Genetics, Viruses and Bacteria

Quick review of Genetics Mendel ◦ Law of segregation: Mendel’s first law, stating that each allele in a pair separates into a different gamete during gamete formation ◦ Law of independent assortment: Mendel’s second law, stating that each pair of alleles segregates independently during gamete formation; applies when genes for two charters are located on different pairs of homologous chromosomes

Allele: different forms of a gene Gamete: sex cell Dominant : always seen Recessive: only seen in the absence of a dominant trait Homozygous : the same Heterozygous : different

Genetic Disorders Result from the combination of genes and can vary in the affect and onset of the disease

DNA makes up your GENES! DNA pairs A-T & C-G DNA has to be made into RNA to complete protein synthesis Recall start codons! TRANSLATION VIDEO CLIP!

VIRUSES Are very small (20 nanometers to.25 micrometers) they are about 1/20 th the size of a prokaryotic bacteria Although viruses have genes they can only replicate with a host. Most viruses can survive for varying amounts of time outside of the host. (WASH YOUR HANDS!!)

So how would you define a virus? Particles consisting of nucleic acid surrounded by a protein coat and sometimes a membrane envelope

Genome of a virus Double strand DNA Single Strand DNA Double Strand RNA Single Strand RNA Around the genome is a capsid made of protein

Structures of Viruses Helical capsid Polyhedral capsid Envelope T-phage – the most complex (bacteriophages or viruses that infect bacteria)

How do viruses work? A virus cannot create proteins without the host. It has all the genetic material but not all the appropriate cellular components. They infect certain organisms based on what the virus is. This is known as the host range. Thus many viruses that infect cats and dogs don’t bother humans or are not as severe and vise versa

Reproduction of Phages (the viruses that infect bacteria) Two types Lytic – causes death in the host is also known as a virulent phage Lysogenic – is non-deadly, it is a genome phage and is mostly silent Will become a part of the genome

Reproduction of animal viruses The virus can only reproduce in animals that are part of the host range. The way that the virus replicates depends on the viral genome (remember there are 4 types) Viral reproduction also differs in the presence or absence of an envelope around the virus

Viral Envelopes Allow the virus to enter the host cell/puncture the cell membrane and infect the cell RNA viruses are complex and have complex reproductive tendencies (HIV) we will learn more about these when we study HIV/AIDS

VIRUS – THE DISEASE The symptoms that a virus may cause will depend on what the virus is doing in the host cell ◦ Damaging cells ◦ Killing cells ◦ Infecting cells to produce toxins ◦ Have envelopes which are toxic ◦ Cause the immune system of the host to react thus trying to fight the virus and causes ill effects in the host

What about Vaccinations? They use the immune system’s fighting ability to help stop people from getting the virus The vaccine is a variant or derivative of the virus (small pox) which starts immunity Vaccine help prevent the virus but medical sciences have little they can do to cure/kill a viral infection (TAMIFLU)

Emerging Viruses Appear suddenly and have a huge impact on the host population some times they are eradicated others become permanent ◦ HIV ◦ SARS To fight these viruses scientists must identify the genome and try to stop the replication of genetic information

How do emerging viruses develop? Mutation of current viruses ◦ Flu Spreading from host species to host species ◦ SARS ◦ Bird Flu Movement from small population to world wide ◦ HIV/AIDS

Viruses in plants Cost the agricultural community $15 billion a year Most are rod shaped and spread like animal viruses

Viroids and Prions Viroids are the smallest class of virus and have circular RNA molecules they cause errors to occur in the growth of host cells Prions are infectious proteins that cause degenerative brain diseases (MAD COW) the protein is malformed but is close enough to the “correct” protein that the host starts to use the “bad” protein instead

Why viruses and bacteria connect First of all remember that viruses can infect bacteria but there is more : Bacteria divide via binary fission (remember that?) so any change that occurs in a bacterial cell does so with genetic mutation

Quick Review Bacterial cells are not as complex as eukaryotic (most organisms) cells. The chromosomal material in a bacterial cell is smaller than in a eukaryotic cell but larger than the genetic material in a virus Bacterial genetic information is circular compared to the linear eukaryotic DNA BUT BOTH ARE DOUBLE STRANDED!

Bacterial Mutations Transformation – alter the genome of the bacteria by uptake of foreign DNA from the surrounding environment – harmless bacteria can become deadly Transduction – phages carry bacterial genes between host cells and genetic material is exchanged Conjugation – “bacteria sex” bacterial cells “share” information Plasmids – self-replicating DNA that is also inside the bacteria

R-Plasmids Cause Antibiotic resistance How? cfm?guidAssetId=F2B D-45B FC75CACF7016