Prof. Dr. Mohammad Ahmed Azmi, Ph.D
A BASIC CELL
Eukaryotic cell
Prokaryotic cell
BASIC STRUCTURE OF CELL
A typical cell has two main components
Cytoplasm
Nucleus
PROTOPLASM
Definition:
The fluid living content of the cell.
OR
The different substances that make up the
cells are collectively called as PROTOPLASM.
COMPOSITION OF PROTOPLASM
The protoplasm is composed of five basic
substances:
Water
Electrolytes
Proteins
Lipids
Carbohydrates
Water:
Principal fluid medium of the cell.
Concentration …….. (65% to 80%).
Many cellular chemicals are dissolved in water.
Others are suspended in membranous form.
ELECTROLYTES
The most important electrolytes are:
K+ , Mg + + , PO4--, SO4-, HCO3Little amount are:
Na+, Ca++, ClProvide in organic chemicals for cellular
reactions
Important for the transmission of electrochemical impulses in nerve and muscle fibers
Intra cellular electrolytes determine the activity
of enzyme-catalyzed reactions
PROTEINS
Complex organic nitrogenous compounds
Consisting of polymers of amino acids
Constitute 10-20 % of the cell mass
Types of proteins
Structural proteins
Globular proteins
Nucleoproteins
Structural Proteins
Present in the form of long thin filaments
o Provide contractile mechanism of all muscles
Also organized into microtubules
o Provide cytoskeleton of many organelles
e.g., cilia, nerve axons, mitotic spindles
Extracellularly, fibrillar proteins are found in
the form of collagen & elastin fibres of
connective tissue, blood vessels, tendons,
ligaments e.t.c.
Globular proteins
Present in the globular form
Act as enzymes and participate in chemical
reactions
e.g. chemical reaction that splits glucose into
the cell providing energy for cellular reactions.
Nucleoproteins
Found in the nucleus in the form of RNA & DNA
Lipids
Most important are:
PHOSPHOLIPIDS
CHOLESTEROL
Constitute about 2-3 % of cell mass
Mainly in soluble in water
In addition some cells also contain TRIGLYCERIDES
also called neutral fats
Carbohydrates
Constitutes only about 1% of cell mass
Have little structural function in the cell
Stored in ECF in the form of glucose
Small amount are stored in the form of glycogen
(an insoluble polymer of glucose supplying energy to
cell
Cytoplasm:
This is a portion of cytoplasm which surrounds
the nucleus
It is peripherally covered by a membrane called
cell membrane
Zones of Cytoplasm:
Ectoplasm(Cortex)
Endoplasm
Ectoplasm (Cortex)
Present just beneath the cell membrane.
Contains microfilaments mainly composed of
ACTIN
Endoplasm:
Contains clear liquid portion of cytoplasm
present between the cortex and nuclear
membrane
This liquid portion is called CYTOSOL in which
inclusions / particles and organelles are present
Cell membrane / Plasma membrane
Outer covering which envelops the cell
Thin and elastic membrane
Its structure cannot be seen easily under light
microscope
About 8-10 nm in thickness
Composition of Cell membrane
Structure
The basic structure is LIPID
Lipid molecules form a bi-layer
Lipid bi-layer is composed of:
PHOSPHOLIPID
CHOLESTROL
One part of both PL and chol molecule is water
soluble……Hydrophilic
Other part is fat soluble……Hydrophobic
The PO4 radical of PL is hydrophilic
& fatty acid radical is hydrophobic .
The hydroxyl (OH) radical of cholesterol
is hydrophilic
The steroid nucleus is hydrophobic
The fatty portions (Hydrophobic) occupying
the centre of the membrane
The hydrophilic portions are directed towards
the inner and outer surfaces of the lipid bi-layer
Membrane Proteins
Integral proteins
These protrude all the way through the membrane.
Many integral proteins provide structural channels or pores through which water-soluble
substances especially ions can diffuse between ECF & ICF.
Others act as carrier proteins specially transporting substances in and out of the cell.
Peripheral Proteins
Do not penetrate the membrane but attached only to the surface on the membrane .
These mainly act as enzymes.
Membrane Carbohydrate
These occur in the form of glyco-lipids and glyco-proteins
The entire surface has a loose layer of carbohydrate called GLYCOCALYX . These have
several functions.
Many are negatively charged that provides over all negative charged surface that repel
other negative objects
Many cells are attached to each other by these carbohydrate moieties
Many act as receptor substances for binding hormones
Some are involved in immune system
Presence of Channels and Pumps
Na+ - K+ leak channel
The cell membrane contains protein channels, called
leak channels
They allow Na+ or K+ to leak down their concentration
gradients INTO or OUT OF the cell.
Cell membranes are considerably more permeable to
K+ than to Na+ because they have many more K+ leak
channels than Na+ leak channels.
Na+ - K+ Electrogenic Pump
The Na+/K+ Pump creates a concentration gradient by
moving 3 Na+ out of the cell and 2 K+ into the cell.
The movement of ions occur against concentration
gradient.
This pump requires energy in the form of ATP during
the movement of ions.
Gating of Protein Channels
Voltage gated - Na+ channel
At – 90mv the gate remain closed from outside.
When potential changes from -90 to +35mv,
conformational changes suddenly occurs and the
gate opens
During this time large amount of Na enters in to
the cell. This causes depolarization
Voltage gated – K+ channel
At-90mv the gate remain closed from inside of
the cell.
When potential changes from -90 to +35mv, the
gate opens slowly to cause the out flux of K+
to the exterior of the cell.
Carrier Protein Channel
A substance cannot pass through the
membrane whiteout specific binding with the
receptor site.
After binding conformational changes occur
and the channel open and the substances in
to the cell
Ligand Gated Channel
Channels open by binding of an other molecule with the
protein.
Conformational changes occur in the protein molecule
that opens or closes the gate. This is called ligand gating
substance that binds with the protein is called ligand
Best example is the effect of acetylcholine also called
acetylcholine channel.
Plays an important role in the transmission of signals
from :
nerve cell …………………………………… nerve cell
nerve cell …………………………………… muscle cell
Ca++ Pump
Calcium ions play a crucial role in the metabolism and
physiology of eukaryotes.
Normally maintained at very low concentration in the
intra cellular cytosol
Two calcium pumps are involved
Present in the cell membrane …………….. Pumps calcium to
the out side of the cell
Pumps calcium into one or more intra vesicular organelles
of the cell
In both cases carrier protein penetrates the membrane
It acts as ATP-ase that transports ions across the
membranes using energy obtained from the hydrolysis of
ATP.
Cell Organelles
Prof. Dr. Mohammad Ahmed Azmi, Ph.D.
Membranous Organelles
Endoplasmic Reticulum (ER)
• Network of tubular and vesicular structures which are interconnected with each
other
•It is covered by limiting membrane composed of protein & lipid bi-layer
•Lumen of ER contains a fluid called endoplasmic matrix
•ER forms a link between nucleus and cell membrane
•OR
•Forms connection of cell membrane with the nuclear membrane
•Granular or Rough
A granular or Smooth ER
Granular or Rough ER
A granular or Smooth ER
• Ribosomes are attached on the surface of ER
• Donot have ribosomes
•Synthesis of proteins
•Synthesize lipids, steroid hormones
•Role in the degradation of worn out cytoplasmic
•Also involved in the detoxification of some
organelles like mitochondria
drugs
Mitochondria
• rod-shaped or oval shaped
•Covered by lipid bi-layer membrane
•Outer membrane is irregular & folded forming shelves – cristae
•Inner space of cristae – called mitochondrial matrix
•Matrix contains many enzymes and protein molecules for involved in respiration &
formation of ATP
Power house of cell
Golgi Apparatus
• Consists of 5 to 8 membranous sacs usually flattened in structure called cisternae
•Situated near the nucleus
•Present in all cells but larger in those that synthesize & export proteins.
•Proteins move from rough ER to the gogli apparatus where they are packaged into
secretory vesicles called secretory granules
•The seceretory vesicles are stored & when proteins are needed they move to the cell
membrane & so proteins are exported.
Lysosomes
• They are oval or spherical membrane bound vesicular organelle
•Found throughout the cytoplasm
•Enzymes formed in rough ER are processed and packed in the form of small
vesicles in the golgi apparatus
•These vesicles are then moved out from golgi apparatus and become the
lysosomes.
Lysosomes
Primary lysosomes
Secondary lysosomes
Inactive in nature containing
Active containing lysosomal enzymes
Hydrolytic enzyme
proteases, lipases amylases
Formed from Golgi apparatus
nucleases
Peroxisomes
• Are microvesicular structures like lysosomes.
• They are pinched off from ER & not from golgi apparatus.
• Contain some oxidative enzymes in the phagocytosis of foreign particles
Centrosome and Centrioles
• Membranous bound cellular organelle, cylindrical in shape
•Situated in the centre of cell and close to nucleus
•Responsible for the movement of chromosomes during cell division.
Non-membranous Organelles
Ribosomes
• Non-limiting cellular organelle
•Granular and small dot-like structure
•Made up of proteins (35%) and RNA (65%)
•RNA present in ribosomes are called r-RNA
•Ribosomes are responsible for protein synthesis
Attached to ER
Protein formation
Free ribosome in the cytoplasm
Responsible for protein of Hb,
peroxisome & mitochondria
Cytoskeleton: Consists of:
-Microtubules
-Microfilaments
•Cell organelles that determine the shape of cell & support
•Also responsible for cellular movement and response of cell to external stimuli
Microtubuls
•Spindle fibers
•Cilia
•Flagella
•Actin & myosin
Cell Organelles
Prof. Dr. Mohammad Ahmed Azmi, Ph.D.
Membranous Organelles
Endoplasmic Reticulum (ER)
• Network of tubular and vesicular structures which are interconnected with each
other
•It is covered by limiting membrane composed of protein & lipid bi-layer
•Lumen of ER contains a fluid called endoplasmic matrix
•ER forms a link between nucleus and cell membrane
•OR
•Forms connection of cell membrane with the nuclear membrane
•Granular or Rough
A granular or Smooth ER
Granular or Rough ER
A granular or Smooth ER
• Ribosomes are attached on the surface of ER
• Donot have ribosomes
•Synthesis of proteins
•Synthesize lipids, steroid hormones
•Role in the degradation of worn out cytoplasmic
•Also involved in the detoxification of some
organelles like mitochondria
drugs
Mitochondria
• rod-shaped or oval shaped
•Covered by lipid bi-layer membrane
•Outer membrane is irregular & folded forming shelves – cristae
•Inner space of cristae – called mitochondrial matrix
•Matrix contains many enzymes and protein molecules for involved in respiration &
formation of ATP
Power house of cell
Golgi Apparatus
• Consists of 5 to 8 membranous sacs usually flattened in structure called cisternae
•Situated near the nucleus
•Present in all cells but larger in those that synthesize & export proteins.
•Proteins move from rough ER to the gogli apparatus where they are packaged into
secretory vesicles called secretory granules
•The seceretory vesicles are stored & when proteins are needed they move to the cell
membrane & so proteins are exported.
Lysosomes
• They are oval or spherical membrane bound vesicular organelle
•Found throughout the cytoplasm
•Enzymes formed in rough ER are processed and packed in the form of small
vesicles in the golgi apparatus
•These vesicles are then moved out from golgi apparatus and become the
lysosomes.
Lysosomes
Primary lysosomes
Secondary lysosomes
Inactive in nature containing
Active containing lysosomal enzymes
Hydrolytic enzyme
proteases, lipases amylases
Formed from Golgi apparatus
nucleases
Peroxisomes
• Are microvesicular structures like lysosomes.
• They are pinched off from ER & not from golgi apparatus.
• Contain some oxidative enzymes in the phagocytosis of foreign particles
Centrosome and Centrioles
• Membranous bound cellular organelle, cylindrical in shape
•Situated in the centre of cell and close to nucleus
•Responsible for the movement of chromosomes during cell division.
Non-membranous Organelles
Ribosomes
• Non-limiting cellular organelle
•Granular and small dot-like structure
•Made up of proteins (35%) and RNA (65%)
•RNA present in ribosomes are called r-RNA
•Ribosomes are responsible for protein synthesis
Attached to ER
Protein formation
Free ribosome in the cytoplasm
Responsible for protein of Hb,
peroxisome & mitochondria
Cytoskeleton: Consists of:
-Microtubules
-Microfilaments
•Cell organelles that determine the shape of cell & support
•Also responsible for cellular movement and response of cell to external stimuli
Microtubuls
•Spindle fibers
•Cilia
•Flagella
•Actin & myosin
Thanks