genetics of living systems

• Homeobox genes are ancient highly conserved genes that code for homeodomain sequences in proteins that regulate anatomical development
• Hox gened are a subset of homeobox genes regulating the axes of embryos dictating the position of anatomical features
• The spatial and temporal expression of Hox genes control where and when parts of the body develop
• Homeobox gene controls identity and developement of body segments - 180 base pairs, 60 amino acids
• When a hox gene is mutates, body parts end up developing in the wrong place on the body
• Post translational regulation of gene expression involves the activation or inactivation of proteins
• Enzymes and other proteins can be phosphorylated to alter their activity increasing or decreasing reaction rates
• Post translation control

  1. Hormones (glucagon) bind to receptor on membrane leading to production of cAMP
  2. cAMP acts as a 2nd messenger leading to activation of protein kinase A (PKA)
  3. PKA phosphorylates enzymes to alter activity e.g. enzymes that convert glycogen to glucose
  4. Transcription factors regulate the transcription of particular genes in the nucleus
• After transcription primary mRNA can be altered to control the final protein structure
• DNA and primary mRNA contain both introns and exons - non coding and coding regions respectively
• Post transcriptional control

  
• Transcription of genes is tightly regulated in both prokaryotes and eukaryotes
• In prokaryotes the lac operon controls transcription of metabolic genes
• In eukaryotes transcription factors control transcription by binding to promoter regions of genes and encouraging or inhibiting the binding of RNA polymerase
• Lac operon

  
• Mutations are changes in the base sequence of DNA. Can be caused by chemical or agents known as mutagens
• Change in DNA sequence ccan be caused by substitution, deletion or insertion
• substitution of a single nucleotide changes the codon in which it occurs - may lead to a change in primary structure
• Insertion or deletion of a nucleotide leads to a frameshift mutation where the code is shifted along and reads as a different triplet codon, leading to major changes in the protein structure
• Effects of mutations

  • No effect - normal functioning proteins still synthesised
  • Damaging - phenotype is effected
  • Beneficial - rare that it positively changes phenotype
• Change in chromosome structure include:

  • Deletion - section of chromosome breaks off and lost within cell
  • Duplication - sections get duplicated on a chromosome
  • Translocation - section of one chromosome breaks off and joins another non-homologous chromosome
  • Inversion - section of chromosome breaks off, reversed and joing back onto the chromosome
• Apoptosis is programmed cell death - used to control developement of tissues e.g. finger and toe formation while ensuring tissues do not overgrow
• Apoptosis

  1. Enzymes break down the cytoskeleton causing the cytoplasm to become dense and packed with organelles
  2. Protrusions called blebs form in the membrane while the DNA breaks into fragments
  3. Cell breaks into vesicles
  4. Vesicles are phagocytosed
• Homeobox genes are in animals, plants and fungi
• Diploblastic organisms have 2 primary tissue layers
• Tribloblastic animals have 3 primary tissue layers
• Body shap in animals shows symmetry
• Radial symmetry - seen in diploblastic animlas like jellyfish. No left or right sides, only a top and bottom
• Bilateral symmetry - seen in most animals. Organisms have both left and right sides and a head and tail
• Assymetry is seen as sponges which have no lateral lines of symmetry