CELL AND PLASMA MEMBRANE CELL: BASIC UNIT OF LIFE

CELL AND PLASMA MEMBRANE CELL: BASIC UNIT OF LIFE

Approximate elementary composition of the human body (dry weight) Carbon - 50% Oxygen - 20% Hydrogen - 10% Nitrogen - 8.5% Calcium - 4% Phosphorus - 2.5% Potassium - 1% Sulfur 0.8% Sodium 0.4% Chloride 0.4% Magnesium 0.1% Iron 0.01% Manganese 0.001% Iodine 0.00005%

Normal chemical composition for a man weighing 65 kg Water 40kg ( 61.6 %) Protein 11 kg (17 %) Fat 9 kg (13.8 %) Minerals 4 kg (6.1 %) Carbohydrates 1 kg (1.5 %)

Major complex organic biomolecules DNA RNA PROTEINS POLYSACHHARIDES LIPIDS

Structural unit of living system is CELL

Cell Basic structural and functional unit of life. 100 Trillion cells in a Human being. The smallest unit that displays the characteristics of life,i.e Growth,Reproduction, Metabolism, Response to stimuli

800g -10 min Subcellular fractionation 15,000g -10 min Nuclear sediment 100,000g - 60 min Mitochondria,Lysosomes, Peroxisomes sediment Fragments of Plasma memb. & Endoplasmic reticulum sediment 200,000g - 3 h Ribosome sediment

Membraneous Organelles 1.Mitochondria 2.Golgi bodies 3.Endoplasmic Reticulum 4. Nucleus 5. Lysosomes 6. Peroxisomes

Mitochondria Golgi Apparatus Site of cellular respiration. Major pathways are Respiratory chain,tca cycle, β-oxidation,ketone bodies synthesis Function Glycoprotein processing, protein sorting, synthesis of Glycolipid and Sphingomylin.

Endoplasmic reticulum & Nucleus ER function Protein synthesis & processing, cholesterol synthesis, PL synthesis, drug detoxification. Nucleus contains chromatin, RNAs and nuclear proteins. Nuclear envelope consists of two nuclear membrane, an underlying nuclear lamina and nuclear pore complexes. Nucleolus site of rrna transcription,processing and ribosome assembly.

Lysosomes Small membrane bound organelle. Contains 50 different degradative enzymes which are active in acidic ph Function: Endocytosis, Phagocytosis, Autophagy

Peroxisomes Small membrane bound organelle H 2 O 2 producing reactions takes place here Has catalase which decompose H 2 O 2 Substrates oxidized in Peroxisomes are fatty acid,purines Biosynthetic reactions Cholesterol, Dolichol, Lysine,Bile acids & Plamalogens

Non Membraneous Organelles 1.Ribosome 2.Cytoskeleton 3.Centrioles 4.Centrosomes 5.Cilia 6.Flagella

Ribosomes Ribosomes - site of protein synthesis --assembled in the nucleolus,exported into the cytoplasm a. Free unbound in the fluid cytoplasm, produce proteins for use in the cell b. Bound attached to the endoplasmic reticulum (ER), produce proteins for export, or for the plasma membrane

PLASMA MEMBRANE Fluid mosaic model proposed by Singer & Nicolson

Membrane Functions 1.Selective Barrier a) Surround cells to hold enzymes and metabolites inside b) surround organelles inside cells 2.Contain Enzyme Systems--energy metabolism (oxidative phosphorylation, glycolysis, etc.) 3.Contain Transport Systems--bring certain molecules inside and also maintain ion concentrations 4.Contain Specific Recognition Sites--for hormones, etc. 5. Helps in shaping cells

FUNCTIONS OF MEMBRANE PROTEIN

Membranes are complex structures composed of lipids, proteins & carbohydrates Lipids- create hydrophobic barrier Glycerophopholipids sphingolipids cholesterol Proteins- Integral or intrinsic Peripheral or extrinsic Composition varies from 75% lipid (mylelin sheath) to 25% lipid (mitochondria) Carbohydrates- Glyproteins glycolipids

Membrane Fluidity

Lipids have rapid lateral movement Lipids flip-flop extremely slowly Lipids asymmetrically distributed in membrane Cholesterol is a moderator of fluidity in the membranes

PLASMA MEMBRANE BILAYER FORMATION

MICELLE & LIPOSOMES Liposomes - 1. Circular bilayer surrounding water compartment. 2. Can form naturally or artificially. 3. Can be used to deliver drugs and DNA to cells.

Membrane Transport Transporter: Passive: Diffusion Carrier mediated: facilitated diffusion Active : Channel : Voltage gated Ligand gated Group translocation: Amino acid translocation

FACILITATED DIFFUSION Carrier mediated process. Structurally similar solutes can competitively inhibit the entry of solutes. Can operate bidirectionally. Does not require energy. Dependent on concentration gradient. Carrier molecules can exist in Ping and Pong states.in Pong state, active sites are open to exterior and solutes bind to sp.sites. In Ping state, active sites are facing interior of cell. This will cause release of solute molecule and protein molecule reverts to pong state.

FACILITATED DIFFUSION Carrier protein Solutes Cell membrane

Energy source used to drive transport from low ==> high concentration ATP used as an energy source: Na+/K+ ATPase Concentration gradient/membrane potential used as energy source: Na+/glucose transporter Active Transport

ION CHANNELS Channels cycle between open and closed conformations. When open, a channel provides a continuous pathway through the bilayer, allowing flux of many ions. The channels generally remain closed, butin response to stimulus, they open allowing rapid flux of ions down the gradient. closed open

LIGAND GATED CHANNELS Ach binding site α β γ Exterior Plasma membrane Binding of a ligand to a receptor site on the channel results in opening/closing of channel. eg. Acetyl choline receptor. Cytosol

VOLTAGE GATED CHANNELS Membrane potential change switches the ion channel to open. They pass from closed through open to inactivated state on depolarisation. eg. Voltage gated sodium channels, voltage gated potassium channels. Function: Conduction of nerve impulse.