bio111 unit 4

parts of a virus

obligate intracellular parasite

1. contains genetic material (DNA/RNA)

2. protein capsid

Sometimes: envelope (remnants of infected cell plasma membrane)

influenza

genetic material: RNA

spike proteins

• bind to receptors and influence function

Influenza A H spikes

bind to receptors on host cell

Influenza A: N spikes

• penetrating host is easier

• break down immune system (mucous membrane in respiratory tract)

• makes us sick

how are viruses named

1. host (if not human)

2. type (a or b)

3. strain (H/N spikes

4. year of isolation

why are viruses not alive

• cannot process own energy without host

• rely on host cells to make copies of genes

• do have own ribosomes

how do virus infect cells

• protein spikes specialized

• infect particular cell types

• bind to surface proteins → virus entry

virus life cycle

1. attachment (bind to host cell w H spikes)

2. penetration (get genetic material in)

3. biosynthesis

4. maturation

5. release (cell burst→more virus)

lytic cycle

• IMMEDIATELY begins biosynthesis/replication

• host cell broken apart → new virus released

• ex: influenza, common cold

lysogenic cycle

• integrate virus DNA into host DNA

• s phase: replicate virus DNA

• sickness occurs after initial infection

• ex: HIV

RNA virus

• usually lytic

• use RNA polymerase from host & ribosomes

  • make own proteins

• makes capsid, Hspikes, Nspikes

retrovirus

• usually lysogenic

• revert RNA to DNA

  • reverse transcriptase

• HIV

influenza infection

• respiratory epithelial cells

• lytic → inflammation

• symptoms caused by body’s immune response

• release cytokines → warning chemicals

influenza symptoms

body heat up (fever) → virus can’t survive

• cough, chills, aches, less appetite

• “stomach flu” is bacteria

outbreak

movement of disease btwn distinct populations

epidemic

number of indivs affected exceeds previous year #s

pandemic

global population influenced

evolution

change in allele frequencies over time

observations that Charles Darwin made on HMS Beagle

• island species resembled mainland nearby species

• extant species strong resemblance to extinct fossils species

theory of evolution by natural selection

• only those adapted to environment reproduce

• species adapts to environment over time

darwin’s postulates

requirements for natural selection to lead to evolution

1. variation in a trait

2. trait must be heritable from parent → offspring

3. trait mulst lead to fitness/reproductive success

directional selection

one extreme trait has higher fitness

ex: farmer only choose big breast turkeys

stabilizing selection

intermediate genotypes have higher fitness

ex: baby birth weight

disruptive selection

both extreme traits→ higher fitness

• intermediate has lower fitness

ex: medium fish

mutations

change in DNA sequence → new alleles

• mutations that increase fitness will spread thru pop over time

• evolution

major pieces of evidence for evolution

1. physical record of fossils

2. comparing anatomy and embryology (homologous structures)

3. molecular bio (DNA similarities)

4. lab and field experiments (multigen)

hox genes

• tell body where to put certain body parts

• high conserved between species (all vertebrates have head, torso, and limbs in roughly same spots)

convergent evolution

different ancestor, same traits bc same environment

• analogous structures

divergent evolution

same ancestor/bone structure, different functions in different environments

antigens

spikes on virus capsid notify body of pathogen

identify → body knows how to fight virus

antigenic drift

small change in RNA sequence

• different proteins

• harder for immune system to recognize

antigenic shift

two viruses come together

• new strain

• body can be immune to one but not other

immune system

fights foreign pathogens

major immune system organs

• lymph nodes

• red bone marrow

• spleen

• thymus

lymph nodes

transport things that can’t go through blood (fat soluble)

• filter pathogen

red bone marrow

produces white and red blood cells

spleen

filters blood

thymus

where T-cells grow

how does immune system recognize our cells

MHC glycoprotein tag

natural killer cells

kills cells that dont have MHC tag

innate immune system

• fast acting, no prior exposure needed

• not disease specific

what does innate immune system cause

inflammation

• white blood cells sent to kill pathogens

• clotting factors close wound

innate immunity types

1. physical barriers (skin, mucous membranes, stomach acid)

2. cytokines (chem signal to trigger other immune cells to fight) ex: histomine

3. phagocytes (engulf and kill pathogens)

inflammatory response steps

1. damage tissue → histamine to increase blood flow and WBC

2. macrophages identify and destroy pathogens

3. neutrophils clean up area

4. clotting factors close wounds

adaptive immune system

• response not as bad 2nd time

• memory of pathogen → swift response

adaptive immune response step 1

exposure to pathogen

• WBC kill pathogens

• takes part of antigen to T-cells

adaptive immune response step 2

T cells in THYMUS

• cytotoxic t cells: kill cells infected

• helper t cells: Take antigens to lymph nodes to B-cells

B cells

mature in BONE marrow

• produce antiBodies

• target specific pathogens

• release antibodies in blood

adaptive immune response step 3

immunity

• B cells share antibodies

• target pathogens and infected cells

adaptive immune response step 4

memory

• B-cells and T-cells become memory celsl

• b cells continue to produce anti bodies

vaccine

inject with portion of virus and antigens

• body creates memory cells

how do vaccines work at the population level

vaccines protect susceptible people

• high vaccination → not enough potential hosts

• herd immunity