Biol 1551 Sep 18^th lecture notes

 

Chapter 3 Biological molecules (continued)

 

8. Nucleic acids

DNA – deoxyribonucleic acid

RNA – ribonucleic acid

 

<function>

            DNA codes for genetic information.

            RNA is mediator of gene expression.

 

Fig 10.6.A, p192, scheme of gene expression

DNA

                                                                           ↓ transcription

RNA

                                                                           ↓ translation

protein

           

 

<structure>

1. nucleotide (monomer unit) Fig 3.20A, p47

·        consists of three parts

1.      phosphate

2.      sugar

3.      nitrogenous base

 

Comparison of DNA and RNA

	sugar	types of base
DNA Fig 3.20A, p47	deoxyribose	A (adenine) T (thymine) C (cytosine) G (guanine)
RNA Fig 10.2 C, p187	ribose	A U (uracil) C G

 

            DNA vs. RNA

                        different sugar

                        different set of nitrogenous bases

 

 

2. Polymerization

·        Nucleotides are joined together by covalent bonds between sugar and phosphate group to make a strand of polynucleotide.  (Fig 10.2A, p186)

 

·        RNA – a single strand of polynucleotide chain

·        DNA – two strands of polynucleotide chains

 

 

3. DNA double helix

 

James Watson and Francis Crick

 

·        Pairing of two DNA strands by hydrogen bonds between nitrogenous bases.

A only pairs with T

C only pairs with G

 

ex.  If the nucleotide sequence of a DNA strand is ATACGGTC, then the nucleotide sequence of opposing strand (complementary strand) is TATGCCAG.

 

·        The two DNA chains are normally twisted to make double helix structure. (Fig 3.20C, p47)