Chapter 6 Metabolism: Fueling Cell Growth

Fundamental Tasks for Growth

Method of ______to invest in

Biosynthetic processes

Transporting nutrients / other molecules

Continual ______of new cell components

Cell walls, membranes, ribosomes, nucleic acids, other

Replacing worn or damaged components

Accumulating enough components so that cell can divide (growth = increase in cell number)

Principles of Metabolism

is coupled to

Energy from breakdown of molecules is invested into buildup of new molecules

reactions are coupled to reactions

Energy

______energy – stored energy

Stored due to position (rock on a hill, water behind a dam)

Stored due to chemical bonds

______energy – energy of motion

Potential energy ______to kinetic

But some is lost as ______

(random energy = entropy)

Kinetic energy ______to potential

Again, some is lost as ______

Lost energy must be replaced

Methods of Acquiring Energy

Phototrophs

Harvest energy in ______

Power synthesis of organic molecules

e.g. glucose

Chemoorganotrophs

Harvest energy from ______molecules

Depend on ______to synthesize high energy organic molecules

Free Energy

______energy released when bonds are broken

Does not include heat

______reactions

If more free energy in reactants

______reactions

If more free energy in products

Multiple ______allows slow release of free energy

Less is lost as heat

“Metabolic pathways”

Metabolic ______

Ordered sequence of steps resulting in an end-product

Starts with reactants

Continues with series of ______

May be in dissociated form (e.g. pyruvate)

May be in undissociated form (e.g. pyruvic acid)

Ends with ______

Pathway may be ______, ______, or ______

Key Components of Metabolic Pathways

Enzymes

ATP

Energy sources

Redox reactions

Electron carriers

Precursor metabolites

Enzymes

Enzymes ______on substrates

Turn substrates into products

Facilitate reactions – “______”

Do not participate directly in reaction

Without enzymes, some catabolic reactions would go very slowly

Enzymes speed up reaction

Enzymes lower the ______of ______

Even exergonic reactions

ATP Couples Energy Production with Energy Investment

______donates energy to reactions

Cycles to ______

ADP accepts energy

Cycles to ATP

ADP + Pi

Cell constantly recycles ATP

Phosphorylation

Ways to add Pi to ADP

______-level phosphorylation

______/ proton motive force

______phosphorylationUsing redox reactions

______phosphorylation

Photoautotrophs only

Sources of energy for phosphorylation

All require ______reactions

Transfer 1 or more electrons from one substance to another

Prokaryotes very versatile

e.g. Glucose

e.g. Ammonia

Redox Reactions

When substance is ______

Loses an electron

When substance is ______

Gains an electron

Where electrons go, protons ______

Lose e- & H+ = lose H atom = oxidation = dehydrogenation

Gain e- & H+ = gain H atom = reduction = hydrogenation

If e- removed to e- carrier

H+ may go, too

H+ may go into aqueous solution

Often ignore the H+ when writing biological reactions, but it’s there!

e- Carriers that Diffuse Easily

NAD+ reduces to ______

FAD+ reduces to ______

NADP+ reduces to NADPH

(reduced = becomes less positive)

Reduced form has ______

NADH & FADH2 reduce other carriers

Drives proton motive force

Proton motive force drives ATP production

NADPH reduces molecules in ______

Precursor Metabolites

______in catabolic reactions

Link catabolic reactions to ______reactions

Some are broken down further

Some are siphoned off for anabolic rxns.

e.g. pyruvate

Oxidized further

Convert to alanine

Use of Precursor Metabolites by E. coli

Central Metabolic Pathways

3 key pathways to gradually oxidize glucose

______

“Embden-Meyerhoff pathway”

“Glycolytic pathway”

______pathway

______cycle

“Tricarboxylic acid cycle”

“Krebs cycle”

“Citric Acid cycle”

Central Metabolic Pathways

Glycolysis

Most ______to initiate sugar breakdown

End products are ATP & NADH & pyruvate

______into Krebs TCA cycle

Pentose Phosphate pathway

Alternative pathway to make pyruvate

Operates in conjunction with glycolysis

______feeds into TCA cycle

Usually feeds into biosynthesis pathways

[Entner-Douderoff pathway]

Add’l alternative to glycolysis

Some bacteria

Less ATP

Fate of Pyruvate

______to TCA cycle from glycolysis, Entner-Douderoff, or Pentose Phosphate

Pyruvate  Acetate + CO2

3C  2C + C

______CoA enters ______cycle

2 pyruvates for each glucose that started

Respiration

Uses reducing power of ______and ______produced in glycolysis and transition step

Powers ______phosphorylation

Electrons from NADH and FADH2 enter e- transport

______pumped to other side of membrane

Produces proton ______

Drives proton motive force

Terminal e- acceptor ______O2 or other

Catabolic Processes of Chemoorganoheterotrophs

______respiration – ______ATP

______– ______ATP

Energy Yields

Energy yields theoretical, as ______may be siphoned off to biosynthesis

Calculated approximately with a theoretical ______

______-level phosphorylation slow

Little ATP produced

______phosphorylation fast

Much ATP produced

Energy Yields in Glycolysis

Glucose (6C) + 2 NAD+ + 2 ADP + 2 Pi

 2 pyruvate (3C) + 2 NADH + 2 H+ 2 ATP (net gain)

Also produces precursor molecules (used by E. coli)

Yields from Glycolysis

Energy expended --- ______ATP per glucose

Energy harvested --- ______ATP

Net gain ------______ATP

Reducing power ----- ______NADH

______metabolites (reduce energy yield) --- ______(based on E. coli) plus pyruvate

ATP produced by ------______level ______

Yields from Pentose Phosphate Pathway

Energy yield ---- ______amts ATP

Reducing power ---- ______amts NADH

Precursor metabolites --- ______plus pyruvate

Most of the products of the Pentose Phosphate Pathway are used as precursors in biosynthesis

ATP produced by ------______level ______

Yields of the Transition Step and TCA Cycle

Transition step (yield per glucose)

Reducing power --- ______NADH

Precursor metabolites --- ______Acetyl CoA

TCA Cycle (yield per glucose)

Energy yield --- ______ATP

GTP in step 5 converts to ATP

Reducing power --- ______NADH + ______FADH2

Precursor metabolites --- ______(based on E. coli)

ATP produced by ______level ______

Electron Carriers in the Plasma Membrane

Electron carriers embedded in the ______

Where in eukaryotes?

Electron transport goes from ______energy to ______energy carriers

Some carry H+, too

Some push H+ to other side of membrane

FADH2 ______chain ______than NADH

Less ______results from FADH2

Terminal e- acceptor ______½ O2

If anaerobic, then ______½ O2

Oxidative Phosphorylation

Chemiosmotic ______(proton motive force) drives ATP synthesis

H+ flow back across membrane through ion ______in ______

Called “______” even if O2 not terminal e- acceptor

Still oxidizing!

Very ______amounts of ATP made

Variation in ______allows differential testing

Oxidase test detects cytochrome c

Theoretical Energy Yields from Oxidative Phosphorylation

All theoretical

Not precise conversion

Siphoning off of precursor metabolites reduces yield from theoretical max

Based on reducing power from other steps

Assume ______ATP / NADH

Assume ______ATP / FADH2

Reducing power from:

Glycolysis

______NADH  ______ATP

Transition step

______NADH  ______ATP

TCA cycle

______NADH  ______ATP

______FADH2 ______ATP

______ATP total

Maximum for oxidative phosphorylation

Maximum Theoretical Energy Yields for Aerobic Respiration = ______ATP

Substrate level phosphorylation – ______ATP

Glycolysis  ______ATP

TCA cycle  ______ATP

Oxidative phosphorylation – ______ATP

Reducing power from glycolysis  ______ATP

Reducing power from transition step  ______ATP

Reducing power in TCA cycle  ______ATP

Anaerobic Pathways

Two types

______

Both use glycolysis & pentose phosphate pathway

Differ in ______e- ______

Differ in what happens to ______

Anaerobic respiration

Terminal e- acceptor not O2 and not organic

______reducers (NO3-) or ______reducers (SO42-)

Pyruvate oxidized to ______

Fermentation

______ terminal e- acceptor

Anaerobic Respiration

______(NO3-) reduced to nitrite (NO2-)

Or to nitrous oxide (N2O)

Or to nitrogen gas (N2)

______(SO42-) reduced to hydrogen sulfide (H2S)

______efficient than aerobic respiration

Fermentation

Fermentation pathways used by

______(e.g. E. coli)

______species

Lactic acid bacteria ferment only – never respire

Obligate fermenters that are not harmed by O2

______that ferment

Harmed by O2

ATP comes only from ______

Other steps recycle NADH from NAD+

______or derivative used as e- ______

End Products of Fermentation

______Acid

Pyruvate is terminal e- acceptor

e.g. Lactic acid bacteria

Streptococcus Lactobacillus spp.

Yogurt, pickles, cheeses, cured sausages

Acid  tooth decay

Food spoilage

______

CO2 removed  EtOH + CO2

e.g. Saccharomyces spp. (yeast)

Wine, beer, bread

______Acid

e.g. Clostridium spp.

______Acid

CO2 removed  modification  propionate

–Propionibacterium spp

Swiss cheese

2, 3 – ______

Differentiates members of Enterobacteriaceae

e.g. Klebsiella spp., Enterobacter spp.

Voges-Proskauer test detects acetoin

Mixed ______

Various pathways branched

Methyl red test differentiates E. coli from other Enterobacteriaceae

Catabolism of Other Compounds

Compounds other than glucose

Broken down by hydrolytic enzymes

May then enter cycles at various points

______

Lipases break down to precursor metabolites

Enter various pathways

______

Proteases break peptide bonds

Deaminases remove amino group

Precursor metabolites enter various pathways

______

Amylase breaks down amylose

Cellulase breaks down cellulose

e.g. fungi

e.g. bacteria in rumen of many herbivores & termites

β-galactosidase breaks down lactose  glucose & fructose

Glucose enters glycolysis directly

Other monosaccharides modified first

Categories of Organisms by Energy and Carbon Sources

Chemolithotrophs

Use ______source of energy

______– hydrogen sulfide

______– ammonia

Products of anaerobic respiration ______

Fix ______into organic molecules from CO2

= Chemolithoautotrophs

Photoautotrophs

Use photosynthesis to

Harvest energy from ______

Fix ______into organic molecules

6 CO2 + 12 H2XC6H12O6 + 12 X + 6 H2O

______depends on source of electrons

Two stages

Light ______– ______

Light ______(“dark”) – carbon ______

Photophosphorylation

Light energy harvested in ______complexes

Many ______absorb light

Pass ______to reaction-center chlorophyll

Excited electrons pass along electron transport chain in membrane e- carriers

______

Generates proton motive force and ______

______

Generates ______power

NADPH generates reducing power for e- transport

Electron Sources in Photosynthesis

Source of ______determines if ______is produced

______photosynthesis

Plants, algae, cyanobacteria

______is source of electrons

O2 is generated

______photosynthesis

Green and purple bacteria

______, ______gas is source of electrons (not water)

_____ O2 is generated

Carbon Fixation

Conversion of ______to organic form

______– requires input of much energy (______)

Several cycles

Calvin cycle most common

Uses ribulose bisphosphate carboxylase

“______”

______abundant / important enzyme on earth

3 turns of the cycle

 one glyceraldehyde–3–phosphate (______, a 3-carbon sugar)

6 turns of the cycle

 one molecule of 6-______sugar (e.g. fructose 6-phosphate)

Consume 18 ATP & 12 NADPH + H+

Calvin Cycle

______Pathways

Using ______Molecules

Variation in ability to utilize substrates

Variation in ability to synthesize intermediates

Basis of selective media

Basis of differential media