DNA and RNA

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DNA and RNA

• Chapter 12

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Genetic facts in 1900

• Both female and male organisms have identical
  chromosomes except for one pair.
• Genes are located on chromosomes
• All organisms have two types of chromosomes
• Sex chromosomes
• Autosomes

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Male vs Female

• MALE
• Usually the Y chromosome.
• Y is usually smaller
• Male genotype XY

• FEMALE
• Usually the X chromosome.
• Larger than the Y
• Female genotype XX

Except Birds Male XX Female XY
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Frederick Griffith

• British bacteriologist
• 1928 designed and performed experiment on rats
  and bacteria that causes pneumonia.
• 2 strains of the bacteria
• Type S causes severe pneumonia
• Type R relatively harmless

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Griffiths Rats

1. First he injected living Type S bacteria into
   rats

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• Second he injected dead Type S into the rats.

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• Next he injected living type R bacteria

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• Finally he injected a mixture of living Type R
  and dead Type S

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Results of experiments

• Because the dead rat tissue showed living Type S
  bacteria, something brought the Type S back to
  life
• Actually one bacterial type incorporated the DNA,
  or instructions, from the dead bacteria into its
  own DNA
• Known as transformation. Confirmed by Avery,
  MacLeod, and McCarty in 1944

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Oswald Avery

• Canadian biologist (1877-1955)
• Discovered DNA in 1944 with a team of scientists.

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Hershey and Chase
DNA

• 1952
• Attempted to solve the debate on whether DNA or
  proteins are responsible for providing the
  genetic material.

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Proteins
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• They used a bacteriophage (a virus which attacks
  bacteria) to prove that DNA was definitely the
  genetic material.

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Phoebus A. Levene

• Russian born immigrated to America, moves to
  Europe.
• 1920s discovered nucleotides (building blocks of
  DNA)
• Sugar
• Phosphate group
• Nitrogenous base

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Composition of DNA
Nitrogen Base
Phosphate
Sugar
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Components and structure of DNA

• A very long molecule. 4 nitrogenous bases

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Chargaffs rules

• The relative amounts of adenine and thymine are
  the same in DNA
• The relative amounts of cytosine and guanine are
  the same.
• Named after Erwin Chargaff

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Rosalind Franklin

• Used X-Ray diffraction to get information about
  the structure of DNA

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Structure of DNA

• Discovered in 1953 by two scientists
• James Watson (USA)
• Francis Crick (GBR)
• Known as the double-helix model.

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The double-helix

• A twisted ladder with two long chains of
  alternating phosphates and sugars. The
  nitrogenous bases act as the rungs joining the
  two strands.

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How long is the DNA molecule?
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Chromosomes DNA replication

• The nucleus of one human cell contains
  approximately 1 meter of DNA.
• Histones DNA tightly wrapped around a protein
• Nucleosome

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Chromosome structure
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DNA replication

• Must occur before a cell divides.
• Each new cell needs a copy of the information in
  order to grow.

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DNA replication. Why needed?

• Before DNA strand can be replicated or copied it
  must be unzipped
• DNA polymerase (enzyme that unzips)
• Starts at many different points. Why?

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Completing the replication

• After the DNA molecule comes apart, bases of free
  nucleotides in the nucleus join their
  complimentary bases.

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RNA

• Very similar to DNA.
• Exceptions
• Ribose is the 5-carbon sugar
• Uracil replaces thymine
• Single-stranded

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mRNA (messenger)

• Copies genetic code of DNA by matching bases.
• Occurs in the nucleus.
• DNA changing to RNA

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TRANSCRIPTION

• DNA is copied into mRNA with the aid of RNA
  polymerase.
• The RNA polymerase will bind to promoters that
  act as signals in the DNA sequence to make RNA.

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Transcription continued
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Exons and Introns

• EXONS
• A segment of DNA in eukaryotic organisms that
  codes for a specific amino acid

• INTRONS
• A segment of DNA that does NOT code for an amino
  acid.

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Confusing genetic terms

• Polypeptide a chain of amino acids.
• Protein a complex structure composed of
  polypeptides
• Amino acids smallest structural unit of a
  polypeptide.
• Gene a distinct unit of material found on a
  chromosome

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Reading the genetic code

• The genetic code is responsible for building all
  the proteins in the body using 20 different amino
  acids.
• How many 3 letter words can you make from the
  letters A,T,G and C?
• Answer 64

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Codons

• A three letter word that specifies an amino
  acid.

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Genetic code
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tRNA (transfer)

• approx. 80 nucleotides in length.
• Cross-like shape
• At one end an amino acid is attached
• At the other end there is an anticodon
• Acts like a truck

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Polypeptide assembly

• Translation reading or translating the RNA
  code to form a chain of amino acids.
• Known as protein synthesis
• Occurs in the cytoplasm. (p.304)

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Mutations

• The source of variation in a genetic sequence.
• Can be either gene or chromosomal mutations.
• Point mutations a change in a single nucleotide
  in a sequence of DNA.

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Frameshift Mutation

• Inserting an extra nucleotide which, in turn,
  shifts the entire sequence one way or the other.

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Chromosomal mutations

• Involves a change in the number or structure of
  the chromosomes.
• Deletion when a piece of a chromosome breaks
  off and is lost.
• Duplication when a segment of a chromosome is
  repeated
• Inversion when a segment of a chromosome is
  reversed.

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More chromosomal mutations

• Translocation when part of a chromosome breaks
  off and is attached to a non-homologous
  chromosome.

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Control of gene expression

• Genes are often like light switches that can be
  turned off and on.
• Operon occur in prokaryotes. (bacteria)
  different genes that work together to activate
  gene functions

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Eukaryotic gene expression

• Controlled by complex sequences of DNA.
• Example TATA box

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Factors

• Overall gene control is more difficult for
  eukaryotes because functional genes may be on
  different chromosomes.
• Environmental such as chemicals and temperature.

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Hox and Oncogenes

• Hox genes
• Genes that actively control embryonic development.

• Oncogenes
• Genes known to cause cancer.
• Usually these are switched off, but can be
  switched on by a number of factors.

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Assignment

• Pages 315-116
• 1-10, 13, 15, 19, 20, 23
• Transcribe this DNA sequence into RNA, then
  translate the RNA into an amino acid chain
  TAGCCGACAGGCCTCTTTACT
• 1-12 page 317