DNA and cell reproduction

• DNA structure

  • Made up of small repeating structures called nucleotides.
  • Double helix
  • Two strands join by specific bases being attracted to one another through weak hydrogen bonds.
• Nucleotide is made up of three parts - sugar, phosphate group and nitrogenous base
• Sugar in DNA= deoxyribose (5 carbon sugars)
• RNA structure

  • Composed of chain of nucleotides
  • sugar molecule is ribose (has more oxygen that deoxyribose)
  • single stranded
• DNA organisation

  • DNA strands wrapped around eight Histone proteins to form a nucleosome.
  • When not dividing coiled DNA forms tangled network called chromatin
  • When dividing become super tightly coiled forming larger chromosomes
• Types of RNA

  • Messenger RNA: Fakes genetic code into cytoplasm to be read by ribosomes.
  • Ribosomal RNA: Ensures correct alignment of mRNA, tRNA and ribosome. Has eneymatic role in formation of peptide bonds between amino acids.
  • Transfer RNA: Small molecule of RNA. Carries a specific amino acid playing a vital role in protein synthesis.
• Role of DNA

  • Determines structure and function of cells.
  • Each chromosome is made up of sections of DNA that code for a particular protein.
  • Each section is a gene.
• General role of RNA

  Single stranded nucleic acid incorporating bases adenine, cytosine, guanine and uracil.
• Types of genes

  • Promoter gene
  • Structural gene
  • Regulator gene
• Structural gene

  Nucleotide sequence which copies to produce polypeptides (proteins) at ribosomes.
• Regulator gene

  Inhibits transcription by

  • produced repressor molecules which block RNA polymerase from binding to promoter/structural gene.
  • No transcription
• Promoter gene

  Indicates which structural gene should be transcribed in protein synthesis.

  Acts as a binding site for RNA polymerase, which attaches then copies the structural gene.
• Genes influence transcription of a gene

  Regulator gene: Off

  Promotor gene: On

  Structural gene: On

  Transcription can occur.
• RNA replication

  Replication of a chromatid to duplicate the number of DNA in a cell during interphase (S phase) of mitosis and meiosis.

  4000 nucleotides per second are replicated
• DNA replication

  HAPPY = Helicase

  PEOPLE = Primase

  DIE = DNA polymerase

  LONELY = Ligase
• DNA methylation

  Addition or removal of a methyl group from between a guanine and a cytosine base.

  • adding a methyl group will silence a gene by blocking RNA polymerase causing transcriptional repression.
  • removing a methyl group activates a gene by allowing RNA polymerase to attach and transcribe a code.
• Genome

  Entirety of an individuals genetic material
• Epigenetics

  The study of changes in gene activity that do not involve alterations to the genetic code but still get passed down to at least one successive generation.
• Epigenome

  Means 'above' the genome. Marks the genome with an epigenetic mark, telling it what to do, when to do it and where to do it.
• Acetylation

  Addition or removal of acetyl groups to the histone.

  • Removal of acetyl groups- DNA is attracted to histones because DNA is negatively charged and histones are positively charged, because they're closely attracted there is less space, therefore transcription cant occur meaning the gene is silent.
• Acetylation

  • Addition of acetyl groups- Acetyl groups are negatively charged therefore they attach to the histones, making them negative therefore since like charges repel each other; there is more space between DNA and histones meaning that RNA polymerase can attach therefore transcription can occur meaning the gene is active.
• Histone modification

  Altering the arrangement of the histones to enhance or prevent transcription of genes.

  • DNA is negatively charged and histones are positively charged therefore they attract each other.
  • Loosely bound genes- transcription can occur- gene is active
  • Tightly bound genes - transcription can't occur - gene is silent