Function of nucleic acid: store, transmit and help express hereditary information
● There are two types:
○ Deoxyribonucleic acid (DNA)
○ Ribonucleic acid (RNA)
○ Both are important in gene expression and protein synthesis
● DNA directs synthesis of mRNA which is read during translation = protein is
synthesised
Polynucleotides and nucleotides
- a polynucleotide is the polymer of a nucleic acid
● Each polynucleotide is made of monomers called nucleotides which each
contain:
○ Pentose sugar: ribose (RNA) or deoxyribose (DNA)
■ Contains 5 carbons (each number 1’-5’)
■ Ribose and deoxyribose are the important sugars in nucleotides
● The difference between them is the group attached to the 2’
carbon
, ■ You must know these structures!!!!!
○ Phosphate (PO43-)
■ (It is weakly acidic)
■ Gives DNA its negative charge (there is always at least one
negative oxygen on the phosphate)
○ Nitrogenous base
■ AGCT in DNA
● A and G are purines
○ Purines are a 6 membered ring fused to a 5
membered ring
, ○
● C and T are pyrimidine
○ 6 membered rings
○
■ AUGC in RNA
● Uracil is a pyrimidine
Joining of the components of a nucleotide
,NB: A NUCLEOSIDE CONSISTS OF ONLY A SUGAR AND A NITROGENOUS BASE,
NO PHOSPHATE GROUP (do not confuse them)
● The pentose sugar and the nitrogenous base are joined by a glycosidic bond,
which forms through a dehydration reaction
○ The bond forms between 1’ of the sugar and the:
■ In a pyrimidine: Nitrogen 1
■ In a purine: Nitrogen 9
—————— the formation of a nucleoside ends here———
● The phosphate group bonds to the sugar via its oxygen
○ It bonds to the 5’ of the sugar
○ When it bonds to the sugar it loses its negative charge
○ If another nucleotide is added, the other oxygen loses its negative charge
■ Thus leaving only one open, negative oxygen
The chemical name of DNA is deoxyadenosine 5’ monophosphate
,Polymerisation of nucleotides
● Polymers are linked together by a phosphodiester linkage
● The links create a backbone of sugar-phosphates with the nitrogenous bases as
appendages
Simple process:
1. One oxygen of the phosphate group of one nucleotide joins with the 3’ carbon
on another nucleotide
2. This process repeats, forming the backbone and increasing the length of the
base
,
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