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DNA & RNA

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Greg Evans

on 16 May 2014

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Transcript of DNA & RNA

12.2 - Chromosomes and
DNA Replication
12.1 - DNA
12.3 - RNA and Protein Synthesis
12.4 - Mutations
changes in the DNA sequence that affect genetic information
12.5 - Gene Regulation
How does an organism know whether to turn a gene on or off?
DNA and RNA
DNA and Chromosomes
DNA is a remarkable molecule!
E. coli has 4,639,221 base pairs
Each DNA molecule is about 1.6 mm long
Think of putting 300 meters of rope into a backpack!
Human cells have almost 1000x as many base pairs
Chromosome Structure
Chromatin is tightly coiled around histones.
DNA and histones form a type of "bead necklace" called a nucleosome.
DNA Replication
DNA can replicate itself by using a process called base pairing.
The DNA strands make complimentary strands by matching up the base pairs.
Replication - the process of duplicating a cells DNA
DNA replication occurs in steps:
enzymes "unzip" the strands
DNA polymerase matches the base pairs up and "proofreads" the new strand
The Structure of RNA
long chain of nucleotides
the sugar is ribose
single stranded
contains uracil instead of thymine
Types of RNA
In most cells RNA is mainly used for protein synthesis.
Three types of RNA
messenger RNA - carries messages from DNA to rest of the cell
ribosomal RNA - helps make up ribosomes
transfer RNA - transfers amino acids to the ribosome as it is coded by the mRNA
Avery-Griffith and Transformation
Transformation
- one strain of bacteria changes into another
Oswald Avery - used enzymes to determine which molecule was most important for transformation, their conclusion was DNA
Frederick Griffith - researched pneumonia
How do genes work?
What are they made of?
How do they determine different characteristics?
The Hershey-Chase Experiment
bacteriophage
- virus that infects and kills bacteria
Radio active markers: phosphorus-32 and sulfur-35
Hershey and Chase concluded that genetic material was in the DNA and not the protein.
The Structure of DNA
Knowing genes were made of DNA wasn't enough! Scientists wanted to know:
How genes carry information from one generation to the next.
How they put the information to work.
How was it copied?
Erwin Chargaff's Rules: A=T and G=C
Rosalinda Franklin used X-ray diffraction to "take a picture" of DNA which showed the double helix.
James Watson and Francis Crick then determined the structure of DNA. Watson and Crick also discovered DNA's hydrogen bonds and base pairing.
Transcription
The copying of DNA into a complementary sequence of RNA.
Requires:
RNA polymerase - enzyme that separates DNA, then uses it
Promoters - specific regions of DNA that RNA polymerase will bind to
Translation
RNA Editing & The Genetic Code
introns - intervening sequences that are cut out of RNA while they are still in the nucleus
exons - expressed sequences that are spliced back together to form the final mRNA
Proteins are made by joining amino acids into long chains.
4 nucleotides 20 amino acids proteins
A codon is made up of three consecutive nucleotides that specify a single amino acid.
the decoding of an mRNA molecule into a protein molecule
The three bases on the tRNA are called the anticodon, they are complementary to one of the mRNA codons.
Gene Mutations
point mutations - affect one nucleotide, one nucleotide is substituted for another
frameshift mutations - occur if a nucleotide is added or removed, thereby "shifting" the reading frame
Chromosomal Mutations
involves a change in the number of structure of chromosomes
operon - group of genes that operate together
lac genes are turned off by repressors and turned on in the presence of lactose
promoter - RNA polymerase binding site and beginning of transcription
operator - region where the repressor binds
repressor - prevents RNA polymerase from bind to the promoter
Eukaryotic Gene Regulation
Why is gene regulation in eukaryotes more complex than in prokaryotes?
Regulation and Development
hox genes - control the organs and tissues that develop in various parts of the embryo
A mutation in one of these genes can completely change the organs that develop in specific areas of the body.
Full transcript