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 -N-glycosidic bond between the anomeric carbon of the ribose and the N9 of a purine or N1 of a pyrimidine.
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Nucleosides and Nucleotides
Efficient H-bonds for only between A-T and G-C
Hydrogen bonds holds DNA strands together
Sugar phosphate backbone
A-T; 2H bonds
G-C; 3H bonds
DNA Double Helix
DNA provides a template for its own duplication
Chromosome painting identifies differenthuman chromosomes
The Human KaryotypeOne 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 differentchromosome 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 ofeight histone proteins (2X four different types) that form a core that wraps around approx. 200 nucleotides. Nucleosomesserve to pack the DNA and alsocontrol 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 synthesis5’-3’ direction
DNA polymerases also have error correction function
5’-3’ elongation of DNA provides an efficient means to correct mistakes.
DNA PrimaseRNA 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
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