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
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2
Q

what is a duplication mutation?

A
  • one or more bases are repeated and therefore produces a frameshift
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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
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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
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5
Q

how can gene mutations occur?

A
  • spontaneously during DNA replication
  • can be caused by mutagenic agents that affect DNA
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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
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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
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8
Q

what are stem cells?

A
  • undifferentiated cells that can keep dividing to give rise to other cell types
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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
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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
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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
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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
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13
Q

what are unipotent stem cells?

A
  • cells can only differentiate into one type of cell
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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
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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)
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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
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 proton-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