Study of Cell
Cell: Cell
is the basic structural and functional unit of life.
-
The word cell was first coined by British
scientist Robert Hook in the year 1665.
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The smallest cell is Mycoplasma gallisepticum.
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The longest cell in Neuron.
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The biggest cell is egg of Ostrich.
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Schilden and Schwan established cell theory in
the year 1838-39
Mian features of the cell theory
1.
All organism are composed of cell.
2.
Body of every organism is made of cell.
3.
Each cell arises form pre-existing cell.
4.
Every organism starts its life form single cell.
Cell is of two kinds
1. Prokaryotic cell: these are primitive
cell having three basic structure of typical cell but lack nuclear membrane,
Nuclear material is present in a region of cytoplasm called nucleoid. Other
membrane bound organelles are absent such as mitochondria, ribosome, golgi
bodies etc. Ex virus, bacteria and cyanobacteria are Prokaryotes.
2. Eukaryotic cell: these are complete
cell which contain membrane bound organelles and nucleus. Unicellular and
multicellular plant and animal have Eurkaryotic cell.
Difference
between Prokaryotes and Eukaryotes
Prokaryotes
|
Eukaryotes
|
|
1
|
Size of cell is generally small
|
Size of cell is generally large
|
2
|
Nuclear absent
|
Nucleus present
|
3
|
It contain single chromosome which is
circular in shape
|
It contains more than one chromosome
|
4
|
Membrane bound cell organelles are
absent
|
Cell organelles present
|
5
|
Cell division takes place by fission
or budding
|
Cell division takes place by mitosis
and meiosis.
|
Structure of
typical cell
1.
Cell wall: In plant cell there is a rigid cell
wall which is nonliving and freely permeable. It is made up f cellulose and
chitin. It provides shape and rigidity to the cell.
2.
Cell membrane: It is also known as plasma
membrane which form the outer covering of animal cell. In plant cell it is
found within cell wall. It is thin, elastic, living, double layer, and
permeable membrane. It is made up of phospholipid molecules. It regulates movement of molecules inside
and outside of the cell.
3.
Protoplasm: the whole fluid present inside
plasma-membrane is protoplasm. The name protoplasm is given by Purkenje in
1839. Protoplasm is made up of various chemical substance like water, ions, salt
and organic molecule. It is the living part of cell. Protoplasm is divided into
two parts.
Cytoplasm : The fluid found outside the
nuclear membrane.
Nucleoplasm: The fluid found inside the
nuclear membrane.
4.
Mitochondria: Discovered by Altman in the year
1886. These are cylindrical, rod shaped or spherical structure found in cytoplasm.
It is surrounded by double layered membrane. Inner membrane has many fold
called cristae. The fluid present inside mitochondria is called Matrix, which
contained many enzyme and co-enzyme.
Function: Mitochondria is the respiratory
site of cellular respiration. Mitochondria synthesize energy rich compound ATP.
It is also known as Power House of the cell
5.
Golgi Bodies: Discovered by scientist Camilo Golgi.
Golgi bodies are made up of group if tubes, vesicles and vacuoles. In plant it
is more in number and here it is known as dictyosomes.
Function: It work as storage, processing
and packaging of material. It also involved in the synthesis of cell wall,
plasma membrane and lysosomes.
6.
Endoplasmic reticulum: Membranous network of
tubules like structure found in cytoplasm is called endoplasmic reticulum. It
is attached with the nucleus on one side and on other side it is joined with
plasma membrance.
Funtion: Endoplasmic reticulum helps in the
distribution of material. It forms supporting framework of cell.
7.
Ribosome: Discovered by Palade. Small granules
like structure found attached to the endoplasmic reticulum or in Free State. It
is made up of ribonucleic acid.(RNA)
Function : Take part in protein synthesis.
8.
Lysosome: Discovered by De Duve. These are sac
like structure bounded by single membrane and contain hydrolytic enzyme.
Function: It helps in intracellular digestion. The enzyme found
in lysosome may digest the entire cell .So it is also known as suicidal bag.
9.
Centrosome: Discovered by Boveri. It is only
found in animal cell taking part in cell division. It is not bounded by
membrane consist of two centriole.
Function: Help in the formation of
spindle fibre during cell division.
10.
Plastid: Only found in plant cell. It is of
three types: a) Chloroplast b) Chromoplast c) Leucoplast.
a) Chloroplasts: There are green pigment
found in green plant involve in photosynthesis. So, it is known as Kitchen of
the cell. Chloroplast is bounded by two unit membrane having grana and stroma.
Grana are membrane bounded sac like structure found in stacks containing
chlorophyll molecule. Stroma is the matrix present inside the chloroplast which
contain photosynthetic enzymes and starch grain. Granum is the site of light
reaction during photosynthesis while stroma is the site of dark reaction.
Function: Chloroplast provides green colour
to plant & take part in photosynthesis.
a) Chromoplast provides various colours to
the plant.
b) Leucoplast is colourless. It stores the
food in the form of starch, fat & protein.
1.
Vacoule :
These are fluid filled single membrane bounded, dead organelles of cell. In
plant cell it is larger in size but in
animal it is smaller in size.
2.
Nucleus :
the nucleus is a spherical, centrally located is a major structure found in
the cell. In plant cell it is shifted towards periphery. It is bounded by
double layered by nuclear membrance having pore. Within nucleoplasm nucleous
and chromatin material is present. Nucleolus is rich in protein and RNA.
Chromatin material is thin thread like structure forming network . This is made
up of genetic substance DNA and histone protein. During cell divion chromatin
breaks into pieces and forms chromosome.
Function :
It controls all the activity of cell. So it is also known as control
room of cell. Chromatin transmits hereditary characters from patents to their
off spring.
Difference
between plant and animal cells
Sr
|
Plant Cell
|
Animal cell
|
1
|
Plant cell are larger in size
|
Animal cells are generally smaller in
size
|
2
|
Cell wall present, made up cellulose
and chitin.
|
Cell wall absent
|
3
|
Plastid present
|
Plastid absent
|
4
|
Centrosome absent
|
Centrosome present
|
5
|
Vacuoles are larger in size
|
Vacoules are smaller in size
|
Chromosome :
Chromosome
is thread like structure found in the nucleus. It becomes visible during cell
division. Each chromosome is made up of two chromatids joined together at a
point centromere. Bead like structure found on chromosome is called gene. Genes
are made up of DNA which is thecarrier of genetic information from generation
to generation. In some viruses RNA is the genetic material called rietrovirus.
In prokaryotes there is only one chromosome, like bacteria and viruses.
Eukaryotic cell possess many chromosome.
A particular kind of species have definite number of chromosome in their cell,
which are in pair known as diploid. The set of unpaired chromosome is called
haploid. Gametes have haploid set of chromosome.
Nucleic Acid: Nucleic and is complex organic compound found
in cell. It contains special genetic instruction in coded form. Nucleic acids
are of two kinds.
A. Deoxyribo nucleic Acid(DNA) : Frederic
Meischer was the first who isolated DNA form the nucleus fo pus cells. DNA is a
macromolecule in which large number of nucleotides are present , chemically a
nucleotids has three components. 1) Nitrogen base 2) Sugar 3) Phosphate group.
Nitrogen
base are to two type : Purines & Pyrimidines purines contain two nitrogen
base Adinine and guanine.
Watson
and Crick give the structural model of DNA
1.
DNA molecule is consists of two polynucleotide
strand, forming a double helix . Each strand has a backbone of sugar and
phosphate. Nitrogen base is attached to the sugar.
2.
Nitrogenous base of the two strands of a double
helix form a pair with the help of hydrogen bonds. Adenine pair with thymine
whereas guanine pairs with cytosine. Adenine and thymine are complementary to
each other and cytosine is complementary to guanine. Hydrogen bonding between
nitrogenous base holds the two strand together. Tis stricture can be compared
with the steps of spiral staircase.
Function 1. It contain genetic information
in coded form
3. DNA synthesise RNA
Note- DNA is mainly found in nucleus. In
small amount it is also found in mitochondria and chloroplast.
Gene: Gene is hereditary unit which is
made by a segment of DNA found on the chromosome.
A. Ribonucleic Acid(RNA): RNA is single
stranded nucleic acid made up of phosphate, ribose sugar and nitrogen base
uracil, adinine, guanine and cytosine. It is found in nucleus as well as
cytoplasm.
RNA is of three kind
1. Messenger RNA : it brings the massage
form DNA found in the nucleus to cytoplasm in the coeded form.
2. Ribosomal RNA: Present in ribosome
which is the site of protein synthesis.
3. Transfer RNA : it is the carrier of
animo acid and transfer it to the ricosome.
Function :
Synthesis of protein
Difference between RNA and DNA
|
Sr
|
DNA
|
RNA
|
|
1
|
Sugar is deoxyribose type
|
Sugar is ribose type
|
|
2
|
It contains the base adenine , thymine and cytosine and guanine.
|
It contains uracil in place of thymine.
|
|
3
|
It is double stranded structure.
|
It is single stranded structure
|
|
4
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It is mainly found in nucleus.
|
It is found in both nucleus and cytoplasm.
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