1. The Cell
Basic structural and functional unit of life.
Structural features of a cell
A cell has 3 main parts:
1. PLASMA MEMBRANE
2. CYTOPLASM &
3. NUCLEUS
Himanshu Aggarwal, KSOP
2. The Plasma Membrane
It is the envelope (cover for the cell),
Structure:
Comprised of lipid bilayer
Acts as a selectively permeable barrier to the
external environment of the cell.
Helps in communication with other neighboring
cells. Himanshu Aggarwal, KSOP
3. The Cytoplasm
Consists of all the cellular contents between the plasma
membrane and the nucleus.
Divided into Cytosol and Organelles
Cytosol = fluid portion of cytoplasm and suspended particles
viz. cellular proteins.
Organelles
Several types of organelles are there having a characteristic
shape and specific functions.
Eg: cytoskeleton, ribosomes, endoplasmic reticulum, Golgi
complex, lysosomes, peroxisomes, and mitochondria.
Himanshu Aggarwal, KSOP
5. The Nucleus
The nucleus is a large organelle that houses
most of a cell’s DNA.
Nucleus has chromosomes that contain DNA
associated with several proteins, contains
thousands of hereditary units called genes that
control most aspects of cellular structure and
function.
Himanshu Aggarwal, KSOP
6. The Plasma Membrane
The lipid bilayer, two back-to-back layers made up of
three types of lipid molecules
1. Phospholipids ( lipids + phosphorus)
2. Cholesterol (a steroid with an attached-OH)
3. Glycolipids ( lipids + carbohydrates)
The layers display an amphipathic nature (dual
nature: hydrophilic and lipophilic both)
Himanshu Aggarwal, KSOP
7. Membrane Proteins
Classified on the basis how they are embedded in
the membrane.
1. Integral : These proteins are firmly attached to
the lipid bilayer
2. Peripheral: these proteins are not deeply
inserted into the membrane, they are in contact
with the membrane polar heads or attached to
the integral membrane proteins.
Himanshu Aggarwal, KSOP
8. Functions of Membrane Proteins
Ion channels
Carrier molecules (transporter proteins)
Enzymes
Receptors
Cell identity markers e.g. MHC molecules
Linker molecules
Himanshu Aggarwal, KSOP
10. Functions of membrane proteins
Ion channels
Allows specific ion to move through
water-filled pore. Most plasma
membranes include specific
channels for several common ions
Himanshu Aggarwal, KSOP
11. Carrier proteins
Transports specific substances
across membrane by changing
shape.
For example, amino acids, needed
to synthesize new proteins, enter
body cells via carriers. Carrier
proteins are also known as
transporters
Himanshu Aggarwal, KSOP
12. Receptors
Recognizes specific ligand and
alters cell's function in some way.
For example, antidiuretic
hormone binds to receptors in the
kidneys and changes the water
permeability of certain plasma
membranes.
Himanshu Aggarwal, KSOP
13. Enzymes
Catalyzes reaction inside or outside
cell (depending on which direction
the active site faces).
For example, lactase in small
intestine splits the disaccharide
lactose in the milk
Himanshu Aggarwal, KSOP
14. Linkers
Anchors filaments inside and
outside the plasma
membrane, providing
structural stability and shape
for the cell.
May also participate in
movement of the cell or link
two cells together.
Himanshu Aggarwal, KSOP
15. Cell Identity Markers
Cell identity marker
(glycoprotein)
Distinguishes your cells from
anyone else's (unless you are
an identical twin).
An important class of such
markers are the major
histocompatibility
(MHC) proteins.
Himanshu Aggarwal, KSOP
16. Cytoplasm
Cytosol= Cytoplasm-Organelles
Cytoskeleton: a network of protein filaments that
provide structural support to the cell as well as
organelles.
Three types of cytoskeletal fibers (based on their diameters)
1) Microfilaments
2) Intermediate fibersHimanshu Aggarwal, KSOP
17. Microfilaments (Thinnest)
•Made up of actin & myosin
proteins
•Present mostly at the edge of the
cell
Functions:
1) Movement
2) Mechanical support
• Provide support for the microvilli
• They also attach the integral
proteins with the cytoskeleton
Himanshu Aggarwal, KSOP
18. Intermediate Filaments
Thicker than
microfilaments but thinner
than microtubules
They are formed by proteins
that are very strong.
They are found in the cells
that are subjected to
mechanical stress
Himanshu Aggarwal, KSOP
19. Microtubules (Thickest)
•They are largest, long and
unbranched hollow tubes
formed by the tubulin protein.
•Help in determining the shape
of the cell.
•They also help in movement of
cell organelles such as vesicles
etc.
• Originate from the
centrosome
Himanshu Aggarwal, KSOP
21. Ribosome
Site of protein synthesis
Made up of 2 subunits that combine together
to synthesize proteins
Some ribosomes are studded on the surface of
an extensively folded membrane endoplasmic
reticulum
Free ribosomes in the cytoplasm make
proteins utilized by the organelles in the
Himanshu Aggarwal, KSOP
22. Endoplasmic Reticulum
It is a network of highly folded membranes.
It extends from the nuclear membrane to the
whole cytoplasm.
Types of ER
Smooth ER
Rough ER (Studded with ribosomes)
Himanshu Aggarwal, KSOP
24. Rough ER
It is continuous with the nuclear membrane
Outer surface is studded with ribosomes that
form proteins
Sometimes enzymes attach a protein to a
carbohydrate that forms glycoprotein
rER forms membrane proteins, secretory
proteins and organellar proteins
Himanshu Aggarwal, KSOP
25. Smooth ER
Start from the rER to form a network of the
membranous tubules.
Do not have ribosomes on their surfaces , but
has enzymes that produce hormones, steroids
such as testosterone etc.
Also detoxify harmful chemicals
It releases calcium in the process of muscle
contraction. Himanshu Aggarwal, KSOP
26. Golgi Bodies
Most of the proteins synthesized by
ribosomes attached to rough ER are
ultimately transported to other regions of
the cell.
Functions
1. Modifies, sorts, packages, and transports
proteins received from the rough ER.
2. Forms secretory vesicles that discharge
processed proteins via exocytosis into
extracellular fluid; forms membrane
vesicles that send new molecules to the
plasma membrane; forms transport vesicles
Himanshu Aggarwal, KSOP
27. Lysosome
Functions
1. Digest substances that enter a cell via
endocytosis and transport final products of
digestion into cytosol.
2. Carry out autophagy, the digestion of worn-
out organelles.
3. Carry out autolysis, the digestion of entire
cell.
Himanshu Aggarwal, KSOP
28. Mitochondria
Mitochondrial membrane contains a
series of folds called cristae. The central
fluid-filled cavity of a mitochondrion,
enclosed by the inner mitochondrial
membrane, is the matrix.
Cristae provide high surface area for
oxidative process.
It also plays an important role in early
apoptosis. Himanshu Aggarwal, KSOP
