Lecture 3 - Prokaryotic vs Eukaryotic Cells

3.Prokaryotic vs. Eukaryotic Cells Introduction Cells are classified into two major categories based on their structural and functional characteristics: bacterial and plant and animal, and other on the basis of their cell organization we can divide them into prokaryotic and eukaryotic. This division is critical to the study of the biosphere since all living things belong to one of the two divisions. Prokaryotic Cells Prokaryotic cells are the most primitive and ancient cells and first emerged over 3. 5 billion years ago. These are organisms which lack well-defined true nucleus and other membranebound organela. Prokaryotic cells are found in two domains of life: These two are the major groups of the domain Bacteria and Domain Archaea. • Structural Features: o Nucleoid: In prokaryotic cells the genetic material is not enveloped by a membrane rather is located in an area known as nucleoid. o Cell Wall: Almost all prokaryotic organisms posses a cell wall, which gives mechanical strength and also shields the organism. In bacteria, this cell wall is made of peptidoglycan or also known as murein; another type is the capsular polysaccharide layer. o Plasma Membrane: This is a double membrane located round the cell and regulates entry and of substances into and out of the cell. o Ribosomes: Prokaryotic cell possesses ribosome which is noted to be smaller (70S) compared to that of a eukaryotic cell and play the role of synthesizing proteins. o Plasmids: Plasmids are small, circular DNA structures that are found in many prokaryotic cells, and, can contain genes helpful for the organism to survive, for example resistance to antibiotics. • Reproduction: o Binary Fission: Prokaryotic cells only reproduce asexually by means of binary fission, which is a division of the cell into two tightly similar new cells. • Examples: o Bacteria: This can include; Escherichia coli (E. coli), Staphylococcus aureus. o Archaea: Methanogens, halophiles. Eukaryotic Cells Eukaryotic cells are more developed due to the fact that they are younger in the evolution as compared to prokaryotic cells. To be more precise, they are located in organisms of the domain Eukarya that includes animals, plants, fungi, and protists. • Structural Features: o Nucleus: The main feature of the eukaryotic cells is the presence of the true nucleus enveloped by the nuclear membrane and containing all the genes of an organism. o Membrane-Bound Organelles: Eukaryotic cells are distinguished from Prokaryotic cells by their large size and the presence of a nucleus and are provided with the following organelles:  Mitochondria: A trademark involved in the process of cellular respiration to produce ATP.  Endoplasmic Reticulum (ER): It has been involved in peptide synthesis, synthesis of fatty acid and other lipids.  Golgi Apparatus: Processes and secrete proteins and lipids; modifies, sorts and packages proteins and lipids.  Lysosomes: They stay containing digestive enzymes that digest food inside the cell.  Chloroplasts: Located in the plant cell and is involve in the process of making food for plants. o Cytoskeleton: Cytoplasm of eukaryotic cells contains more than one type of filamentous proteins as follows microfilament, intermediate filament and micro tubule which gives structural support and mobility to the cell. • Reproduction: o Mitosis and Meiosis: In the eukaryotic cells, cell division is either through mitosis as in yeast laboratory fungi, bacteria and some plant/single celled organisms, and by meiosis as in animals and plants with sexual reproduction. • Examples: o Animal Cells: Such cells as skin cells in human beings, muscles cells amongst others. o Plant Cells: mesophyll cells and epidermis cells of the leaves, root parenchyma cells. o Fungal Cells: These are cells of the yeast. o Protists: Amoeba, Paramecium.