• DNA molecules are very long but?only certain regions code?for the production of polypeptides
  • These are called?coding sequences
• In humans only?1.5% of the genome?contains coding sequences
• The majority of a eukaryotic genome contains non-coding regions of DNA that do not code for polypeptides but?have other important functions
• Non-coding gene?regulatory sequences?are involved in the control of gene expression by enhancing or suppressing transcription
• Non-coding sequences can produce functional RNA molecules like transfer RNA (tRNA)
• Introns?are non-coding sequences of DNA found within genes of eukaryotic organisms
  • Different proteins can be produced from a gene depending on how introns are removed
• Telomeres?are regions of?repeated nucleotide sequences?at the end of chromosomes that provide protection during cell division
  • The repeated sequence?facilitates binding of an RNA primer?at the end of the chromosome leading to synthesis of an Okazaki fragment
  • Without telomeres, DNA replication could not continue to the end of the DNA molecule and?chromosomes would become shorter?after every cell division
  • Nonetheless, telomeres shorten with age due to oxidative damage within cells
    • Loss of telomeres?during ageing can be accelerated by smoking, exposure to pollution, obesity, stress and poor diet
    • Antioxidants?in the diet are claimed to reduce the rate of telomere shortening

The RNA molecule produced from the transcription of a gene contains introns that must be removed before translation can occur.

• • DNA profiling?(sometimes called?genetic fingerprinting) enables individuals to be identified based on their DNA profiles
    • It can be used in?forensic investigations?or?paternity testing
  • Short, non-coding regions of DNA called?variable number tandem repeats (VNTRs)?are analysed
    • The frequency that VNTRs are repeated is?unique between different individuals
    • VNTRs are inherited and are?similar in close relatives?but?different in unrelated people
    • Monozygotic (identical) twins?inherit identical VNTRs?so can’t be differentiated through profiling
  • To compare the respective DNA profiles of individuals, different regions of DNA containing the VNTRs can be?excised with restriction enzymes?or?amplified by PCR?(Polymerase Chain Reaction)
  • The VNTR region for individuals will be?a different size?as they have?different numbers of repeats
    • The resulting restriction fragment or amplified DNA will also be a different size
    • Different sized fragments will generate?a unique DNA profile?in?gel electrophoresis