Molecular genetics

• Each DNA(deoxyribonucleic acids) molecules is wrapped around histone proteins to form a chromatin thread
• During cell division the chromatin threads condense(coil) more tightly to form chromosomes inside the cell nucleus
• when the cell is dividing DNA appears as chromosomes but when cell is not dividing DNA appears as chromatin threads
• Each DNA molecule is a macromolecule that is made up of anti-parallel polynucleotide strands twisted together to form a double helix structure
• Each polynucleotide strand is made up of many nucleotides
• A nucleotide is made of

  • deoxyribose sugar
  • phosphate group
  • nitrogen-containing base
• 4 types of bases

  • adenine (A)
  • thymine (T)
  • guanine (G)
  • cytosine (C)
• The base unit of DNA molecule is a nucleotide
• Adenine (A) binds with thymine (T) and Guanine (G) binds with cytosine (C) this is according to the rule of complementary base pairing
• The bases on one strand form hydrogen bonds with the bases on the other side
• Each chromosome contains 1 DNA molecule and a gene is a small segment of a DNA molecule
• A gene is s segment of a DNA molecule
• Each gene is a specific sequence of nucleotides
• The nucleotide sequence in the gene codes for the production of one polypeptide
• Each gene is a unit of inheritance
• DNA is used to carry the genetic code which is used to synthesis specific polypeptides
• There nucleotides in a gene form a codon and each codon does form one amino acid
• The genetic codes state which amino acid each codon codes for
• Codon

  • TAC
  • TAT
  • CAT
  • GAG
  • ACA

  Amino acid coded for

  • methionine (M)
  • alanine (A)
  • lysine (L)
  • glutamic acid (E)
  • serine (S)
• What will happen if the nucleotide sequence in a gene is altered?

  change in the nucleotide sequence of a gene(gene mutation) mutation many or many not lead to a change in the protein product change in the protein product may or may not lead to an observable phenotype