Topic 8 - Biology Paper 2

• 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
• Proteome


  All the proteins that the genome can code for
• Comparing genomes between species allows evolutionary relationships to be determined and is beneficial for medical research
• Comparing genomes of individuals enables differences to be identified which can 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 has successfully determined the sequence of bases of a human genome
• Potential applications of the Human Genome Project

  • Screening for mutated sequences, carriers and pre-implantation screening
  • Screening for disorders such as Huntington's disease before 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, allowing working versions of DNA to be made

  
• Using restriction endonucleases to cut DNA fragments


  Restriction endonucleases cut DNA at specific sequences, with staggered cuts leaving sticky ends that can be joined

  
• In-vivo gene cloning


  1. Plasmids are used as vectors to insert DNA fragments into cells

  2. Plasmid and gene are cut with same restriction enzyme to create complementary sticky ends

  3. Fragments are incubated with plasmids and joined by DNA ligase, creating recombinant DNA molecule

  
• Electroporation


  Technique used to stimulate bacterial cells to take up plasmids by increasing membrane permeability
• Gene markers


  Genes incorporated into plasmids to allow identification of bacteria that have taken up the plasmid

  
• Polymerase chain reaction (PCR)

  1. Reaction mixture with DNA sample, primers, nucleotides and DNA polymerase is heated to separate strands, cooled to allow primers to bind, then heated to allow DNA polymerase to create copies

  2. Cycle repeated around 30 times to amplify DNA sample

  
• In-vitro gene cloning


  Gene cloning using PCR, which is fast, automated and reliable but does not require living cells

  
• In-vivo gene cloning


  Gene cloning using recombinant plasmids in bacteria, which is accurate and allows gene expression but is time-consuming

  
• DNA probe


  Short, single-stranded DNA molecule complementary to a sequence to be detected, labelled with radioactive isotope or fluorescent dye

  
• Genetic fingerprinting


  1. Uses variable number tandem repeats (VNTRs) to detect differences in DNA between individuals

  2. Involves gel electrophoresis to separate DNA fragments by size

  
• Genetic fingerprinting can be used in forensic science, medical diagnosis, and animal/plant breeding