6.2 Transcription

6.2 Transcription

Day 3 Lesson Activities

• Transcription is the first step in protein synthesis.

• It is the process of forming a short strand of mRNA from one gene on a long DNA strand.

• When you think of transcription, think of the word "script" and associate it with letters. In this stage we are changing the script of one gene from DNA letters into RNA letters.

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Transcription:
DNA -> RNA

​The mRNA strand serves as a "disposable photocopy" of the master DNA code for a gene locked in the "vault" (the nucleus). We wouldn't want to use our master code (DNA) to make our protein recipes because we might damage it.
We use a photocopy (mRNA) instead!

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mRNA

RNA polymerase separates DNA to make transcription bubble.
RNA polymerase begins matching complementary base pairs of RNA nucleotides to the DNA.  
A with T U with A
C with G G with C

1. Initiation

Steps for Transcription

2. Elongation

3. Termination

The mRNA sequence elongates as RNA polymerase moves along the DNA matching bases.

This occurs at a rate of 40 nucleotides per second!

RNA polymerase reaches a termination sequence and detaches from the DNA.

The completed mRNA molecule is released.

Draw a simplified version of the three steps to transcription in your notes.

Label the following:
RNA Polymerase Initiation
DNA Elongation
mRNA strand Termination
transcription bubble

Transcription Model

The resulting strand of mRNA is made of codons and codes for the making of a protein. 

A codon is a sequence of three letters on mRNA or DNA that codes for a specific amino acid.

It begins with a start codon and ends with a stop codon.

mRNA will now travel out of the nucleus and into the cytoplasm to find a ribosome to translate its code.

​mRNA Structure

Transcription Animation

Watch the video on the next slide and identify the steps of initiation, elongation, and termination.

Does anything happen to the mRNA strand after it is terminated from the DNA, but before it leaves the nucleus?

Multiple Choice

What is the purpose of transcription?

• To duplicate the DNA strand

• To make an mRNA strand that will leave the nucleus

• To build a protein.

• To make a tRNA strand that will deliver amino acids

Multiple Choice

Where does transcription occur?

• In the endoplasmic reticulum

• In the ribosomes

• In the nucleus

• In the cytoplasm

Work Session

Now you are going to take the information you have learned about transcription to complete part of a worksheet that will help you visualize the processes in protein synthesis.

You will only complete the TRANSCRIPTION portion of the page.