Lecture 23 - Viruses and Prokaryotes

infectious particle w/gene packed in protein coat - not living … “borrowed life”

Must infect host cell to reproduce and carry out metabolic activities

Viruses

• double stranded dna

• Single stranded dna

• Double strand RNA

• Single stranded rna

Single linear or circular molecule

Genome of viruses

Capsid

Protein shell enclosing viral genome… made up of capsomeres. # of different kinds of proteins is small, but duplicate number may be high

Membranous envelope - viral envelopes

Surrounds flu virus… derived from membrane of host cell… made up of phospholipids and glycoproteins from host and from viral origin

Bacteriophages / phage

Virus that infect bacteria… most complex capsids, may have protein tailpiece to attach to host and injects viral dna

Obligate intracellular parasites

Can only replicate within host… lack enzymes, ribosomes, etc.

Host range

The number of host cells a virus can infect

Recognition system determines what cells a virus can infect… proteins match up on outside of virus and receptor molecule on hosts surface

Specific host recognized by “lock and key”

West Nile can effect multiple types organisms, birds horses humans and mosquitos.

Measles can only effect humans

Human cold virus infects all cells in upper respiratory track

AIDS only binds to certain white blood cells

Viruses have a range to infect several species,while others only infect a single species

"T - even “ use tail to inject DNA

Others taken up by endocytosis ov fusion of viral envelope w/ plasma membrane of hosts

Ways viruses share DNA with host cell

Once inside… reprogram cell to produce viral dna and proteins

Host provides materials and atp

Dna viruses use dna polymerase

RNA virus use rna polymerase

nuclei acid and capsomeres self-assemble into viral particles

Exits cell, resulting in Cellular damage which results in symptoms of infection

Lytic cycle or lysogenic cycle

double stranded dna viruses replicate by two alternative mechanisms

The phage replicative cycle culminates in death of host… bacterium lyses and releases phases

Virulent phages - replicate only by this cycle

Lytic cycle is…

1. Natural selection favors mutations where receptor site can no longer be recognized by phages

2. Restriction enzymes will cut up foreign dna

3. Methylation of its own dna prevents destruction

Bacteria have defenses against phages… (3)

Instead of losing cell, places can coexist w/ host - this state is ____

What is lysogeny?

During a lysogenic cycle, Viral dna is added into the bacteria’s chromosome, this segment within the bacteria dna is called ________

Viral proteins can break circular dna and join together

Single infected cell can result in population of bacteria with the virus in the dna

Prophage?

Can resist high salt concentration, found in great salt lake

Halobacteria

• increased radiation

• acidic pH

• salt concentration

• Under ground

Prokaryotes adapt to harsh conditions like…

Prokaryotes

Most abundant and diverse group of organisms on the planet

• no membrane bound nucleus… nucleoid region. looped chromosome

• Cell wall

• No membrane bound organelles

• Have fimbriae and pili for attaching and anchoring

• Flagella for motility (analogous to eukaryotic flagellum)

Characteristics of Prokaryotes (5)

Prokaryotes

First organisms to live on Earth and are typically unicellular

Common shapes: bacilli, cocci, and spirals

• cell wall protects cell from hypotonic environment

Capsule if dense or slime layer if poorly organized

1. protects against dehydration

2. increases resistance to host defenses

Secrete sticky protective layer of polysaccharide or protein… allow cells to adhere to substrate or other individuals. Name 2 benefits.

1. are small

2. reproduce by binary fission (asexual)

3. short generation times

3 key features in prokaryotes for reproduction

Increased chances for mutations… they adapt rapidly to environmental changes as natural selection favors those that are of greater fitness

Benefit of having a short generation time and large population…

Photoautotrophs

Examples: cyanobacteria, plants and algae

Photosynthetic organisms that use light to drive synthesis of organic compounds from CO2.

Chemoautotrophs - unique to prokaryotes

Need inorganic molecules like CO2 for carbon source, but get energy from oxidizing inorganic substances (like H2S, NH3, Fe2+)

Photoheterotrophs

Ex: few marine and halophilic prokaryotes

Use light to generate ATP but get carbon from organic form

Chemoheterotrophs

Ex: prokaryotes, protists, fungi, and animals

Humans

Consume organic molecules for both energy and carbon

Obligate aerobes

Require O2 for cellular respiration

Facultative anaerobes

Use O2 if it is present, but can also grow by fermentation in anaerobic environment

Obligate anaerobe

Die by O2, use either fermentation or anaerobic respiration (inorganic molecules other than O2 accepts electrons from ETC)

Nitrogen-fixing Prokaryotes

*Most self-sufficient

Convert N2 to NH3, can incorporate it into organic molecules

Result is large portions of the genome in many prokaryotes are actually a mosaic of genes and imported from other species.

Horizontal gene transfer in the evolution of prokaryotes

Extremophiles

Live in extreme environments - archaea species

Extreme halophiles

Live Salty places

extreme thermophiles

Live in hot environments

Methanogens — strict anaerobes

Obtain energy by using CO2 to oxidize H2, producing methane as waste

Gram -

Subgroups:

1. Proteobacteria

2. Chamydias

3. Spirochetes

4. Cyanobacteria

Pathogenic species deadlier than gram +… 4 subgroups

Decomposers

Chemoheterotrophic prokaryotes act like ____, by breaking down dead organisms and waste products = C, N, and other elements

Symbiosis

Ecological relationship between organisms that are in direct contact.

Host

Larger organism in a symbiotic relationship

Symbiont

Smaller organisms in a symbiotic relationship

Parasitism

A symbiotic organism that benefits at expense of host - parasite

Parasite

Eats cell contents, tissues, or body fluids of hostPa

Pathogens

Parasite diseases, _____ are prokaryotic M

Mutualism

Both symbiotic organisms benefit

Bioremediation

Use of organisms to remove pollutants from air, water, and soil

• anaerobic bacteria decompose organic matter in sewage for landfill or fertilizer

Vitamins, antibiotics, hormones, and many other products

Through genetic engineering, humans have developed prokaryotes that can produce…

1/2

Prokaryotes cause what percentage of human diseases?

Exotoxins

Proteins released by certain bacteria that can produce disease

Endotoxins

Lipopolysaccharide components of outer membrane of some gram - bacteria

released when bacteria dies and cell wall breaks