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