Lecture 7

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Chapter 5, part B Microbial Metabolism

Overview of Respiration and Fermentation

Figure 5.11

Fermentation

• Fermentation releases energy from sugars or other

organic molecules

by oxidation.

• Pyruvate is metabolized to various compounds •

O 2 is not required

in fermentation.

• Does not use the

Krebs

cycle or

ETC

• Electrons removed from the substrate

reduce NAD+ to NADH.

• The final electron acceptor is an endogenous

organic molecule.

• Produces only small amounts of ATP (

one or two ATP

molecules for each molecule of starting material) • ATP molecules are produced by

substrate level phosphorylation.

Fermentation

Alcohol fermentation -

acetaldehyde is reduced by NADH to

produce ethanol

.

– Product ethyl alcohol + CO 2

(gas)

• •

Lactic acid fermentation (homolactic)-

pyruvic acid is reduced by NADH to

lactic acid.

– Product - lactic acid only

Heterolactic

fermentation – Product lactic acid as well as other acids and alcohols.

Fermentation

Fermentation

Figure 5.18b

Lipid Catabolism

• Lipases hydrolyze

lipids glycerol

and

fatty acids.

into • Fatty acids and other hydrocarbons are catabolized by

beta-oxidation.

• Catabolic products can be further broken down in

Krebs cycle.

glycolysis

and the

(hydrolase)

Figure 5.20

Protein

Protein Catabolism

Extracellular proteases

Amino acids

Deamination, decarboxylation, dehydrogenation

Organic acid

Krebs cycle

Urea Urease NH 3 + CO 2

Catabolism

Highly reduced complex molecules Oxidized NAD + NADH

Energy

ADP

ATP

Metabolic Pathways of Energy Use Anabolism

• Polysaccharide Biosynthesis

ADPG (adenosine diphosphoglucose).

UGPG (uridine diphosphoglucose) UDPNAc ( UDP-N-acetylglucoseamine)

Figure 5.28

Metabolic Pathways of Energy Use

• Lipid Biosynthesis – Lipids are synthesized from

fatty acids

and

glycerol

.

• Glycerol is derived from dihydroxyacetone phosphate.

• Fatty acids are built from acetyl CoA.

Figure 5.29

Metabolic Pathways of Energy Use

• Amino Acid and Protein Biosynthesis • All amino acids can be synthesized either directly or indirectly from intermediates of carbohydrate metabolism, particularly from the Krebs cycle.

Figure 5.30a

Metabolic Pathways of Energy Use

• Purine and Pyrimidine Biosynthesis.

– The sugars composing nucleotides are derived from either the pentose phosphate pathway or the Entner-Doudoroff pathway.

– Carbon and nitrogen atoms from certain amino acids form the backbones of the purines and pyrimidines Figure 5.31

Reversible Reactions

• Can readily go in either direction.

• Each direction may need special conditions.

NADH

AB A + B

NAD+ [Product concentration]

Amphibolic pathways

• Anabolic and catabolic reactions are integrated through a group of common intermediates.

• Both anabolic and catabolic reactions also share some metabolic pathways, such as Krebs • Such integrated metabolic pathways are referred to as

amphibolic pathways

.

Phototrophs - Photosynthesis

Energy from sunlight

is used to convert carbon dioxide( CO 2 ) and water (H 2 O) into organic materials to be used in cellular functions such as biosynthesis and respiration •

Photo:

Conversion of light energy Light-dependent

into chemical energy (ATP) (light) reactions •

Synthesis:

Fixing carbon Light-independent

into organic molecules (dark) reaction, Calvin-Benson cycle • Process is localized in

chloroplasts

(eukaryotes) or

chlorosomes

(prokaryotes)

Light-dependent

(light) reactions

Cyclic Photophosphorylation

- the electrons return to the chlorophyll

Noncyclic photophosphorylation -

The electrons are used to reduce NADP + and form NADPH -The electrons from: -

H 2 O

or

H 2 S

chlorophyll replace those lost from

(H 2 S)

(

S

) Figure 5.24a

• •

Photosynthesis

Oxygenic

:

6CO 2 + 12H 2 O + Light energy  C 6 H 12 O 6 +

6 O 2

+ 6H 2 O

Anoxygenic

:

6CO 2 + 12H 2 S + Light energy  C 6 H 12 O 6 +

12 S

+ 6 H 2 O

Light-independent

(dark) reaction

• • •

Photosynthesis: Fixing carbon Calvin-Benson cycle

• Use NADPH as cofactor (

CO 2 )

into organic molecules • Characteristic of: -

Cianobacteria,

-

Green and Purple bacteria Algae

and Plants

Autotrophs:

Carbon dioxide (CO 2 ) is used as source of carbon Figure 5.25

A Summary of Energy Production Mechanisms

Nutritional types of organisms by

Sources of energy Chemotrophs: Phototrophs:

Bond energy is released from a chemical compound Light is absorbed in photo receptors and transformed into chemical energy.

Chemoheterotrophs

Chemotroph

s - Organisms that use energy from organic chemicals Glucose NAD + ETC • Pyruvic acid NADH ADP + P ATP

Heterotrophs:

Organic compounds are metabolized to get carbon for growth and development.

• Cannot fix carbon

Chemoautotrophs

• Use energy from

inorganic chemicals

• Energy is used in the Calvin-Benson cycle

to fix CO 2

2Fe 2+ NAD + ETC 2Fe 3+ NADH ADP + P ATP 2 H + •

Chemoautotroph

Thiobacillus ferrooxidans

Phototrophs

• Use

Energy from sunlight

Chlorophyll ETC Chlorophyll oxidized ADP + P ATP • Energy is used in the Calvin-Benson cycle to fix CO 2 –

Photoautotrophs

• Energy is used in anabolism (carbon from organic compounds) -

Photoheterotrophs

A nutritional classification of organisms

Metabolic Diversity Among Organisms

Nutritional type

Photoautotroph

Energy source

Light CO 2

Carbon source

Photoheterotroph Chemoautotroph Chemoheterotroph Light Organic compounds Chemical CO 2 Chemical Organic compounds

Example

Oxygenic: Cyanobacteria plants.

Anoxygenic: Green, purple bacteria.

Green, purple nonsulfur bacteria.

Iron-oxidizing bacteria.

Fermentative bacteria.

Animals, protozoa, fungi, bacteria.

Carbon cycle Nitrogen cycle Sulphur cycle Phosphorus cycle

Biochemical tests and bacterial identification

Bacillus subtilis Staphylococcus aureus

Gram stain •

Pseudomonas aeruginosa Kelbsiella pneumonia K. pneumonia

and

Ps. aeruginosa

look alike through a microscope after Gram stain; so how can they be differentiated?

Different species produce different enzymes determine what type of metabolic reactions an organism can carry out – Oxygen requirements – Fermentation of different substrates (sugars) – Enzymes of respiration – Amino acid catabolizing enzymes

Toxic Forms of Oxygen

• Singlet oxygen: O 2 boosted to a higher-energy state • Superoxide free radicals: O 2 – • Peroxide anion: O 2 2– • Hydroxyl radical (OH  )

Chemical Requirements Oxygen (O

2

)

•Fermentation tests are used to determine the substrates the organism can metabolize by the products it generates.

Control tube S.epidermidis

S.aureus

E.coli

.

Medium: Carbohydrate

Mannitol

, inverted Durham tube Products: Acid and gas.

Figure 5.23

Protein Catabolism

Urease NH 3 + CO 2

Dichotomous Key

• •

A dichotomous key is a series of questions which leads to the identification of an item.

– a device on paper or computer that aids identification of a species or other type of entity.

Dichotomous keys

are used for the identification of organisms. • A dichotomous key works by offering two alternatives at each juncture, and the choice of one of those alternatives determines the next step.

Learning objectives

• Describe the chemical reactions of, and list some products of, fermentation.

• Describe how lipids and proteins undergo catabolism.

• Provide two examples of the use of biochemical tests to identify bacteria.

• Compare and contrast cyclic and noncyclic photophosphorylation.

• Compare and contrast the light-dependent and light-independent reactions of photosynthesis.

• Compare and contrast oxidative phosphorylation and photophosphorylation.

• Write a sentence to summarize energy production in cells.

• Categorize the various nutritional patterns among organisms according to carbon source and mechanisms of carbohydrate catabolism and ATP generation.

• Describe the major types of anabolism and their relationship to catabolism.

• Define amphibolic pathways

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