prof. dr. mohammad ahmed azmi, ph.d a basic cell eukaryotic cell prokaryotic cell
TRANSCRIPT
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:
WaterElectrolytes Proteins LipidsCarbohydrates
Water:Principal fluid medium of the cell.
Concentration …….. (65% to 80%).
Many cellular chemicals are dissolved in water.
Others are suspended in membranous form.
ELECTROLYTESThe most important electrolytes are: K+ , Mg + + , PO4--, SO4-, HCO3- Little amount are: Na+, Ca++, Cl-Provide in organic chemicals for cellular
reactions Important for the transmission of electro-
chemical impulses in nerve and muscle fibers Intra cellular electrolytes determine the
activity of enzyme-catalyzed reactions
PROTEINSComplex 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 filamentsoProvide contractile mechanism of all muscles
Also organized into microtubulesoProvide 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 proteinsPresent 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.
NucleoproteinsFound in the nucleus in the form of RNA &
DNA
LipidsMost 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
StructureThe basic structure is LIPIDLipid molecules form a bi-layer
Lipid bi-layer is composed of:PHOSPHOLIPIDCHOLESTROL
One part of both PL and chol molecule is water soluble……HydrophilicOther 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 CarbohydrateThese 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 channelThe 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 ChannelsVoltage 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 ChannelChannels 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 gatingsubstance 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 OrganellesEndoplasmic 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
• Ribosomes are attached on the surface of ER
•Synthesis of proteins
•Role in the degradation of worn out cytoplasmic
organelles like mitochondria
• Donot have ribosomes
•Synthesize lipids, steroid hormones
•Also involved in the detoxification of some
drugs
Granular or Rough ER A granular or Smooth ER
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
Inactive in nature containing
Hydrolytic enzyme
Formed from Golgi apparatus
Secondary lysosomes
Active containing lysosomal enzymes
proteases, lipases amylases
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 OrganellesRibosomes
• 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 Free ribosome in the cytoplasm
Responsible for protein of Hb, peroxisome & mitochondria
Protein formation
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 OrganellesEndoplasmic 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
• Ribosomes are attached on the surface of ER
•Synthesis of proteins
•Role in the degradation of worn out cytoplasmic
organelles like mitochondria
• Donot have ribosomes
•Synthesize lipids, steroid hormones
•Also involved in the detoxification of some
drugs
Granular or Rough ER A granular or Smooth ER
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
Inactive in nature containing
Hydrolytic enzyme
Formed from Golgi apparatus
Secondary lysosomes
Active containing lysosomal enzymes
proteases, lipases amylases
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 OrganellesRibosomes
• 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 Free ribosome in the cytoplasm
Responsible for protein of Hb, peroxisome & mitochondria
Protein formation
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