1. A cell is the basic structural and functional unit of living organisms, with over 200 cell types that vary in shape, size, and function. 2. The plasma membrane defines the boundary of the cell and is composed of a lipid bilayer with embedded and peripheral proteins. It regulates what enters and exits the cell. 3. The cytoplasm contains organelles like mitochondria, ribosomes, the endoplasmic reticulum, Golgi apparatus, and lysosomes that carry out specialized functions to keep the cell working properly.

1. • Saqib Khan
FA16-=PHM-=060
Department of Pharmacy
COMSATS Institute of Information And Technology Abbottabd

2. CELLS THE LIVING
UNIT

3. Introduction
1. A cell is the basic structural and functional unit of living
organisms
2. The activity of an organism depends on both the individual
and the collective activities of its cell.
3. over 200 different cell types that vary greatly in shape, size,
and function
4. The spherical fat cells, disc-shaped red blood cells, branching
nerve cells, and cube like cells of kidney tubules.
5. Depending on type, cells also vary greatly in length ranging
from 2 micrometres in the smallest cells to over a meter in
the nerve cells

5. Components of Cells
1-Plasma membrane
2-Cytoplasm
3-Nucleus

6. Plasma membrane
• The flexible plasma membrane defines the extent of a cell,
thereby separating two of the body’s major fluid compartments
the intracellular fluid within cells and the extracellular fluid
outside cells.
• The fluid mosaic model of membrane structure depicts the
plasma membrane as an exceedingly thin (7–10 nm) structure
composed of a double layer, or bilayer, of lipid molecules with
protein molecules dispersed in it.

8. Plasma membrane
• The lipid bilayer (phospholipids, with smaller amounts of cholesterol
and glycolipids.)
• Each phospholipid molecule has a polar “head” that is charged and is
hydrophilic (hydro = water, philic = loving), and an uncharged,
nonpolar “tail” that is made of two fatty acid chains and is
hydrophobic (phobia = hating).
• The polar heads are attracted to water the main constituent of both the
intracellular and extracellular fluids and so they lie on both the inner
and outer surfaces of the membrane.
• The nonpolar tails, being hydrophobic, avoid water and line up in the
center of the membrane.
• They are composed of two parallel sheets of phospholipid molecules
lying tail to tail, with their polar heads exposed to water inside and
outside the cell.

9. Plasma membrane
• Glycolipids , phospholipids with attached sugar groups, are found only
on the outer plasma membrane surface and account for about 5% of the
total membrane lipid.
• Their sugar groups, like the phosphate-containing groups of
phospholipids, make that end of the glycolipid molecule polar, whereas
the fatty acid tails are nonpolar.
• Some 20% of membrane lipid is cholesterol, which wedges its plate like
hydrocarbon rings between the phospholipid tails, decreasing their
orderliness and increasing the mobility of the phospholipids.
• About 20% of the outer membrane surface contains lipid rafts, dynamic
assemblies of saturated phospholipids associated with unique lipids called
sphingolipids and lots of cholesterol. These quilt like patches are more
stable and orderly and less fluid than the rest of the membrane. Because
of these qualities, lipid rafts are assumed to be concentrating platforms
for molecules needed for cell signalling.

10. Plasma membrane
There are two distinct membrane proteins,
• Integral Proteins
• Peripheral Proteins
• Proteins make up about half of the plasma membrane by
mass and are responsible for most of the specialized
membrane functions

11. Plasma membrane
• Integral proteins are firmly inserted into the lipid bilayer.
• trans membrane proteins that span the entire width of the membrane
and protrude on both sides.
• have both hydrophobic and hydrophilic regions. This structural
feature allows them to interact both with the nonpolar lipid tails
buried in the membrane and with water inside and outside the cell.
• involved in transport. Some cluster together to form channels, or
pores, through which small, water-soluble molecules or ions can
move, thus bypassing the lipid part of the membrane.
• Others act as carriers that bind to a substance and then move it
through the membrane.
• Still others are receptors for hormones or other chemical messengers
and relay messages to the cell interior (a process called signal
transduction).

12. Plasma membrane
Peripheral proteins
• are not embedded in the lipid
• they attach rather loosely to integral proteins or membrane lipids
and are easily removed without disrupting the membrane.
• Peripheral proteins include a network of filaments that helps
support the membrane from its cytoplasmic side.
• Some peripheral proteins are enzymes. Others are involved in
mechanical functions, such as changing cell shape during cell
division and muscle cell contraction, or linking cells together.
• Many of the proteins that abut the extracellular space are
glycoproteins that sport branching sugar groups. The term
glycocalyx (“sugar covering”) is used to describe the fuzzy, sticky
carbohydrate-rich area at the cell surface.

15. Specializations of the Plasma Membrane
• Microvilli are extensions of the plasma membrane that increase
its surface area for absorption.
• Membrane junctions join cells together and may aid or inhibit
movement of molecules between or past cells.
• Tight junctions are impermeable junctions;
• desmosomes mechanically couple cells into a functional
community;
• gap junctions allow joined cells to communicate.

17. 2- Cytoplasm
The cytoplasm, the cellular region between the nuclear and
plasma membranes, consists of the
• cytosol (fluid cytoplasmic environment), inclusions
• nutrient stores
• lipid droplets,
• glycosomes—pigment granules, crystals, etc.),
• cytoplasmic organelles

18. a) Mitochondria
• Mitochondria, organelles limited by a double membrane, are
sites of ATP formation. Their internal enzymes carry out the
oxidative reactions of cellular respiration.

19. b) Ribosomes
• Ribosomes, composed of two subunits containing
ribosomal RNA and proteins, are the sites of protein
synthesis.
• They may be free or attached to membranes.

20. c) Endoplasmic reticulum
• The rough endoplasmic reticulum is a ribosome-studded
membrane system.
• Its cisternae act as sites for protein modification.
• Its external face acts in phospholipid synthesis.
• Vesicles pinched off from the ER transport the proteins to other
cell sites.
• The smooth endoplasmic reticulum
• synthesizes lipid and steroid molecules.
• It also acts in fat metabolism and in drug detoxification.
• In muscle cells, it is a calcium ion depot.

22. d) Golgi apparatus
• The Golgi apparatus is a membranous system close to the
nucleus
• packages protein secretions for export,
• packages enzymes into lysosomes for cellular use
• modifies proteins destined to become part of cellular
membranes.

23. e) Lysosomes
• Lysosomes are membranous sacs of acid hydrolases packaged
by the Golgi apparatus.
• Sites of intracellular digestion, they degrade worn-out
organelles, and tissues that are no longer useful, and release
ionic calcium from bone.

24. f) Peroxisomes
• Peroxisomes are membranous sacs containing oxidase enzymes
that protect the cell from the destructive effects of free radicals
and other toxic substances by converting them first to hydrogen
peroxide and then water.

26. Cytoplasmic organelles
The cytoskeleton includes
• Microfilaments, formed of contractile proteins, are important in
cell motility or movement of cell parts.
• Microtubules organize the cytoskeleton and are important in
intracellular transport. Motility functions involve motor
proteins.
• Intermediate filaments help cells resist mechanical stress and
connect other elements.

28. Centrosome and Centrioles
• microtubules are anchored at one end in a region near the
nucleus called the centrosome.
• The centrosome, contains paired centrioles, small, barrel-
shaped organelles oriented at right angles to each other.
• The centrosome matrix is best known for its generation of
microtubules and its role of organizing the mitotic spindle in
cell division.
• Each centriole consists of a pinwheel array of nine triplets of
microtubules, arranged to form a hollow tube. Centrioles also
form the bases of cilia and flagella.

30. The Nucleus
• Most cells have only one nucleus, but some, including skeletal
muscle cells, bone destruction cells, and some liver cells, are
multinucleate
• Anucleate cells cannot reproduce. RBCs
• The nucleus is 5 µm in diameter
• The nucleus has three recognizable regions or structures:
1. The nuclear envelope (membrane),
2. Nucleoli,
3. Chromatin

31. Nuclear envelope
• The nucleus is bounded by the nuclear envelope, a double
membrane barrier.
• The outer nuclear membrane is continuous with the rough ER of
the cytoplasm and is studded with ribosomes on its external
face.
• The inner nuclear membrane is lined by the nuclear lamina, a
network of lamins that maintains the shape of the nucleus
• Selectively permeable
• The nuclear envelope encloses a jellylike fluid called
nucleoplasm in which other nuclear elements are suspended.
• The nucleoplasm contains dissolved salts, nutrients, and other
essential solutes.

32. Nucleoli
• Nucleoli are the dark-staining spherical bodies found within the
nucleus.
• Typically, there are one or two nucleoli per nucleus.
• Are sites where ribosome subunits are assembled

33. Chromatin
• Chromatin is composed of about 30% DNA, about 60%
globular histone proteins and about 10% RNA chains, newly
formed or forming.
• The fundamental units of chromatin, nucleosomes , consist of
flattened disc-shaped cores or clusters of eight histone proteins
connected like beads on a string by a DNA molecule.
• When a cell is preparing to divide, the chromatin threads coil
and condense enormously to form short, barlike bodies called
chromosomes