Lecture 6: Global Structure of Chromosomes

DNA

he molecule of heredit

RNA

DNA is transcribed into an ________ intermediate

RNA

Single-stranded nucleotides with directionality

RNA

• Composed of a phosphate group, a pentose sugar (ribose) and bases (Adenine, Uracil, Cytosine, Guanine

Double Helix

Most stable configuration of DNA

antiparallel

DNA Contains two ________ strands

Hydrogen Bonds

In DNA nitrogenous bases are bound together by_______

B-form

DNA form - closest form in the physiological env't, relatively high humidity (92%)

A form

DNA form with lower humidity (75%)

Z form

DNA form with left-handed helix

Chromatin

• Loosely packed DNA found in the nucleus
• Complex of DNA and histones

Nucleosomes

First level of chromatin Structure
• Composed DNA molecules wrapped around core histones

30nm fiber

Second level of Chromatin Structure
• Nucleosomes fold into a 30 nm fiber in-vitro. • 2 proposed structures: the solenoid model and the zigzag model

solenoid model and zigzag model

2 proposed structure of 30nm fiber

Fiber contacts

Third level of Chromatic Structure

Histones

• Proteins which complex with DNA in the nucleus

Beads on a String

Nucleosome resembles _________

46

Chromosome numbers of Homo sapiens

8

Chromosome numbers of Drosophila melanogaster

40

Chromosome numbers of Mus muculus

20

Chromosome numbers of Zea mays

24

Chromosome numbers of Oriza sativa

24

Chromosome numbers of lycopersicum esculentum

Banding Patterns

• Banding patterns are unique to chromosomes within a species
• Bands are given designations based on their location in the chromosomes