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

Ribosome – the definition non membranous organelle 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 Also called as Translation complex Are non membranous organelle www.biology- online.gov

Ribosome – the background has 80 different proteins Ribosome has rRNA 60% and proteins 40% (Riboproteins) Each ribosome has 3- 4 moles of rRNA, can bind to one (1 ) mole of mRNA and up to 3 tRNA Ribosome decode genetic information stored in mRNA for translation Polysome is a single mRNA with many Ribosome www.bscb.org

Ribosome – background cont. Single Ribosome can add 200AA/mint to product protein Ribosome is short lived and dies after completion of product protein Like Titin is a muscle protein(30,000 AAs) It takes 2 to 3 hrs for completion Ribosome are synthesized in Nucleolus. short www.bscb.org

Ribosome

Ribosome- Types and location synthesize proteins 2 types: free and fixed Free Ribosome are floating in the Cytosole- are mobile Free Ribosome, synthesize proteins which are released and used in the Cytosole Fixed ribosome are located on the surface of ER membrane, giving beaded appearance to ER Produce proteins for intra/extra cellular use

Ribosome – A protein assembly plant

Protein distribution after synthesis

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

Ribosomal enzymes of 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 Ribosome have the enzymes to carry out this function Smaller subunit is for decoding and larger one for the catalytic activity

enzymes of larger subunit Major enzymes - 2 Large ribosomal subunit has Peptidyl Transferase which establishes the peptide bond B/W the: Amino acids at P site 1 This enzyme is rRNA and is also known as Ribozyme

Enzymes of Large Subunit cont. A 2nd enzyme is also available at E site which sets free the empty tRNA for reuse in the cytoplasm Reaction is carried out by the hydrolysis of Peptidyl Transferase 2 Hydrolysis of enzyme changes its activity and sets free the peptide chain by the appearance of : Stop Codon at A site and Releasing factor (A protein)

Termination of translation

Nucleus – structure A prominent organelle Nucleus is the prominent cell organelle that contains the genetic material -1o% of cell It is Bilayered which separate it from the cytoplasm Nuclear envelope has the nuclear pores that allow the entry and exit of small moles B/W nucleus and cytoplasm Is well connected with the Endoplasmic reticulum www.biology – on line.gov

Nucleus, nucleoplasm and nucleoli Nucleus is surrounded by jell like fluid called Nucleoplasm It contains condensed form of DNA – the chromatin Chromatin is organized into chromosome during cell division Nucleoplasm also contain one or more nucleoli that produces Ribosome and tRNA Ribosome is a protein producing factory www.ghr.nlm.nih.org

The nucleus

Chromatin and Chromosomes Chromatin is DNA and protein 6 feet DNA is divided into 46 molecules of DNA Each DNA mole give rise to a chromosome - 1.5 inches long DNA binds with the proteins and arranges into a dense string like fiber called chromatin It condenses further into chromosome in cell division It makes the DNA to function properly www.ghr.nlm.nih.gov

Chromatin and Chromosome

Nucleolus Nucleolus is a membrane less organelle? within the Nucleus It appears like a dark spot in the nucleus by microscope A nucleus may contain up to 4 nucleoli It disappears during cell division and reappears again Nucleoli produce Ribosome and tRNA www.micro.magnet.fsu.edu (Florida state university)

Enzymes of 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. These include: Phospholipases; Phosphatases Cholesterol Oxidases, Sphingomyelinases www.wikepedia.com

Nuclear enzymes – NO: 3 the major ones 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 cont. 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 www,wikepedia.com

Nuclear Enzymes – DNA polymerase

Nuclear - RNA polymerase