Unit 8 bio

• Gene mutations are a change in the DNA base sequence of a gene
• Gene mutations mainly occur during DNA replication in the cell cycle
• Exposure to mutagenic agents like ionizing radiation increases the frequency of gene mutations
• Gene mutation


  Can result in a different amino acid being coded for, leading to a different protein structure and function
• A gene mutation that affects the cell cycle can result in cancer
• Types of gene mutations

  • Addition
  • Deletion
  • Substitution
  • Inversion
  • Duplication
  • Translocation
• Addition mutation


  • One extra nucleotide/base is added to the sequence, shifting all subsequent bases
• Deletion mutation


  • One nucleotide/base is deleted from the sequence, shifting all subsequent bases back
• Substitution mutation


  • One nucleotide/base is swapped for another
• Inversion mutation


  • A section of bases detaches and rejoins in the opposite orientation
• Duplication mutation


  • One or more bases are duplicated in the sequence
• Translocation mutation


  • A section of bases detaches from one chromosome and attaches to a different chromosome
• Stem cells


  Undifferentiated cells that can continually divide and become specialized
• Types of stem cells

  • Totipotent
  • Pluripotent
  • Multipotent
  • Unipotent
• Totipotent stem cells


  Can differentiate into any type of body cell
• Pluripotent stem cells


  Can differentiate into almost every cell type except placenta cells
• Multipotent stem cells


  Can differentiate into a limited number of cell types
• Unipotent stem cells


  Can only differentiate into one type of cell
• Induced pluripotent stem cells are produced from adult body cells using protein transcription factors
• Transcription factors


  Proteins that move from the cytoplasm into the nucleus and bind to DNA to stimulate or inhibit transcription of target genes
• Transcription factor binds to DNA


  Transcription of the gene can occur
• Transcription factor does not bind to DNA

  Transcription of the gene is inactive
• Epigenetics


  Heritable changes in gene function without changes to the DNA sequence
• DNA methylation


  Addition of methyl groups to DNA inhibits transcription by preventing transcription factor binding
• Histone acetylation


  Addition of acetyl groups to histones decreases DNA-histone binding, allowing transcription
• RNA interference (RNAi)


  Small interfering RNA (siRNA) binds and degrades mRNA, preventing translation
• Mutations in genes regulating mitosis can lead to uncontrolled cell division and cancer
• Benign tumour


  Grows slowly, does not spread, can often be surgically removed
• Malignant tumour


  Grows rapidly, can spread to other tissues (metastasize), difficult to remove surgically
• Benign tumors


  Not classed as cancerous, grow slower, have a capsule or adhesive layer
• Malignant tumors


  Classed as cancerous, grow quicker, do not have a capsule or adhesive layer, can metastasize
• Malignant tumors


  Cells can break off, spread through the blood, and lodge in other tissues to form secondary tumors
• Malignant tumors


  Can grow projections to reach the blood supply, receive oxygen and glucose for rapid growth
• Removal of malignant tumors often requires supplementary treatment like radiotherapy and chemotherapy, and recurrence is more likely</b>
• Tumor development


  Can be due to gene mutation in tumor suppressor genes or oncogenes, or abnormal methylation, or increased estrogen
• Oncogenes


  Mutated version of proto-oncogenes, code for proteins involved in initiating cell division
• Tumor suppressor genes


  Code for proteins involved in controlling the cell cycle and causing cell death
• Tumor suppressor gene mutation


  Protein not produced, cell division not slowed down
• Oncogene hypomethylation


  Gene permanently switched on, lots of protein produced to initiate constant cell division
• Tumor suppressor gene hypermethylation

  Gene switched off, protein not produced to slow down cell division