AS Biology F212: Nucleic Acids

• DNA is a polynucleotide
• usually double stranded
• made up of nucleotides containing bases adenine, thymine, guanine and cytosine
• DNA is found mainly in the nucleus of cells in chromosomes association with histones.
• Small amounts are found in the mitochondria and chloroplasts
• DNA is built up of units called nucleotides
• a nucleotide is made of three parts:
• a pentose sugar (deoxyribose) (RNA sugar is ribose)
• a nitrogenous base (A, T, C, G)
• a phosphate group

• RNA is a polynucleotide
• usually single stranded
• made up of nucleotides containing the bases adenine, uracil, guanine and cytosine

• RNA molecules exist in three thorms
• messengerRNA (mRNA) - made as a strand complementary to one strand f a DNA molecule
• ribosomalRNA (rRNA) - is found in the ribosomes
• transferRNA (tRNA) - carries amino acids to the ribosomes to form polypeptides.

• Nucleotides are join together by condensation reactions to form a polynucleotide
• they are joined when a covalent bond forms between carbon-3 of the sugar in one nucleotide and phosphate group of the next nucleotide aka PHOSPHODIESTER LINKS
• Too much nucleic acidcauses gout
• uric acid is produces when excess purines are broke down in the liver
• it is excreted in the urine
• some people have too much in their blood
• as it is insoluble at low temperature, crystal form in the joints at extremities e.g. toes
• the toes become swollen and painful - gout

DNA

Structure

• A DNA molecule consists of two polynucleotide strands in the form of a double helix
• two stands of the double helix are held together by hydrogen bonds between the bases on adjacent nucleotides
• there is a specific base pairing A-T, C-G (A-U in RNA)
• 2 H bonds joins A=T and three H bonds joins CºG
• hydrogen bonds are easy to break and make
• In order for the base pairs to form, the polynucleotides has to run in opposite directions, the two polynucleotides strands are described as 'antiparallel'

• GENOME - The genome of an organism is the entire DNA sequence of that organism
• The human genome consists of about 3 billion nucleotide pairs

• DNA replication takes place during interphase
• it creates identical sister chromatids
• this process by which it is carried out is called semi-conservative replication
• Function of DNA
• The double helix gives the molecule stability
• weak hydrogen bonds allow easy unzipping for copying information
• complementary base pairings mean that information can be accurately copied
• the information is in the form of codes to build proteins
• the molecule is long, a large amount of information can be stores
• Each gene is part of a DNA molecule
• a gene is a sequence of DNA bases that determines a polypeptde and a polypeptide is a sequence of amino acids
• the coded information is in the form of a specific sequence of bases aloong the DNA molecule

PROTEIN SYNTHESIS

• takes place in two steps
• transcription
• translation