Enzymatic Constituents of Cell Organelles - 1 Lecture NO: 1st MBBS Dr. Muhammad Ramzan

Cell Organelles – the definition Organelle - Little organ- analogous to an organ Are the specialized components of the living cell Carry out various functions that are essential for cell life and metabolism www.biology- online.org

Cell organelle – the background Are insulated by membrane All the organelle are Bilayered. Peroxisome is single layered Ribosome has no membrane Are always present and able to self replicate Ribosome is produced by the Nucleolus Their numbers , size and shape is variable Are abundant in metabolically active cells like thyroid/ Pancreas www.wikepedia.com – www.Khan academy.com

Cell Organelles - the list of 8 Nucleus, Endoplasmic Reticulum and Golgi complex Lysosome, Mitochondria and : Ribosome Peroxisome/ Micro bodies and Secretary Vesicles www.wikepedia. com

Cell organelle – Nucleus to secretary vesicles

Lysosomes – the definition Present in all cells except RBC Are spherical vesicles which contain acid Hydrolases (50) to degrade all types of biological polymers (Proteins; nucleic acids, CHO and lipids) Lysosomes are referred to as Suicide bags because of their role in Autolysis www.biology- online org. www.wikipedia.com

Lysosomes- the background Lysosomal enzymes are synthesized in ER and pinched off from Golgi as Transport vesicles Acid Hydrolases work best at acidic pH(5) VS pH 7.2 Lysosome actively concentrate proton(H+) via Proton pump in its membranes via ATP hydrolysis Degrade extra cellar material and damage organelle www.biology – online.org – www.NCBI book shelf.org

Lysosome

Proton pump - Conc. H+

Role of Lysosomal Membranes Prevention of Damage Lysosomal membranes prevent the leakage of the acid hydrolytic enzymes into Cytosole 1 Their damage causes release of acid hydrolases which are inactive at neutral Cytosolic pH 7.2 2 This provides double protection against the digestion of Cytoplasmic contents in membrane rupture

Synthesis of Lysosome 2 pathways Secretary pathway Secretary endocytic pathway Secretary pathway: Lysosome and their enzymes are produced separately and pinched off from Golgi Enzymes in Transport vesicles and Lysosome bind together cytoplasm to have mature Lysosome

Synthesis of Lysosome Endocytic/secretary Pathway ```` Extra cellular moles are taken up in the cell as endocytic vesicles which fuse with the early endosome Early endosome matures into late endosome Transport vesicles from Golgi fuse with late endosome that also contain certain moles taken up by the Endocytosis Enzymes in Transport vesicles are delivered to endosome via receptors of Mannose – 6 Phosphate Transport vesicles and endosome are transformed into Lysosome

Endocytosis and Lysosome formation

Lysosome – the waste boxes Constitute an Intracellular Digestive System for the : Damaged cellular structures / debris The materials taken by Endocytosis and Phagocytosis EXT Food particles ingested by the cell Unwanted Matter like Bacteria Macromolecules like Proteins; nucleic acids, CHO and lipids

Lysosomal enzymes- Disposal of products Lysosomes are now known to contain ˃ 50 acid Hydrolases that can digest all macro moles in the cells The breakdown products are transported back to the Cytosole by specific transport proteins in the Lysosomal membrane Functional deficiencies of these enzymes result in the Lysosomal storage disease like Gauchors" disease

Lysosomal enzymes – the list Proteases : that degrade Proteins/peptides into AAs Nucleases: Degrade DNA/RNA into mononucleotides Phosphatases: Remove PO4 group from mononucleotides/Phospholipids Lipases degrade lipids into fatty acids and glycerol

Lysosomal Storage diseases Gauchors" disease The mutations of the genes for Lysosomal enzymes give rise to 30 different genetic diseases Lysosomal storage diseases There is accumulation of un degraded materials due to the deficiency of Lysosomal enzymes Guachars" Disease: is due to the deficiency of the enzyme for the degradation of Glycolipids

Peroxisome – Produces H2O2 is single layered Peroxisome are so called as they all produce H2O2 through the process of per oxidation Peroxisome are produced through self replication or from endoplasmic reticulum (ER) Is a single layered organelle and is self replicated Are present in all animal cells except RBC

Peroxisome – Oxidases and Catalases the major enzymes Contain about 50 enzymes – Oxidases and Catalases Oxidases split organic moles (FA) to produce H2O2 by the process of oxidation – A free radical Catalases then split H2O2 to water and O2 to make it safe Peroxisome also break down uric acid and amino acids

Mitochondria – the cellular power house Mitochondria, are power house of cells and the principal site for ATP production in aerobic cells Extract energy from the nutrients to carry out cell function. No. of mitochondria are variable and depend upon activity of the cell - from100 to several thousands like : Thyroid gland, Pancreas and renal tubules

Mitochondria - structure in general are mobile Mitochondria are variable in size and shape May be Globular or elongated Mitochondria move freely with in the cells Mitochondria are bilayered with Inner and Outer membranes.1 An inter membranous space exists B/w the 2 layers 2

Mitochondria – structure

Composition of the Mito.membranes Outer membrane of mitochondria is composed of about half lipids and half protein Low Protein in the outer membrane render it permeable to molecules having molecular weight < 10,000KD The inner one has 80% proteins and 2o% lipids and is less permeable to large molecules like LCFAs This is significant for entry of FAs into matrix for oxidation

Mitochondria – Enzymes of membranes and matrix Inner membrane has folding shelves and Cristie to ↑ the surface area for enzyme action Cavity under inner membrane has fluid – the Matrix Matrix contains abundantly dissolved Oxidative enzymes to extract energy from nutrients Liberated energy is utilized to synthesize ATP

Enzymes of outer Mitochondria membrane NO:2 External surface of Outer mitochondrial membrane has Fatty Acyl Co A Synthetase for the: Activation of Long chain saturated fatty acid (LCSFA) Inner surface of outer mitochondrial membrane has : Carnitine Acyltransferase(CAT 1) to transfer LCSFA to the mitochondrial matrix

Enzymes of inner Mitochondrial membrane No:2+5 Inner surface of external Mitochondrial membrane has : Carnitine Acyltransferase 11 It separates Carnitine from Acyl Carnitine so that LCSFA remains in the matrix for oxidation Carnitine is translocated to the inter membranous space for reuse by the Carnitine Translocase

Enzymes of inner Mitochondrial membrane cont. and Matrix Inner surface of the Inner Mitochondrial membrane has 5 enzymes including ATP Synthase and: enzymes for Oxidative Phospho rylation (ETC) Ribosome and Ribosomal DNA for protein synthesis Matrix has the enzymes for : Citric acid cycle and Fatty acid oxidation

Carnitine shuttle

Mitochondria – the synthetic role Mitochondria have their own DNA with 37 no of genes that encode for the required Mitochondrial proteins Have their Ribosomes and DNA on the : inner Mitochondrial Membrane Expression of these genes leads to the translation and synthesis of proteins via mRNA in the matrix The product proteins are used with in the mitochondria

Mitochondria – the Metabolic role Mitochondria carry out oxidation of the nutrients in matrix like FAs to yield energy for ATP synthesis The process is called oxidation of FAs that releases 129 no of ATP for a single mole of Palmatic acid(16C) This energy is used to carry out cell function and survival

Electron transport chain Oxidative Phosphorylation