Central Dogma

Introduction

The Central Dogma of Molecular Biology
Cell

DNA

Transcription

mRNA
Translation

Ribosome

Polypeptide
(protein)

Protein Synthesis
Flow of Information:
DNA
RNA
Proteins
Transcription
Translation
Transcription is the process by which a molecule of DNA is copied into a complementary strand of RNA.
This is called messenger RNA (mRNA) because it acts as a messenger between DNA and the ribosomes where protein synthesis is carried out.

Protein Synthesis Transcription
Transcription process
•RNA polymerase (an enzyme) attaches to
DNA at a special sequence that serves as a
“start signal”.
•The DNA strands are separated and one strand serves as a template.
•The RNA bases attach to the complementary
DNA template, thus synthesizing mRNA.

Protein Synthesis: Transcription
Transcription process continued
•The RNA polymerase recognizes a termination site on the DNA molecule and releases the new mRNA molecule.
(mRNA leaves the nucleus and travels to the ribosome in the cytoplasm.)

Protein Synthesis: Transcription

Eukaryotic Transcription
Cytoplasm
DNA

Transcription
RNA

RNA
Processing
mRNA G

G

AAAAAA

Nucleus

Export

AAAAAA

Protein Synthesis: Translation
Translation is the process of decoding a mRNA molecule into a polypeptide chain or protein. Each combination of 3 nucleotides on mRNA is called a codon or three-letter code word.
Each codon specifies a particular amino acid that is to be placed in the polypeptide chain
(protein).

Protein Synthesis: Translation

A Codon
OH
P

HO

NH2

O
N

O

N

CH2

H

P

O

O
N

O
CH2

P

NH

N

Guanine

NH2

N

O

Arginine

H

O
HO

N

O

O
HO

Adenine

N

NH2

O
N

O
CH2

N
O

OH

H

N
N

Adenine

Protein Synthesis: Translation
•A three-letter code is used because there are
20 different amino acids that are used to make proteins.
•If a