B20 Gene Expression Flashcards
What is a mutation
An alteration to the DNA base sequence. Often arise spontaneously during DNA replication
What are addition and deletion mutations
Where 1 or more nucleotides (bases) are either inserted/deleted from the DNA sequence
What is a substitution mutation
Where 1 nucleotide (bases) in the DNA sequence is replaced by another
What is a duplication mutation
Where 1 or more nucleotides (bases) duplicate and repeat
What is an inversion mutation
Where a group of nucleotides (bases) 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 (bases) 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, 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, inversion
Because they only alter 1 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
Give examples of mutagenic agents
Chemical mutagens such as: alcohol and benzene.
Ionising radiation such as UV and x-ray
What is the genome
The complete set of genetic information contained in the 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, du 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
What is a stem cell
Undifferentiated cells, that can divide indefinitely and turn into other specific cell types
Name 3 types of stem cell
Totipotent
Pluripotent
Multipotent
Define a totipotent stem cell
Can develop into any cell type including the placenta and embryo
Define a pluripotent stem cell
Can develop into any cell type excluding the placenta and embryo
Define a multipotent stem cell
Can only develop into any cell 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 1 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 types of stem cells are found in embryos
Totipotent and pluripotent
Multipotent and unipotent cells are only found in mature mammals
Give some uses of stem cells
Medical therapies e.g. bone marrow transplants, treating blood disorders.
Drug testing on artificially grown tissues.
Research e.g. on formation of organs and embryos.
How are induced pluripotent stem cells produced
From mature, fully specialised (somatic) cells. The cell regains capacity to differentiate through the use of proteins, in particular transcription factors.
How are induced pluripotent stem cells produced
From mature, fully specialised (somatic) 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, e.g. in order to allow a cell to specialise.
How do transcription factors work
- Move from cytoplasm into nucleus
- Bind to promoter region upstream of target gene
- Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases transcription rate.
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 alpha 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 a 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. Binning 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 (such as in cancer) or by suppressing it.
Give an application of epigenetics
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 tumour
- slow growth
- defined by a clear boundary due to cell adhesion molecules
- cells retain function and normal shape
- don’t spreads easily
- easy to treat
Give some characteristics of malignant tumours
Rapid, uncontrollable growth
Ill-defined boundary ( finger-like projections)
Cells do not retain function and often die
Spreads quickly and easily (metastasis)
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 non functional 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 into a permanently activated 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 of RNA polymerase. Therefore in areas of high oestrogen concentration, such as adipose tissue in the breasts, cell division can become uncontrolled
