GN 301 Module 3: Transcription, RNA Types, Gene Structure and RNA Processing

DNA and RNA differences

DNA has thymine, RNA has uracil DNA is double-stranded, RNA is single-stranded DNA has deoxyribose, RNA has ribose

  • The process of making RNA from DNA is called transcription.
  • The process of making protein from mRNA is called translation.

RNA

The 3 main RNA Types, their full names and their functions:

  • ==tRNA:== Transfer RNA. Transports amino acids from the cytoplasm to the ribosome.
  • ==mRNA:== Messenger RNA. Genetic information transcribed from DNA as a sequence of bases is transferred to a ribosome.
  • ==rRNA:== Ribosomal RNA. Ribozyme that carries out protein synthesis in ribosomes.

The ==template strand== of DNA is used as a pattern for RNA synthesis. The other strand is called the ==coding strand== and gives the code for a new RNA strand.

  • ==Phosphodiester bonds== join the nucleotides together in transcription
  • ==DNA polymerase== is the enzyme that joins the nucleotides
  • ==Transcription== goes from 5’ to 3’
  • ==RNA is complementary and antiparallel== to the template strand of DNA

PRACTICE EXAMPLES:

  1. A template strand of DNA has the sequence:

5’ – G T T T A G C T A – 3’.

What is the sequence of the RNA produced using this template?

5’ – U A G C U A A A C -3’

  1. A coding strand of DNA has the sequence:

5’ – A T G C A T T T G – 3’

What is the sequence of the RNA that came from this segment of DNA?

3’ – A U G C A U U U G – 5’

  • ==Replication== occurs in the nucleus
  • ==Transcription== occurs in the nucleus
  • ==Translation== occurs in the cytoplasm

mRNA Processing and Gene Structure

==mRNA== is produced as a primary transcript and is processed to become mature mRNA 3 types of processing are:

1. ==Capping==- when a cap is added to the 5’ end

2. ==Tailing==: The 3’ end is cleaved and a tail of adenine is added

3. ==Removing the introns and joining the exons==

Roles

  • Role of the ==Promotor:== to be a region of DNA where proteins like RNA polymerase can bind to initiate transcription of a gene
  • ==Introns==: a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes.
  • ==Exons==: a segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence.
  • The type of small RNA that helps in processing is ==sRNA== which stands for bacterial small RNA

Why is it important to remove introns?

  • to get the proper RNA sequence
  • to alternate between forms of proteins that can be produced if different exons are included

What is alternative splicing and why is it important?

  • Alternative splicing is a cellular process in which exons from the same gene are joined in different combinations, leading to different, but related, mRNA transcripts. These mRNAs can be translated to produce different proteins with distinct structures and functions — all from a single gene.