April 16th - Wednesday

 

The following are the summaries of Ch 18 -- on Viruses & Prokaryotes. Below is is CH 19 - on Eukaryotic Genomes

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A little about Viruses...

• made up of nucleic acids with a protein coat.
• Capsid Proteins (make up the coat)
• Nucleic acid-could be DNA or RNA
• Double stranded or Single stranded.

 

They are Obligatemolecular parasites: -- They have No Choice but to be parasites

They can only reproduce in a host cell.

 

Given they have

• No metabolism
• No enzymes.

We consider them to be not alive.

 

All they do is infect the host cell, and use the host machinery to replicate & reproduce

Viruses attack prokaryotes and Eukaryotes (Plants & animals)

 

Given they have no metabolism - you can't take any antibiotics - because you're using your cell machinery

Lots of the fever and aches are not directly because of the virus, but due to the cell death they cause.

 

Most viruses have 3-10 genes - hardly any at all.

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Prokaryotic Cells

 

Genome Organization -

1 circular chromosome - DNA  ~5mb

mb = 1 megabase = 10⁶ bp = 5 million base pairs

 

~1500 genes / genome

 

Most of the DNA codes for proteins or are regulatory sequences.

= genes. Only a few repetitive sequences in prokaryotes ---> those that are repeated are usually for ribosomal RNA.

 

Gene expression - Control is primarily at the transcriptional level.

Which genes will be turned on and when.

 

Operons = gene oranization

An operon is one promoter and several genes that code for different proteins - acting in one pathway.

(Example - the synthesis of an amino acid.)

All genes are on same mRNA

 

ASIDE:(Because only 1 promoter it assures bacterium that al enzymes are turned on at same time - don't need to worry about genes on other places of hte chromsomes, they're all going to turn on when they need.)

 

(LE 18-21) - there are no introns

 

Plasmids

• Smaller circles of DNA
• non-essential genes
• Antibiotic resistance is carried as genes on plasmids (not an essential trait, but would help deal with environment at hand)
• (bacteria that die leave their plasmids behind, if another one picks it up, it gains dea one's resistance - that's why bacterial resistance is quick!)
• Important for Genetic Engineering.

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CHAPTER 19 -

 

Eukaryotic Genomes

• Multiple linear chromosomes
• Each chromosome in humans averages >100 mb DNA (over 100 million base pairs)
• Many genes on each chromosome
• Gene number for each organism varies

 

As Examples:

Fruit flies: ~14,000 genes

Yeast:  ~5,000 genes (beer or bread)

Plants: 25,000 ~ 40,000 genes

Humans: 30,000 - 50,000

 

The amount of DNA in a genome is not directed about complexities of the organism (more DNA doesn't mean bigger, advanced, smarter, etc)

 

Types of DNA sequences in the human genome:

1 - Genes, tRNA, rRNA  ~1.5% of genome

2 - Introns, & regulatory sequences for genes ~24% of the genome

3 - Non-coding DNA  ~75%  (used to be called "junk") - full of repetititive sequences

 

Only a small fraction of the Genome codes for genes --> proteins

(in contrast to prokaryotes - they were practially entirely made of genes!)

 

DNA Packing

• Dna is always associated with protein in prokaryotes and eukaryotes

 

Eukaryotic packaging:

• Chromatin = DNA + protein (called "Histones" - primary protein associated with DNA)
• 1st - nucleosome - core of histone proteins with DNA wrapped around the core
•  Under an electron microscope - look like "beads on a string" where beads = nucleosomes and string = the DNA between them
• Histones - very basic proteins (+) charged
• DNA - negatively charged

• Histones - very evolutionarily conserved - (there's little difference from one species's histomes from another.)

 

Higher levels of packing -

• 30 nm fiber
• loops, folds, coils (not really understood) --> eventually gives us a mitotic or meiotic chromosome

 

Interphase chromatin:

• much less condensed than mitotic chromosomes  --- its really "diffuse"
• Euchromatin -- (eu - true) = chromatin that is more open and accessible to enzymes like RNA Polymerase transcription
• Heterochromatin -- very condensed chromatin -(not accessible to transcripiton) - stains more intensely