2.3:NUCLEOTIDES+NUCLEIC ACIDS

• nucleotides are the monomers from which nucleic acids like DNA and RNA are formed
• nucleic acids contain nitrogenous bases , phosphate group and a pentose sugar
• the nitrogenous bases are categorised by their ring structures and organised into purines and pyrimidines
• purines have a 2 carbon ring structure and are adenine and guanine
• pyrimidines have a single carbon ring structure and are cytosine, thymine and uracil
• guanine is always paired with cytosine
• adenine is always paired with thymine or uracil
• uracil is only found in RNA
• deoxyribose sugar is found in DNA
• ribose sugar in RNA
• purines and pyrimidines bases are always opposite each other in dna maintaining order
• both RNA and DNA undergo condensation reaction forming phosphodiester bonds
• the phosphodiester bond between adjacent nucleotides form the polymer polynucluotides
• phosphodiester bonds are very strong covalent bonds
• DNA codes for the sequence of amino acids in primary structure of protein which determines the 3d shape of tertiary structure
• polymer forms a double helix made of two antiparelel strands joined together by hydrogen bonds
• DNA has a stable structure due to the phosphodiester bonds that form between nucleotides
• weak hydrogen bonds between bases makes it easier for strands to separate for DNA replication
• DNA is a large molecule so can carry a lot of information
• DNA can be extracted out of cell using the method of precipitation
• RNA is single-stranded, whereas DNA is double-stranded.
• three types of RNA are tRNA rRNA and mRNA
• rRNA forms part of the ribosome which is where proteins are made
• mRNA leaves the nucleus via nuclear pores and carries genetic code to ribosomes in cytoplasm
• mRNA is single stranded and every 3 bases in the sequence codes for a specific amino acid these are called codons
• tRNA has an anticodon that matches with the codon on mRNA so it brings the correct amino acid to the ribosome
• tRNA is single stranded but folds into clove leaf like structure held in place by hydrogen bonds
• tRNA carries specific amino acids to ribosomes this is determined by the 3 bases on tRNA called anticodons
• DNA replication is described as semi conservative as one single strand of DNA is conserved and one entire new strand is created from new nucleotides
• copying errors can occur but they are random and they result in the change in DNA sequence this is called a mutation
• DNA replication occurs in s phase in interphase of cell cycle
• the genetic code has 3 features which are that it is degenerate universal and non overlapping
• degenerate means that the amino acids are coded for by more that one triplet of bases of DNA
• the genetic code being degenerate is an advantage as even if a mutation occurs changing a base in triplets still codes for the same amino acid meaning no impact on final sequence of amino acids
• universal means the triplet of bases codes for same amino acids in all organisms
• the genetic code being universal is an advantage as it means we are able to remove a human gene and insert into the plasmids of a bacterium
• on overlapping means each base in a gene is only part of one triplet base that codes for one amino acids
• the genetic code being non overlapping is an advanatage as if there was a mutation the mutation will only affect one codon
• protein synthesis is when proteins are being created on ribosomes on RER
• protein synthesis occurs in two stages translation and transcription