control of gene expression

    Cards (38)

    • Mutation
      Change in the sequence of nucleotides in DNA molecules
    • Types of mutations
      • Insertion/deletion
      • Duplication
      • Inversion
      • Translocation
    • Causes of gene mutations
      • Chemical mutagens (alcohol, benzene, asbestos, tar in tobacco)
      • Ionising radiation (alpha, beta, UV, X-ray)
      • Spontaneous errors in DNA replication
    • Neutral mutation
      Mutation causes no change to the organism (e.g. in non-coding region or silent mutation)
    • Beneficial mutation
      Humans developed trichromatic vision through a mutation
    • Harmful mutation

      Mutation in the CFTR protein causes cystic fibrosis
    • Types of stem cells
      • Totipotent
      • Pluripotent
      • Multipotent
      • Unipotent
    • Totipotent stem cells

      Can differentiate into any type of cell in the body and into extra-embryonic cells
    • Pluripotent stem cells
      Can form any cell type in the body, but cannot form extra-embryonic cells
    • Multipotent stem cells
      Can differentiate into other cell types but are more limited (e.g. cells in bone marrow and umbilical cord)
    • Unipotent stem cells

      Can only differentiate into one type of cell
    • Pluripotent stem cells can be created from unipotent stem cells and are known as induced pluripotent stem cells (iPS)
    • Control of transcription by oestrogen
      1. Oestrogen diffuses across cell membrane and binds to receptor on transcription factor
      2. Binding alters shape of DNA binding site on transcription factor
      3. Transcription factor enters nucleus and binds to DNA, stimulating transcription
    • Small interfering RNA (siRNA)

      Binds to complementary sequence of mRNA, causing mRNA to be broken down and preventing translation
    • Epigenetics
      Heritable changes in gene function without changes to DNA sequence
    • DNA methylation
      Addition of methyl groups to DNA, typically acting to suppress gene transcription
    • DNA acetylation
      Changes DNA structure by decreasing acetylation of histones, causing them to bind DNA more tightly and preventing transcriptional factors from accessing DNA
    • Factors involved in cancer
      • Proto-oncogenes
      • Oncogenes
      • Tumour suppressor genes
      • Abnormal methylation of tumour suppressor genes and oncogenes
      • Increased oestrogen concentrations
    • Sequencing projects have read the genomes of a wide range of organisms, including humans
    • Determining the genome of simpler organisms allows the sequences of the proteins that derive from the genetic code to be determined
    • In more complex organisms, the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome
    • Comparing genomes between species allows evolutionary relationships between species to be determined, and is beneficial to medical research
    • Comparing genomes of individuals enables differences to be identified which can then be used for development of personalised medicine and studies of human diseases
    • Gene sequencing has allowed for the sequences of amino acids in polypeptides to be predicted and has allowed for the development of synthetic biology
    • The Human Genome Project is an international scientific project which has successfully determined the sequence of bases of a human genome
    • Potential applications of the Human Genome Project include screening for mutated sequences, carriers and pre-implantation screening, as well as screening for disorders such as Huntington's disease before the symptoms appear
    • There are many ethical concerns regarding the Human Genome Project, such as people being discriminated against as well as regarding the misuse and ownership of the genetic information
    • Using reverse transcriptase to make DNA

      Reverse transcriptase catalyses the formation of double-stranded DNA from single-stranded RNA
    • Using restriction endonucleases to cut DNA fragments
      1. Restriction endonucleases cut DNA at specific sequences, usually six base pairs long
      2. Staggered cuts leave sticky ends on the DNA fragments
    • In-vivo gene cloning
      1. Plasmids are used as vectors to insert DNA fragments into cells
      2. Plasmid and gene are cut with the same restriction enzyme to create complementary sticky ends
      3. Fragments are incubated with plasmids, and DNA ligase seals the phosphodiester linkages to create a recombinant DNA molecule
    • Electroporation in formation of transgenic microorganisms
      Increases permeability of bacterial membranes to facilitate uptake of plasmids, using calcium salts and rapid temperature change
    • Gene markers

      Used to check whether desired DNA has been taken up by bacteria, including antibiotic resistance genes, fluorescent markers, and enzyme markers
    • Polymerase chain reaction (PCR)

      1. Reaction mixture is heated to separate DNA strands, then cooled to allow primers to bind
      2. DNA polymerase creates copies of the DNA sample by complementary base pairing
    • In-vitro gene cloning
      Uses PCR, which is fast, automated and reliable but can have problems like contamination and errors
    • In-vivo gene cloning
      Uses recombinant plasmids in bacteria, which is accurate and allows gene expression but is time-consuming and requires monitoring of cell growth
    • DNA probe
      Short, single-stranded DNA molecule complementary to a sequence to be detected, labelled with radioactive isotopes or fluorescent dyes
    • Genetic fingerprinting
      1. Uses variable number tandem repeats (VNTRs) to detect differences in people's DNA
      2. Involves gel electrophoresis to separate DNA fragments by size
    • Genetic fingerprinting can be used in forensic science, medical diagnosis, and animal/plant breeding
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