CELLSSTRUCTURE & FUNCTION

TOPICS Discovery of CELL The Cell Principal structures of an animal cell Number of cell Types of cell Shape & Size of cell Parts of cell and their function Cell Membrane Cell wall Cytoplasm Nucleus Nuclear membrane Chromosomes Dividing Chromosomes Gene

Discovery of CELL

Robert Hooke

Born : July 18, 1635

Died : March 3, 1703

In 1665 he observed Slices of cork Under a simple magnifing device.

Cork is a part of the bark of the bark of a tree. He took thin slice of cork and observed a under a microscope. He noticed partitioned boxes or compartments in the cork slice. These box appeared like a honey comb. Hooke coined the term ‘cell’ for each box. What hooke observed as boxes or cell in

the cork were actually dead cells.

THE CELL

In biology, the basic unit of which all living things are composed; the smallest structural unit of living matter that is able to function independently.

A single cell can be a complete organism in itself, as in bacteria and protozoans. Groups of specialized cells are organized into tissues and organs in multicellular organisms such as higher plants and animals. There are two distinct types of cells: prokaryotic cells and eukaryotic cells. Though the structures of prokaryotic and eukaryotic cells differ (see prokaryote, eukaryote), their molecular compositions and activities are very similar. The chief molecules in cells are nucleic acids, proteins, and polysaccharides. A cell is bounded by a membrane that enables it to exchange certain materials with its surroundings. In plant cells, a rigid cell wall encloses this membrane.

Principal structures of an animal cellCytoplasm surrounds the cell's specialized structures, or organelles. Ribosomes, the sites of protein synthesis, are found free in the cytoplasm or attached to the endoplasmic reticulum, through which materials are transported throughout the cell. Energy needed by the cell is released by the mitochondria. The Golgi complex, stacks of flattened sacs, processes and packages materials to be released from the cell in secretory vesicles. Digestive enzymes are contained in lysosomes. Paroxysms contain enzymes that detoxify dangerous substances. The centrosome contains the centrioles, which play a role in cell division. The microvilli are fingerlike extensions found on certain cells. Cilia, hairlike structures that extend from the surface of many cells, can create movement of surrounding fluid. The nuclear envelope, a double membrane surrounding the nucleus, contains pores that control the movement of substances into and out of the nucleoplasm. Chromatin, a combination of DNA and proteins that coil into chromosomes, makes up much of the nucleoplasm. The dense nucleolus is the site of ribosome production.

Number of cellHUMAN BODY OR ANIMAL BODY HAS BILLIONS AND TRILLIONS OF CELLS WHICH VARY IN SHAPES AND SIZES. DIFFERENT GROUP OF CELLS PERFORM A VARIETY OF FUNCTION.

TYPES OF CELL IN ORGANISMA :

I. ORGANISMS MADE OF MORE THAN ONE CELL ARE CALLED MULTICELLULAR (MULTI : MANY; CELLULAR : CELL).

EX : PARAMECIUM

II. ORGANISMS MADE OF MORE THAN ONE CELL ARE CALLED UNICELLULAR (UNI : SINGLE OR ONE; CELLULAR : CELL).

EX : AMOEBA

Types of cell in organisma :

UNICELLULAR MULTICELLULAR

Shape & Size of cell

Shape of cell :

I. The cell have no definite shape

For ex: Amoeba has no definite Shape, unlike other organisms. It keep change its shape.

Size of cell :

I. The size of cell in living organisms may be as small as a millionth of metre or may be as large as a few centimeters.

II. The smmallest cell is 0.1 to0.5 micrmetre in bacteria. The Largest Cell Measuring 170mm to 130mm is the egg of ostrich.

III. The size of the cells has no relation with the size of the body of the animal or plant.

IV. The size of cell is related to function.

Parts of Cell & their Function

cell

CytoplasmCell

membrane

Cell wall

Nucleus

Nuclear membrane

CELL MEMBRENE

The basic components of a cell are

Cell membrane, Cytoplasm and Nucleus. The cytoplasm and nucleus are enclosed within the cell membrane, also called Plasma membrene.

In biology, the thin layer that forms the outer boundary of a living cell or of an internal cell compartment.

The outer boundary is the plasma membrane, and the compartments enclosed by internal membranes are called organelles. Biological membranes have a dual function: separation of vital but incompatible metabolic processes conducted in the organelles; and passage of nutrients, wastes, and metabolic products between organelles and between the cell and the outside environment. Membranes consist largely of a double layer of lipids in which are embedded large proteins, many of which transport ions and water-soluble molecules

CELL WALLCell Membrane (Plasma membrane)

Covred by another thick cobering called the cell wall. Cell wall gives shape to the cell.

Function:

This additional layer surrounding the cell membrane is required by plant for protection. Plant cell need protection against variations in temperature, high wind speed atmosphere moisture etc. they are exposed to these variaions because they cannot move.

CYTOPLASMIt is the jelly-like substance present between the cell membrane and the nucleus

Portion of a eukaryotic cell outside the nucleus.

The cytoplasm contains all the organelles . The organelles include the mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes. The cytoplasm also contains the cytoskeleton and the cytosol (the fluid mass that surrounds the various organelles).

 

NUCLEUSIt is an important component of the living cell. It is the generally spherical and located in the centre of the cell. It can be stained and seen easily with the help of a microscope. Nucleus is separated from the cytoplasm by a membrane called the nuclear membrene.

FUNCTION :

Its role in inheritance, acts as control centre of the activities of the cell. The entire content of a living cell is known as protoplasm.

NUCLEAR MEMBRANESpecialized structure occurring in most cells (except bacteria) and separated from the rest of the cell by the nuclear membrane.

This membrane seems to be continuous with the cell's endoplasmic reticulum and has pores that permits the passage of large molecules. The nucleus controls and regulates the cell's activities (e.g., growth and metabolism) and carries the genes. Nucleoli are small bodies often seen within the nucleus that play an important part in the synthesis of RNA and protein. A cell normally contains only one nucleus.

PROKARYOTIC

I. Any cellular organism that lacks a distinct nucleus.

II. Organisms classified in the domains Bacteria (including blue-green algae, or cyan bacteria) and Achaea are prokaryotes; all other organisms are eukaryotes and are placed in the domain Eukaryote. Prokaryotic cells lack a nuclear membrane and most of the components of eukaryotic cells. The cytoplasm includes ribosome's that carry out protein synthesis and a double-stranded DNA chromosome, usually circular. Many prokaryotes also contain additional circular DNA molecules called plasmids. The flagella are distinct from those of eukaryotes in design and movement.

EUKARYOTIC

I. Any organism composed of one or more cells, each of which contains a clearly defined nucleus enclosed by a membrane, along with organelles (small, self-contained, cellular parts that perform specific functions).

II. The organelles include mitochondria, chloroplasts, a Golgi apparatus, an endoplasmic reticulum, and lissome. All organisms except bacteria and archaea are eukaryotes; bacteria and archaea are prokaryotes.

CHROMOSOMES

The Nucleus contain thread-like structures called Chromosomes.

The structure and location of chromosomes differentiate prokaryotic cells from eukaryotic cells (see prokaryote, eukaryote). Every species has a characteristic number of chromosomes; humans have 23 pairs (22 pairs of autosomal, or nonsex, chromosomes and one pair of sex chromosomes). Human chromosomes consist primarily of DNA. During cell division (see meiosis, mitosis), chromosomes are distributed evenly among daughter cells. In sexually reproducing organisms, the number of chromosomes in somatic (nonsex) cells is diploid, while gametes or sex cells (egg and sperm) produced by meiosis are haploid (see ploidy). Fertilization restores the diploid set of chromosomes in the zygote.

DIVIDING CHROMOSOME

During the first stages of cell division, the recognizable double-stranded chromosome is formed by two tightly coiled DNA strands (chromatids) joined at a point called the centromere. During the middle stage of cell division, the centromere duplicates, and the chromatid pair separates. Following cell division, the separated chromatids uncoil; the loosely coiled DNA, wrapped around its associated proteins (histones) to form beaded structures called nucleosomes, is termed chromatin.

GENE

Unit of heredity that occupies a fixed position on a chromosome.

Genes achieve their effects by directing protein synthesis. They are composed of DNA, except in some viruses that contain RNA instead. The sequence of nitrogenous bases along a strand of DNA determines the genetic code. When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene splits, and a complementary strand of RNA, called messenger RNA (mRNA), forms and then passes to ribosomes, where proteins are synthesized. A second type of RNA, transfer RNA (tRNA), matches up the mRNA with specific amino acids, which combine in series to form polypeptide chains, the building blocks of proteins. Experiments have shown that many of the genes within a cell are inactive much or even all of the time, but they can be switched on and off. Mutations occur when the number or order of bases in a gene is disrupted.

Thank you

Name : Mukul

Class : X ‘B’

K.V.S sec-14 Gurgaon

Second Shift