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Nucleus and Chromatin

About Cell Biology (Fifth Edition Nucleus and Chromatin) edited by Ding Mingxiao, including nuclear structure and function, chromatin, chromosomes, etc.

Edited at 2023-11-18 16:35:50

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Nucleus and Chromatin

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Outline

Nucleus and Chromatin

Nucleus structure and function

Definition and function of the nucleus: the storage place for genetic material in eukaryotic cells and the regulatory center of genetics and metabolism

nuclear envelope

outermost layer of cell nucleus

nuclear pore complex

A complex structure embedded in the fusion of the inner and outer nuclear membranes into nuclear pores

Structural components

nucleocytoplasmic ring

cytoplasmic loop

spoke

central hitch

Function (dual function bidirectionality)

passive diffusion

active transport

Transport of nucleophilic proteins across the nuclear pore complex

combine

transfer

Dual function: mediates the nuclear transport of proteins and the nuclear export of RNA and RNPs

double nuclear membrane

outer nuclear membrane

There are often ribosome particles attached to the surface, often continuous with the rough endoplasmic reticulum.

inner nuclear membrane

The surface is smooth, no ribosome particles are attached, and the inner surface is in close contact with the nuclear lamina

perinuclear space

nuclear lamina

The inner side of the inner nuclear membrane is a fibrous network structure assembled from V-shaped intermediate filament proteins. It is connected to the nuclear matrix inside the nucleus and to the intermediate filaments outside the nucleus.

composition

3 lamin proteins (mainly found in mammals): laminA, laminB, and lamin C

Function

① Structural support function: supports the inner side of the cell nucleus: ②Regulate gene expression: silent genes are more likely to be distributed near the nuclear lamina: ③Regulate DNA repair: laminA lamin is an essential substance for repairing double-stranded DNA breaks.

Nucleolus and nuclear body

The nucleolus is the most prominent spherical body structure in interphase

structure

Fiber center FC, contains rDNA, RNA polymerase 1 and transcription factors

The dense fiber component DFC contains RNA as its transcription site

Granule component GC: main structure of nucleolus, ribosomal subunit unit assembly, maturation, composition site

nucleolar skeleton

nucleolar chromatin

Function

①Synthesis and processing of rRNA; ②Assembly and maturation of ribosomes; ③Export and degradation of mRNA

nuclear body

Nuclear body: subnuclear domain other than chromatin and nucleolus, including Cajal bodies, GEMS, and interchromatin granules

nuclear matrix

Chromatin

The nucleus of interphase cells consists of DNA, Histones, non-histones, and A linear complex structure composed of a small amount of RNA, It is the form in which genetic material exists in interphase cells.

chromatin DNA

Genome size comparison

Genomic DNA type

protein coding sequence Tandem repeats encoding rRNA, tRNA, snRNA, and histones DNA containing repetitive sequences unclassified spacer DNA

Three configurations of DNA secondary structure

Type A

Type B (right-handed double helix)

Z type

chromatin proteins

Histones

Classification (according to function)

nucleosomal histones

H2A

H2B

H1 histone (larger molecule)

non-histone proteins

nucleosome

The basic unit of chromatin assembly

structure

(1) Each nucleosome unit includes about 200 bp of DNA supercoil, a histone octamer and a molecule of histone H1. (2) Histone octamers constitute the disc-shaped core particle of the nucleosome (3) The 146 bp DNA molecule is supercoiled and coiled around the histone octamer to form 1.75 turns. Histone H1 binds an additional 20 bp of DNA outside the core particle, Locks the entry and exit ends of nucleosome DNA and stabilizes nucleosomes. (4) Two adjacent nucleosomes are connected by linker DNA. The typical length is 60bp, and the value varies from 0 to 80bp in different species. Chromosome, electron microscopy, about 5.0kb. (5) The interaction between histones and DNA is mainly structural and basically does not depend on the specific sequence of nucleotides. DNA that does not bind to histones under normal circumstances (such as phage DNA or synthetic Polymeric DNA of histones), when incubated with histones isolated and purified from plants and animals, are just long enough to assemble into nucleosomal units in vitro. (6) The positioning of nucleosomes along DNA is affected by different factors.

Chromatin assembly

Preliminary process of assembly

Assembled into a solenoid with a diameter of 3 0nm

Multilevel spiral model

DNA→nucleosome-solenoid-supersolenoid→chromatids

Chromatin type

Euchromatin and heterochromatin

Active chromatin and inactive chromatin

Active chromatin: Transcriptionally active Histone acetylation is high Histone H1 rarely associates with active chromatin Methylation of the 4th lysine at the N-terminus of H3: 9th and 14th lysine acetylation: phosphorylation of the 10th serine Sensitive to DNase1

Inactive chromatin: Inactive H3 N-terminal lysine 9 is methylated instead of acetylated

Chromatin replication and expression

Chromatin replication and repair

Chromatin activation and deactivation

activation

DNA structure and phase changes of nucleosomes

Histone modifications

Acetylation of lysine residues in core histones

Histone H1 phosphorylation

Different histone modifications

The influence of HMG protein

HMG protein binds to the DNA double helix, selecting pyrimidine-rich nucleotide originals with a 40-fold advantage, which is related to DNA bending and the formation of higher-order structures of DNA-protein complexes.

inactivate

Inactivation of the X chromosome

positional mottling effect

Gene expression has position effects. Some active genes will be inactivated when transferred near chromatin regions.

Chromatin and gene expression regulation

Chromatin-templated transcription

nucleosome plow

Transcription factor-mediated regulation of gene expression

DNA binding domain

activation domain

repressing transcription factors

DNA methylation-mediated regulation of gene expression

inhibit transcription

Interfere with recognition of DNA binding sites by transcription factors

The DNA sequence recognized by the transcriptional activator is transcribed into a binding site for the inhibitory factor.

Genomic imprinting

Three-dimensional dynamic distribution of chromatin and cell ID

chromosome

form and structure

Centromere and kinetochore

central domain

Kinetochore domains along the outer surface of mitochores

Inner plate (associated with centromere central domain)

middle gap

Outer panel

Fiber crown (covers the 4th zone of the outer panel)

paired domain

Secondary constriction scar

The main component is the nucleolar tissue area

nucleolar organizing zone

Follow the body

telomeres

functional elements of chromosomes

at least one origin of DNA replication

a centromere

Chromosomes must have telomeres at both ends

Chromosome banding pattern

Band pattern and karyotype discovery experiments

special chromosomes

Polytene chromosomes: Diptera chironomid larvae salivary gland cells

Lamp brush chromosomes: shark oocytes, amphibian oocytes