Metabolism – the sum of all chemical reactions within
a living organism
A. Catabolism
Complex molecules à simple molecules + energy
Exergonic – release energy
Ex: Sugar à CO2 + H2O + energy
B. Anabolism
(biosynthesis)
Simple molecules + energy à complex molecules
Endergonic – requires energy input
Ex: Amino
acids + energy à
protein
Coupled reactions
Catabolic and anabolic reactions linked together
DRAW
Enzymes
A. Collision
theory
Atoms and molecules collide with each other and form
bonds or break bonds
The higher the temperature, the faster the molecules
travel, the more collisions, the faster the reaction
Activation energy – the energy required for a
chemical reaction
B. Enzymes
and Chemical reactions
Enzyme –
Biological catalyst
A substrate binds to the active site of an enzyme and
a reaction is catalyzed
Acts on a specific substrate
Enzyme is not consumed by reaction
Lowers activation energy of a reaction
à speeds up reaction (Fig. 5.2)
C. Naming enzymes
Usually chemical they act on + “-ase”
Ex: Lipase,
protease
D. Enzyme
components
Most enzymes consist of 2 components
1. Apoenzyme
– protein portion
2.
Cofactor - nonprotein component
Necessary to activate apoenzyme
Ex: Iron,
zinc, magnesium, calcium
Holoenzyme = apoenzyme + cofactor (Fig. 5.3)
Coenzyme
Cofactors
that are organic molecules
Many
are derived from vitamins
Ex: NAD+,
NADP+, FAD (used in cellular respiration and photosynthesis)
E. The
mechanism of enzymatic action (Fig. 5.4)
1. The
substrate contacts the active site on the enzyme
2. An
enzyme-substrate complex forms
3. Substrate
transformed into products
4. Products
are released
5. The enzyme
is recovered unchanged
F. Factors
that influence enzymatic activity
1. Temperature
(Fig. 5.5a)
As temp. increases, enzyme activity increases to
optimal temp., then decreases due to denaturation
Denaturation of proteins (Fig 5.6)
Hydrogen bonds broken
Protein shape altered
Loses enzymatic activity
Usually due to heat or pH extremes
2. pH (Fig
5.5b)
Most enzymes have optimum pH where enzyme activity is
greatest
Above or below this optimum, the enzyme activity
decreases
3. Substrate
Concentration (Fig. 5.5c)
As substrate concentration increases, enzyme activity
increases up to a point, then saturation occurs
4. Inhibitors
(Fig.5.7)
Combine with enzymes and prevent them from
functioning
Can be reversible or irreversible
a.
Competitive inhibitors
Inhibitors that bind with the active site of enzymes
Compete with the substrate for the active sites
b.
Noncompetitive inhibitors
Inhibitors that bind with the allosteric site (site
other than the active site) of an enzyme
Binding causes the active site to change shape
Enzyme loses activity
Energy Production
A.
Oxidation-reduction reactions
Oxidation – Removal of electrons from an atom
Reduction – Gain of electrons
Oxidation and reduction reaction are always paired
à redox reactions (Fig. 5.9)
H+ is usually transported along with electron (Fig.
5.10)
B. The
generation of ATP
ADP + P + energy à ATP
Phosphorylation – The addition of a phosphate (P) to
a compound
1. Substrate
level phosphorylation
P is directly transferred from a substrate to ADP
Occurs in glycolysis and Krebs cycle
Ex: C-C-C-P +
ADP à C-C-C + ATP
2. Oxidative
Phosphorylation
Electrons are passed through an electron transport
chain to oxygen
Occurs
only in the electron transport chain
Energy released is used to phosphorylate ADP
3.
Photophosphorylation
Uses light energy to phosphorylate ADP
Occurs only in photosynthetic cells
Carbohydrate Catabolism – carbohydrates oxidized to
generate ATP
Overview of respiration and fermentation (Fig. 5.11)
A. Cellular
Respiration
Final electron acceptor is an inorganic molecule
Uses an electron transport chain
1. Aerobic
Respiration
Final electron acceptor is oxygen (O2)
a. Glycolysis
(Fig. 5.12)
Oxidation of one glucose to two pyruvic acid
2 ATP produced by substrate level phosphorylation
b. Pyruvic
acid decarboxylation (Preparation step, Transition reaction) (Fig. 5.13)
Pyruvic acid loses a C and becomes Acetyl-CoA
c. Krebs
Cycle (Fig 5.13)
Cyclic series of reactions
2 ATP produced by substrate level phosphorylation
d. Electron
Transport Chain (System) and Chemiosmosis
(1) Electron
transport system (Fig. 5.14)
A series of electron carriers attached to a membrane
In eukaryotes à mitochondrial membrane
In prokaryotes à plasma membrane
Process
(a) Electrons transported to chain by
NADH and FADH2
NADH à 3 ATP
FADH2 à 2 ATP
(b) Electrons are transferred down the chain by oxidation and reduction reactions, releasing energy at each step.
(2)
Chemiosmosis
Mechanism that uses a proton gradient across a
membrane to generate ATP (Fig 5.15)
Process
(a) Energy
from electron transport chain is used to pump protons (H+) out of membrane
(b) Proton
gradient is created
(c) Protons
flow back through ATP synthase, generating ATP by oxidative phosphorylation
(Fig. 5.16)
Summary of Aerobic Respiration
C6H12O6 + 6O2
+ 38 ADP +38 P à
6 CO2 + 6 H2O + 38 ATP
(Fig. 5.17) Be able to draw and label
DRAW
2. Anaerobic
Respiration
Final electron acceptor is an inorganic substance
(nitrate, sulfate, carbonate) other than oxygen
Process of anaerobic respiration
a. Glycolysis
b. Pyruvic
acid decarboxylation
c. Krebs
cycle
d. Electron
transport chain and chemiosmosis
Only parts of the Krebs cycle and elect. trans. chain
are used, therefore, ATP yield is not as high as aerobic respiration
Ex: Pseudomonas
and Bacillus can use nitrate ion as the final electron acceptor
B.
Fermentation (Fig. 5.18)
Final electron acceptor is an organic molecule
Does not use an electron transport chain
1. Types of
fermentation
a. Lactic
acid fermentation (Fig. 5.19)
(1)
Glycolysis
(2) Pyruvic
acid reduction
à produces 2 molecules of lactic acid
Ex:
Streptococcus and Lactobacillus
àused to make yogurt, sauerkraut, pickles
b. Alcohol
Fermentation (Fig. 5.19)
(1)
Glycolysis
(2) Pyruvic
acid conversion
à produce acetaldehyde and CO2
(3)
Acetaldehyde reduction
à produce ethanol
Ex:
Saccharomyces (yeast)
à used to make alcoholic beverages & bread
2.
Classification of organisms based on fermentation products
a. Homolactic
(or homofermentative)
Produce only lactic acid
b.
Heterolactic (or heterofermentative)
Produce lactic acid as well as other acids or
alcohols
3. Using
fermentation to identify bacteria (Fig. 5.23)
Fermenters produce acid and/or gas
Lipid and Protein Catabolism (Fig. 5.21)
Lipids and proteins are enzymatically converted to
molecules that can then enter glycolysis or Krebs cycle
Photosynthesis
6CO2
+ 12H2O + light energy à C6H12O6 + 6 O2
+ 6H2O
A. Two stages
of photosynthesis
1.
Light-dependent reactions (light reactions) (Fig. 5.24)
ADP + P + light energy à ATP + NADPH
Occurs by photophosphorylation
a. Light
energy absorbed by chlorophyll, exciting electrons
b. Electrons
pass down an electron transport chain releasing
energy
c. Energy
used to produce ATP and NADPH
2. Light
independent reactions (dark reactions) (Fig. 5.25)
Carbon fixation occurs
CO2 à sugars
B.
Photosynthesis in various organisms
1. Plants and
algae
Use chlorophyll a found in thylakoid membranes in
chloroplasts
2.
Cyanobacteria
Use chlorophyll a found in thylakoid membranes in
cytoplasm (no chloroplasts)
3.
Photosynthetic bacteria
Use bacteriochlorophyll found in thylakoid membranes
in cytoplasm (no chloroplasts)
Classification of organisms based on energy and
carbon source
A. Energy
sources
1.
Phototrophs – obtain energy from sunlight (photosynthesis)
2.
Chemotrophs – obtain energy from inorganic or organic compounds
B. Carbon
sources
1. Autotrophs
– obtain carbon from CO2
2.
Heterotrophs – obtain carbon from organic compound
Classification combining energy and
carbon sources
A. Photoautotrophs
Ex:
cyanobacteria, algae, plants
B.
Photoheterotrophs
Ex: Green
nonsulfur bacteria, purple nonsulfur bacteria
C.
Chemoautotrophs
Ex: Iron
oxidizing bacteria
D.
Chemoheterotrophs
Ex: most
bacteria, protozoa, fungi, animals
The integration of metabolism (Fig 5.32)
Anabolism (biosynthesis) and catabolism use the same
reversible pathways
Chapter
6 Microbial growth
The Requirements for growth
A. Physical
requirements
1.
Temperature
Microbial classification based on temperature of optimum
growth
a.
Psychrophiles
Optimum growth 0 – 20° C & can grow at 0° C
Found in deep ocean or polar regions
b.
Psychrotrophs
Optimum growth 20 - 30° C, but can grow at 0° C
Often responsible for food spoilage in refrigerator
(4° C)
c. Mesophiles
Optimum growth 20 – 40° C, cannot grow at 0° C
Most common type of microbe
Includes most spoilage and disease microbes
d.
Thermophiles
Optimum growth 40 – 80° C
Found in hot springs
e.
Hyperthermophiles
Optimum growth 80 - 110°C
All members of Archaea
In hot springs and deep sea hydrothermal vents
2. pH
a. Review of
pH
0 –14
pH = 7 à neutral
pH < 7 à acidic
pH > 7 à alkali
(basic)
Buffer = chemical that resists change in pH of
solution
b.
Classification of bacteria based on pH of optimum growth
(1)
Neutrophiles à
pH 6 – 8
Most bacteria
(2)
Acidophiles à pH < 6
Ex: Thiobacillus
Found in acid runoff from coal mines
(3)
Alkalophiles à pH > 8
Found in alkaline lakes and soils
c. Inhibiting
action of non-optimum pH
à Destroys (denatures) enzymes in cytoplasm and plasma
mem.
High or low pH can be used to preserve foods
Ex:
sauerkraut, pickles, cheese
3. Osmotic
pressure
a. Effects of
osmotic pressure
(1) Hypotonic
solutions
Rigid
cell wall protects bacteria
(2)
Hypertonic solutions (Fig. 6.4)
Most microbes undergo plasmolysis (cell mem. shrinks)
Hypertonic environments used to preserve foods
Ex: Salted
meats, honey
b.
Classification based on osmotic pressure requirements
(1) Obligate
halophiles
Require high salt concentrations (~30%)
Found in Dead Sea
(2)
Facultative halophiles
Optimum growth at low salt conditions, but can
tolerate higher salt concentrations
B. Chemical
requirements
1. CHNOPS
2. Trace
elements – iron, copper, molybdenum, zinc
3. Oxygen
(Table 6.1)
Classifications based on oxygen requirements
a. Obligate
aerobes
Require oxygen
b.
Facultative anaerobes
Grow better with oxygen, but can grow in anaerobic
environment
c. Obligate
Anaerobes
Harmed by oxygen
d.
Aerotolerant anaerobes
Tolerate oxygen, but do not use it
e.
Microaerophiles
Require narrow range of oxygen, less than in air
4. Organic
Growth Factors
Compounds that organism cannot synthesize, must get
from environment
Ex: Vitamins,
amino acids
Culture media
A. All media
are divided into two main groups
1. Chemically
defined media
Exact chemical composition is known
Ex: X g
glucose, Y g amino acid, ….
2. Complex
media
Made from extracts of yeast, meat, plants
Exact chemical composition varies
B. Special
Culture techniques
1. Anaerobic
chambers and media (Fig. 6.5)
Chemically remove oxygen from environment or media
2. Candle
jars (Fig 6.7a)
Lit candle adds CO2 to environment for
capnophiles (microbes that grow better at high CO2 concentration)
C. Special
types of media
1. Selective
Media
Selects some bacteria, inhibits others
Ex: MacConkey
agar selects Gram negative bacteria, inhibits Gram pos.
2.
Differential media
Differentiates different microbes based on appearance
Ex: Blood
agar,
Streptococcus pyogenes will produce a clear ring around colonies
3. Enrichment
culture
Similar to selective media à selects some but inhibits others
But designed to increase small numbers to detectable
levels
The Growth of bacterial cultures
A. Bacterial
Division –
à most bacteria use binary fission (divide into two
equal cells)
(Fig. 6.11)
B. Generation
time
à time required for a cell to divide (and its
population double)
C.
Logarithmic representation of bacterial populations (Fig. 6.12, 6.13)
Bacterial growth is logarithmic (exponential)
D. Phases of
growth
DRAW
1. Lag
No growth
Period of adjustment
2. Log
Logarithmic growth
Most metabolically active
3. Stationary
Nutrients decline, wastes build
Bacteria dying as fast as produced
Many cells stop dividing
4. Death
Conditions deteriorate
Live cell numbers decrease logarithmically
Chapter 7 The
Control of Microbial Growth
Terminology of Microbial control
A.
Sterilization
Destruction of all forms of microbial life, inc.
endospores
Usually by heating or radiation (gamma rays)
B. Commercial
sterilization
Heating
Enough heat to destroy endospores of C. botulinum,
but not other endospores
Food quality not degraded
C.
Disinfection
Destroys vegetative non-endospore forming pathogens
on inert surface
Use chemicals, UV, boiling water, or steam
D. Antisepsis
Destroy vegetative pathogens on living tissue
E. Degerming
Mechanical removal rather than killing
Ex: alcohol swab before shot
F.
Sanitization
Lowers microbial counts on eating and drinking
utensils
Types of treatments
A.
“-cide”
Kills microorganisms
Ex: fungicide
B. “-stat” or
“-stasis”
Inhibits growth
Once gone, growth resumes
Ex:
Bacteriostat
Factors that influence antimicrobial effectiveness
A. Number of
microbes
The more start with, the longer to eliminate
(Fig 7.1b)
B.
Environmental influences
1. Organic
matter à inhibits chemical
antimicrobials (blood, vomit, feces)
2.
Temperature à
disinfectant work better when warm
3. Fats and
proteins à protect microbes
4. Acidic
conditions à
help in disinfection
C. Time of
exposure
Longer the exposure à the more effective the treatment
D. Microbial
characteristics
Some microbes more resistant to others due to
physical structure
Ex:
endospores more resistant than vegetative cells
Actions of Microbial Control agents
A.
Alterations of Membrane Permeability
Damage plasma membrane à cytoplasm leaks out
B. Damage to
proteins
Damage enzymes à hinder cellular reactions
C. Damage to
nucleic acids
Damage RNA or DNA à cell can’t replicate or produce enzymes
Physical methods of Microbial Control
A. Heat
Denatures microbial enzymes
Types of heat treatments
1. Moist heat
à breaks H-bonds in protein à coagulation
Water or steam transfers heat more effective than dry
heat (hand in 100 °C
oven vs. in boiling water)
Examples:
a. Boiling
b. Autoclave
(15 psi, 121 C for 15 min) (Fig 7.2)
Kills all organisms and endospores
But steam has to actually contact
à dry material in aluminum foil won’t sterilize
2.
Pasteurization
Mild heating
Kills pathogens
Lowers overall microbial numbers à retard spoilage
63°
C for 30 min.}
72°
C for 15 sec.} equivalent treatments
3. Dry heat
sterilization
Kills by oxidation effects
Examples
a. Flaming
b.
Incineration
c. Hot air
sterilization (170°
C for 2 hrs in oven)
B. Filtration
(Fig. 7.4)
0.45 mm filters will filter out bacteria, but not viruses
C. Low
Temperatures
Refrigeration (0 - 7° C) is bacteriostatic on most bacteria
D.
Desiccation
Bacteria won’t grow, but most remain viable
Neisseria gonorrhea ~ 1 hour
Mycobacterium tuberculosis ~ months
endospores ~ centuries
E. Osmotic
pressure
High concentration of salts and sugars à hypertonic solutions
Fungi more resistant than bacteria à mold on fruit
F. Radiation
(Fig. 7.5)
1. Ionizing
radiation
Higher energy à gamma rays, x-rays
Ionizes water à O2-
is toxic
Hits DNA