Download MBP 1022, LECTURE 3 DAN-ct30

Chapter 4
• DNA and Chromosomes
HIGHLIGHTS
DNA
Exact duplication of genetic material from generation to
generation is crucial to continuity and survival
Genes: hereditary units controlling identifiable traits
General structure of nucleic acids
Mechanism of DNA synthesis
Not responsible for nucleosomes and heterochromatin
Chromosomes in Cells
DNA is composed of 4 different nucleotides A,C,G,T
Nucleic Acids are the building blocks of DNA and RNA
•DNA (deoxyribonucleic acid)
•RNA (Ribonucleic acid)
Both are linear polymers of nucleic acids
Pentose
•Ribose
•2-Deoxyribose
*
*
It is the chemical basicity of the nucleotides that has given them the
common term "bases" as they are associated with nucleotides present in
DNA and RNA. There are five major bases found in cells. The
derivatives of purine are called adenine and guanine, and the derivatives
of pyrimidine are called thymine, cytosine and uracil. The common
abbreviations used for these five bases are, A, G, T, C and U. The purine
and pyrimidine bases in cells are linked to carbohydrate and in this form
are termed, nucleosides. The nucleosides are coupled to D-ribose or 2'deoxy-D-ribose through a b-N-glycosidic bond between the anomeric
carbon of the ribose and the N9 of a purine or N1 of a pyrimidine.
Nucleosides and Nucleotides
Efficient H-bonds for only between A-T and G-C
Hydrogen bonds holds DNA strands together
A-T; 2H bonds
G-C; 3H bonds
Sugar phosphate backbone
DNA Double Helix
DNA provides a template for its own duplication
Chromosome painting identifies different
human chromosomes
The Human Karyotype
One set of human chromosomes. Each somatic cell will
have a maternal and paternal set, thus 44 chromosomes
plus two sex chromosomes XX, female or XY, male
= 46 TOTAL
Two closely related species of deer with very different
chromosome numbers, but very similar number of genes.
Conserved synteny (gene order) between human
and mouse genomes demonstrates that many of the human
genes are shared by mice and that they are organized in a
similar fashion within their genomes, which suggests that
their expression is also controlled in a similar fashion
DNA in the cell is organized into protein-DNA
complexes known as nucleosomes
Nucleosomes are composed of
eight histone proteins (2X four
different types) that form a core
that wraps around approx. 200
nucleotides. Nucleosomes
serve to pack the DNA and also
control the expression of genes.
Chapter 5
• DNA Replication,
Repair, and
Recombination (Not
responsible for)
Common rules of DNA Synthesis:
1. Limited # of distinct monomeric subunits
(5 nuc. acids)
2. Monomers are added one at a time
(step by step addition)
3. Specific starting point
Growth proceeds in one direction
4. DNA polymerases can not initiate synthesis de novo
need RNA or DNA primer to provide free 3’ OH group
Fixed terminus
(5’ end to 3’ end in polynucleotides)
DNA Replication:
Watson Crick Model of DNA suggested semiconservative DNA
Multiple enzymes are required at the replication fork
(helicase, topoisomerase, DNA polymerase, ligase and more)
Leading strand and lagging strand (Okazaki fragments)
Energy requiring process; requires a primer (RNA or DNA)
DNA Replication is very accurate
DNA synthesis is catalyzed
by DNA polymerase.
DNA template is replicated through a
semiconserved mechanism.
Incorrect model of DNA replication:
DNA is always processed 5’-3 this diagram suggests
that DNA can be synthesized 3’-5’ direction
Correct model of DNA synthesis
5’-3’ direction
DNA polymerases also have error correction function
5’-3’ elongation of DNA provides an efficient
means to correct mistakes.
DNA Primase
RNA polymerase
Okazaki fragments
Nicks are ligated together by DNA ligase.
DNA helicase helps unwind DNA
Helicase movie
Proteins found at the DNA replication fork
DNA replication in action.
Replication occurs in both directions
DNA Replication Movies