Cell Biology Lecture 3 PDF

Cell structure Plasma membrane & its modifications PROF.DALIA A. EL-GAMAL HEAD OF BASIC MEDICAL SCIENCE DEPARTMEANT BADR UNIVERSITY IN ASSIUT  After the lecture, students should be able to: Identify the components of the cell. LEARNING Describe the struct...

Cell structure Plasma membrane & its modifications PROF.DALIA A. EL-GAMAL HEAD OF BASIC MEDICAL SCIENCE DEPARTMEANT BADR UNIVERSITY IN ASSIUT  After the lecture, students should be able to: Identify the components of the cell. LEARNING Describe the structure of plasma membrane. OBJECTIVES Recognize the role of transmembrane proteins in membrane transport. Identify endocytosis & exocytosis.  LEVEL OF ORGANIZATION ▪ The human body represents the highest level of organization. ▪ E.g. (systems, organs, tissues, cells, organoids, macromolecules, atoms)  THE CELL ▪ Eukaryotic cells (Eu = true, Karyon = Nucleus) are the cells which have well defined nuclei. ▪ Prokaryotic cells (karyo = nucleus) can not be considered as true cells, since they do not have definite nucleus (including bacteria and some algae).  CELL STRUCTURE The cells is composed of; Eukaryotic cells Cytoplasm Organelles Membranous Non-membranous Cytoskeleton Inclusions Nucleus  CELL SHAPE ▪ Free cells tend to be spherical in shape because this is considered to be the most suitable and economic shape  CELL SIZE ▪ Cells are 10-12 μm in diameter ▪ Some cells may reach a very large size (100 μm) as in the case of the ovum. ▪ Others are very small size (6 μm as in some blood cells). ▪ The size of cell is constant for each cell type regardless of the size of the animal. Liver or kidney cells have the same size in man, horse or rat. This is called the "Law of constant volume". Skeletal muscle fibers – up to 60 um in cross-sectional diameter and 10 cm in length Megakaryocyte in bone marrow smear Primary oocyte in Graafian follicle  CELL NUMBER ▪ The human body starts as one cell ( the fertilized egg ). ▪ Nerve cells and cardiac muscle cells do not increase in number after birth. ▪ Cells of the kidney or liver increase with age and reach a constant number at adulthood ▪ Cells of the blood or skin are continuously produced but their number remains almost constant  QUESTION Regarding cells, which of the following is CORRECT: a. Skeletal muscle cells (fiber) are the smallest cell b. Nerve cells are continuously renewable c. Liver cells can not proliferate d. Cell nucleus can stain pink because it is acidophilic e. Red blood corpuscles are renewable Answer: e  PLASMA MEMBRANE ▪ Plasma membrane ranges from 7.5-10 nm in thickness. ▪ Acts as a boundary layer to contain the cytoplasm (fluid in cell) ▪ Selectively permeable to select chemicals that pass in and out of cells ▪ Interlocking surfaces bind cells together  PLASMA MEMBRANE ▪ The plasma membrane is made of: phospholipids ▪ Cholesterol ▪ protein ▪ oligosacharides. ▪ Membrane phospholipids are arranged into a double layer (bilayer). (Junqueira’s Basic Histology 2018)  PLASMA MEMBRANE ▪ The trilaminar appearance of the plasma membrane after fixation with osmium tetroxide.. (Junqueira’s Basic Histology 2013) PLASMA MEMBRANE (Junqueira’s Basic Histology 2018)  Plasma membrane Integral proteins Functions: 1. Transmembrane proteins transport glucose and amino acids. 2. They may act as ion channels permit passive diffusion of certain ions. 3. Some serve as pumps for moving Ca++ , Na+ , K+ and H+ against concentration gradients. 4. Form receptors that recognize hormones, neurotransmitters. 5. Glycoproteins are involved in the Formation of glycocalyx.  PLASMA MEMBRANE Peripheral proteins: They are present loosely associated with the membrane surfaces (particularly the inner surface) and therefore can easily be extracted Oligosaccharides in the plasma membrane: Oligosaccharides are present in the PM combined with integral proteins and lipids forming glycoproteins and glycolipids respectively. The oligosaccharide parts project at the outer surface of the PM to form the cell coat or glycocalyx. PLASMA MEMBRANE TRANSPORT PROCESSES Methods of transport Active transport Bulk Passive Energy requiring transport transport process 1-Ionic pore 1-Simple 2-carrier protein diffusion 2-Facilitated diffusion  EXOCYTOSIS & ENDOCYTOSIS *Exocytosis: Means bulk movement of macromolecules out of the cell *Endocytosis: Means bulk movement of macromolecules into the cell. It includes: 1. Phagocytosis: Is a type of endocytosis meaning the ingestion of particles (cell eating). 2. Pinocytosis: Is a type of endocytosis in which extracellular fluid is taken up by the cell (cell drinking). BULK TRANSPORT MODIFICATION OF PLASMA MEMBRANE Plasma membrane modifications Apical part Lateral part Basal part  MODIFICATIONS ALONG THE APICAL PART OF THE PLASMA MEMBRANE I. Cuticle: a substance rich in proteins is deposited on the outer lamina of the plasma membrane. Example; the cells lining the urinary bladder and ureter. II. Caveoles: These are invaginations which result from the process of exocytosis  MODIFICATIONS ALONG THE APICAL PART OF THE PLASMA MEMBRANE III. Cilia: for transportation A cilium is a projection from the surface of the cell in the form of long cylindrical membrane- bound known as the shaft. Note: Shaft has microtubuluar structure known as axoneme IV. Microvilli :to increase absorptive surface area; Contains microfilaments in its core  MODIFICATIONS ALONG THE LATERAL PART OF THE PLASMA MEMBRANE 1.Anchoring junctions are sites of strong cell adhesion : a.Tight Junction: ("zonula occludens) adjacent cell membranes fuse leaving no intercellular space, creates a seal between cells b.Intermediate Junction:(zonula adherens) In two facing membranes, dense plaques are deposited and numerous actin microfilaments are inserted into these plaques. - produces a certain degree of rigidity to the apex of the cell c.Desmosomes: (macula adherens) ▪ - It consists of two cytoplasmic adhesion plaques ▪ -The two plaques are connected by transmembrane linker proteins. ▪ - In the region of the desmosome, intermediate filaments connect the filaments in the plaques giving support to the junction. 2. Electric coupling; (nexus or gap junction) ▪ Represent regions of low electrical resistance or coupling as in between cardiac muscle fibers ▪ Formed of a complexed ionic pore or ionic channel (connexon) through which ions can passfrom one cell to another. 3. Interdigitations: The PM of two adjacent cells may be thrown into a complex interdigitation to give a very wide surface area for intercellular passage of material. example : cells of the of the kidney tubules. 4.Intercellular Canaliculi:Secretory material from adjacent cells is accumulated in channels known as intercellular canaliculi which carry the secretions to ducts. The intercellular canaliculi between liver cells are examples.  MODIFICATIONS AT THE BASAL PART OF THE PLASMA MEMBRANE A. Basal infoldings: Membranous infoldings at the base of certain cells are present to help in increasing the surface of the membrane for effective basal flow of material as in the cells of kidney tubules. B. Hemidesmosomes: are present at the basal membrane of protective cells to hold them firmly to underlying tissues.  QUESTION Concerning plasma membrane, which of the following is INCORRECT? a. Plasma membrane is 7-10 nm and can not be seen by light microscope b. Microvilli is a modification at the basal part of the plasma membrane c. Desmosomes is a type of cell junction that form a band surrounding the cells. d. Hemidesmosomes connect cell to the underlying tissue e. Gap junction is ionic channel known as "connexon“ Answer: b & c Thank you