nutrition = how an organism obtains –energy and –a carbon source to build the organic molecules...

• 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

1st Law of Thermodynamics:In any process, the total energy of the universe remains constant.In any process, the total energy of the universe remains constant.

(e.g. some bacteria, animals, humanshumans)

complex carbon, glucose, amino acids

CO2, H2O

Autotrophs:Phototrophs

& chemotrophsHeterotrophs

Chemical oxidations(via iron & sulfur

bacteria)

Light (via Light (via plantsplants))

Need 9 amino acids & 15 vitamins from

outside sources

Energy of sunlight

Useful chemical bond energy

• 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?


Several ways to generate energy!

All organisms

Chemotrophs (use chemical compounds as

10 energy source)

Phototrophs

(use light as 10 energy source)

Chemolithotrophs

(use inorganic chem)Chemoorganotrophs

(use organic chem)

Includes: Animals, bacteria, fungi Includes: plants,

bacteria

pp. 375

What is the main role for enzymes?MetabolismMetabolism

1) All biochemical reactions are integrated. 3) Energetics

and the reactions in the pathways are

important.2) All living organisms

have similar metabolic pathways.

The Tokyo subway system is much like cellular metabolism.

Food molecules: complex carbohydrates, etc.

Adapted from Molecular Biology of the Cell, 4th ed.

Building blocks for biosynthesis: sugars, amino acids, etc.

Useful forms Useful forms of energyof energy

Catabolic Catabolic pathwayspathways

Anabolic Anabolic (biosynthetic) (biosynthetic)

pathwayspathways

Molecules that form the cell: lipids, proteins, etc.

How are catabolism and anabolism coupled?

Heterotrophic metabolism: Interconversion of material and energy

CatabolismCatabolism (breakdown):Yields energy,

precursors

AnabolismAnabolism (synthesis):

Requires energy, precursors

coupledcoupled

pp. 381

ATPATP couples energy between catabolism and anabolism

catabolismcatabolism

anabolismanabolism

ADPATP + Pi

Energy from food (fuel molecules) or from

photosynthesis

Energy available for work & chemical synthesis (e.g.

movement, signal amplification, etc.

ATPATP is the principal carrier of chemical energy in the cell!

Major activities promoted by ATP:

-locomotion-membrane transport-signal transduction-keeping materials

in the cell-nucleotide synthesis

ATP: the universal currency of free energy;“high energy” phosphate compound

ATP + H2O ADP Pi H+ Go’ = -7.3 kcal/mol+ +

Go’ = -7.3 kcal/molPi H+ADP H2O+ + +AMP

(G in cells = -12 kcal/mol)

ATP

ADPMolecular Biology of the Cell, 3rd ed. Fig. 2-28

pp. 380

Why ATP? It’s not the highest energy compound… It (and other nucleotide triphosphates) are stable

& the high free energy of hydrolysis

ATP is an intermediate “high energy” compound

Another source of energy is the coupling of Oxidation & Reduction reactions

anabolismanabolism

catabolismcatabolismReduced fuel

Reduced Products

Oxidized Fuel

Oxidized Precursors

NADH(reduced)NAD+(oxidized)

“LEO the lion goes GER.”

Losing Electrons (is) Oxidation … Gaining Electrons (is) Reduction.

NADNAD++ (and NADP (and NADP++) carry high-energy electrons and hydrogen atoms.) carry high-energy electrons and hydrogen atoms.

Nicotinamide adenine dinucleotide

(PO4) NADP+ NADPHpp. 383

H: (hydride ion)

NAD+(oxidized) NADH(reduced)

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 themes3. 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 1:Breakdown of large macromolecules to

simple subunits

Part 2:Breakdown of

simple subunits to acetyl CoA

accompanied by production of

limited amounts of ATP and NADH

Part 3:Complete oxidation

of acetyl CoA to H2O and CO2

accompanied by production of large amounts of NADH

and ATP in mitochondrion

fats

fatty acids and glycerol

polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2

8 e- (Reducing power as NADH)

oxidative phosphorylatio

n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH

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


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH



simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH

Cellular Metabolism


Glucose catabolismcatabolismO

O

O

O

OO

glucose (a sugar)

C6H12O6 +O

O

6 CO2Carbon dioxide

OHH

6 H2Owater

3 stages involved:1) Glycolysis

2) TCA (citric acid) cycle3) Electron transport/oxidative phosphorylation

–Food = electron donor–Oxygen = terminal electron acceptor

oxidation reduction G= -686 kcal/molExergonic rxn

+ 6O2

(requires O2)


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH

Regulation of Energy Metabolism


glycolysis

TCA cycle

electron transport &ox. phosphorylation

Glucose catabolismcatabolism

Go’ = -686 kcal/mol

O

O

O

O

OO

glucose (a sugar)

C6H12O6 (requires O2)+

O

O

6 CO2Carbon dioxide

OHH

6 H2Owater

3 stages involved:1) Glycolysis

2) TCA (citric acid) cycle3) Electron transport/oxidative phosphorylation

glucose lactate (muscle)ethanol (yeast)

no O2 requiredGlycolysis:Glycolysis:

What organisms use glycolysis?1. Anaerobes (grow without O2)2. Facultative organisms (grow with & without O2)3. Aerobes (grow only with O2)

Cellular Metabolism


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH


GlycolysisGlycolysis

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


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH


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


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH


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+ + Cl-

oxidation 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


simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH



simple subunits

Part 2:Breakdown of








fats


polysaccharides

simple sugars

proteins

amino acids

Acetyl CoA

glucose

Citric acid cycle

CoA

2 CO2



n

O2

H2O

ATPATP

glyc

olys

is

pyruvate

ATPATP

NADH

Cellular Metabolism


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)

• 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



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.


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

• 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.


• 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

• 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


• First prokaryotes were probably heterotrophs– Ate the primordial soup of early earth

• But photosynthesis (harnessing the sun) shows up early in the fossil record)

2. Photosynthesis evolved early in prokaryotic life


• Similarity in complex machinery suggests photosynthesis evolved once.– = most parsimonious hypothesis,

– Thus:heterotrophic groups represent a loss of photosynthetic ability during evolution.


nutrition = how an organism obtains –energy and –a carbon source to build the organic molecules...

Documents

total energy

kinds of energy

potential energy

kinetic energy

conversion of energy

atp atp couples energy

energy source phototrophs

major carrier of energy