1Metabolism IV:

VI. Anaerobic respirationVII. ChemolithotrophyVIII. Anabolism

2

Reoxidation of reduced electron carriers by a process analogous to aerobic respiration, but using a terminal electron acceptor other than O2.

VI. Anaerobic respiration

PMF is formed and ATP is synthesized by electron transport phosphorylation.

Used by microbes capable of anaerobic respiration when O2 is not available.

TB

3A. Anaerobic respiration

external terminal electron acceptoris not O2

eg. NO3- (nitrate), Fe3

+, SO4-,

CO2, CO32-, fumarate or

another organic molecule

O2

4

Growth substrates

Oxidized products

Oxidized electron carriers

Reduced electron carriers

fumarateNO3

-

SO42-

CO2

succinateNO2

-, N2

H2SCH4 PMF

various electrontransport chains

51. Nitrate reduction

NO3- NO2

-

• a form of anaerobic respiration in which NO3

- is the terminal electron acceptor

nitrate reductase

• used by Escherichia coli and some other microorganisms when O2 is absent

6

NO3-

denitrification

2. Denitrification reduction of nitrate all the way to N2 through anaerobic respiration

Important in agriculture and sewage treatment

N2gas

73. Respiration with sulfur or sulfate

SO42- H2S

• elemental sulfur or SO42- is the

terminal electron acceptor

S0 H2Sreduction

smelly gases

8B. Less free energy is released in anaerobic respiration than in aerobic respirationOxidized form / Reduced form Reduction potential

Eo' (Volts)

CO2 / glucose (C6H12O2) (- 0.43)2 H+ / H2 (- 0.42)NAD+ / NADH (- 0.32)SO4

2- / H2S (- 0.22)pyruvate / lactate (- 0.19)

O2 / H2O (+ 0.82)

fumarate / succinate (+ 0.03)NO3- / NO2- (+ 0.42)

9VII. ChemolithotrophyUse of inorganic compounds as the energy source (primary electron donor)

Many chemolithotrophs use O2 as the terminal electron acceptor

H2 + 1/2 O2 H2O

10A. Examples of chemolithotrophs

H2 hydrogen-oxidizing bacteriaH2S sulfide-oxidizing bacteria

Fe2+iron-oxidizing bacteriaNH3 ammonia-oxidizing bacteria

(NH3 NO2

- )

NO2- nitrite-oxidizing bacteria

(NO2- NO3

- )

111. Example of chemolithotrophy: aerobic sulfide (H2S) oxidation

H2S + 2 O2

inorganic electron donor

Boiling sulfur pot, Yellowstone National Park

SO42- + 2H+

12

Ammonia oxidizer NH3 NO2

-

Nitrite oxidizerNO2

- NO3-

2. Examples of chemolithotrophy: ammonia oxidation and nitrite oxidation

13B. Possible metabolic strategies for generating energy on early earth

anaerobic chemolithotrophyfermentationanaerobic respirationanoxygenic photosynthesis

14

H2

ADP + Pi

ATP

Cytoplasmic membrane

In

Out

A hypothetical primitive energy- generating system on early earth

primitive ATPase

primitivehydrogenase

Proton motive force (PMF)

2 H+

2 e-

inorganic electron acceptor (not O2)

15VIII. Anabolism (Biosynthesis)

Nutrients

Nutrients

Macromolecules and other cell components

Anabolism Energy

Energy source(eg. sugar or H2)

Waste

Catabolism

Energy

16Cells are made of molecules.

Nucleic acids

ProteinsPolysaccharides

Lipids

small molecules

17A. Building cell components requires

energy (ATP) reductant (NADPH)

C H O N P S

a source of carbona source of nitrogensome P and other nutrients

18

carbon source

(organic carbon)heterotroph autotroph

(CO2)

energy source

chemoorganotroph (organic chemical) chemolithotroph

(inorganic chemical

e.g. H2S, H2, NH3)

phototroph (light)

B. Classification of organisms according to

19C. Cell carbon

sugarsacetyl CoA organic acids

CO2

autotrophs

NH3

aminoacids protein

fattyacidslipid

nucleotidesnucleicacids

P, NH3

Cell carbon:

organic carbon source (e.g. glucose)

glycolysis, TCA heterotrophs

20D. Sugar / polysaccharide metabolismSugars are needed for

polysaccharides (cell wall, glycogen)nucleic acids (DNA, RNA)

O O

hexoses pentoses

small molecules (ATP, NAD(P)+

cAMP, coenzymes, etc.)

211. UDP-glucose is a precursor to polysaccharides and peptidoglycan.

O — P-O- O -

O O= P-O O -

HOCH2O

CH2

OH OH

O N

ONH

O

(don't memorize structure)

UDP = uridine

diphosphate

222. Gluconeogenesis

A pathway for making glucose-6-P from noncarbohydrate sources (e.g. acids from TCA).

233. Gluconeogenesis is the reversal of glycolysis starting with PEP, but with a few different enzymes.

glucose-6-P

PEP CO2

pyruvate

TCA

OAA

succinate

gluconeogenesis

244. Pentose phosphate pathway

a. makes pentoses (ribulose-5-P) from the decarboxylation of glucose-6-P

b. also makes NADPH for biosynthetic reactions

255. Deoxyribonucleotides for DNA are made from the reduction of the 2'- hydroxyl of ribonucleotides.

OCH2

HOH

O N

NH2

N

N

N

OP PPOCH2

OHOH

O N

NH2

N

N

N

OP PP

NADPH NADP+

ATPdeoxy-ATP

26

ribose-5-P

ribonucleotides RNA

deoxyribo-nucleotides DNA

glucose

glucose-6-P

glucose-1-P

UDP-glucose(uridine diphosphoglucose)

ribulose-5-P

Sugar summary Gluconeogenesis TCA

PEP OAAglycolysis

UTP

polysaccharides peptidoglycan, cell walls

pentose phosphate pathway

NADPHNADP+

pyruvate

27E. Amino acid biosynthesis

1. Requires an acid (carbon skeleton) and an amino group

O C – OH

H2N – C – H R

carboxylic acidaminogroup

282. Some carbon skeletons are made in glycolysis and the TCA cycle

5 main amino acid precursorsa. -ketoglutarate (5C)b. oxaloacetate (4C)c. pyruvate (3C)d. phosphoglycerate (3C)e. PEP (3C), (erythrose-4-P)

29Carbon skeletons for amino acids

PEP CO2pyruvate

TCA

OAA

(glucose)

(acCoA)

-KG

phosphoglycerate

30

O C - O-

O = C CH2

CH2

COO-

-ketoglutarate

O C - O-

H3N - C - H CH2

CH2

COO-

glutamate

+NH3

NADPH NADP+

3. The amino group for glutamate can come directly from ammonia.

31

O C - O-

O = C CH2

COO-

-ketoglutarateglutamate

4. The amino group for most other amino acids comes from glutamate through transamination (amino transfer).

oxaloacetate (OAA) aspartate

O C - O-

H3N - C - H CH2

COO-

+

32F. Purine and pyrimidine biosynthesis is very complex.

1. The carbons and nitrogens come from amino acids, NH3, CO2, and formyl (HCOO-) groups.

N

N

N

N

CC

from formyl attached to folic acid

**

332. Folic acid carries the formyl groups in purine biosynthesis.

3. Sulfanilamide is a "growth factor analog" that inhibits purine biosynthesis by inhibiting the production of folic acid.

34D. Fatty acids1. In general, saturated fatty acids are built two carbons at a time from acetyl CoA.

CH 3

C~SCoAO(8)

ATP, NADPHCOO-

palmitic acid

352. Unsaturated fatty acids • have 1 or more cis-double bonds • increase fluidity of membranes

COO-

363. Acetyl CoA and succinyl CoA and play important roles in anabolism.

acetyl CoA fatty acid biosynthesissuccinyl CoA heme biosynthesis

37Study objectives1. Understand anaerobic respiration and the examples presented in class. Define nitrate reduction, denitrification, sulfate reduction.2. Understand chemolithotrophy and the examples presented in class.3. Examples of integrative questions: Compare and contrast aerobic respiration, anaerobic respiration, chemolithotrophy, and fermentation. Given the description of a catabolic strategy, be prepared to identify the type of metabolism being used. Contrast sulfate reduction and sulfide oxidation. 4. Be able to classify microorganisms based on energy source and carbon source.5. Understand the roles of glycolysis and the TCA cycle in the synthesis of cellular macromolecules.6. What type of polymers are synthesized from UDP-glucose?7. What are the functions of gluconeogenesis and the pentose phosphate pathway?8. How are deoxyribonucleotides for DNA made from ribonucleotides?

3810. Know the sources of carbon and nitrogen for amino acid biosynthesis. How are amino groups transferred to acids to make amino acids?11. Understand the role of folic acid in nucleotide biosynthesis.12. How does sulfanilamide inhibit the growth of microorganisms? 13. Humans do not make their own folates. Why is the drug sulfanilamide toxic to certain microorganisms but not to humans? 14. Know the anabolic roles of acetyl CoA and succinyl CoA as described in class.