Molecular different between Prokaryotic and eukaryotic cell By KK Sahu Sir

SYNOPSIS
Introduction to cell
Historical Aspects
Cell Diversity
Types Of Cell Diversity
Cell Diversity In Origin
Cell Diversity In size
Cell Diversity In Shape
Some Other Types
5) Differentiation And Specialisation Of Cell Diversity
6) Conclusion
7) References

1. MOLECULAR DIFFERENCE BETWEEN PROKARYOTIC AND EUKARYOTIC CELL By KAUSHAL KUMAR SAHU Assistant Professor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )

2. SYNOPSIS Introduction Types of Cell a. Prokaryotic b. Eukaryotic Basis of differentiation a. General Difference b. Molecular Difference i . Difference in Molecular Structure of cell membrane of Pro and Eukaryotes ii. Difference in Molecular Structure of DNA iii . Ribosomal Difference iv. Protein synthesis v. Bimolecular difference Conclusion Reference Thank You Queries

3. INTRODUCTION Billions of years ago when the first life began on earth, most scientists believed that it were like that of the prokaryotic organisms . Slowly the primitive life form changed as evolution took place and prokaryotic organisms changed into eukaryotic type. During 1950s developed the concept that all cells can be classified as prokaryotic and eukaryotic cells.

4. Introduction to Basic Terms Cell: Cell are the smallest simplest functional and structural unit of life that have been classified as living thing. Prokaryotic Cell: The term is composed of two Greek words ‘pro’ and ‘ karyo ’ . Pro means before and karyos means ‘kernel’ as in kernel of grains. Prokaryotic means before a nucleus. Thus true nucleus is absent in prokaryotic cell. Eukaryotic cell : ‘ Eu ’ means true or good. As in prokaryotes the meaning possesses a true nucleus. Thus true nucleus is present in eukaryotic cells. They are more complex in nature.

5. Examples Prokaryotic : Bacteria the most numerous prokaryotes are single celled organisms; the Cynobacteria or Blue Green Algae can be unicellular or filamentous chain of cells. E.g. E. Coli bacteria, Salmonella Typhi Eukaryotic : The typical animal and plant cell can be categorized under this group. There are other single celled eukaryotes also. E.g. Epithelial Cells of Human

6. Diagram Prokaryotic and Eukaryotic Cells

7. General differences The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms. The most fundamental difference is that eukaryotes do have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound.   Cell organelles : In eukaryotes, the mitochondria and chloroplasts perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare.

8. General Differentiation Eukaryotic Cell Prokaryotic Cell Mitochondria: Present Absent Chloroplasts: Present (in plants) Absent Plasma membrane with steriod : Yes Usually no Golgi apparatus: Present Absent Endoplasmic reticulum: Present Absent Differentation: Tissue and organs Radimentary Ribosomes: 80S especially in Mitochondria and chloroplast 70S Cytoskeleton: Present May be absent Vacoules: Present Present Number of chromosomes: More than one One

9. Eukaryotic Cell Prokaryotic Cell DNA complexed histones: Yes No True Membrane bound Nucleus: Present Absent Cell wall: Chemically simpler Usually chemically complexed Nucleolus: Present Absent Mitosis Occurs: Yes No Genetic Recombination: Mitosis and fusion gametes Partial, undirectional transfers DNA Flagella: Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlets Submicroscopic in size, composed of only one fiber Lysosomes and peroxisomes : Present Absent Microtubules: Present Absent or rare Vesicles: Present Present

10. Molecular level of differences Differences in molecular structure of plasma membrane The plasma membrane of eukaryotic and prokaryotic cells is very similar in function and structure. There are, however, differences in the types of proteins found in the membranes. Eukaryotic membranes also contain carbohydrates, which serve in cell to cell recognition.. Eukaryotic plasma membranes also contain sterols, which are complex lipids not found in prokaryotic plasma membranes instead they contain hapanoids (with the exception of Mycoplasma ). Sterols help the membranes resist lysis from increased osmotic pressure. All living cells, prokaryotic and eukaryotic, have a plasma membrane that encloses their contents and serves as a semi-porous barrier to the outside environment. The membrane acts as a boundary, holding the cell constituents together and keeping other substances from entering. The plasma membrane is permeable to specific molecules, however, and allows nutrients and other essential elements to enter the cell and waste materials to leave the cell.

11. Structure and Composition Like all biological membranes in nature, the bacterial cytoplasmic membrane is composed phospholipid and protein molecules . It is actually a fluid phospholipid bilayer imbedded with proteins prokaryotic membranes lack sterols. Many bacteria, however, do contain sterol-like molecules called hopanoids. Like the sterols found in eukaryotic cell membranes, the hopanoids most likely stabilize the bacterial cytoplasmic membrane . The phospholipid bilayer is arranged so that the polar ends of the molecules (the phosphate and glycerol portion of the phospholipid that is soluble in water) form the outermost and innermost surface of the membrane while the non-polar ends (the fatty acid portions of the phospholipids that are insoluble in water) form the center of the membrane.

12. Phospholipid bilayer structure

13. Eukaryotic plasma Membrane Eukaryote cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. The nucleus is surrounded by a double membrane. According to the accepted current theory, known as the fluid mosaic model , the eukaryotic plasma membrane is composed of a double layer ( bilayer ) of lipids, oily substances found in all cells. Most of the lipids in the bilayer can be more precisely described as phospholipids , that is, lipids that feature a phosphate group at one end of each molecule. Within the phospholipid bilayer of the plasma membrane, many diverse proteins are embedded,important is sterol protien while other proteins simply adhere to the surfaces of the bilayer. Some of these proteins, primarily those that are at least partially exposed on the external side of the membrane, have carbohydrates attached to their outer surfaces and are, therefore, referred to as glycoproteins . . The arrangement of proteins also involves the hydrophobic and hydrophilic regions found on the surfaces of the proteins

14. Differences in molecular structure of DNA Eukaryotic DNA is linear while prokaryotic DNA is circular.  Also, Eukaryotic DNA is organized into chromosomes and is complexed with specialized proteins called histones.  In Contrast, prokaryotic DNA does not have histones associated with it and prokaryotic DNA does not form chromosomes. Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organised chromosomes. Prokaryotes also differ from eukaryotes in the structure, packing, density, and arrangement of their genes on the chromosome. Prokaryotes have incredibly compact genomes compared to eukaryotes, mostly because prokaryote genes lack introns and large non-coding regions between each gene. Prokaryote genes are also expressed in groups known as operons, instead of individually, as in eukaryotes

15. The organization of prokaryotic DNA The bacterial DNA is packaged in loops back and forth.  The bundled DNA is called the nucleoid.  It concentrates the DNA in part of the cell, but it is not separated by a nuclear membrane (as in eukaryotes.)  The DNA does form loops back and forth to a protein core, attached to the cell wall. The organization of prokaryotic DNA is quite different from the eukaryotic DNA DNA Supercoiling enable bacteria, lacking a nucleus, organize and pack their genome into the cell.

16. DNA Supercoiling Eukaryotes wrap their DNA around proteins called histones to help package the DNA into smaller spaces, most prokaryotes do not have histones Prokaryotes compress their DNA into smaller spaces is through supercoiling . Structure can be compared with twisting a rubber band so that it forms tiny coils. Multiple proteins act together to fold and condense prokaryotic DNA, In particular one protein called HU. Works with an enzyme called topoisomerase I to bind DNA and introduce sharp bends in the chromosome Other proteins, including integration host factor (IHF), can bind to specific sequences within the genome and introduce additional bends. . The folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein, much like eukaryotic chromosomes are wrapped around histones.

17. Eukaryotic Chromosome Structure Eukaryotic cells contain their DNA within the nuclear membrane . The DNA double helix is bound to proteins called histones .  The histones have  positively charged (basic) amino acids to bind the negatively charged (acidic) DNA. The DNA is wrapped around the histone core of eight protein subunits, forming the nucleosome .

18. Difference between Prokaryotic and Eukaryotic Ribosome In prokaryotes the ribosomes are only in free forms in the cytoplasm or protoplasm. It is of 70s type in prokaryotes and divided in two subunits as 50s and 30s.50s: split protein and core r-RNA 23s and 5s 30s: core r-RNA of 16s and split proteins In eukaryotes ribosomes are either free in the cytoplasm or are attached to the outer membrane of endoplasmic reticulum through ribophorins and by larger subunits (60s). In the cytoplasm of eukaryotes ribosomes are 80s ( s: svedberg's unit of sedimentation) type, and have two subunits. The bigger subunit is 60s type and the smaller subunit is of 40s type. 60s: have split proteins and core r-RNA 28s, 5.8s and,5s 40s: corer-RNA of 18s and split protein.

19. Difference in Protein Synthesis The basic plan of protein synthesis in eukaryotes and archaea is similar to that in bacteria. However, eukaryotic protein synthesis entails more protein components than does prokaryotic protein synthesis, and some steps are more intricate. Prokaryotic Protein Synthesis Primarily differ in Translation Initiation In bacteria, transcription and translation take place at the same time... In eukaryotes, the initiating amino acid is methionine rather than N - formylmethionine . However, as in prokaryotes, a special tRNA participates in initiation. This aminoacyl-tRNA is called Met- tRNA i or Met- tRNA f The initiating codon in eukaryotes is always AUG. Eukaryotes, in contrast with prokaryotes, do not use a specific purine -rich sequence on the 5′ side to distinguish initiator AUGs from internal ones. Elongation and termination. Eukaryotic elongation factors EF1α and EF1βγ are the counterparts of prokaryotic EF-Tu and EF- TsTermination in eukaryotes is carried out by a single release factor, eRF1, compared with two in prokaryotes

20. In eukaryotic cells , transcription occurs in the nucleus, and the mRNA must be exported to the cytoplasm for translation. In eukaryotes, the mRNA is modified at both ends - the 5' end is "Capped" with a modified GTP, and to the end is added a long "tail" of poly(A) (usually greater than 150 A's are added).  In bacteria, transcription and translation take place at the same time...

21. Biomolecules Nutrient storage structures Most bacteria do not live in environments that contain large amounts of nutrients at all times. To accommodate these transient levels of nutrients bacteria contain several different methods of nutrient storage in times of plenty for use in times of want. For example, many bacteria store excess carbon in the form of polyhydroxyalkanoates or glycogen. Some microbes store soluble nutrients such as nitrate in vacuoles. Sulfur is most often stored as elemental (S ) granules which can be deposited either intra- or extracellularly. Sulfur granules are especially common in bacteria that use hydrogen sulfide as an electron source. Most of the above mentioned examples can be viewed using a microscope and are surrounded by a thin non-unit membrane to separate them from the cytoplasm

22. CONCLUSION At the morphological level the prokaryotic and eukaryotic cells look quite dissimilar in their cellular organization. Prokaryotic cells are simple in organization with no true nucleus whereas a eukaryotic are highly organized with a distinctive nucleus and the presence of cellular organs. Prokaryotic cell lacks sterol protein instead they contain hapanoids proteins which give stability to the cell membrane. At molecular level they are dissimilar in their genetic make-up and gene packaging. They basically differ in the way they function during protein synthesis and or gene expression.

23. REFERENCE Cell Biology by P.K. Gupta Cell Biology by C.B. Pawar Cell and Molecular Biology by Pelzer Microbiology by Ananth Narayan