Lecture 3- Gene organisation and transcription I Flashcards
What are Housekeeping Genes?
Genes expressed in all cells, needed for normal cell function and viability.
What is RNA?
Ribo Nucleic Acid, it is the initial product of gene expression to make proteins. It can act as the template of protein translation.
What are the differences between RNA and DNA?
- RNA: single-stranded, shorter, A-U, ribose sugar
- DNA: double-stranded, longer, A-T, deoxyribose sugar
What happens when cells specialise?
All cells contain the same DNA and genes but different genes are switched on and off so they make different proteins.
Outline what happens during transcription…
1) DNA helix unwinds
2) Ribonucleotides base pair with DNA bases on antisense strand
3) RIbonucleotide bases are joined by phosphodiester bonds.
4) RNA chain grows one base at a time in a 5’-> 3’ direction
Which enzyme carries out gene transcription?
RNA polymerase
What is a transcription factor?
A special gene regulatory protein which binds to DNA and regulates gene activity.
What is a gene promoter?
The DNA sequence at which the transcription complex binds.
What do transcription activators do?
Activate gene expression
What do transcription repressors do?
Suppress gene expression
What are the three different types of RNA polymerases and what do they transcribe?
1) RNA Polymerase I - rRNA genes
2) RNA Polymerase II- transcribes genes encoding proteins into mRNA
3) RNA Polymerase III- tRNA and 5S RNA genes
What is found in the gene promoter region of a gene?
- A transcription factor binding site
- The TATA sequence
What is the purpose of the TATA DNA sequence?
Found in the gene promoter region, it specifies the initiation point for transcription by RNA Pol II.
1) What is the first thing to bind to the TATA sequence
2) What does it contain to help bind?
1) TF IID
2) TATA Binding Protein (TBP) and TBP Accessory Factors (TAF)
After TF IID binds to the TATA sequence what happens
- Partially unwinds the DNA helix, widening the minor groove to allow extensive contact with bases within the DNA
- Unwinding is asymmetric w.r.t. the TBP-TATA complex, assuring transcription is unidirectional
What binds to TF IID and why?
- TF IIA and TF IIB bind with TF IID.
- This is because TF IIB can bind with both TF IID and RNA Pol II
What binds to TF IIA and TF IIB
RNA Pol II which is bound to TF IIF
What binds to RNA Pol II and why?
- TF IIE, TF IIH and TF IIJ
- TF IIH promotes further unwinding of the DNA helix to facilitate RNA synthesis by RNA Pol II.
What is the purpose of the Basal Transcription Complex?
- Allows RNA Pol II to be phosphorylated and then engage in transcription
- Produces BASAL level of transcription in the absence of other Transcription Factors
What are the two ways that transcription factors can work?
1) Bind to transcription factor binding sites and ‘bend’ DNA. They interact with each other and the Basal Transcription Complex.
2) Can remodel chromatin by using proteins with enzymatic activity to modify histones
How do you get gene expression?
Hyperacetylation- histone tails, which extend from nucleosomes, are acetylated. This causes the core DNA to be coiled less tightly
How do you get gene repression?
Hypoacetylation- histone tails, are deaceylated so the DNA is closed and coiled tightly.
What are the major determinants of Transcription Factor expression?
1) Cell Lineage
2) External Signals- Hormones, Growth Factors, Mechanical Stress, Heat, Light etc.
3) Cancers- abnormal transcription factor expression
