Cell: The cell is the ultimate structural and functional unit of the body. The three principal constituents of the cell are: 1. Cell membrane 2. Cytoplasm and its organelles 3. Nucleus

1. CELL STRUCTURE,
ORGANELLES &
INTERCELLULAR
CONNECTIONS
BY
DR. K. AMBAREESHA PhD.,
Assistant Professor, Department of Physiology
MNR Medical College, Sangareddy

2. CONTENTS
1. Introduction of cell
1. Cytoplasm and its Organelles- endoplasmic
Reticulum (ER), Mitochondria, Golgi Complex,
Lysosomes, Peroxisomes, Centrioles or
Centrosomes & Microtubules and Microfilaments .
2. The nucleus
3. Junctional complexes/ Cell junctions –
Tight Junction, Desmosomes or Adherens Junction
& Gap junctions

3. INTRO- THE CELL

4. INTRO- THE CELL
Cell: The cell is the ultimate structural and
functional unit of the body.
The three principal constituents of the cell
are:
1. Cell membrane
2. Cytoplasm and its organelles
3. Nucleus

5. Cell membrane

6. Cell membrane

7. Cell membrane
Channels

8. Functions of cell
membrane
• It forms outermost boundary of cell organelles.
• It takes food and excretes waste products.
• The selective permeability helps in maintaining difference of
composition between ICF & ECF.
• It provides framework for the arrangement of all protein
molecules (Enzymes, pumps, receptors, ions, channels).
• It links adjacent cells together by juctional complexes to form
tissues.

9. *2m(Jan-2011)
Cytoplasm and its
organelles: Mitochondria

10. Cytoplasm and its
organelles: Mitochondria
• Are sausage shaped structures covered by two protein lipid membranes an outer and an inner which
has many folding forming shelves.
• The mitochondria contain many enzymes and is the power house of the cell responsible for
the release of energy.
• The outer layer has enzymes concerned with biological oxidation and provide raw material for the
reactions that occur inside the mitochondria. The inside contains enzymes that oxidize the nutrients
glucose , amino acids, fatty acids via the citric acid cycle to form H2O and CO2. The energy is
utilized to synthesize the high energy phosphate compound ATP.
• Mitochondria also contain a special form of DNA and hence self replicative and when required can
form a second and third mitochondria. They are derived from the mother through ovum, as spem
makes no contribution in the zygote.

11. Cytoplasm and its
organelles- Endoplasmic reticulum

12. Cytoplasm and its
organelles- Endoplasmic reticulum
RER/ Granular
• Contains granules called ribosomes which are
attached to the cytoplasmic side of the
membrane, 3-5 ribosomes clump together to
from polyribosomes or polysomes.
• It is the site of protein synthesis e.g.,
hormones that are secreted by the cell; and
proteins that are found in enzymes.
• Free ribosomes are also found in the
cytoplasm, they synthesize cytoplasmic protein
e.g., Haemoglobin.
SER/ A Granular
• It is site of steroid (Adrenocortical
hormone) synthesis in steroid
secreting cells and the site of
detoxification processes in other
cells.
• As the sarcoplasmic reticulum, it
plays important role in skeletal and
cardiac muscle.

13. Cytoplasm and its
organelles- RIBOSOMES

14. *4m (Sep,Oct – 2005)Cytoplasm and
its organelles- Functions of Ribosomes
They are tiny organelles are made up of RNA and
proteins.
It consists of 2 sub units one about half the size of the
other, both are made separately in the nucleolus
combine to form a single unit in cytoplasm.
The are present in free form in the cytoplasm or
attached to ER.
They synthesize different proteins, for hormones
and enzymes of lysosomes

15. Cytoplasm and its
organelles- Golgi Apparatus

16. Cytoplasm and its
organelles- Golgi Apparatus/ Golgi Bodies)
• These are membranous tubules and vesicles
prominent in actively secreting gland cells.
• Wrapping and packaging department of the
cell.
• Produces secretion granules, which store
hormones and enzymes in secreting cells.
• Site of formation of lysosomes.

17. Cytoplasm and its
organelles- Lysosomes

18. Cytoplasm and its
organelles- Lysosomes
• Large irregular structures, filled with large number of small granules, contain variety of
enzymes, called lysozymes.
• The interior is kept acidic (near pH 5.0), they function best at acidic pH.
• Acts as a form of digestive (lytic) system for the cell mainly macromolecules, Engulf
worn out components of the cells in which they are located.
• Engulf exogenous substances e.g bacteria etc. and degrade them.
• When a cell dies, lysosmal enzymes cause autolysis of the remnant i.e why lysosomes are
called as suicidal bags.

19. Cytoplasm and its
organelles- Peroxisomes
• Is similar to that of lysosomes,
contain oxidases (enzymes that
produce H2O2) rather than
hydrolases.
• They destroy certain products
formed form oxygen, especially
hydrogen peroxide, that can
be toxic to the cells.
• The alcohol, a person drinks is
mainly detoxified by the
peroxisomes of the liver cells.

20. Cytoplasm and its
organelles- Centrioles or Centrosomes

21. Cytoplasm and its
organelles- Centrioles or Centrosomes
• Two short cylinders called ‘centrioles’ visible only during
cell division.
• They are located at each pole near the nucleus and are so
arranged at right angles to each other.
• Tubules in group of three (triplets) run longitudinally in
the walls of the centrioles. There are nine of these triplets
spaced at regular intervals.
• They are concerned with the movement of the chromosomes
during cell division.

22. Cytoplasm and its
organelles- Microtubules and Microfilaments

23. Cytoplasm and its
organelles- Microtubules and Microfilaments
 Microtubules are long hollow structures, make up tracts of
chromosomes, mitochondria and secretion granules move from
one part of the cell to another.
 Microfilaments are long solid fibers. They comprise the
contractile protein actin and are responsible for the cell motion.
 They are involved in movements of the chromosomes; Cell
movement; move secretion granules and movement of proteins
within the cell membrane.

24. Cytoplasm and its
organelles- CYTOSKELETON

25. Cytoplasm and its
organelles- CYTOSKELETON
Cells have filaments in cytoplasm, which form the flexible network is cytoskeleton
They are:
1. Microfilaments made up of actin
2. Intermediate filaments,
3. Microtubules – tubulin protein
4. Molecular motors:
cause movement of organelles and movement of cell itself. The are of 3 types:
kinesin, Dynein and Myosin.
kinesin, Dynein: help in movement of vesicle along with cilia and flagella.
Myosin I along with actin filaments help in movement of villi, Myosin II help in contraction
of skeletal and cardiac muscles by causing sliding action.
They all give mechanical support to the cells, form imp. transport system in nerve
cells, some organelles move to different parts of the cell by them and
chromosomal movements occur during cell division by them.

26. THE NUCLEUS

27. THE NUCLEUS
• It is surrounded by membrane called nuclear membrane (or envelope) with the
pores.
• It is made up of chromosomes, which is made up of -DNA, on which genes are present.
Gene is a portion of DNA molecule which carries a complete blue print for all the
heritable characteristics of an animal.
• Between cell divisions the irregular clumps of dark material called chromatin are the
only evidence of their presence.
• It contains a nucleolus which is patch work of granules rich in Ribonucleic Acid (RNA).
They synthesize the RNA for the ribosomes. DNA in nucleus serves as a ‘template’
(block) for synthesis of RNA, which then moves to the cytoplasm where it regulates the
synthesis of proteins by the cells.
• The information coded into the DNA molecules is conveyed from the nucleus to the
cytoplasm by messenger RNA where actually the synthetic work of the cell takes place.

28. JUNCTIONAL COMPLEXES
BETWEEN CELLS
Tight junction
Adherens junction
Desmosome
TJ
Gap junctions
Hemidesmosome

29. INTERCELLULAR CONNECTIONS-
Tight Junction:

30. INTERCELLULAR CONNECTIONS-
Tight Junction:
 Here membranes of two cells become opposed and
layers of the membranes fuse strongly, thus obliterating
the space between the cells.
 This type of junction is characteristically seen in the
intestinal mucosa, the walls of the renal tubules,
and the choroid plexus.
 Tight junction forms a barrier to the movement of ions
and other solutes from one side of the epithelium to the
other.

31. INTERCELLULAR CONNECTIONS-
Desmosomes or Adherens Junction
Here two membranes are separated
by a 15-20 nm space.
There is dense accumulation of
proteins on both the surfaces of the
membrane with fibers extending
from the cytoplasmic surface of each
membrane into the cell.
The holds, adjacent cells firmly
together in areas that are subjected
to stretching. Such as the skin

32. INTERCELLULAR CONNECTIONS-
Gap Junction/ Nexus

33. INTERCELLULAR CONNECTIONS-
Gap Junction/ Nexus
 There is 2-20 nm space between the opposing membrane.
 The gap is filled with densely packed particles through each of
which there appears to be a channel that connects the two cells.
 The diameter of each channel is regulated by intracellular Ca, pH
and voltage.
 It permits rapid propagation of electrical potential changes from
one cell to the another, e.g. cardiac and smooth muscle
cells.
 The permits the direct transfer of ions and other small molecules
e.g. sugar, amino acids between the cell without traversing the
extra cellular space.