L1 - Cell Structure PDF

Prof. Dr. Shehab Hafez Medicine (Semester 1) Foundations of Normal Human Structure (BMS111) 1 Cell Structure (1) Prof. Dr. Shehab Hafez Professor of Histology & Cell Biology Head of Histology Department. Mansoura University ...

Prof. Dr. Shehab Hafez Medicine (Semester 1) Foundations of Normal Human Structure (BMS111) 1 Cell Structure (1) Prof. Dr. Shehab Hafez Professor of Histology & Cell Biology Head of Histology Department. Mansoura University  Prof. Dr. Shehab Hafez 1. To demonstrate structure of the cell membrane. 2. To determine functions of cell membrane & cell coat. 3. To recognize classification of cell organelles. 4. To demonstrate the basis of routine histology staining. 5. To determine structure and functions of mitochondria. 6. To recognize structure, types and functions of ribosomes.  Prof. Dr. Shehab Hafez Cell structure 1. Cell membrane 2. Nucleus 3. Cytoplasm A. Cytoplasmic organelles ▪ Mitochondria. ▪ Endoplasmic reticulum. Membranous ▪ Golgi apparatus. organelles ▪ Lysosomes. Non-membranous ▪ Ribosomes organelles B. Cytoskeleton C. Cell inclusions  Prof. Dr. Shehab Hafez Cell Membrane ▪ It is the outer limiting membrane which surrounds the cell. ▪ Also called plasma membrane or plasmalemma. ▪ Thickness: 7.5 : 10 nm & thus visible only by electron microscopy (E.M). E.M. The cell membrane shows: Trilaminar appearance:- Two electron dense lines (black) separated by an electron lucent one (white). Trilaminar appearance PM: Plasma membrane MV: microvilli  Prof. Dr. Shehab Hafez Molecular structure of cell membrane I. Lipid molecules The cell membrane is II. Proteins formed of III. Carbohydrates I. Lipid molecules 1. Phospholipids Phospholipid molecules consist of: Head: Hydrophilic (water attracting). Tail: Hydrophobic (water-repelling). Organized into a double layer (bilayer); The hydrophobic tails are directed toward the middle, away from water & the hydrophilic heads facing water. Phospholipids Prof. Dr. Shehab Hafez Head: Hydrophilic (water attracting). Tail: Hydrophobic (water-repelling). Organized into a double layer (bilayer);The hydrophobic tails are directed toward the middle, away from water & the hydrophilic heads facing water.  Prof. Dr. Shehab Hafez 2. Cholesterol ▪ Between the phospholipid molecules. ▪ They regulate the fluidity of the phospholipid bilayer & stabilise it. II. Protein molecules 1. Integral proteins Types 2. Peripheral proteins 1. Integral proteins ▪ Firmly embedded in the lipid bilayer. ▪ Not easily extracted. Transmembrane proteins ▪ Large, Completely span the lipid bilayer. ▪ Usually attached to microfilaments in the cytoplasmic side (for fixation). ▪ Act as channels. 2. Peripheral proteins Prof. Dr. Shehab Hafez ▪ Loosely attached to the outer or inner membrane surfaces. ▪ Can be easily extracted. III. Carbohydrate molecules ▪ Glycolipids and glycoprotein. ▪ They are projecting from the external surface of the membrane, forming the Cell Coat or Glycocalyx.  Prof. Dr. Shehab Hafez Molecular structure of cell membrane  Prof. Dr. Shehab Hafez Functions of cell membrane 1. Exchange of materials ▪ Passive diffusion: for gases and ions. According to concentration gradient. ▪ Active transport: for amino acids, glucose & fatty acid. Needs enzymes & energy. ▪ Selective transport: for hormones, drugs & bacteria. Needs receptors & energy. 2. Endocytosis A. Phagocytosis B. Pinocytosis For solid particles: (Cell eating): For fluids: (Cell drinking). Example: macrophages can engulf certain bacteria. C. Receptor-mediated endocytosis Prof. Dr. Shehab Hafez Needs receptors (integral proteins). For large molecules: Example: protein hormones & some drugs. 3. Exocytosis ▪ Opposite to phagocytosis. The cell expels any waste product. 4. Functions of cell coat ▪ Adhesive function: for adjacent cells. ▪ Plays a role in immunity (recognize the cell of its own type and the foreign cells). ▪ Participates in the formation of basement membrane.  Prof. Dr. Shehab Hafez Mitochondria Definition: membranous organelles containing enzymes specialized for production of energy (ATP). (Power house of the cell) Size and shape: Mitochondria vary in size and shape. May be elongated, rod-shaped or spherical. Number: Highly variable depending on the activity of the cell e.g. liver cells contain numerous mitochondria, whereas lymphocytes contain very few. The number of mitochondria is modified by mitochondrial division.  Prof. Dr. Shehab Hafez Sites: Mitochondria are very mobile. They localise at sites of maximum energy requirement e.g. Between myofibrils in cardiac muscle cells.  Prof. Dr. Shehab Hafez The routine stain for light microscopy (LM) A. Hematoxylin & Eosin (H & E) Hematoxylin (H) Eosin (E) Nature Basic (alkaline). Acidic. Colour Blue. Red. E.M. Reacts with acidic structures Reacts with basic structures inside the cell: inside the cell: usually the ▪ DNA: (in the nucleus). cytoplasm which is rich in mitochondria. ▪ RNA: (in ribosomes & RER). Cytoplasm rich in ribosomes & Cytoplasm rich in mitochondria RER is basophilic eg plasma cell is acidophilic eg renal tubules  Prof. Dr. Shehab Hafez Light microscopy (LM) of mitochondria 1. H.& E. 2. Succinic dehydrogenase ▪ Mitochondria are responsible for enzyme activity the acidophilic cytoplasm. Succinate dehydrogenase is an enzyme of Krebs citric acid cycle and is exclusive to mitochondria. Renal tubules: appear acidophilic due to rich mitochondria  Prof. Dr. Shehab Hafez Electron microscopy (EM) The mitochondria is a double membranous organelle. Each mitochondrion consists of 4 compartments: 1. Outer membrane Smooth, no folds. 2. Inner membrane Forms complex folds called cristae. The number of cristae is increased in more active cells. 3. Intermembranous space 4. Mitochondrial matrix: Contains: Mitochondrial DNA. Ribosomes.  Prof. Dr. Shehab Hafez EM of mitochondria  Prof. Dr. Shehab Hafez Functions of mitochondria 1. Provide the cell with ATP: Aerobic respiration takes place within the matrix & on the inner membrane to produce energy. 2. The mitochondrial matrix contains one or more circular strands of DNA & Thus can divide and increase their number according to energy need of the cell. 3. The matrix also contains ribosomes & thus the Mitochondria can synthesise most of its own proteins.  Prof. Dr. Shehab Hafez Ribosomes Definition: Non-membranous organelles. The ribosome is the protein factory of the cell. Size: very small (20-30 nm in diameter). L.M. The individual ribosome is too small to be seen by L.M. Aggregation of ribosomes leads to basophilia of the cytoplasm due to rRNA.  Prof. Dr. Shehab Hafez E.M. ▪ Ribosomes are small electron-dense particles. ▪ Composed of two subunits; small & large subunits. ▪ The two subunits are formed of rRNA and about 80 different protein molecules. Types 1. Free ribosomes: Polyribosomes: Polysomes 2. Attached Ribosomes: Rough endoplasmic reticulum: (RER)  Prof. Dr. Shehab Hafez A. Free ribosomes (polyribosomes B. Attached ribosomes: or polysomes): Many ribosomes The single ribosome or polysomes bound to a single mRNA molecule. are attached to the surface of endoplasmic reticulum forming RER. Free ribosomes Attached ribosomes (RER) Functions Prof. Dr. Shehab Hafez A. Free ribosomes Synthesize proteins for the use of the cell: Cytoplasmic and cytoskeletal proteins. B. Attached ribosomes Synthesize proteins ▪ To be secreted outside the cell as secretory proteins OR ▪ Remain in the cytoplasm as primary lysosomes.  Prof. Dr. Shehab Hafez Resources ▪ Junqueira LC, Carneiro J: Junqueira’s Basic Histology. Text and Atlas, thirteenth edition (2013), LANGE Mc Graw Hill. ▪ Gartner LP and Hiatt JL: Color Textbook of Histology. Third edition (2007). Saunders Elsevier. Prof. Dr. Shehab Hafez