Control of Gene Expression Flashcards
1
Q
what is an insertion or deletion mutation?
A
- one or more nucleotide pairs are inserted or deleted from the sequence
- alters the sequence of nucleotides after the insertion/deletion point known as frame shift
2
Q
what is a duplication mutation?
A
- one or more bases are repeated and therefore produces a frameshift
3
Q
what is an inversion mutation?
A
- a group of bases become separated from the DNA sequence and rejoin at the same position but in the reverse order
- affects amino acid produced
4
Q
what is a translocation mutation?
A
- a group of bases becomes separated from the DNA sequence on one chromosome and are inserted into the DNA sequence on another chromosome
- this can lead to significant effects on the phenotype
5
Q
how can gene mutations occur?
A
- spontaneously during DNA replication
- can be caused by mutagenic agents that affect DNA
6
Q
what are examples of mutagenic agents?
A
- chemical mutagens - including alcohol, benzene and substances in asbestos, and tar in tobacco
- ionising radiation - alpha and beta, also UV and X-ray
7
Q
how can a gene mutation have neutral effects on the organism?
A
- mutation occurs in non-coding region of DNA
- change to tertiary structure of protein has no effect on the organism
- base sequence is degenerate and there are multiple triplets of bases that code for one amino acid
8
Q
what are stem cells?
A
- undifferentiated cells that can keep dividing to give rise to other cell types
9
Q
what are totipotent stem cells?
A
- able to differentiate into any cell type found in the body and extra embryonic cells
- found in the embryo at an early stage in the blastomere
10
Q
how do totipotent stem cells differentiate to form an embryo?
A
- totipotent cells are initially unspecialised but become specialised and differentiate to form tissues
- this is caused by a change in gene expression where some genes are selectively switched on and off
11
Q
what are pluripotent stem cells?
A
- can form any cell type in the body, but can’t form extra embryonic cells
- found in the early stages of an embryo
- often used in replacing damaged tissues in human disorders
12
Q
what are multipotent stem cells?
A
- can differentiate into other cell type but are more limited
- e.g. cells in bone marrow and umbilical cord
13
Q
what are unipotent stem cells?
A
- cells can only differentiate into one type of cell
14
Q
how can pluripotent stem cells be used to treat diseases?
A
- they can repair damaged tissue
- e.g. heart muscle tissue can treat heart damage, beta cells of the pancreas can be used to treat type 1 diabetes
15
Q
what are induced pluripotent stem cells?
A
- can be created from unipotent stem cells and are known as induced pluripotent stem cells (iPS)
16
Q
what are transcription factors?
A
- molecules bind to a specific site on DNA and begin the process of transcription
17
Q
how can oestrogen control transcription?
A
- oestrogen is lipid soluble and so freely diffuses across the cell membrane and binds to receptor molecule on transcription factor
- this alters the shape of the DNA binding site on the transcription factor and makes it able to bind to the DNA
- the transcription factor therefore enters the nucleus via the nuclear pore and binds to DNA
- transcription of the gene that makes up the DNA is stimulated
18
Q
what is siRNA?
A
- small interfering RNA (silencing RNA)
- short term switches off of genes
19
Q
how does siRNA switch off genes?
A
- siRNA binds to a complementary sequence of mRNA
- mRNA is usually single stranded and so the double strand is detected and viewed as abnormal
- the mRNA is broken down by enzymes preventing translation
20
Q
what is epigenetics?
A
- heritable changes in gene function without changes to the base sequence of DNA
- it shows that environmental factors can make changes to the function of genes which can be inherited
21
Q
what is DNA methylation?
A
- methyl groups are added to the DNA
- methylation modifies the function of DNA, acting to suppress gene transcription
- CH3 group is added to cytosine bases, preventing binding of transcription factors to DNA and stimulates decreased acetylation of histones
22
Q
what is DNA acetylation?
A
- histones are positively charged proteins closely associated with DNA, which is negatively charged
- decreased acetylation of histones increases their positive charge, so they can bind to DNA more tightly
- transcriptional factors can no longer access the DNA, so the gene is switched off
- more acetylation = switching on
23
Q
how are tumours formed?
A
- uncontrolled cell division
- cancer can arise as a result of mutation
24
Q
what are the types of tumours?
A
- benign tumours - don’t cause much harm apart from mechanical damage when pressed against blood vessels or other cells, benign tumours grow slowly and don’t spread
- malignant tumours - grow rapidly and spread to neighbouring cells via metastasis (through blood stream or lymphatic system) thus causing damage as they disrupt important processes
25
Q
what are proto-oncogenes?
A
- stimulate cells to divide by producing proteins that stimulate cell division
- allow checkpoints of the cells cycle to be passed
- can cause cancer if mutated
26
Q
what are oncogenes?
A
- formed from mutated proto-oncogenes
- are permanently switched on resulting in uncontrolled cell division
- a cell surface receptor is permanently activated or permanently coding for a growth factor
27
Q
what are tumour suppressor genes?
A
- control cell division and cause the cell cycle to stop when damage is detected
- have a role in apoptosis (cell death)
- when these are switched off, the cell cycle becomes unregulated
28
Q
how can abnormal methylation of tumour suppressor genes cause cancer?
A
- hyper-methylation can cause tumour suppressor genes and oncogenes to be switched off
- hyper-methylation of the tumour suppressor gene BRAC1 can lead to breast cancer
29
Q
how are increased oestrogen concentrations linked to breast cancer development?
A
- oestrogen binds to the transcription factor which activates genes promoting cell division and so increased oestrogen levels can cause the formation of tumours
30
Q
what are sequencing projects?
A
- determining the genomes of organisms allows the sequence of proteins that derive from the genetic code to be determined
31
Q
what are the applications of genome sequencing projects?
A
- e.g. identification of potential antigens for use in vaccine production
32
Q
what is the proteome?
A
- all the proteins that the genome can code for
- however due to selective gene expression, not all of these genes will be found in every cell in the body
33
Q
what is importance of genome sequencing projects?
A
- genome-wide comparisons between individuals and between species
- evolutionary relationships between species can be determined
- development of personalised medicines tailored to certain genomes and studies of human diseases
- sequences of animo acids in polypeptides can be predicted and development of synthetic biology
34
Q
how to determine the genome and proteome of simple organisms?
A
- DNA samples from many different organisms are collected
- DNA samples are then sequenced and compared to create a reference genome
35
Q
how to determine the genome and proteome of complex organisms?
A
- similar method to more simple organisms
- the presence of non-coding DNA and regulatory genes means that the genome cannot easily translated into the proteome
36
Q
what is the Human Genome Project?
A
- international scientific research project which has successfully determined the sequence of bases of a human genome
- potential applications of this: screening for mutated sequences, carriers and pre-implantation screening , as well as screening for disorders such as Huntington’s disease
- there are also ethical concerns such as people being discriminated against and misuse and ownership of the genetic information
37
Q
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