CELL INTRODUCTION , FLUID MOSAIC MODEL AND TRANSPORT SYSTEM

1. D R . A R E E B A G H A Y A S
T U T O R
D E P T O F B I O C H E M I S T R Y
BIOMOLECULES
&
THE CELL

2.  Biochemistry in medicine deals with the study of
chemistry and biological importance of various bio-
organic molecules such as carbohydrates, proteins,
lipids , nucleic acid and vitamins.

3. Chemical Molecules Of Life
 Life is composed of lifeless chemicals molecules
 Mainly six elements:
Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous, And Sulfur.
(90%) of the dry weight of the human body.
 A single cell of the bacterium E.coli contains about 6,000
different organic compounds.
 Human beings contains 1,00,000 different types of organic
compounds.

4. Carbon –A unique elements of life
 Carbon is the most predominant and versatile
element of life.
 This is attributed to the ability of carbon to form
Stable covalent bonds and C-C chains of unlimited
length.

5. COMPLEX BIOMOLECULES
Biomolecules Building block Major functions
1) Protein Amino acids Fundamental basis of
structure and function
cell
2) DNA Deoxyribonucleotides Repository of hereditary
information
3) RNA Ribonucleotides Protein biosynthesis
4) Polysaccharide Glucose Storage form of energy to
meet short term demands

6. Chemical Composition of Man
Constituent Percent Weight(kg)
Water 61.6 40
Protein 17.0 11
Lipid 13.8 9
Carbohydrates 1.5 1
Minerals 6.1 4

7. The Cell
 The cell is the structural and functional unit of life.
 All animal tissues including human are also organised from
collections of cells. Thus cell is the fundamental unit of life.
 Modern cell theory can be divided into the following fundamental
statements:
1. All living things are made of cells.
2. Cells carry out the functions needed to support life.
3. Cells come only from other living cells.

8. CONTRIBUTING SCIENTISTS
 Robert Hooke: Coined the term “cell” after observing that cork
consisted of tiny chambers.
 Schleiden & Schwann: proposed the famous Cell theory which
says “cells are structural and functional unit of living
organisms”.
 Louis Pasteur: Discovered that cells come only from other living
cells.

9. TYPES OF CELLS
 The cells of the living kingdom may be divided into two
categories.
1) Prokaryotes: pro-before ,karyon- nucleus Ex: bacteria
2) Eukaryotes: Eu-true , karyon- nucleus Ex: animals and plants

10. Comparison Between Prokaryotic & Eukaryotic Cells
Characteristic Prokaryotic Cell Eukaryotic Cell
1) Size Small Large
2) Cell Membrane Cell Is Enveloped By A
Rigid Cell Wall
Flexible Plasma
Membrane
3) Sub Cellular Absent Present
4) Nucleus Absent Present
5) Energy Metabolism Absent Present
6) Cell Division No Mitosis Mitosis
7) Cytoplasm Absent Present

11. Prokaryotic Cell
 Typical prokaryotic cells include the bacteria and cyanobacteria.
Most studied prokaryotic cell is Escherichia coli (E. coli).
 CHARACTERISTICS
• It has a minimum of internal organization and smaller in size
• It does not have any membrane bound organelles.
• Its genetic material is not enclosed by a nuclear membrane
• Its DNA is not complexed with histones.
• Its respiratory system is closely associated with its plasma
membrane
• Its does not involve mitosis or meiosis.

12. Eukaryotic Cell
 The eukaryotic cells include the protozoa, fungi, plants and animals
including humans. Cells are larger in size
 CHARACTERISTICS
• It has considerable degree of internal structure with a large number
of membrane bound organells having specific functions
• Nucleus is the site for informational components collectively called
chromatin
• It involves both mitosis and meiosis
• The respiratory site is the mitochondria
• In the plant cells, the site of the conversion of radiant energy to
chemical energy is the highly structural chloroplasts

13. Eukaryotic cell
1) The human body is composed of about 10 ¹⁴ cells.
2) There are about 250 types specialized cells in the human body.
ex: erythrocytes, nerve cells, muscle cells, β cells.
3) An eukaryotic cell is generally 10 to 100 μm in diameter.

14. 1) Nucleus
2) Mitochondria
3) Endoplasmic reticulum
4) Golgi apparatus
5) lysosomes
6) peroxisomes
7) cytosol and cytoskeleton
THE CELL ORGANELLES

15. 1) NUCLEUS
1) Nucleus was first discovered by ROBERT BROWN
2) Nucleus is the largest cellular ,surrounded by a double
membrane nuclear envelope.

16. Functions of nucleus
 DNA replication and RNA transcription of DNA occur in the
nucleus.
 The nucleolus is non-membranous and contains RNA polymerase,
RNAase, ATPase and other enzymes but no DNA polymerase.
Nucleolus is the site of synthesis of ribosomal RNA (r-RNA).
 Nucleolus is also the major site where ribosome subunits are
assembled.

17. 2) MITOCHONDRIA
1) They are spherical, oval or rod-like bodies, about 0.5–1 μm in
diameter and up to 7 μm in length.
2) Erythrocytes do not contain mitochondria. The tail of
spermatozoa is fully packed with mitochondria.
3) Mitochondria are the powerhouse of the cell, where energy
released from oxidation of food stuffs is trapped as chemical
energy in the form of ATP

18. Structure & Function Of Mitochindria
 The mitochondrion is bounded by two concentric membranes that
have markedly different properties and biological functions.
Mitochondrial Membranes
(a) Outer mitochondrial membrane: The outer mitochondrial
membrane consists mostly of phospholipids and contains a
considerable amount of cholesterol. The outer membrane also
contains many copies of the protein called Porin.
(b) Inner mitochondrial membrane: The inner mitochondrial
membrane is very rich in proteins. Cristae: The inner
mitochondrial membrane is highly folded. The tightly packed
inward folds are called “cristae”.

19. (c) Intermembrane space: The space between the outer and inner
membranes is known as the intermembrane space. The outer
membrane is freely permeable to small molecules, the
intermembrane space has about the same ionic composition as the
cytosol.
(d) Mitochondrial matrix: The region enclosed by the inner
membrane is known as the mitochondrial matrix.

20. 3) ENDOPLASMIC RETICULUM
 Eukaryotic cells are characterised by several membrane complexes
that are interconnected by separate organelles.
 These organelles are involved in protein synthesis, transport,
modification, storage and secretion.
 It is a network of interconnecting membranes enclosing channels
or cisternae, that are continuous from outer nuclear envelope to
outer plasma membrane.

21. TYPES OF ER
There are two kinds of endoplasmic reticulum (ER):
(i) Rough surfaced ER, also known as ergastoplasm. They are coated with
ribosomes. Near the nucleus, this type of ER merges with the outer membrane
of the nuclear envelope.
(ii) Smooth surfaced ER: They do not have attached ribosomes.
 Functions
(a) Function of rough ER: Rough ER synthesises membrane lipids, and
secretory proteins. These proteins are inserted through the ER membrane into
the lumen of the cisternae where they are modified and transported through the
cell.
(b) Function of smooth ER: Smooth endoplasmic reticulum is involved:
(i) In lipid synthesis and
(ii) Modification and transport of proteins synthesised in the rough ER.

22. 4) GOLGI APPARATUS
 Camillo Golgi described the structure in 1898.
 The Golgi organelle is a network of flattened smooth membranes
and vesicles. It may be considered as the converging area of
endoplasmic reticulum.
 The Golgi complexes, which contain flattened, fluid filled golgi
sacs.
 The Golgi complex has a Proximal or Cis compartment, a
medial compartment and a distal or trans compartment.

23. FUNCTION
1. Golgi bodies are secretory cell organelles.
2. They play an important role in “storage”, “package”, &
“secretion of various secretory products” such as zymogens,
lipoproteins, plasma proteins, steroids, lipid,etc.
3. Post- translational modification of proteins occurs in golgi
lumen
4. Golgi bodies & ER give rise to primary lysosomes &
peroxisomes
5. It is believed the Acrosome of sperm cell is derived from golgi
bodies

24. 5) LYSOSOMES
 Lysosomes are cell organelles found in cells which contain packet of
enzymes.
 Lysosomes are regarded as the digestive tract of the cell,since they are
actively involved in digestive of cellular substances namely proteins,
lipids, carbohydrates and nucleic acids.
 The lysosomal enzymes have an optimum pH around 5.These enzymes are
a. Polysaccharide hydrolysing enzymes
(alpha-glucosidase, alpha-fucosidase, beta-galactosidase, beta-
glucuronidase, hyaluronidase, lysozyme)
b. Protein hydrolysing enzymes
(cathepsins, collagenase, elastase, peptidases)
c. Nucleic acid hydrolysing enzymes (ribonuclease, deoxyribonuclease)

25.  Lysosomal enzyme destroy the foreign substances and pathogens
like bacteria ,virus that are englufed by the cells of immune
system.
 They also destroy aging cell organelles that are no longer
required by the host cell.
 They are capable of self-destruction of the cell.
 Lysosomes are also called ‘suicide bags’ and play an important
role in apoptosis.
 They play crucial role in postmortem autolysis.
FUNCTION

26. 6) PEROXISOMES
1) Peroxisomes ,also known as microbodies,are single membrane
cellular cell.
2) These vesicles are concerned with the metabolism of hydrogen
peroxide (H2O2).
3) They contain such enzymes that forms, uses and destroy the
H2O2.
4) The H2O2 produced in the cell are highly toxic & is
decomposed into H2O and oxygen by the enzyme Catalase
present in microbodies.

27. FUNCTION OF PEROXISOME
 Peroxisomes protect the cell and its organelles from toxic effects
of H2O2 produced within the cell . Intracellulary produced H2O2
is decomposed by catalase.
 They are present in hepatic cells takes part in oxidation of long
chain fatty acid,D-amino acid to ethanol.
 They also help in synthesis of glycolipids, plasmalogens and
isoprenoids.

28. 7) CYTOSOL AND CYTOSKELETON
1) The cellular matrix is collectively referred to as cytosol.
2) The cytoplasmic filaments are of three types:
1) microtubules 2) actin filaments 3) intermediate filaments.
The cytoskeleton also play a role in movement of cell organelles from
one position to other within the cell.
(a) Microtubules: They are long unbranched slender
cylindrical structures with an average diameter of about 25 nm.
Function-
 Their role in the assembly and disassembly of the spindle structures
during mitosis.
 They may be involved in transmembrane signals.

29. (b) Microfilaments: They are more slender cylinder like
 structures made up of the contractile protein actin. They are linked
to the inner face of the plasma membrane.
Function
 These structures may be involved in the generation of
 forces for internal cell motion.
(c) Microtrabeculae: They appear to be very fragile tubes that form
a transient network in the cytosol.
Function
 Soluble enzymes are associated or clustered with these structures
to form unstable multienzyme complexes.

30.  The plasma membrane is an envelop surrounding
the cell.
 It separates and protect the cell from the external
environment.
 Plasma membrane also provide a connecting system
between the cell and its environment .
BIOLOGICAL MEMBRANES

31. Detailed Structure Of The
Plasma Membrane

32. Chemical Composition
 The membranes are composed of lipids,
proteins, and carbohydrates.
 The actual composition differs from tissue to
tissue.

33.  Among the lipids, amphipathic lipids
(containing hydrophobic and hydrophilic
groups) namely phospholipids, glycolipids
and cholesterol are found in animal
membranes.
 Many animal cell membranes have thick
coating of complex polysaccharides referred
to as glycocalyx.

35. Structure Of Membranes
 A lipid bilayer model originally
proposed for membrane structure in
1935 by Danielle and Davson has been
modified.

36. FLUID MOSAIC MODEL

38.  The hydrophobic (nonpolar) regions of
the lipids face each other at the core of the
bilayer while the hydrophilic (polar)
regions face outward.
 Globular proteins are irregularly
embedded in the lipid bilayer.

39.  Membrane proteins are categorized into two
groups.
1) Peripheral Membrane Proteins
2) Integral Membrane Proteins

40. 1) Peripheral Membrane Proteins:
are loosely held to the surface of the
membrane and they can be easily separated.
2) Integral Membrane Proteins: are
tightly bound to the lipid bilayer and they
can be separated only by the use of
detergents or organic solvents.

41. TRANSPORT ACROSS MEMBRANES
 The biological membrane are relatively
impermeable.
 The membrane, therefore forms a barrier for the
free passage of compounds across it.
1) Passive Diffusion
2) Facilitated Diffusion
3) Active Transport.

43.  This is a simple process
which depends on the
concentration gradient of a
particular substance across
the membrane.
 Passage of water and gases
through membrane occurs by
passive diffusion. This
process does not required
energy.
1) PASSIVE DIFFUSION:

44. 1) Solute moves along the concentration gradient
(from higher to lower concentration) and no
energy is required.
2) But the most in distinguishing feature is that
facilitated diffusion occurs through the mediation of
carrier or transport proteins.
ex: glucose, galactose, leucine,
phenylalanine have been isolated and
characterized.
2) FACILITATED DIFFUSION:

45.  A ping pong model is put forth to explain
the occurrence of facilitated diffusion.
 According to this mechanism, a transport
protein exists in two conformation, in the
pong conformation it is exposed to the side
with high solute concentration.
 This allow the binding of solute to specific
sites on the carrier protein.
Mechanism Of Facilitated Diffusion:

46.  The protein then undergoes a conformational
change(ping state) to expose to the side with
low solute concentration where the solute
molecule is released.
 Insulin increases glucose transport in muscle
and adipose tissue.

47. Mechanism of facilitated diffusion

48. 3) ACTIVE TRANSPORT
 Active transport occurs against a
concentration gradient and this
depend upon the supply of metabolic
energy (ATP).
 Active transport is also carrier
mediated process like facilitated
diffusion.
 The most important primary Active
transport systems are ion pumps.

50.  The cells have a high intracellular K+
Concentration and a low Na+ concentration.
 High cellular K+ is required for the optimal
glycolysis and for protein biosynthesis.
 Na+ - K+ is used for the transmission of
nerve impulse.
Na+ - K+ pump

51.  Na+-K+ pump is responsible for the maintenance of
high K+ and low Na+ concentration in the cells.
 This is brought about by an integral plasma
membrane protein, namely the enzyme Na+-K+
ATPase.
 Na+ - K+ ATPase pumps 3Na+ ions from inside the
cell to outside and brings 2K+ ions from the outside
to the inside with a concomitant hydrolysis of
intercellular ATP.

53.  Ouabain inhibit Na+-K+ ATPase pump.,
 Ouabain is a steroid derivative extracted from the
seed of an African Shrub.
 It is a poison used to tip the hunting arrows by the
tribal in Africa.
 Digoxin inhibits Na+-K+ ATPase .
Na+ co transport system: The amino acids and
sugars are transported into the cells by a Na+ co
transport system.

54. TRANSPORT SYSTEMS
 The transport systems may be divided into 3
categories:
1) Uniport
2) Symport
3) Antiport

56. 1) Uniport System: This involves the movement of
single molecule through the membrane .
ex: transport of glucose to the erythrocyte.
2) Symport System: transport of two different
molecules in the same direction.
ex: transport of Na+ and glucose to the intestinal
mucosal cells from the gut.
3) Antiport System: transport of two different
molecules in the opposite direction .
ex: exchange of Cl- and HCO3 in the erythrocytes.

57. Cotransport system:
 The symport and antiport systems referred to
above are good examples of co transport system.
Proton pump in the stomach:
ex: antiport transport system.
H+ - K+ ATPase to maintain highly acidic conditions
in the lumen of the stomach.
2(H+) and two extracelluar potassium (2K+) ions for a
molecules of ATP hydrolysed.

58.  Omeprazole is a drug used in the treatment of
peptic ulcer.
Passive transport of water osmosis: the
movement of water from low osmotic pressure to
high osmotic pressure across biological
membranes. Does not require energy .
Certain medical and health complications are
due to disturbances in osmosis.
ex: edema, diarrhea,

59. Transport of Macromolecules
 The transport of macromolecule such as protein,
polysaccharides and polynucleotide across the
membrane is equally important.
1) Endocytosis: intake of macromolecules by the
cells.
2) Exocytosis: release of macromolecules from the
cells to the outside .

61. 1) Endocytosis: Intake of macromolecules by the
cells.
 It is estimated that approximately 2% of the exterior
surface of plasma membrane possesses characteristic
Coated-pits.
 The pits can be internalized to form coated vesicles
which contain an unusual protein called Clathrin.
 The uptake of LDL molecules by the cells is a good
example of endocytosis.

62.  Endocytosis occurs when the plasma membrane is
pulled inwards and will form a “pocket” around a
particular substance.
 The substance will become
enclosed in the vesicle which
is then pinched off and begins
moving through the cytoplasm.
 Cells can bring in solids and
liquids using this process.

63. 2. Exocytosis: Release of macromolecules from the cells
to outside.
 The release of macromolecules to the outside of the
cells mostly occurs via the participation of Golgi
apparatus.
 The macromolecules are transported to the plasma
membrane in a vesicles and let out.
 The secretion of hormone e.g. Insulin usually
occur by Exocytosis.

64.  Exocytosis is internal vesicles will fuse with the
plasma membrane and the contents of the vesicle are
released into the external environment of the cell.
 The cell can secrete substances they produced this way
or excrete waste products.

65. Diseases due to loss of membrane transport
systems:
 Hartnups disease
 Cystinuria
 Rickets