copyright © 2009 pearson education, inc. chapter 12 dna organization in chromosomes copyright ©...

Copyright © 2009 Pearson Education, Inc.

Chapter 12DNA Organization in

Chromosomes



• Single nucleic acid molecule

• No proteins

• DNA or RNA

• Single or double stranded

• Circular or linear

• Packed into a small volume

Viral Genetic Material


• Single nucleic acid molecule

• Some proteins

• Always double stranded DNA

• Large, circular chromosome

• Packed into a small volume (nucleoid region)

Bacterial Genetic Material


Supercoiling


• Polytene chromosomes

• Lamp brush chromosomes

Specialized Eukaryotic Chromosome Organizations


Polytene


Lamp Brush


• Only visible during mitosis

• Easier to move DNA around

• Normally uncoiled and dispersed

• Chromatin

• Available for genetic activity

Eukaryotic Chromosomes


• DNA has a substantial amount of associated proteins

• Histones

• Non-histones

Chromatin


• Highly folded DNA presents a problem – genes are inaccessible

• High resolution images showed how chromatin could be remodeled

• Histone tails

• Remodeling

• Acetylations

• Methylation

• Phosphorylation

Chromatin Remodeling


• Euchromatin

• Light staining

• Active genes

• Uncoiled during interphase

• Heterochromatin

• Heavy staining

• No (few) active genes

• Tightly packed during interphase

Euchromatin vs Heterochromatin


• Enabled further characterization of chromosomes (previously only size)

• C – banding

• Centromeres stain darkly

• G – banding

• Digest with trypsin before staining

Banding Patterns


C – Banding


G – Banding


X chromosome banding pattern


• Satellite DNA

• Centromeric sequences

• Telomeric sequences

• Middle (moderate) repetitive DNA

• VNTRs

• STRs

• Transposable sequences

• Pseudogenes

Repetitive Sequences


Satellite DNA


Centromeric Sequences

copyright © 2009 pearson education, inc. chapter 12 dna organization in chromosomes copyright ©...

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