Download LECTURE 18 - Budostuff

Summer
School
2015
L6 – Cellular respiration
Dr Agnieszka Adamczewska
Images from Wikimedia Commons
Major Concepts
1. Identify the three end-product options for glycolysis,
and under what conditions these end-products form
2. State in words (not chemical formulae) the overall
reaction of the glycolytic pathway, understand parts
that are common and different
3. Understand how the overall balance sheet for
glycolysis is obtained, and show the methods of
reaction “coupling” that the cell uses
4. Say where the enzymes of the glycolytic pathway are to
be found in eukaryotic cells and in prokaryotic cells
5. Explain what oxidation reduction reactions are and the
special role of the coenzyme NAD+/NADH
Major Concepts
6.
7.
8.
9.
Give the names of, and recognise the equations for,
the overall reactions of, the two major parts of the
cellular respiration sequence - glycolysis and
tricarboxylic acid (TCA) cycle.
Describe how a H+ pumping mechanism is coupled to
a proton-driven ATP synthase.
State how many ATP molecules are produced per
glucose molecule in the glycolytic pathway and in the
whole respiratory pathway.
Describe where in the respiratory pathway CO2 is
released, and where O2 is consumed.
Macromolecules store energy
Energy is stored in
carbon-carbon bonds
e.g. glycogen or starch,
fats and oils
Get energy out of food
through catabolic
reactions
Image from Campbell Biology 8e Australian Version © Pearson Education Inc.
Metabolism (L3)
Metabolism: chemical reactions that occur within cells
• Catabolism – breaking down organic matter to release
energy
• Anabolism – using energy to produce cellular components
Complex molecules
Simple molecules
Catabolism
Pi
ADP
Anabolism
ATP
ATP: energy carrier
Made through metabolism of energy rich molecules.
- carbohydrates are converted into glucose
- lipids are processed by β-oxidation
Complex molecules
Simple molecules
Catabolism
Pi
ADP
ATP
ATP: Adenosine triphosphate
Hydrolysis
ADP Adenosine diphosphate
Energy conversions in cells
Energy from macromolecules is released by cellular respiration.
Initial breakdown of macromolecules produces simple sugars,
fatty acids, glycerol, and amino acids. Subsequent gradual
oxidation of the fuel molecules by removal of electrons from C-C
and C-H bonds releases energy:
Energy conversions located in the cytosol
1. Glycolysis converts glucose to pyruvate
2. Fermentation to lactate and alcohol
Energy conversions located in mitochondria in the presence of O2
3. -oxidation of lipids produces acetyl CoA
4. Citric acid cycle converts pyruvate to acetyl CoA and finally CO2
5. Electron transport chain (NADH, FADH2 > O2 > H2O) drives proton
pumps, proton gradient is coupled to synthesis of ATP
Energy conversion
pathways
Cellular respiration
CYTOSOL
1
2
MITOCHONDRION
3
5
4
Glycolysis
Pathway described in 1930's
- a major biochemical triumph
- involves a number of steps
one glucose (C6)
two pyruvate (2 x C3)
Glycolysis
Cytosol
Glucose (6C)
2 ATP
3 steps
2 ADP
Fructose 1,6-bisphosphate (unstable)
G3P (3C)
G3P (3C)
NAD+
NADH
2 ADP
2 ATP
5 steps
Pyruvate (3C)
Mitochondria image from Wikimedia Commons
glyceraldehyde 3 phosphate
NAD+
NADH
2 ADP
2 ATP
Pyruvate (3C)
Glycolysis Energy Conversions
Net yield
2 NADH
2 ATP
Glycolysis
“Splitting glucose”
Glucose
• from hydrolysis of polysaccharides (L2)
• enters cell via facilitated diffusion - Glucose-Na+
symport (L5)
Cytosol – 10 enzymes
Glucose (6C) + 2 ATP + 2 NAD+ + 2 ADP + 2 Pi 
2 Pyruvate (3C) + 4 ATP + 2 NADH
Net yield: 2 ATP
NAD+ Nicotinamide Adenine Dinucleotide
NAD+ reduced to NADH
by transfer of H+ from food
Image from Wikimedia Commons
Electron carrier (coenzyme )
1. Glycolysis:
Processing of glucose to pyruvate
a) Glucose (6C) is phosphorylated using 2 ATP and split into two
molecules of glyceraldehyde 3-phosphate (3C). Total 5 steps,
consuming 2 ATP
b) Oxidation in another 5 steps to 2 molecules of pyruvate (3C)
and production of 4 ATP (net yield =2 ATP/glucose)
• Pyruvate can be converted in the absence of O2 by alcoholic
fermentation to ethanol (in yeast and bacteria) or by lactate
fermentation to lactate (muscle tissue)
• In the presence of O2 pyruvate enters mitochondria, is
converted (decarboxylated) to a 2C compound acetyl CoA (a
substrate for citric acid cycle) CO2, and NADH;
2. Fermentation
Anaerobic conversion of pyruvate
to alcohol or lactic acid
Alcohol fermentation
By yeast
and many
bacteria.
Used by humans
for thousands of
years in brewing,
winemaking, and
baking (CO2
bubbles from
baker’s yeast)
REDUCTION
Lactic acid fermentation
By certain
fungi and
bacteria
Used in dairy
industry to make
cheese and yogurt
A product of muscle
exercise, may
enhance muscle
performance (pain
from K+ ions)
REDUCTION
Fermentation
No oxygen
2ADP + 2Pi
1×
Glucose
Glycolysis then
fermentation
Glycolysis
2NAD+
Fungi, bacteria, animals
2ATP
2× Pyruvate
2NADH + 2H+
2×
Lactic acid
 lactic acid
2ADP + 2Pi
Yeast, plants
1×
Glucose
 ethanol + CO2
Glycolysis
2NAD+
2×
Ethanol
2ATP
2× Pyruvate
2NADH + 2H+
2×
CO2
Pyruvate
A key juncture in catabolism
Food
Chloroplast
Mitochondria (L4)
• Site of cellular respiration (energy production)
• Double membrane: permeable outer membrane
and impermeable, folded inner membrane (cristae)
containing enzymes of respiration
Inner membrane
Outer membrane
Matrix
Crista
Images from Wikimedia Commons
Mitochondria: number, shape, and
subcellular location are highly variable
Fuel in, energy out
Glucose + oxygen  carbon dioxide + water + energy
Cytosol
NADH
FADH2
Oxidative
phosphorylation
Krebs cycle
NADH
Glycolysis
Crista
Matrix
ATP
Mitochondria image from Wikimedia Commons
Intermembrane
space
Mitochondria
ATP
ATP
Intermediate reaction
Pyruvate to Acetyl CoA
Outer mitochondrial membrane
Inner mitochondrial membrane
CoA
Matrix
CO2
Acetyl-CoA
CoA
Pyruvate
NADH + H+ NAD+
Mitochondria image from Wikimedia Commons
Pyruvate
dehydrogenase
complex
Other fuel molecules
• Other carbohydrates
(apart from glucose)
• Fats and proteins can
also be broken down
and enter pathways
Image from Campbell Biology 8e Australian Version © Pearson Education Inc.
-oxidation
3.
-Oxidation
of lipids
-oxidation degrades
long-chain fatty acids
by 2C atoms at a time
Last reaction splits
off acetyl CoA
(energy in C-C bond)
and enters Citric acid
cycle
NADH, FADH2,
energy (electron)
carriers
h
4. Krebs cycle
8 steps, each
catalysed by
different
enzyme
TCA cycle
Citric acid cycle
AcetylCoA (2C)
Oxaloacetate (4C)
4C
Citrate (6C)
NADH
6C
Krebs cycle
4C
FADH2
NADH
CO2
NAD+ and FAD
reduced to
NADH and
FADH2
accept e- from
intermediates
NADH
5C
4C
4C
ATP
CO2
CO2 evolved
ATP is formed
Chemical bonds to electrons
C6H12O6 + 0O2  6CO2 + 0H2O + energy
6×
NADH
glucose
CO2
2×
NADH
2×
FADH2
Krebs cycle
Glycolysis
ATP
Mitochondria image from Wikimedia Commons
ATP
CO2
Chemical bonds to electrons
1 glucose:
Glycolysis  2 pyruvate + 2 ATP + 2 NADH
2 pyruvate  2 acetyl CoA + 2 NADH + 2 CO2
TCA cycle: 2 acetyl CoA  6 NADH + 2 FADH2 +
4 CO2 + 2 ATP
1 glucose  4 ATP + 8 NADH + 2 FADH2 + 6 CO2
5. Electron transport chain (ETC)
(Proton-motive force i.e. the power in movement of protons)
NADH and FADH2
Inner membrane of mitochondria
Inner membrane
Four protein complexes of acceptors
Oxygen needed
Matrix
Crista
Mitochondria image from Wikimedia Commons
5. Electron transport chain
Start with NADH
(or FADH2) as
primary electron
donor
Intermembrane space
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Inner
mitochondrial
membrane
C
Finish with O2
as terminal
electron
acceptor
Q
e–
e–
H+
NADH
FADH2
NAD+
NADH
dehydrogenase
Mitochondrial matrix
H+
2H+ + 1/2O2
FAD
bc1
complex
H+
H2O
Cytochrome
oxidase complex
Chain of redox reactions
Inner mitochondrial membrane
Electrons move to higher redox potentials, towards oxygen
with highest electron affinity
Energy released is used to pump H+ from matrix to intermembrane space
NADH + H+
Energy
released
2H+ + NAD+
2e
High energy
Electrons
“falling” from
NADH to
oxygen
Cyt b (Fe3+)
Cyt b (Fe2+)
Cyt c (Fe2+)
Cyt c (Fe3+)
Cyt a (Fe3+)
Cyt a (Fe2+)
H 2O
Low energy
½ O2 + 2H+
Generating proton gradient
Start with NADH
(or FADH2) as
primary electron
donor
Intermembrane space
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Inner
mitochondrial
membrane
C
Finish with O2
as terminal
electron
acceptor
Q
e–
e–
H+
NADH
FADH2
NAD+
NADH
dehydrogenase
Mitochondrial matrix
H+
2H+ + 1/2O2
FAD
bc1
complex
H+
H2O
Cytochrome
oxidase complex
Chemiosmosis couples the ETC
to ATP synthesis!
OMM
IMS
ATP synthase
IMM
FADH2 FAD
NADH + H+
NAD+
H 2O
½ O2 + 2H+
H+ + OH-
Electron transport chain
H 2O
ADP + Pi
ATP
ATP synthase
complexity of 1o, 2o,
3o and 4o structure
Intermembrane
space
Inner membrane
embedded in inner
membrane of
mitochondria
highly conserved in
nature
Matrix
Image from http://www.rcsb.org/pdb/101/motm.do?momID=72
H+
ATP synthase
H+ binding Rotor
H+
ions flow down gradient
and enter half channel in
stator
H+
H+
Intermembrane
space
Inner
membrane
H+ ions enter binding sites
in rotor, changing shape of
subunits so rotor spins
Each H+ ion makes one
complete turn before being
released to matrix
Catalytic
knob
Matrix
Spinning of rotor causes
internal rod to spin
Turning rod activates
catalytic sites in knob
H+
ADP + Pi
ATP
Image from http://www.rcsb.org/pdb/101/motm.do?momID=72
Fuel in, energy out
Glucose + oxygen  carbon dioxide + water + energy
Cytosol
NADH
FADH22
Oxidative
phosphorylation
Krebs cycle
NADH
Glycolysis
Crista
Matrix
2x
ATP
Mitochondria image from Wikimedia Commons
Intermembrane
space
2x
Mitochondria
ATP
~34x
ATP
Aerobic respiration = lots of energy
C6H12O6 + 6 O2  6 CO2 + 6 H2O + ~38 ATP
Where are these ATPs from?
Glycolysis = 2 ATP
TCA = 2 ATP
Oxidative phosphorylation (ETC + chemiosmosis)
= ~34 ATP
Cristae increases surface area
• Infoldings of the inner mitochondrial membrane
(cristae) greatly increase the number of electron
transport chain proteins and ATP synthase proteins
Lack of oxygen?
Need oxygen to accept final electrons
If no oxygen, complex IV keeps electrons
 All protein complexes keep electrons
 No pumping of H+ into intermembrane space
 No H+ gradient
 No energy for ATP synthase
No ATP made in ETC - ATP from glycolysis and
TCA not enough
Most cells cannot survive long without oxygen
Prokaryotic cell – no mitochondria
Still need ATP!
Plasma
membrane
Capsule
Cell wall
Nucleoid region
Flagellum
Pilus
Image from Wikimedia Commons
Ribosome
Aerobic Bacteria do it too!
Enzymes embedded in
bacterial cell membrane
H+
ATP synthase
complex
ATP
ADP + Pi
Cell
membrane
O2
+
H2O NAD
NADH
Electron carrier
H+
Anaerobic respiration
Prokaryotes living in anaerobic environment
- no oxygen e.g. waterlogged soils, intestines
Nitrate (NO3-) or sulfate (SO42-) are the terminal
electron acceptors
Products include CO2, inorganic substance, ATP
e.g. C6H12O6 + 12 KNO3 (potassium nitrate) 
6 CO2 + 6 H2O + 12 KNO3 (potassium nitrite) + ATP
Summary
Cytoplasm and mitochondria are sites of cellular respiration
Glucose + oxygen  carbon dioxide + water + energy
Aerobic respiration has four stages
For one glucose molecule:
Glycolysis = 2 ATP, TCA = 2 ATP, Oxidative
phosphorylation (ETC, chemiosmosis) = ~34 ATP
Chemiosmosis - electrons in ETC used to pump protons
into inter-membrane space, this establishes a proton
gradient across inner membrane, protons accumulate,
lowers pH
Redox reactions integral to ETC
Fermentation and anaerobic respiration in absence of O2
Aerobic respiration
Stage
Where
Main starting Main end
materials
products
Glycolysis
Cytoplasm
Glucose
Pyruvate, ATP,
NADH
forming Acetyl
CoA
Matrix of
mitochondria
Pyruvate
Acetyl CoA,
CO2, NADH
Citric acid cycle
Matrix of
mitochondria
Acetyl CoA,
H2O
CO2, NADH,
FADH2, ATP
O2, NADH,
FADH2
ATP, H2O
Inner
Oxidative
membrane
phosphorylation
mitochondria
• Read:
• Knox B, et al. (2010) Biology: an Australian
perspective.
- Chapter 6 Harvesting energy