Prokaryotes

Or 100 Trillion Friends That You Didn’t Know You Had

The Human Microbiome We are actually a giant ecosystem of

microbes Prokaryotes comprise between 1-3% of the

mass of a human body - up to 6lbs of a 200 lb person can be

microbes

Classification: Some Old, Some New

Biologists have typically classified living things into 5 large groups called kingdoms

- Monera, Protista, Fungi, Plantae & Animalia

Then biologists discovered organisms called Archea – they are prokaryotic organisms but aren’t bacteria.

- What to do?

The Challenge of Archea Archea present a problem, they a

are prokaryotes – They have no nucleus or organelles

They also share traits with eukaryotes - similarities in DNA and synthesis

They have traits unique to themselves - cell membrane lipids, ability to survive extremely high temperature

Enter the Domain System of Classification

Scientists divided living things into 3 Supergroups called domains these consist of Bacteria, Archea and Eukarya

Archea can be Extremophiles

Some species of archea can be found in environments so extreme, that nothing else lives there- extreme temps, extreme pH, extremely salty etc…

Bacteria Earth’s oldest life forms

– between 3.5 and 3.8 billion years old

Most abundant life form – up to 2.5 billion individual bacteria in 1 gram of fertile soil

Very adaptable – found in all of Earth’s

ecosystems

Bacteria Characteristics Unicellular Circular DNA No organelles 1/10th the size of eukaryotic cells Flagella-long hair-like structure used

for movement Reproduce asexually –Binary Fission

Bacterial Shapes

3 main shapes - coccus – sphere

- bacillus – rods

- spirillum - spiral

Bacterial Characteristics Metabolic diversity – Bacteria can

produce energy in a variety of circumstancesautotroph – (self-feeding) – some

bacteria can produce their own food

- some use photosynthesis – get energy from light

- some use chemosynthesis – get energy from

chemicals Heterotroph - (other feeding) – many

bacteria are unable to produce their

own food and are required to eat other things

Bacterial Characteristics: Metabolic diversity continued

obligate aerobe – like us these bacteria need oxygen

obligate anaerobe - these bacteria need to be in an oxygen free environment – human gut

facultative anaerobe – these bacteria can live in either an oxygen or oxygen free environment

Bacterial Structure

Cell WallCell Membrane

Pilus

chromosome

plasmid

flagellum

nucleoid

ribosomecytoplasm

capsule

Bacterial Structure: Cell Wall Made of peptidoglycan – a combination of protein and

polysaccharides Some bacteria called Gram negative bacteria have an

additional layer of membrane that contains lipopolysaccharide

- this extra layer inhibits the uptake of antibiotics – protecting

the bacteria

cellmembrane

cell wall

cellmembrane

Outer membrane

lipopolysaccharide

cell wall

Gram + vs. Gram -

Absorb stain appear purple

Don’t absorb stain appear pink

The type of cell wall is used by doctors to help diagnose disease

The bacteria are stained with aspecial stain called Gram stain

Bacteria without the extra

membrane, appear purple. These are Gram positive (Gram +) bacteriaBacteria with the extra membrane appear pink. These are Gram negative ( Gram -) bacteria

Bacterial Structure continued

Pili – hairlike structures usually found in Gram neg. bacteria. Help the

bacteria stick to surfaces. Also forms conjugation bridge

Chromosome – a single loop of DNA that is folded on itself

- controls the cell’s function Nucleoid – the region of the cytoplasm where the DNA is found Plasmid – an accessory loop of DNA – small contains only a

few genes - can be responsible for: conjugation, antibiotic resistance, unique metabolic properties – like the ability to use hydrocarbons

Capsule – found outside some bacteria stores nutrients and protects the bacteria from changing environmental conditions

Reproduction - Binary Fission

Bacterial cells undergoing binary fission

Reproduction - Binary Fission

Asexual reproduction - offspring are genetically identical to parent – no new genetic combinations - under ideal conditions can occur every 20 min - creates large numbers of bacteria in a short time

Each spot represents a single bacterial cell that reproduced by binary fission to produce millions of genetically identical cells.

Genetically identical, good or bad?

Exchanging Genetic Information Bacterial cells need to be able to exchange

genetic information - creates new genetic combinations which

increases the ability of the bacteria to survive Bacteria have 3 methods for exchanging DNA

-Transduction – viruses carry DNA from one bacterial cell to another

-Transformation – bacteria can absorb “naked” DNA released by dead bacteria from the environment

- Conjugation – two bacteria join at a conjugation bridge, one bacteria passes on a

copy of its plasmid or chromosome

Exchanging Genetic Information

Transduction – DNA is carried from one bacteria to another by a virus

Transformation: Bacteria absorb “naked” DNA from the

environment

Conjugation

Conjugation- one cell passes a copy of its plasmid or chromosome to another

Donor CellRecipient Cell

A special pilus formsa connection calleda conjugation bridgebetween 2 bacterialcells

Plasmid Conjugation bridge

The donor cell copies its plasmidor chromosome andpasses the copy through the conjugation bridge

Cells separate

Bacteria Play Important Roles in Ecosystems Decomposers – recycle dead organisms releasing

their nutrients back to the environment for use by other organisms – SPONCH

Without decomposers,

the elements on earth

would have remained

locked up in dead organisms

and life would have ceased

Bacterial Roles: Nitrogen Fixation

some bacteria contain enzymes which allow them to convert (or fix) nitrogen from the air into a useable form

- they are nitrogen fixing bacteria- Why do living things use nitrogen?

Bacterial Roles: Producers In some ecosystems chemosynthetic and photosynthetic bacteria serve as the basis of the food chain

– chemosynthetic bacteria in deep ocean vents convert hydrogen sulfide (H2S) gas into energy

- cyanobacteria are photosynthetic bacteria

which act as producers in many aquatic ecosystems

Bacterial Roles: Symbiotic BacteriaMany bacteria live in or on other organisms

(including humans) and aid their host

- some live in the gut of herbivores helping to digest cellulose

- bacteria in the gut of humans aid digestion and produce vitamins

- bacteria on skin and in body openings help prevent infection by harmful organisms

Bacterial Roles: Pathogenic Bacteria Pathogens are organisms that cause

disease - only a small portion of bacteria are pathogens- most bacteria diseases are caused by toxins

released by the bacteria - these toxins: - poison cells and damage tissue - interfere with cell signaling - over-stimulate cells causing them to

malfunction

Pathogenic Bacteria: Biofilms

Some bacteria can form a biofilm – a matrix made of polysaccharide

- once formed, the matrix traps other bacteria

- the biofilm protects the bacteria, making it hard to kill them

Antibiotics Antibiotics are chemicals which either kill bacteria

or prevent their growth and reproduction Bacteria and other microbes produce antibiotics

to reduce competition from other organisms Penicillin was the first to be use to fight disease

- discovered accidently by Alexander Fleming in 1928 Two scientists Walter Florey and Ernst Chain

determined how to use penicillin to treat disease in 1939. The discovery of antibiotics revolutionized the treatment of disease

Antibiotic Action Antibiotics effect bacteria, but not eukaryotic cells Antibiotics attack bacteria in 5 ways

- some damage the cell walls or prevent new cell wall from forming

- some damage the cell membrane - some prevent protein synthesis

- some prevent DNA from being copied

- some interfere with bacterial metabolism

Antibiotic Resistance Some bacteria have developed a resistance to the

effect of some antibiotics - the number of resistant bacteria is growing The problem is increased by overuse and misuse

of antibiotics - use of antibiotics to treat viral infections – antibiotics

don’t effect viruses - the use of antibiotics in livestock (cattle, chickens, pigs) antibiotics show up in the meat and milk - people take the antibiotics until they feel better, but stop

before all of the bacteria are destroyed - this kills the most susceptible bacteria, but leaves the

more resistant bacteria

Black Plague-Yersinia pestis

Syphilis--Treponema pallidum/Bacterial

Mycobacterium leprae/Bacteria

Clostridium perfringes/Bacteria

VocabularyMicrobiome Archeaautotroph piliheterotroph nucleoidpeptidoglycan capsule plasmid conjugation bridgeGram - obligate aerobeGram + obligate anaerobebinary fission facultative anaerobeconjugation nitrogen fixing bacteriatransduction cyanobacteriatransformation pathogensbiofilm