8.5
Translation
The student is expected to:
4B investigate and explain cellular
processes, including homeostasis,
energy conversions, transport of
molecules, and synthesis of new
molecules
and
6C explain the purpose and process
of transcription and translation using
models of DNA and RNA
TEKS 4B, 6C
Translation
(In the cytoplasm)
The mRNA made during transcription is
used to make a protein. mRNA  protein
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picture for video
8.5
Translation
TEKS 4B, 6C
Amino acids are coded by mRNA base sequences.
• Translation converts mRNA messages into polypeptides.
• A codon is a sequence of three nucleotides that codes for
an amino acid.
codon for
methionine (Met)
codon for
leucine (Leu)
Proteins
Remember that proteins, which are
sometimes called polypeptides, are
macromolecules made of monomers
called amino acids.
Translation
(In the cytoplasm)
•
During translation, ribosomes decode the mRNA message
(made of nucleotides) to make polypeptide chains (made of
amino acids).
nuclear pore
Step 1: Two subunits of the ribosome attach to
the mRNA.
Step 2
Ribosomes read the mRNA 5’  3’. As
each codon of the mRNA moves through
the ribosome, the correct amino acid is
brought to the ribosome by tRNA.
The Genetic Code
– In RNA, the nucleotides are read in “words” made
of 3 nucleotide “letters”. Each “word” is called a
codon and contains the genetic code for one
amino acid.
Move from the inside out!
–
–
–
The first “word” or start codon is always the same for every
protein. It is always AUG.
Using the genetic code wheel you can figure out which amino
acid a codon represents. What amino acid is associated with
the codon AUG?
Methionine
There are a total of 20 different amino acids that can be
arranged in different ways to make different proteins.
Step 3
Each tRNA molecule
has a group of three
nucleotides called the
anticodon. These three
nucleotides pair with the
nucleotides in the
codon. The tRNA
molecule also has an
amino acid attached.
amino acid
Anticodon
(3 bases)
Transfer RNA
Step 4: Peptide bonds
form between amino
acids to form the
polypeptide chain in a
process called
elongation (it makes
the polypeptide chain
longer.)
Step 5: The ribosome
continues to match the
codons in the mRNA
with anticodons in tRNA
until it reads a codon in
the mRNA that says
“stop.” A tRNA for
“stop” does not carry an
amino acid. No peptide
bond will form, so the
ribosome releases the
mRNA and the protein.
Step 6: The newly
formed polypeptide will
start to coil and bend,
forming the 3-D shape
of proteins (recall the 4
levels of protein
structure)
Why are proteins important?
Each protein has a specific function within
living cells. Some functions of proteins are:
1. acting as enzymes, to speed up and regulate
chemical reactions.
2. making pigments
3. determining your blood type.
4. regulating cell growth and development.
Where in the cell does
transcription occur?
-Nucleus
Where in the cell
does translation
occur?
-Cytoplasm
Activity 1
Transcription in nucleus
AUG CGG
Translation in cytoplasm
Activity 1
Transcription in nucleus
AUG CGG
Translation in cytoplasm
Met, Arg,