Translation
PROTEIN SYNTHESIS
• Transcription = Nucleic acid sequence (a gene)
 an identical copy of the Nucleic acid
sequence (mRNA)
• Translation = Nucleic acid sequence (mRNA)
 a sequence of Amino acids (a protein).
• How do we decode the sequence of nucleotides
on mRNA and turn it into a sequence of amino
acids (a protein)?
• How many different amino acids
are there?
• So can one base code for one
amino acid ex. Can adenosine (the
base) code for tryprophan (an
amino acid)?
• Can two bases?
• What about three?
Meet tRNA … “the decoder”
• There are 64 species of tRNA, each
species recognizes the code for an amino
acid or a start or stop signal
• Why 64?
Codons and Anticodons
• A codon is a group of three nucleotides on
an mRNA molecule
• An Anticodon is the complimentary group
of three nucleotides on a tRNA
• When the codon is recognized by the
complimentary anticodon on the tRNA the
correct amino acid corresponding to that
codon is made available.
4 Components used in Translation
1. mRNA- the message to be translated
into protein.
2. Amino acids- the building blocks that
are linked together to form the protein.
3. Ribosomes- the “machines” that carry
out translation.
4. tRNA (transfer RNA)- brings an amino
acid to the mRNA and ribosome.
•
•
•
One end of a tRNA molecule has an
anticodon that complements with an mRNA
codon.
The other end has a specific amino acid.
A tRNA molecule with a particular anticodon
always carries the same type of amino acid.
How does translation occur?
1. The ribosome binds to the mRNA molecule.
2. The tRNA with the anticodon that
complements the first codon on the mRNA
binds to the first site on the ribosome.
3. Another tRNA with the anticodon that
complements the second codon on the mRNA
binds to the second site on the ribosome.
4. A peptide bond forms between the first two
amino acids.
5. The first tRNA leaves, and the ribosome
moves along the mRNA to the next codon.
6. The next tRNA brings in the next amino acid,
and a peptide bond is formed between this
amino acid and the growing amino acid chain.
7. The process continues with the ribosome
moving along the mRNA molecule and the
amino acids linking together until a STOP
codon is reached.
The CODE of translation
mRNA nucleotides are translated in groups
of 3 called codons.
AUGCACUGCAGUCGAUGA
CODONS
Each codon codes for a specific amino acid.
20 different amino acids can be used in
different combinations to form a protein.
For example:
mRNA codon
AAU
CGC
GGG
amino acid
asparagine
arginine
glycine
Amino Acid sequence determines
the 3-D protein shape
• Interactions between amino acids cause
folding and bending of the chain
Examples:
– positive (+) and negative (-) parts of amino
acids are attracted to each other.
– hydrophobic regions are attracted to each other
• Folding
http://www.stolaf.edu/people/giannini/flashanimat/proteins/hydrophobic%20force.swf
•
Structure levels
http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein structure.swf
How is the amino acid sequence
determined?
• The mRNA
• Each codon is a code for one amino acid
DNA sequence:
mRNA sequence:
amino acid sequence:
TACCGAGATTCA
AUGGCUCUAAGU
Met -- Ala -- Leu -- Ser
U
U
C
G
G
UUU Phenylalanine
(Phe)
UCU Serine (Ser)
UAU Tyrosine (Tyr)
UGU Cysteine (Cys)
U
UUC Phe
UCC Ser
UAC Tyr
UGC Cys
C
UUA Leucine (Leu)
UCA Ser
UAA STOP
UGA STOP
A
UUG Leu
UCG Ser
UAG STOP
UGG Tryptophan
(Trp)
G
CUU Leucine (Leu)
CCU Proline (Pro)
CAU Histidine (His)
CGU Arginine (Arg)
U
CUC Leu
CCC Pro
CAC His
CGC Arg
C
CUA Leu
CCA Pro
CAA Glutamine
(Gln)
CGA Arg
A
CUG Leu
CCG Pro
CAG Gln
CGG Arg
G
AUU Isoleucine (Ile)
ACU Threonine
(Thr)
AAU Asparagine
(Asn)
AGU Serine (Ser)
U
AUC Ile
ACC Thr
AAC Asn
AGC Ser
C
AUA Ile
ACA Thr
AAA Lysine (Lys)
AGA Arginine (Arg)
A
AUG Methionine
(Met) or START
ACG Thr
AAG Lys
AGG Arg
G
GUU Valine Val
GCU Alanine (Ala)
GAU Aspartic acid
(Asp)
GGU Glycine (Gly)
U
GUC (Val)
GCC Ala
GAC Asp
GGC Gly
C
GUA Val
GCA Ala
GAA Glutamic acid
(Glu)
GGA Gly
A
GUG Val
GCG Ala
GAG Glu
GGG Gly
G
C
A
A
Your turn
• Decoder construction-DNA Bingo
• Translation exercise (Find the secret
message)
• Genes to proteins-practice worksheet.
– or
• Complete the “Translation Practice”
worksheet