DNA

• DNA in eukaryotic cells

  Long, linear and wrapped around histone proteins
• DNA in mitochondria and chloroplasts

  Short, circular and not associated with proteins

  same as in eukaryotes
• DNA in prokaryotic cells

  Short, circular and not associated with proteins
• Intron


  Non-coding region of DNA

  removed during splicing
• Exons


  Coding region of DNA
• Position on DNA that specific genes are found

  Locus/loci
• Genetic code is universal

  each triplet codes for the same amino acid in all organisms
• Genetic code is degenerate


  multiple triplets code for the same amino acid
• Genetic code is non-overlapping

  each base triplet is read in sequence, separate from the triplet before and after it. base triplets do not share their bases
• Genome


  complete set of genes in a cell
• proteome


  complete set of proteins the cell can produce
• RNA nucleotide structure

  ribose sugar, uracil instead of thymine
• Types of RNA

  m-RNA, tRNA
• t-RNA structure

  single-stranded

  clover leaf shape

  specific amino acid attached

  anticodon at base which is complementary to m-RNA codon
• mRNA structure

  Long and single-stranded

  made up of a sequence of bases which is complementary to DNA
• What is transcription?

  the production of a complementary mRNA from DNA
• Process of transcription

  DNA helicase breaks hydrogen bonds between complementary base pairs in DNA

  one DNA strand acts as a template

  RNA polymerase catalyses the addition of free complementary RNA nucleotides

  Each base binds to its complementary base

  RNA splicing removes introns

  mRNA leaves nucleus through nuclear pores
• What is translation?


  The synthesis of a polypeptide from mRNA
• Process of translation


  mRNA attached to a ribosome in the cytoplasm/on RER

  free molecules of tRNA with a specific amino acid attached move towards ribosome

  anticodon on tRNA binds to codon on mRNA

  2 tRNA molecules can fit onto the ribosome at one time

  this allows a peptide bond to form between the adjacent amino acids

  this continues until the stop codon is reached
• gene mutation


  a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
• why don't most mutations alter the polypeptide produced?

  as the genetic code in degenerate
• Insertion mutation


  a mutation in which one nucleotide is randomly inserted, this causes a frameshift and may dramatically change the polypeptide produced and the polypeptides ability to function
• Deletion mutation


  a mutation in which one nucleotide is randomly deleted, this causes a frameshift and may dramatically change the polypeptide produced and the polypeptides ability to function
• Substitution mutation

  mutation in which a base is randomly swapped for a different base, this only affects one triplet and does NOT cause a frame shift, however it may produce a stop codon
• mutagenic agents


  environmental factors that increase the mutation rate of cells
• non-disjunction


  when chromosomes fail to separate during meiosis,

  gametes may have an extra copy of a chromosome or no copies of a chromosome

  
• what processes ensure that meiosis produces genetically different daughter cells?

  independent segregation of homologous chromosomes and crossing over
• Independent segregation of homologous chromosomes


  - Random alignment of homologous pairs at equator → random which chromosome from

  each pair goes to each daughter cell

  - Creates different combinations of maternal and paternal chromosomes and alleles in

  daughter cells
• Crossing over


  Process in which homologous chromosomes exchange portions of their chromatids during meiosis.
• what is formed from meiosis?

  4 haploid cells
• How many meiotic divisions are there?

  2
• what happens during prophase 1?

  - DNA condenses and becomes visible as chromosomes

  - homologous chromosomes pair up (side by side), in homologous pairs

  -centrioles move to opposite poles and the spindle is formed

  - The nuclear envelope and the nucleolus breaks down
• What happens during metaphase 1?

  homologous chromosomes line up alone the equator of the cell, the spindle fibres attach to the centromeres
• what happens during anaphase 1?

  Homologous chromosomes separate
• what happens during telophase 1?

  -chromosomes arrive at opposite poles

  -spindle fibres break down

  -nuclear envelope reforms
• cytokinesis

  division of the cytoplasm
• is DNA replicated in-between meiosis 1 and 2?

  no
• what happens during prophase 2?

  -chromosomes condense

  -nuclear envelope breaks down

  -spindle forms at a right angle to the old one
• what happens during metaphase 2?

  Chromosomes line up at the equator of the cell
• what happens during anaphase 2?

  centromeres divide and sister chromatids are pulled to opposite poles of the cell