Class 10:

Transcription

SBI4UMolecular Genetics

From Friday…

What is the Central Dogma?

CENTRAL DOGMA

Fundamental principle of molecular genetics,

which states that genetic information

flows from DNA to RNA to proteins

Why is gene expression important?

The Genetic Language Uses 4 Letters Written Into 3-Letter Words

What will be the chain of Amino Acids for the

following mRNA sequence?

AUGUGCAACCGUCGAUAG

Today we are going to talk about…

TRANSLATION

INTRODUCTION

During transcription the DNA code is chemically rewritten as an RNA code

Transcription: divided into 3 sequential stages

1. Initiation2. ElongationTermination

INITIATIONIn prokaryotes and eukaryotes

begins with RNA polymeraseBinds to the DNA strand, unwinds

the helix near the beginning of a gene

The binding occurs at the promoter which is a nucleotide sequence that lies just before the gene

A key to the promoter sequence in the eukaryotes is TATA box

TATA BOXA region of the DNA with high

percentage of TA bases, which is recognized by the RNA polymerase

Prokaryotes have a TATAAT sequenceA and T because 2 hydrogen bonds,

less energy needed to break RNA expends less energy

The part of the gene that is transcribed into RNA is called the Transcription Unit

ELONGATIONNo primer needed 5’ to 3’ directionThe opposite strand of DNA is

known as the coding strand, it contains the same base pair sequence as the new RNA

RNA elongates as nucleotides are added one at a time

The new RNA molecule winds temporarily with template DNA into hydrid RNA/DNA double helix

ELONGATION CONTINUED..Beyond this region RNA unwinds

from DNA

When a cell requires a particular protein they need to produce thousands or even millions of copies example.

A single red blood cell contains 375 million hemoglobin molecules

TERMINATION• Transcription is terminated when RNA polymerase recognizes the termination sequence

• In prokaryotes 1 termination mechanism involves a protein binding to the mRNA and stopping transcription or when mRNA binds with itself in a hairpin loop

• In eukaryotes 1 termination is string of A

• The newly made RNA descoiatates from the DNA template