Why mutation location matters?

I. http://www.teachersdomain.org/resource/novat10.sci.life.evo.evodevo/

I. Chromosome StuctureA. Strand of DNAB. Histones

1. Grouped in fours2. DNA wraps around these four histones3. Four histones + DNA = nucleosomes

C. 30nm Fiber1. Histone groups link together

D. Looped Domain1. 30nm fibers form loops

E. Chromosome1. Coiling of looped domains.

I. What Is the structure of a virus?A. Inner Structures

1. ds DNA or RNA, ss DNA or RNA2. Usually either a circle or single strand

B. Outer Structures1. Capsid

a) Protein shell surrounding genomeb) Built from multiple proteins called

capsomeres

2. Other Structuresa) Viral envelope - membranous

envelope around capsid to help infect cells1) Derived from host cell membrane

– has host specific proteins2) Also contain specific viral proteins

b) Protein Tail1) Attached to the head2) Example: bacteriophages

II. Virus Reproduction • Host range – types of hosts a

virus can infectA. General Features

1. Bindinga) Viral surface protein

binds to protein surface receptor on outside of the cell

2. Genome Entrya) Can be injectedb) Entire virus can be

taken in by receptor mediated endocytosis

c) Virus may fuse with cell membrane

3. Reproductiona) Virus takes control of cell

1) Uses cell’s own proteins to make new virus proteins

b) Viral proteins spontaneously assembleinto new viruses

4. Releasea) Viruses lyse the cell pouring out into

body orb) Viruses take cell membrane with them

similar to vacuoles coming off ER or golgi body

A. Reproductive Cycle in Detail1. The Lytic Cycle – Death of the host cell

– Virulent phage – phage that only uses lytic cycle

a) Follows the same steps as shown in A.

2. Why have bacteriophages killed off all bacteria?

a) Natural selection favors mutants that have receptors that no longer can be bound by phages

b) Bacteria contain restriction enzymes which cut up foreign DNA1) Bacteria’s DNA is methylated to

protect itself from restriction enzymes

c) Some phages don’t kill host bacteria3. The Lysogenic Cycle

– Phages use both lytic and lysogenic cycles

– Called temperate phages

a) After insertion of viral DNA, the viral DNA is incorporated into bacteria DNA1) Viral protein does the cutting and

insertion of viral DNA into bacterial DNA

2) Called prophage» one gene prevents transcription of

viral DNA1) When bacteria reproduce, viral DNA

is reproduced and passed along to new cells

b) Viral DNA can leave the bacterial DNA and start the lytic cycle1) Occurs in response to an

environmental signal

B. Reproduction of Animal Viruses1. Most have envelope and fuse with cell

membrane to enter cell

2. Retroviruses (HIV)a) RNA virus that carries

reverse transcriptase which makes DNA from RNA

a) Works in cytoplasm to make DS DNA from RNA

b) Integrasea) In nucleus

c) Proteasea) In cytoplasm

Drugs to combat HIV Infection

I. Host Cell EntryA. Fusion Inhbitors

II. Reverse transcriptaseA. Nucleoside inhibitorsB. Non-nucleoside reverse transcriptase

inhibitorsIII. Integrase InhibitorsIV. Protease Inhibitors

C. Evolution of Viruses1. Probably started as DNA in the

environment from damaged cellsa) Plasmids are circular DNA found in

bacteria and yeastb) Transposons – DNA segments that can

move from one location to another2. Somehow evolved protein coat to help get

into cells3. Interestingly, DNA of a virus is more

closely related to host DNA than to a different type of virus.

a) Suggests multiple evolutions

III. Scary StuffA. Viral diseases in Animals

1. Causes of viral symptomsa) Kill or damage cellsb) Cause cells to produce toxinsc) Contain proteins that act as toxins.

2. Why do people recover from some viruses but not others?

a) Can the cells surrounding the infected cells reproduce?

1) Colds- epithelial cells reproduce easily

2) Polio – nerve cells don’t reproduce

3. What is a vaccine?a) A heat-killed or attenuated (modified to

not be disease causing) version of the virus.

b) Vaccine induces an immune response towards the virus

c) This immune response primes the immune system in case it encounters the virus again.

4. Why can’t we cure viral infections?a) There is very little in a virus to target with

a chemical to kill since it uses the cell’s own machinery to replicate.

b) Inside cellsc) Most affected replication of the virus or

try to target reverse transcriptase

B. Emergent Viruses1. New viruses or ones the appear apparently

out of nowherea) AIDSb) Ebolac) SARS

2. Where do they come from?a) Mutations of new virusesb) Spread from small populations (gay men

and HIV)c) Spread from animals

1) When an animal is exposed to multiple viruses, they can recombine making novel viruses that can infect humans.

3. Why are they bad?a) We have no immunity to them since we

have never been exposed to them before1) epidemics2) Pandemics

b) Ease of travel makes the virus’ ability to spread easier….infect more people quicker.

C. Viral diseases in Plants1. Significant economic effect2. Types of transmission

a) Horizontal – enters plant through physical damage already present

b) Vertical – inherits disease from parents3. Spread via plasmodesmata

C. Viroids and Prions1. Viroids

a) Small circular RNA molecules that infect plants1) Only a few 100 nucleotides long2) Do not encode proteins but replicate

using host proteins3) Cause errors in regulatory systems

that control plant growth

1. Prionsa) Short infectious proteins

1) Cause mad cow disease and other brain diseases

b) Most likely transmitted in foodc) Problems

1) Prions act slowly» incubation periods of

years» Means identification of disease doesn’t

occur for a long time…more time to infect

2) Seem to be indestructible» Not destroyed or deactivate by heating » ie. cooking

d) How do prions replicate?a) Appear to come from normal

proteinsb) When a mutated/misfolded protein

gets into the cell it causes the normal proteins to be misfolded

c) Somehow this group of misfolded proteins get together which cause other proteins to misform.