Disclaimer: OK…so I’m not VCAA so I don’t really know but a short answer question on the steps of translation and / or transcription has been in every exam since 1998 so the odds are in my favour.

Learning Objectives:

By the end of this session you should be able to:

• List the basic steps in transcription, RNA processing and translation in eukaryotes

Gene Expression

Transcription

The process of making an pre-mRNA molecule from a gene (DNA sequence).

Cellular location of transcription and translation

Videos to help you understand transcription

Animation showing transcription occurring in the cells nucleus.

Transcription video

Transciption Steps Question

Try to put the steps in order in the PollEv below before viewing the steps written underneath.

See how other students ordered the transcription steps

Reveal Transcription Steps

• RNA polymerase binds at the promoter of the gene
The DNA double strand is unzipped by RNA polymerase to expose the bases of the section to be copied
• RNA polymerase runs in the direction 3' to 5' (Mnemonic: Remember we like to run shorter distances over longer distances!)
• The template strand is copied into a complementary strand of premRNA using RNA polymerase
• The premRNA strand is synthesised in the 5' to 3' direction (Mnemonic: Remember we build towers from bigger foundations to smaller tops)

Post-transcriptional processing

In Eukaryotic organism, the pre-mRNA molecule must be processed before it can be translated. Once post-transcriptional modification is complete, the pre-mRNA is considered ‘mature mRNA’, and it can leave the nucleus via a nuclear pore.

Post-transcriptional processing is the stage of gene expression that most students neglect to mention in the exam - and it often costs them valuable marks, so don’t count yourself among them!

Introduction question for post-transcriptional processing

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Splicing

Splicing is one important step in post-transcriptional processing for Eukaryotic organisms.

In splicing some parts of the pre-mRNA molecule are excised (‘introns’), so others can be joined together (‘exons’).

A neat trick to help you remember whether introns or exons are the ones that are spliced out of the molecule is to remember the phrase: exons get to exit the nucleus.

Splicing Question

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Explanation

Transcription alone will lead to a pre-mRNA molecule that is the same length as the coding section of the gene (meaning - not including any regulatory components of a gene). However, in post-transcriptional processing in Eurkaryotic organisms the pre-mRNA molecule is 'spliced' (ome parts of the pre-mRNA molecule are excised), and lots of As are added to the end. Thus, the processed mRNA molecule that results from this process is no longer the same length as the original sequence coded in the DNA.

Post-transcriptional Modification Steps Question

Again, try to put the steps in order yourself before revealing the answers…

Reveal Post-transcriptional Modification Steps

• Introns are removed
• Exons are joined together
• poly A-tail is added to the 3' end
• 7-methylguanosine cap is added to 5' end

Translation

The process of building a polypeptide molecule from a mRNA molecule.

The responsibility of ribosomes.

Introductory translation question

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Videos to help you understand the process of translation

Animation showing translation occurring in a free ribosome.

Translation Steps Question

For the last time today, try putting the steps in order before revealing any answers …

See how other students answered this question

Reveal Translation Steps

• the mRNA travels to a ribosome which reads the START codon sequence (encodes for a methionine)
• tRNA carry the correct amino acids to the ribosomes
• the anticodon on the tRNA is matched to the codon by complementary base pairing
• the amino acid on the tRNA is added to the growing polypeptide chain
• the tRNA molecule leaves, the ribosome moves a codon along the mRNA molecule
• the process repeats until the STOP codon is reached and the ribosomes dissociates from the mRNA molecule. NOTE: It is not a protein at this stage, it needs to undergo modification and folding into its specific 3D shape.

Today’s TL;DR

• The basic steps of transcription, post-transcriptional modification and translation are very important for the exam! (And for you to live!)

Extra Resources:

Douchy’s VCE Biology Podcast