In this post, we are reading about the work of Nucleus Diagram and Function which you read in biology, but we are providing you notes made in a simple and easy way so that you can clear this topic in a short time and clear it, you have been provided all the information related to this topic below.
Nucleus Diagram and Function
– The nucleus was discovered by ‘Robert Brown’ in the cells of the roots of the orchid plant.
– Normally each cell has 1 nucleus which is almost spherical.
– Bone marrow in plant and animal cells and multinucleated in straight muscles.
– The four major structures in the nucleus are-
(i) Nuclear Membrane/Kargo-Theca
(ii) Nucleoplasm
(iii) Chromatin
(iv) Nucleolus
(i) Nuclear Membrane – fat+protein
– A double membrane is found around the nucleus. (in eukaryotic cells)
– Absent in prokaryotic cells.
– Small pores are found in this membrane, through which materials are transported between the nucleus and the cytoplasm.
(ii) Nucleoplasm
– The thick, jelly-like, semi-solid substance in the nucleus is called the nucleoplasm.
– Apart from chromatin, nucleus, various enzymes are found in it which are related to protein-synthesis and other metabolic activities.
(iii) Chromatin
– These were made up of DNA and proteins and ‘Fleming’ told about them for the first time.
– When the cell divides, the process of condensation takes place in these chromatin fibers and they appear in the form of chromosomes.
Nucleolus
– Discovered by – Fontana
– Discription – Wagner
– Named by – Baumann
– Membrane-Less Structure
– It is attached to chromatin fibers.
– It is related to protein synthesis and RNA formation.
Functions of the Nucleus
– It controls other cell organelles and the whole cell.
– Activities like protein-synthesis, cell division are under its control.
– Genetic information is also present in the nucleus.
Notes :
– Double Membranous Structures – Mitochondria, Plastids, Nucleus
– Membraneless Structures – Centrosome, Ribosomes, Nucleolus
– Structures with single membrane :- Golgibody, E.R., Lysosomes, Microbodies
Chromosomes
– The human body is made up of cells and each cell has a nucleus in its center.
– Chromosomes are present in the nucleus on which genes are present.
– It is through genes that various traits such as eye color, blood group and sex are determined in the organisms.
– There are 23 pairs of chromosomes found in any human cell, of which one pair is sex chromosomes. Those are called ‘X’ and ‘Y’ chromosomes. These chromosomes play an important role in sex determination.
– A pair of ‘XX’ chromosomes are found in females as sex chromosomes while one ‘X’ and one ‘Y’ chromosome are found in males.
– Chromosomes discovered by Hoffminster in Tradescancia plant.
– Strassberger did the detailed study of chromosomes.
– Chromosome name – ‘Valdair’ gave it.
– The chromosomal theory of inheritance was given by Walter Sutton and Theodore Boveri.
– Chromosomes are visible only at the time of cell division.
– In the nucleus of eukaryotic cells, eight molecules of histone proteins combine to form the histone octave to which DNA is attached.
[DNA+Histone octave à Nucleosome]
– These nucleosomes are arranged on chromatin threads, when these threads are condensed during cell division, they appear as chromosomes.
– Outer transparent covering of chromosome – pellicle
– Condensed gelatinous material in a chromosome – matrix
– Acetocarmine is used for staining chromosomes.
Note –
– Large sized chromosomes are found in insects, which are called ‘giant chromosomes’.
– E.g. Lampbrush chromosome (reported by Ruckert), polytene chromosome (described by Balbiani)
– On the basis of presence of centromere, chromosomes are of four types-
(i) Centromere exactly in the middle – ‘V’ shape (metacentric)
(ii) Centromere slightly away from center – ‘L’ shape (sub-metacentric)
(iii) Centromere exactly on edge – ‘J’ shape (acrocentric)
(iv) Centromere at the end of the same arm – ‘i’ shape (telocentric)
Nucleic Acid
– Two types of nucleic acids are found in organisms (animals and plants) –
(i) DNA
(ii) RNA
(i) DNA (Deoxyribonucleic Acid)–
– In 1869, Friedrich Mischer first observed DNA in pus cells and named it as nuclein.
– The term DNA was given by Jacaris.
– DNA is mainly found in the nucleus of the cell but its own DNA is also found in mitochondria and plastids.
– The main DNA present in the nucleus is double helix, spiral, but in addition to this main DNA in prokaryotes cell, a circular DNA is also found, which is called ‘plasmid’.
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