Download Ch 07 Microbial Metabolism

Ch 07
Microbial
Metabolism
•
•
•
•
•
•
•
•
•
•
•
•
•
•
SLOs
Differentiate between metabolism, catabolism, and anabolism.
Fully describe the structure and function of enzymes.
Differentiate between constitutive and regulated enzymes.
Describe how enzymes are controlled.
Name the chemical in which energy is stored in cells.
Create a general diagram of a redox reaction.
Identify electron carriers used by cells.
List three basic catabolic pathways and the estimated ATP yield
for each.
Construct a paragraph summarizing glycolysis.
Describe the Krebs cycle, and compare the process between
bacteria and eukaryotes.
Discuss the location and the significance of the ETC.
Compare and contrast aerobic and anaerobic respiration.
Summarize the steps of microbial fermentation, and list three
useful products it can create.
Describe how other COHs and how proteins are catabolized.
Metabolism and the Role of Enzymes
• Metabolism: Def?
• Catabolism: Provides __________ and
_________________ for anabolism.
• Anabolism: Uses __________ and
_________________ to build large molecules
Compare to Fig 7.1
Big Picture
Enzymes: Biological _________
Increase reaction rate by ______________
Do not become part of the products
Are unchanged in the process
Simple enzymes consist of protein alone
Conjugated enzymes = Holoenzymes
contain protein and nonprotein molecules
Fig 7.2
Enzyme Substrate Interaction
Fig 7.3
Active site highly specific
Model:
Common cofactors: Fe, Mg, Mn Zn ……
Many coenzymes are Vitamin derivatives
Oxidoreductases and dehydrogenases,
transferases, Hydrolases, Ligases …
Regulation of Enzyme Action
• Constitutive enzymes, e.g.: ?
• Regulated enzymes  Induction and
repression
• Enzyme function is dependent on
temperature, pH, osmotic pressure
?
Fig 7.4
Metabolic Pathways
Fig 7.5
Terminology: Intermediate products, common
intermediates, branching points
Metabolic Pathways of Energy Production:
COH Catabolism
• Cellular respiration
– Aerobic respiration
– Anaerobic respiration
• Fermentation
The three steps of aerobic respiration
1. Glycolysis (oxidation of _____ to ______)
2. Krebs cycle (oxidation of acetyl CoA to ___)
3. Oxidative phosphorylation (e- transport chain)
Control of Enzyme Action: Inhibitors
Noncompetitive –
Competitive
vs.
allosteric inhibitors
inhibitors
Compare to Fig 7.6
Example:
Sulfa drugs
Feedback
Inhibition
Also known as endproduct inhibition
Controls amount of
substance produced
by a cell
Mechanism is
allosteric inhibition
Control of Enzyme Synthesis
Enzyme repression
– Protein expression 
– Response time longer
than for feedback
inhibition
Enzyme induction
– Protein expression 
when suitable
substrates present
– E.g.: lactase induction in E. coli
Fig 7.7
Utilization of Energy
• Energy is needed to do work.
• Energy comes directly from the sun, or is
contained in chemical bonds.
Exergonic vs. Endergonic reactions
Exergonic and endergonic rxs. often coupled
 released energy immediately put to work.
Energy Production:
Oxidation-Reduction Reactions
• Oxidation = loss of e
Redox reaction: Oxidation
-
• Reduction = gain of e
-
reaction paired with
reduction reaction.
When a compound
loses electrons, it is
oxidized.
When a compound
gains electrons, it is
reduced.
Fig. 7.8
Rredox reactions are
common in cell and
indispensable to the
required energy
transformations.
Oxidation-Reduction cont.
In biological systems, the electrons are
often associated with hydrogen atoms.
Biological oxidations are often
dehydrogenations.
Electron Carriers
-
• NAD and FAD are molecular shuttles for e .
• They are coenzymes for Oxidoreductases
(= enzymes that remove electrons from one
substrate and add them to another)
Fig. 7.9
ATP
ATP hydrolysis
powers biosynthesis.
Input of energy is
required to replenish
ATP.
In heterotrophs,
catabolic pathways
provide the energy
that generates ATP
from ADP.
Fig. 7.10
Catabolism
• Enzymes catabolize organic molecules to
precursor molecules and/or energy that cells
then use for anabolism.
• Energy is stored in
– electrons available in NADH and FADH2
– bonds of ATP
• Both are are produced during __________
and needed in large quantities for
__________ metabolism.
3 Catabolic Pathways
Glycolysis
Multi – step breakdown of glucose into
pyruvate
Part of which catabolic pathways (s)?
Generates
• small amount of ATP (how many?)
• small amount of reducing power
– (?)
The Steps of
Glycolysis
Compare to
Fig 7.2
Pyruvate to Acetyl CoA
Transition step
generates Acetyl-CoA from
Pyruvate (decarboxylation)
Acetyl group of acetyl-CoA enters TCA
cycle
Krebs cycle generates ATP and reducing
power Precursor metabolites
Other names for Krebs cycle?
The Krebs Cycle:
A Carbon and Energy Wheel
Takes place where?
Krebs
Cycle
Compare to
Fig 5.13
Electron Transport Chain
• Formed by series of electron carriers located in
....
• Oxidation/Reduction reactions. Reduced electron
carriers from glycolysis and TCA cycle transfer
their electrons to the electron transport chain
• Allows transport of protons (H+) outside of the
membrane  Generates proton gradient or
proton motive force (pmf)
• In final step, O2 accepts electrons and hydrogen,
forming water.
-
Principal Compounds in the e Transport Chain
NADH dehydrogenase, Flavoproteins, Coenzyme Q,
Cytochromes
The Generation of ATP
Phosphorylation:
Substrate level phosphorylation:
ATP synthesis via direct transfer of
a high-energy PO4– to ADP.
Oxidative phosphorylation: ATP synthesis
coupled to electron transport.
– NADH entering electron transport chain gives
rise to 3 ATP
– FADH2 enter electron transport chain at later
point  less energy released and only 2 ATP
produced
The Terminal Step
• Catalyzed by cytochrome aa3, also known as
cytochrome oxidase.
2H+ + 2e- + ½ O2  H20
• Potential side reaction of respiratory chain:
Incomplete reduction of O2 to superoxide
ion (O2-) and hydrogen peroxide (H2O2)
• Aerobes produce enzymes to deal with these
toxic oxygen products:
– Superoxide dismutase
– Catalase
– Streptococcus lacks these enzymes but still grow
well in O2 due to the production of peroxidase.
Anaerobic Respiration
Inorganic O2-containing molecules, other than free
oxygen is final e- acceptor,
e.g.: NO3Terminal step utilizes Nitrate reductase

NO3- + NADH  NO2- + H2O + NAD+
Examples for other final e- acceptors: SO42-, CO33Strict anaerobes and facultative anaerobes
Involves glycolysis, Krebs cycle, and ETC
ATP yield lower than in aerobic resp. because only part
of TCA operates under anaerobic conditions.
Anaerobic Respiration cont.: Denitrification
• Further reduction of nitrite to nitric oxide
(NO), nitrous oxide (N2O), or N2
• Some species of Pseudomonas and
Bacillus
• INSERT Denitrifying rx from
Nitrogen reduction lab
Fermentation
- Incomplete oxidation of glucose. Does not
involve Krebs cycle or ETC
- Organic molecules are final electron acceptors.
- Some organisms can repress production of ETC
proteins when no O2
• Energy yield low
• Great diversity of end products: …
Alcohol and Lactic Acid Fermentation
Catabolism of other Compounds
• Polysaccharides and disaccharides
– Amylases for digestion of ___________
(very common)
– Cellulase for digestion of __________
(only bacteria and fungi have this enzyme)
– Disaccharidases: Sucrase, Lactase, etc.
• Proteins are broken down into amino acids by
proteases:
- Amino groups are removed through
deamination.
In Lab: Biochemical Tests for Bacterial
Identification: Fermentation Tests
Different bacterial species produce different
enzymes  Test detects presence of
enzyme
Example:
Lactose
Fermentation
Protein Catabolism
Protein
Extracellular proteases
Deamination, decarboxylation,
dehydrogenation, desulfurylation
Amino acids
Organic acid
Decarboxylation
Krebs cycle
Overview of
COH
Catabolism
Summary of
Aerobic
Respiration in
Prokaryotes
Location of Carbohydrate
Catabolism
Pathway
Glycolysis
Preparatory step
Krebs cycle
ETC
Eukaryote
Prokaryote
ATP produced from complete
oxidation of one glucose using
aerobic respiration
Pathway
By Substrate-Level
Phosphorylation
By Oxidative Phosphorylation
From NADH
Glycolysis
Intermediate step
Krebs cycle
Total
From FADH
Anabolic Pathways not covered,
except for protein and DNA
biosynthesis, which will be covered
in Ch 8.
Case File: Not so sweet
Inside the Clinic:
Vitamin D Deficiency