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
b) RNA is usually single-stranded, DNA double-stranded
c) RNA uses Uracil in place of Thymine (DNA)
a) Adenine : Thymine
b) Guanine : Cytosine
5. Chromosome structure:
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
1. General patterns
b) Replication of eucaryotic linear chromosomes
2. Mechanism (& enzyme)
b) Synthesize DNA in 5’ – 3’ direction using base-pairing rules (DNA polymerase)
c) Proofreading (DNA polymerase)
d) Join DNA pieces together (DNA ligase)
1. RNA
a. Messenger RNA à leader + message + tail
b. Ribosomal RNA à part of ribosome
c. Transfer RNA à an "adapter" for amino acids/mRNA
2. Transcription of a gene
a. 3 steps are involved: Initiation, elongation, termination
b. RNA polymerase copies DNA à RNA
1. The DNA code:
a. Codon = group of 3 nucleotides specifying 1 amino acid
b. Ribosomes "read" mRNA codons à __ 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 (______, _______, ________)
