white dirty shoes on

Early evidence of viruses

Mayer found disease transmitted from rubbing sap of sick plants onto healthy ones, Ivanowsky showed this sap still caused disease even after passing through filter

Why are viruses difficult to study

-extremely small
-lack structures / metabolic system found in cells
-Cant grow without host ( no petri dish test)
-No tools to visualize until 1940s

How did Stanley contribute to knowledge of viruses

Crystallized tobacco mosaic virus, proving that viruses could behave like chemical molecules, not cells

What did Stanley’s crystallization of TMV reveal

No living cell can form crystal, only molecules can, revealed viruses were noncellular, simple in structure, capable of retaining infectivity even when crystalized

four forms of viral genomes

dsDNA
ssDNA
dsRNA
ssRNA

What is a capsid

protein shell that protects viral genome

What are capsomeres

protein subunits that assemble to form capsid

What are the different shapes of capsids

Helical
Icosahedral
Complex

Phospholipid bilayer

outer membrane surrounding capsid, derived from host cell

Host membrane proteins

provides envelope basic membrane structure, derived from host cell

Viral glycoproteins

proteins encoded by viral genome and inserted into host derived membrane before viral budding, allows virus to bind to specific receptors, derived from virus

What is the role of an envelope in animal viruses?

Bind to receptors using viral glycoproteins (spikes)
Fuse viral membrane with host cell membrane
Deliver capsid and genome into cytoplasm

Structure circled in red

Head / Capsid

Structure circled in red

Tail sheath

Structure circled in red

Tail fibers

Structure circled in red

Genome / Dna

What type of virus

Bacteriophage, specifically t-even phage (t2 t4 t6)

What does bacteriophage mean?

Bacteria Eater

What is it’s host

Bacteria

Is the genome of this virus DNA or RNA

dsDNA

What property of a virus determines its attachment to a host cell membrane?

Attachment proteins must match specific receptor molecules on host cell surface

Obligate intracellular parasites meaning

Must infect and live inside host cell to replicate

What is a host range

range off organisms a virus is capable of infection

broad host range vs limited host range

broad can infect multiple species whereas narrow host range can only infect one species

broad host range example

rabies / influenza

limited host range example

HIV

host range of rabies vs host range of human cold virus

rabies is more broad, infects many mammal species
hcv is more narrow, infects only humans

what components of a host cell does virus use to reproduce itself

enzymes ribosomes nucleotides amino acids atp and membranes

How does a DNA virus reproduce its genome

-Capsid delivers viral DNA into host nucleus
-Viral DNA acts as a template, host enzymes (pol, hel, prim) replicate the viral genome
-Copies of viral DNA are produced

How does a RNA virus reproduce its genome

-Viral genome enters host cell
_Viral RdRp makes new RNA genomes and mRNA for protein synthesis
-new viral proteins + new genomes = self assembly

Process circled in red

Self assembly, capsid proteins assemble around genomes to form complete viral particles

Process circled in red

Transcription, genome is used as template to make mRNA

Process circled in red

Replication, Viral genome is replicated to produce many copies for packing into new virions. DNA viruses use host DNA pol

Process circled in red

infection, virus binds to host cell receptors and enters cell.

What are bacteriophages?

Viruses that infect bacteria

Distinguish between virulent and temperate phages.

Virulent phages reproduce only by lytic cycle, killing host cell
Temperate phages use either lytic or lysogenic cycle, allowing DNA to integrate in host genome and remain dormant

What portion of a phage enters the host cell?

only the viral genome enters, usually dsDNA

how does a phage enter bacteria

tail fibers recognize specific receptors on bacterial cell wall, tail sheath contracts like a spring loaded syringe, contraction forces tail tube through bacterial envelope, viral genome is injected

what are restriction enzymes, what is there role in bacteria

bacterial enzymes that cut dna at specific sequences, protect bacteria by cutting foreign DNA.

Why don’t restriction enzymes destroy the DNA of the bacterial cells that produce them?

Bacteria methylates their own DNA at restriction enzyme recognition sites, methylation blocks enzyme from cutting so only foreign DNA gets destroyed

What are three ways bacteria may win the battle against the phages

-mutating surface receptors so phages cant attach
-restriction enzymes cutting injected phage DNA
-CRISPR can recognize phage DNA

What is a prophage?

phage DNA that has been integrated into bacterial chromosome during lysogenic cycle and is copied along with host DNA

What might trigger the switchover from lysogenic to lytic mode

when a host is in danger, prophage bails out and activates lytic cycle

Structure circled in red

Phage DNA

Which cycle?

Lycitic

What structure

Prophage,

Which cycle

Lysogenic

How does the lytic cycle work

-attaches to bacterial surface receptor
-injects phage DNA
-viral DNA shuts down host cell machinery
-host ribosomes synthesize viral proteins and replicate viral genome
-self assembly assembles capsids into new phage genomes
-lysis, host cell membrane wall breaks open releasing many new phages.

How does the lysogenic cycle work

-attaches to bacterial surface receptor
-injects phage DNA
-Viral DNA integrates into bacterial chromosome, becoming a prophage
-Every time bacterium divides, prophage is copied
-No phages are produced, virus is dormant

Two elements that nearly all animal viruses have

Envelope/outer membrane and glycoproteins

What is a retrovirus

RNA virus that uses reverse transcriptase to convert RNA to DNA

structure circled in red

HIV envelope

structure circled in red

HIV capsid

structure circled in red

RNA

structure circled in red

reverse transcriptase

prophage vs provirus

prophage is a DNA integrated into bacterial chromosome
provirus is a viral DNA integrated into eukaryotic host chromosome

how does HIV work

HIV enters a helper T cell by fusing its envelope with the plasma membrane,

reverse-transcribes its RNA genome into DNA, integrates that DNA as a provirus into the host chromosome, uses the host to transcribe and translate viral RNA and proteins, assembles new virions, and buds from the cell with a host-derived envelope studded with viral glycoproteins

plasmids

small circular dsDNA molecules that replicate independently of main chromosome

Transposons

Segments of DNA that can move from one location to another within a cell genome (jumping gene)

Why do we recover completely from a cold but not from polio?

cold virus infects surface cells of upper respiratory tract, those cells divide and are easily replaced
polio infects and destroys motor neurons in spinal cord, cns neurons don’t regenerate

What tools are in the medical arsenal against human viral diseases?

vaccines train immune system
antiviral drugs stop steps in replication

public health- sanitation condoms masks

Emerging viruses such as HIV, Ebola, and SARS seem to burst upon the human scene. What

are three processes that contribute to this sudden emergence

-high mutation rates = more transmissible
-spread=travel lets viruses transmit easy
-transmission from animal to human

The current flu pandemic is H1N1. What does this name mean?

h1=hemagglutinin, helps attach virus to host cell
n1=neuraminidase, helps virus exit infected cell

horizontal transmission in plants

virus comes from outside plant (nearby infected plant, soil, sap)

Vertical transmission in plants

virus is inherited from parent

two ways viruses spread throughout plant bodies?

-Cell to cell through plasmodesmata

-systemic spread through vascular system,

What is a viroid? What important lesson do they teach?

Short circular ssRNA

highlights how RNA alone can be an infectious agent

Viroid disease example

potato spindle tuber viroid

what are prions

infectious misfolded protein that contains no DNA or RNA

how are prions transmitted

eating infected nervous tissue, contaminated surgical instruments, inherited

what do prions do

convert normal brain proteins into misfolded prion form, causing brain damage.

four diseases caused by prions

scrapie
mad cow disease
CJD
Kuru

Two alarming characteristics of prions

slow acting but always fatal
virtually indestructible

stage 1 origin of life

abiotic synthesis of small organic molecules
-simple molecules (amino acid nucleotide sugar) forms from lightning uv radiation volcanic activity

stage 2 origin of life

small organic molecules link together to form polymers such as proteins, rna, polysaccharides

stage 3 of life

Polymers become enclosed in lipid membranes or vesicles, forming protocells capable of maintaining internal environment

stage 4 origin of life

rna molecules can self replicate, allowing inheritance and evolution

what gas was missing from early earth mix

oxygen, earth had no plants to photosynthesize

how old is earth

4.6 bil years

oldest evidence of life

microorganism fossils 3.5 bil years ago

Oparin and Haldane hypothesized that early atmosphere was a reducing environment. What did they suggest as a source of energy for early organic synthesis

Lightning and UV radiation

Identify process circled in red

Sparks to mimic lightning

Identify process circled in red

Water to mimic sea

Identify process circled in red

atmosphere containing mixture of h2 ch4 nh to mimic early earth atmosphere

identify process circled in red

condenser, cooled atmosphere = raining water, dissolved molecules go into flask

What was collected

organic molecules that are common in organisms

what are the two processes circled

heating and sparking to provide energy

what would happen if o2 was introduced

oxygen would oxidize and break down organic molecules before they can accumalate

List all molecules that appeared in the sample collection of Miller-Urey experiment

amino acids
simple organic acids

hydrocarbons

small organic molecules (aldehydes + hydrogen cyanide)

what did miller-urey experiment reveal

organic molecules can form spontaneously from inorganic molecules under conditions that simulate early earth

what was concluded from results of miller-urey

simple inorganic molecules can be converted into biologically important organic molecules in a reducing atmosphere

what does the miller-urey results imply about origins of life

life may have begun through natural and chemical processes on early earth

What other hypotheses explain abiotic organic synthesis besides Miller–Urey?

Volcanic atmosphere, hydrothermal vents, and meteorite delivery.

what are protocells

abiotically formed membrane bound droplets containing organic molecules and show properties of living cells.

what properties of life to protocells demonstrate

growth, reproduction, metabolism, selective permeability, compartmentalization (membrane boundary separating inside / outside environment)

What was most likely the first genetic material, DNA or RNA, why

RNA, rna can catalyze chemical reactions including making copies of itself, dna needs enzymes proteins etc to copy.

what are ribozymes

rna molecules that act like enzymes

Explain the evidence for an early “RNA world.

rna contains nucleotide sequences just like dna

how do tectonic plates move

heat from earth interior raises mantle, dragging plates above them

What continent / era

Pangea in the Paleozoic era