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Translation
Start codon. Each codon codes for an amino acid. This three letter sequences “tells” the ribosome to start creating a polypeptide (lots of amino acids linked together).
Once outside of the nucleus, the mRNA strand is Translated into an amino acid.
Codons & Translation
Each codon = 1
amino acid.
A codon is made up
of 3 bases (letters).
There are 20 amino
acids, but there are
multiple codons for
each amino acid.
Codons & Translation
This is a codon chart.
The 20 amino acids
are represented by
the different colored
circles.
The amino acids
have different
characteristics like
positive or negative
charges,
hydrophobic, or
hydrophyllic
1ST
LETTER
2ND LETTER
3RD
LETTER
Quick Ribosome Review
Ribosomes make
proteins
Located throughout the
cell and on the ER.
Have 2 parts:
Large subunit
Small subunit
mRNA is “sandwiched”
between the large and
small subunits.
Translation
The mRNA joins the small ribosomal subunit (SRS) at the 5’ untranslated region.
The large ribosomal subunit (LRS) has 3 binding sites: E,P, and A.
Translation
The LRS attaches to the SRS so the first codon lines up with the P-binding site.
Translation
A tRNA (transfer RNA)carrying the amino acid Met attaches to the start codon (AUG).
This starts elongation (making the protein).
Translation
What does GAC code for?
How does the ribosome “know” to
stop adding amino acids?
There is a STOP
codon.
When the ribosome
reaches this codon it
stops adding amino
acids and falls away
from the polypeptide.
Translation is now
complete!
Information on Translation
To practice transcribing and translating your
own protein click here.
For a detailed description and images for
translation click here.
To learn about mutations that can occur
during transcription and translation keep
reading!
Now it’s your turn..
You should be able to use the notes you took
for homework to complete the questions up
through the elongation stage of translation.
Remember: There are lots of resources on the
blog to help you!
Mutation
Is this what you
think of when you
think of
mutation?
Mutation: Fact & Fiction
All mutations are bad…………………….
Mutations are a source of evolution…
Mutation can be silent……………………
Mutations only happen when DNA is exposed to
things like radiation………………………..
FICTION
FICTION
FACT
FACT
Fiction #1:
All mutations are bad
Sickle Cell Anemia:
Replacement of A with T at the 17th nucleotide in
a beta chain of hemoglobin.
The mutation changes from GAG (glutamic acid)
to GTG (valine).
People with sickle cell anemia are resistant to
malaria (very helpful in areas with a high rate of
the disease).
Fact #1:
Mutations are a source of evolution
All new genetic
variation comes
from mutation.
Antibiotic resistance
Peppered Moth?
Fact #2:
Mutations can be silent
Most amino acids
are encoded by
several different
codons.
A mutation at the 3rd
codon is likely to
have little effect.
Fiction #2:
Mutations only happen when DNA is
exposed to things like radiation.
Environmental
causes are a source
of mutation, but not
the only source.
Mutations can also
occur when the DNA
is being copied for
cellular division.
Types of Mutations
Single Base substitutions
Insertions and Deletions
Duplications
Translocations
Single base substitutions
A is substituted for T
and vice versa.
C is substituted for G
and vice versa.
These subst. are not
as detrimental as non-
pair substitutions (e.g.:
T for C).
Insertions and Deletions
Insertion: a base
pair is added to the
DNA.
Deletion: a base pair
is subtracted from
the DNA.
This shifts the
reading frame for
the codons.
Fragile XHuntington Disease
Duplications
Doubling of a section
of the genome.
Duplicates can be be
beneficial.
Over time, duplicates
can acquire new
function.
Translocations
Translocations are
the transfer of a
piece of one
chromosome to a
nonhomologous
chromosome.
Translocations are
often reciprocal; that
is, the two
nonhomologues
swap segments.
Are all mutations passed on to the
next generation?
Somatic Mutations:
• Occur in non-reproductive body cells (bone marrow, liver, etc.)
• Mutation does NOT get passed onto the offspring.
Germline Mutations:
• Found in every cell descended from thezygote (fertilized egg & sperm).
• Mutation CAN be passed onto theoffspring.
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