Molecular Biology 2.6 Structure of DNA and RNA
Nucleic Acids Nucleotides consist of 3 parts:
A sugar 5 carbon sugars = pentose sugars
A base contains nitrogen 1 or 2 rings of atoms
1 ring = Pyrimidine 2 rings = Purine
A phosphate group negatively charged
acidic
Nucleic Acids Covalent bonds are
formed between the phosphate of one nucleotide and the sugar of the next.
This creates a “backbone” of alternating sugar and phosphate.
Nucleic Acids The bonds holding the
phosphate group to the sugar and the base to the sugar are both products of condensation reactions.
Water is eliminated when they form.
The oxygen to form the water has come from the sugar's -OH groups.
Nucleic AcidsDNA differs from RNA in the number of strands normally present, the base composition and the type of pentose
Nucleic Acids DNA has 2 polymers of nucleotides
(double-stranded) RNA has 1 polymer (single-stranded)
Nucleic Acids The sugar within DNA is deoxyribose The sugar with RNA is ribose
Draw both sugars. Compare the structures.Predict the reason for the difference in their names.Compare to the previously examined carbohydratesugars.
Nucleic Acids There are 4
different bases for each type of nucleic acid
These can be linked in any sequence
Draw the 2 generic base types.
Complete the “data-based question” p109
Nucleic AcidsThe amino acid sequence of polypeptides is coded for by genesThe sequence of nucleotide bases provides the code3 bases of the gene are needed to code for each amino acid
More about this later
Nucleic Acids The variety of
combinations of bases is the key to nucleic acids acting as a store of genetic information.
Nucleic AcidsRNA Pyrimidines =
Uracil (U) and Cytosine (C)
Purines = Adenine (A) and
Guanine (G)
Note the change from T to U
Nucleic AcidsDNA is a double helix made of 2 antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs
Nucleic Acids The strands are held together
by hydrogen bonds between the complementary base pairs. Adenine always pairs with
Thymine Guanine always pairs with
Cytosine The 2 strands are parallel but
run in opposite directions one runs 5’ to 3’ the other 3’ to 5’
Nucleic AcidsDraw simple diagrams of DNA using circles, pentagons, and rectangles to represent phosphates, pentoses, and bases. The base is attached to the
C1
The phosphate is linked to the C5
The phosphate of another nucleotide will link to the C3
Review quiz http://www.rsc.org/Education/Teachers/R
esources/cfb/quiz.cfm?qzid=15