Download 4 - Protein synthesis 2

Aim: How are proteins synthesized?
What are the main jobs of DNA?
Replication & Protein Synthesis
Why does DNA replicate?
So when cells divide, new cells can get a
copy of the instructions on how to make
proteins
How are proteins synthesized?
•Transcription
•Translation
Transcription
The process where the
larger DNA molecule
inside the nucleus is
transcribed into the
smaller mRNA molecule
that can exit the nucleus
and aid in making proteins.
Why does mRNA have to leave the
nucleus?
mRNA
Because the cytoplasm contains the
sites of protein synthesis (ribosomes)
and the free amino acids which make
up the proteins.
Ribosomes are in the cytoplasm
Ribosomes are the site of protein
synthesis
• Shows Transcription (DNA > mRNA)
• Shows Translation (mRNA > Amino Acid Chain)
• tRNA not shown here, but would be attached to A.A.
What transports the amino acids to the
ribosomes?
tRNA
Bases:
A, U, G, C
tRNA
Parts of tRNA;
1) Anticodon- three
bases that are
complimentary to a
specific codon in the
mRNA.
2)Binding Site- a
specific amino acid
binds here.
How does tRNA know what amino acid
to deliver?
tRNA
Anti-codon
mRNA
Codon
mRNA - tRNA
GGG…… CCC
AUC…… UAG
ACC…… UGG
CGU…… GCA
It has an anti-codon and also
attaches to amino acids – bringing
them to the ribosome
mRNA - tRNA – amino acid
GGG……CCC - Gly
AUC……UAG - Ile
ACC……UGG - Thr
CGU……GCA Arg
Express the following gene:
TAC-GGC-TTA-ACG
AUG-CCG-AAU-UGC(mRNA=codon)
UAC-GGC-UUA-ACG(tRNA=anticodon
Use mRNA codon
To get amino acid
sequence
Methionine-Proline-asp-cyst-
mRNA vs. tRNA
Messenger RNA
Transfer RNA
Carries copy of
instructions from
Carries amino acids
nucleus to ribosome to the ribosome
Steps of Protein Synthesis:
1. DNA is Transcribed into mRNA
Start Codon:
2. mRNA enters the cytoplasm. AUG (met)
3. tRNA picks up amino acids
and carries them to the
ribosome and the mRNA.
4. The anti-codon on the tRNA matches up
with the mRNA codon.
Steps of Protein Synthesis:
5. Peptide bonds are formed between
adjacent amino acids.
6. A releasing factor binds to one of the 3
“stop codons” and this signals the release of
the polypeptide chain.
Stop Codons:
UGA, UAA, UAG
Polypeptide synthesis
MOVIE