Transcript Document

• Nutrition = how an organism obtains
– energy and
– a carbon source to build the organic molecules of cells.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Metabolism & energetics
• Metabolism – sum total of all chemical reactions
occurring in living organisms.
– Anabolic pathways – synthesize compounds, generally
endergonic.
– Catabolic pathways – break down compounds, usually
exergonic.
• Many reactions also involve conversion of energy
from one form to another.
• Energy can exist as potential energy or kinetic
energy.
There are many kinds of energy that can
interconvert from one form to another.
1. How does a cell maintain & regulate its
metabolism?
2. How does a cell garner & utilize energy?
3. From where does this energy come?
Organisms within the biosphere exchange
molecules and energy
Energy of
sunlight
Light (via plants)
Useful chemical
bond energy
complex carbon,
Autotrophs:
glucose, amino acids
Phototrophs
& chemotrophs
CO2, H2O
Chemical oxidations
(via iron & sulfur
bacteria)
Heterotrophs
(e.g. some bacteria,
animals, humans)
Need 9 amino acids
& 15 vitamins from
outside sources
1st Law of Thermodynamics:
In any process, the total energy of the universe remains constant.
• Ways to obtain energy:
– phototrophs use light energy
– chemotrophs get energy from chemicals.
• Ways to obtain Carbon
– autotrophs only need only CO2 (inorganic C)
– Heterotrophs need organic carbon sources
• How do we get energy and carbon?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Several ways to generate energy!
Includes: Animals,
bacteria, fungi
All organisms
Chemotrophs
(use chemical compounds as
10 energy source)
Chemolithotrophs
(use inorganic chem)
Includes: plants,
bacteria
Phototrophs
(use light as 10 energy
source)
Chemoorganotrophs
(use organic chem)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is the main role for enzymes?
Metabolism
1) All
biochemical
reactions are
integrated.
2) All living
organisms
have similar
metabolic
pathways.
3) Energetics
and the
reactions in the
pathways are
important.
pp. 375
The Tokyo subway system is much like
cellular metabolism.
Food molecules:
complex carbohydrates, etc.
Molecules that form the cell:
lipids, proteins, etc.
Useful forms
of energy
Catabolic
pathways
Anabolic
(biosynthetic)
pathways
Building blocks for biosynthesis:
sugars, amino acids, etc.
Adapted from Molecular Biology of the Cell, 4th ed.
Heterotrophic metabolism:
Interconversion of material and energy
Catabolism
(breakdown):
Yields energy,
precursors
coupled
Anabolism
(synthesis):
Requires energy,
precursors
How are catabolism and anabolism coupled?
ATP couples energy between catabolism
and anabolism
Energy available for work
& chemical synthesis (e.g.
movement, signal
amplification, etc.
ADP + Pi
ATP
Major activities
promoted by ATP:
-locomotion
-membrane transport
-signal transduction
-keeping materials
in the cell
-nucleotide synthesis
anabolism
Energy from food (fuel
molecules) or from
photosynthesis
catabolism
ATP is the principal carrier of chemical energy in the cell!
pp. 381
ATP: the universal currency of free energy;
“high energy” phosphate compound
ATP + H2O
ADP + Pi + H+
ADP + H2O
AMP + Pi + H+
Go’ = -7.3 kcal/mol
(G in cells = -12 kcal/mol)
Go’ = -7.3 kcal/mol
ATP
ADP
Molecular Biology of the Cell, 3rd ed. Fig. 2-28
ATP is an intermediate “high energy”
compound
Why ATP? It’s not the highest energy compound…
 It (and other nucleotide triphosphates) are stable
& the high free energy of hydrolysis
pp. 380
Another source of energy is the coupling of
Oxidation & Reduction reactions
NAD+ (and NADP+) carry high-energy electrons and hydrogen atoms.
Reduced fuel
catabolism
NAD+(oxidized)
Reduced Products
Oxidized Fuel
NADH(reduced)
anabolism
Oxidized Precursors
“LEO the lion goes GER.”
Losing Electrons (is) Oxidation … Gaining Electrons (is) Reduction.
NAD+(oxidized)
NADH(reduced)
Nicotinamide adenine dinucleotide
H: (hydride ion)
(PO4) NADP+
NADPH
pp. 383
Summary
1. Metabolism consists of many coupled & connecting
reactions
•
•
• Major source of energy = oxidation of carbon fuels
• ATP = major carrier of energy
2. Few kinds of reactions; many recurring themes
3. Two major activated carrier molecules couple
catabolism/anabolism reactions:
•
•
ATP/ADP couples energy (through hydrolysis)
NAD+/NADH couples oxidation/reduction (by carrying
electrons & hydrogen atom)
pg. 373
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Respiration
• The 3 types of bacterial respiration
– Aerobic - require oxygen for their growth and existence
– Anaerobic – do not require oxygen for any respiration
– Anaerobes - prefer growing in the presence of oxygen, but
can continue to grow without it
Catabolism - Respiration, fermentation
Respiration:
• Glycolysis
• Krebs/Tricarboxylic acid (TCA)
Cycle
• Electron transport chain &
oxidative phosphorylation
Fermentation:
– Glycolysis followed by
NAD+ regeneration reactions.
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Glucose catabolism
O
O
O
O
O
O
O
C6H12O6
glucose
(a sugar)
oxidation
(requires O2)
+ 6O2
O
H
O
H
6 CO2 + 6 H2O
Carbon
dioxide
reduction
water
G= -686 kcal/mol
Exergonic rxn
3 stages involved:
1) Glycolysis
2) TCA (citric acid) cycle
3) Electron transport/oxidative phosphorylation
–Food = electron donor
–Oxygen = terminal electron acceptor
Regulation of Energy Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
glycolysis
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Adapted from MBOC4,
fig. 2-70 & pp. 383
Citric
acid
cycle
2 CO2
TCA cycle
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
electron transport &
ox. phosphorylation
O
O
Glucose catabolism
O
O
O
O
O
O
C6H12O6
glucose
(a sugar)
(requires O2)
H
O
H
6 CO2 + 6 H2O
Carbon
dioxide
water
Go’ = -686 kcal/mol
3 stages involved:
1) Glycolysis
2) TCA (citric acid) cycle
3) Electron transport/oxidative phosphorylation
no O2 required
lactate (muscle)
glucose
ethanol (yeast)
What organisms use glycolysis?
1. Anaerobes (grow without O2)
2. Facultative organisms (grow with & without O2)
3. Aerobes (grow only with O2)
Glycolysis:
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Adapted from MBOC4,
fig. 2-70 & pp. 383
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Glycolysis
Glycolysis
• Splitting of glucose: yield of 2 pyruvate molecules
from one glucose molecule. (Also H2O.)
• ATP invested in early steps, energy generated in later
steps. Net energy yield: 2 ATP, 2 NADH + 2 H+.
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Krebs Cycle
• Transition step required after pyruvate enters
mitochondrion; pyruvate converted to Acetyl CoA.
(NAD+ reduced to NADH during this process.)
• Krebs cycle doesn’t directly need oxygen, but
won’t occur without it.
• Krebs cycle involves decarboxylation, oxidation to
generate NADH, FADH2, ATP. CO2 is byproduct
of these steps.
• NADH, FADH2 will relay electrons to electron
transport chain.
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Electron transport system
• Electron transport chain and oxidative
phosphorylation produce ATP from products of
glycolysis, Krebs.
• Electron transport chain = protein complexes with
prosthetic groups in/on inner mitochondrial
membrane. (Some groups are able to move! E.g.
Cyt C)
• ETC facilitates series of redox reactions, with
oxygen as final electron acceptor.
• ATP formation uses proton motive force - voltage
across membrane (ion gradient) that results from
high [H+] in intermembrane space.
Redox reactions
• Many energy transfers involve transfer of
electrons (or hydrogen atoms).
• Oxidation and reduction occur together.
–
–
–
–
Loss of electrons from one substance = oxidation.
Addition of electrons to a substance = reduction.
Oxidizing agent - accepts electrons.
Reducing agent - gives up electrons.
E.g. Na + Cl -> Na+ + Cloxidation
reduction
Electron transport chain - series of redox
reactions
• Cells release energy in stages.
Electron transport system
Development of Proton Motive Force
from Chemiosmosis
Formation of ATP from Proton Motive
Force and ATP Synthase
ATP Production during Aerobic Respiration by
Oxidative Phosphorylation involving Electron
Transport System and Chemiosmosis
Bacterial electron transport
ASM digital image collection:
http://www.asmusa.org
Bacterial chemiosmotic ATP generation
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Cellular Metabolism
Part 2:
Breakdown of
simple subunits to
acetyl CoA
accompanied by
production of
limited amounts of
ATP and NADH
fats
polysaccharides
proteins
fatty acids
and glycerol
simple sugars
amino acids
glucose
glycolysis
Part 1:
Breakdown of large
macromolecules to
simple subunits
ATP
NADH
pyruvate
Acetyl CoA
CoA
Part 3:
Complete oxidation
of acetyl CoA to H2O
and CO2
accompanied by
production of large
amounts of NADH
and ATP in
mitochondrion
Citric
acid
cycle
2 CO2
8 e- (Reducing power as NADH)
oxidative
phosphorylation
ATP
O2
H2O
Adapted from MBOC4,
fig. 2-70 & pp. 383
Fermented … food?
• Yogourt
– Fermented milk, fermentation carried out by lactic acid
bacteria.
• Bread
– Simple fermentation of sugar to alchohol and CO2 by bread
yeast Saccharomyces cerevisiae. CO2 makes bread rise.
• Kimchee
– Cabbage and other veggies fermented by lactic acid bacteria.
• Even some meat & fish products!
– E.g. Country-cured ham, Katsuobushi (tuna)
Unusual catabolism
• Badger Ammunitions Plant - 1942-1976 provided weapons for the military and
handled large quantities of explosive
nitroglycerin (NG).
CONTAMINATION!!!!!
How can we clean the NG up?
• Organisms capable of degrading NG?
– Microorganisms: e.g. Pseudomonas fluorescens,
Pseudomonas putida
Pseudomonads only convert NG to mononitroglycerin
(MNG). Other microbes in soil degrade MNG to
glycerol. Glycerol can be converted to
glyceraldehyde-3-phosphate and further
metabolized.
Amazing enzyme
• P. fluorescens & P. putida
use single enzyme:
xenobiotic reductase.
• Nonspecific enzyme,
recognizes many
molecules carrying nitro
group (like
trinitrotoluene: TNT).
Many bacteria important in bioremediation!
Two nutritional modes are unique to
prokaryotes
• Chemoautotrophs
– use CO2 as a carbon source, but they obtain energy by
oxidizing inorganic substances,
– Inorganic energy sources = hydrogen sulfide (H2S),
ammonia (NH3), and ferrous ions (Fe2+).
– E.g. Nitrobacter - key in N-cycle converts ammonia (NH4)
to nitrate (NO3)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Photoheterotrophs
– use light to generate ATP but obtain their carbon in organic
form.
– This mode is restricted to prokaryotes.
– E.g. purple bacteria - make salt flats purple & red
– E.g. green bacteria
– Where does “red herring” come from?
• dead herring have salt coating: halophiles grow on salt (red color;
smelly); dragged around by animal rights activists to stop fox hunts
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Carbon cycle
• The majority of known prokaryotes are
chemoheterotrophs.
– parasites, which absorb nutrients from the body fluids
of living hosts.
– saprobes, decomposers that absorb nutrients from dead
organisms,
• Almost any organic molecule is food for one of the many
chemoheterotrophic bacteria (like oil)
• If it can’t be broken down by bacteria its called
nonbiodegradable.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Nitrogen Cycle
– Eukaryotes can only use organic nitrogen, NO3 or
NH4.
– Diverse prokaryotes can metabolize most nitrogenous
compounds.
• Prokaryotes are essential to converting N into usable forms for
eukaryotes
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Prokaryotes are responsible for the key steps in the
cycling of nitrogen through ecosystems.
– Some chemoautotrophic bacteria convert ammonium
(NH4+) to nitrite (NO2-).
– Others “denitrify” nitrite or nitrate (NO3-) to N2, returning
N2 gas to the atmosphere.
– A diverse group of prokaryotes, including cyanobacteria,
can use atmospheric N2 directly.
– During nitrogen fixation, they convert N2 to NH4+, making
atmospheric nitrogen available to other organisms for
incorporation into organic molecules.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Cyanobacteria fix N and C (photosynthesis)
– = most self-sufficient of all organisms.
– Only need: light, CO2, N2, water and some minerals to
grow.
Fig. 27.11
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Cyanobacteria thought to put 02 in atmosphere.
– = Massive change in the world
• Great for aerobes (who require O2)
• Deadly for anerobes (who are poisoned by o2)
– Forced to live in remaining anerobic environments
– Prokaryotes can be facultative or obligate aerobes or
anerobes
• Eukaryotes are all aerobic
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
2. Photosynthesis evolved early in
prokaryotic life
• First prokaryotes were probably heterotrophs
– Ate the primordial soup of early earth
• But photosynthesis (harnessing the sun) shows up
early in the fossil record)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Similarity in complex machinery suggests
photosynthesis evolved once.
– = most parsimonious hypothesis,
– Thus:heterotrophic groups represent a loss of
photosynthetic ability during evolution.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings