2. structure and function of organelles

Structure and function of organelles
07-11-2020

Content
● Introduction
● Cell organelles
● Cell membrane
● Cell wall
● Chloroplast
● Cytoplasm
● Cytoskeleton
● Endoplasmic reticulum (ER)

Content
● Endosomes
● Golgi apparatus
● Intermediate filaments
● Lysozyme
● Lysosomes
● Microfilaments
● Microtubules

Content
● Mitochondria
● Nucleus
● Peroxisomes
● Plasmodesmeta
● Ribosomes

Content
● Storage granules
● Vacuole
● Vesicles

• Robert Hooke discovered the cell in 1665. Robert Hooke observed a
piece of bottle cork under a compound microscope and noticed
minuscule structures that reminded him of small rooms. Consequently,
he named these “rooms” as cells. However, his compound microscope
had limited magnification, and hence, he could not see any details in
the structure. Because of this limitation, Hooke concluded that these
were non-living entities.
Introduction

• Ultrastructure (or ultra-structure) is the architecture of cells and
biomaterials that is visible at higher magnifications than found on a
standard optical light microscope.
• A cell is defined as the smallest, basic unit of life that is responsible
for all of life’s processes.”
• Cells are the structural, functional, and biological units of all living
beings. A cell can replicate itself independently. Hence, they are
known as the building blocks of life.
Introduction

Characteristics of Cells:-
• Cells provide structure and support to the body of an organism.
• The cell interior is organised into different individual organelles
surrounded by a separate membrane.
• The nucleus(major organelle) holds genetic information necessary for
reproduction and cell growth.
• Every cell has one nucleus and membrane-bound organelles in the
cytoplasm.
Introduction

• Cell organelle is a specialized entity present inside a particular type of
cell that performs a specific function.
• There are various cell organelles, out if which, some are common in
most types of cells like cell membranes, nucleus, and cytoplasm.
However, some organelles are specific to one particular type of cell-
like plastids and cell walls in plant cells.
Characteristics of cells

• A plasma membrane is composed of lipids and proteins where the
composition might fluctuate based on fluidity, external environment,
and the different stages of development of the cell.
• Structure
• Structurally, it consists of a phospholipid bilayer along with two types
of proteins viz. embedded proteins and peripheral proteins that
function in providing shape and allowing the movement of particles in
and out of the cell.
Cell membrane

Structure
• The most abundant lipid which is present in the cell membrane is a
phospholipid which contains a polar head group attached to two
hydrophobic fatty acid tails.
• The embedded proteins act as channels for the transfer of particles
across the cell with some proteins acting as receptors for the binding
of various components.
• The peripheral proteins function as to provide fluidity as well as
mechanical support to the structure of the cell.
•
Cell membrane

Functions
• The cell membrane provides mechanical support that facilities the
shape of the cell while enclosing the cell and its components from the
external environment.
• It regulates what can be allowed to enter and exit the cell through
channels, acting as a semi-permeable membrane, which facilities the
exchange of essential compounds required for the survival of the cell.
• It generates and distributes signals in and outside of the cell for the
proper functioning of the cell and all the organelles.
Cell Membrane

• It allows the interaction between cells required during tissue formation and cell
fusion.
•
Cell Membrane

• The cell wall is the most prominent part of the plant’s cell structure. It is made up
of cellulose, hemicellulose and pectin.
• The cell wall is present exclusively in plant cells. It protects the plasma membrane
and other cellular components. The cell wall is also the outermost layer of plant
cells.
• It is a rigid and stiff structure surrounding the cell membrane.
• It provides shape and support to the cells and protects them from mechanical
shocks and injuries.
Cell Wall

• An additional non-living layer present outside the cell membrane in
some cells that provides structure, protection, and filtering mechanism
to the cell is the cell wall.
Structure
• In a plant cell, the cell wall is made up of cellulose, hemicellulose, and
proteins while in a fungal cell, it is composed of chitin.
• A cell wall is multilayered with a middle lamina, a primary cell wall,
and a secondary cell wall.
Cell Wall

• Middle lamina contains polysaccharides that provide adhesion and
allows binding of the cells to one another.
• After middle lamina is the primary cell wall which is composed of
cellulose. The last layer, which is not always present, is the secondary
cell wall made of cellulose and hemicellulose.
Cell Wall

Functions
• The critical function of the cell wall is protecting and maintaining the
shape of the cell. It also helps the cell withstand the turgor pressure of
the cell.
• It initiates cell division by providing signals to the cell and allows the
passage of some molecules into the cell while blocking others.
Cell Wall

• Chloroplast:-Chloroplasts are the primary organelles for
photosynthesis. It contains the pigment chlorophyll
• A chloroplast is a type of plastic that is involved in photosynthesis in
plants and algae.
• Chloroplast contains an essential pigment called chlorophyll necessary
to trap sunlight for the production of glucose.
• Structure
• It is a double-membraned structure with its own DNA which is
inherited from the previous chloroplast.
Chloroplast

• These are usually lens-shaped with shape and number varying
according to cells. They have an outer membrane, an inner membrane,
and a thylakoid membrane that enclosed the gel-like matric called the
stroma.
• The outer and inner membrane is porous and allows transport of
materials while the stroma contains DNA, chloroplast ribosomes,
proteins, and starch granules.
Chloroplast

Functions
• The chloroplast is the primary center for light-dependent and light-
independent reactions during photosynthesis.
• Different proteins present in chlorophyll are involved in the regulation
of photorespiration.
Chloroplast

Cytoplasm
• Cytoplasm refers to everything present inside the cell except the
nucleus.
• Structure
• The cytoplasm consists of a cytosol; a gel-like substance that contains
other matter; cell organelles; smaller cell-like bodies bound by
separate membranes; and cytoplasmic inclusions; insoluble molecules
that store energy and are not surrounded by any layer.
• The cytoplasm is colorless and has about 80% water along with
various nutrients required for the cell.

Cytoplasm
• It is known to have the properties of both viscous matters as well as
elastic matter. Under its elasticity, cytoplasm helps in the movement of
materials inside the cell by a process termed cytoplasmic streaming.
•

Cytoplasm
Functions
• Most of the vital cellular and enzymatic reactions like cellular
respiration and translation of mRNA into proteins occur in the
cytoplasm.
• It acts as a buffer and protects genetic materials as well as other
organelles from damage due to collision or change in the pH of the
cytosol.
• The process called cytoplasmic streaming helps in the distribution of
various nutrients and facilitates the movement of cell organelles within
the cell.

• A number of fibrous structures are present in the cytosol that helps
give shape to the cell while supporting cellular transport.
Structure
• Around three different classes of fibers make up the cytoskeleton
which is: microtubules, microfilaments, and intermediate filaments.
• These are separated based on a protein present in them.
Cytoskeleton

Functions
• The critical function of the cytoskeleton is to provide shape and
mechanical support to the cell against deformation.
• It allows the expansion and contraction of the cell which assists in the
movement of the cell.
• It is also involved in intracellular and extracellular transport of
materials.
Cytoskeleton

• Endoplasmic Reticulum (ER) is present as an interconnection of
tubules that are connected to the nuclear membrane in eukaryotic cells.
• There are two types of ER based on the presence or absence of
ribosomes on them:
• Rough ER (RER) with ribosomes attached on the cytosolic face of
Endoplasmic Reticulum and thus is involved in protein synthesis
• Smooth ER (SER)which lacks ribosomes and has a function during lipid
synthesis.
Endoplasmic Reticulum (ER)

Structure
• Endoplasmic Reticulum exists in three forms viz. cisternae, vesicles,
and tubules.
• Cisternae are sac-like flattened, unbranched structures that remain
stacked one on top of another.
• Vesicles are spherical structures that carry proteins throughout the cell.
• Tubules are tubular branched structures forming a connection between
cisternae and vesicles.

Functions
• ER contains many of the enzymes required for several metabolic
processes, and the surface of the ER is essential for other operations
like diffusion, osmosis, and active transport.
• One of the crucial functions of ER is the synthesis of lipids like
cholesterol and steroids.
• Rough ER allows for the modification of polypeptides emerging out of
the ribosomes to prepare secondary and tertiary structures of the
protein.

• ER also synthesizes various membrane proteins and has a crucial role
in preparing the nuclear envelope after cell division.

• Endosomes are membrane-bound compartments within a cell
originating from the Golgi network
Structure
• There are different types of endosomes based on morphology and the
time it takes for the endocytosed materials to reach them.
• The early endosomes are made with the tubular-vesicular network
while the late endosomes lack tubules but contain many close-packed
intraluminal vesicles. The recycling endosomes are found with
microtubules and are mainly composed of tubular structures.
Endosomes

Functions
• Endosomes allow the sorting and delivery of internalized materials
from the cell surface and transport of materials to the Golgi or the
lysosomes.
Endosomes

• The Golgi Apparatus is the cell organelle mostly present in eukaryotic
cells which is responsible for the packaging of macromolecules into
vesicles so that they can be sent out to their site of action.
Structure
• The structure of the Golgi Complex is pleomorphic; however, it
typically exists in three forms, i.e. cisternae, vesicles, and tubules.
• The cisternae, which is the smallest unit of Golgi Complex, has a
flattened sac-like structure which is arranged in bundles in a parallel
fashion.
Golgi apparatus

• Tubules are present as tubular and branched structures that radiate
from the cisternae and are fenestrated at the periphery.
• Vesicles are spherical bodies that are divided into three groups as
transitional vesicles, secretory vesicles, and clathrin-coated vesicles.
Functions
• Golgi Complex has an essential purpose of directing proteins and
lipids to their destination and thus, act as the “traffic police” of the
cell.
Golgi apparatus

• They are involved in the exocytosis of various products and proteins
like zymogen, mucus, lactoprotein, and parts of the thyroid hormone.
• Golgi Complex is involved in the synthesis of other cell organelles
like a cell membrane, lysozymes, among others.
• They are also involved in the sulfation of various molecules.
Golgi apparatus

• The third class of filament that makes up the cytoskeleton are the
intermediate filaments.
• They are designated at intermediate filaments because of the
intermediate diameter of the filaments as compared to microfilaments
and myosin proteins.
Structure
• Intermediate filaments contain a family of related proteins.
• The individual filaments are coiled around each other in a helical
structure called coiled-coil structure.
Intermediate filaments

Functions
• Intermediate filaments contribute to the structural integrity of a cell
while playing a crucial role in holding tissues of various organs like
the skin.
•
Intermediate filaments

• Lysozymes are membrane-bound organelles that occur in the
cytoplasm of animal cells.
• These organelles contain an array of hydrolytic enzymes required for
the degradation of various macromolecules.
• There are two types of lysozymes:
• Primary lysosome containing hydrolytic enzymes like lipases, amylases,
proteases, and nucleases.
• Secondary lysozyme formed by the fusion of primary lysozymes
containing engulfed molecules or organelles.
Lysozyme

• Structure
• The shape of lysozymes is irregular or pleomorphic; however, mostly,
they are found in the spherical or granular structure.
• Lysozymes are surrounded by a lysosomal membrane that contains the
enzymes within the lysosome and protects the cytosol with the rest of
the cell from the harmful action of the enzymes.
Lysozyme

Functions
• These organelles are responsible for intracellular digestion where the
larger macromolecules are degraded into smaller molecules with the
help of enzymes present in them.
• Lysozymes also perform the critical function of the autolysis of
unwanted organelles within the cytoplasm.
• Besides these, the lysosome is involved in various cellular processes,
including secretion, plasma membrane repair, cell signaling, and
energy metabolism.
Lysozyme

• Mitochondria are double membrane-bound cell organelles responsible
for the supply and storage of energy for the cell.
• The oxidation of various substrates in the cell to release energy in the
form of ATP (Adenosine Triphosphate) is the primary purpose of
mitochondria.
Structure
• A mitochondrion contains two membranes with the outer layer being
smooth while the inner layer is marked with folding and finger-like
structures called cristae.
Mitochondria

• The inner mitochondrial membrane contains various enzymes,
coenzymes, and components of multiple cycles along with pores for
the transport of substrates, ATP, and phosphate molecules.
• Within the membranes is a matrix that contains various enzymes of
metabolic processes like Kreb’s cycle.
• In addition to these enzymes, mitochondria are also home to single or
double-stranded DNA called mtDNA that is capable of producing 10%
of the proteins present in the mitochondria.
Mitochondria

Functions
• The primary function of mitochondria is the synthesis of energy in the
form of ATP required for the proper functioning of all the cell
organelles.
• Mitochondria also help in balancing the amount of Ca+ ions within the
cell and assists the process of apoptosis.
• Different segments of hormones and components of blood are built
within mitochondria.
• Mitochondria in the liver have the ability to detoxify ammonia.
Mitochondria

• The nucleus is a double membrane-bound structure responsible for
controlling all cellular activities as well as a center for genetic
materials, and it’s transferring.
• It is one of the large cell organelles occupying 10% of total space in
the cell.
• It is often termed the “brain of the cell” as it provides commands for
the proper functioning of other cell organelles.
• A nucleus is clearly defined in the case of a eukaryotic cell; however,
it is absent in prokaryotic organisms with the genetic material
distributed in the cytoplasm.
•
Nucleus

• Structure
• Structurally, the nucleus consists of a nuclear envelope, chromatin,
and nucleolus.
• The nuclear envelope is similar to the cell membrane in structure and
composition. It has pores that allow the movement of proteins and
RNA in and outside the nucleus. It enables the interaction with other
cell organelles while keeping nucleoplasm and chromatin within the
envelope.
Nucleus

• Peroxisomes are oxidative membrane-bound organelles found in the
cytoplasm of all eukaryotes.
• The name is accredited due to their hydrogen peroxide generating and
removing activities.
• Structure
• Peroxisome consists of a single membrane and granular matrix
scattered in the cytoplasm.
• They exist either in the form of interconnected tubules or as individual
peroxisomes.
Peroxisome

• The compartments within every peroxisome allow the creation of
optimized conditions for different metabolic activities.
• They consist of several types of enzymes with major groups being
urate oxidase, D-amino acid oxidase, and catalase.
Peroxisomes

Functions
• Peroxisomes are involved in the production and elimination of
hydrogen peroxide during biochemical processes.
• Oxidation of fatty acids takes place within peroxisomes.
• Additionally, peroxisomes are also involved in the synthesis of lipid-
like cholesterol and plasmalogens.
Peroxisomes

• Plasmodesmata are tiny passages or channels that allow the transfer of
material and communication between different cells.
• Structure
• There are 103 – 105 number of plasmodesmata connecting two
adjacent cells with 50-60 nm in diameter.
• A plasmodesma has three layers:
• The plasma membrane is continuous with the plasma membrane of the
cell and has the same phospholipid bilayer.
Plasmodesmeta

• The cytoplasmic sleeve that is continuous with the cytosol that allows
the exchange of materials between two cells.
• Desmotubule which is a part of the endoplasmic reticulum that provides
a network between two cells and allows the transport of some molecules.
Plasmodesmeta

Functions
• Plasmodesmata are the primary site for the communication of two
cells. It allows the transfer of molecules like proteins, RNA, and viral
genomes.
Plasmodesmeta

• Plastids are double membrane-bound structures present in plants and
other eukaryotes involved in the synthesis and storage of food.
Structure
• Plastids are usually oval or spherical with an outer and an inner
membrane between which lies the intermembrane space.
• The inner membrane enclosed a matrix called stroma that contains
small structures called grana.
• Each granum consists of several sac-like thylakoids piled one on the
other and connected by stroma lamellae.
Plastids

• Plastids contain DNA and RNA that allows it to synthesize necessary
proteins for different processes.
Plastids

Functions
• Chloroplasts are the center for many metabolic activities, including
photosynthesis as it contains enzymes and other components required
for it.
• They are also involved in the storage of food, primarily starch.
Plastids

• Ribosomes are ribonucleoprotein containing equal parts RNA and
proteins along with an array of other essential components required for
protein synthesis.
• In prokaryotes, they exist freely while in eukaryotes, they are found
either free or attached to the endoplasmic reticulum.
• Structure
• The ribonucleoprotein consists of two subunits.
• In the case of prokaryotic cells, the ribosomes are of the 70S with the
larger subunit of 50S and the smaller one of 30S.
Ribosomes

• Eukaryotic cells have 80S ribosomes with 60S larger subunit and 40S
smaller subunit.
• Ribosomes are short-lived as after the protein synthesis, the subunits
split up and can be either reused or remain broken up.
•
Ribosomes

Functions
• Ribosomes are the site of biological protein synthesis in all living
organisms.
• They arrange the amino acids in the order indicated by tRNA and
assist in protein synthesis.
Ribosomes

• Storage granules are membrane-bound organelles, also called
zymogen granules storing cell’s energy reserve and other metabolites.
Structure
• These granules are surrounded by a lipid bilayer and are composed
mostly of phosphorus and oxygen.
• The components inside these storage granules depend on their location
in the body with some even containing degradative enzymes yet to
participate in digestive activities.
Storage granules

Functions
• Many prokaryotes and eukaryotes store nutrients and reserves in the
form of storage granules in the cytoplasm.
• Sulfur granules are characteristic of prokaryotes that utilize hydrogen
sulfide as a source of energy.
Storage granules

• Vacuoles are membrane-bound structures varying in size in cells of
different organisms.
Structure
• The vacuole is surrounded by a membrane called tonoplast, which
encloses fluid containing inorganic materials like water and organic
materials like nutrients and even enzymes.
• These are formed by the fusion of various vesicles, so vacuoles are
very similar to vesicles in structure.
Vacuole

Functions
• Vacuoles act as a storage for nutrients as well as waste materials to
protect the cell for toxicity.
• They have an essential function of homeostasis as it allows the balance
of pH of the cell by influx and outflow of H+ ions to the cytoplasm.
• Vacuoles contain enzymes that play an important role in different
metabolic processes.
Vacuole

• Vesicles are structures present inside the cell which are either formed
naturally during processes like exocytosis, endocytosis or transport of
materials throughout the cell, or they might form artificially, which are
called liposomes.
• There are different types of vesicles like vacuoles, secretory and
transport vesicles based on their function
• Structure
• A vesicle is a structure containing liquid or cytosol which is enclosed
by a lipid bilayer.
Vesicles

• The outer layer enclosing the liquid is called a lamellar phase which is
similar to the plasma membrane. One end of the lipid bilayer it
hydrophobic whereas the other end is hydrophilic.
Vesicles

Vesicles
Figure: A liposome (left) and dendrimersome. The blue parts of their molecules are
hydrophilic, the green parts are hydrophobic.

• Functions
• Vesicles facilitate the storage and transport of materials in and outside
the cell. It even allows the exchange of molecules between two cells.
• Because vesicles are enclosed inside a lipid bilayer, vesicles also
function in metabolism and enzyme storage.
• They allow temporary storage of food and also control the buoyancy
of the cell.
Vesicles

Ultrastructure of Eukaryotic cell

Ultrastructure of Prokaryotic cell

• Prokaryotic cells are single-celled microorganisms known to be the
earliest on earth. Prokaryotes include Bacteria and Archaea. The
photosynthetic prokaryotes include cyanobacteria that perform
photosynthesis.
• A prokaryotic cell consists of a single membrane and therefore, all the
reactions occur within the cytoplasm. They can be free-living or can
be found within the gut of other organisms.
Prokaryotic Cell

• Prokaryotic cells have different characteristic features. The
characteristics of the prokaryotic cells are mentioned below.
• They lack a nuclear membrane.
• Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent.
• The genetic material is present on a single chromosome.
• The histone proteins, the important constituents of eukaryotic
chromosomes, are lacking in them.
Characteristics of Prokaryotic Cell

• The cell wall is made up of carbohydrates and amino acids.
• The plasma membrane acts as the mitochondrial membrane carrying
respiratory enzymes.
• They divide asexually by binary fission. The sexual mode of
reproduction involves recombination.
Characteristics of Prokaryotic Cell

• A prokaryotic cell does not have a nuclear membrane. However,
the genetic material is present in a region in the cytoplasm known as
the nucleoid. They may be spherical, rod-shaped, or spiral. A
prokaryotic cell structure is as follows:
• Capsule–It is an outer protective covering found in the bacterial cells,
in addition to the cell wall. It helps in moisture retention, protects the
cell when engulfed, and helps in the attachment of cells to nutrients
and surfaces.
Prokaryotic Cell Structure

• Cell Wall– It is the outermost layer of the cell which gives shape to
the cell.
• Cytoplasm– The cytoplasm is mainly composed of enzymes, salts,
cell organelles and is a gel-like component.
• Cell Membrane– This layer surrounds the cytoplasm and regulates
the entry and exit of substances in the cells.
• Pili– These are hair-like outgrowths that attach to the surface of other
bacterial cells.

• Flagella– These are long structures in the form of a whip, that help in the
locomotion of a cell.
• Ribosomes– These are involved in protein synthesis.
• Plasmids– Plasmids are non-chromosomal DNA structures. These are not
involved in reproduction.
• Nucleoid Region– It is the region in the cytoplasm where the genetic
material is present.
• A prokaryotic cell lacks certain organelles like mitochondria,
endoplasmic reticulum, and Golgi bodies.

• The prokaryotic cells have four main components:
• Plasma Membrane- It is an outer protective covering of phospholipid
molecules which separates the cell from the surrounding environment.
• Cytoplasm- It is a jelly-like substance present inside the cell. All the
cell organelles are suspended in it.
• DNA- It is the genetic material of the cell. All the prokaryotes possess
a circular DNA. It directs what proteins the cell creates. It also
regulates the actions of the cell.
Components of Prokaryotic Cells

• Ribosomes- Protein synthesis occurs here.
• Some prokaryotic cells possess cilia and flagella which helps in
locomotion.
Components of Prokaryotic Cells

Compare prokaryote and eukaryote cells

Similarities:-
• Both have a cell membrane
• Both contain ribosomes
• Both have DNA and cytoplasm

• Differences:

Difference between plant and animal cell

Plants
• The cell wall in plants is made from cellulose secreted from the cell,
which serves the following functions:
• Provides support and mechanical strength for the cell (maintains cell
shape)
• Prevents excessive water uptake by maintaining a stable, turgid state
• Serves as a barrier against infection by pathogens

Animals
• The extracellular matrix (ECM) is made from glycoproteins secreted
from the cell, which serve the following functions:
• Provides support and anchorage for cells
• Segregates tissues from one another
• Regulates intercellular communication by sequestering growth factors

• http://www.old-ib.bioninja.com.au/standard-level/topic-2-cells/23-
eukaryotic-cells.html
• http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/golgi.html#c1
• https://byjus.com/biology/prokaryotic-cells/
References

• https://microbenotes.com/cell-organelles/
Reference

2. structure and function of organelles

More Related Content

What's hot (20)

Similar to 2. structure and function of organelles (20)

Recently uploaded (20)

2. structure and function of organelles