Biology

Review sheet 2nd Exam

I.) Prokaryotes

A. Characteristics of prokaryotes

1. Shape of prokaryotes  

   - Spheres (Cocci)

   - Spherical (Helices)

   -  Rods (Bacilli)

2.) The cell

   - Very small

   -  One circular chromosome located in a region called nucleoid

   - Some species have a smaller ring of DNA called plasmid – confer antibiotic resistance

  - Cell wall – protects the plasma membrane and helps resist it from rupturting

  - Flagella – allows for movement

- Pili- proteins that helps cells adhere to a surface or facilitate conjuction

Capsule – slime layer made of polysaccharide that can surround the wall

Plasmid- DNA molecule that carries accessory genes separate from those of a bacterial chromosome.

 **Antibiotic resistance in bacteria in relation to plasmids are drugs, which contain killer components for bacteria but the bacteria are able to penetrate and survive**

3.) Gram stain

- Stain in which tests to see if peptidoglycan is present

- Eubacterial cell wall includes peptidoglycan

- if positive (purple, thick cell wall and consist primarily of peptidoglycan

- if negative (pink, cell wall has 2 layers, a thin peptidoglycan layer and thick outer membrane)

Peptidoglycan - TYPE OF polymer in bacterial cell walls consisting of modified sugars cross linked by short polypeptides

B. Bacterial growth and reproduction

  1. Nature of bacterial growth

  - Counted by number (division) some less than 20 mn

  - Bacteria grows exponentially,  1 bacteria could be 2 million in a few hours

  - Divide by bacterial fission – cell mechanism used only by bacteria , involves replication of single bacterial chromosome and division of a parent cell into two genetically equivalent daughter cells

Budding- cell develops a bulge or bud that enlarges and eventually separates from the mother cell

Fragmentation – wall develops within the cell, which then separates into several new cells

Conjuction – plasmids are transmitted to daughter cells and may be transferred to the cells of the same species or different species

Transduction- virus carries bacterial gene from one bacterial cell to another (virus gets inside)

Transformation- cell can absorb and integrate fragments of DNA from their environment (allows genetic transfer between prokaryotes even across species lines)

Archaebacteria

• Live in extreme environments (no peptidoglycan)
• Methanogens (anaerobiv strict, use H2 as a source of energy) Ex: Methanobacterium
• Halophiles (salt lakes, use animal hides, spoil salted fish, make ATP by aerobiv pathway or photosynthesis) Ex: Halobacterium
• Thermaoacidophiles : hot water and highly acidic, use H2S as electron donor to make ATP. Ex: Thermoplasma

Eubacteria

• Have peptidoglycan in the cell wall
• Gram negative – Proteobacteria (enterobacteria – E.Coli, Salmonella)
• Vibrio- Cholera
• Chlamydias
• Spirochetes
• Cyanobacteria

Gram Positive

• actinomycetes
• lactic acid bacteria
• streptococci
• stahyloccocci
• clostridia

Photoautotrophs – use sunlight and CO2 during photosynthesis Ex: cyanobacteria

Photoheterotrophs- sunlight, energy, and organic compounds as source of common Ex: Rhodospirilum

Chemoautotrophs- use CO2 (not sunlight) obtain energy by stripping electrons from organic or inorganic substances Ex: nitrobacter

Chemoheterotrophs- most common, either parasites (draw carbon and energy from living hosts) or saprobes (feed on organic products, wastes or remains of other organisms , most bacteria fall under this category Ex: E.coli, lactobacillus

Viruses

Characteristis of Viruses

• Non-living
• No cellular agents that infect particular species of nearly all organisms

Each virus particle consist of :

1. core of DNA or RNA
2. protein coat tha sometimes in enclosed in a lipid envelope
3. many glycoprotein spikes project from these envelopes
4. coats of complete viruses have sheaths, tail fibers and other accessory structures

Virus Multiplication

• Cannot reproduce on its own
• Genetic material must enter a host cell and direct the cellular machinery to synthesize the materials necessary to produce new virus particles

1. Attachment to a suitable host cell
2. Penetration of it
3. DNA replication and protein synthesis
4. Assembly of new VIRAL particles
5. Release

Lytic infection: multiplication is rapid and new viral particles are released by lysis.  Ex: will attach to a genome and then as a result you will get sick

Lysogenic infection: infection enters a latent period. The host cell is not killed at first and then the viral nucleic acid can undergo genetic recombination with a host cell chromosome, attaches to a genome and stays there forever.  Stress can cause this to be lethal