Lecture 11 Review
• DNA is the material of heredity
• Consists of 4 nucleotides joined between
the 3’ carbon of the deoxyribose group of
the first nucleotide and the phosphate
group of the next nucleotide (which is
attached to the 5’ carbon of deoxyribose)
• Direction: 5’ to 3’
• Structure: double stranded helix
» A pairs with T; G pairs with C
DNA in the nucleus
• Compacted by interactions with proteins
• (1) nucleosomes are formed by DNA
interactions with histones H2A, H2B, H3,
and H4
• (2) histone H1 helps nucleosomes interact
with each other
• (3) this form of DNA forms loops – some
portions interact with scaffold, such as the
nuclear matrix
Cont’d
• Heterochromatin – highly compacted DNA
• Facultative heterochromatin – is highly
compacted in some cells and not in others
• Euchromatin – not so tightly compacted
DNA (actively transcribed genes)
• Metaphase chromosomes – very highly
compacted
DNA replication
• (1) helicase, topoisomerase, ssBP
– Opens up DNA and prepares it for replication
• (2) primase – adds in short stretches of
RNA to act as primers
• (3) DNA polymerase III adds
deoxyribonucletides to the 3’ end of the
RNA primers
• Direction of synthesis is 5’ to 3’
Cont’d
• Leading strand synthesis vs. lagging
strand synthesis…..
– Okazaki fragments