1 Structure De La Chromatine

Question 1

What are chromosomes composed of?

Answer 1

Chromosomes are composed of chromatin, a complex of DNA and proteins.

Question 2

What types of proteins are found in chromatin?

Answer 2

There are two types of proteins: histones and non-histone proteins.

Question 3

What are histones?

Answer 3

Histones are small proteins that carry positive charges and are rich in basic amino acids.

Question 4

What is the structure of a nucleosome?

Answer 4

A nucleosome consists of DNA wrapped around a core of 8 histones (2 H2A, 2 H2B, 2 H3, and 2 H4).

Question 5

What is the diameter of a nucleosome?

Answer 5

The diameter of a nucleosome is 10 nm.

Question 6

What role does histone H1 play in nucleosomes?

Answer 6

Histone H1 binds to the internucleosomal DNA near the nucleosome.

Question 7

How do histones interact with DNA?

Answer 7

Histones are electrostatically attracted to negatively charged DNA at the phosphate groups, promoting a compact structure.

Question 8

What maintains the association of DNA with histones?

Answer 8

The association is maintained throughout the cell cycle but is constantly modified by remodeling complexes.

Question 9

What is the function of ATP-dependent remodeling complexes?

Answer 9

These complexes can move or modify nucleosomes to transiently increase DNA accessibility.

Question 10

What is the diameter of 30 nm chromatin fibers?

Answer 10

The diameter is 30 nm.

Question 11

How are 30 nm chromatin fibers formed?

Answer 11

They are formed by the winding of a chain of nucleosomes.

Question 12

What is required for the formation of 30 nm chromatin fibers?

Answer 12

The intervention of histones H1 and the tails of central histones is required.

Question 13

What form does most chromatin take during interphase?

Answer 13

Most chromatin is in the form of fibers.

Question 14

What is the diameter of loop domains formed by 30 nm fibers?

Answer 14

The diameter of loop domains is 300 nm.

Question 15

How do 30 nm fibers relate to loop domains?

Answer 15

The 30 nm fibers form loop domains attached to the protein scaffold of the chromosome in metaphase or to the matrix and nuclear lamina in interphase.

Question 16

What happens to chromatin during metaphase?

Answer 16

The chromatin folds to reach a maximum level of compaction.

Question 17

What is required for the final compaction of metaphase chromosomes?

Answer 17

Large multiprotein complexes called condensins are required.

Question 18

What are condensins composed of?

Answer 18

Condensins are formed of dimeric proteins known as SMC.

Question 19

What do condensins do?

Answer 19

They bind to DNA and hydrolyze ATP.

Question 20

What is the process of nucleosome sliding?

Answer 20

Nucleosome sliding is catalyzed by ATP, allowing changes in chromatin structure.

Question 21

What are chromosomes métaphasiques mitotiques?

Answer 21

They are in a state of maximum condensation of chromatin.

Question 22

What is the structure of chromosomes métaphasiques mitotiques?

Answer 22

They are formed of two sister chromatids.

Question 23

What does each chromatid contain?

Answer 23

Each chromatid contains a molecule of DNA.

Question 24

Why are sister chromatids genetically identical?

Answer 24

They are genetically identical because they originate from the replication of the same DNA molecule.

Question 25

How are the two chromatids connected?

Answer 25

The two chromatids are connected by their centromere.

Question 26

What is the centromere?

Answer 26

It is a heavily condensed region that takes the form of a constriction.

Question 27

What do telomeres correspond to?

Answer 27

Telomeres correspond to the ends of the chromosomes.

Question 28

What do centromeric and telomeric regions contain?

Answer 28

They contain repeated non-coding DNA sequences.

Question 29

What is euchromatin?

Answer 29

Euchromatin allows gene expression as it is accessible to enzymes and is dispersed in the nucleoplasm.

Question 30

How is euchromatin structured?

Answer 30

Euchromatin is formed of 30nm fibers organized into loops of 50 to 200 kb anchored to the nuclear lamina and nuclear matrix.

Question 31

What happens to euchromatin during gene expression?

Answer 31

The loop of euchromatin decondenses to allow easy access to DNA for gene expression.

Question 32

What is heterochromatin?

Answer 32

Heterochromatin is the most compact state of chromatin, containing DNA that is not expressed due to compacted 30nm fibers.

Question 33

Where is heterochromatin located?

Answer 33

Heterochromatin is located at the periphery of the nucleus and is also dispersed in the nucleoplasm.

Question 34

What is the replication timing of heterochromatin?

Answer 34

Heterochromatin replicates later (at the end of S phase) compared to euchromatin.

Question 35

What are the two types of heterochromatin?

Answer 35

The two types are facultative heterochromatin and constitutive heterochromatin.

Question 36

What characterizes facultative heterochromatin?

Answer 36

Facultative heterochromatin can be converted to euchromatin and its state depends on cell type and developmental stage.

Question 37

What modifications affect facultative heterochromatin?

Answer 37

Facultative heterochromatin is influenced by histone acetylation and methylation of CpG islands (epigenetic modifications).

Question 38

What characterizes constitutive heterochromatin?

Answer 38

Constitutive heterochromatin is absent of coding DNA, is common to all cells, and has a high degree of cytosine methylation.