Gene Expression Flashcards
What is a mutation?
An alteration to the DNA base sequence. Often arise during DNA replication
What are addition and deletion mutations?
Where one or more nucleotides are either inserted or deleted from the DNA sequence
What is a substitution mutation?
Where one nucleotide in the DNA sequence is replaced by another
What is a duplication mutation?
Where one or more nucleotides duplicate and repeat
What is an inversion mutation?
Where a group of nucleotides become separated from the DNA sequence then rejoin in the reverse order i.e they have flipped
What is a translocation mutation?
Where a group of nucleotides become separated from the DNA sequence and are then inserted into the DNA of a different chromosome
Which mutations are most likely to have a significant impact and why?
Insertion, deletion, duplication and translocation because they produce a frameshift meaning the entire amino acid sequence produced will be different
Which mutations are less likely to have a significant impact and why?
Substitution and inversion because they only alter one or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code
Is a mutation resulting in a change to the amino acid sequence always harmful?
No; may be neutral if the resulting change in protein has no effect on the organism
Also may be beneficial which is the basis for evolution and natural selection
What is a mutagenic agent?
Factors that increase the rate of gene mutation. Chemical mutagens such as alcohol and ionising radiation such as UV and X ray
What is a stem cell?
Undifferentiated cells that can divide indefinitely and turn into other specific cell types
Name and define the three types of stem cell
Totipotent = can develop into any cell type including the placenta and embryo
Pluripotent = can develop into any cell type excluding the placenta and embryo
Multipotent = can only develop into a few different types of cell
What happens to totipotent cells during embryonic development?
Certain parts of the DNA are selectively translated so that only some genes are switched on in order to differentiate the cell into a specific type and form the tissues that make up the foetus
Give a unique feature of pluripotent cells and the use of this feature
They can divide in unlimited numbers and can therefore be used to repair or replace damaged tissue
What is a unipotent cell, give an example
A cell that can only develop into one type of cell. This happens at the end of specialisation when the cell can only propagate its own type. An example is cardiomyocytes (heart cells)
Which type of stem cells are found in embryos?
Totipotent and pluripotent
Multipotent and unipotent are only found in mature mammals
Give some uses of stem cells
Medical therapies e.g bone marrow transplants
Drug testing on artificially grown tissues
Research e.g on embryos
How are induced pluripotent stem cells produced?
From mature, fully specialised cells. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors
What is a transcription factor?
A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
How do transcription factors work?
- Move from the cytoplasm into nucleus
- Bind to promoter region upstream of target gene
- Makes it easier or more difficult for RNA polymerase to bind to the gene. This increases or decreases rate of transcription
Give an example of a hormone that affects transcription and explain how it works
- Steroid hormone oestrogen diffuses through cell membrane
- Forms hormone receptor complex with ER a receptor in the cytoplasm
- Complex enters the nucleus and acts as transcription factor to facilitate binding of RNA polymerase
What is meant by epigenetics?
A heritable change in gene function without change to the base sequence of DNA
How does increased methylation of DNA affect gene transcription?
Involves addition of CH3 group to cytosine bases which are next to guanine. Prevents transcription factors from binding. Therefore gene transcription is suppressed
How does decreased acetylation of histones affect gene transcription?
Positively - charged histones are positively charged bind to negatively charged DNA. Decreasing acetylation increases positive charge of histones.
Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed
How might epigenetic changes affect humans?
They can cause disease, either by over activating a gene’s function or by suppressing it
Give an application of epigenetic’s
Treatments of various diseases. Development of ways to reverse epigenetic changes
Describe the process of RNA interference, including the organisms in which it occurs
RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated. Occurs in eukaryotes and some prokaryotes
Give some characteristics of benign tumours
Slow growth
Defined by a clear boundary due to cell adhesion molecules
Cells retain function and normal shape
Don’t spread easily
Easy to treat
Give some characteristics of malignant tumours
Rapid, uncontrollable growth
Finger-like projections
Cells do not retain function and often die
Spreads quickly and easily
Difficult to treat
Describe the role of tumour - suppressor genes
Code for proteins that control cell division; in particular, stopping the cell cycle when damage is detected. They are also involved in programming apoptosis i.e self destruction of the cell
Explain how tumour suppressor genes can be involved in developing cancer
A mutation in the gene could code for a nonfunctional protein. Increased methylation or decreased acetylation could prevent transcription
Cells will divide uncontrollably resulting in a tumour
Describe the role of proto-oncogenes
Control cell division; in particular, code for proteins that stimulate cell division
Explain how proto-oncogenes can be involved in developing cancer
Mutation in the gene could turn it into permanently acitvated oncogene. Decreased methylation or increased acetylation can cause excess transcription
This results in uncontrolled cell division and formation of a tumour
Explain how abnormal methylation of genes can cause cancer
Hyper-methylation of tumour - suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably
Explain how oestrogen can be involved in developing breast cancer
We already know oestrogen is an activator or RNA polymerase. Therefore in areas of high oestrogen concentration, such as adipose tissue in the breasts, cell division can become uncontrolled
What is a genome?
The complete set of genetic information contained in cells of an organism
What is genome sequencing?
Identifying the DNA base sequence of an individual. This allows us to determine the amino acid sequence of the polypeptides coded for by that DNA
What is the proteome?
The complete set of proteins that can be produced by a cell
Can we directly translate the genome into the proteome?
In simple organisms, yes. In complex organisms due to the presence of non-coding DNA and regulatory genes, it is much harder to obtain the proteome
Give an application of sequencing the proteome in simple organisms
Identifying potential antigens for use in vaccine production
Give some applications of genome sequencing
Comparing genomes between species to determine evolutionary relationships
Genetic matching
Personalised medicine
Synthetic biology
How have sequencing methods changed over time?
Used to be a manual process, however now it has become automated. A reaction mixture is created and after the process is complete a machine reads the base sequence
