Molecular Genetics: From DNA to protein

A. Nucleic acid structure (DNA, RNA)

    1. Three components of a nucleotide

a) Nitrogenous base

b) Ribose/deoxyribose

c) Phosphate

    2. The DNA "polymer":

a) Sugar-phosphate backbone, 5’ – 3’

b) Nitrogenous bases "stick out": A, T, C, G

    3. Differences between RNA and DNA

a) RNA has ribose, DNA deoxyribose sugar

b) RNA is usually single-stranded, DNA double-stranded

c) RNA uses Uracil in place of Thymine (DNA)

    4. Base-pairing rules:

a) Adenine : Thymine 
b) Guanine : Cytosine

    5. Chromosome structure:

a) Chromosomes are double-stranded DNA

b) The 2 strands are complementary

c) The 2 strands are joined by hydrogen bonds between N-bases (see #4)

d) The 2 strands are wound around each other in a helix (10 bases/turn)

e) The DNA is associated with packaging proteins: histones

f) Chromosomes are linear in eucaryotes, circular in bacteria

B. DNA synthesis: replication

    1. General patterns

a) Bidirectional replication of bacterial chromosomes

b) Replication of eucaryotic linear chromosomes

    2. Mechanism (& enzyme)

a) Unwind the double helix (DNA helicase/gyrase)

b) Synthesize DNA in 5’ – 3’ direction using base-pairing rules (DNA polymerase)

c) Proofreading (DNA polymerase)

d) Join DNA pieces together (DNA ligase)

C. Making RNA: Transcription

    1. RNA

a. Messenger RNA   leader + message + tail

b. Ribosomal RNA   part of ribosome

c. Transfer RNA   an "adapter" for amino acids/mRNA

    2. Transcription of a gene

a. 3 steps are involved: Initiation, elongation, termination

b. RNA polymerase copies DNA RNA

   D. Making protein: Translation

    1. The DNA code:

a. Codon = group of 3 nucleotides specifying 1 amino acid

b. Ribosomes "read" mRNA codons __ possible combinations of A, T, C, U

c. Redundancy: >1 codon for many amino acids

d. The universal genetic code (handout chart) - Exceptions:

    2. Translation of mRNA

a. Initiation: ribosome reads the START codon: ___________ = ____________

b. Elongation: Amino acids are added by the ribosome with the help of _______

c. Termination: Ribosome stops at STOP codon (______, _______, ________)