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RNA

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RNA Protein Synthesis Mutations * Substitution Insertion Deletion Chromosomal mutations involve changes in the number or structure of chromosomes. – PowerPoint PPT presentation

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Title: RNA


1
Chapter 8
  • RNA
  • Protein Synthesis
  • Mutations

2
RNA Structure Function
3
Structure of RNA
  • RNA differs from DNA in three ways
  • an RNA molecule consists of a single-strand of
    nucleotides
  • RNA has ribose (5-C sugar) rather than
    deoxyribose
  • RNA has the pyrimidine uracil instead of thymine

4
Types of RNA
Function
mRNA transmits information from DNA and serves as a template for protein synthesis
tRNA brings amino acids to ribosomes for protein synthesis
rRNA rRNA and proteins make up ribosomes
5
3 Types of RNA
6
Protein Synthesis
  • Has 2 stages
  • Transcription and Translation

7
Protein Synthesis Part 1 Transcription
  • Transcription is the first part of protein
    synthesis.
  • What does it mean to transcribe?
  • Step 1 An enzyme called RNA polymerase attaches
    to DNA and unzips it.
  • Step 2 RNA polymerase then uses one strand of
    DNA as a template from which nucleotides are
    assembled into a strand of mRNA.

8
Adenine (DNA and RNA) Cystosine (DNA and
RNA) Guanine(DNA and RNA) Thymine (DNA
only) Uracil (RNA only)
RNApolymerase
DNA
RNA
9
Protein Synthesis Part I Transcription
  • The nucleotide sequence of DNA is converted into
    an RNA nucleotide sequence.
  • Lets say one strand of a DNA molecule had this
    sequence
  • AGCCTACGTAAG
  • What would the mRNA sequence produced be?

10
Protein Synthesis Part 1 Transcription
  • DNA AGCCTACGTAAG

mRNA UCGGAUGCAUUC
11
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12
Review of Proteins
  • Proteins are made by joining amino acids together
    into a long chain. This chain is a protein.
  • The functions and properties of a protein are
    determined by the order in which 20 different
    types of amino acids are joined.
  • The language of mRNA is called the genetic
    code.

13
The Genetic Code
  • RNA has 4 bases adenine, uracil, cytosine, and
    guanine.
  • The language of RNA is written in only 4
    letters AUGC
  • The code is read three letters at a time
  • Each word is 3 letters long
  • Each word of 3 nucleotides is called a codon

14
The Genetic Code
  • The 4 different bases can be arranged into 64
    possible codons (4X4X464), but make only 20
    different amino acids.
  • This is because some amino acids correspond to
    several different codons.
  • Example

15
Genetic Code
  • Practice
  • For what amino acid does the codon CGG code?
  • For what amino acid does the codon AUG code?
  • For what amino acid does the codon UGA code?

16
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17
Codons With Special Roles
Start Codon
Stop Codons
18
Protein Synthesis Part 2 Translation
  • The 2nd stage of protein synthesis is
    translation.
  • What does it mean to translate?
  • The sequence of nucleotides in mRNA serves as
    instructions for the order in which amino acids
    should be joined together in a protein. Think of
    mRNA as the recipe for a protein.

19
Protein Synthesis Part 2 Translation
  • Transcription occurs in the nucleus.
  • In translation, the mRNA travels out of the
    nucleus, and moves through the cytoplasm and
    attaches to a ribosome. So, translation occurs
    at the ribosomes.

20
Protein Synthesis Part 2 Translation
  • Steps of translation
  • 1. mRNA attaches to a ribosome
  • 2. As each codon of the mRNA molecule moves
    through the ribosome, the proper amino acid is
    brought to the ribosome by tRNA molecules.
  • 3. Each tRNA molecule has 3 unpaired bases on
    it. These bases are called anticodons.

21
Protein SynthesisPart 2 Translation
  • 4. The amino acids are strung together like a
    chain (remember, a protein is a polymer) by the
    ribosome, forming a long protein molecule.
  • 5. The tRNAs are released from the amino acids.
  • 6. The protein chain grows longer and longer
    until the ribosome reaches a stop codon on the
    mRNA molecule. Then the protein is released from
    the ribosome.

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28
Practice
DNA
mRNA
tRNA
Poly- peptide
29
Mutations
  • Gene Mutation produce changes in a single gene
  • Chromosomal Mutations produce changes in an
    entire chromosome

30
Gene Mutations
  • A gene mutation is a change in a DNA sequence.
  • Gene mutations that involve changes in only one
    or just a few nucleotides are called point
    mutations b/c they occur at a single point in the
    DNA sequence.
  • There are 3 types of point mutations
    substitutions, deletions, and insertions.

31
Gene Mutations
  • Substitution Mutations
  • One base is changed to another
  • Usually affect no more than a single amino acid,
    but could still have an effect on a protein.

32
Gene Mutations
  • Insertion Mutations
  • One extra base is inserted into the DNA sequence.
  • Deletion Mutations
  • One base is left out of the DNA sequence.

33
Genetic Mutations
  • Since the genetic code is read 3 letters at a
    time, the message is shifted for every codon that
    follows. Hence, insertions result in frameshift
    mutations. They have a dramatic effect on the
    amino acid sequence, and thus, the protein.
  • Questionduring what event do these mutations
    usually occur?

34
Gene Mutations
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36
Chromosomal Mutations
  • Chromosomal mutations involve changes in the
    number or structure of chromosomes.
  • We discussed many of these last chapter.
    Examples are Down syndrome, Turner syndrome,
    Fragile-X syndrome, Prader-Willi syndrome, and
    Klinefelters syndrome.

37
Chromosomal Mutations
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