L.10 Chromatin Stucture and DNA replication

Chromatin is what?

Repeating stricte of DNA and proteins (histones)

Each histone has this structure

Octomeric core

• 2H2A

• 2H2B

• 2H4

Nucleosome structre

146 DNA base pairs wrapped around histone

Chromatin fiber structure

Nucleosomes (beads) and linker DNA (string)

How to release nucleosomes

Digest chromatin with nucleus

How to link nucleosomes

Histone H1

Structure of histone H1

Globular NH2-terminal domain and COOH-terminal “arm”

How does H1 Link nucleosomes

• binds to nucleosomes via globular domain

• COOH arm reach to next H1

H1 linking is the first step of?

Chromosomal condensation/compacting

Chromatin condensation needed for?

Packaging of metaphase chromosomes

4 levels of condensation

1. 11-nm chromatin fibre (DNA with meleosomes)

2. 30-nm histone H1 pulls closer

3. 300-nm 10 fold packing of looped/ folded part of chromosome

4. 700-nm looped area get 20 loop (visible in metaphase)

Types of chromosomes, how many, and how to number

• 22 autosomal

• 2 sex

• Numbered by length

G-banding karotype analysis

Classic giemsa staining allows to see dark bands (heterochromatin)

Normal (____ploid) karyotype for females

• euploid

• 46, XX

Karyotype of male with Down syndrome

(47, XY, +21)

Philadelphia chromosome is example of _____ explain

• oncogenic translocation

• T(9;22) chromosome translocation forms new. (BCR/ABL) fusion gene

Burkitts lymphoma

• t(8;14 translocation

• Move proto-oncogene (c-myc) to enhancer of heavy gene → fires to much

_____ are readily seen with major chromosome abreirations

DNA instability syndromes

Mouse chromosome centromere location vs humans, but they have high ___ with people

Mouse - aeroccntric (at end)

Human - metacentric (centre)

Synteny (gene order)

Types of aberrations

• aneuploidy (too many)

• Segregation

• Centromere loss

• Fusion

• Breakage

Structural elements of chromosome maitenee/replication

1. Telomere (caps ends to keep enzymes from destroying)

2. Organs of replication (inflation* points during S phase)

3. Kineochore (after nuclear breakdown, chromosomes segregated by kinelochore, formed at centromere

DNA replication begins at?

Origins of replication

Direction of DNA synthesis

Both directions form initiation complexes

What occurs when synthesis complexes meet

Strands lighted/joines to form daughter DNA

DNA polymerases synthesize in this direction, therefore stands are _____

• 5’ → 3’

• Antiparallel

Leading strand process

5‘ → 3’ using 1 polymerase somplex

Lagging strand process

• many proteins

1. Single strand binding proteins (keep strands apart)

2. Primate to “prime” DNA synthesis with RNA

3. Synthesis from RNA stands creat Okazaki fragments

4. Legate together

DNA pol III direction, how it works on leading strand

• 5’ → 3’ (created

• Continuous replication

A = leading

B = lagging

Lagging strands requires ____ synthesis, where ____ templates made to prime ____ of _____ fragments, which are lighted together

• discontinuous

• Short RNA

• DNA synthesis

• Okazaki

Synthesis of both strands occurs ___, as what also occurs, forming this structure in the DNA

• simultaneously

• Chromosome unzipped form origin (DNA)

• Replication fork

All steps of DNA replication

1. Replication origins recruit mutation complexes*

2. DNA unwound by toposiomerelase And helicases

3. Single strands stabilized by binding proteins

4. Leading synthesised by DNA pol III

5. Lagging synthesized by RNA primer and DNA primate to make Okazaki fragments with DNA pol I, DNA ligaments fuses

Example lagging strand with enzymes

• RNA primer and DNA primate discontinuously

• Okazaki fragments synthesized by DNA pol I

• DNA ligaments fuses fragments together