This document discusses cell membranes and transport mechanisms. It describes the four main mechanisms of transport through cell membranes: diffusion, facilitated diffusion, osmosis, and active transport. Diffusion is the passive movement of molecules or ions from an area of higher concentration to lower concentration down a concentration gradient. Facilitated diffusion utilizes membrane proteins to transport specific molecules. Osmosis is the passive movement of water across a membrane, moving from an area of lower solute concentration to higher. Active transport requires energy and transports molecules against a concentration gradient using membrane proteins like pumps and channels.

1. CELL
BIOCHEMISTRY
By
Prof. Dr. Muhammad Shafique
MBBS, M.Phil, Ph.D

2. Types
• Prokaryotes: without a true nucleus
• Eukaryotes: Having a predefined or
true nucleus

4. CELL MEMBRANE
• It defines the periphery of the cell, separating its
contents from the surroundings. It is composed of
enormous numbers of lipids & protein
molecules, held together by primarily non
covalent hydrophobic interactions ,forming a
thin, tough, pliable hydrophobic bilayer around
the cell.
• It is 7.5 to 10 nanometers thick.

5. CELL MEMBRANE
• The approximate composition of cell membrane is
55% proteins, 25% phospholipids, 13%
cholesterol 4% other lipids & 3% carbohydrates.
The plasma membrane of RBC contains
approximately 52% proteins, 40% lipids & 8%
carbohydrates.
• Its basic structure is a lipid bilayer, which is a
thin double layered film of lipids, each layer
only one molecule thick, that is continuous
over the entire cell surface.

6. • Most abundant class of membrane lipids is phospholipid &
less abundant class of membrane lipids is sphingolipids.
• Membrane lipids are amphipathic in nature.
1. HYDROPHILIC END 2. HYDROPHOBIC END
• Phospholipids and cholesterol make this bilayer almost
entirely impermeable to water & water soluble substances
as ions, glucose, Urea & others.
• Fat soluble substances such as oxygen, carbondioxide
& alcohol can penetrate this portion of the membrane.

8. CELL MEMBRANE
• A special feature of lipid bilayer is that it is a
fluid & not a solid. Therefore, portions of
membrane can literally flow from one point to
another point in the membrane.
• It is semi permeable and acts as a barrier.

10. CELL MEMBRANE PROTEINS
• These are the glycoproteins.
1. Integral Proteins:
That penetrate into lipid bilayer which
protrude all the way through the cell. These
proteins provide structural pathways through
which water & water soluble substances,
especially ions, can diffuse between the extra
cellular & intracellular fluid, thus providing
so called cell membrane pores. some of them
can also act as enzymes.

11. CELL MEMBRANE PROTEINS
2. Peripheral proteins:
Which are attached only to integral proteins
& do not penetrate or occur inside the
membrane. They almost act as enzymes &
control many of the chemical reactions inside
the cell
3. Lipid anchored proteins:
They are located outside the lipid bilayer but
are covalently linked to a lipid molecule that
is situated within bilayer.

12. THE MEMBRANE CARBOHYDRATES
• They occur almost outside the membrane.
• These are the glyco-portion of protruding
glycoproteins molecules.
• Depending on the species & cell type, the
carbohydrate contents of plasma membrane
ranges b/w 2 to 10% by weight.

13. Chemical Structure of Plsma Membrane

14. CYTOPLASM & CYTOSOL
• Cytoplasm is viscous & collidal material
which is more or less transparent in visible
lights.
• Cytoplasm is composed of an aqueous
solution the cytosol, & a variety of
insoluble suspended particles.
• The cytosol is not simply a dilute aqueous
solution it has a complex composition & gel
like consistency.

15. DISSOLVED SUBSTANCES IN CYTOSOL
Dissolved in the cytosol are:
• Many enzymes & the RNA molecules
• The monomeric subunits (AA & nucleotide)
• Small organic molecules called metabolites
• Intermediates in metabolic pathways
• Coenzymes
• Inorganic ions.

16. MEMBRANE BOUNDED ORGANELLES
• Nucleus
• Endoplasmic reticulum
• Mitochondria
• Lysosome
• Golgicomplex
• Peroxisomes

17. Nucleus
• It is the control center of the cell .
• It controls both chemical reactions and
reproduction of the cell.
• The nucleus contains more than 95% of the cell's DNA.
• A double membrane structure, nuclear membrane
separates the nucleus from the cytosol.

20. Endoplasmic Reticulum
• Was discovered in 1945 by Albert Claude in Belgium,
and Keith Porter at Rockefeller Institute (It was first
noticed in the cytoplasm of chick embryo cells).
• The endoplasmic reticulum is a network of folded
membranes that form channels.
• The Endoplasmic Reticulum makes protein and lipid
components.
• Consists of a smooth ER and a rough ER.
• This organelle is responsible of moving proteins and
other carbohydrates to the Golgi Apparatus,
lysosomes, and other places.

22. Rough Endoplasmic Reticulum
• The RER is dotted with ribosomes.
(Which is why it is called “rough.”)
• The RER is involved with protein
production, protein folding, quality
control and dispatch.
• The RER is involved with the
synthesis of proteins. They produce
and process specific proteins at
ribosomal sites.
• Consists of network-like tunnels
with tubules, vesicles and cisternae
which is held together by the
cytoskeleton of the cell.

23. Smooth Endoplasmic Reticulum
• SME is more tubular then RER and forms a
separate interconnecting network. (Is found evenly
distributed among the Cytoplasm.)
• SME has no ribosomes on it.
• Smooth ER manufactures lipids and in some cases
the metabolism of them and associated products.

24. THE MITOCHONDRIA
• It is called the “powerhouse” of the cell.
• The number of mitochondria per cell varies from less than a
hundred to many thousand depending upon the amount of
energy required by each cell .
• It is mainly composed of outer membrane & inner membrane.
• The liberated energy is used to synthesize a high energy
substance called (ATP). ATP is then transported out of the
mitochondrion & diffuses throughout the cell to release its
energy wherever it is needed for performing cellular
functions.
• Mitochondria are self-replicative.

25. Cross - Section

26. Respiratory Chain

27. GOGI COMPLEX
 The name comes from Italian anatomist Camillo Golgi,
who identified it in 1898.
 It is closely related to the ER. Its membrane is
similar to that of SER.
 It is composed of four or more stacked layers of thin
,flat vesicles lying near the nucleus (cisternae).
 It is very prominent in secretory cells.

29. Functions of Golgi Apparatus
1. They function mainly in association with the ER.
2. They are concerned with cell secretions .
3. The proteins or enzymes that have to be transported
out of the cell, pass through Golgi apparatus.
4. Carry out the modification of lipids and proteins
5. Most important function is to modify the proteins and
lipids by adding corbohydrates and converting them into
Glycoproteins and Glycolipids.
6. Storage and packaging of materials that will be exported
from the cell.

30. THE LYSOSOMES
• The lysosomes provide an intracellular digestive
system that allows the cell to digest & remove
unwanted substances & structures especially damaged
and foreign structures such as bacteria.
• Its diameter is 250-750 nm.
• Lysosomes are spherical organelles that contain
enzymes (acid hydrolases). They break up food so it is
easier to digest. They are found in animal cells, while in
yeast and plants the same roles are performed by lytic
vacuoles.

31. Lysosomal Enzymes
• Some important enzymes found within
lysosomes include:
• Lipase, which digests lipids
• Amylase, which digest carbohydrates (e.g.,
sugars)
• Proteases, which digest proteins
• Nucleases, which digest nucleic acids

32. Lysosomal Enzymes
• All these hydrolytic enzymes are produced in
the endoplasmic reticulum, and to some
extent in cytoplasm are transported and
processed through the Golgi apparatus.
• And through golgi apparatus they pinch off as
single membrane vesicles.

33. 33
• Lysosomes are sometimes called "suicide bags“
• A lysosome is a membrane bag containing
digestive enzymes
• to digest food, the lysosome membrane fuses
with the membrane of a food vacuole and squirts
the enzymes inside.
• The digested food can then diffuse through the
vacuole membrane and enter the cell to be used
for energy or growth.

34. 34

36. Lysosomes
Lysosomes are the cells' garbage disposal
system. They are used for the digestion of
macromolecules from phagocytosis (ingestion of
other dying cells or larger extracellular material,
like foreign invading microbes) .

37. Lysosomes
• Lysosomes are responsible for autolysis and
programmed cell death called apoptosis.
• Intracellular digestive system. It digests
o Foreign particles
o Unwanted substances
o Damaged structures of the cell.

38. Lysosomes
• Lysosomes pick up foreign invaders such
as bacteria, food and old organelles and
break them into small pieces that can
hopefully be used again.
• The only thing that keeps the cell itself
from being digested is the membrane
surrounding the lysosomes.

40. PEROXISOMES
• Peroxisomes are similar physically to
lysosomes.
• First observed by electron microscopy in animal
cells (1950s), then in plant cells (1960s)
• Oxidase enzymes present in large quantity in
peroxisomes, oxidize many substances
poisonous to the cell.

41. PEROXISOMES
• The oxidases combine oxygen and
hydrogen ions to form H2O2.
• H2O2 is used by catalase enzyme.

42. DIFFERENCE B/W LYSOSOMES & PEROXISOMES
LYSOSOMES
• They are formed by
Golgi apparatus.
• They contain enzymes
hydrolases
PEROXISOMES
• They are formed by
budding off from the SER.
• Enzymes present are
oxidases

43. Cytoskeleton
• Acts as skeleton and
muscle
• Provides shape and
structure
• Helps move organelles
around the cell
• Made of three
types of filaments:
• microtubulues,
• microfilaments,
• intermediate filaments.

44. MICROFILAMENTS
 The febrile proteins of the cell cytoplasm are organized
in to microfilaments or microtubules.
 At first they are present in dissolved form in
the cytoplasm.
 Then they are polymerized to form microfilaments.
 Microfilaments are made up of contractile actin
protein linked to the inner surface of the plasma
membrane.
 The are involved in internal cell motion.
 Muscle contraction through out the body is due to
microfilaments present in the muscle cells.

45. MICROTUBULES
 Microtubules are hollow, cylindrical structures.
 They are made up of protein called TUBULIN
• Primary function of microtubules is to act as
cytoskeleton, providing rigid physical structures
for certain parts of cell.
• The are involved in internal cell motion.
--------------------------

46. An example of the role of microtubules in transporting
organelles. The peroxisomes are shown in green and MT in red
The machinery that moves materials and organelles withincells
Peroxisome
Microtubule (MT)

47. BIOCHEMICAL COMPOSITION OF CELL
Includes Macro molecules and micromolecules:
Carbohydrates Water
Lipids Electrolytes
Proteins Minerals
Nucleotides Vitamins
Enzymes Hormones

48. WATER
It is the main fluid medium of the cell having a
remarkably constant proportion ranging from 75-85%.
ELECTROLYTES/IONS
They are calcium , magnesium, phosphate, sulphate, potassium ,
bicarbonate sodium , chloride
PROTEINS
The protein content is usually on the order of 10-20% next
to water.

49. LIPIDS
• Lipids constitute about 2-3%.
• The most important lipids in majority of the cells are
phospholipids & cholesterol which is used to form cell
membrane & intracellular membrane barriers that separate
the different cell compartments.

50. CARBOHYDRATES
• Most of the cells do not have large stores of
carbohydrates
• usually about 1% of total mass.
• 3% in muscle cells
• 6% in liver cells

51. Interactive session(MCQs)
• Each of the following is a cell organelle
except one. Which one of these is NOT a cell
organelle?
a. Mitochondrion b. Lysosome
c. Cytoplasm d. Nucleus
e. Endoplasmic reticulum

52. • What structure is common to ALL cells?
a. Chloroplast
b. Cell membrane
c. Cell wall
d. Mitochondria
e. Flagella

53. • When a large proportion of a cell's ribosomes
are attached to the endoplasmic reticulum, it
is a sign that the cell is specialized to:
a. Manufacture glucose for storage
b. Manufacture phospholipids for cell growth
c. Perform photosynthesis with high efficiency
d. Manufacture proteins for export

54. • The chromosomes of a eukaryotic cell
are located in the:
a. Mitochondria
b. Nucleus
c. Ribosome
d. Endoplasma

55. • The organelle most directly involved in
cellular aerobic respiration is the
a. ribosome
b. mitochondrion
c. nucleus
d. lysosome
e. golgi apparatus

56. • You are told that the cells on a microscope
slide are plant, animal, or bacterial. You look
at them through a microscope and see cell
walls and membrane-bound organelles. You
conclude that the cells
a. Are plant cells.
b. Could be either plant or bacterial.
c. Are animal cells.
d. Could be plant, animal, or bacterial.

57. • Organelles found outside a eukaryotic cell
and usually involved in movement of the cell
or movement of substances past the cell are
called:
a. Cilia and flagella
b. Cell walls and plasmodesmata
c. Nucleus and nucleolus
d. Cytoplasm and endoplasm

58. Microtubules, microfilaments and intermediate
filaments are components of the:
a. Cell wall in plants
b. Plasma membrane in prokaryotes
c. Chromosome in eukaryotes
d. Chromosome in prokaryotes
e. Cytoskeleton

59. Transport through cell
membranes
AS Biology, Cell membranes
and Transport
59

60. Transport through cell
membranes
The phospholipid bilayer is a good barrier around
cells, especially to water soluble molecules. However,
for the cell to survive some materials need to be
able to enter and leave the cell.
• There are 4 basic mechanisms:
1. DIFFUSION and FACILITATED DIFFUSION
2. OSMOSIS
3. ACTIVE TRANSPORT
4. BULK TRANSPORT
AS Biology, Cell membranes and
Transport
60

61. •Diffusion is the net movement of molecules (or
ions) from a region of their high concentration to
a region of their lower concentration.
The molecules move down a concentration gradient.
Molecules have kinetic energy, which makes them move
about randomly.
As a result of diffusion molecules reach an equilibrium
where they are evenly spread out.
This is when there is no net movement of molecules
from either side.
AS Biology, Cell membranes
and Transport
61

62. Diffusion of liquids
AS Biology, Cell membranes and
Transport
62

63. DIFFUSION
AS Biology, Cell membranes and
Transport
63
Diffusion is a PASSIVE process which means no energy is used
to make the molecules move, they have a natural kinetic energy.

64. Diffusion through a membrane
Cell membrane
AS Biology, Cell membranes and
Transport
64
Inside cell Outside cell

65. Diffusion through a membrane
AS Biology, Cell membranes and
Transport
65
Cell
membrane
Inside cell Outside cell
diffusion

66. Diffusion through a membrane
AS Biology, Cell membranes and
Transport
66
Cell
membrane
Inside cell Outside cell
EQUILIBRIUM

67. What determines the rate of diffusion?
There 4 factors:
1. The steepness of the concentration gradient. The bigger
the difference between the two sides of the membrane
the quicker the rate of diffusion.
2. Temperature. Higher temperatures give molecules or ions
more kinetic energy. Molecules move around faster, so
diffusion is faster.
3. The surface area. The greater the surface area the
faster the diffusion can take place. This is because the
more molecules or ions can cross the membrane at any one
moment.
4. The type of molecule or ion diffusing. Large molecules
need more energy to get them to move so they tend to
diffuse more slowly. Non-polar molecules diffuse more
easily than polar molecules because they are soluble in the
non polar phospholipid tails.
AS Biology, Cell membranes and
Transport
67

68. Molecules that diffuse through cell
membranes
1. Oxygen – Non-polar
so diffuses very
quickly.
1. Carbon dioxide –
Polar but very small
so diffuses quickly.
2. Water – Polar but
also very small so
diffuses quickly.
AS Biology, Cell membranes and
Transport
68

69. Facilitated diffusion
• Large polar molecules such as
glucose and amino acids,
cannot diffuse across the
phospholipid bilayer. Also
ions such as Na+ or Cl- cannot
pass.
• These molecules pass
through protein channels
instead. Diffusion through
these channels is called
FACILITATED DIFFUSION.
• Movement of molecules is
still PASSIVE just like
ordinary diffusion, the only
difference is, the molecules
go through a protein channel
instead of passing between
the phospholipids. AS Biology, Cell membranes and
Transport
69

70. AS Biology, Cell membranes and
Transport
70

71. Facilitated Diffusion through a membrane
AS Biology, Cell membranes and
Transport
71
Cell
membrane
Inside cell Outside cell
Protein channel

72. Facilitated Diffusion through a membrane
AS Biology, Cell membranes and
Transport
72
Cell
membrane
Inside cell Outside cell
Protein channel
diffusion

73. Facilitated Diffusion through a membrane
AS Biology, Cell membranes and
Transport
73
Cell
membrane
Inside cell Outside cell
Protein channel
diffusion
EQUILIBRIUM

74. Facilitated Diffusion:
Molecules will randomly move through the opening like pore, by
diffusion. This requires no energy, it is a PASSIVE process.
Molecules move from an area of high concentration to an area of
low conc.
AS Biology, Cell membranes and
Transport
74

75. AS Biology, Cell membranes and
Transport
75

76. Osmosis
‘The diffusion of water from an area
of high concentration of water
molecules (high water potential) to
an area of low concentration of
water (low water potential) across a
partially permeable membrane.’
AS Biology, Cell membranes and
Transport
76

77. Osmosis
AS Biology, Cell membranes and
Transport
77
Cell
membrane
partially
permeable.
Inside cell Outside cell
VERY High conc.
of water
molecules. High
water potential.
VERY Low conc.
of water
molecules. High
water potential.
Sugar molecule
DILUTE SOLUTION CONCENTRATED SOLUTION

78. Osmosis
AS Biology, Cell membranes and
Transport
78
Cell
membrane
partially
permeable.
Inside cell Outside cell
High conc. of
water molecules.
High water
potential.
Low conc. of
water molecules.
High water
potential.
OSMOSIS

79. Osmosis
AS Biology, Cell membranes and
Transport
79
Cell
membrane
partially
permeable.
Inside cell Outside cell
OSMOSIS
EQUILIBRIUM. Equal water concentration on each
side. Equal water potential has been reached. There is
no net movement of water

80. AS Biology, Cell membranes and
Transport
80

81. AS Biology, Cell membranes and
Transport
81

82. Effects of Osmosis on Life
• Water is so small and there is so much
of it the cell can’t control it’s movement
through the cell membrane.
82

83. Hypotonic Solution
• Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than inside
the cell. (Low solute; High water)
• Result: Water moves from the solution to inside the cell): Cell
Swells and bursts open (cytolysis)!
83

84. Hypertonic Solution
• Hypertonic: The solution has a higher concentration of solutes
and a lower concentration of water than inside the cell. (High
solute; Low water)
• Result: Water moves from inside the cell into the solution: Cell
shrinks (Plasmolysis)!
84
shrinks

85. Isotonic Solution
• Isotonic: The concentration of solutes in the solution is
equal to the concentration of solutes inside the cell
• Result: Water moves equally in both directions and the cell
remains same size! (Dynamic Equilibrium)
85

86. What type of solution are these cells in?
86
Hypertonic Isotonic Hypotonic

87. Active Transport
• Movement of molecules and ions against their
concentration gradients.
• From lower to higher concentrations.
• Requires ATP
• Passive transport Active transport
87
high
low
Weeee!!
!
high
low
This is
gonna
be hard
work!!

88. • Two Types of Active Transport:
– Primary
– Secondary
Transport of small substances is of 3 types.
• Uniport
• Symport
• Antiport
AS Biology, Cell membranes and
Transport
88

89. AS Biology, Cell membranes and
Transport
89

90. • EXAMPLES:( primary active transport)
• Ca pump
• It is an example of uniporter pump.
• H-K ATPase/Proton pump.
• It is an example of antiporter pump.
• Na-K ATPase/ Na K Pump
• It is example of antiporter pump.
AS Biology, Cell membranes and
Transport
90

91. Primary Active Transport
• ATP directly required for
the function of the carriers.
• Molecule or ion binds to
carrier site.
• Binding stimulates
phosphorylation
(breakdown of ATP).
• Conformational change
moves molecule to other
side of membrane.
AS Biology, Cell membranes and
Transport
91

92. AS Biology, Cell membranes and
Transport
92

93. Secondary Active Transport
• Coupled transport.
• Energy needed for
uphill movement
obtained from downhill
transport of Na+.
AS Biology, Cell membranes and
Transport
93

94. COTRANSPORT
• It also uses the process of diffusion.
• In this case a molecule that is moving naturally
into the cell through diffusion is used to drag
another molecule into the cell.
• Example: Glucose hitches a ride with sodium.
AS Biology, Cell membranes and
Transport
94

95. GLUCOSE TRANSPORT
AS Biology, Cell membranes and
Transport
95

96. Membrane Transport of Glucose
• Glucose transport is an
example of:
– Cotransport
– Secondary active
transport
– Facilitated diffusion
AS Biology, Cell membranes and
Transport
96

97. AS Biology, Cell membranes and
Transport
97

98. Endocytosis is the case when a molecule causes the
cell membrane to bulge inward, forming a vesicle.
• Phagocytosis is the type of endocytosis where an
entire cell is engulfed.
• Pinocytosis is when the external fluid is engulfed.
• Receptor-mediated endocytosis occurs when the
material to be transported binds to certain specific
molecules in the membrane. Examples include the
transport of insulin and cholesterol into animal cells.
AS Biology, Cell membranes and
Transport
98

99. AS Biology, Cell membranes and
Transport
99

100. Donnan Equilbrium

110. Membrane receptors
• membrane receptors are specialized
protein molecules in the membranes of
cells, to which external molecules
(hormones, neurotransmitters, drugs)
attach, triggering changes in the function
of the cell. This process is called
transduction: the external signal is
transduced into action.

115. Adenylcyclase

123. Techniques to study cell
1. Centriguation
2. Ultracentrifugation
3. Rdioimmunoassay
4. ELISA
5. Chromatography
6. Electrophoresis
7. Specrophotometry
8. pH metry

124. Centrifugation

125. Ultracentrifugation

126. Radioimmunoassay

128. ELIZA
• ELISA (enzyme-linked
immunosorbent assay) is a plate-
based assay technique designed for
detecting and quantifying peptides,
proteins, antibodies and hormones.
• In an ELISA, an antigen must be
immobilized to a solid surface and
then complexed with an antibody that
is linked to an enzyme.

132. Chromatography

137. pH metre
• pH is a measurable parameter between the
values of 0 and 14, provided the
concentration of the solution does not
exceed 1M.
• Solutions with a pH<7 are acidic, whereas
those with a pH>7 are alkaline. A pH
meter is a device that measures the changes
in the activity of hydrogen ions in solution.

141. Spectrophotometre

145. Thank You
Good Luck 145