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Cell Structure
& Function
Cells Make up Plants
Cells make up all living things.
What is the definition of a cell?
The basic unit of life.
A cell is the smallest unit that is
capable of performing life functions.
Can you think of reasons
why cells need nutrition
and a good environment?
Cells produce tissues
Tissues produce organs
Organs produce organ systems
Organs systems produce organisms
Cellular Organization
 Tissue
– group of cells functioning
together.
 Organ – group of tissues
functioning together.
 Organ System – group of organs
functioning together.
 Organism – group of organ
systems functioning together.
CELL STRUCTURE
 The
modern theory of cellular
organization states that:
1. All living organisms are composed of cells
2. All new cells are derived from other cells.
3. Cells contain the hereditary material of
an organism which is passed from parent
to daughter cells.
4. All metabolic processes take place within
cells.
CELL STRUCTURE


There are two basic
types of cells
known:
Prokaryotic


Bacteria
Archaea
Eukaryotic
Unicellular
Protists
Multi-cellular
Fungi
Plants
Animals
Prokaryote

Characteristics
 Old Greek for “Before nut (kernel)”
 Unicellular
 Lacks a membrane bound nucleus
 Lacks membrane bound organelles
 Has a cell membrane (cell wall)
 Has ribosomes (protein production)
 Circular DNA
Eukaryote
 Has
several internal structures
(organelles).
 True nucleus.
 Either unicellular or multi - cellular.
unicellular example : Protists
multi -cellular examples:
plants and animals
All cells have several basic features
in common
They are all bounded by a membrane,
called plasma membrane (cell
membrane).
 All cells have chromosomes carrying
genes made of DNA.
 And all cells contain ribosomes, tiny
structures that make proteins according to
instructions from the genes.

Cell Organelles
Cell Organelles
Organelle= “little
organ”
 Found only inside
eukaryotic cells
 All the stuff in
between the
organelles is
cytosol
 Everything in a cell
except the nucleus
is cytoplasm

Animal Cell
Cytoplasm
Nucleolus
Nucleus
Ribosomes
Cell Membrane
Mitochondria
Rough Endoplasmic
Reticulum
Golgi Bodies
Smooth Endoplasmic
Reticulum
Plant Cell
Cytoplasm
Vacuole
Smooth ER
Ribosomes
Chloroplasts
Cell Membrane
Cell Wall
Nucleolus
Golgi Bodies
Nucleus
Mitochondria
Rough ER


Plants and animals cells have many of
the same type of structures. These
structures perform the same type of
activities.
Plants and animals cells have some
structures that are not the same. These
structures perform different activities,
but necessary to it’s particular cell.
PROKARYOTIC CELLS
Structure of a
prokaryotic cell
 Prokaryotic cells (pro‘before’, karyo –
‘nucleus’) were
probably the first
forms of life on earth.
 DNA, is not
enclosed within a
nuclear membrane.
This absence of a true
nucleus
Structure prokaryotic cell




The DNA of bacteria is a single,
large, circular molecule.
No nuclear envelope so the DNA
lies free in the cytoplasm.
The cytoplasm contains
ribosomes. These are made of
ribosomal RNA and protein and
are the sites of protein synthesis.
The ribosomes is smaller and
different from eukaryotes.
Cont.. Prokaryotic cell



Many bacteria have a thick
layer of jelly-like material
surrounding them called a
capsule.
The capsule is made of
polysaccharides which
absorb water to form a
slimy material.
The capsule protects the
bacterium from attack by
viruses, and from
antibodies.
Cont.. Prokaryotic cell



Next to the capsule is the cell wall, which gives
support and protection to the cell and is made of a
variety of polysaccharides -large amounts of
substances known as peptidoglycans, which are
made up of molecules- peptides and sugars.
Cell walls are very important to bacteria. They stop
them from bursting when they absorb water and
help to protect them from invasion by viruses. If
you can damage the cell wall you can kill the
bacterium.
Beneath the cell wall is a cell surface membrane. It
is being made up of a phospholipid bilayer in
which protein molecules float.
Cont.. Prokaryotic cell


In addition to capsules,
some prokaryotes have
surface projections. Short
projections called pili
help attack prokaryotes
to surfaces.
Longer projection called
flagella, which is used
for movement.
Comparison of prokaryotic and
eukaryotic cells
Comparison of prokaryotic and
eukaryotic cells
Prokaryotic cells
Eukaryotic cells
No distinct nucleus
A distinct, membrane –bound
nucleus
No chromosomes – circular
strands of DNA
Chromosomes present on which
DNA is located
No membrane – bound
organelles such as chloroplasts
and mitochondria
Chloroplasts and mitochondria
may be present
Ribosomes are smaller
Ribosomes are larger
No mitosis or meiosis occurs
Mitosis and /or meiosis occurs
EUKARYOTIC
The structures & organelles of eukaryotic cells
can be organized into four basic functional
groups
1.
2.
3.
4.
The nucleus, ribosomes, endoplasmic reticulum
and golgi apparatus function in manufacturing
Organelles involved in breakdown or hydrolysis of
molecules include lysosomes, vacuoles and
peroxisomes.
Mitochondria in all cells and chloroplasts in plant
cells are involved in energy processing.
Structural support, movement, and communication
among cells are the functions of components of the
cytoskeleton, plasma membrane and cell wall.
Cell Membrane
All cells, the cell membrane forms a
boundary between the living cell and its
surroundings
 Boundary of the cell
 Made of a phospholipid bilayer

What’s a Phospholipid?

It’s a pair of fatty acid chains and a
phosphate group attached to a glycerol
backbone.
 Polar
(water-soluble) heads face
out and the nonpolar fatty acids
hang inside.
Cont … Cell membranes
Interspersed amongst the phospholipids
molecules are cholesterol molecules.

Floating amongst
the phospholipids
and cholesterol
molecules are
many globular
protein molecules,
many of which
span from one
side to the other.
Cont … Cell membranes


These proteins tend to be
arranged with hydrophilic
parts of their chains on the
outer surfaces of the
membrane, and
hydrophobic parts within
the membrane amongst the
hydrophobic tails of the
lipids.
These proteins act as pores
or transporters, allowing
substances to pass from
one side of the membrane
to the other.
Cont … Cell membranes


The protein molecules
and the lipid molecules
have short carbohydrate
chains attached to them.
These molecules are
called glycoproteins
and glycolipids.
The carbohydrate chains
are all on the outer
surface of the
membrane.
Glycolipids and glycoproteins help to stabilise membrane
structure by forming hydrogen bonds with water molecules
outside the membrane.
Why this structure is called a fluid
mosaic?

All of these molecules are in constant
motion, vibrating and bumping into each
other and changing place within layer. So
the membrane behaves rather like a fluidalthough it does not flow away into its
surroundings! The mosaic part of the
name refers to the mosaic pattern protein
molecules.
Nucleus
Control center of the
cell
 Contains DNA
(deoxyribonucleic
acid)
 Surrounded by a
double membrane
 Usually the easiest
organelle to see
under a microscope
 Usually one per cell

Nucleus is the cells’ genetic control
center



Most of the cell’s DNA is
located inside the nucleus.
The DNA molecules make
up the genes, which
contain the chemically
coded instructions for
producing most of the
protein needed by the cell.
DNA is contained in
chromosomes. A
chromosome is made of a
DNA molecule.
The cell nucleus contains DNA
DNA is associated with proteins, forming a
complex known as chromatin, which
appears as a network of granules and
strands in cells that are not dividing.
 Although chromatin appears disorganized,
it is not. Because DNA molecules are
extremely long and thin, they must be
packed inside the nucleus in a regular
fashion.
 In dividing cells, the chromatin condenses
and become visible as distinct threadlike
structures called chromosomes.


Enclosing the nucleus
is a nuclear
envelope, a double
membrane

The outer nuclear
envelop connects
with the cell’s
network of
membranes called
endoplasmic
reticulum
Nuclear envelope


These two membranes
have many gaps in them
which are called
nuclear pores. The
gaps are relatively large
much.
They allow partially
assembled ribosomes
from the nucleolus to
pass through, as well as
messenger RNA on its
way out of the nucleus
and enzymes such as
DNA polymerase on
their way in.
Within the nucleus there is a darkly
staining region called the nucleolus.


It, is the site where a special
type of RNA (ribonuclei
acid) called ribosomal RNA
(rRNA) is synthesized
according to instructions in
the DNA.
Proteins brought in through
the nuclear pores from the
cytoplasm are assembled
with this rRNA to form the
subunits of ribosomes. These
subunits then exit through
the pores to the cytoplasm,
where they will join to form
functional ribosomes.
The nucleus directs protein synthesis by
making another type of RNA, messenger
RNA (m RNA) according to instructions in
the DNA.
 The messenger RNA moves through the
pores to the cytoplasm and is translated
there by ribosomes into the amino acid
sequences of proteins.

The functions of a nucleus are:
To contain the genetic material of a cell in
the form of chromosomes.
 To act as a control centre for the activities
of a cell
 To carry the instructions for the synthesis
of proteins in the nuclear DNA.
 To be involved in the production of
ribosomes and RNA.
 In cell division.

Cytoplasm



It refer the background
material inside cell, within
which all the organelle
found.
Mostly water, with a variety
of other molecules dissolved
or suspend in it.
Many of these are proteins,
especially enzymes.
Cytoplasm

Many important biochemical
processes, including
glycolysis, occur within the
cytoplasm.

It is not static but capable of
mass flow, which is called
cytoplasmic streaming.
Ribosomes
Under EM it appear as small
black dots. They are usually
in clusters called
polyribosomes.
 Ribosomes are found in 2
location in the cell
 Free ribosomes –
cytoplasm
 Bound ribosomes –
attached to the outside of
the ER

Ribosome
Site of protein
synthesis.
 Produced in a part
of the nucleus
called the
nucleolus.
 They move from
the nucleus to the
cytoplasm.

That looks familiar…what is a
polypeptide?
Cont …Ribosomes
Each ribosome has two
main components:
a large subunit and a small
subunit.
 Each subunit contains
ribosomal RNA and several
ribosomal proteins.


Ribosomes are the
cellular components that
carry out protein
synthesis.
Endomembrane system

Composed of:






Nuclear envelope,
Endoplasmic reticulum (smooth and rough)
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
Many of these organelles work together in
the synthesis, storage and export of
molecules.
Endoplasmic Reticulum
“ER”
 Connected to
nuclear membrane
 Highway of the cell
 ‘Endoplasmic’
means ‘inside the
cytoplasm’, and
‘reticulum’ means
‘network’ .

Endoplasmic reticulum



An extensive network of
flattened sacs and tubules
called the ER
The tubules and sacs of the
ER enclose an interior space
that is separate from the
cytoplasmic fluid.
The membranes enclose
spaces called cisternae which
form an interconnecting
channel throughout the
cytoplasm.
Smooth endoplasmic reticulum
•
Smooth endoplasmic reticulum (or SER) no ribosome attached.


Functions – synthesis of lipids and steroids
hormones
Providing a structural skeleton to maintain
cellular shape.
Rough endoplasmic reticulum
•
Rough endoplasmic reticulum
(or RER) –ribosomes
attached.



These ribosomes synthesise
proteins.
Providing a large surface area for
chemical
Providing a pathway for the
transport of materials through
the cell
Golgi Apparatus
Looks like a stack of
plates
 Consists of flattened
sacs stacked on top
of each other. The
sacs are not
interconnected like
ER sacs.
 Each of the flattened
sacs has an internal
space.

Golgi apparatus

The Golgi apparatus (or Golgi
body) is a stack of curved
cisternae with several smaller
vesicles entering and leaving
it Vesicles containing newly
synthesized proteins break off
from the rough endoplasmic
reticulum, and travel towards
the Golgi apparatus where
they fuse with its convex face
(cis). Here the proteins are
‘finished off’ and packaged
before being exported from
the cell.
Golgi apparatus

When the protein is ready, small vesicles
break away from the concave face (trans)
of the Golgi apparatus and move towards
the surface of the cell. They fuse with the
cell surface membrane and release their
contents to the outside. The membranes
of the vesicles, which were originally part
of the rough endoplasmic reticulum
membrane, become incorporated in the
cell surface membrane.
Funtion - Golgi apparatus





Stores, modifies and packages proteins
Molecules transported to and from the Golgi by
means of vesicles
Vesicles bud from rough ER and merge into first
layer of golgi complex.
Has several layers called cisternae, arranged like a
stack of pancakes cis face towards ER, trans face
towards cell membrane.
Completes synthesis of some proteins membrane
lipids

1 Nucleus 2 Nuclear
pore 3 Rough endoplasmic
reticulum (RER) 4 Smooth
endoplasmic reticulum
(SER) 5 Ribosome on the
rough ER 6 Proteins that
are
transported 7 Transport
vesicle 8 Golgi
apparatus 9 Cis face of the
Golgi apparatus 10 Trans
face of the Golgi
apparatus 11 Cisternae of
the Golgi apparatus
Lysosomes


Garbage
disposal of the
cell
Contain
digestive
enzymes that
break down
wastes
Which organelles do
lysosomes work
with?
Lysosomes




They are tiny vesicles, surrounded
by single membrane, no structure
inside them, but contain a variety
of hydrolytic digestive enzymes in
solution made in the rough ER.
The name lysosomes is derived
from two Greek words meaning
“breakdown body”.
Vesicles is formed by budding from
golgi complex.
The enzymes and membranes of
lysosomes are made by rough ER
and then transferred to the golgi
apparatus for further processing.
Lysosomes


Their function is to fuse with
other vesicles in the cell which
contain something which
needs to be digested, for eg. a
bacterium which has been
brought into the cell by
phagocytosis or a worn-out
mitochondrion which needs to
be destroyed.
The enzymes in the lysosome
then digest the contents of
this vesicle, producing soluble
substances which can be
absorbed into the cytoplasm.
Vacuoles
Large central
vacuole usually in
plant cells
 Many smaller
vacuoles in animal
cells
 Storage container
for water, food,
enzymes, wastes, The membrane surrounding
pigments, etc.
a plant cell vacuole is often

known as the tonoplast.
Functions of Vacuole





It contain many different substances in solution in
water; it includes sugars, storage proteins, pigments
(coloured substances) and enzymes.
The central vacuole also helps the cell grow in size
by absorbing water and enlarging, and it can store
vital chemicals or waste products.
The colours of some flower petals are caused by
pigments held inside vacuoles.
Some plants store sucrose in their vacuoles, either
temporarily or for much longer periods; the sugar
which we obtain from sugar beet, sugar cane and
many fruits comes from vacuoles.
Central vacuoles may also contain poisons that
protect the plant against predators.
Is a food vacuole part of the
endomembrane system?
YES, IT FORMS BY PINCHING
IN FROM THE CELL
MEMBRANE, WHICH IS PART
OF THE ENDOMEMBRANE
SYSTEM
Microbodies
Microbodies are small spherical
membrane-bound bodies between 0.5 and
1.5µm in diameter.
 They have no internal structure.
 They contain a number of metabolically
important enzymes, the enzyme catalase,
which catalyses the breakdown of
hydrogen peroxide.
 Hence these Microbodies are sometimes
called peroxisomes.

Mitochondria
“Powerhouse of the
cell”
 Cellular respiration
occurs here to
release energy for
the cell to use
 Bound by a double
membrane
 Has its own strand
of DNA

Mitochondria
 It
has two
membranes,
separated by an
intermembrane
space. The outer
membrane smooth, inner
membrane is
folded to form
projections called
cristae.
Cont …Mitochondria


Between the cristae is the
matrix, which fills the rest
of the space inside the
mitochondrion. The matrix
also contains ribosomes
and DNA, which are used
to make some of the
mitochondrion’s own
proteins.
Mitochondria are the site
of the aerobic stages of
respiration, Krebs cycle
and oxidative
phosphorylation.
Chloroplast
Found only in plant
cells
 Contains the green
pigment
chlorophyll
 Site of food
(glucose)
production
 Bound by a double
membrane

Structure of Chloroplasts




Inside the chloroplast is a
third system of membranes,
forming many tiny flattened
sacs called thylakoids.
In places these thylakoids are
stacked on top of each other
to form grana.
Grana are linked by extensions
of some of the thylakoids,
forming long membranebound tubes called intergranal
lamellae.
These entire membranes lie in
a matrix called the stroma.
Function of Chloroplasts
The thylakoid membranes contain
chlorophyll molecules, which give the whole
leaf its green colour.
 The thylakoid membranes - involved in the
light-dependent reactions of photosynthesis,
including photophosphorylation.
 The stroma contains the enzymes required
for the Calvin cycle, in which carbohydrates
are made from carbon dioxide and water.
 The most abundant of these enzymes is
ribulose bisphosphate carboxylase, usually
known as Rubisco.

Cell Wall
Found in plant and
bacterial cells
 Rigid, protective
barrier
 Located outside of
the cell membrane
 Made of cellulose
(fiber)

Cell wall
This extracellular structure not only
protects the cells but provides the skeletal
support that keeps plants upright on
land.
 They are made of glycoproteins and
several different polysaccharides, the
most important of which is cellulose.





The cell walls has three layers
The layer, which is laid down
first, and is far from the cell, is
the middle lamella.
It is called the middle lamella
because, when two plant cells
are next to each other, it is
this layer which forms the
dividing line between their two
cell walls.
The middle lamella is made of
polysaccharides called
pectins.
Cell wall
The primary cell wall,
which lies next to the
middle lamella, and the
secondary cell wall,
which is closest to the
cell surface membrane.
 Both of these contain
pectins, but this time
mixed with other
polysaccharides called
hemicelluloses and
lignin.

Plasmodesmata
A plasmodesma is a gap in
the cell wall, running right
through the walls of two
adjacent cells.
 This makes it possible for
many different kinds of
molecules to pass easily
from one cell to the next,
although this passage does
appear to be regulated by
the cells.

Cilia and flagella
They are long, thin extensions from the
cell surface which can produce movement.
 Cilia -short structures, which usually occur
in large numbers on a particular cell.
 Flagellum is longer, only one or two
usually occurring on any one cell.

Cytoskeleton
Acts as skeleton
and muscle
 Provides shape and
structure
 Helps move
organelles around
the cell
 Made of three
types of filaments

Microtubules



Microtubules are straight,
hollow tubes composed of
globular proteins called
tubulins.
They are responsible for
moving materials with the
cell.
It help determine the cell
shape, move chromosomes
during cell division, and
provide the internal
structure of cilia and
flagella
Actin filaments
Actin filaments are made from many
globular protein molecules linked into a
long chain, with two chains twisted
together. The filaments are very small, so
known as microfilaments.
 Muscle cells contain especially large
amounts of actin filaments, which are
involved in the contraction of the muscle.

Intermediate filaments
Intermediate filaments are tough, fibrous
protein molecules structured in an
overlapping.
 They are intermediate in size when
compared to actin filaments and
microtubules.
 Several different, but similar, proteins
form intermediate filaments of which one
is keratin.


Keratin is found in many cells, but is present in
especially large amounts in cells in the epidermis
of the skin
Centriole
Aids in cell division
 Usually found only
in animal cells
 Made of
microtubules

Where else have we
talked about
microtubules?
Cross – Section of a Plant and Animal
Cell
Difference between plant and animal
cells
Plant cells
Tough, slightly elastic
cellulose cell wall present
(in addition to the cell
membrane)
Pits and plasmodesmata
present in the cell wall
Animal cells
Cell wall absent – only a
membrane surrounds the
cell
Plastids, present in large
numbers
Plastids absent
No cell wall and therefore
no pits or plas
Tonoplast present around Tonoplast absent
vacuole
Cont…Difference between plant and
animal cells
Lysosomes not normally
present
Lysosomes almost always
present
Mature cells normally have Vacuoles - are small and
a large single, central
scattered throughout the
vacuole filled with cell sap cell
Nucleus at edge of the cell Nucleus anywhere in the
cell but often central
Cytoplasm normally
confined to a thin layer at
the edge of the cell
Cytoplasm present
throughout the cell
Quick Review

Which organelle is the control center of the cell?
Nucleus

Which organelle holds the cell together?
Cell membrane

Which organelles are not found in animal cells?
Cell wall, central vacuole, chloroplasts

Which organelle helps plant cells make food?
Chloroplasts

What does E.R. stand for?
Endoplasmic reticulum