Transcription

What I need to know:-

1. What transcription is2. The stages of transcription3. The use of enzymes in transcription4. To identify what an intron and exon is5. The process of RNA splicing

Protein synthesis

DNA(containing all the genetic material/coding)

messengerRNA

Protein“The middle man”

Transcription

Transcription is the synthesis of mRNA from a section of DNA.

The newly synthesised mRNA strand will contain the code to make a specific protein.

The stages are : -

TranscriptionSTAGE 1 – DNA double helix unwinds

STAGE 2 – weak hydrogen bonds breaking between bases, causing DNA strands to separate

STAGE 3 – free RNA nucleotides (moving freely in the nucleus) find complimentary pair on the DNA strand

STAGE 4 – weak hydrogen bonds are formed between the new bases pairing

STAGE 5 – strong chemical bonds are formed between the new RNA nucleotides, opposite the DNA. This allows a new strand to be formed

STAGE 6 – weak hydrogen bonds are breaking between DNA & RNA, allowing mRNA to break from the DNA template

STAGE 7 – new mRNA strand is ready to be transported out of the nucleus into the cytoplasm

STAGE 8 – weak hydrogen bonds reunite the two original DNA strands into a double helix again.

RNA polymerase

This enzyme is responsible for transcription as it moves along the gene, unwinding and opening the DNA strand.

It also forms the mRNA strand (template) by joining nucleotides together

Nucleotides can only join at the 3’ end of the mRNA strand

Primary transcript of mRNA

Modifying the primary transcript

A transcribed mRNA strand can be up to 8000 nucleotides long.

How many of these nucleotides do you think are needed to make the protein?

Around 1200!!

There are long sections of DNA that do not code for a polypeptide. These are called INTRONS.

Introns are found between the sections of DNA that do code for the proteins.

These coding regions are called EXONS

Since the introns are not needed, they are cut out

RNA Splicing

Mature transcript with continuous coding sequence of nucleotides

Animations

• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html

• http://www.educationscotland.gov.uk/highersciences/humanbiology/animations/transcription.asp#

Now attempt the following questions1) Draw a diagram of the mRNA strand that would be

transcribed from section X of the DNA molecule below

2) What enzyme is responsible for transcription? 3) What is an intron and an exon?4) Which of these is removed from the primary transcript of

mRNA? By what process?

Section x

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