Cells and Viruses PDF

CELLS AND VIRUSES NIES-PORT SAID The shorter the wavelength of the light (or other form of electromagnetic radiation) being used, the better the resolution. This is because when light interacts with an object, it can either be absorbed, reflected, refracted, or diffracted. Why is a spe...

CELLS AND VIRUSES NIES-PORT SAID The shorter the wavelength of the light (or other form of electromagnetic radiation) being used, the better the resolution. This is because when light interacts with an object, it can either be absorbed, reflected, refracted, or diffracted. Why is a specimen placed in a vacuum in an electron microscope? Without a vacuum, the electrons would strike and be scattered by the atoms / particles of the air components. Cells are divided into two main classes, initially defined by whether they contain a nucleus. Prokaryotic cells (bacteria) lack a nuclear envelope; eukaryotic cells have a nucleus in which the genetic material is separated from the cytoplasm. Both prokaryotic and eukaryotic cells have structures in common. All cells have a plasma membrane, ribosomes, cytoplasm, and DNA. The plasma membrane, or cell membrane, is the phospholipid layer that surrounds the cell and protects it from the outside environment. Ribosomes are the non-membrane bound organelles where proteins are made, a process called protein synthesis. The cytoplasm is all the contents of the cell inside the cell membrane, not including the nucleus. Structure of a prokaryotic cell. Structure of a eukaryotic cell  Prokaryotic Eukaryotic Cell size (1 – 10um) larger (10 – 100um) Cell arrangement unicellular multicellular True membrane-bound No Yes nucleus DNA structure DNA is circular and is linear and complexed with neither associated with "histones," before histones nor organized into organization into a number chromosomes. of chromosomes Membrane-bound organelles do not contain Contain membrane-bound organelles such as the mitochondria, golgi apparatus, lysosomes, peroxisomes and ER Ribosome size 70S 80S Cytoskeleton No Yes Sexual reproduction Asexually Most Sexually Cell division Binary fission Mitosis Ribosomes coordinates the interaction between mRNA and tRNA and Protect mRNA from nucleases.  Cell wall (Plant cell) The plant cell wall is generally arranged in 3 layers and composed of carbohydrates, like pectin, cellulose, hemicellulose. The three major layers are:  Primary Cell Wall  The Middle Lamella (an interface between the other neighboring cells and glues them together)  The Secondary Cell Wall The cell wall of plant cells is permeable to all substances. The main function of the cell wall is to provide structural strength and support (rigid and regular shape). It allows cells to develop turgor pressure, which is the pressure of the cell contents against the cell wall.  Plasmodesmata Plasmodesmata are cytoplasmic bridges that connect adjacent plant cells. The plasmodesmata is a channel through the plant cell wall that allows molecules and substances to move in and out of the cell.  Cell membrane The cell membrane consists of a lipid bilayer that is semipermeable (Selective). The cell membrane regulates the transport of materials entering and exiting the cell. Most plasma membranes consist of approximately 50% lipid and 50% protein by weight, with the carbohydrate portions of glycolipids and glycoproteins constituting 5 to 10% of the membrane mass.  Endoplasmic reticulum (ER) The transportation system of the cell Endoplasmic reticulum is an organelle found in both eukaryotic animal and plant cells.. The endoplasmic reticulum (ER) is a network of membrane-enclosed tubules and sacs (cisternae) that extends from the nuclear membrane throughout the cytoplasm. There are two distinct sub-compartments of the ER – the rough and the smooth ER. SER RER Structure Tubular structure Flat sacs which are and does not have embedded with ribosomes on its membrane-bound surface ribosomes on the outer surface Function Synthesis and Synthesis and transport lipids. transport proteins to Golgi or other parts and may in vesicles.  Golgi apparatus, Golgi body, is a membrane-bound organelle found in eukaryotic cells (cells with clearly defined nuclei) that is made up of a series of flattened stacked pouches called cisternae. It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. The Golgi apparatus, or Golgi complex, functions as a factory in which proteins received from the ER are further processed and sorted for transport to their eventual destinations: lysosomes, the plasma membrane, or secretion. The Golgi apparatus is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations.  Lysosome Lysosomes are sphere-shaped sacs filled with hydrolytic enzymes that have the capability to break down many types of biomolecules. Enzymes of the lysosomes are synthesized in the rough endoplasmic reticulum and exported to the Golgi apparatus transported from the Golgi apparatus to lysosomes in small vesicles, which fuse with larger acidic vesicles What are the functions of lysosome? 1. Intracellular digestion 2. Removal of dead cells (autolysis) 3. Destruction of old organelles (autophagy) 4. Help in fertilization (sperms head or acrosome secrete some lysosomal enzymes which help in the penetration of sperm into vitelline layer of ovum).  Mitochondria Mitochondria are surrounded by a double-membrane system, consisting of inner and outer mitochondrial membranes separated by an intermembrane space. The inner membrane forms numerous folds (cristae), which extend into the interior (or matrix) of the organelle and has highly selective permeability. Containing DNA and ribosomes.  Chloroplast They are double-membrane organelle with the presence of outer, inner and intermembrane space. The inner membrane surrounds a large space called the stroma, which is analogous to the mitochondrial matrix and contains many metabolic enzymes. Stroma is the fluid-filled internal space of the chloroplasts which encircle the grana and the thylakoids composed of membranes that contain photosynthetic chlorophyll. like the mitochondrion, the chloroplast has its own Chloroplasts produce energy through photosynthesis genome and genetic system. The stroma therefore and oxygen-release processes, which sustain plant growth and crop yield. As such, chloroplasts are also contains a special set of ribosomes, RNAs, and responsible for the biosynthesis of active compounds the chloroplast DNA. such as amino acids, phytohormones, nucleotides, vitamins, lipids, and secondary metabolites  Ribosomes Ribosomes can be found floating within the cytoplasm or attached to the endoplasmic reticulum. A ribosome is made out of RNA and proteins, and each ribosome consists of two separate RNA-protein complexes, known as the small and large subunits. Ribosomes receive information from the cell nucleus and construction materials from the cytoplasm. Ribosomes translate information encoded in messenger ribonucleic acid (mRNA). They link together specific amino acids to form polypeptides and they export these to the cytoplasm. (Protein synthesis)  Nucleus The nuclear envelope is made up of two lipid bilayer membranes, an inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. passage of substances). The outer nuclear membrane is continuous with the endoplasmic reticulum. The nucleoplasm is a gel-like substance inside the nucleus of a cell. The primary components of the nucleoplasm are chromatin, protein fibers called fibrils, and water. Chromatin is made from DNA and protein molecules that code genetic information for protein synthesis. The nucleus houses the nucleolus. The nucleolus is not membrane bound synthesizes the parts that make up the ribosomes.  Centrioles Centrosomes are structures found inside of animal cells. They are made from two centrioles. Centrioles are microtubule rings. Each centriole is a cylinder of microtubules, typically consisting of a ring of 27 microtubules (arranged as 9 triplets). The main purpose of a centrosome is to organize microtubules and provide structure for the cell, as well as work to pull chromatids apart during cell division.  Microtubules Microtubules are composed of alpha- and beta-tubulin subunits assembled into linear protofilaments. A single microtubule contains 10 to 15 protofilaments (13 in mammalian cells) that wind together to form a wide hollow cylinder. The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division.  Sap Vacuoles Sap vacuoles are little sac-like structures found in cells that are filled with fluid and used for material storage (cell sap). It creates a sealed compartment within the cell that is filled with water, dissolved inorganic and organic molecules (enzymes). Their job is to store resources and sustain the cell mechanically. It also keeps the cell's Turgor pressure constant.  Microvilli Microvilli are tiny finger-like projections found on the surface of certain cells. Their purpose is to increase the surface area of the cell's apical surface, resulting in more effective absorption or secretion of substances. These microvilli are predominantly present in cells lining the small intestine, kidney tubules, and certain cells in the respiratory and reproductive systems. By significantly expanding the surface area of the cell membrane, microvilli enhance the cell's capacity to exchange materials with its surroundings.