Chapter 20 - Control Of Gene Expression Flashcards
What are epigenetics
The heritable change in gene function without changing the DNA base sequence
What is the epigenome
A single layer of chemical tags on the DNA
Explain how epigenomes can affect gene expression
It impacts the shape of the DNA histone complex and whether the DNA is tightly wound so won’t be expressed or unwound so it will be expressed, these changes may either switch on or off genes allowing cells to control which genes are active and influence cell function
Explain the affect of increased DNA methylation on gene expression
- Increased DNA methylation will result in the addition of a methyl group to DNA
- This increases hydrophobic interactions, tightening DNA coiling resulting in the chromatin condensing
- This prevents the binding of transcription factors inhibiting transcription causing the gene to not be expressed
Explain the affect of decreased histone acetylation on gene expression
- Decreased acetylation involves the enzymatic removal of acetyl groups from histones
- This increases the histones positive charge and become more attracted to the phosphate group on DNA resulting in the chromatin to condense
- This makes the DNA and histones more strongly associated and hard for transcriptional factors to bind inhibiting transcription
Explain the affect of Decreased methylation
- Decreased DNA methylation will result in the removal of a methyl group to DNA
- This decreases hydrophobic interactions, loosening DNA coiling resulting in the chromatin unwinding
- this results in the gene to be expressed
Explain the affect of increased acetylation
- Increased acetylation involves the addition of acetyl groups to histones
- This decreases the histones positive charge resulting in the chromatin to unwind
- This results in the gene to be expressed
What are tumour suppressor genes
Genes that produces proteins to slow cell division and cause cell death if DNA copying errors are detected
Explain the affect of mutations to tumour suppressor genes
It would result in the formation of a non functional protein that would not be able to identify and destroy errors during cell division resulting in the formation of tumours
Examples of mutated tumours suppressor genes that are linked to breast cancer
- BRCA1
- BRCA2
Explain the affect of hypermethylation on tumour suppressor genes
- Hypermethylation will increase the number of methyl groups attached to the tumour suppressor gene
- This will result in the tumour suppressor gene to tightly coil causing it to become inactivated and switched off so no protein will be produced so mitosis cannot be controlled leading to uncontrolled cell division causing tumour formation
Explain the affect of hypomethylation on oncogenes
- This reduces the number of methyl groups attached to the oncogenes causing the oncogene to be permanently switched on causing uncontrolled cell division leading to tumour formation
What is a gene mutation
The alteration of a base in the sequences of bases for one gene
Explain how a gene mutation can lead to a non functional protein
- mutation can result in a different amino acid sequence in the encoded polypeptide
- this causes the primary structure to change resulting in the hydrogen and ionic binds to form in different locations resulting in the tertiary structure to change
- this will result in a different 3D shape and therefore a non functioning protein
What mutagenic agents can increase the risk of mutations
- Ionising radiation - can disrupt and damage the structure of DNA
- Carcinogens - alter the structure of DNA and interfere with transcription
How does mutagenic agents increase the risk of mutations
- acting as a base - analogues (chemicals) substitute a base during DNA replication changing the base sequence
- altering bases - some chemicals delete and alter bases
- changing the structure of DNA - ionising radiation can change the structure of DNA causing problems with DNA replication
Different types of gene mutations
- Addition
- Deletion
- Substitution
- Inversion
- Duplication
- Translocation
STI DAD
Explain the effect of the addition mutation to a gene
- When one extra base is added to the sequence it causes a frame shift mutation to the right
- So all the altered codons will code for a different amino acid, resulting in a different sequence of amino acids, changing the primary structure of the protein
- resulting in the tertiary structure to change causing a non functional protein to form
Explain the affect of the deletion mutation to a gene
- When one base is removed from the sequence it causes a frame shift mutation to the left
- resulting in a different sequence of amino acids, changing the primary structure of the protein
- resulting in the tertiary structure to change causing a non functional protein to form
Explain the affect a substitution mutation on a gene
- May create stop codons - (Nonsense mutation) - This stops transcription, causing the change of the structure of the protein resulting it to be non functional
- May create a codon for a different amino acid - (Misense mutation) - This changes the protein’s amino acid sequence, changing the primary and tertiary structure resulting in a non functional protein
- May create a codon for the same amino acid - (silent mutation) - does not affect the protein product or the phenotype, due to the degenerate coding as there will be no change to the sequence of the amino acid
What happens in an inversion mutation
A section of bases detach from the DNA sequence but when they rejoin they are inverted so the section of the code is flipped resulting in a different amino acid being coded for in this region
What happens in translocation mutation
A section of bases on one chromosomes detaches and attaches onto a different chromosome which can affect gene expression resulting in a different phenotype
What happens in duplication mutations
This is when one or more DNA bases are repeated, altering the reading frame of the codons and causing a frame shift to the right
Difference between mutations in body cells and mutations in gametes
- Mutations in body cells can disrupt normal functions like cell division, potentially causing cancer.
- Mutations in gametes can be inherited by offspring, while those in body cells cannot.
What are stem cells
undifferentiated cells that continually divide and become specialised
Types of stem cells
- totipotent
- pluripotent
- multipotent
- unipotent
What are totipotent stem cells
Stem cells that can divide and produce any type of body cell
What is the life expectancy of totipotent cells
It is very limited as they only occur for a limited amount of time in early mammalian embryos
What are pluripotent stem cells
Stem cells found in embryos that can become almost any type of cell
Advantages of pluripotent stem cells
- They can be used in research to treat human disorders by replacing damaged cells
- Testing new drugs - Drugs can be tested for toxicity and side effects before being tested on humans.
- Studying development of organisms - Scientists can find out how organisms grow and develop from a single cell.
Disadvantages of pluripotent stem cell treatment
- sometimes pluripotent stem cell treatment does not work or the stem cells will continuously divide to create tumours
- it has low ethics as there is a debate whether it is right to clone yourself and destroy the embryo
What are multipotent stem cells
Stem cells that can only differentiate into a limited number of different cell types
What are unipotent stem cells
Stem cells that can only differentiate into one type of cell
Where are multipotent stem cells found
In the umbilical cord and placenta
What are iPS (induced pluripotent stem cells)
These are Stem cells produced from adult somattic cells using transcription factors, which switch on the genes that were switched off making the cell to return to the state of pluripotenty, which aims to overcome the ethical issue using embryonic stem cells
Features of stem cells
- undifferentiated
- can divide to produce exact copies of themselves through the process of self renewal
Advantages of iPS
- They can self-renew indefinitely.
- They can differentiate into various cell types.
- They avoid ethical issues associated with using embryonic stem cells.
- They could provide an unlimited source of stem cells for research and medical treatments.
What type of stem cells are found in animals and plants
Animals - multipotent or unipotent
Plants - pluripotent
Explain how transcription factors initiate transcription and form a protein
They bind to the complementary base sequence of the DNA stimulating RNA polymerase to bind initiating transcription, this creates the mRNA molecule for that gene which then can be translated to create a protein
Explain how oestrogen activates transcription factors
- Oestrogen is complementary in shape to the receptor site on the transcriptional factor
- It binds to the receptor site on the transcriptional factor resulting in the transcriptional factor to change in shape, activating it, making it complementary and able to bind to the DNA to initiate transcription
Explain how the process of translation can be disrupted
1) An enzyme cuts the mRNA into siRNA
2) One strand of the siRNA combines with another enzyme
3) This siRNA enzyme complex will bind via complementary base pairing to another mRNA molecule
4) once bound the enzyme will cut the mRNA so it cannot be translated
What is cancer
A result of mutations in genes that regulate mitosis
Features of benign tumours
- Grow large but at a slow rate
- They produce adhesion molecules, sticking them together to keep them in place, so impact is localised
- Retain their specific functions
- surrounded by a capsule so remain compact
- can be removed by surgery
- not life threatening but can impact organ function
Features of malignant tumours
- grow large rapidly (as it can develop its own blood supply since it has no capsule)
- the nucleus become so large the cell becomes unspecialised
- do not produce adhesive molecules and do not have a capsule allowing the cells to metastasis (spread)
- highly dangerous and can replace healthy tissue
- treated with chemotherapy and radiotherapy
What are the ways and tumour could develop
- gene mutation to tumour suppressor genes or oncogenes
- abonormal methylation of tumour suppressor genes and oncogenes
- increased oestrogen concentration
What are oncogenes
The mutated version of proto-oncogene
What is the function of proto-oncogenes
To create proteins involved in the initiation of DNA replication and cell division when the body needs new cells
How do (mutations of proto-oncogene) oncogenes lead to tumour formation
It causes the oncogene to become permanently activated leading to uncontrolled cell division forming a tumour
Explain how increased oestrogen concentration can lead to tumour formation
- Oestrogen can activate a gene by binding to a gene that initiates transcription and if this is a proto-oncogene it can be permanently switched on and cause uncontrolled cell division which can result in tumour formation
- tumour formation can also lead to an increase in oestrogen concentration causing the tumour to increase in size, the tumour will also attract white blood cells causing further increase in size at a faster
Why is there a high risk of breast cancer
As menopause stops oestrogen production in the ovaries, so instead fat cells in breast tissue produced oestrogen, increasing the concentration of oestrogen in the breast tissue leading to cancer
Functions of tumour suppressor genes
- regulate cell division
- repair DNA
- initiate apoptosis to prevent tumour formation
What is the genome
The entire genetic material of an organism in the nucleus of a cell
What is meant by sequencing a genome
Working out the DNA base sequence for all the DNA in the cell
What technological advances do we use to analyse biological data
- Bioinformatics - This involves developing software to collect, store, and analyse the sequence of genomes and amino acids
- Computational biology - This field uses bioinformatics tools and biological data to model biological systems and processes.
- Genomics - This applies DNA sequencing and computational biology to study the genomes of organisms.
What process is used to sequence our human genome and identify patents in our DNA and disease risk
- Whole genome shot gun sequence (WPS)
Explain the process of WGS and what it identifies
1) DNA is cut into fragments.
2) DNA fragments are sequenced.
3) DNA fragments are aligned to determine the whole DNA sequence
4) This can help identify Single nucleotide polymorphisms (SNPs), which are single-base variations in the genome and are associated with diseases and disorders.
What is DNA barcoding
comparing the DNA sequence of an unidentified organism to a standard DNA sequence for known species to find similarities between DNA sequence and hence to see whether there is a common ancestor between both organisms
Advantages of DNA barcoding
- Fast and affordable
- classifies of new species.
- help construct evolutionary trees with greater accuracy
What are genomics
the study of genomes, using DNA sequencing and computational biology to analyse the human genome
What are proteomics
The study of the complete set of proteins produced by the genome (the proteome)
One hypothesis for the cause of cancer of the colon (large intestine) is that Clostridium bacteria present in the gut can convert bile steroids into cancer causing substances
Explain the presence of bile in the colon
- Bile is secreted by the liver and released from the gall bladder into the duodenum (small intestine)
- Bile passes unchanged from small intestine into colon
