cells and its components

1. CELLS AND ITS
COMPONENTS
SWATILEKHA DAS
(RN, MSN)

2. • CELL STRUCTURE
• CELL MEMBRANE
• CYTOPLASM
• NUCLEUS

3. STRUCTURE OF A CELL
Cell forms the structural unit of all tissues and
organs of the body.
Different cells perform different functions. e.g.
nerve cell helps in conduction, cells of intestine
help in absorption and muscle cell helps in
contraction.

4. Human cell is eukaryotic. It consists of:
A. Cell Membrane
B. Cytoplasm
C. Nucleus

5. CELL WITH VARIOUS ORGANELLES

6. A. CELL MEMBRANE
The cytoplasm of a cell is bound on the outer aspect
by cell membrane which is also known as plasma
membrane or plasmalemma. It is 7.5 nm thick. It is
trilaminar structure consisting of phospholipid layer
sandwiched between outer and inner protein layer.
Function:
It maintains the shape of the cell.
Presents receptors on the surface of cell membrane,
which are specific for particular molecules that are
enzymes or hormones.
It helps in exocytosis and endocytosis.

7. FLUID MOSAIC MODEL(Proposed by SJ
Singer And GL Nicolson in 1972)
• According to this model, the cell membrane consists of a
phospholipid bilayer. It is made up of a polar head (hydrophilic)
and a non polar tail(hydrophobic).
• In aqueous solution phospholipids form a bilayer with the
heads directed outwards and the tails directed inwards.
• Presence of unsaturated fatty acids increases the fluidity and
the flexibility of cell membrane. Almost half of the total mass of
the cell membrane is formed of protein molecules. Some
protein molecules are present within the cell membrane and
are known as intrinsic proteins. The proteins which are held at
the outer aspect of cell membrane are known as extrinsic
proteins. Some proteins occupying the entire thickness of the
cell membrane are known as transmembrane proteins.

8. FLUID MOSAIC MODEL

9. B. CYTOPLASM
• It is an aqueous substance in which cytoskeleton
is dispersed while organelles and inclusion bodies
are suspended.
• Membrane bound bodies in the cytoplasm are
known as cell organelles.
• The organelles found in a cell are endoplasmic
reticulum, golgi apparatus, peroxisome,
mitochondria, ribosome, centrosome and
lysosome.

10. 1. ENDOPLASMIC RETICULUM
Endoplasmic reticulum is a double membrane
bound interconnected network of tubules, vesicles
or flattened sacs.
a. Rough endoplasmic reticulum(rER)- is involved in
synthesis of proteins.
b. Smooth endoplasmic reticulum(sER)- is involved
in lipid synthesis.

11. 2. GOLGI APPARATUS
It is made up of anastomosing tubules of
membranes and vesicles. It helps in formation of
secretary products of carbohydrates.

12. 3. PEROXISOMES
Peroxisomes are also known as microbodies and are
membrane bound organelles. They are involved in
catabolic pathway. It results in the production of
H2O2 which is cytotoxic.

13. 4. MITOCHONDRIA
• It is a double membrane bound organelle. Although the
shape of mitochondria is variable but usually it is elongated,
cigar shaped. It localizes inside the cell at a site of
maximum energy requirement. An active cell, like liver cell
contains as many as 2000 mitochondria. Very few
mitochondria are present in an inactive cell.
• Each mitochondria consists of four compartments. Outer
membrane, inner membrane, matrix bound by outer and
inner membrane, space present between the two
membranes containing enzymes.
• The inner membrane is thrown into folds called cristae.
Aerobic respiration takes place in the matrix which is
enhanced by the cristae.

15. 5. RIBOSOMES
Complexes of RNA and proteins are ribosomes.
They lie either freely in cytoplasm of cells or are
found attached to endoplasmic reticulum or can
even be present in the mitochondria. They are the
principal organelles involved in protein synthesis.

16. 6. CENTROSOME
There is a pair of centrioles in each cell. Each
centriole has two cylindrical bodies placed at right
angles to each other.
Transverse section of the centriole shows three
tubules in single group and thus 9 groups of
tubules.
They help in synthesis of microtubules during cell
division.

17. 7. (a) LYSOSOME
They are vesicle like structures, which contain
enzymes, which include proteases,
carbohydratases, lipases, hydrolytic enzymes
etc. Lysosomal enzymes help in destruction of
bacteria.
All cells contain lysosomes except mature
erythrocytes.

18. (b) CYTOPLASMIC INCLUSIONS
Circumscribed masses present in the cytoplasm
are called as cytoplasmic inclusions. They can
be:
 Lipid droplets
 Glycogen granules
 Pigments
 Proteins

19. 8. CYTOSKELETON
It is the skeleton formed of fibres within the
cytoplasm of a cell. It maintains the shape of the
cell and helps in movement of the organelles
present in the cell.
 Microfilaments
 Intermediate filaments
 Microtubules

20. C. NUCLEUS
It is the largest organelle of the cell. It consists of a
nuclear membrane surrounding the nucleoplasm.
Nucleolus is suspended in the nucleoplasm.

22. i) Nuclear membrane- It is a double membrane bound
structure. Nuclear membrane consists of numerous
pores which regulate the exchange of metabolites
between nucleus and cytoplasm.
ii) Nucleoplasm- it is a gel like substance containing
genetic material. When the cell is at rest, the
nucleoplasm appears as a dark staining.
Nucleoplasm contains thread like material called
nuclear chromatin.
iii) Nucleolus- cells which are involved with active
protein synthesis have one or more nucleoli in their
nucleoplasm. The ribosomal RNA is transcribed in
the nucleolus.