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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