Enzymatic Constituents of Cell Organelles-3 Lecture NO: 1st MBBS Dr. Muhammad Ramzan

Ribosome – the definition Are small rounded particles in a cell, made up of proteins and rRNA that are primarily involved in the : Assembly of proteins by translating the mRNA Named because of ↑of rRNA 60% - Translation complex Are non membranous organelle

Ribosome – the background synthesizes about 1 billion proteins A minute rounded Cytoplasmic organelle with 60%rRNA and 40% proteins (nucleoproteins) Each ribosome has 3- 4 moles of rRNA and can bind to 1mole of mRNA and up to 3 tRNA Ribosome decodes the genetic information stored in mRNA for protein synthesis A single Ribosome can add 200AAs/mint to a Protein chain Ribosome are synthesized in Nucleolus (British society for cell biology 2016)

Types and location of Ribosomes Free and membrane bound There are 2 types of Ribosome Free / floating in cytoplasm and 1 Membrane bound that are attached to the membranes of Rough Endoplasmic Reticulum – RER 2

Ribosome – A protein assembly plant

Free Ribosomes- synthesize proteins for intracellular use Free Ribosome are floating in the Cytosole Can migrate from one portion of cytoplasm to the other Free Ribosome, synthesize proteins which are released and used in the Cytosole

Free Ribosome

Membrane bound Ribosome or Fixed Ribosome Membrane bound or fixed Ribosome are located on the surface of membranes of RER Give beaded/granular or rough appearance to RER

Membrane bound ribosome

Fixed Ribosome – synthesize proteins for intracellular and extracellular use Proteins synthesized by the membrane bound Ribosomes are inserted into the cavity of ER and Are transported to their destination through secretary pathways to inside and outside of cell They are used within the plasma membrane or exported from the cell via Exocytosis or Secreted into the Lysosomes as acid Hydrolases

Protein transport in a cell after synthesis

Protein transport in a cell after synthesis 3 pathways

Parts of a Ribosome – 2 Large and small subunits A Ribosome has 2 portions : Small or 40S (Svedberg's) Large 60S Synthesize proteins together

Ribosomal units and sites

Ribosomal enzymes of both the subunits Functional ribosome is the major share holder in protein synthesis and gives attachment to the : mRNA and product protein at the smaller and larger subunit respectively Ribosomes have the enzymes to carry out this function

Ribosomal enzymes – larger subunit Major enzymes - 2 Large ribosomal subunit has Peptidyl transferase which establishes the peptide bond B/W the AAs at P site 1 Peptide bond is consolidated by the Ribo proteins This enzyme is rRNA and is also known as Ribozyme Hydrolysis of the Peptidyl transferase changes its activity And releases the product protein at P- site by binding of Release factor with stop Condon

Termination step in protein synthesis Stop Codon and releasing factor

Dismantling of translation complex

Nucleus It is the major Bilayered organelle, is well connected with the ER and regulates all the activities of a cell Is covered by an envelop having inner ; outer membrane, intra membranous space and nuclear pores The membranes has the structure like rest of the cells Major content is the DNA and nucleoproteins

Nucleus

Enzymes in the nuclear membrane Peripheral proteins are attached to integral proteins / lipid layer and act as enzymes also participate in the : Metabolism of different membrane compounds. Enzymes: Phosphatases; Phospho lipases, Cholesterol Oxidases, Sphingomyelinase and Glycosyl transferses

Nuclear enzymes – major ones 3 Nucleus is the hub for the production of enzymes as it contains Genes It produces 3 major enzymes DNA Polymerase DNA Ligase and RNA Polymerase

Major Nuclear Enzymes DNA polymerase is an enzyme that catalyzes the replication of DNA molecule DNA Ligase is yet another enzyme that binds the useful parts (Exones) of the newly synthesized DNA molecule Also repairs the damaged DNA Duplex RNA Polymerase catalyses the Transcription of RNA

Nuclear Enzymes – DNA polymerase

Nuclear - RNA polymerase

Nucleolus Nucleolus has no membrane. Accumulation of RNA and proteins found in the Ribosomes- His tones Nucleolus produces Ribosome and tRNA