STRUCTURE AND FUNTION OF CELL ORGANELLES

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STRUCTURE AND FUNCTIONS OF CELL ORGANELLES:

STRUCTURE AND FUNCTIONS OF CELL ORGANELLES Ms. SHRUTI S KULKARNI DEPARTMENT OF CHEMICAL PATHOLOGY USM-KLE INTERNATIONAL MEDICAL SCHOOL

Objectives::

Objectives: Describe the biochemical composition and properties of cell membranes Describe the fluid mosaic model of membrane structure Outline the biochemical functions of the subcellular organelles

THE CELL:

THE CELL

THEORY:

THEORY All living things are made of cells. The cell is the smallest living thing that can perform all the functions of life. All cells must come from preexisting cells. Cell > Tissue > Organ > System > Organism

Cells kingdom— Two categories:

Cells kingdom— Two categories

Difference between prokaryotic & eukaryotic cell:

Difference between prokaryotic & eukaryotic cell

Cell Organelle:

Cell Organelle A membrane-bound compartment or structure in a cell that performs a specific function. Found only in eukaryotic cells— Nucleus Endoplasmic reticulum Golgi apparatus Mitochondria Entities such as ribosomes, cytoskeleton and cytosol are not subcellular organelles and are designated as subcellular entities or fractions

CELL / PLASMA MEMBRANE:

CELL / PLASMA MEMBRANE The cell is enveloped by cell membrane which separates cells from exterior. ECF – The fluid outside the cell membrane ICF- intracellular fluid Consists of lipids, proteins and carbohydrates. Protein: lipid ratio=1:4 to 4:1 Electron microscopy reveals lipid bilayer – phospholipids and protein molecules forming a MOSAIC LIKE PATTERN.

PowerPoint Presentation:

At body temperature lipids are in fluid state which is essential for exocytosis , endocytosis and lysosomal activity. The major classes of membrane lipids are : Phospholipids Gycolipids Cholesterol

PHOSPHOLIPIDS:

Hydrophilic head – phosphoric acid and alcohol Hydrophobic tail – fatty acid Allow for diffusion of lipid soluble molecules (O 2 ,CO 2 , and alcohol). Allows for flexibility of the cell membrane. Act as a boundary keeping organelles within the cell. Classes of phospholipids are : phosphoglycerides and sphingomyelins . PHOSPHOLIPIDS

GLYCOPROTEINS & GLYCOLIPIDS:

GLYCOPROTEINS & GLYCOLIPIDS Glycolipids - carbohydrate chains attached to a phospholipid head Glycoproteins - carbohydrate chains attached to a protein. Outside of the cell membrane As recognition sites allowing organisms to recognize foreign cells/molecules

Cholesterol:

Cholesterol Cholesterol - almost exclusively present in mammalian cells, providing stability Cholesterol which is present between phospholipids also effects membrane fluidity At warm temp it restrict the movement At low temp it prevents close packing, so membrane remains fluid

MEMBRANE PROTEINS:

Two major populations of membrane proteins: Integral proteins : Embedded in the membrane Can be trans-membrane or just partway Transmembrane proteins are integral proteins which completely span the membrane Act as enzymes and transport carriers for ions and substances like glucose. Peripheral proteins: Not embedded in the membrane Loosely bound to the surface of the membrane, often to the exposed parts of integral proteins Peripheral proteins act as receptor sites A membrane is a collection of different proteins embedded in the fluid matrix of the lipid bilayer MEMBRANE PROTEINS

Fluid mosaic model of cell membrane:

Fluid mosaic model of cell membrane Theory of fluid mosaic model - by Singer and Nicolson.1972 Mosaic- structure made up of many different parts. consist of a continuous double layer of lipid molecules. Membrane proteins are embedded in the lipid bilayer The bilayer - fluid -- mixture of saturated and unsaturated fatty acids Proteins are interspersed in the lipid bilayer producing a mosaic effect. This is called as the fluid mosaic model because the membrane consists of a mosaic of proteins and lipids which are free to drift about in the plane of the membrane

FLUID MOSAIC MODEL OF CELL MEMBRANE:

FLUID MOSAIC MODEL OF CELL MEMBRANE

Functions of membranes:

Functions of membranes

NUCLEUS:

NUCLEUS

NUCLEUS:

NUCLEUS Most prominent organelle All cells in the body contain nucleus except mature RBCs & uppermost layer of skin Nucleus occupies most of the space in small lymphocytes spermatozoa

Cell Nucleus: Functions:

Cell Nucleus: Functions Bag of chromosomes : It contains most of the cell's genetic material Storage of DNA, DNA maintenance Replication & repair of DNA Site of transcription & post transcriptional processing/ modification The control center of a cell Controls the activities of cell by regulating gene expression Production of ribosomal subunits in the nucleolus Nucleolus: Actively transcribing region of nucleus Synthesis of rRNA Formation of ribosome subunits

FUNCTIONS CONT.:

FUNCTIONS CONT . Nuclear membrane Compartmentalizes the nucleus Nuclear pore Transport of molecules between the cytoplasm and the nucleus Chromatin DNA Replication and transcription Nuclear matrix Replication, DNA repair and transcriptional process nucleolus Synthesis of rRNA and ribosomes

ENDOPLASMIC RETICULUM:

ENDOPLASMIC RETICULUM ‘The Cell’s Delivery System’

PowerPoint Presentation:

like a factory conveyor belt Def -A network of interconnecting membranes enclosing channels or cisternae that are continuous from perinuclear envelope to plasma membrane. Types R ough ER- Ribosomes are attached – synthesis of new protein molecules in the cell,glycoproteins,lipoproteins Smooth ER – Synthesis of lipid substances like steroid hormones,cholesterol.. Detoxification of drugs, toxins

Functions of rough endoplasmic reticulum:

Functions of rough endoplasmic reticulum

Functions of smooth endoplasmic reticulum:

Synthesis of lipids Triacylglycerol Phospholipids, Sterols Metabolism of drugs (in liver) Cytochrome P 450 system Supply of calcium ions for cellular functions The ER is the site of membrane synthesis. Both RER and SER cooperate in membrane synthesis The smooth ER helps transport materials within the cell Functions of smooth endoplasmic reticulum

MICROSOMES:

MICROSOMES During cell fractionation the ER is disrupted and the membrane reseals to form small vesicles called microsomes Isolated by differential centrifugation As such they do not occur in cells

THE GOLGI APPARATUS:

THE GOLGI APPARATUS

PowerPoint Presentation:

Stores, modifies and packages proteins Temporary storage of newly synthesized proteins Chemical modification : Addition of carbohydrates, lipids , sulfate or phosphate moieties to the protein Targeting, sorting, packaging and secretion of proteins Molecules transported to and from the Golgi by means of vesicles It also produces lysosomes, vesicles that contain powerful hydrolytic enzymes

Cis face & trans face of Golgi:

Cis face & trans face of Golgi Proteins are received by the cis face of the Golgi and exit through the trans face after modification

LYSOSOMES:

LYSOSOMES ‘Packages of Destruction’

LYSOSOMES:

LYSOSOMES A lysosome is a membranous bag with hydrolytic enzymes to digest macromolecules. Primary-formed on rough ER Secondary-formed on smooth ER due to fusion of phagosome with primary lysosome .

PowerPoint Presentation:

Contains over 40 enzymes Internal pH is around 5(acidic) because lysosome has a proton pumping ATPase in its membrane.

Lysosome - functions:

Lysosome - functions Degradation of proteins, carbohydrates, lipids and nucleotides Destruction of bacteria, foreign bodies Removal of excessive secretory products Removal of unwanted cells in embryo Postmortem autolysis

PEROXISOMES:

PEROXISOMES

PEROXISOMES:

PEROXISOMES These resemble lysosomes in their appaerence . Peroxidase and catalase Involved in detoxification of peroxide β- oxidation of fatty acid Participates in the synthesis of bile acids Peroxisomes play an important role in the liver, where they detoxify alcohol

Mitochondria:

M itochondria

Mitochondria:

Mitochondria

Metabolic pathways in mitochondria:

Metabolic pathways in mitochondria Electron transport chain ATP generation Citric acid cycle Ketone body production β- oxidation of fatty acids Gluconeogenesis Pyrimidine synthesis Urea synthesis-the first 2 steps Heme synthesis-the initial step and the last 3 steps

Mitochondria: ‘Cellular power plants’:

Mitochondria: ‘Cellular power plants’

Mitochondria: Functions:

Mitochondria: Functions

Ribosomes ‘Factories of protein biosynthesis’:

Ribonucleoprotein complexes Composed of rRNA & proteins Two subunits Large subunit Small subunit Ribosomes manufacture proteins Ribosomes of RER: Synthesizes proteins for export Free ribosomes in cytosol: Synthesizes cellular proteins Ribosomes ‘Factories of protein biosynthesis’

CYTOSOL (Cell sap):

CYTOSOL (Cell sap)

Cytosol— Metabolic role:

Site of glycolysis Pentose phosphate pathway Gluconeogenesis (Major part) Part of heme synthesis Part of urea cycle Purine synthesis Part of pyrimidine synthesis Fatty acid synthesis Part of cholesterol synthesis Cytosol — Metabolic role

Cytoskeleton- cells skeleton:

Intracellular network of protein Plasma membrane is anchored to the cytoskeleton FUNCTIONS: Characteristic shape and form Attachment of organelles Allows communication Acts as a track- organelles move Participates in Intracellular translocation of organelles, microvillus movements, cell division, exocytosis , endocytosis The three fibers of the cytoskeleton–microtubules in blue, intermediate filaments in red, and actin in green–play countless roles in the cell. Cytoskeleton- cells skeleton

Cytoskeleton:

The cytoskeleton supports the cell . Cytoskeleton

Structure - cytoskeleton:

Structure - cytoskeleton Protein filaments Microfilaments Microtubules Intermediate filaments Microfilaments - Actin Microtubules -Tubulin Intermediate filaments – fibrous protein

Clinical aspects of subcellular organelles:

Clinical aspects of subcellular org anelles

Summary::

Summary:

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