Cell Structure and Functions class 11 Notes Biology

                         

cell structure and Function

Living:-

Both living and non-living things are composed of molecules made from chemical elements such as Carbon, Hydrogen, Oxygen, and Nitrogen. The organization of these molecules into cells is one feature that distinguishes living things from all other matters.Cell Structure And Function/Cell Biology decide the organism living or not

Discovery:-

(1)The cell was discovered by Robert Hooke (1665).

(2) Cell Theory, First Proposed by 1839,shiellden and Schwann but Modified Form of Cell Theory is given by Rudolf Virchow.

(3) The Discovery of Nucleus is given by Robert Brown.

(4) The structure of cell Membrane is given by Singer and Nicolson.

 

    Nucleus Structure

           

                                                    

Nucleus:- 

The nucleus is a specialized double the membrane-bound protoplasmic body which contains all the genetic information for controlling cellular metabolism and transmission to the posterity.

Nucleus is the largest cell organelle. Though first observed by Leeuwenhoek in red blood cor­puscles of fish, the nucleus was first studied in orchid root cells by Robert Brown in 1831.

Mainly cells are Uninucleated so they possess One nucleus in each cell

The protistan Paramecium caudatum has two nuclei (binucleate), and the protistan Opalina contains many nuclei.

Multinucleate animal or protistan cells are called syncytial cells.

Position of Nucleus:-

In plant cell the Nucleus is Present in the periphery due to the presence of large central vacuole present. It is suspended in central vacuole by cytoplasmic strands in Spirogyra.

Shape of cell:- 

Note : The shape of the cell is elliptical,round-shaped and spiral-shaped and large and small shaped.

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Biochemical Nature of Nucleus:-

DNA- 9-12%. RNA- 5%. Lipids- 3%. Basic Proteins- 15%. Acid proteins, neutral proteins, and enzymes- 65%. Traces of minerals like Calcium, Mag­nesium, Potassium and Sodium Phosphorus is a constituent of DNA, RNA, and acid pro­teins.

The membrane of the Nucleus:-

Note : Nucleus has differentiated into five parts -Nucleoplasm, Nuclear Envelope, Matrix and chromatin.

(a) Nuclear Envelope:-Which is called Karyotheca -

(1) Exokaryotheca (2) Endokaryotheca

The Endokaryotheca is smooth and Without any rough Ribosomes.

It is made up of two lipoproteins and tri- laminar membranes, each of which is 60-90A thick. The inner membrane is smooth.

About 10% of the membrane is covered by pores for transfer of cytoplasmic material to the Nucleus.

Nucleoplasm (Nuclear Sap, Karyolymph, Strasburger, 1882):- 

It is a transparent, semifluid, and colloidal substance that fills the nucleus. It contains nucleosides and a number of enzymes (e.g. DNA polymerase, RNA polymerase, nucleoside phosphorylase) which are required for the synthesis and functioning of DNA, RNA, nucleoproteins.

Nuclear Matrix:- 

It is a network of fine fibrils of acid proteins that function as a scaffold for chromatin. On the periphery, below the nuclear envelope, nuclear matrix forms a dense fibrous layer called nuclear lamina.

Nuclear matrix and nuclear lamina form:-

(i)Attachment sites to telomeric parts,

(ii) Mechanical strength of the nuclear envelope.

 Nucleolus (plural-nucleoli):- 

It was first discovered by Fontana in 1781, described by Wagner in 1840 and provided with its present name by Bowman in 1840. The nucleolus is a naked, round or slightly irregular structure which is attached to the chromatin at a specific region called the nucleolar organizer region (NOR).

Chromatin:- 

Nucleus contains hereditary material called chromatin. Chromatin is a DNA- protein complex. It is made of a number of fine fibers that condense to form chromosomes. The number of chromosomes is fixed for a species. They bear genes.

The shape of Chromosomes:-

Every chromosome essentially has a primary constriction of the centromere on the sides of which disc-shaped structures called kinetochores are present. Based on the position of the centromere, the chromosomes can be classified into four types. The metacentric chromosome has a middle centromere forming two equal arms of the chromosome. The sub-metacentric chromosome has centromere nearer to one end of the chromosome resulting in one shorter arm and one long arm. In the case of an acrocentric chromosome the centromere is situated close to its end forming one extremely short and one very long arm, whereas the telocentric chromosome has a terminal centromere.

Cell Structure And Function/Cell Biology