO
Citrate
9.12
COO–
Isocitrate
COO–
H2O
COO–
CH
CO2
Citric
acid
cycle
7
3
NAD+
COO–
Fumarate
HC
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
4
C O
COO–
CH2
5
CH2
FADH2
COO–
NAD+
NADH
+ H+
NADH
+ H+
a-Ketoglutarate
CH2
COO–
Figure 9.12
CH
CO2
Pyruvate  AcetylCoA  Citric Acid Cycle
Yield from each 2 pyruvate molecules (from 1 glucose)
• 6CO2 (2 from Pyr.AcetylCoA, 4 from CAC
• 8NADH (2 from Pyr.  AcetylCoA, 6 from CAC)
• 2FADH2 (All from CAC)
• 2 ATP
(All from CAC)
Two pyruvates are produced from the glycolysis of each
glucose molecule resulting in a total of 2 ATP from
Citric Acid Cycle, and the NADH and FADH2 go to
power the Electron Transport Chain
Oxidative phosphorylation
•
Chemiosmosis couples ETC to ATP synthesis
•
ETC (fig 9.13) = collection of mostly proteins embedded in the inner
mitochondrial membranes (cristae = foldings that increase SA)
•
Each electron acceptor along the ETC is more electronegative than the
previous  O2 at the end, the final electron acceptor (most electronegative)
•
NADH transfers e- to the 1st molecule of ETC (flavoprotein) in multiprotein
complex I
•
Ubiquinone (= small hydrophobic non-protein that’s mobile within the
membrane system) transfers e- from multiprotein complex I  II
•
FADH2 transfers e- to the 2nd multiprotein complex (provides 1/3 less E than
NADH)
•
ATP is not directly made by the ETC  Chemiosmosis couples this E release
with making ATP
•
ETC – stores energy by pumping protons from the matrix across the inner
mitochondrial membrane into the intermembrane space. (fig. 9.15)
•
Chemiosmosis = E stored in H+ gradient across a membrane (proton-motive
force) is used to drive ATP synthesis
•
ATP synthase complexes in the membrane = only place H+ can freely move
along concentration gradient and back into the matrix (fig. 9.14)
Oxidative Phosphorylation
• During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2
– Donate electrons to the electron transport
chain, which powers ATP synthesis via
oxidative phosphorylation through
chemiosmosis
The Pathway of Electron Transport
• In the electron transport chain
–
Electrons from NADH and FADH2
lose energy in several steps
NADH
50
FADH2 passes electrons directly to
multiprotein complex II.
Electrons are passed to more electron
acceptors in the remaining multiprotein
complexes. Finally they are passed to
oxygen, the most electronegative
acceptor, forming water.
FADH2
Free energy (G) relative to O2 (kcl/mol)
NADH passes electrons to multiprotein
complex I. They are then passed to
Ubiquinone which transfers them to
multiprotein complex II.
40
I
Fe•S
30
20
Multiprotein
complexes
FAD
Fe•S II
O
III
Cyt b
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
Figure 9.13
FMN
2 H + + 12 O2
H2 O
ETC stores energy in an ion gradient
• At certain steps along the electron transport
chain
– Electron transfer causes protein complexes to
pump H+ from the mitochondrial matrix to the
intermembrane space
• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a proton-motive force
Chemiosmosis
• Chemiosmosis
– Is an energy-coupling mechanism that uses
energy in the form of a H+ gradient across a
membrane to drive cellular work
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase
– Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
H+
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
ATP
A rod (for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
Phosphate to ADP
to make ATP.
Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
Figure 9.15
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
(Carrying electrons
from, food)
ATP
Pi
H+
Chemiosmosis
Electron transport chain
+
ATP
synthesis
powered by the flow
Electron transport and pumping of protons (H ),
+
+
which create an H gradient across the membrane Of H back across the membrane
Oxidative phosphorylation
Energy Transfer Efficiency
• Complete oxidation of 1 mole of glucose releases
686 kcal of energy
• Phosphorylation of ADP  ATP stores 7.3
kcal/mol
• Respiration makes 38 ATP (x 7.3 kcal/mol) = 277.4
kcal (40% of 686 kcal)
• Only about 40% of E stored in glucose is used to
make ATP (the rest is lost as HEAT)
An Accounting of ATP Production by Cellular
Respiration
• During respiration, most energy flows in this
sequence
– Glucose to NADH to electron transport chain to
proton-motive force to ATP
Three main processes in this metabolic enterprise
About 40% of the energy in a glucose molecule is transferred to ATP
during cellular respiration, making approximately 38 ATP
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
Figure 9.16
6 NADH
Citric
acid
cycle
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Fermentation
Fermentation = extension of glycolysis that can generate ATP solely by substratelevel phosphorylation (as long as there’s plenty of NAD+) by transferring e- from
NADH to pyruvate (or its derivatives). Does not use oxygen.
2 common types of fermentation:
1. Alcohol fermentation (fig 9.17a)
•
•
Pyruvate  ethanol (2 steps)
–
1st step: releases CO2 from pyruvate  acetaldehyde (2-C)
–
2nd step: acetaldehyde reduced by NADH  ethanol
–
NAD+ continues glycolysis
Used to make beer/wine and in baking
2. Lactic acid fermentation (fig 9.17b)
•
Pyruvate  lactate
•
Used to make cheese & yogurt (bacteria and fungi)
•
Your muscles also make ATP this way when O2 is scarce
Facultative anaerobes = organisms that can either use pyruvate in fermentation OR
in respiration (depending of O2 availability)
To make the same amt of ATP an organism w/o O2 would have to consume sugar at a
much faster rate
Fermentation enables some cells to produce ATP w/o oxygen:
• In aerobic respiration, O2 pulls e- through the ETC
– Yields up to 19 times more ATP
• w/o O2, other e- acceptors can be used
• Glycolysis = exergonic process that uses NAD+
(not O2) as an e- acceptor
Fermentation
• Fermentation enables some cells to produce
ATP without the use of oxygen
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen
– Cells can still produce ATP through
fermentation
Glycolysis
• Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
– Under anaerobic conditions, it couples with
fermentation to produce ATP
Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate
NAD+, which can be reused by glyocolysis
Alcohol Fermentation
• In alcohol fermentation
2 ADP + 2
– Pyruvate is converted to
ethanol in two steps, one
of which releases CO2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
2 NADH
CH3
2 pyruvate
Lactic Acid Fermentation
• During lactic acid
fermentation
2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
– Pyruvate is reduced
directly by NADH to form
lactate as a waste
product
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
2 NADH
CH3
2 pyruvate
Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cellular respiration
– Produces more ATP
Pyruvate
• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes (3.5
bya) before there was oxygen in the
atmosphere
– They did not have oxygen or mitochondria
Versatility in Catabolism
• Glycolysis and the citric acid cycle connect to many other metabolic
pathways
• Our bodies generally use many sources of energy in respiration (fig
9.19)  regulated by feedback inhibition (fig 9.20)
• Carbohydrates  simple sugars, enter glycolysis
• Proteins  amino acids (used to build new proteins)
–
Excess amino acids are deaminated  intermediates of glycolysis
or citric acid cycle, or form acetyl CoA
• Fats  gylcerol + fatty acids (where most E stored)
–
Gylcerol  intermediate of glycolysis
–
Beta oxidation breaks fatty acids down to 2-C fragments 
citric acid cycle as acetyl CoA
The Versatility of Catabolism
• Glycolysis and the citric acid cycle connect to
many other metabolic pathways
• Catabolic pathways
– Funnel electrons from many kinds of organic
molecules into cellular respiration
The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
Fatty
acids
Biosynthesis (Anabolic Pathways)
• The body
– Uses small molecules to build other
substances
• These small molecules
– May come directly from food or through
glycolysis or the citric acid cycle
Regulation of Cellular Respiration via Feedback
Mechanisms
• Cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
– Is controlled by
allosteric
enzymes at key
points in
glycolysis and
the citric acid
cycle
– Releases energy,
but does not
produce it.
–
Inhibits
AMP
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Figure 9.20
Oxidative
phosphorylation