8.2 - DNA & Chromosomes

• where is eukaryotic DNA found?

  in the nucleus
• what's eukaryotic DNA like?

  long & linear so has to be wound up tightly so it can fit into the nucleus (forms a chromosome)
• what's eukaryotic DNA associated with?

  proteins called histones that help support DNA and to form chromosomes
• Where is eukaryotic DNA also found and what is it like ?

  mitochondria and chloroplast but it's more similar to prokaryotic DNA because it'ss circular, shorter & not associated with histones
• what's prokaryotic DNA like?

  shorter and circular not wound around histones so no chromosomes - it condenses to fit in the cell by supercoiling
• when are chromosomes visible and what do they look like?

  when all starts to divide

  a sister chromatids joined at the untromere
• vwwhat's the length of DNA in each human cell?

  2 metres
• chromosome structure - smallest to largest

  base

  nucleotide

  gene

  DNA

  chromatin

  chromatid

  chromosome
• how most of DNA is condensed into a chromosome

  double helix is wound around histones to fix it in position

  DNA-his tone complex is coiled then looped and coiled further
• number of chromosomes in humans

  46

  also called the diploid number
• number of chromosomes in potato plants

  48
• number of chromosomes in dogs

  78
• what are homologous chromosomes?

  pair of chromosomes (one from each parent) that have the same size and carry the same gene but not always the same alleles
• what's the diploid number?

  total number of homologous pairs
• what are alleles?

  different forms of the same gene

  code for the same thing but order of bases is different so form different polypeptides
• how many alleles in genes?

  2 in each gene - one from each parent

  they can be the same or different
• what are mutations?

  changes in the base sequence which produces a new allele
• what can mutations lead to?

  different base sequence so codes for a different aminoacid so produces a different polypeptide so a different protein

  polypeptide maybe different, non-functional, dysfunctional or harmful as it may not carry out its job
• mutations in enzymes

  enzyme may have a different shaped active site so substrate may not fit will so enzyme may not function
• what can genes code for?

  polypeptides or functional RNA
• What are introns?

  non- coding regions of DNA

  junk DNA/non-coding repeats

  not present in prokaryotes
• what are exons?

  coding regions of DNA
• what's splicing?

  removeing introns

  done in transcription to make mRNA from pre-MRNA