Cell Biology Lecture 1, Dr Hanan, October 2024 PDF

Hanan Elimam, Ph.D Associate prof. of Biochemistry and Molecular Biology Faculty of Pharmacy, University of Sadat City, Al Ryada University ž2 Quizzes: 2 x 7.5 = marks ž1 assignment = marks žMidterm exam = Marks žFinal Exam = Marks  Biology: Is science of life and living org...

Hanan Elimam, Ph.D Associate prof. of Biochemistry and Molecular Biology Faculty of Pharmacy, University of Sadat City, Al Ryada University ž2 Quizzes: 2 x 7.5 = marks ž1 assignment = marks žMidterm exam = Marks žFinal Exam = Marks  Biology: Is science of life and living organisms, including their Structure, Function, Growth, Evolution, Distribution, Identification and Taxonomy Microbiology – the study of microscopic organisms (microorganisms) and their interactions with other living things Bacteriology - the study of bacteria Mycology – the study of fungi Parasitology – the study of parasite Virology – the study of viruses and some other virus-like agents Cell biology – the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell. Genetics – the study of genes and heredity. Objectives: 1. To study all living beings and how organisms interact in the biosphere. 2. Biology also studies the origin of diseases, such as the etiology of cancer, infections, 3. discovery and production of medicines 4. Biology can aid in the prevention or cure of diseases 5. To produce and ensure high quality food is available at lower costs Organization of living organism Cellular Level ( Atoms molecules organelles cells) Organism Level ( Cell Tissues organs organ systems)  Major difference between Prokaryotes and Eukaryotes: Biological Membranes  Membranes structure: Different membranes within the cell and between cells have different compositions, as reflected in the ratio of protein to lipid according to the function of the cell. The inner mitochondrial membrane is of high protein content (75%) due to its many biological functions, whereas, myelin membrane which has lower biological functions has much less protein (20%) Membrane lipids Membrane Lipids are Amphipathic As more kinks are inserted in the tails, the membrane becomes less tightly packed and therefore more fluid. kinked tails Membrane Lipids form Bilayers??? A micelle is such a structure; the hydrophobic regions are shielded from water while the hydrophilic polar groups are immersed in the aqueous environment. Membrane Lipids form Bilayers??? A bilayer exists as a sheet in which the hydrophobic regions of the phospholipids are protected from the aqueous environment, while the hydrophilic regions are immersed in water. It is impermeable to most water-soluble molecules since they would be insoluble in the hydrophobic core of the bilayer  The Cell Membrane Proteins Are Associated with The Lipid Bilayer Proteins can be inserted into the amphipathic and form an integral part of the membrane by having hydrophilic regions protruding at the inside and outside faces of the membrane but connected by a hydrophobic region traversing the hydrophobic core of the bilayer The proteins consist of enzymes, transport proteins, structural proteins, antigens, and receptors for various molecules.  The fluid mosaic model (Singer & Nicloson,1972) A lipid bilayer in which the protein molecules are embedded. The lipid bilayer gives fluidity and elasticity to the membrane Irregular shaped proteins are floating randomly in a lipid sea The mosaic model describes important features relevant to many cellular processes, including: cell-cell signaling, apoptosis, cell division, membrane budding, and cell fusion. The fluid mosaic model is the most acceptable model of plasma membrane  Are membrane symmetric or asymmetric structures? irregular distribution of proteins within the membranes. An inside-outside asymmetry is also provided by the external location of the carbohydrates attached to membrane proteins specific enzymes are located exclusively on the outside or inside of membranes  Membrane Fluidity A vital feature of the lipid bilayer in biologic membrane is the ability its hydrocarbon chains to move within it. The property of movement is called fluidity. This fluidity is highly dependent upon: l- The lipid composition of the membrane. The longer and more saturated fatty acid chains, the less fluid the membrane structure is. 2- The presence of unsaturated fatty acid tends to increase the fluidity & decrease the compactness of the side chain packing. 3- Cholesterol / phospholipid ratio, an increase in this ratio decrease fluidity. At high cholesterol: phospholipid ratio, the fluidity is completely abolished.  Membrane transport l- Transport of small molecules either by passive diffusion or by active transport. 2- Transport of large molecules either by endocytosis or exocytosis. Passive diffusion This is spontaneous movement toward equilibrium passive diffusion (simple diffusion or facilitated diffusion).  A- Simple diffusion A small molecule (solute) such as gases can enter the cell by diffusion down an electrochemical gradient across the membrane and do not require metabolic energy.  Remember Passive transport is always down an electrochemical gradient, toward equilibrium.  Transport systems Described in a functional sense according to the number of molecules moved and the direction of bilayer movement Na+- sugar Na+-amino acid Na+ in and Ca2 + out  B) Facilitated diffusion: diffuse down electrochemical gradients across membranes Many facilitated diffusion systems are stereospecific but, like simple diffusion, require no metabolic energy. These systems require carrier protein.  B- Facilitated diffusion: "Ping-Pong" mechanism "pong" state, it is exposed to high concentrations of solute, and molecules of the solute bind to specific sites on the carrier protein. Transport occurs when a conformational change exposes the carrier to a lower concentration of solute (ping state). Pong Ping Pong  II- Active Transport The process of active transport differs from diffusion in that molecules are transported away from thermodynamic equilibrium; Energy is required (ATP) Why?? Energy is required to change either the conformation or the nature of transporter proteins Stoichiometry of the ATPase pump  Transport of macromolecules (Large molecules):- Endocytosis:- invagination of the membrane to engulf the substance Endocytosis require:- Energy (hydrolysis of ATP) Calcium in extracellular fluids Contractile elements in the cell (microfilaments). Types of endocytosis:- a)- Phagocytosis:- which occurs in macrophages and granulocytes. (large particles such as viruses, bacteria, cells or depris) b)- Pinocytosis:- which is a property of all cells and leads to the cellular uptake of fluid and its contents.  Transport of macromolecules (Large molecules):- Exocytosis:- most cells also release large molecules Exocytosis require:- signal, which is often hormone and change in calcium concentrations. Molecules released by exocytosis are:- antigens, collagen, glycosaminoglycans and hormones such as insulin Water Balance © 2009 McGraw-Hill Higher Education. All rights reserved. During diffusion molecules tend to move: (A) Up concentration gradient. (B) Down concentration gradient (C) From n area of lower concentration to an area of higher concentration (D) in a direction that does not depend on Concentration The Cell must expand energy to transport substances using: (A) Diffusion. (B) Facilitated Diffusion (C) Osmosis. (D) Endocytosis. Membrane fluidity is increased by: (A) High proportions of membrane cholesterol. (B)High proportions of long chain saturated acyl groups. (C) High proportion of sphingomyelins than phosphatidylcholines. (D)Elevated temperature. The following are functions of plasma cell Membrane Except: (A) It contains specific receptors. (B) It is site of Energy production. (C) It contains Specific pumps and channels. (D)It separates cell organism from external environment. The best described cotransport system involving glucose and sodium are: (A) Uniports. (B) Two oppositely oriented uniports. (C) Antiports. (D)Symports. The following are mechanisms for transfer of small molecules across cell membrane Except: (A) Endocytosis and Exocytosis. (B) Passive simple diffusion. (C) Facilitated simple diffusion. (D)Active transport that need energy. Phospholipids are important cell membrane constituents because: (A) they contain glycerol. (B) they contain saturated fatty acids. (C) they are amphoteric. (D) they are amphipathic molecules.