Salivary gland- polytene chromosomes

Brain-diploid metaphase chromosomes

Same Objective Lens:

Why are the salivary glandchromosomesso much larger?

Alyssa and Tyler

Fig. 14.8

MPF (Cdk/Cyclin Protein Complexes) Regulate Progression through Cell Cycle

MPF=_________ (Cyclin-dependent Kinase) - regulates proteins by phosphorylation

__________- cell cycle phase- specific kinase regulators

Cdk

Cyclin

SKIPPED in Polytene Tissues (Salivary Gland)

How might cell cycle regulation differ ?

Chromatin: DNA Complexed with Protein

7x compaction

40x compaction

10,000x compactionFig. 12.1210,000x compaction

Chromatin Packagingin MetaphaseChromosomes

Chromatin Packagingin Salivary Gland Squash

thro

ugho

ut c

ell c

ycle

M phase only

7x compaction

40x compaction

10,000x compactionFig. 12.1210,000x compaction

Dark Bands?

Light Interbands?

30 nm fiber and higher

Lower than 30 nm fiber

Compaction Levelheat shocked

non-heat shocked

HP1

HP1 in transcriptionally silenced centromeric heterochromatin

Which proteins would you expect to co-localize with HP1 here?

Fig. 12.17

HP1 binding to Me-K9 histone H3to silence TransposableElements incentromericheterochromatin

Nucleosome

- ~200 bp DNA wrapped around histone core octamer containing 2 each of 2 different heterodimers: histones

- between (-) chgd. DNA backbone and (20-30% Lys/Arg)

- highly conserved amino acid sequence

- packing ratio 7:1

- -sites of covalent modifications Fig. 12.9

H2A/H2B and H3/H4ionic bonds

(+) chgd. histones

N terminal tails

N-terminal CovalentModifications Give a “Histone Code”

Acetylation:

Deacetylation:

Methylation ( , K20H4): Heterochromatin

Fig. 12.14

Active Chromatin

Inactive Chromatin

K9H3, K27H3

7x compaction

40x compaction

10,000x compactionFig. 12.1210,000x compaction

heat shocked

non-heat shocked

Acetylated Histones?

De-acetylated Histones?

Bands or Interbands?

Interbands

Bands