Biology 1009
Microbiology-Summer 2003
Johnson
Unit 2
Chapters 5, 6, 7, and 14
Chapter 5
Microbial Metabolism
Metabolism-sum of all chemical
reactions within living organisms
Two types:
1) Catabolism (catabolic)
Ø
Breakdown of complex organic molecules into
simpler compounds
Ø Release energy
2) Anabolism (anabolic)
Ø
The building of complex organic molecules from
simpler ones
Ø Requires energy
Enzymes-proteins (catalysts) that
speed up and direct chemical
reactions
Enzymes are substrate specific
l
l
l
l
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Lipase
Sucrase
Urease
Protease
Dnase
lipid
sucrose
urea
protein
DNA
Enzymes have 3 D shape
Enzymes are efficient and work at low temps
Enzyme Specificity
Explained by Lock and Key Theory
E + S ---à ES ----à E + P
Naming Enzymes-most named
by adding “ase” to substrate
Maltose
Lipids
Proteins
Remove a “P”
Remove a “H”
Maltase
Lipase
Protease
Phosphatase
Dehydrogenase
Naming Enzymes-Classes
Grouped based on the type of reaction
they catalyze
1) Oxidoreductase=electrons gained or
lost
2) Hydrolases=catalyze hydrolysis
3) Ligases=join two molecules
(synthesis)
Enzyme Components
Two portions
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Apoenzyme-protein portion
Coenzyme-non-protein
Holoenzyme-entire enzyme
Coenzymes
Many derived from vitamins
Important examples:
Niacin-NAD (nicotinamide adenine
dinucleotide)
l Riboflavin-FAD (flavin adenine
dinucleotide)
*Both have roles in ETS
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Factors Influencing Enzymatic
Activity
Temperature-drastic increase may
cause denaturation
pH-extreme pH may denature enzymes
Substrate concentration-enzyme activity
increases as substrate { } increases
until saturation occurs
Inhibitors-two main types
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Competitive and noncompetitive
Temperature, pH, and
substrate concentration
Competitive Inhibitors
Compete with substrate for active site
Two types:
1)
2)
Irreversible
Reversible
Examples:
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Penicillin
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Compete for the active site on the enzyme
involved with the synthesis of the amino acid
crossbridge in the bacterial cell wall
Noncompetitive Inhibitors
Attach to an allosteric site of enzyme,
not the active site
Energy Production
Oxidation-Reduction Reactions
1)
2)
Oxidation-loss of electrons from an atom
or molecule
Reduction-molecule or atom gains an
electron
*As one substance in oxidized, another is
simultaneously reduced
Oxidation-reduction
Generation of ATP
Phosphorylation-generation of ATP that
occurs when a phosphate group is added to
an organic molecule
Three Mechanisms of Phosphorylation
1)
2)
3)
Substrate Level Phosphorylation-P directly
added to ADP
Oxidative Phosphorylation-ETS(chemiosmosis)
Photophosphorylation-ETS in plants
Carbohydrate Catabolism
Microbes oxidize carbohydrates as
their primary source of energy
Most common sourceàglucose
Energy obtained from glucose via two
main mechanisms:
1)
2)
Respiration
Fermentation
Aerobic Cellular Respiration
Electrons released by oxidation and are
passed down ETS (electron transport
system) with oxygen being the final
electron acceptor
General equation:
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Glucose + oxygen --à carbon dioxide +
water + ATP
Respiration-Chemical
Equation
C6H12O6 + 6 O2 à 6 CO2 + 6 H2O +
38 ATP
Aerobic Cellular Respiration
Four subpathways
1)
2)
3)
4)
Glycolysis
Transition Reaction
Kreb’s Cycle
Electron Transport System
Glycolysis
Splitting of sugar (6 carbons)
Oxidation of glucose molecule into 2
molecules of pyruvic acid (3 carbons)
End products
2 pyruvic acid molecules
l 2 NADH
l 2 ATP
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Summary of Glycolysis
Transition Reaction
Connects glycolysis to the Kreb’s Cycle
End Products
2 Acetyl CoEnzyme A
l 2 Carbon dioxide molecules
l 2 NADH
l
Krebs Cycle
(Citric Acid Cycle)
Series of chemical reactions that begin
and end with citric acid (6 carbons)
End products
2 ATP
l 6 NADH
l 2 FADH2
l 4 CO2
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Krebs Cycle
Electron Transport System
Occurs within the cell membrane of
prokaryotes
Electrons transferred from compound to
compound, generating ATP via
oxidative phosphorylation =
Chemiosmotic Model of ATP Synthesis
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Yields 34 ATP for each glucose molecule
ETS
Chemiosmotic Generation of
ATP
Uses proton gradient
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Energy produced from movement of
protons across cell membrane used by
ATP synthase (protein channel) to make
ATP from ADP and “P”
Chemiosmosis
Summary of ATP Production
from ETS
3 ATP for each NADH
2 ATP for each FADH2
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NADH
Glycolysis
Ø Transition
Ø Krebs Cycle
Total=
10 times 3 =
Ø
2
2
6
10
30 ATP
FADH2
0
0
2
2
2 times 2 = 4 ATP
Total ATP Production for the
complete oxidation of 1 glucose
in aerobic respiration
Glycolysis
Transition Reaction
Krebs cycle
ETS
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Total
ATP
2
0
2
34
38 ATP
Summary of Aerobic
Respiration in Prokaryotes
Anaerobic Respiration
Electrons released by oxidation are
passed down an ETS but oxygen is not
the final electron acceptor
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Final electron acceptors:
Nitrate
l Sulfate
l Carbonate
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Note: Lower amts of ATP produced
Fermentation
Anaerobic process that does not utilize
the ETS or the Krebs Cycle.
Usually involves the incomplete
oxidation of a carbohydrate which then
becomes the final electron acceptor.
Involves glycolysis plus an additional
step
Yields many different end products
Lactic Acid Fermentation
Involved in food spoilage
Involved in food production (yogurt, milk,
pickles)
Two genera= Streptococcus/Lactobacillus
Two steps:
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Step 1=Glycolysis-1 glucose broken down into 2
pyruvic acid molecules + 2 ATP
Step 2=Reduction of 2 molecules of pyruvic acid
into 2 molecules of lactic acid
Alcohol Fermentation
Only 2 ATP
End products: alcohol + carbon dioxide
Used to make alcoholic beverages & it makes
bread dough rise
Example= yeast (Saccharomyces cerevisiae)
Three steps:
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Glycolysis-yields 2 ATP & 2 pyruvic acid
2 pyruvic acid broken down into 2 molecules
aldehyde and 2 CO2
2 aldehyde reduced into 2 ethanol molecules
Types of Fermentation
Lipid Catabolism
Lipase breaks down lipid into glycerol
and fatty acids
Glycerol-converted into DHAP and
catabolized via glycolyis and the Krebs
Cycle
l Fatty acids-undergo beta oxidation to
produce Acetyl CoA, which is catabolized
via Krebs Cycle
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Lipid Catabolism
Protein Catabolism
Proteins too large to pass through cell
membrane
Proteases and peptidases produced by
microbe to break proteins and peptides
into amino acids
Amino acids then enzymatically
converted to substances that can enter
Krebs Cycle
Catabolism of Organic Foods
Photosynthesis
Conversion of light energy from the sun into
chemical energy
Chemical energy used to reduce CO2 into
sugar
Involved in carbon fixation-recycling of carbon
in the environment (living organisms rely on
this)
Photosynthesis-occurs in plants, algae, and
cyanobacteria
Photosynthesis-Two Parts
Light Reaction-Light energy converts ADP
and P into ATP via photophosphorylation
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Two types of photophosphorylation: cyclic &
noncyclic
Chlorophyll from plants contain electrons that go
through ETS to make ATP
Dark Reaction-No light required-CO2 fixed to
produce glucose
General Chemical Equation
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6 CO2 + 12 H2O + sun à C6H12O6 + 6 O2 + 6 H2O
Cyclic Photophosphorylation
Noncyclic
Photophosphorylation