Control of gene expression 1 Flashcards
Give details on controlling gene expression
- gene expression is carefully controlled (highly regulated)
- only genes needed for function of the cell will be expressed
- some proteins are needed in large amounts whereas other in small
- the levels of various proteins may need to go up and down in a given cell depending on the stage e.g. during the cell cycle
- synthesis of unnecessary proteins is wasteful of cells energy and resources
What are 3 times when gene expression is regulated?
- During differentiation and development
- As a response to the environment
- Depending on the function of the cell
4 problems with regulation of gene expression?
- cancer (absence of transcription off switch leads to wrong genes being expressed and cell division)
- developmental disease (mistakes in early protein synthesis can lead to organ developmental problems)
- exposure to toxins or drugs
- chronic diseases (abnormal gene expression as a result of the wrong signals in the cell can cause inflammation)
What six levels is eukaryote gene expression regulated at?
- Transcription
- RNA processing
- mRNA transport
- mRNA translation
- mRNA degradation
- Protein degradation
Explain how transcription initiation can regulate gene expression
Transcription initiation is the major point of regulation in eukaryotic gene expression and is controlled by interactions between DNA and proteins.
This comes about by an interactions between DNA and proteins.
Proteins come and bind to the DNA.
Trans-acting molecules are ones which come from other areas not from the DNA. They are proteins.
This makes a transcription factor which goes back into the nucleus and binds to another place on the DNA sequence. This allows polymerase II to start transcribing this region.
Give 4 points on regulatory molecules
- Proteins which control transcription initiation by binding to DNA
- Can diffuse through the cell from its site of synthesis to bind to the regulatory sequence (such a promoter) and affect transcription
- Usually have 2 domains, a DNA binding domain and a transcription activation domain
- e.g. general transcription factors which are needed for transcription initation
Give 4 points on regulatory sequences
- Short sequences of DNA which control transcription initiation
- Usually found in the non-coding regions of the genome
- Interact with DNA binding proteins e.g. transcription factors resulting in induction or repression of transcription initiation
- Called ‘cis’ because they influence genes on the same DNA molecule
- e.g. TATA box
What is TATA box?
a highly conserved promoter in eukaryotic DNA
Promoters:
Short sequence found —- of a coding region.
Important in the —- of transcription.
The site where the ‘—- —- —-‘ is assembled.
The TATA box helps to —- the RNA polymerase II for correct transcription initiation. There can be other regulatory sequences.
Upstream
Initiation
Transcription initiation complex
Position
What are transcription factors and what are the two types?
They are proteins which ensure that genes are correctly expressed at a specific time and in response to internal or external stimuli.
- General Transcription Factors: proteins which can bind DNA and are needed to form a pre-initiation complex and to recruit RNA Polymerase II
- Sequence-specific DNA binding TF: these facilitate or prevent transcription initiation of specific promoters
What are general transcription factors needed for?
Needed for all RNApol II transcribed genes.
The ‘core’ promoter is the one where RNA pol II and GTFs will bind.
The ‘proximal’ promoter is where other transcription factors will bind.
Give 3 steps in transcription initation
- A transcription initiation complex has to assemble upstream of the start site which helps RNA polymerase II to get started. A specific order is needed of these transcription factors (8 of them in total).
- A number of proteins have come together in a specific order to help RNA pol II transcribe genes. These are general transcription factors
- The GTFs position RNA pol II at the promoter resulting in a transcription initiation complex. The polymerase then copies the DNA into RNA.
Regulation is achieved by the specific combination of protein factors in the —- —-
Initiation complex
What can a mutation in the coding sequence of a TF do?
Abnormal mRNA is produced, abnormal expression of proteins and an altered regulation of pathways.
Explain of regulation of gene expression by hormones:
Sometimes the signal to switch genes on/transcribe comes from a distant source in the body e.g. via the endocrine system
Hormones are exogenous chemicals released into circulation which can travel and affect target tissues
Hormones signals to switch genes on and off by binding to receptors in the cell membrane and starting a signalling cascade
The effect of hormones can stimulate synthesis of large amounts of protein in certain tissues (target tissues)
Some hormones enter the cell and then bind to a receptor, the receptor-hormone complex moves to the nucleus where is interacts with DNA and stimulates transcription of target genes (transcription initiation) to bring about a physiological change in the cell. Other hormones initiate a signalling cascade which can affect gene expression
The endocrine system can regulate and co-ordinate changes in gene expression of many systems.
