AP Bio Ch 10The Genetics of Bacteria & Viruses

Easy Hines!

Bacteria, Baby!•Short gen span facilitates their evolutionary adaptation to changing env.•Div every 20 min•Most clones except mutations•Genetic recombination adds diversity

Bacteria Genome• 1 double stranded, circular DNA• Nucleoid – dense region of DNA • Plasmids – smaller circles of DNA with only a few

to several dozen genes. Not req. for survival. Can replicate indepdently

How do they accomplish genetic recombination?

Recombination – the combining of DNA from 2 individuals into the genome of a single individual.

3 ways this is accomplished:• Transformation • Transduction• Conjugation

Transformation• The alteration of a bacterial cell’s genotype by the uptake

of naked foreign DNA from the surrounding env.– How?

• Surface proteins• Closely related species• No surface proteins – then increase Ca levels to

stimulate uptake

http://www.sinauer.com/cooper/4e/animations0402.html

TransductionDNA transfer process where phages carry

bacterial genes from 1 host to another.• How?

–Random pieces of host chromosome are packaged within phage capsid. Host DNA gets injected into next bacterial cell the virus infects.

http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html

http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html

Generalized animation

Specialized animation

ConjugationThe direct transfer of genetic material between 2 bacterial cells that are temporarily joined.• “bacterial sex”• 1 way transfer• Transfer through sex pili• Ability to produce sex pili comes from F plasmid

(fertility). Can replicate on its own – sep. from chromosome.

• Accepting bacterium is now able to produce sex pili• http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/ani

mation_quiz_3.html• http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/ani

mation_quiz_4.html

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

Another diagram of conjugation:

R Plasmids• Contain genes coding for resistance to specific

antibiotics.• Can transfer by conjugation.

More & more bacteria are becoming resistant to antibiotics… How?

Antibiotics attack and kill off bacteria without the mutation...

The mutated ones survive after the antibiotics are gone...

...and reproduce, passing along the mutation to their offspring...

Eventually there are more antibiotic-resistant bacteria than non-resistant.

Other mutations have helped microbes adapt to all sorts of environments from salty to icy to extremely hot and live off everything from decaying leaves to sunlight to bubbling sulfur.

Transposons• Pieces of DNA that can move from 1

location to another in a cell’s genome. “jumping genes”

• Some R plasmids carry 10 genes for resistance b/c of transposons

Review of the 3 ways bacteria undergo recombination:

Virus – nonliving infectious particle

• All they do is reproduce

• Requires host cell

• Named by…

Papillomavirus cause benign skin tumours

(warts).

Adenoviruses cause respiratory illness or conjunctivitis (so-called "pink eye“).

Herpes viruses have an envelope surrounding a

capsid.

Ebola

1st Virus Discovered• Tobacco Mosaic Virus• Stanley – 1935• So small…slipped through filters

Virus Structure

• Contains 2 main parts:1. Capsid – protein coat

• Can be different shapes2. Nucleic acid

• Can be DNA or RNA (retrovirus)

Bacteriphage• infects bacteria• Aka phage• Most complex capsids

Size?• Smallest – 20 nanometers• 1 nanometer is one-billionth of a meter

(a water molecule is less than 1 nm)

• http://www.cellsalive.com/howbig.htm

Host Range• Limited range of cells each virus can

infect– Lock & key– 1 species – many (change can occur

through mutation)– Some tissue specific

• Cold viruses, HIV

How do viruses get into host cells?attach to the cell membrane surface.

– Molecules on the viral capsid or envelope must bond to receptor molecules on the host cell surface.

– Enter cell

Viral Replication• make more

capsid proteins & nucleic acids.– Use host cell

ribosomes to make capsid proteins based on the viral genes

– Use host cell enzymes & nucleic acids to make more DNA or RNA

Can you think of any way viruses could be used in the medical field, now that

you know how they replicate?1. ________________2. ________________

Viral Replication2 main cycles• _______cycle – virus begins replicating as

soon as it enters cell; killing cells______________. Aka virulent

• _____________ cycle – viral genome integrates with host cell genome, spreading to new cells each time the host cell _________. Eventually viral genome comes out of hiding and begins active ___________, killing the cells.

Lytic Cycle

How do bacteria defend against viruses?

• Restriction nucleases, aka restriction enzymes

• “_____ up” viral DNA

Lysogenic Cycle

Lysogenic Cycle• Viral genome

spreads to many cells without killing them. Ex: HIV, Herpes

• Aka temperate• Provirus – the viral

genome as it “_____ ____” in a eukaryotic host cell genome.

• Prophage – the viral genome as it “hides out” in _________

RetrovirusesGenome is RNA• Use RNA

transcriptase –

• Ex: HIV

Why so hard to develop vaccines against retroviruses? Why must new flu vaccine be produced each year?

• http://www.whfreeman.com/kuby/content/anm/kb03an01.htm

• The above is HIV life cycle animation

Viral Envelopes

• Bind & fuse w/ host____ ________

• Composed of host cell mem obtained when exiting cell by way of _________– taking cell mem with them.

Viral Diseases in Animals• Cause symptoms by causing

– lysosomes to release _________– Production of ________– Damage depends on tissue type destroyed– Ex: colds vs polio

• Vaccines – weakened viruses or particles of the virus that stimulate _______ _______to defend against pathogen.– 1st – ________ – late 1700 – Edward Jenner

• Brittish, 1796 he carried out his now famous experiment on eight-year-old James Phipps. Jenner inserted pus taken from a cowpox pustule on the hand of milkmaid Sarah Nelmes and inserted it into an incision on the boy's arm. He was testing his theory, drawn from the folklore of the countryside, that milkmaids who suffered the mild disease of cowpox never contracted smallpox.

Edward Jenner

• The immediate reaction to Jenner's work was ridicule. Critics, especially the clergy, claimed it was repulsive and ungodly to inoculate someone with material from a diseased animal. A satirical cartoon of 1802 showed people who had been vaccinated sprouting cow's heads. However the obvious advantages of vaccination and the protection it provided won out, and vaccination soon became widespread.

• Jenner subsequently proved that having been inoculated with cowpox Phipps was now immune to smallpox. He submitted a paper to the Royal Society in 1797 describing his experiment but was told that his ideas were too revolutionary and that he needed more proof. Undaunted, Jenner experimented on several other children, including his own 11-month-old son. In 1798 the results were finally published and Jenner coined the word vaccine from the Latin vacca for cow, and called the process vaccination.

original manuscript of Jenner’s is in the library of the Royal College of Surgeons.

Cures• None – nothing really to attack

Emerging Viruses• Mutation of existing – esp RNA

– Ex: flu• Spread of existing to new hosts

– Ex: hantavirus to humans• Spread from small isolated pops

– Ex: HIV

Plant Viruses• Serious agricultural pests

– Most rod RNA– 2 routes of infection

• Horizontal transmission (insects, pruning sheers)• Vertical – asexual reproduction or

– Spread through plant by _____________– No cures

Viroids• Tiny molecules of circular ___ that infect

plants

Prions• Infectious __________

– Ex: Mad Cow, Creutzfeldt-Jacob

Originate?• Came after cells?• Fragments of nuc acids that jump from cell

to cell