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

2. 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

3. 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)

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

5. Ribosome – A protein assembly plant

6. 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

7. Free Ribosome

8. 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

9. Membrane bound ribosome

10. 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

11. Protein transport in a cell after synthesis

12. Protein transport in a cell after synthesis 3 pathways

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

14. Ribosomal units and sites

15. 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

16. 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

18. Termination step in protein synthesis Stop Codon and releasing factor

19. Dismantling of translation complex

20. 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

21. Nucleus

22. 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

23. 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

24. 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

25. Nuclear Enzymes – DNA polymerase

26. Nuclear - RNA polymerase

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