This document discusses the structure and function of cellular organelles and components of the plasma membrane. It describes the nucleus, endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, peroxisomes, and plasma membrane. It also discusses mechanisms of transport across the plasma membrane including passive diffusion, facilitated diffusion, active transport, and examples like the sodium-potassium pump. Clinical aspects related to defects in the plasma membrane are also summarized.

1. THE CELL
Objectives:
• -Structure & function of subcellular organelles
• marker enzymes of subcellular organelles
• -structure & function of plasma membrane &
its components
• Transport mechanisms across the plasma
membrane

2. Structure & function of subcellular organelles
Subcellular organelle Structure Functions
Nucleus Nuclear membrane, nuclear
pore,matrix, chromatin,
nucleolus
Replication, transcription, DNA
repair, ribosome synthesis
Endoplasmic reticulum Ribosomes Protein synthesis, post translational
modification of proteins, glycogen
metabolism, fatty acid synthesis,
steroid metabolism, detoxification
Golgi complex Flattened membrane lined
cisternae
Protein sorting & packaging
Mitochondria Outer & inner membrane,
inner membrane space, matrix
Oxidative phosphorylation, TCA
cycle, FA oxidation, mitochondrial
DNA metabolism
Lysosomes Spherical membrane bound
sacs, contain hydrolytic
enzymes in acidic environment
Intracellular digestion of
macromolecules, phagocytosis
peroxisomes Membrane bound sacs
containing catalase.
Oxidation of amino acids & long
chain fatty acids, hydrogen peroxide
metabolism.

3. Identification of subcellular organelles
Subcellular organelle Marker enzymes
Nucleus DNA polymerase
Mitochondria ATP synthase
Lysosome Acid phosphatase
Peroxisome Catalase
Golgi complex Galactosyl transferase
Endoplasmic reticulum Glucose-6-phosphatase

4. Mitochondrial enzymes
Location Enzyme Function
Outer membrane Monoamine oxidase Catabolism of
biogenic enzymes
Inner membrane Respiratory enzymes Electron transport
matrix Citrate synthase
Fatty acyl CoA
dehydrogenase
Oxidation of acetyl
CoA
Β oxidation of fatty
acids

5. Lysosomal enzyme deficiencies in
lysosomal disorders
Disorder Substrate accumulated Enzyme deficiency
Gaucher’s disease Glucocerebroside Glucocerebrosidase
Pompe’s disease Glycogen Acid maltase
Hunter’s disease Heparan sulfate
Dermatan sulfate
iduronidase

6. Structure of plasma membrane
Composition &
organization
Fluid mosaic model Phospholipid bilayer with embedded proteins &
cholesterol.
Carbohydrates present on surface as glycoproteins &
glycolipids
Lipids Phospholipids, glycolipids, cholesterol, cholesterol esters
Proteins Intergral proteins;NaK ATPase
Peripheral proteins; adenyl cyclase
carbohydrates galactose, mannose, glucose, N acetyl glucosamine, N
acetyl galactosamine

15. Characteristics of plasma membrane
• Selectively permeable
• Membrane fluidity; factors affecting are;
temperature
chain length of fatty acids
degree of unsaturation of fatty acids
cholesterol content
• Membrane asymmetry;
lipids: PC-exterior, PS & PE-interior
proteins ;C terminal end on the cytosolic side
• Membrane skeleton:
spectrin: erythrocyte membrane
dystrophin ; muscle

16. Functions of plasma membrane
• Transport of molecules
• Cell-cell communication
• Cell signalling
• Compartmentalization
• modifications

17. Clinical aspects of plasma membrane
• Mechanical injury; sickle cell disease- Hb S
• Chemical injury; snake bite-phospholipase activation
• Hypoxic injury; ischaemia-phospholipase activation
• Antibodies to receptors; myasthenia gravis- antibodies
to acetylcholine receptor.
• Abnormal lipid components; gaucher’s disease-
glucocerebroside accumulation
• Membrane skeletal disorders; duchenne muscular
dystrpohy- mutated dystrophin
hereditary spherocytosis-RBC spectrin mutation.

18. Mechanisms of transport of solutes
• 1)passive diffusion: a)simple process
• b)does not require energy
• c)movement of solute along the
concentration gradient
• d) movement from high to low concentration
d)Passage of water and gases across membranes
• 2) facilitated diffusion
• 3)active transport

20. Passive transport

21. Facilitated diffusion
• Solute moves along the conc. Gradient
• No energy required
• Transport mediated by a carrier or transport protein
• Mechanism: ping-pong model ( two conformations of
the carrier protein)
• Pong conformation:protein exposed to high solute
conc. Side
• Allows binding to specific sites
• Then Change to ping conformation: side exposed to
low solute conc. & release of molecules.
• Regulated by hormones: eg: insulin

22. Active transport
• Molecule transport against conc. Gradient
• Dependent on metabolic energy supply(ATP)
• Carrier mediated
• Eg: ion pumps like sodium potassium pump.
• Intracellular high K+ & low Na+ conc.
• K+ required for cell survival, optimal glycolysis
& protein synthesis. Ion gradient across
membranes required for nerve transmission.

23. Active transport

25. Sodium potassium pump
• Integral membrane protein: N+K+ATPase.
• Pimary active transport mechanism.
• Responsible for maintenance of high K+ & low
Na+ conc. In cells.
• In the cell:Pumps 3Na+ ions from inside to
outside & brings 2K+ ions from outside to
inside along with intracellular ATP hydrolysis.

28. Na+ cotransport system( secondary
active transport)
• The difference in the electrochemical
potential(created by the primary active
transport) builds up a diffusion energy that
under appropriate conditions can pull other
substances along through the cell memrane.
• Eg: transport of Amino acids & sugars into cell
along with sodium.

30. Based on direction of movement of
molecules,facilitated diffusion can occur giving rise to
different transport systems
• uniport system: movement of a single molecule
through membrane: eg: glucose transport into
erythrocytes.
• Symport system: simultaneous transport of 2
different molecules in the same direction.
Eg: transport of Na+ & glucose into intestinal
mucosal cells.
• Antiport system: simultaneous transport of 2
different moleculesin opposite direction.eg: Cl- &
HCO3- in erythrocytes.

32. Difference between passive & active transport
Property Passive
transport(simple
diffusion)
Passive
transport(facilita
ted diffusion)
Primary active
transport
Secondary active
transport
Requires specific
protein
No Yes Yes Yes
Solute
transported
against a
gradient
No No Yes Yes
Through direct
ATP hydrolysis
No No Yes No
Through co-
transported
movement down
the gradient
No No No Yes
examples Gases: oxygen,
carbondioxide,
steroid hormones
Glucose, ions,
water
Ions, small water
soluble
molecules
Glucose & amino
acids