Download Prokaryotic Cell

CELL
Topics
 Cell structure
 Cell function
 Cellular organization
 Cellular metabolism
(by Dr. Amjad Ali Khan)
Introduction
 The cell is the structural and functional
basic unit of life.
 It was discovered by Robert Hooke and is
the functional unit of all known living
organisms.
 It is the smallest unit of life that is
classified as a living thing, and is often
called the building block of life.
Introduction
 Some organisms, such as most bacteria,
are unicellular (consist of a single cell).
 Other organisms, such as humans, are
multicellular.
 Humans have about 100 trillion or 1014
cells; a typical cell size is 10 µm
(micrometer) and a typical cell mass is
1 nanogram.
Types of Cells
 There are two types of cells:
prokaryotic and
eukaryotic
 Prokaryotic cells are usually
independent, while eukaryotic cells
are often found in multicellular
organisms.
Prokaryotic Cell
 The prokaryote cell is simpler, and
therefore smaller, than a eukaryote cell,
lacking a nucleus and most of the other
organelles of eukaryotes.
 Nuclear material of prokaryotic cell consist
of a single chromosome which is in direct
contact with cytoplasm. Here the
undefined nuclear region in the cytoplasm
is called nucleoid.
 On the outside, flagella and pili may
be present. These facilitate the
movement and communication
between cells.
 Enclosing the cell is the cell envelope
– generally consisting of a cell wall
covering a plasma membrane
General structure of a Prokaryotic cell
Eukaryotic Cell
 Eukaryotic cells are far more advanced
and complex than a Prokaryotic cell.
 Eukaryotic cell can be as much as 1000

times bigger in size than a prokaryotic
cell.
eukaryotic cells contain membrane-bound
compartments (organelles) in which
specific metabolic activities take place.
 Most important among these is a nucleus,
a membrane bound compartment that
contains DNA. This nucleus gives the
eukaryote its name, which means "true
nucleus.
 There are some differences in the structure
and function of animal and plant cells.
Though both cells are eukaryotic.

In the cytoplasm the eukaryotic cell
contains many organelles such as:


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Mitochondria
Endoplasmic reticulum (rough and smooth)
Golgi bodies
Lysosomes
Peroxisomes
Ribosomes
Chloroplast (found in plant cells)
Vacuole
centriole
Simple structure of a eukaryotic cell
Eukaryotic cell organelles
 There are several types of organelles in a


cell.
Some (such as the nucleus and golg
apparatus) are typically solitary, while
others (such as mitochondria,
peroxisomes and lysosomes) can be
numerous (hundreds to thousands).
The cytosol is the gelatinous fluid that fills
the cell and surrounds the organelles.
Nucleus



The cell nucleus is the most conspicuous
organelle found in a eukaryotic cell. It
contains the chromosomes,
The nucleus is spherical and separated
from the cytoplasm by a double
membrane called the nuclear envelope.
The nuclear envelope isolates and protects
a cell's DNA
 The nucleolus is a specialized region
within the nucleus where ribosome
subunits are assembled.
 In prokaryotes, DNA processing takes
place in the
cytoplasm.
Mitochondria




Mitochondria play a critical role in
generating energy in the eukaryotic cell so
it is also called “power house of a cell.
Mitochondria are self-replicating
organelles that occur in various numbers,
shapes, and sizes in the cytoplasm of all
eukaryotic cells.
Mitochondria multiply by splitting in two.
Respiration occurs in the cell
mitochondria.
General structure of Mitochondria
Endoplasmic reticulum


The endoplasmic reticulum (ER) is the
transport network for molecules targeted
for certain modifications and specific
destinations.
The ER has two forms: the rough ER,
which has ribosomes on its surface and
secretes proteins into the cytoplasm, and
the smooth ER, which lacks them.
Endoplasmic Reticulum
Golgi apparatus
 The primary function of the Golgi
apparatus is to process and package the
macromolecules such as proteins and
lipids that are synthesized by the cell.
 It is particularly important in the
processing of proteins for secretion.
 It consists of -cis and -trans faces
Golgi apparatus
Ribosomes
 The ribosome is a large complex of
RNA and protein molecules.
 They each consist of two subunits,
and act as an assembly line where
RNA from the nucleus is used to
synthesize proteins from amino
acids.
Ribosomes
 Ribosomes can be found either
floating freely or bound to endoplasmic reticulum in eukaryotes, or the
cell membrane in prokaryotes).
 In prokaryotic cells 70S ribosomes
are present while in eukaryotic cells
80S ribosomes are present
Lysosomes
 Lysosomes contain digestive
enzymes. They digest excess or
worn-out organelles, food particles,
and engulfed viruses or bacteria.
 These organelles (lysosomes and
peroxisomes) are often called a
"suicide bag" because of their ability
to detonate and destroy the cell.
Vacuoles
 Vacuoles store food and waste. Some
vacuoles store extra water.
 The vacuoles of eukaryotic cells are
usually larger in those of plants than
animals.
Centriole
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In animal cells, centrioles are short
cylinders present near the nucleus.
There is always one pair of centrioles
near the nucleus.
Before a cell divides, the centrioles
duplicate.
During cell division, the pair of
centrioles separate so that each cell
gets one pair of centrioles.
The cytoskeleton


Several types of filamentous proteins
form a cytoskeleton that helps
maintain the cell’s shape and either
anchors the organelles or assists
their movement.
The cytoskeleton includes microtubules and actin filaments.
MICROTUBULES
 Microtubules are shaped like thin
cylinders and are several times
larger than actin filaments.
 Microtubules are made up of tubulin.
 Microtubules can assemble and disassemble.
 It is well known that during cell
division, microtubules form spindle
fibres, which assist the movement of
chromosomes
Cilia and Flagella

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Cilia and flagella are projections of
cells that can move.
Cilia are short (2-10µm) while
flagella are longer about 200 µm.
Cells that have these organelles are
capable of self movement or moving
material along the surface of the cell.
Cellular metabolism


Cellular metabolism includes all the
chemical reactions that occur in a
cell.
Quite often these reactions are
organized in a metabolic pathways,
which can be shown as:
A
B
C
D
1
2
3
A


B
C
D
1
2
3
The letters A,B,C,D are the reactants
and products whereas 1,2,3 are the
enzymes which take part in the
reactions.
Every reaction in a cell requires a
specific enzyme

Different types of enzymes present
in a cell which act on different
substrates are:

Substrate
Enzyme
•Lipid
•Protein
•Urea
•Maltose
•Lactose
lipases
protease
urease
maltase
lactase
General structure of a Plant cell
Difference between prokaryotic
and eukaryotic cell
Typical organisms
Prokaryotic
Eukaryotic
bacteria, archaea
plants, animals, fungi
Size of cell
1 – 10 µm
10 – 100 µm
Type of nucleus
No real nucleus
True nucleus
Cell organelles (mitochnodria,
chloroplast, ER, golgi bodies,
lysosomes etc)
Absent
present
Ribosomes
70S
80S
Cell division
Binary fission
Mitosis and meiosis
DNA
Circular , in cytoplasm
In chromosomes, in nucleus
Difference and common between animal cell and plant cell
Structure
Animal Cell
Plant cell
Cell membrane
yes
Yes
nucleus
Yes
yes
Nucleolus
Yes
yes
Ribosomes
Yes
yes
ER
Yes
yes
Golgi bodies
Yes
yes
Centrioles
yes
No
Cell wall
No
Yes
Mitochnondria
yes
Yes
Chloroplast
No
Yes
One big vacuole
No
Yes
cytoskeleton
Yes
Yes
Cell theory
 The cell theory, first developed in 1839 by
Schleiden and Schwann, states that
 all organisms are composed of one


or more cells,
that all cells come from pre-existing
cells,
that vital functions of an organism
occur within cells,
Cell theory
 and that all cells contain the
hereditary information necessary for
regulating cell functions and for
transmitting information to the next
generation of cells.
 The word “Cell” was first coined by
Robert Hooke in 1665
Thank you