Week 8 (1) - Cytoplasm.pptx

Week 8 (1) HISTOPATHOLOGY (BMS4470A) CYTOPLASM – Part 1 Dr. Merin Thomas [email protected] Office hours : Tuesday & Thursday – 1.00pm to 3.00pm  Learning Objectives...

Week 8 (1) HISTOPATHOLOGY (BMS4470A) CYTOPLASM – Part 1 Dr. Merin Thomas [email protected] Office hours : Tuesday & Thursday – 1.00pm to 3.00pm  Learning Objectives Cell differentiation The plasma membrane Cytoplasmic organelles The cytoskeleton Inclusions  What are cells? Cells and extracellular material together comprise the tissues that make up organs. In all tissues, cells are the basic structural and functional units, the smallest living parts of the body. Cell theory How did the cell get its name? Robert Hooke first observed cells in a thin piece of cork (plant). He saw walled boxes that reminded him of the tiny rooms, cellula, occupied by monks in monasteries, and the name "cell“ was coined. Monastery cellula:  How did the cell get its name? Monastery cellula: Cells in an Cells in a  plant  Types of Cells Cells can be broadly classified into TWO types: 1. Prokaryotes 2. Eukaryotes Prokaryotes DO NOT have nucleus or membrane bound organelles; eukaryotes have both. Types of Cells  Types of Cells Animal cells are enclosed by cell membranes and are eukaryotic, each with a distinct, membrane- enclosed nucleus surrounded by cytoplasm, fluid containing a system of membranous organelles, non- membranous molecular assemblies, and a cytoskeleton. In contrast, the smaller prokaryotic cells of bacteria typically have a cell wall and lack nuclei and membranous cytoplasmic structures  Slide bullet text  How many cells are there in the human body? The average adult human body consists of nearly 40 trillion cells These cells exist as hundreds of histologically distinct cell types, all derived from the zygote, and the single cell formed by the merger of a spermatozoon with an oocyte at fertilization.  Cell Differentiation The first zygotic cellular divisions produce cells called blastomeres, and as part of the early embryo’s inner cell mass blastomeres give rise to all tissue types of the fetus. Explanted to tissue culture cells of the inner cell mass are called embryonic stem cells.  Cell Differentiation Most cells of the fetus undergo a specialization process called differentiation in which they predominantly express sets of genes that mediate specific cytoplasmic activities, becoming efficiently organized in tissues with specialized functions and usually changing their shape accordingly.  Slide bullet text Differentiated cells typically specialize in one activity  The Plasma Membrane The plasma membrane (cell membrane or plasmalemma) that envelops every eukaryotic cell consists of phospholipids, cholesterol, and proteins, with oligosaccharide chains covalently linked to many of the phospholipids and proteins. Although the plasma membrane defines the outer limit of the cell, a continuum exists between the interior of the cell and extracellular macromolecules  The Plasma Membrane – Roles/Functions This limiting membrane functions as a selective barrier regulating the passage of materials into and out of the cell and facilitating the transport of specific molecules One important role of the cell membrane is to keep constant the ion content of cytoplasm, which differs from that of the extracellular fluid. Membrane proteins also perform several specific recognition and signaling functions, playing a key role in the interactions of the cell with its The Plasma Membrane – Roles/Functions  The Plasma Membrane - Structure Membranes range from 7.5 to 10 nm in thickness and consequently are visible only in the electron microscope. Membrane phospholipids are amphipathic, consisting of two nonpolar (hydrophobic or water-repelling) long- chain fatty acids linked to a charged polar (hydrophilic or water-attracting) head that bears a phosphate group. Phospholipids are most stable when organized into a double layer (bilayer) with the hydrophobic fatty acid chains located in a middle region away from water and the hydrophilic polar head groups contacting Lipids & Cholesterol in membrane  The Plasma Membrane - Structure Molecules of cholesterol, a sterol lipid, insert at varying densities among the closely-packed phospholipid fatty acids, restricting their movements and modulating the fluidity of all membrane components Proteins are major constituents of membranes (~50% by weight in the plasma membrane). Integral proteins are incorporated directly within the lipid bilayer, whereas peripheral proteins are bound to one of the two membrane surfaces, particularly on the cytoplasmic side  The Plasma Membrane – Transmembrane Proteins & Membrane Transport The plasma membrane is the site where materials are exchanged between the cell and its environment.  The Plasma Membrane – Transmembrane Proteins & Membrane Transport Most small molecules cross the membrane by the following general mechanisms Diffusion transports small, nonpolar molecules directly through the lipid bilayer. Lipophilic (fat- soluble) molecules diffuse through membranes readily, water very slowly. Channels are multipass proteins forming transmembrane pores through which ions or small molecules pass selectively. Cells open and close specific channels for Na+, K+, Ca2+, and other ions in response to various physiological stimuli. Water  The Plasma Membrane – Transmembrane Proteins & Membrane Transport Most small molecules cross the membrane by the following general mechanisms Carriers are transmembrane proteins that bind small molecules and translocate them across the membrane via conformational changes.  The Plasma Membrane – Transmembrane Proteins & Membrane Transport Diffusion, channels, and carrier proteins operate passively, allowing movement of substances across membranes down a concentration gradient due to its kinetic energy. In contrast, membrane pumps are enzymes engaged in active transport, utilizing energy from the hydrolysis of adenosine triphosphate (ATP) to move ions and other solutes across membranes, against often steep concentration gradients. Because they consume ATP pumps, they are often referred  The Plasma Membrane – Signal Reception &Transduction Cells in a multicellular organism communicate with one another to regulate tissue and organ development, to control their growth and division, and to coordinate their functions. Many adjacent cells form communicating gap junctions that couple the cells and allow exchange of ions and small molecules. Cells also use different types of receptors to detect and respond to various extracellular molecules and physical stimuli.  The Plasma Membrane – Signal Reception &Transduction Each cell type in the body contains a distinctive set of cell surface and cytoplasmic receptor proteins that enable it to respond to a complementary set of signaling molecules in a specific, programmed way. Cells bearing receptors for a specific ligand are referred to as target cells for that molecule Receptors for hydrophilic signaling molecules, including polypeptide hormones and neurotransmitters, are usually transmembrane proteins in the plasmalemma of target cells  The Plasma Membrane – Signal Reception &Transduction Three important functional classes of such receptors are Channel-linked receptors open associated channels upon ligand binding to promote transfer of molecules or ions across the membrane. Enzymatic receptors, in which ligand binding induce catalytic activity in associated peripheral proteins. G-protein–coupled receptors upon ligand binding stimulate associated G-proteins which then bind the guanine nucleotide GTP and are released to activate other cytoplasmic proteins.  REFERENCES Mescher, A. L. (2018). Junqueira’s Basic Histology Text and Atlas, FIFTEENTH. In McGraw-Hill Education eBooks. http://125.212.201.8:6008/handle/DHKTYTHD_123/5904