LEC 1: Overview of Cellular Physiology PDF

LEC. 1 PHYSIOLOGY Dr. Ihab Al -Khalifa Overview of Cellular Physiology Introduction The cell is the fundamental working unit of all organisms. In humans, cells can be highly specialized in both structure and function; alternatively...

LEC. 1 PHYSIOLOGY Dr. Ihab Al -Khalifa Overview of Cellular Physiology Introduction The cell is the fundamental working unit of all organisms. In humans, cells can be highly specialized in both structure and function; alternatively, cells from different organs can share features and function The Cell  Basic building blocks of life  Smallest living unit of an organism  A cell may be an entire organism (unicellular) or it may be one of billions of cells that make up the organism (multicellular).  Grow, reproduce, use energy, adapt, respond to their environment  Many cannot be seen with the naked eye  a typical cell size is 10µm; a typical cell mass is 1 nanogram.) Cells May be Prokaryotic or Eukaryotic  Prokaryotes (Greek: pro-before; karyon-nucleus) include various bacteria  lack a nucleus or membrane-bound structures called organelles  Eukaryotes (Greek: eu-true; karyon-nucleus) include most other cells (plants, fungi, & animals)  have a nucleus and membrane-bound organelles Cell Organelles 1 Cell Organelles 1- Cell Membrane  The membrane that surrounds the cell is a remarkable structure, that controls movement in and out of the cell.  It is made up of double layer of phospholipids & proteins and is semipermeable, allowing some substances to pass through it and excluding others. However, its permeability can also be varied because it contains numerous regulated ion channels and other transport proteins that can change the amounts of substances moving across it. It is generally referred to as the plasma membrane  Although the chemical structures of membranes and their properties vary considerably from one location to another, they have certain common features :  They are generally about 7.5 nm (75 Å) thick.  The major lipids are phospholipids such as phosphatidylcholine, and phosphatidylethanolamine.  The shape of the phospholipid molecule reflects its solubility properties: the head end of the molecule contains the phosphate portion and is relatively soluble in water (polar, hydrophilic) and the tails are relatively insoluble (nonpolar, hydrophobic).  The possession of both hydrophilic and hydrophobic properties make the lipid an amphipathic molecule.  In the membrane, the hydrophilic ends of the molecules are exposed to the aqueous environment that bathes the exterior of the cells and the aqueous cytoplasm; the hydrophobic ends meet in the water-poor interior of the membrane. Cell Membrane Components  In prokaryotes , the membranes are relatively simple, but in eukaryotes, cell membranes contain various glycosphingolipids, sphingomyelin, and cholesterol in addition to phospholipids and phosphatidylcholine.  Many different proteins are embedded in the membrane, with different structure and functions , these can be summarized as: o Integral proteins o peripheral proteins 2  The proteins in the membranes carry out many functions: 1. Some are cell adhesion molecules that anchor cells to their neighbors or to basal laminas. 2. Proteins function as pumps, actively transporting ions across the membrane. 3. Other proteins function as carriers, transporting substances down electrochemical gradients by facilitated diffusion. 4. Still others are ion channels, which, when activated, permit the passage of ions into or out of the cell. 5. Proteins in another group function as receptors that bind ligands or messenger molecules, initiating physiologic changes inside the cell. 6. Proteins also function as enzymes, catalyzing reactions at the surfaces of the membrane. Movement Across the Plasma Membrane  A few molecules move freely  Water, Carbon dioxide, Ammonia, Oxygen  Carrier proteins transport some molecules 3 2. Cytoplasm  Viscous fluid surrounded by cell membrane  It houses the membranous organelles 3. Nucleus  Nucleus is the cell information center.  It has double membrane surrounding the chromosomes and the nucleolus.  It is the place where almost all DNA replication and RNA synthesis occur.  The nucleolus is a site for synthesis of RNA making up the ribosome  The nucleus is made up in large part of the chromosomes, the structures in the nucleus that carry a complete genetic features & blueprint for all the heritable species and individual characteristics of the animal.  Except in germ cells, the chromosomes occur in pairs, one originally from each parent.  Each chromosome is made up of a giant molecule of DNA. The DNA strand is about 2 m long, but it can fit in the nucleus because at intervals it is wrapped around a core of histone proteins to form a nucleosome.  The whole complex of DNA and proteins is called chromatin.  The ultimate units of heredity are the genes on the chromosomes, each gene is a portion of the DNA molecule. 4 4. Mitochondria Mitochondria is the power generators Mitochondria Surrounded by a double membrane with a series of folds called cristae and mitochondrial DNA It Functions in energy production : 1. Mitochondria, providing the eukaryotic cells with the ability to form the energy- rich compound ATP by oxidative phosphorylation (respiratory complexes ) , 2. Mitochondria perform other functions, including a role in the regulation of apoptosis (programmed cell death), but oxidative phosphorylation is the most crucial. Respiratory complexes generating ATP 5. Cytoskeleton All cells have a cytoskeleton, a system of fibers that not only maintains the structure of the cell but also permits it to change shape and move. Filaments & fibers made of 3 types Microfilaments Microtubules Intermediate filaments 5 It Has 3 functions: Mechanical support Anchor organelles Help move substances 6. Rough Endoplasmic Reticulum RER The endoplasmic reticulum is a complex series of tubules in the cytoplasm of the cell.The tubule walls are made up of membrane. The RER membranous organelle is covered with ribosomes (causing the "rough" appearance) Manufacture proteins Not all ribosomes attached to rough ER May modify proteins from ribosomes 7. Smooth Endoplasmic Reticulum SER Not attached to ribosomes The agranular endoplasmic reticulum is the site that help build molecules Carbohydrates Lipids Steroid synthesis in steroid-secreting cells and the site of detoxification processes in other cells. 6  8. Ribosomes The ribosomes are complex structures, containing many different proteins and at least three ribosomal RNAs. Each is made up of a large and a small subunit. The ribosomes in eukaryotes measure approximately 22 × 32 nm. Each cell contains thousands ribosomes They are the sites of protein synthesis. Found on RER & floating freely throughout the cell 9. Golgi Apparatus The Golgi apparatus considered the packaging & shipping station of cell. It is a collection of membrane-enclosed sacs that are stacked like dinner plates. There are usually about six sacs in each apparatus, but there may be more. One or more Golgi apparati are present in all eukaryotic cells, usually near the nucleus. Functions : the Golgi is directed at proper glycosylation of proteins and lipids, There are more than 200 enzymes that function to add, remove, or modify sugars from proteins and lipids in the Golgi apparatus 10 - Lysosomes Lysosomes are large, irregular structures surrounded by membrane found in the cytoplasm of the cell. The interior of these structures, is more acidic than the rest of the cytoplasm. External material such as endocytosed bacteria, as well as worn-out cell components, are digested in them. Lysosomes can contain over 40 types of hydrolytic enzymes. Not surprisingly, these enzymes are all acid hydrolases, in that they function best at the acidic pH of the lysosomal compartment. 7  Lysosomal enzymes 11- Peroxisomes A peroxisome ] is a type of organelle known as a microbody, found in virtually all eukaryotic cells. They are involved in catabolism of very long chain fatty acids, branched chain fatty acids, D-amino acids, and polyamines, reduction of reactive oxygen species – specifically hydrogen peroxide. Peroxisomes are 0.5 µm in diameter, Peroxisomes can form by budding of endoplasmic reticulum. 12. Centrioles Pairs of microtubular structures Near the nucleus in the cytoplasm of eukaryotic cells is a centrosome. Play a role in cell division , When a cell divides, the centrosomes duplicate themselves, and the pairs move apart to the poles of the mitotic spindle, where they monitor the steps Q/ Discuss the role of centrioles in cell division ? A/ Through a mechanism that is still incompletely understood, the centrosome replicates , if a cell is going to divide during prophase of mitosis,. two identical centrosomes then move away from each other and take up positions at opposite poles of the cell , At this time, the centrosomes produce new dynamic microtubules for chromosomes. A microtubule becomes stabilized when it finally binds to the proper region of a chromosome and the spindle fibers are contractile actin and myosin 8 proteins pull the chromosomes to opposite poles of the cell during mitosis so that cell pinches inward into two identical daughter cells. The role of centrioles in cell division ( mitosis). ‫لالطالع‬ 9 Summary for cell structure and functions 10 Microscope : is A tool for examining cellular constituents is the microscope. A light microscope can resolve structures as close as 0.2 µm, while an electron microscope can resolve structures as close as 0.002 µm. Although cell dimensions are quite variable, this resolution can give us a good look at the inner workings of the cell. Many of them can be isolated by ultracentrifugation combined with other techniques. When cells are homogenized and the resulting suspension is centrifuged, the nuclei sediment first, followed by the mitochondria. High-speed centrifugation that generates forces of 100,000 times gravity or more causes a fraction made up of granules called the microsomes to sediment. This fraction includes organelles such as the ribosomes and peroxisomes 11