Nucleus and Chromosome Structures

• Nucleus and Chromosome structures

Nucleus

• The nucleus is a membrane-bound structure containing hereditary information and controls cell growth/reproduction.
• The nucleus is the most prominent organelle, surrounded by a nuclear envelope.

Nuclear Components

• Nucleolus
• Nuclear pore
• Nuclear envelope
• Nucleoplasm
• Chromatin

Nucleus Details

• The nucleus is the largest cellular organelle in animal cells
• The average nuclear diameter is 6 micrometers, occupying about 10% of the cell volume
• The viscous liquid within is called nucleoplasm, similar to cytosol.
• The nucleus appears as a dense, roughly spherical, or irregular organelle.
• The composition by dry weight: DNA 9%, RNA 1%, Histone Proteins 11%, Acidic Proteins 65%.
• The nuclear envelope consists of two nuclear membranes and an underlying nuclear lamina.
• The nucleus is surrounded by inner and outer nuclear membranes
• The outer nuclear membrane is continuous with the endoplasmic reticulum.
• Each nuclear membrane is a phospholipid bilayer permeable only to small molecules.
• Outer nuclear membranes join at nuclear pore complexes where molecules pass through.
• Underlying the inner nuclear membrane is the nuclear lamina, a fibrous network for structural support.
• Nuclear lamina consists of 60-80 kilodalton fibrous proteins called lamins.
• Nuclear lamina offer mechanical support and regulate cell events like DNA replication and cell division and participates in Chromatin organization.

Progeria

• Progeria was first described in 1886 by Jonathan Hutchinson and Hastings Gilford.
• The LMNA gene codes for lamin A.
• Progeria's cause is a point mutation in the LMNA gene, where cytosine is replaced with thymine.

Chromosome Position

• Chromosomes are located inside the nucleus.
• Chromosomes consist of coiled DNA molecules.

Chromosome History

• Chromosomes are rod-shaped, dark-stained bodies seen during metaphase of mitosis.
• Strausberger discovered chromosomes in 1875.
• The term chromosome was coined by Waldeyer in 1888.
• Term initiated as (Chroma= Colour and Soma = body)

Eukaryotic Chromosome Features

• Chromosomes are best visible during metaphase.
• Chromosomes bear genes in a linear fashion.
• The shape, size, and number of chromosomes vary in different species.
• Chromosomes can self-duplicate and mutate.
• Chromosomes are composed of DNA, RNA, and protein.

Chromosome Size

• Chromosome size is measured at mitotic metaphase in length and diameter.
• Plants usually have longer chromosomes than animals.
• Plant chromosomes are 0.8-7μm in length, while animal chromosomes are 0.5-4μm in length.
• Chromosome size varies from species to species.

Chromosome Diagram

• Chromatid
• Centromere
• Short arm
• Long arm

Ribosome Hub

• Nucleolus, made of proteins and RNA, is responsible for ribosome synthesis.