Name: Date:

Biology 11: Prokaryotes

Purpose: Analyze Bacteria as a life form at the prokaryotic level of organization

Evaluate the effectiveness of various antibiotics, disinfectants or antiseptics on bacterial cultures.

Text Pages: 319 to 329 *This is required reading!

What are Prokaryotes and why do We Care?

-In the table below list some major differences between Prokaryotic and Eukaryotic Cells:

Characteristics Prokaryotes Eukaryotes

Size Small Large (in comparison)

Cell Wall Some have one Plants only

Organelles Only Ribosomes Many

Nucleus No Yes, membrane bound

Genetic Material Nucleoid (1 long chromosome) Many chromosomes (46 in humans)

-Prokaryotes represent the earliest forms of life that existed on Earth, with the Geologic Record indicating that they were present almost 4 bya!

-Today, most people associate Prokaryotes with Bacterial Pathogens but it is important to remember that there are many times more beneficial or benign prokaryotes than there are harmful ones.

-Here are some important roles of Prokaryotes in our world:

a) Ancient photosynthetic prokaryotes are responsible for the creation of our atmospheric oxygen, allowing aerobic life to develop.

b) The hundreds of bacteria species living on/in our bodies perform functions necessary for humans to live! e.g. The bacteria in our intestines release nutrients from food molecules that we can’t digest and also supply us with essential vitamins!

c) Act as decomposers by breaking down dead animal and plants remains, releasing their nutrients back into the environment so that they can be used again.

*In short, Prokaryotes made it possible for all other forms of life to exist on Earth and continue to do so today!

Why are Prokaryotes so Successful?

-The collective biomass of Prokaryotes is at least 10 times as much as that of all Eukaryotes and they are also able to survive in habitats that are too cold, hot, salty, acidic or alkaline for any Eukaryote.

-What characteristics make them so successful?

External Features

a) Cell Shape:

-Remember that phenotypes like cell shape are subject to natural selection.

-This means that cell shapes can provide important survival advantages in their specific environments.

b) Cell Wall

-The cell wall functions in two ways:

-Physical protection

-Prevents cell from lysing in hypotonic environments.

-There are two different types of Prokaryote cell walls:

Gram Positive Gram Negative

Cell Wall Structure -Thick layer of peptidoglycan (polymer of sugars linked by short polypeptides)

-Thinner layer of peptidoglycan.

-Outer layer of lipids bound to carbohydrates.

-Lipids are toxic.

-Outer membrane protects bacteria against host immune system and antibiotics.

Gram Stain Reaction Purple None

Prokaryotic Cell Type Bacteria and Archaea Bacteria and Archaea

-Many Prokaryotes have cell walls that are covered by capsules:

- A sticky polysaccharide or protein layer.

-This lets the cell stick to a surface or other prokaryotes to form a colony and can also provide protection from the host immune system

-The image right shows a streptococcus bacteria attached to a tonsil cell.

c) Projections

-Flagella: Scattered all over the cell or concentrated at one end.

-Do prokaryotes move at random?

-No, in response to physical and chemical signals.

-Fimbriae/pili: Permit attachment to surfaces and other cells (prokaryotic or host).

d) Rapid Adaptation to Changes in Environment

i) Reproduction

-Prokaryotes can produce a new generation every 20 minutes in ideal environmental conditions.

-Through what process do prokaryotes reproduce?

Binary Fission.

-Is binary fission method of reproduction sexual or asexual? If the latter is true, how is genetic variation created in Prokaryotic cells?

a) Mutation: Can occur each time DNA is replicated. A rapid reproduction rate means that the mutation rate is also higher, creating more genetic diversity.

b) Conjugation: Plasmid copy is transferred from one cell to another. Plasmids often contain genes coding for antibiotic resistance and other emergency functions.

-http://www.hhmi.org/biointeractive/animations/conjugation/conj_frames.htm

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Why is genetic variation important? Permits adaptation to changing environmental conditions.

ii) Endospore Formation

-If the environment becomes too extreme to sustain an active metabolism (e.g. food or water depletion), an endospore can form.

-Endospore: Thick protective coat surrounding a dehydrated and dormant cell. Capable of surviving extreme conditions and remaining dormant for centuries. It will absorb water and continue growth in response to appropriate environmental cues.

-Canned food is heated to high temperatures (110-150°C) with high pressure steam to ensure that endospores of the bacteria Clostridium botulinum are killed to protect against the potentially fatal disease botulism. (Botox is made of small amounts of this bacteria).

e) High Nutritional Diversity

-Diversity of nutritional modes means that prokaryotes can obtain energy and carbon in almost any habitat!

i) Energy Source:

Photo: Sun

Chemo: Organic or inorganic chemicals

ii) Carbon Source:

Autotroph: Make their organic compounds from inorganic carbon sources (CO2)

Heterotroph: Make their organic compounds from organic sources (other plants/animals).

-In which of the categories above would you be classified? Chemoheterotroph

Prokaryotic Domains

Domain Archaea

-Some archaea possess unusual proteins and other molecular adaptations to living in extreme environments and, as such, are called extremophiles:

a) Halophiles

-Salt loving: Can thrive in 15-30% salinity (most cells die in 3%)

-Have colourful pigments.

b) Thermophiles

-Heat loving: Can survive in over 100C water!

-Yellow pigment in photo is archaea in Yellowstone hot springs.

c) Methanogens

-Live in anaerobic environments (no O2) and produce methane as a waste product of their respiration.

-Methane is explosive, but can be collected to produce energy.

-Many archaea also live in non-extreme environments.

-Little is known about Archaea as bacteria have thus far been the subject of most prokaryotic research.

Domain Bacteria

1. Types of Bacteria

-Genetic analysis (molecular biology) has resulted in bacteria being divided into five groups. Take your own brief notes on these groups.

a) Proteobacteria (Gram Negative)

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b) Gram Positive Bacteria _______________________________________________________________

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c) Cyanobacteria ______________________________________________________________________

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d) Chlamydias ________________________________________________________________________

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e) Spirochetes _________________________________________________________________________

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2. Disease Causing Bacteria

-Bacteria cause diseases by producing either:

a) Exotoxins Proteins secreted by bacteria into their environment while they are alive. Exo means outside.

b) Endotoxins Lipid component of the outer membrane in gram negative bacteria is released when the cell dies or is ingested by defensive cells, causing fever, aches and septic shock. Endo means inside.

3. Helpful Bacteria

-Conduct your own research to discover some beneficial and important bacteria that benefit humans.

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4. Bacteria and Antibiotic Resistance

-What is an antibiotic and where have they been harvested from?

Drugs that kills infectious micro-organisms (Vaccines are for Viruses!)

Derived from chemicals produced by fungi and bacteria that are used by those organisms to combat/compete with other bacteria.

-How does a population of bacteria adapt to become resistant to antibiotics?

-Natural Selection:

1. Heritable Variation

-Produced through mutation or conjugation

2. Competition/struggle to survive

-Selective pressure is the antibiotic

3. Over-production of offspring

4. Adaptive alleles accumulate over generations.

-Organisms that have the resistance gene/allele survive, reproduce at a higher rate and leave more offspring.

*Watch the Frontline PBS Video: Hunting the Nightmare Bacteria

http://video.pbs.org/video/2365104403/