Chromosomes and Chromatin

Question 1

Prokaryotic chromosomes are ?

Answer 1

Circular and typically have one origin of replication

Question 2

The E. coli chromosome is about ?

Answer 2

4.6 million bases long and encodes 4300 different proteins

Question 3

Eukaryotes genomes are?

Answer 3

Larger and more complex

Question 4

Explain Eukaryotes further?

Answer 4

• 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

Question 5

Eukaryotic chromosomes are ?

Answer 5

Linear

Question 6

In eukaryotes, the genome is broken up into ?

Answer 6

Long, linear, double-stranded structures called chromosomes

Question 7

How many chromosomes does the human genome have ?

Answer 7

The human genome has 24 chromosomes

22 autosomes and 2 sex chromosomes

Question 8

Human cells are ?

Answer 8

Diploid (2n = 46)

Question 9

Even closely related species can have ?

Answer 9

Different numbers of chromosomes

Question 10

Chromosomes change during ?

Answer 10

The cell cycle

Question 11

In Interphase nuclei, the chromosomes are ?

Answer 11

Distributed throughout the nucleoplasm

Question 12

At mitosis the chromosomes?

Answer 12

Condense - individual chromosomes can be seen with the light microscope

Question 13

What are telomeres ?

Answer 13

Stabilise ends

Question 14

What is the function of the centromere ?

Answer 14

To segregate the sister chromosome

Question 15

What is the use of replication origins ?

Answer 15

To duplicate the DNA

Question 16

A chromosome consists of?

Answer 16

Two sister chromatids

Question 17

After replication there are?

Answer 17

Two identical sister chromatids

Question 18

Each chromatid contains ?

Answer 18

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

Question 19

Sisters are held together until ?

Answer 19

Chromosomes segregation during mitosis

Question 20

In some cells, chromosomes adopt the Rabl configuration with ?

Answer 20

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

Question 21

During Interphase, individual chromosomes occupy ?

Answer 21

Particular regions of the nucleus

Question 22

This arrangement minimises?

Answer 22

Tangles between the chromosomes and helps condensation and segregation during mitosis

Question 23

Chromosomal DNA is ?

Answer 23

Highly condensed

Question 24

DNA is compacted by association with proteins -

Answer 24

Chromatin

Question 25

Individual nucleosomes are arranged on ?

Answer 25

The DNA like beads on a string

Question 26

DNA isolated from an interphase nucleus appears as ?

Answer 26

A 30 nm thick fibre

Question 27

The nucleosome core particle consists of ?

Answer 27

147 base pairs of DNA wound around a protein core

Question 28

Explain Histones ?

Answer 28

The protein core is made of a small highly basic proteins

Question 29

The octomeric histone core contains ?

Answer 29

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

Question 30

DNA is wound around?

Answer 30

Histones

Question 31

An additional histone, Histone H1, arranges ?

Answer 31

Nucleosomes into the 30nm fibre

Question 32

During mitosis, this 30 nm fibre is further ?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

Euchromatin is ?

Answer 34

Transcriptionally active

Question 35

Heterochromatin is ?

Answer 35

Transcriptionally inactive

Question 36

Decondensed or open chromatin (= euchromatin) is associated ?

Answer 36

With transcriptionally active regions of the genome

Question 37

Closed Condensed chromatin (=heterochromatin) is associated ?

Answer 37

With transcriptionally repressed regions of the genome

Question 38

Chromatin condensation can vary along ?

Answer 38

The length of the chromosome

Question 39

Telomeres and centromeres are typically?

Answer 39

Heterochromatic. These regions are also gene poor

Question 40

The gene-rich regions of the chromosomes are typically?

Answer 40

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

Question 41

Each core histone has a ?

Answer 41

‘tail’ that extends out of the nucleosome core

Question 42

These tails can be modified by ?

Answer 42

Methylation and acetylation to influence chromatin structure and thus gene expression

Question 43

DNA + histones =

Answer 43

Chromatin