Transcript Genetic Code & Mutations

Genetic Code
&
Mutations
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.

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

“Language of RNA”
RNA contains 4 different bases: A,U,C,G
 The genetic code is responsible for
building all the proteins in the body using
20 different amino acids.
 Codon: three consecutive nucleotides that
specify a single amino acid.

 Amino
acids are attached to make a
polypeptide, protein.

Anticodon: the complimentary RNA
bases of a codon.
Codons
A
three letter “word” that
specifies an amino acid.


There are “start” codons & “stop” codons
Tells ribosome where to start reading the
RNA strand.
Genetic code:
Translation

TRANSLATION: the process by which mRNA is read
and protein produced.
 mRNA has a codon that codes for a particular
anticodon, attached to tRNA (translational RNA)
 tRNA also has the amino acid attached to it.
tRNA (transfer)
approx. 80
nucleotides in length.
 Cross-like shape
 At one end there is an
anticodon
 At other end an
amino acid is
attached

Mutations
 Mutation
is a change in genetic
material.
 Types of Mutations:
 Gene
Mutations
A. Point Mutation
B. Frameshift Mutation
 Chromosomal
Mutations
Gene Mutations

Point Mutation: occur at a single point
 Includes
substitution, addition, and deletions
of bases.
 May only change one amino acid coded for.

Frameshift Mutation: when codons get
changed because of additions or deletions
 Changes
the combinations so that different
amino acids are coded for.
Chromosomal Mutations
These mutations change the entire
chromosome.
 Types include:

 Deletions:
loses part of chromosome
 Duplications: doubles part of chromosome
 Inversions: inverts part of chromosome
 Translocations: takes part of chromosome and
moves it to other part of chromosome
 Translocation
Insertion 
A six-legged green frog
A white American alligator
shows a genetic mutation
known as leucism. This allele
controls migration of pigment
cells during development;
absence in cells leads to white
patches on the skin
An African clawed frog (Xenopus laevis), mutated, with three hind legs
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
Eukaryotic gene expression
Controlled
by
complex
sequences of
DNA.
Example:
“TATA box”
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.
