Lecture 26, 11/12 (Maybruck 11); Viruses

Audio for lecture on 11/12 is available here.

• • Slide 1 handout from 11/9
• o Regulation of gene expression at the level of translation: Inhibit gene expression of a dominant protein. This is done by regulating translation. Bacteria do it using antisense RNA. Antisense RNA will complimentary bind its sequence to a specific mRNA sequence. This forms an RNA double stranded. RNA must be single stranded in order for it to translate. We use antisense DNA because it is easier to manufacture. Antisense DNA makes its way into the nucleus of the cell where it binds to a specific sequence and translation can no longer occur (double stranded → doesn’t work AND the double stranded nucleic acid doesn’t leave the nucleus. Translation usually occurs in the ER)
• o Another therapy is triplet DNA therapy regulation at transcription level: DNA strand that is complimentary to template strand. This is important because in transcription it only reads off the template strand DNA. This prevents DNA polymerase from attaching, binding and reading.
• • This process in its early stages – trouble getting DNA into nucleus
• • Can be used for cancer
• • Slide 1 11/12 VIRUSES
• o Ways to tell a virus is alive: growth, heredity, metabolism, protective mechanisms, transport of substances
• o A virus cant do this stuff independently → it can do it once it infects a cell. Virus should be considered as infectious particle.
• • Slide 2 Virus size
• o Virus size are less than .2 um → VERY small
• • Slide 3 virus structure
• o Virion – completed virus particle which has two parts
• • Outer covering – consists of a capsid and an envelope
•  Capsid (made with same protein subunit called capsomer) comes in two different forms: helical and Icosahedron.
• • Helical form - Capsids bind to one another and extend in a condensed helix. It manifests itself in a rod → called a naked virus.
• • Icosahedron – a polyhedron (3-d structure that contains sides that are polygons – a polygon has three straight sides and three angles). Icosahedron is made up of twenty polygons. This formation is called a facet. The facets are made up of 20 capsomers. As a result of this geometric formation there are 12 equally spaced corners. At each corner is 5 capsomers called penton center.
•  Envolope
• • Taken from the cell host. The envolope provides additional protection for the genetic material AND aids in release of genetic material into cell host.
• • Central core – consists of genetic material and enzymes
• o All viruses will have a capsid and genetic material meaning they also must have an outer covering and central core.
• • Slide 4 genetic material of viruses
• o Viruses contain either DNA or RNA (not both)
• o Viruses also use single stranded nucleic acids as their genetic code.
• o Because viruses are very small their genetic material must be concise. Hepatitis B has 4 genes (Human eukaryote has tens of thousands of genes). Those genes in a virus must code for synthesis of the viral capsid and genetic material, produce protein products that will regulate the actions of their cell host, they need to code for genes that will help package the virus (virion).
• • Slide 5 viral multiplication
• o 1st step – absorption
• o viruses attack specific cells. They determine it based on receptors of the cell host. This can help us characterize viruses into these categories:
• • restricted: example hep B → only infects liver cells
• • intermediate: example polio virus → infects intestinal cells and nerve cells
• • broad: example rabies virus → infects a bunch of eukaryotic cells
• • slide 6
• o it needs to release its genetic material into the cell host. This can be done by endocytosis (similar to how an amoeba eats food). Food vacuole is formed. Food vacuole is bombarded with enzymes and breaks down the capsid. As a result genetic material is released into the cell.
• o It can also transfer its DNA by merging. As it merges it will spread open and genetic material is released.
• • Slide 7 synthesis and assembly
• o Double stranded DNA virus can recombine into our genome and creates potential for cancer.
• o RNA polymerase transcribes viral DNA → it then moves to the ER where it is translated → proteins are then brought back in to the cytoplasm.
• • Slide 8 viral release
• o There will either be cell lyses or exocytosis.
• o Cell membrane is critical to life of cell