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Cell Biology > Chromosomes and Chromatin > Flashcards

Chromosomes and Chromatin Flashcards

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1
Q

Prokaryotic chromosomes are ?

A

Circular and typically have one origin of replication

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2
Q

The E. coli chromosome is about ?

A

4.6 million bases long and encodes 4300 different proteins

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3
Q

Eukaryotes genomes are?

A

Larger and more complex

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4
Q

Explain Eukaryotes further?

A
  • More genes which contain introns
  • More regulation eg cell type specific expression
  • More ‘junk’ DNA
  • No correlation between genome size and evolution
  • Organised in linear chromosomes
  • Packaging problem - 2m DNA into 6μm human cell nucleus
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5
Q

Eukaryotic chromosomes are ?

A

Linear

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6
Q

In eukaryotes, the genome is broken up into ?

A

Long, linear, double-stranded structures called chromosomes

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7
Q

How many chromosomes does the human genome have ?

A

The human genome has 24 chromosomes

22 autosomes and 2 sex chromosomes

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8
Q

Human cells are ?

A

Diploid (2n = 46)

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9
Q

Even closely related species can have ?

A

Different numbers of chromosomes

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10
Q

Chromosomes change during ?

A

The cell cycle

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11
Q

In Interphase nuclei, the chromosomes are ?

A

Distributed throughout the nucleoplasm

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12
Q

At mitosis the chromosomes?

A

Condense - individual chromosomes can be seen with the light microscope

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13
Q

What are telomeres ?

A

Stabilise ends

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14
Q

What is the function of the centromere ?

A

To segregate the sister chromosome

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15
Q

What is the use of replication origins ?

A

To duplicate the DNA

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16
Q

A chromosome consists of?

A

Two sister chromatids

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17
Q

After replication there are?

A

Two identical sister chromatids

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18
Q

Each chromatid contains ?

A

One old and one new strand (semi-conservative replication)

19
Q

Sisters are held together until ?

A

Chromosomes segregation during mitosis

20
Q

In some cells, chromosomes adopt the Rabl configuration with ?

A

The centromeres clustered at one end, and the telomeres abutting the nuclear envelope at the opposite pole reflecting the arrangement of the chromosomes at anaphase

21
Q

During Interphase, individual chromosomes occupy ?

A

Particular regions of the nucleus

22
Q

This arrangement minimises?

A

Tangles between the chromosomes and helps condensation and segregation during mitosis

23
Q

Chromosomal DNA is ?

A

Highly condensed

24
Q

DNA is compacted by association with proteins -

A

Chromatin

25
Q

Individual nucleosomes are arranged on ?

A

The DNA like beads on a string

26
Q

DNA isolated from an interphase nucleus appears as ?

A

A 30 nm thick fibre

27
Q

The nucleosome core particle consists of ?

A

147 base pairs of DNA wound around a protein core

28
Q

Explain Histones ?

A

The protein core is made of a small highly basic proteins

29
Q

The octomeric histone core contains ?

A

Two molecules of each of four histones, H2A, H2B, H3 and H4

30
Q

DNA is wound around?

A

Histones

31
Q

An additional histone, Histone H1, arranges ?

A

Nucleosomes into the 30nm fibre

32
Q

During mitosis, this 30 nm fibre is further ?

A

Condensed at

two additional levels to achieve the packing that is observed in mitotic chromosomes

33
Q

By TEM, the chromatin in the nucleus appears in two forms:

A

A diffuse open configuration, called euchromatin and a condensed electron dense form called heterochromatin

34
Q

Euchromatin is ?

A

Transcriptionally active

35
Q

Heterochromatin is ?

A

Transcriptionally inactive

36
Q

Decondensed or open chromatin (= euchromatin) is associated ?

A

With transcriptionally active regions of the genome

37
Q

Closed Condensed chromatin (=heterochromatin) is associated ?

A

With transcriptionally repressed regions of the genome

38
Q

Chromatin condensation can vary along ?

A

The length of the chromosome

39
Q

Telomeres and centromeres are typically?

A

Heterochromatic. These regions are also gene poor

40
Q

The gene-rich regions of the chromosomes are typically?

A

Euchromatic. Regional modifications to produce blocks of different degrees of extension or condensation

41
Q

Each core histone has a ?

A

‘tail’ that extends out of the nucleosome core

42
Q

These tails can be modified by ?

A

Methylation and acetylation to influence chromatin structure and thus gene expression

43
Q

DNA + histones =

A

Chromatin

Cell Biology (16 decks)

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