Cell & its Functions a physiological concept

for medical and biology students

1. Cell Structure
Dr. ZaheerIqbal
Department of Physiology

3. The Discovery of cells
In 1665, Robert Hooke discovered
the cell
“ I took a clear piece of cork and
sharpened it as keen as a razor. I cut
a piece of it and then examining with
a microscope, me thought I could
perceive it appear a little
porous….much like a honeycomb”.

4. The Discovery of cells
•Anton van Leewenhoek -examined a drop of pond
water under the microscope and saw “animalcules”
darting back and forth before his eyes. Also
discovered sperm cells of animals and humans and
saw that fertilization requires sperm to enter the egg
cell
•Mathias Schleiden-plants were made of cells and
that plant embryo rose from a single cell
•Theodor Schwann –concluded that plant and
animal cells have similar structures and proposed the
three tenets of the Cell Theory

5. The Cell Theory
The three tenets to the cell theory
are :
•All living organisms are composed
of one or more cells
•The cell is the most basic unit of life
•All cells arise from pre-existing,
living cells

7. The Cell: Criteria for life
Growth
Criteria for lifeGrowth Ability to increase in size
Reproduction Ability to replicate ones self

Homeostasis Ability to work together to maintain
equilibrium
Respiration Conveying O2to tissues & cells and giving
off CO2& H2O

Irritability Ability to respond to a stimulus

Conductivity Ability to transmitthatstimulus
Metabolism Anabolism and Catabolism
Excretion Ability to eliminate waste products
Assimilation The conversion of absorbed food into the
substance of the body

8. Cells vary according to the size,
shape, structure and function

9. Protoplasm
Water
```PRINCIPAL Fluid medium of cell
•70-85%, chemicals are dissolved or
suspended in water
Ions
•potassium, magnesium, phosphate,
sulfate, bicarbonate, smaller amount of
sodium, chloride and calcium
•Ions provide inorganic chemicals for
chemical reactions, also are important in
cellular control mechanism
•For Transmission of electrochemical
impulse

10. Protoplasm
;Proteins
•10-20%
•Two types of proteins:
•Structural proteins; long filament form,
microtubules for cytoskeleton of cellular
organelles as cilia,nerveaxons, mitotic
spindles
•Tangled mass of thin filamentous tubules
to hold Cystoplasmand Nucloplasm
•Fibrillerprotiensfound in Collagen and
Elestinfibresin connective tissues,blood
vessel wall,tendonsand ligements.

11. Protoplasm
The functional proteins are an entirely
different type of protein and are usually
composed of combinations of a few
molecules in tubular-globular form.
These proteins are mainly the enzymes of the cell and
are often mobile in the cell fluid.
Also, many of them are adherent to membranous
structures inside the cell. The enzymes come into direct
contact with other substances in the cell fluid and
catalyze specific intracellular chemical reactions

12. Protoplasm
Lipids 2%
•Phospholipids
•Cholesterol
Are insoluble in water, so used to form
membranes & barriers to separate cell
compartments.
In some cells like fat cells triglycerides
constitute up to 95% of cell mass,
forming main storehouse of energy-
giving nutrient

13. Protoplasm
Carbohydrates
`Little structural functions
•Part of glycoprotein in skeleton
•Major role in nutrition, stored as
glycogen
•About 1% of body mass on average
•Up to 3% in muscle cells
•Max 6% in liver cells

14. Cytosol: Cell Gel
The cytosol is the semiliquid portion
of the cytoplasm that surrounds the
organelles.
It is actually a highly organized, gel
like mass with differences in
composition and consistency from
one part of the cell to another.

15. Cytosol: Cell Gel
Three general categories of activities
are associated with the cytosol:
(1) enzymatic regulation of
intermediary metabolism
(2) ribosomal protein synthesis
(3) storage of fat, carbohydrate, and
secretory vesicles.

16. Physical Structure of Cell
Fluid and chemicals is not the end,
cell has highly organized physical
structures called as organelles
Every organelle performs its
important part in cell function

18. Membranous structures of Cell
Most of organelles are covered by a
membrane of lipids and proteins
•Lipids provide a barrier for water and
water soluble substances to move
across the membrane among different
cell compartments
•Some proteins of membrane provide
channels for passage of specific
substances, other are enzymes that
catalyze many reactions

19. Cell Membrane
Thin, pliable and elastic
7.5-10 nm thick
•Proteins 55 %
•Phospholipids 25%
•Cholesterol 13%
•Other lipids 4%
•Carbohydrates 3%

20. Fluid Mosaic Model of the cell
membrane according to
Singer and Nicolson

21. The physical barrier formed by
the tail to tail arrangement of the
phospholipid molecules

22. Lipid Barrier
A 2 molecule thick, continuous Bi-
Layer,
Large globular protein molecules are
interspersed in this thin film
Lipid bi-layer is made of
phospholipids molecules, having 2
ends
•Phosphate end is hydrophilic
•Fatty acid portion is hydrophobic

25. Lipid Barrier
This layer is actually in FLUID form
Protein and other molecules float in
bi-layers
Cholesterol molecules are dissolved
in lipid bi-layer and control
permeability to water soluble
substances and the fluidity of
membrane

26. Lipid Barrier
The basic lipid bilayer is composed of
three main types of lipids: phospholipids,
sphingolipids, and cholesterol.
Sphingolipids, derived from the amino alcohol
sphingosine, also have hydrophobic and hydrophilic
groups and are present in small amounts in the cell
membranes, especially nerve cells.
Complex sphingolipids in cell membranes are thought
to serve several functions, including protection from
harmful environmental factors, signal transmission,
and as adhesion sites for extracellular proteins.

27. Cell Membrane Proteins
Most are Glycoproteins
•Integral proteins
Penetrate all the way through membrane
Form structural channels, carrier proteins,
and enzymes
•Peripheral proteins
Attached only to surface of membrane
usually on inside of an integral protein,
mostly act as enzyme

28. Cell Membrane Proteins
•Structural reinforcement
•Receptor –hormones, neurotransmitters,
immunoglobulinsantibodies
•Trans membrane proteins (transport
materials through bi-layer)
•Surface membrane proteins (receptors
AB & hormones)

29. Cell Membrane Proteins
Other proteins, located on the inner
membrane surface, serve as docking-
marker acceptors; they bind lock-and-
key fashion with the docking markers of
secretory vesicles
Still other proteins serve as cell adhesion
molecules (CAMs). Many CAMs protrude
from the outer membrane surface and form
loops or hooks by which cells grip each other
or grasp the connective tissue fi bers between
cells.

30. Membrane Carbohydrates
In combination with proteins
(Glycoproteins) or lipids (Glycolipids)
Most of integral proteins are Glycoproteins
and 10% of lipids are Glycolipids
Glyco portions always lie towards outside
the cell
Other Carbohydrates molecules are
Proteoglycanes
Sometime there a loose carbohydrate coat
all around cell called as Glycocalyx

31. Functions of Membrane
Carbohydrates
Being Negatively charged, give a –ve
charge on membrane outer surface
repelling negatively charged ions
Glycocalyx of a cell attaches to
others’, thus attaching cells
Receptor substances for binding
hormones
Some are involved in immune
reaction

32. Cytoplasm and its organelles
Clear fluid portion cytosol has proteins,
glucose and electrolytes
Dispersed in cytoplasm are neutral fat
globules,glycogen granules, ribosomes,
secreory vesicles, and organelles:
•Endoplasmic reticulum
•Golgi apparatus
•Mitochondria
•Lysosome
•peroxisomes

33. Network of tubular and flat vesicules
Wall structure is similar to cell membrane
Inside tubules and vesicles is fluid
endoplasmic matix-different from ctyosol
Substances formed in a part of cell are
transported through space of ER
Enzyme system attached to it have role in
metabolic function of cell
Endoplasmic Reticulum

37. Endoplasmic Reticulum
When ribosomes are attached to ER,
it is called as Granular ER
Ribosomes are made of RNA and
Proteins and function in synthesis of
new protein molecules
Part of ER not having the Ribosomes,
is called agranular or Smooth ER and
is important for synthesis of lipids
and other enzymatic process

38. Golgi Apparatus
Closely related to ER
Membranes similar to agranular ER
4 or more stacked layers of vesicles near
a side of nucleus
More prominent in secretery cells
Function in association with ER
ER vesicles pinch off and fuse to Golgi
Apparatus where they are processed to
form lysosome, secretery vesicles or other
substances

42. Golgi Apparatus
This is especially true for the
formation of large saccharide
polymers bound with small amounts
of protein; important examples
include hyaluroninacid and
chondroitin sulfate.
A few of the many functions of
hyaluronic acid and chondroitin
sulfate in the body are as follows:

43. Golgi Apparatus
(1) they are the major components
of proteoglycans secreted in mucus
and other glandular secretions;
(2) they are the major components
of the ground substance, or
nonfibrouscomponents of the
extracellular matrix, outside the cells
in the interstitial spaces, acting as
fillers between collagen fibers and
cells;

44. Golgi Apparatus
(3) they are principal components of
the organic matrix in both cartilage
and bone; and
(4) they are important in many cell
activities, including migration and
proliferation.

50. Lysosomes
lysosomes are small (0.2 to 0.5 m in
diameter) oval or spherical bodies
On average,acell contains about300
lysosomes.
A lysosome contains more than 30 diff erent powerful hydrolytic
enzymes That are synthesized in the ER,then transported to the Golgi
complex for Packaging in the budding lysosome
These enzymes catalyze hydrolysis, reactions that break down
organic Molecules by the addition of water at a bond site (hydrolysis
means “splitting with water”).

53. Lysosomes
Break off from golgi apparatus as vesicles
Intracellular digestive system
Damage cellular structures
Digest food particles
Destroy unwanted material
Vesicle membrane is a typical one
Has hydrolase enzyme system that
ordinarily remains inside vesicle but may
be releaseed inside the cell

54. Peroxisomes
Similar to lysosomes
But
•Formed by self replication
•Have oxidase and catalase enzyme
system rather than hydrolase
•They oxidise many substances that
otherwise may be very harmful

55. Secretory Vesicles
Formed by ER-
Golgi system
Released from
Golgi apparatus
into cytoplasm in
form of secretory
vesicles or
granules

56. Mitochondria

57. Mitochondria

58. Mitochondria
Cellular respiration refers
collectively to the intracellular
reactions in which energy-rich
molecules are broken down to form
ATP, using O2 and producing CO2 in
the process.

59. Mitochondria

60. Mitochondria
In most cells, ATP is generated from
the sequential dismantling of
absorbed nutrient molecules in three
stages ;
glycolysis in the cytosol,
the citric acid cycle in the
mitochondrial matrix, and
oxidative phosphorylation at the
mitochondrial inner membrane :

61. Mitochondria

62. Mitochondria

63. Mitochondria

64. Mitochondria

65. Mitochondria

66. Mitochondria

67. Mitochondria

68. Cytoskeleton: Cell
“Bone and Muscle”
Cellcytoskeletonisanetworkof
fibrillarproteinsorganizedinto
filaments or tubules I,e
cytoskeleton,anelaborateprotein
scaffoldingdispersed throughout
thecytosolthatactsasthe“bone
andmuscle”ofthecellbysupporting
andorganizingthecellcomponents
andcontrollingtheirmovements..

69. Cytoskeleton: Cell
“Bone and Muscle
The cytoskeleton has three distinct
elements:
(1) microtubules,
(2) microfilaments, and
(3) intermediate fi laments

72. Cytoskeleton: Cell
“Bone and Muscle”
Microtubules are the largest of the
cytoskeletal elements. They are
slender (22 nm in diameter), long, hollow,
unbranchedtubes composed primarily of
tubulin, a small, globular, protein
molecule (1 nanometer (nm) 1 billionth
ofameter).Microtubules position many of
the cytoplasmic organelles such as ER
Golgi Apparatus Mitohondriaetc.

73. Cytoskeleton: Cell
“Bone and Muscle”
Microtubules also play an important role in
some complex Cell movements, including
(1) transport of secretory vesicles or her
materials from one region of the cell to
another,
(2) movement ofSpecialized cell
projections suchas cilia and flagella
(3) distribution ofChromosomes during
cell division roughformationofa mitotic
spindle.

77. Microfilaments
Microfilaments are important to
cellular contractile systems and as
mechanical stiffeners.
Microfilaments are the smallest (6 nm
in diameter) elements of the
cytoskeleton.
The most obvious microfilaments in most
cells are those composed ofactin, a
protein molecule that has a globular
shape similar to that of tubulin.

78. Intermediate filaments
Intermediate filaments are important
in cell regions subject to mechanical
stress.
Intermediate filaments are
intermediate in size between
microtubules and microfilaments (7 to
11 nm in diameter)—hence their name.
The proteins that compose the
intermediate filaments varybetween cell
types.

79. Intermediate filaments
they appear as irregular, threadlike
molecules.Theseproteins form tough,
durable fibers that play a central role
in maintaining the structural integrity
of a cell and in resisting mechanical
stresses externally applied to a cell.