Cell Biology
Outline
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Cell
Structure and Organelles
Cell Molecular Components
Functions of cells
Cell Membrane
Smallest and functional unit of life.
The invention of the lens
Robert Hooke (1665): observed a thin slice of cork
(dead plant cells) with a microscope. He described
what he observed as “little boxes” (cells).
Discovery of Cells
• Anton van Leeuwenhoek (1675):
was the first person to observe
living cells.
• Robert Hooke (mid1600s)
– Observed sliver of cork
– Saw “row of empty boxes”
– Coined the term cell

All living things are made of cells

Smallest living unit of structure and
function of all organisms is the cell

All cells arise from preexisting cells
(this principle discarded the idea of
spontaneous generation)
Cell Diversity
Size
Shape
Internal Organization/ Functional
Activity
Cell
DiversitySize
Smallest Cells:
Longest
Cells
Cell Diversity- Size
Biggest Cells:
6 inches long, 5 inches wide, 3 pounds
Ostrich Egg
Cell varies and differ a lot in
size and shape.
ALL the cell have:
•CELL WALL
•CELL
MEMBRANE
•PLASMA
MEMBRANE
Cell Types
• Prokaryotic
• Eukaryotic
Prokaryotic Cells
• First cell type on earth
• Cell type of Bacteria and
Archaea
Prokaryotic Cells
• No membrane bound nucleus.
• Nucleoid = region of DNA
concentration.
• Organelles not bound by membranes.
PROKARYOTIC CELLS
• represented by bacteria, blue-green algae,
mycoplasma and PPLO (Pleuro Pneumonia Like Organisms).
• they are generally smaller in size and multiply more rapidly.
• The four basic shapes of bacteria are
• bacillus (rod like),
• coccus (spherical),
• vibrio (comma shaped)
• Spirillum (spiral).
• Prokaryotes have a cell wall surrounding the cell membrane
• Fluid matrix filling the cell is the cytoplasm.
• no well-defined nucleus. The genetic material is basically ,not
enveloped by a nuclear membrane.
Eukaryotic Cells
• Nucleus bound by
membrane
• Include fungi, protists, plant,
and animal cells
• Possess many organelles
Prokaryotes
Eukaryotes
nucleus?
NO (nucleoid)
YES
membrane-bound
organelles?
NO
YES (Many)
size
1 - 10 m
10 - 50 m
when evolved?
3.5 billion years ago
1.5 billion years ago
cytoplasm?
YES
YES
cell membrane?
YES
YES
cell wall?
Some Do
Plants
ribosomes?
YES
YES
DNA?
Circular
Free Floating
Chromosomes in Nucleus
examples
Bacteria
Plants, Animals, Fungi, and
Protists
NUCLEUS
CYTOSKELETON
RIBOSOMES
ROUGH ER
MITOCHONDRIO
N
CYTOPLASM
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
LYSOSOME
VESICLE
cell wall
The cell wall is only in plant cells.
Its purpose is to shape and protect the cell
like the outside wall of a shopping mall,
which provides shape and protection for it
“ Supporter and Protector”
 The
cell membrane holds and protects
the cell. It controls what substances come
into and out of the cell.
 “Gate of the Cell”
 cell membrane is composed of lipids
that are arranged in a bilayer
• Semi-permeable and fluid-like
• “lipid bilayer
cell membrane is composed of lipids that are arranged in a
bilayer.
the lipids are arranged within the membrane with the polar
head towards the outer sides and the hydrophobic tails towards
the inner part.
The lipid component of the membrane mainly consists of
phosphoglycerides.
The cell membranes also possess protein and carbohydrate.
The ratio of protein and lipid varies considerably in different
cell types.
In human beings, the membrane of the erythrocyte has
approximately 52 per cent protein and 40 per cent lipids.
Made of hydrophobic and hydrophillic components
Protein
Suga
r
Cholesterol
fluid mosaic model
According to this, the quasi-fluid nature of lipid
enables lateral movement of proteins within the
overall bilayer. This ability to move
within the membrane is measured as its fluidity.
Role of plasma membrane is to transport
molecules across it.
The membrane is selectively permeable to some
molecules present on either side of it
Many molecules can move across the membrane without any requirement of
energy and this
is called the passive transport.
Neutral solutes may move across the membrane by the process of simple
diffusion along the concentration gradient, i.e., from higher concentration to
the lower.
As the polar molecules cannot pass through the nonpolar lipid bilayer, they
require a carrier protein of the membrane to facilitate their transport across
the membrane.
A few ions or molecules are transported across the membrane against their
concentration gradient, i.e., from lower to the higher concentration.
Such a transport is an energy dependent process, in which ATP is utilised
and
is called active transport, e.g., Na+/K+ Pump.
CYTOPLASM
ENDOPLASMIC
RETICULUM
GOLGI COMPLEX
 LYSOSOMES AND VACOULES
MITOCHONDRIA
CHLOROPLAST
PERIXOSOMES
Cytoplasm
The cytoplasm is the watery, gel-like material in which cell parts move and
cell activities take place.
Most of the metabolic reaction of the cell takes place.
“Area of Movement”
• presence of a network or reticulum of tiny tubular
structures scattered in the cytoplasmic region
called the endoplasmic reticulum (ER).
ER divides the intracellular space into two distinct
compartments.
• Rough Endoplasmic reticulum(RER)
•
•
Smooth Endoplasmic reticulum(SER)
Ribosomes are attached to surface for
Manufacturing of proteins.
Not all ribosomes are attached to rough ER
RER is frequently observed in the cells actively
involved in protein synthesis and secretion. They are
extensive and continuous with the outer
membrane of the nucleus.
No attached ribosomes
•Has enzymes that help build molecules
•
•Carbohydrates
•Lipids.
The smooth endoplasmic reticulum is the
major site for synthesis of lipid. In animal
cells lipid-like steroidal hormones are
synthesised in SER.
•
Ribosomes are associated with the plasma membrane
of the cell.
They are about 15 nm by 20 nm in size and are made of
two subunits - 50S and 30S units which when present
together form 70S prokaryotic ribosomes.
Ribosomes are the site of protein synthesis.
Several ribosomes may attach to a single mRNA and
form a chain called polyribosomes or polysome.
The ribosomes of a polysome translate the
mRNA into proteins.
Camillo Golgi (1898) first observed densely
stained reticular structures near the
nucleus.
They consist of many flat, disc-shaped sacs or
cisternae of 0.5μm to 1.0μm diameter.

 These are stacked parallel to each other.
 Varied number of cisternae are present in a
Golgi complex.

 The Golgi cisternae are concentrically arranged
near the nucleus.
 With distinct convex cis or the forming face and
concave trans or the maturing face.
Function
Involved in synthesis of plant cell wall
Packaging & shipping station of cell
. Molecules come in vesicles
. Vesicles fuse with Golgi membrane
. Molecules may be modified by Golgi
. Vesicle leaves Golgi apparatus
. Vesicles may combine with plasma membrane to
secrete contents
Contain digestive
enzymes.
Functions
Aid in cell renewal
Break down old cell parts
Digests invaders
LYSOSOMES:
membrane bound vesicular structures
formed by the process of packaging in the
Golgi apparatus.
very rich in almost all types of hydrolytic
enzymes (hydrolases – lipases, proteases,
carbohydrases)
Optimally active at the acidic pH.
These enzymes are capable of digesting
carbohydrates, proteins, lipids and nucleic
acids.
Membrane bound storage sacs
More common in plants than animals
Contents
Water
Food
wastes
Outer
membrane
Inner
membrane
Crista
Matrix
• Have their own DNA
• Bound by double membrane Each mitochondrion is a double
• membrane-bound structure with the outer membrane and the inner
membrane dividing its lumen distinctly into two aqueous
compartments,i.e., the outer compartment and the inner
compartment.
• The inner compartment is called the matrix.
• The outer membrane forms the continuous limiting boundary of the
organelle. The inner membrane forms a number of in foldings
called the cristae .
• Break down fuel molecules (cellular
•Glucose
•Fatty acids
respiration)
• Release energy :The mitochondria produces most of the energy for the
cell, like an electrical system, which supplies electrical energy.
• “Powerhouse of the Cell”
Plastids are found in all plant cells.
They bear some specific pigments, thus imparting
specific colours to the plants.
Based on the type of pigments plastids can be
classified into
chloroplasts, (chlorophyll and carotenoid
pigments)
Chromoplasts(fat soluble carotenoid pigments)
leucoplasts colourless plastids with stored
nutrients
•chloroplasts of the green plants are found in the
mesophyll cells of the leaves.
•lens-shaped, oval, spherical, discoid or even ribbon-like
organelles having variable length(5-10mm) and width (24mm).
•The chloroplasts are also double membrane bound.
• The space limited by the inner membrane of the
chloroplast is called the stroma.
• A number of organised flattened membranous sacs
called the thylakoids, are present in the stroma.
• Thylakoids are arranged in stacks like the piles of coins
called grana
The nucleus regulates and controls cell
activities, acting like the “brain” of the
cell, which regulates and controls
activities of the cell.
“Control Center”
described by Robert Brown
The nucleus has highly extended and elaborate nucleoprotein fibres called
chromatin.
The nuclear matrix or the nucleoplasm contains nucleolus and chromatin. It
is a site for
active ribosomal RNA synthesis.
one or more spherical bodies called nucleoli.
nuclear envelope/nuclear membrane, which consists of two parallel
membranes with a space between (10 to 50 nm) called the perinuclear space
forms a barrier between the materials present inside the nucleus and that of
the cytoplasm. The nuclear membrane protects the nucleus and also allow
substances to pass in and out of the nucleus.
The nuclear pores are the passages through which movement of RNA and
protein
molecules takes place in both directions between the nucleus and the
cytoplasm.
Filaments & fibers
Made of 3 fiber types
Microfilaments
Microtubules
Intermediate filaments
3 functions of Cytoskeleton:
mechanical support
anchor organelles
help to move