Bio Chapter 18

7/30/2019 Bio Chapter 18

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c Chapter 18

Virus- Discovered in the 1800s with the tobacco mosaic virus, the virus was destroying the

crop, a scientist of the time isolated it ands sprayed other plants with the virus, he named the

thing invisible death because the plants were still dying despite not being able to see what was

causing the problem.

Viruss are extremely small, much smaller than what is detectable through light microscopes.

Viral Genomes- Viruses contain genomes with double stranded/single stranded DNA and

double/single stranded RNA. The smallest viruses may only have 4 genes but the largest ones

can have several hundred.

Capsid- The protein shell that encloses the viral genome is called a capsid. Capsids are built

from a large number of proteins called capsomeres and they are found in the animal cells with

viral envelopes around their capsid. The capsid is usually found in a geometric shape

Reproduction

Viruses need a host cell. They are not living thus viruses need help to reproduce.

The host range are the different type of cells similar to the host that a virus can effect.

Viruses make extensive uses of enzymes like DNA polymerase.

Phages go through two cycles the Lytic Cycle and the Lysogenic Cycle

In the Lytic cycle viruses inject their genetic material into the host cell and the

host cell takes the genetic material and it replaces the original genetic material.

The cell becomes a virus factory.

The lysogenic cycle is much more devastating, the virus incorporates its DNA

with the hosts and reproduces with the host, not until there is an environmental

change and all of the viruses that reproduced with the host cell all burst out at

once.

In animals the Viruses use exocytosis to get their viral envelopes, some haveenvelopes some dont.

Types ssRNA viruses

RNA is mRNA- goes straight to ribosomes

Or the RNA can act as template for other RNA

Retroviruses come with coding for an enzyme called reverse transcriptase, goes

from RNA to DNA then back to RNA. RNA viruses are made quicker, provides

incorporates into DNA and can hide in the cell.

Causes of Animal Viral Diseases

VIruses release hydrolytic enzymes killing the cell and its lysosomes

Viruses can cause certain cells to release toxins.

Prevention of Animal Viral Diseases- When theres a cold virus killing cells in the

respiratory lining, theses cells have the ability to regenerate quickly with too much

damage being done to the organism.

Sources of emerging viruses can be mutations from other viruses, an isolated population

introduces it into another population or the virus can make a jump between species.

Viruses and Cancer


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Viruses can insert DNA in front of proto-oncogenes to stimulate the cell cycle,

these oncogenes can cause cancer. Although this is a risk with all viruses it is

more common in specific types of virus

Plant Viruses are usually RNA viruses, these are cylindrical capsid that can be

transmitted from an external sources or passed down from a parent, Horizontal/Verticle

Viroids and Prions- Viroids are naked pieces of circular RNA that infect plants, prionsare mutated proteins that infects the traits of other proteins.

Evolution of Viruses- Cells came first then viruses because viruses need cells to exist.

Also the Gnome of a particular virus resembles host cell more than any other virus type.

Bacteria

Bacterial Genome (Nucleoid, plasmid, episome)- nucleoid contains bacterial DNA in a

region of the prokaryote. Plasmids under normal conditions are not necessary but can

be useful under stressful conditions. Episomes are genetic material that can exist on its

own or can exist as part of the chromosome can be considered an episome.

Binary Fission- Bacteria always can undergo Binary Fission despite other types of

genetic recombination.

Genetic Recombination- combining the DNA from one bacteria to another, is good for

evolution and is possible despite bacteria being asexual.

Transformation- Bacteria picks up DNA from the environment, Some bacteria have

proteins that look for DNA

Transduction

Generalized transduction- When a bacteriophage transfers a piece of DNA from one

bacterium to another. A mistake is made with the bacteriophage and it transfers DNA

from another bacteria to another allowing for genetic recombination.

Specialized Transduction- Prophage takes DNA and adds DNA to new bacteria but goes

through the lysogenic cycle, R plasmids- contain genes for antibiotic resistances.

Conjugation (pili, f factor, plasmid, episome, f plasmid, HFr, R plasmids)

If F factor is present two bacteria form a cytoplasmic bridge, in order to transfer genetic

material from on bacteria to another. If a bacteria has F+ factor then they can send a

bridge F- factor means they can't send a bridge. The F plasmid has F+ factor in the

plasmid. HFr just means there is high frequency of recombination but HFr cannot send

an entire chromosome.

Transposons- genes that have the ability to move from one location to another on the

chromosome. Plasmids are transposons

Insertions sequences are the genes for transposase (cuts genes and moves to a new

location) therefore it all it takes is the code for transposase to move genes

Composite Transposons- Move other genes along with transposons, alle sequence,

occurs in humans Jumping genes are in all organisms

Bacterial Metabolic Regulation- Enzymes can be regulated through genes

Enzyme activity regulation (feedback inhibition) if too much of something is made then it can act

as an inhibitor

Gene Expression regulation (operons)

Operon (promoter, operator, and transcription unit) *Repressor-


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promoter- part of DNA where RNA polymerase attacthes Operator is after the promoter acts as

the on/off switch, genes transcribed- multiple genes can be codded on the same mRNA strand

multiple start/stop codons

Negative Gene Regulation

Repressible operon- When this is on, the RNA polymerase can go to

transcribe the RNA, tryptophan can bind to a repressor protein thenattach to the operon and stop the process (normally in the active state)

Inducible operon- a catabolic operon, the repressor is active normally and

blocks the transcription pathway

Positive Gene Regulation- If there is a high concentration of glucose the cell will use

glucose for respiration, if cAMP is high and glucose is low then lactose willl be used.

CRP activated with cAMP and makes RNA polymerase bind easier

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Bio Chapter 18