Download Lesson 4 - protein synthesis

Aim: How are proteins synthesized?
What are the main jobs of DNA?
Replication & Protein Synthesis
Why does DNA replicate?
So 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
What transports the amino acids
to the ribosomes?
tRNA
tRNA
Parts of tRNA;
1) Anticodon- three bases that are
complimentary to a specific codon
in the mRNA.
Bases:
A, U, G, C
2) Binding Site- a specific amino
acid binds here.
How does tRNA know what
amino acid to deliver?
tRNA
Anti-codon
mRNA - tRNA
GGG…… CCC
AUC…… UAG
mRNA
Codon
ACC…… UGG
CGU…… GCA
It has an anti-codon and also attaches to amino acids
and brings them to the ribosome.
mRNA - tRNA – amino acid
GGG……CCC
AUC……UAG
ACC……UGG
CGU……GCA
mRNA vs. tRNA
Messenger RNA
Carries copy of instructions
from nucleus to ribosome
Transfer RNA
Carries amino acids
to the ribosome
Steps of Protein Synthesis:
1. mRNA enters the cytoplasm.
2. tRNA picks up amino
acids and carries them to the
ribosome and the mRNA.
Start Codon:
AUG (met)
3. The anti-codon on the
tRNA matches up with the
mRNA codon.
4. Peptide bonds are formed between adjacent amino acids.
Steps of Protein Synthesis:
5. 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
MOVIE
Polypeptide synthesis