Transcription and processing of eukaryotic genes

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The three types of mRNA and their relative abundancies
Messenger RNA, Ribosomal RNA, Transfer RNA. 3%, 71%, 15%
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Features of a mature mRNA
5'UTR, AUG initation codon, ORF, Termination codon UGA, polyadenation signal AAUAAA, poly A tail
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Two types of genes expressed in cells. Example of each
Consitiuative, eg actin. and regulated, eg, cyclins expressed for cell division
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Why would we need to regulate gene expression/protein production
to make proteins specific to that cell's needs. Some protiens are needed in different abundance. The abundance can vary over time. Synthesis of unnecessary protiens is wasteful
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Points where eukaryotic genes can be regulated
DNA, transcription, translation, post-translational
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Examples of regulation at the DNA level
DNA rearrangement to influence gene expression, changes in access to DNA by chromatin structure
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Regulation at the level of transcription
Transcription initation, alternative splicing, mRNA stability, mRNA editing.
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Regulation at the level of translation
microRNAs
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What two factors control eukaryotic initation of transcription
cis acting factors and trans acting factors.
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What needs to happen before a gene is transcribed
Transcription initiation complex. Helps RNA polymerase get started
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What are cis acting factors?
Short sequences of DNA which control transcription
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Where are cis acting factors found?
In the non-coding regions of the genome
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Why are they called cis acting factors?
They influence genes on the same dna molecule
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an example of cis regulatory sequences
Hormone responsive elements
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What are trans acting factors?
Regulatory molecules that diffuse through the cell from it's site of synthesis to bind to the regulatory sequence
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What are trans acting factors like?
They are usually proteins which can bind to DNA. The have 2 domains - DNA binding domain and transcription activation domain
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What do cis-acting reg sequences bind?
cis acting reg. sequences bind to trans acting reg. proteins.
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Genes and hormones
H. stimulate synthesis of large amounts of protien in target tissues. Bind to receptors in the cell membrane and start a signalling cascade
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Do all hormones act on extracellular receptors?
No, some enter the cell and form a receptor hormone complex that interacts with DNA in the nucleus
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Example of a hormone that acts on a cell surface protien
Glucogon, acts on cell surface GPCR to send a signal via cAMP
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What are promotors?
A short sequence found upstream of a coding region where the TIC assembles
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An example of a promotor conserved in most eukaryotic genes
the TATA box, 25-35bp upstream from the start site. Positions RNA pol II
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What does the 5' end of a regulated gene contain?
Many cis regulatory elements.
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Examples of cis reg. elements that are not promotors
Enhancers - upstream. Upstream promotors like SP1. Regulatory elements that bind hormones or other signals, eg GRE. glucagon repsonse element
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What are GTFs?
Generalised transcription factors that are needed for the TIC to be formed.
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What roles to GTFs have?
Help RNA pol find the start of genes.
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Structure of RNA Polymerase II
Large multimeric subunit protien = 8-12 subunits. 500kDA
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What is the first step in TIC assembly?
Tata-binding protein binds to TATA box in DNA and bends it.
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What then binds to TBP complex? Effect of this?
TFIIB binds and acts as a bridging factor - allowing recruitment of RNA pol II to the complex.
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What comes with rna pol II when it binds>
TFIIF
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What happens after Rna pol II binds
TFIIE and TFIIH rapidly associate with the complex.
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What does TFIIH do?
its a large multi-meric protien with both kinase and helicase activity
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What do we call this after TFIIH has joined?
Pre-initation complex
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What happens after TFIIH is activated?
Phosphorylation of the carboxyl terminal domain of RNA pol II. Allows the polymerase to leave the promoter region, leading to elongation.
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What does this phosphorylation do?
Results in polymerase leaving the promotor region, causing elongation
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What does TFIIB do?
recognises the BRE element in promotors. accurately positions RNA polymerase at the start site of transcription.
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What does TFIIH do?
Unwinds DNA at the transcription start point, phosphorylates Ser5 at RNA polymerase CTD
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Card 2

Front

Features of a mature mRNA

Back

5'UTR, AUG initation codon, ORF, Termination codon UGA, polyadenation signal AAUAAA, poly A tail

Card 3

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Two types of genes expressed in cells. Example of each

Back

Preview of the front of card 3

Card 4

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Why would we need to regulate gene expression/protein production

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Card 5

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Points where eukaryotic genes can be regulated

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