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BACTERIAL METABOLISM

Krishna Priya. KLecturer

Dept. of Microbiology

Metabolic Pathways- Bioenergetics

Sunlight

Photosynthesis by autotrophs :CO2 + H2O → carbohydrates

Anabolism requiring energy

Catabolismgenerating energy,e.g ATP

Autotrophsor heterotrophs

Differences between Respiration and Photosynthesis

aerobic respiration

photosynthesis

energy is released

energy (light) is absorbed

produces carbon dioxide and water

requires carbon dioxide and water

an oxidative process

a reductive process

aerobic respiration

photosynthesis

occurs in all living cells at

all times

occurs in green plants only when light is available

a breaking down process

a synthetic process

occurs in mitochondria

occurs in chloroplasts

Respiration reactions are catalyzed by enzymes

main food substance which oxidized in cells isglucose

C6H12O6 + 6O2 enzymes

6CO2 + 6H2O + energy

as it takes place in all living cells, it is called cellular respiration which is used to produce energy for cells to use

ATP energy is mainly released as heat and ATP

during respiration in cells

however, during respiration, some ATP should be consumed first before other ATP can be formed

the ATP consumed is used to form other ATP from ADP and phosphate groups

ADP + energy (from breakdown

of glucose)

+ phosphate ATP

ATP is a high-energy compound while ADP is a low-energy one

ATP can only store energy for a short period

ATP is made inside organelles, mitochondria, which is scattered in the cytoplasm of a cell

Uses of the Energy Released during Respiration

Human Other Animals Plants♣ produce light

in fireflies♣ muscle

contraction♣ absorb

mineral salts by active transport

♣ keep warm ♣ produce sound in some birds

♣ transport food substances

♣ absorb food by active transport

♣ produce smell in some mammals

Respiration suppliesthe energy for

musclecontraction

germination

cell divisionchemical changes in cells

Some examples of the useof energy in organisms

10

Anaerobic Respirationrespiration in human is mainly aerobic

respiration as oxygen is essential

when oxygen is not needed during respiration, it is called anaerobic respiration

yeast and muscle cells are examples which they can respire anaerobically for a short time

Alcoholic Fermentation without oxygen, yeast cells respire as follows:

C6H12O6 + energy+ 2C2H5OH (ethanol)

2CO2enzymes

amount of energy released anaerobically is smaller when compared with the aerobic method

anaerobic respiration

aerobic respiration

amount of energy released

large small

oxidation of glucose completely partly

place of occurrence mitochondria cytoplasm

Differencesaerobic

respirationanaerobic

respiration

complete oxidation

incomplete oxidation

oxidation of sugar

essentialoxygen requirement nil

energy released

large amount

small amount

aerobic respiration

anaerobic respiration

in most living cells

in lower organisms (e.g. bacteria and

yeast) and vertebrate muscles

occurrence

inorganic: CO2 and H2O

end products

organic: ethanol or lactic acid

Glucose CatabolismGlycolysis

• The overall reaction in glycolysis is:

Glucose + 2ADP + 2 NAD+ + 2 Pi →2 pyruvate + 2 ATP+ 2 (NADH + H+)

Produce - e ;- Key metabolite: pyruvate

Glucose Catabolism

Glucose

Aerobic metabolismAnaerobic metabolism

Tricarboxylic acid (TCA)or (Krebs)or (Citric acid cycle)

Oxidative phosphorylation

Glycolysis orEmbden-Meyerhof-Parnas (EMP)

Fermentation: ethanol, acetic acid, lactate.

Phosphofructokinase (PFK): key enzyme of the EMP pathway

PFK

• (1) Phosphorylates fructose-6-phosphate to fructose-1,6-bisphophate.

• (2) Requires Mg2+.

• (3) Catalyzes an irreversible reaction, meaning PFK is an key enzyme in the EMP pathway.

• (4) Its presence indicates that this organism may catabolize glucose through the EMP pathway.

Energy yield in glycolysis

1 NADH= 2ATP

Pentose Phosphate Pathway

Also known as:• Pentose shunt • Hexose monophosphate shunt • Phosphogluconate pathway

• It occurs in the cytosol.

One fate of G6P is the pentose pathway.

The pentose pathway is a shunt.

• The pathway begins with the glycolytic intermediate glucose 6-P.

• It reconnects with glycolysis because two of the end products of the pentose pathway are glyceraldehyde 3-P and fructose 6-P; two intermediates further down in the glycolytic pathway.

• It is for this reason that the pentose pathway is often referred to as a shunt.

Moderate glucose flux

Glycolysisonly

Large glucose flux

Glycolysis

PentosePhosphatePathway

It’s a shunt

What does the pentose phosphate pathway achieve?

• The pathway yields reducing potential in the form of NADPH to be used in anabolic reactions requiring electrons.

• The pathway yields ribose 5-phosphate.– Nucleotide biosynthesis leading to:

• DNA• RNA• Various cofactors (CoA, FAD, SAM, NAD+/NADP+).

The pentose pathway can be divided into two phases.

Non-oxidative interconversion of sugars

• Transketolase (TPP) and transaldolase are the link back to glycolysis.

• Glyceraldehyde 3-phosphate• Fructose 6-phosphate• Net result:

3C5 2C6 + C3

5 carbon atoms

Regulatory enzyme

Glucose → Pyruvate via

PPP Found in most bacteria.

Can produce pentoses (5C) from hexoses (6C) via oxidative decarboxylation, which forms NADPH. Source of ribose for nucleosides.

Other unique sugars are produced (4C, 7C); source of erythrose for aromatic amino acids (Phe, Tyr, Trp)

G3P enters Gycolysis to produce ATP and pyruvate.

(GP)

(GP)

ED pathwayor

Ketogluconate Pathway

Glucose -------> 2 ethanol + 2 CO2 + 1 ATP (net)

Dehydration

Glucose → Pyruvate via E-DP

Two stage linear pathway like Glycolysis; First stage unique; second stage identical.

KDPG the unique intermediate.

Yields 1 ATP, 1 NADH, 1NADPH.

Note one pyruvate is generated at each stage of the pathway.

Found in some Gram negative bacteria instead of Glycolysis (Rhizobium, Agrobacterium, Azotobacter, Pseudomonas)

(KDPG)

6 phosphogluconatedehydratase

Hexokinase

Glucose 6 p dehydrogenase, 6 phosphogluconolactonase

KDPG aldolase

*Sole metabolic pathway in Zymomonas mobilis, other gram negatives

*This is the only organism which utilizes this pathway anaerobically

*Gluconate in the medium stimulates this pathway in gram positives

*This pathway is present in both aerobes and anaerobes, but absent in eukaryotes

*This pathway can occur independent of EMP or HMP, as direct pyruvate formation occurs here.

Phosphoketolase pathway

Hexokinase

Glucose 6 P dehydrogenase

Decarboxylase(Xylulose 5 P,Ribulose 5 P)

Phosphoketolase

Other carbohydrates

EMP

Acetokinase

Pentose Phosphoketolase Pathway

Hexose Phosphoketolase PathwayFructose 6 Phosphate Acetyl Phosphate + Erythrose 4 P

Fructose 6 P+Eryhtrose 4 P

Glyceraldehyde 3 P Sedoheptulose 7 P

Xylulose 5 P Ribose 5 P

Glyceraldehyde 3 P Acetyl P

EMP

Pyruvate

Phosphoketolase

Transketolase

Phosphoketolase

Transaldolase