APB Unit 6.1 - Cell Expression & Regulation #GoBioRams

APB Unit 6.1 - Gene Expression & Regulation 1.0 #GoBioRam

Transcription & RNA Splicing

Chapter 17

The Central Dogma

DNA is used to make RNA (Transcription)

then

RNA is used to make Proteins (Translation).

Transcription

DNA LARGE font to RNA small font.

Change the script.

Change the font.

Translation

Translate from the language of RNA (Nucleic Acid)

to the language of Proteins

Unless stated otherwise

We are looking at a Eukaryotic System

Transcription

DNA to RNA

Changing the script or font.

Initiation of Transcription

DNA Regulatory Mechanisms

• Some chemical will trigger the need to begin Transcription.

• https://ib.bioninja.com.au/higher-level/topic-7-nucleic-acids/72-transcription-and-gene/epigenetics.html

DNA Regulatory Mechanisms

• Transcription will occur in the Euchromatin (True chromatin).

• Heterochromatin is too condensed.

Acetylation v. Methylation

• Acetylation will allow transcription to occur.

• Methylation will NOT allow transcription to occur.

Assuming that we have acetylation...

• RNA Polymerase must find a starting point upstream from the gene of interest.

• It looks for a Promoter Sequence.

• The Promoter Sequence has a TATA Box inside.

Transcription Factors

• Several Transcription Factors must land on the Promoter forming a Transcription Initiation Complex.

• This is where a lot of Gene Regulation of Gene Expression occurs.

• More on this later.

RNA Polymerase II

• Only after the correct Transcription Factors have landed on the Promoter, will RNA Poly II land.

• Note that Transcription can then begin.

• We will make a 5' to 3' RNA using the 3'-5' Template or Crick DNA Strand.

Elongation

Start and Stop

• The gene begins at the Start Codon TAC in DNA speak or AUG in RNA speak

• Transcription continues until you reach a Terminator sequence that includes a Stop Codon.

• ATT , ATC, and ACT in DNA speak or UAA, UAG, or UGA in RNA speak.

After the gene has been transcribed

AAAUAAA Polyadenylation signal is added.

The pre mRNA is released for RNA processing.

Termination

Biochemistry of RNA

Single stranded

Ribose sugar

Replace the T with a U nitrogen bas

Reminder

• A = Adenine

• G = Guanine

• T = Thymine

• C = Cytosine

• U = Uracil

RNA processing

• The RNA has to be "stabilized."

• A 5' Guanine Cap is added at the beginning.

• A Poly-A Tail is added at the end.

RNA splicing

Exons will be expressed, so these regions are kept.

Introns will be removed through editing.

RNA Splicing uses Spliceosomes.

These Spliceosomes were discovered after Ribozymes.

Ribozymes are RNA that act like enzymes.

Alternative RNA splicing

Different mRNAs are possible depending on how the pre mRNA is spliced.

Each Exon that is kept is called a Domain.

Pre mRNA enters the cytoplasm.

Review

• The Central Dogma = DNA -> RNA -> Proteins

• Transcription = DNA -> RNA

• Translation = RNA -> Proteins

• Euchromatin is loose chromatin caused by acetylation events.

• Heterochromatin is tight chromatin caused by methylation events.

Review

• Transcription has three main steps: Initiation, Elongation, and Termination.

• Transcription begins only after a Promoter Sequence that includes a TATA Box is found upstream from the gene.

• Transcription Factors bind to the Promoter Sequence forming a Transcription Initiation Complex.

• RNA Polymerase II binds and begins transcription, a.k.a. the Elongation Phase.

Review

• Transcription forms a 5' to 3' pre mRNA.

• The template strand is the Crick or 3'-5' strand of DNA.

• Transcription continues until a STOP codon has been reached.

• Then, a Polyadenylation sequence is added at the end.

• The pre mRNA is now ready for RNA Processing.

Review

• A 5' cap is added.

• A Poly-A tail is added.

• This is done so that the pre mRNA is chemically stable.

• RNA splicing can occur using Spliceosomes that will remove introns.

• Exons that are kept are called domains.

• We will talk about alternative splicing later.

Review

• The pre mRNA is now officially called mRNA.

• mRNA is now ready to enter the cytoplasm.

• Once in the cytoplasm, the mRNA will bind to a ribosome.

• Translation will begin.