Transcript Foundations in Microbiology

PowerPoint to accompany
Foundations
in
Microbiology
Fifth Edition
Talaro
Chapter
8
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microbial Metabolism: The Chemical
Crossroads of Life
Chapter 8
Metabolism
The sum total of all chemical
reactions & physical workings
occurring in a cell
2 types of metabolism
• Anabolism - biosynthesis
– building complex molecules from simple ones
– requires energy (ATP)
• Catabolism - degradation
– breaking down complex molecules into simple
ones
– generates energy (ATP)
4
5
6
7
Enzyme structure
• Simple enzymes – consist of protein alone
• Conjugated enzymes or holoenzymes –
contain protein and nonprotein molecules
– apoenzyme –protein portion
– cofactors – nonprotein portion
• metallic cofactors – iron, copper, magnesium
• coenzymes -organic molecules - vitamins
8
9
Enzyme-substrate interactions
10
• Exoenzymes – transported extracellularly,
where they break down large food
molecules or harmful chemicals; cellulase,
amylase, penicillinase
• Endoenzymes – retained intracellularly &
function there
11
12
• Constitutive enzymes – always present,
always produced in equal amounts or at
equal rates, regardless of amount of
substrate; enzymes involved in glucose
metabolism
• Induced enzymes – not constantly present,
produced only when substrate is present,
prevents cell from wasting resources
13
14
• Synthesis or condensation reactions –
anabolic reactions to form covalent bonds
between smaller substrate molecules,
require ATP, release one molecule of water
for each bond
• Hydrolysis reactions– catabolic reactions
that break down substrates into small
molecules, requires the input of water
15
16
Transfer reactions by enzymes
1. Oxidation-reduction reactions – transfer of
electrons
2. Aminotransferases – convert one type of amino
acid to another by transferring an amino group
3. Phosphotransferases – transfer phosphate groups,
involved in energy transfer
4. Methyltransferases – move methyl groups from
one molecule to another
5. Decarboxylases – remove carbon dioxide from
organic acids
17
Metabolic pathways
18
Control of enzyme activity
1. Competitive inhibition – substance that
resembles normal substrate competes with
substrate for active site
2. Feedback inhibition – concentration of product at
the end of a pathway blocks the action of a key
enzyme
3. Feedback repression – inhibits at the genetic
level by controlling synthesis of key enzymes
4. Enzyme induction – enzymes are made only
when suitable substrates are present
19
Competitive inhibition
20
Energy –capacity to do work or
cause change
• Endergonic reactions – consume energy
• Exergonic reactions – release energy
21
Redox reactions
• always occur in pairs
• There is an electron donor and electron
acceptor which constitute a redox pair
• The process salvages electrons & their
energy.
• released energy can be captured to
phosphorylate ADP or another compound
22
Electron carriers
• resemble shuttles that are loaded and
unloaded with electrons and hydrogen
• most carriers are coenzymes, NAD, FAD,
NADP, coenzyme A & compounds of the
respiratory chain
23
NAD reduction
24
Electron carriers
25
ATP
• 3 part molecule consisting of
– adenine – a nitrogenous base
– ribose – a 5-carbon sugar
– 3 phosphate groups
• Removal of the terminal phosphate releases
energy
26
ATP
27
Phosphorylation of glucose by
ATP
28
Formation of ATP
1. substrate-level phosphorylation
2. oxidative phosphorylation
3. photophosphorylation
29
substrate-level phosphorylation
30
Catabolism of glucose
1. Glycolysis
2. Tricarboxylic acid cycle, Kreb’s cycle
3. Respiratory chain, electron transport
31
Metabolic strategies
Aerobic
respiration
Pathways
Final eacceptor
involved
Glycolysis, O2
TCA, ET
Anaerobic
respiration
Glycolysis, NO3-, So4-2, variable
TCA, ET
CO3-3
Fermentation Glycolysis
Organic
molecules
ATP yield
38
2
32
Overview of aerobic respiration
33
Overview of aerobic respiration
• Glycolysis – glucose (6C) is oxidized and
split into 2 molecules of pyruvic acid (3C)
• TCA – processes pyruvic acid and generates
3 CO2 molecules
• Electron transport chain – accepts electrons
NADH & FADH, generates energy through
sequential redox reactions called oxidative
phosphorylation
34
Glycolysis
35
TCA cycle
36
Electron transport system
37
Chemiosmosis
38
Fermentation
• Incomplete oxidation of glucose or other
carbohydrates in the absence of oxygen
• Uses organic compounds as terminal electron
acceptors
• Yields a small amount of ATP
• Production of ethyl alcohol by yeasts acting on
glucose
• Formation of acid, gas & other products by the
action of various bacteria on pyruvic acid
39
Fermentation
40
Products of fermentation
41
• Many pathways of metabolism are bi-directional
or amphibolic
• Metabolites can serve as building blocks or
sources of energy
– Pyruvic acid can be converted into amino acids through
amination
– Amino acids can be converted into energy sources
through deamination
– Glyceraldehyde-3-phosphate can be converted into
precursors for amino acids, carbohydrates and fats
42
43
44