TRANSLATION

Translation is the final step of protein synthesis - it involves

ALL THREE types of RNA (mRNA, tRNA and rRNA).

• Translation is a process in which the mRNA that was

manufactured during transcription is translated into an
amino acid sequence (proteins).

• occurs in the cytoplasm

and on the ribosomes

Ribosomal RNA (rRNA)= a major

component of ribosomes; also helps bond
amino acids together to make polypeptides
(proteins)!

The goal of the 3 types of RNA is to work

together to make proteins using the DNA’s
instructions!

TRANSLATION

Transfer RNA (tRNA)= helps transfer amino acids to the corresponding mRNA

codons (tRNA is always complementary to the mRNA strand)

mRNA codons: U G C A A U C G G

tRNA anticodons: A C G U U A G C C

tRNA bases are referred to as “anti-codons” because they are

complementary to mRNA codons.

mRNA strand (codons) U G C A A U C G G

tRNA strand (anti-codons) A C G U U A G C C

TRANSLATION

tRNA transfers amino acids

to the ribosome. The amino
acids are attached to the
tRNA via a specialized
enzyme called tRNA
synthetase.

Analogy: tRNA is a librarian; mRNA
codons are the book codes; amino acids
are the books. tRNA reads the mRNA and
fetches the appropriate amino acid.

Example)

If the mRNA codon is

CUU, that would
translate to the amino
acid leucine.

The tRNA molecule that

will deliver leucine to the
ribosome has the
anticodon GAA.

Once the amino acid is delivered, the tRNA releases
itself from the ribosome, and leaves to find another
amino acid to add to the growing polypeptide chain.

ANTICODON

LEUCINE

DNA Template Strand: A C G T T A G C C

mRNA strand: U G C A A U C G G

Codons?

1)

UGC

2)

AAU

3)

CGG

Which three amino
acids do these
mRNA codons
code for?

1.
2.
3.

LABEL THE FOLLOWING:

MRNA, TRNA, RIBOSOME, PEPTIDE (PROTEIN) CHAIN,

AMINO ACID

START AND STOP SIGNALS

Proteins are made up of a very specific sequence of amino

acids.

DNA contains “start” and “stop” codons so that the cell knows

where to start decoding proteins and where to stop.

The start codon= AUG (codes for the amino acid methionine)

Stop codons = UAA, UAG, UGA

PUTTIN’ IT ALL TOGETHER

DNA codes for proteins
Proteins are made during

protein synthesis

Transcription occurs in the

nucleus. The final product
of transcription is an
mRNA strand.

Translation occurs on the

ribosomes in the
cytoplasm. The final
product of translation is a
protein.

Overview

● When a particular protein is needed, the cell must make the

protein through the process of transcription and translation.

● DNA molecules (which contain the code) do not leave the

nucleus of the cell.

● Protein synthesis occurs on ribosomes located outside of the

nucleus.

● Therefore, the code must be carried from the nucleus to the

cytoplasm.

● RNA plays an important role in protein synthesis but it can also

have other functions in the cell.

○ mRNA is essential to the process of transcription, tRNA is

essential to the process of translation, and rRNA makes up
the ribosomes in which translation takes place.

Overview

●

Transcription is the process by which a portion of the molecule of
DNA is copied into a complementary strand of RNA. The process of
transcription takes place as follows:

○

An enzyme attaches to the DNA molecule at the gene of interest.

○

The two strands of DNA separate at that location.

○

Complementary RNA nucleotides bond to the nitrogenous bases on
one of the separated DNA strands.

○

The chain of RNA nucleotides forms a single-stranded molecule of
RNA by using the DNA strand as a template.

○

When a stop codon is reached, the RNA strand separates from the
DNA molecule, leaves the nucleus and goes through the nuclear
membrane into the cytoplasm.

○

The two DNA strands rejoin.

Overview

●

Translation is the process by which the genetic message, carried by the
mRNA, is used to assemble a protein.

○

The mRNA attaches to a ribosome, which contains proteins and ribosomal
RNA (rRNA). The function of ribosomes is to assemble proteins according
to the genetic message.

○

Each three-base nucleotide sequence on the mRNA is called a codon. Each
codon specifies a particular amino acid that will be used to build the
protein molecule. For example, if the DNA sequence was GAC, then the
RNA sequence becomes CUG (transcription) and the amino acid that is
coded is Leucine (translation).

○

Another type of RNA, transfer RNA (tRNA), brings amino acids to the
ribosome in the order specified by the codon sequence on the mRNA. At
one end of each tRNA is the anticodon, a region that consists of three
nucleotide bases that are complementary to the codon of mRNA. The
other end of the tRNA molecule binds to the specific amino acid that is
determined by the mRNA codon.

Overview

● The translation process takes place as follows:

○

The anticodon of the tRNA, with its attached amino acid, pairs
to the codon of the mRNA, which is attached to a ribosome.

○

When a second tRNA with its specific amino acid pairs to the
next codon in sequence, the attached amino acid breaks from
the first tRNA and is bonded to the amino acid of the second
tRNA.

○

The ribosome forms a peptide bond between the amino acids,
and an amino acid chain begins to form.

○

The empty tRNA moves off and picks up another matching
amino acid from the cytoplasm in the cell.

○

This sequence is repeated until the ribosome reaches a stop
codon on the mRNA, which signals the end of protein synthesis.