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

Cell Organelles – specialized cellular parts 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 Always present and membrane bound Often able to divide (self replicate)

Cell Organelles - the list 8 Nucleus, Endoplasmic Reticulum and Golgi complex Lysosomes and Mitochondria Ribosome Peroxisome/ Micro bodies Secretary Vesicles

Cell organelle – Nucleus to secretary vesicles

Lysosomes – the definition Membranous boxes Are membranous bags which contain hydrolytic enzymes to digest macromolecules : Cell debris and microorganisms

Lysosomes- the background Lysosomes are synthesized in ER and pinched off from Golgi apparatus and : Can undergo self replication Are dispersed through out the cytoplasm Are more abundant in secretary cells like Pancreas and Thyroid glands – 100s to thousands

Lysosomes – Structure and self replication

Lysosomes – the waste boxes Constitute an Intracellular Digestive System for the : Damaged cellular structures / debris The materials taken by Endocytosis and Phagocytosis Food particles ingested by the cell Unwanted Matter like Bacteria Macromolecules like proteins (Proteolysis)

Lysosomal action

Enzymes of Lysosomes – the nature 1 Contain a Group of enzymes, Hydrolases that degrade polymers into their monomer units (hydrolysis) Over 40 in number and include : Nucleases- degrade DNA and RNA into mononucleotides Proteases- degrade proteins and peptides to Amino acids

Enzymes of Lysosomes - the nature 2 Phosphatases – Remove phosphate groups from mononucleotides and phospholipids Lipases degrade lipids into fatty acids and glycerol Deficiency of Hydrolases result in building of toxic products that are digested by Lysosomes

Damage to Lysosomal Membranes The consequences Bilayered membranes of the Lysosomes prevents the leakage of the hydrolytic enzymes into cytoplasm Damage to Lysosomal membrane causes release of hydrolytic enzymes which work at acid medium 5 Released Lysosomal enzymes, split intra cellular organic compounds that cause cell death

Peroxisome – Produce 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 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

Biogenesis of Peroxisome- ER

Peroxisome – Detoxication uric acid and amino acid

Mitochondria – the background the power house Mitochondria, are the power house of cells and are the principal site for ATP production in aerobic cells Extract energy from the nutrients to carry out cell function. Number of mitochondria is variable and depends upon activity of cell-100 to several thousands like : Thyroid gland, ,Pancreas and epithelium

Mitochondria - structure in general are mobile Mitochondria are variable in size and shape May be Globular or elongated Mitochondria migrate from one place to another with in the cells Mitochondria are doubled layered with Inner and Outer membranes. An inter membranous space exists B/w the 2 layers

Mitochondria – power house of the body

Mitochondria – membrane composition outer and inner Mit.Membranes The 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 – Inner membrane and matrix Ultra structure Inner membrane has folding shelves and Cristie to increase 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 Mitochondria membranes and matrix

Enzymes of Mitochondria membranes and matrix Outer Mitt. membrane has Fatty Acyl Co A Synthetase for the activation of LCFAs (outer surface) and Carnitine Acyl Transferase(CAT 1) for Carnitine shuttle(inner surf. Inner Mitt. membrane has ATP Synthase and enzymes for Oxidative Phosphorylation (ETC) Ribosomes and DNA are also part of the inner Mitt. Membrane Matrix has the enzymes for Citric acid cycle and FA oxidation

Carnitine shuttle

Mitochondria – the synthetic role Mitt.DNA and Ribosomes Mitochondria have their own DNA with 37 no of genes that encode for all the Mitochondrial proteins Have their Ribosomes and DNA on inner Mitt. Membrane Expression of these genes leads to the translation, and synthesis of proteins via mRNA in the matrix These proteins are then shifted to have their place in Mitt. Membranes to carry out various functions Ketogenesis by hepatic 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

Major role of Mitochondria – ATP synthesis