Gene Control and Mutations

1
Gene Control and Mutations

• How do we know which genes are used when and is
  there room for error?

2
Protein synthesis and beyond

• How does RNA polymerase know where to start
  transcription?
• -RNA Polymerase binds to Promoter region on DNA
  (TATA box) ? signals start of Transcription
• -Pre-mRNA is produced ? contains INTRONS and
  EXONS
• -Exons gene coding regions 2.4 cm/2 meters
• -Introns rest junk DNA!!!

3
RNA editing from pre-mRNA to mRNA

• Result functional gene with only regions coding
  for protein, coding for trait
• Only edited mRNA is Translated at ribosome
• Not the exact same as the DNA!!!

4
Gene Control

• Genes Transcribed only when needed
• Saves energy control
• Feedback molecules/signals will either cause
  transcription of gene or block it
• Luciferase production in deep sea fish NEMO
• Hormones bind to promoter ? transcribe luciferase
  gene ? glowing

Luciferase protein
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Promoter site of RNA Polymerase binding
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Genetic Mutations -11.3

• Changes in DNA that also change the protein
  produced
• Can happen spontaneously (no reason they
  occurred) - mistake
• OR
• By mutagens substances or agents that can cause
  changes in DNA increase w/age
• Ex. Chemicals, radiation, x-rays, viruses,
  smoking
• Thymine dimer UV rays causing T to pair w/T

7
Mutations can affect org. or may notwhy?

• Mutations of DNA at promoter region or EXON
  sequences of gene may lead to visible/harmful/heri
  table mutations
• May lead to over expression of gene
• Oncogenes, p53 ? cancer
• Mutations in INTRON areas of DNA will not be seen
  in the organismwhy?
• What is the purpose of Intron sequences?

8
Mutations in reproductive cellsvs. Mutations in
body cells

• Changes in reproductive cells
• code is changed in sperm or egg (Meiosis)
• wont effect the parent, but CAN effect the
  offspring produced from those altered sex cells
• can be POSITIVE new, adaptive traits
• Most of the time fatal or harmful!

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Mutations in conception or meiosis Hereditary
Mutations
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Somatic Mutations

• Changes in body cells
• not passed on to offspring, but can cause
  MAJOR complications for the individual effected
• Ex. Solar radiation skin cancer
• again process is thought to be cumulative
  effect of exposure to mutagens over time

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Somatic Cell Mutations only affect that organism
12
Point mutations vs. Chromosome mutations

• Point Mutation change in single base pair of
  DNA or just a few base pairs
• Chromosome mutation change in a large portion
  of an entire chromosome effects MANY genes
• Which one could be more harmful?

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Point/Gene mutations

• Change in 1-2 base pairs of DNA 2 types
• if does not effect the length of the code,
  will just change the amino acid in that position
  1. SUBSTITUTION
• Ex A to G
• if changes the length of the code, is called a
  2. frameshift mutation, and are two types of
  these
• INSERTIONS AND DELETIONS

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Point/Gene Mutations affect only ONE base in the
codeSubstitutions, Insertions, and Deletions
Section 12-4
Deletion
Substitution
Insertion
Gene Mutations only affect ONE point of the code
-- often called Point Mutations
Go to Section
15
Example Problem

• Normal gene TACGGTAATACT
• mRNA?
• aa sequence?
• of aas in protein
• Mutated gene TACGTAATACT
• mRNA?
• aa sequence?
• of aas in protein
• What type of mutation is this?

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Chromosome mutationsEffect Chromo numbers and
Chromo shape

• 1. Mistakes in numbers of chromosomes
• -nondisjunction what is this?
• -Trisomy or Monosomy or Polyploidy
• 2. Mistakes in shape of chromos
• a. deletion part of chromo is broken off and
  lost completely
• b. duplication broken fragment of chromo
  attaches to sister chromatid so section is
  repeated on that chromatid
• c. inversion when fragment reattaches to
  original chromo but in reverse order
• d. translocation broken fragment attaches to
  a nonhomologous chromo
• (can exist as reciprocal or nonreciprocal)

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Chromosomal Mutations affects LARGE portions
of the code (entire genes or entire chromosomes)
Section 12-4
Deletion
Duplication
Inversion
Translocation
Go to Section
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Trisomy 21 Down SyndromeKaryotype

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Trisomy 16 cause of most miscarriages in first
trimester of pregnancy
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Benefits of Mutations

• -MOST mutations are either unnoticed or harmful!
• -Some add new phenotypes ? adaptive advantages
  (evolution)the moth
• -Some mutations tell us what a gene (DNA
  sequence) codes for can detect only when
  sequence is changed (compare)

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Moth Evolution in Industrialized England

• Many not all recessive phenotypes may have
  began as mutation of normal gene

Dominant gene (non mutated) ? Lighter phenotype
Mutated gene ? darker phenotype
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Mutated Fruit fly