Protein synthesis

Pranabjyoti Das

Protein Synthesis

CENTRAL DOGMA OF MOLECULAR BIOLOGY

DNA

 RNA 

  Protein

transcription

translation

GROWING CELL

Before cell division the cell’s DNA has to duplicate

(DNA REPLICATION)

While the cell is growing it needs enzymes and extra proteins…

TRANSCRIPTION

THE PROTEINS ARE MADE IN THE CYTOPLASM IN THE RIBOSOMES

THE INFO FROM THE DNA IS COPIED INTO m RNA, WHICH CAN LEAVE THE NUCLEUS AND GET TO THE RIBOSOMES IN THE CYTOPLASM.

THE INFORMATION FOR PROTEIN SYNTHESIS IS IN THE DNA IN THE NUCLEUS.

DNA INFO COPIED TO mRNA

TRANSCRIPTION: the process

Only 1 strand of DNA in a gene gets transcribed:

RNA polymerase: enzyme that initiates transcription by binding to promoter at the 3' end of DNA, unwinds and unzips it.

RNA activated nucleotides pair with the complementary bases of the DNA strand

RNA polymerase, binds the RNA nucleotides together to form the mRNA poynucleotide.

TRANSLATIONDNA

M RNA

PROTEIN

transcription

DNA info is copied into to RNA code, which is still in the “language” of nitrogenous bases, except that adenine on the DNA pairs with uracil (in place of thymine) on the RNA. HAPPENS IN NUCLEUS.

translationThe RNA code is then translated to protein code, which is a different “language.” (nitrogenous bases to aminoacids.

This process involves ribosomes and two kinds of RNA: mRNA and tRNA. HAPPENS IN CYTOPLASM

INFORMATION IN THE mRNA

Codon: sequence of 3 nucleotides on

m-RNA that codes for one amino acid.

The GENETIC CODE states which codon stands for which aminoacid.

1 aminoacid

1 aminoacid

GENETIC CODEEven though there are only 20 amino acids

that exist, there are actually 64 possible

tRNA molecules:

4 X 4 X 4 = 64 possible combinations

CODONCODON CODON G C U

1º NUCLEOTIDE

2º NUCLEOTIDE

3º NUCLEOTIDE

=Gly

GENETIC CODE (II)

The GENETIC CODE can be reffered as well to the DNA, as in this case.

How can you tell this GENETIC CODE reffers to DNA?

Why can it be reffered to the DNA?

CHARACTERISTICS OF THE GENETIC CODE

It can be reffered to DNA or RNA.

It is UNIVERSAL. All living organisms share the same code.

We can “read” the DNA of a bacterium, a plant or a worm using the same code!! PROOF FOR EVOLUTION!!!

It is DEGENERATEAs there are ONLY 20 aminoacids but 64 possible codons Each aminoacid has MORE

than ONE codon!

There are codons that code for punctuation (START and STOP)

TRANSLATIONLOADED tRNA

RIBOSOME

mRNA

COMPONENTS PRESENT IN THE PROCESS

anticodon

Aminoacid carried

codon

TRANSLATIONThe newly made mRNA (transcription) leaves the nuceus and binds with the ribosome in the cytoplasm.

ONE codon is exposed at site P and another codon at site A

A tRNA with a complementary codon in its anticodon site will bind with the codon at site P, bringing an aminoacid.

1º AMINOACID:Methionine (AUG) in site P.

TRANSLATION

Even though every protein begins with the Methionine amino acid, not all

proteins will ultimately have methionine at one end. If the "start"

methionine is not needed, it is removed before the new protein goes to

work (either inside the cell or outside the cell, depending on the type of

protein synthesized)

TRANSLATION

A

2º AMINOACID: Glycine (only in this case) in site A.

PEPTIDIC BOND IS FORMED

TRANSLATION

STOP codon NO aminoacid is added. Its the END of the polypeptide!

Growing polypeptide

POLYSOMES

Thanks !