The control of gene expression Flashcards
Definition of gene expression.
The process of converting geentic information into functional proteins.
Definition of differentiation.
Process by which cells become specialised for a particular function.
Definition of stem cell.
Cells that have the ability to differentiate into specilaised cells (potency). Have the ability to replicate themselves indefinitely- self renewal.
Definition of totipotent stem cells.
Can differentiate into any type of cell.
Definition of pluripotent stem cells.
Can differentiate into most types of cells.
Definition of multipotent stem cells.
Can differentiate into a limited number of cells.
Definition of unipotent stem cells.
Can differentiate into a single type of cell.
What type of stem cell are embryonic stem cells?
From embryos up to 16 cell stage, they are totipotent. 16 cell stage to blastocyst are pluripotent.
What type of stem cells are umbilical stem cells?
From umbilical cord to blood are mulitpotent.
What type of stem cell are placental stem cells?
Found in the placenta and develop into specific types of cells- multipotent.
What type of stem cell are adult stem cells?
Found in tissues of foetus and adult. Specific to a particular tissue and maintain / repair that tissue. Can be multipotent or unipotent.
What are IPS cells?
Induced Pluripotent Cells.
IPS cells involve reverting a unipotent stem cell, what does this involve?
Inducing genes and trasncription factors. Turns genes on that were otherwise switched off.
What does IPS cells being able to induce genes and transcription factors prove about adult stem cells?
Adult stem cells retain the same genetic information that was present in the embryo.
What is a key feature of the IPS cells that is important for medical research and treatment?
Capable of self-renewal.
List some of the ethical objections to use of embryonic stem cells (3 points).
- Undermines respect for human life.
- Could lead to use of foetuses for reasearch.
- Could lead to reproductive cloning.
List some the arguments for using embryonic stem cells (3 points).
- Ball of cells don’t represent humans.
- Laws already in place to provide enough protection.
- Shouldn’t allow continuous suffering of human if can be treated.
Describe transcription (5 points).
- DNA helicase breaks the hydrogen bonds.
- One strand acts as a template.
- Free RNA nucleotides form complementary base pairs: adenine-uracil, cytosine-guanine.
- RNA polymerase joins nucleotides togetehr forming phosphodiester bonds.
- Introns are removed from pre-mRNA via splicing to form mRNA.
Defintion of transcription factor.
A protein or molecules that moves from the cytoplasm to the DNA and binds toa specific base sequence of the DNA molecule.
Definition of promotor.
DNA sequence before gene allowing RNA polymerase to bind to initiate transcription.
Describe how a hormone / estrogen effects transcription (5 points).
- Oestrogen binds to the receptor as complemtary in shape.
- Shape of the DNA binding site changes.
- Easier for RNA polymerase to bind to the promotor.
- Binds to the promotor on the DNA.
- Transcription occurs.
Definition of epigenetics.
Environmental factors can cause heritable changes in gene function without changing the base sequence of DNA.
What is the epigenome?
The layer formed by the chemical tags attached to the DNA and histones.
Describe how addition of methyl groups to DNA causes genes to be switched off / not expressed (4 points).
- DNA more tightly packed.
- Harder for genes to be transcribed.
- Transcription factors cannot bind to the promtor.
- Genes switched off / not expressed.
Describe how addition of acetyl groups to histones causes genes to be switched on / expressed (4 points).
- DNA more loosely packed.
- Genes can be transcribed more easily.
- Transcription factors can bind to the promotor.
- Genes switched on / expressed.
Describe translation (6 points).
- mRNA attaches to a ribosome.
- Each amino acid is joined together by a peptide bond.
- Ribosome moves to start codon.
- tRNA brings amino acid.
- Anticodon to codon.
- Ribosome moves along to next codon.
Describe how RNA interfernce (RNAi) can be used to block gene expression by preventing translation of mRNA into a polypeptide chain (4 points).
- Double sranded RNA. Large double stranded RNA molecule are cut into smaller sectionscalled small interfering RNA (siRNA) by an enzyme. siRNA poduced around 21 nucleotides long.
- Guid strand and enzyme. One of the two siRNA strands- guide strand, combines with an enzyme.
- Bind to mRNA. The siRNA guid strand guides the enzyme to the mRNA and siRNA guid strand pairs with the complementary bases on mRNA strand.
- mRNA is broken down.The enzyme cute the mRNA into smaller sections so it can no longer be translated.
Describe the stages of mitosis (5 points).
- Prophase- chromosomes appear due to supercoiling around histones. 2 chromtids held by centromere.
- Metaphase- Chromosomes line up along the equator, centrioles produce spindle fibres.
- Anaphase- Spindle fibres contract pulling chromatids apart to polar ends of the cell.
- Telophase- chromosomes uncoil and become invisible again.
- Cytokinesis- cytoplasm splits forming two daughter cells.
Definition of cancer.
Disease caused by damage to genes that regulate mitosis and the cell cycle leading to uncontrolled mitosis. Forms abnormal mass of cells called a tumour.
Definition of a benign tumour.
(Non-cancerous) Grows slowly and does not spread. Mitosis occurs at the centre of the tumour.
Definition of malignant tumour.
(Cancerous) Grows quickly and spreads. Mitosis occurs at the edges of the tumour.
Definition of metastasis.
Movement of cells around the bodt.
Describe proto-oncogenes (4 points).
- Codes for proteins that stimulate cell division.
- Maintains normal tissues.
- Not permanently switched on.
- Needs a growth factor to be turned on.
What are the effects of a mutation occurring in the proto-oncogenes? (4 points).
- Permanently switched on.
- Production of proteins increase.
- Leads to cells dividing out of control.
- Tumour formation.
Describe the tumour supressor gene (4 points).
- Produces proteins which inhibits cell division.
- Repairs mistakes in DNA.
- Stimulates apoptosis (cell death).
- Can inhibit prot-oncogenes and stop cell division. `
Describe the effect of a mutation that occurs in the tumour supressor gene (4 points).
- Protein is not produced.
- Cell division not inhibited, so uncontrolled cell division.
- Malignant tumour formed.
- The faster the rate, the faster the tumour will grow.
Describe abnormal methylation of the tumour suppressor gene (6 points).
- Hypermethylation.
- Adds methyl group to promotor of TSG.
- DNA more tightly packed.
- Prevents transcription factors binding, so proteins not produced.
- TSG not activated.
- Uncontrolled cell division and tumour formation.
Describe the link between oestrogen and breast cancer (5 points).
- Fat cells in the breast produce high levels of oestrogen after the menopause, which can trigger breast cancer.
- Oestrogen binds to the receptors of transcription factors, activating it.
- Transcription occurs, gene is switched on.
- If this genecontrols cell division, then uncontrolled cell division could occur.
- For example: Proto-oncogenes become oncogenes.
