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BSC 160: UNIT 3A
2 types of cell activity
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Growth and reproduction
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2 types of metabolic reactions
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Catabolic and Anabolic
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Catabolic
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Breakdown of larger molecules
Produces smaller molecules
Releases energy
Examples:
Breaking down starch into simple sugars
Breaking down simple sugars into CO2 and H2O
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Anabolic
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Building of larger molecules
Uses smaller molecules
Requires energy
Examples:
Joining amino acids into proteins
Linking carbs + amino acids into cells walls
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Macronutrient
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Chemicals needed in large amounts for building macromolecules
Structural components
Enzymes |
Macronutrients needed by bacteria
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Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur
**OCHNPS
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Why are macronutrients needed?
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To build structural components and macromolecules in the cell
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Micronutrients
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Metals; structural components of enzymes
*Critical to cell function
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Growth factors
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Organic compounds required in trace amounts
Form part of enzymes
Include vitamins, amino acids, purines, pyrimidines
Most microbes can synthesize these
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Cellular energy
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Powers the anabolic reactions in cells
In the form of electrons
Given off when chemical nutrients are broken down
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Photosynthetic organisms
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Obtain some of their energy from sunlight
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Energy stored in cells
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Electrons are never loose in the cytoplasm
Captured and stored in ATP (chemical 'battery')
ATP donates or accepts electrons
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Generation time
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The time it takes a microbial cell to divide
The population doubles
Always measured under ideal conditions
Varies among microbial species (e. coli-17 min; treponema pallidum - 33 hrs)
Most bacteria range from 1-3 hrs
Varies with growth conditions
Nutrition available in their environment
Temperature
Oxygen
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Growth curve - Lag Phase
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1 hr - several days
Period of adjustment to new environmental conditions
No cell division!! (Population does not increase)
Bacteria adapting to new environment
Phase of intense metabolic activity
Energy spent on anabolic activities
Making new enzymes needed to use nutrients in new environment
There IS cell activity but not cell division!!
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Growth curve - Log or Exponential Phase
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Cell division begins
Generation time becomes constant
Period of rapid growth with a big increase in population
Cells are very susceptible to adverse environmental factors
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Growth curve - Stationary Phase
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Population stabilizes and growth rate slows down; NOT a dormant period
Number of new cells = number of dying cells
Cell size is smaller
Nutrients becoming scarce
Waste products accumulate and become toxic
pH becoming acidic
Oxygen decreasing |
Growth curve - Death (decline) Phase
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Population begins to decline
Number of dying cells exceeds number of new cells
Cells die at logarithmic rate
Population will eventually die off
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Influences on microbial growth
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Temperature
Oxygen
pH
Water
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Temperature
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Different organisms grow at different temperatures
Temperature affects enzyme rates
Growth is slower below optimum temperature
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3 groups based on optimal growth temperature
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Psychrophile
Mesophile
Thermophile
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Psychrophile
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"Cold-loving"
Found in polar regions and ocean depths
Membranes have unique fatty acids that are fluid at low temperatures
No medical importance; don't grow at our body temperature
Can grow in refrigerator and spoil food
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Mesophile
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"Middle loving"
Most of the organisms we will study
Pathogens!!
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Thermophile
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"Heat-loving"
Found in hot springs and compost heaps
Not medically important; don't grow at our temperature
Food spoilage organisms; withstand pasteurization, canning process
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How do high and low temperature affect cells?
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Two targets:
Membranes - solidify, no movement in or out (thermal lysis - collapse membrane)
Proteins (especially enzymes) - as you add heat, speeds it up, until max is reached
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3 types of Oxygen requirements
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Aerobic
Anaerobic
Aerotolerant
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Aerobic |
Obligate - grow at surface
Oxygen is essential
Found on skin and dust
2. Facultative - grow with or without oxygen
Found in large intestine
3. Microaerophiles - require less oxygen than in the atmosphere
Found in mouth; Sexually transmitted organisms
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Anearobic |
Oxygen harms them
Found in colon
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Aerotolerant
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Indifferent to oxygen
Found in respiratory tract
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pH range in microbial growth
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Intracellular pH remains neutral
Most around pH of 7.0 with a range of 3 pH units
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Function of water in microbial cells
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Acts as a solvent and a reactant
A medium for chemical reactions inside the cell
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Bacterial DNA
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Bacteria have one large chromosome
Single strand of DNA in double helix
Floats free in cytoplasm
Packed very tightly
Single largest molecule in microbial cell
Configured in closed loops
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Description and size of Plasmids
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Not all bacteria have plasmids!
Like chromosomes, but MUCH smaller
Less than 2% its size
About 5-100 genes
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Advantages of Plasmids to cells
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All cells are able to live without them
Plasmids can encode a product that might aid the cell
Antibiotic resistance
Toxin (poison) production
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Mutation |
Change in a base sequence of the DNA molecule (usually a small change)
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2 types of mutation
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Insertion of something that was not in the parent strand
Deletion of information that was in the parent strand
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Rates of mutation
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DNA mutations occur regularly in nature
If change is beneficial, altered cells will flourish and outgrow other cells
Rate once every billion base pair replications
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2 causes of mutation
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Spontaneous
Mutagen
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Spontaneous
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Simple mistake of nature that occurs during cell replication (replication error)
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Mutagen
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Agents which interfere with DNA replication
Increase the mutation rate 10-1,000 times
Mutagens can cause insertion and deletion errors
High energy radiation
Benzopyrene
Nitrosamines |
Genetic Recombination
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Transfer of genetic information between bacteria
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Mechanisms of Genetic Recombination
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Acquired from environment (transformation)
Exchanged between bacteria (conjugation)
Transfered from viruses (transduction)
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Transformation |
DNA is absorbed directly from the environment by live bacteria
Donor cell dies and disintegrates
DNA released into environment and degrades
Live component bacterium takes up a fragment
Same species or very similar species
Fragments contain a few genes
Occurs everywhere; in your intestine, in a swamp, in soil
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Conjugation
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Transfer of DNA between 2 living bacteria
One organism is a donor and transfers DNA to another organism
Transfer chromosome or plasmid through pilus
Usually donate part; rarely entire chromosome
Occurs among closely related species
Common method for transfer of antibiotic resistance among bacteria
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Process of conjugation
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Pilus of donor contacts recipient and pulls it close
Channel forms (conjugate bridge) through which the genetic material passes
Takes about 90 minutes
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Transduction
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Virus transfers bacterial DNA
Bacteria get viral infections, shuts down, and uses resources to manufacture virus particles.
Sometimes there are mistakes during viral replication
Abnormal virus can infect a bacterium
Antibiotic resistance is NOT transferred this way; amount of genetic material carried by a virus is too small
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