Interphase and Metaphase Chromosomes

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14 Terms

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Interphase Chromosomes

Is the compaction level of interphase chromosomes uniform or not?

Not completely uniform

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Interphase Chromosomes

Therefore, what are the 2 types of regions in interphase chromosomes?

Euchromatin
Heterochromatin

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Interphase Chromosomes

Euchromatin vs Heterochromatin

Level of compactness

Transcriptionally active or inactive

Radial loop domains

Euchromatin:

Level of compactness: Less compacted
Transcriptionally active or inactive: Active
Radial loop domains: Regions where 30nm fiber forms radial loop domains

Heterochromatin:

Level of compactness: Tightly compacted
Transcriptionally active or inactive: Inactive (in general)
Radial loop domains: Compacted even further

<p><strong><u><span style="color: green">Euchromatin:</span></u></strong></p><ul><li><p><strong><u><mark data-color="green">Level of compactness:</mark></u></strong> <strong><span style="color: green">Less compacted</span></strong></p></li><li><p><strong><u><mark data-color="green">Transcriptionally active or inactive:</mark></u></strong> <strong><span style="color: green">Active</span></strong></p></li><li><p><strong><u><mark data-color="green">Radial loop domains:</mark></u> </strong>Regions where <strong><span style="color: green">30nm fiber </span></strong>forms <strong><span style="color: green">radial loop domains </span></strong></p></li></ul><p><strong><u><span style="color: purple">Heterochromatin:</span></u></strong></p><ul><li><p><strong><u>Level of compactness:</u></strong><span style="color: purple"> </span><strong><span style="color: purple">Tightly compacted</span></strong></p></li><li><p><strong><u>Transcriptionally active or inactive:</u></strong> <strong><span style="color: purple">Inactive</span> </strong>(in general) </p></li><li><p><strong><u>Radial loop domains:</u></strong> <strong><span style="color: purple">Compacted even further </span></strong></p></li></ul>

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Interphase Chromosomes

What are the 2 types of heterochromatin?

Constitutive heterochromatin
Facultative heterochromatin

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Interphase Chromosomes

What is the difference between constitutive and facultative heterochromatin?

Constitutive: Always heterochromatic

Which means it is permanently transcriptionally inactive

Facultative: Can interconvert between euchromatin and heterochromatin

EX: Barr body

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Interphase Chromosomes

However, during interphase chromosomal regions are mostly?

Euchromatic

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Metaphase Chromosomes

What happens to the level of compaction?

It changes dramatically

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Metaphase Chromosomes

At the end of prophase, sister chromatids are entirely?

Heterochromatic

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Metaphase Chromosomes

Therefore, if they are highly condensed, what is their level of transcription?

Highly condensed = little gene transcription

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Metaphase Chromosomes

How are metaphase chromosomes are highly compacted?

Because radial loops are highly compacted and stay anchored to a scaffold

Scaffold is formed from nuclear matrix

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Metaphase Chromosomes

When chromosomes are compacted, do the number of loops change?

Number of loops don’t changed BUT diameter of each loop gets smaller

<p>Number of loops <strong><span style="color: purple">don’t changed</span> </strong>BUT <strong><span style="color: purple">diameter</span> </strong>of each loop gets <strong><span style="color: purple">smaller</span> </strong></p>

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Metaphase Chromosomes

Mutltiprotein Complexes

What 2 multiprotein complexes help form and organise metaphase chromsomes?

What are their roles

Both contain what

What multiprotein complexes:

Condensin
Cohesion

Roles:

Condensin: In chromosome condensation
Cohesion: In sister chromatid alignment

Both contain: SMC proteins that uses ATP energy

Structural Maintenance of Chromosome

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Metaphase Chromosomes

How does condensin work?

During interphrase, condensin is in the cytoplasm
After G2 phase, it travels into nucleus
Where it binds to chromosomes and compacts the radial loops

<ul><li><p>During <strong><span style="color: blue">interphrase</span></strong><span style="color: blue">, </span><strong><span style="color: blue">condensin</span></strong> is in the <strong><span style="color: blue">cytoplasm</span></strong></p></li><li><p>After <strong><span style="color: blue">G2 phase</span>, </strong>it travels <strong><span style="color: blue">into nucleus</span></strong></p></li><li><p>Where it <strong><span style="color: blue">binds</span> </strong>to <strong><span style="color: blue">chromosomes</span> </strong>and <strong><span style="color: blue">compacts</span> </strong>the<span style="color: blue"> </span><strong><span style="color: blue">radial loops</span></strong></p></li></ul>

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Metaphase Chromosomes

How does cohesions work?

Beginning of prophase: Cohesions are along the chromosome arms

Middle of prophase: Cohesions are only at centromere

This means the chromosome arms are free

Anaphase: Cohesion at centromere is degraded

This means that condensed chromatid have separated

<p><strong><u>Beginning of prophase:</u></strong> <strong><span style="color: red">Cohesions</span> </strong>are along the <strong><span style="color: red">chromosome arms </span></strong></p><p><strong><u>Middle of prophase:</u></strong> <strong><span style="color: red">Cohesions</span> </strong>are <strong><span style="color: yellow">only</span> </strong>at <strong><span style="color: yellow">centromere</span></strong></p><ul><li><p>This means the <strong><span style="color: red">chromosome arms</span> </strong>are <strong><span style="color: red">free</span> </strong></p></li></ul><p><strong><u>Anaphase:</u></strong> <strong><span style="color: red">Cohesion</span> </strong>at <strong><span style="color: yellow">centromere</span> </strong>is <strong><span style="color: red">degraded</span> </strong></p><ul><li><p>This means that <strong><span style="color: red">condensed chromatid</span> </strong>have <strong><span style="color: red">separated</span> </strong></p></li></ul>