1 Structure De La Chromatine Flashcards
What are chromosomes composed of?
Chromosomes are composed of chromatin, a complex of DNA and proteins.
What types of proteins are found in chromatin?
There are two types of proteins: histones and non-histone proteins.
What are histones?
Histones are small proteins that carry positive charges and are rich in basic amino acids.
What is the structure of a nucleosome?
A nucleosome consists of DNA wrapped around a core of 8 histones (2 H2A, 2 H2B, 2 H3, and 2 H4).
What is the diameter of a nucleosome?
The diameter of a nucleosome is 10 nm.
What role does histone H1 play in nucleosomes?
Histone H1 binds to the internucleosomal DNA near the nucleosome.
How do histones interact with DNA?
Histones are electrostatically attracted to negatively charged DNA at the phosphate groups, promoting a compact structure.
What maintains the association of DNA with histones?
The association is maintained throughout the cell cycle but is constantly modified by remodeling complexes.
What is the function of ATP-dependent remodeling complexes?
These complexes can move or modify nucleosomes to transiently increase DNA accessibility.
What is the diameter of 30 nm chromatin fibers?
The diameter is 30 nm.
How are 30 nm chromatin fibers formed?
They are formed by the winding of a chain of nucleosomes.
What is required for the formation of 30 nm chromatin fibers?
The intervention of histones H1 and the tails of central histones is required.
What form does most chromatin take during interphase?
Most chromatin is in the form of fibers.
What is the diameter of loop domains formed by 30 nm fibers?
The diameter of loop domains is 300 nm.
How do 30 nm fibers relate to loop domains?
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.
What happens to chromatin during metaphase?
The chromatin folds to reach a maximum level of compaction.
What is required for the final compaction of metaphase chromosomes?
Large multiprotein complexes called condensins are required.
What are condensins composed of?
Condensins are formed of dimeric proteins known as SMC.
What do condensins do?
They bind to DNA and hydrolyze ATP.
What is the process of nucleosome sliding?
Nucleosome sliding is catalyzed by ATP, allowing changes in chromatin structure.
What are chromosomes métaphasiques mitotiques?
They are in a state of maximum condensation of chromatin.
What is the structure of chromosomes métaphasiques mitotiques?
They are formed of two sister chromatids.
What does each chromatid contain?
Each chromatid contains a molecule of DNA.
Why are sister chromatids genetically identical?
They are genetically identical because they originate from the replication of the same DNA molecule.
How are the two chromatids connected?
The two chromatids are connected by their centromere.
What is the centromere?
It is a heavily condensed region that takes the form of a constriction.
What do telomeres correspond to?
Telomeres correspond to the ends of the chromosomes.
What do centromeric and telomeric regions contain?
They contain repeated non-coding DNA sequences.
What is euchromatin?
Euchromatin allows gene expression as it is accessible to enzymes and is dispersed in the nucleoplasm.
How is euchromatin structured?
Euchromatin is formed of 30nm fibers organized into loops of 50 to 200 kb anchored to the nuclear lamina and nuclear matrix.
What happens to euchromatin during gene expression?
The loop of euchromatin decondenses to allow easy access to DNA for gene expression.
What is heterochromatin?
Heterochromatin is the most compact state of chromatin, containing DNA that is not expressed due to compacted 30nm fibers.
Where is heterochromatin located?
Heterochromatin is located at the periphery of the nucleus and is also dispersed in the nucleoplasm.
What is the replication timing of heterochromatin?
Heterochromatin replicates later (at the end of S phase) compared to euchromatin.
What are the two types of heterochromatin?
The two types are facultative heterochromatin and constitutive heterochromatin.
What characterizes facultative heterochromatin?
Facultative heterochromatin can be converted to euchromatin and its state depends on cell type and developmental stage.
What modifications affect facultative heterochromatin?
Facultative heterochromatin is influenced by histone acetylation and methylation of CpG islands (epigenetic modifications).
What characterizes constitutive heterochromatin?
Constitutive heterochromatin is absent of coding DNA, is common to all cells, and has a high degree of cytosine methylation.
