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.