8 - Control Of Gene Expression Flashcards
What are mutagenic agents
Increase the rate of gene mutation
Eg: ionising radiation & carcinogens
Explain how a single base substitution causes a change in polypeptide structure
- change in sequence of amino acids/primary structure
- change in hydrogen bonds
- alters tertiary structure
What is a substitution mutation
1 base replaced with another
How can mutations lead to the production of a non-functional protein/enzyme
- change in base sequence of DNA
- changes sequence of codons on mRNA
- changes sequence of amino acids in primary structure
- changes position of hydrogen bonds
- changes tertiary structure so active site changes shape
- no ESC’s can form
How can a chemical stop the enzyme that causes methylation
- it can bind to the active site of the enzyme
- so that the enzyme cannot methylate
- transcription factors can bind to the promoter region
- so less methylation
What is the definition of epigenetics
Heritable changes in gene function without changes to the base sequence of DNA
How can increased methylation cause cancer
- methyl groups added to both copies of a tumour suppressor gene
- the transcription of tumour suppressor genes is inhibited
- leading to uncontrollable cell division
What does oestrogen bind with
Protein
What do methyl groups bind with
DNA
What do Acetyl groups bind with
Protein
Give one way benign tumours differ from malignant tumours
Cells of benign tumours cannot spread to other parts of the body
Explain how the methylation of tumour suppressor genes can lead to cancer
- methylation prevents transcription of genes
- protein is not produced that prevents cell division
- no control of mitosis
Why can cells in tumours be destroyed by the immune system 4m
- the faulty protein recognised as an antigen
- T cells will bind to the faulty protein
- T cells stimulate clonal selection of B cells
- so antibodies are released against the faulty protein
How can a molecule stimulate gene expression
- it can be a transcription factor
- which will bind to the promoter
- stimulates RNA polymerase
What are unspecialised stem cells capable of
- self renewal
- can develop into other cells (specialisation)
What are the 4 types of stem cells
- totipotent
- pluripotent
- multipotent
- unipotent
Describe stem cells specialisation
- there is a stimulus
- causes selective activation of genes
- mRNA only transcribed from active genes
- proteins that are translated modify the cell permanently and determine it s function
Describe totipotent stem cells
- occur for a limited time in early mammalian embryos
- can differentiate into every cell type in the body
Describe Pluripotent stem cells
- found in embryos
- can differentiate into most cell types (not cells of the placenta)
Describe multiplotent stem cells
- found in mature mammals
- can differentiate into a limited number of cell types
Describe Unipotent stem cells
- found in mature mammals
- can differentiate into only one cell type
How are induced pluripotent stem cells produced
- produced from adult somatic cells
- specific protein transcription factors associated with pluripotency put into cells causing the cell to express genes associated with pluripotency
- cells are cultured
Why are induced pluripotent stem cells used instead of embryonic cells
- no immune rejection as can be made using patients own cells
- more ethical
What are arguments for the use of embryonic stem cells in treating humans
- Tiny ball of cells, incapable of feeling pain, not equivalent to a human
- Would otherwise be destroyed (if from infertility treatment which creates more
than needed) - Duty to apply knowledge to relieve human suffering
What are arguments against the use of embryonic stem cells in treating humans
- Embryo is a potential human; should be given rights
- Induced pluripotent stem cells – cannot yet reliably reprogramme stem cells
- Could begin to multiply out of control, and cause tumours
What are transcription factors
- proteins that move from cytoplasm → nucleus
- Bind to DNA at a specific DNA base
sequence on a promotor region - they either Stimulate or inhibit transcription of target gene(s) by helping or preventing RNA polymerase binding
Why can oestrogen diffuse across the phospholipid bilayer
It’s lipid soluble
How does oestrogen initiate transcription
- In cytoplasm, oestrogen binds to a
receptor of an inactive transcription factor, (ITF) forming a hormone-receptor complex - the ITF changes shape causing it to become an ACTIVE transcription factor
- it then diffuses into nucleus and binds to a specific DNA base sequence on a promotor region
- stimulates transcription of genes by helping RNA polymerase to bind
What is the nucleosome ?
DNA wrapped around histone proteins
- how closely the DNA and histone are packed together affects transcriptor
What are the two types of epigenetic change
- methylation of DNA
- decreased acetylation of associated histones
Describe methylation of DNA
- methyl groups added to cytosine bases in DNA
- Nucleosomes pack more tightly together → prevents transcription
factors binding; genes not transcribed (RNA polymerase can’t bind) - methylation is Irreversible
Describe decreased acetylation of associated histones
- Decreased acetylation of increases positive charge of histones
- Histones bind DNA (which is negatively charged) more tightly→
preventing transcription factors binding; genes not transcribed - is Reversible
How can cancer be detected early from epigenetic change
Abnormal levels of methyl and acetyl
What is RNA interference (RNAi)
RNA molecules inhibit translation of mRNA produced by transcription
What are the two genes that can cause development of tumours?
Tumour suppressor genes and proto-oncogenes
Describe how tumours suppressor (TS) genes could be part of tumours developing
1 - Mutation alters primary and tertiary structure of protein - non functional protein
2 - increased methylation prevents transcription of TS genes so uncontrolled cell division
Describe how Proto-oncogenes could be part of tumours developing
1- Mutation could turn it into permanently activated oncogene
2- decreased methylation or increased acetylation causes excess transcription so uncontrolled cell division
What is the normal function of proto-oncogenes?
Stimulating cell division
What is the normal function of tumour suppressor genes?
Decrease cell division
- Causing self destruction of cells, (apoptosis)
Describe the role of increased oestrogen concentrations in development of breast cancer
At areas of high oestrogen conc - cell division is uncontrolled
What is the definition of a genome?
The complete set of genes in a cell
How can sequencing projects be used on simple organisms?
- Easy because less non-coding DNA
- identify the antigens on the surface of viruses, which can help develop vaccines
Why are sequencing projects on complex organisms harder to use
- Non-coding DNA
- Regulatory genes
What are DNA probes
- short single stranded pieces of DNA
- bases complementary with DNA
Why are probes longer than just a few bases
- a sequence of a few bases would occur at many places throughout the genome
- longer sequences only likely to occur in target allele
Describe DNA hybridisation
- binding of a single stranded DNA probe to complementary single strand of DNA
- forming hydrogen bonds
What are benefits of screening people for genetic conditions and drug responses
- can allow people to make better lifestyle choices
- people can decide whether to have their own biological children
What are drawbacks of screening people for genetic conditions and drug responses
- screening for an incurable disease may be pointless and cause unnecessary stress for someone
What are 3 features of proteins that allow them to be separated by gel electrophoresis
- by mass of amino acids
- charge
- R groups differ
Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment 4m
- it requires DNA fragment, DNA polymerase, nucleotides and primers
- heat to 95C° to break hydrogen bonds and separate strands
- reduce temperature so primers bind to DNA
- increase temperature, DNA polymerase joined nucleotides
Describe how enzymes could be used to insert a gene into a plasmid
- restriction endonucleases cuts plasmid
- ligase joins gene to plasmid
What’s the role of reverse transcriptase and DNA polymerase in PCR
reverse transcriptase produces DNA using mRNA
DNA polymerase joins nucleotides to produce DNA
Why is DNA hydrolysed before the sample is added to the reaction mixture in PCR
- to remove any DNA present
- as this DNA would be amplified
Describe the process of inserting genes into plasmids 3m
- cut the plasmid with restriction endonuclease
- so both have sticky ends
- mix and add ligase to join the sticky ends
What’s the role of siRNA
- destroys mRNA for gene
- prevents translation of gene
What is the name of the method used to clone DNA in vitro
Polymerase chain reaction (PCR)
Why are a variety of primers used in PCR
- base sequences differ
- so different complementary primers needed
What is the gene machine method of producing DNA fragments
- synthesises fragments of DNA from scratch without the need for a pre existing DNA template
- DNA fragments produced quickly/accurately
- free of introns
What are the advantages of using mRNA to make DNA fragments rather than restriction enzymes to cut the gene
- more mRNA in the cell than DNA so easily extracted
- introns removed by splicing whereas DNA contains introns
- bacteria cannot remove introns
How can DNA fragments be produced using mRNA
- isolate mRNA from the cell
- mix mRNA with DNA nucleotides and reverse transcriptase
- reverse transcriptase uses mRNA as a template to synthesise a single strand of cDNA
- DNA polymerase forms second strand of DNA using cDNA as a template
What is the role of promoter and terminator regions in vivo
Promoter - DNA sequences that tell RNA polymerase when to start producing mRNA
Terminator - tell RNA polymerase when to stop
