Biology Lecture 1 PDF

Biology By: Dr. Shaimaa Zaher  Objectives Define biology and identify its branches, cell theory and cell organization Compare between prokaryotes and eukaryotes Identify the general structure of eukaryotic animal cells Describe microscopic and molecular structure...

Biology By: Dr. Shaimaa Zaher  Objectives Define biology and identify its branches, cell theory and cell organization Compare between prokaryotes and eukaryotes Identify the general structure of eukaryotic animal cells Describe microscopic and molecular structure of cell membrane Outline cell membrane function  Biology Biology is the science of life studying all aspects about living organisms (plants, animals and humans) including their structure, functions and interactions with their environment. Branches of biology: cell biology, histology, genetics, physiology, embryology and more others.  Cytology & Cell Biology It is a branch of biology that studies the cell (their structure ,physiological properties, interactions with their environment, division, function and death). This is done both at a microscopic and molecular level. Cell Theory  Matthias Schleiden (1838) concluded that all plants are made of cells Cell Theory Theodore Schwann (1839) All living organisms are made up of cells. concluded that all Cells are the basic structural and functional animals are made of units of all living organisms. cells New cells are produced from pre-existing cells. Rudolf Virchow (1855) concluded that all cells came from pre-existing cells  Cellular organization There are two basic types of cellular organization (as detected by electron microscope): 1- Prokaryotes 2- Eukaryotes (before nucleus) (true nucleus) They are more complex. They are simple cells. They have nuclear envelope and They don’t have nuclear compartments known as cell envelope or membranous organelles (mitochondria, Golgi organelles. apparatus, lysosomes…..). e.g. Bacteria e.g. cells of plants, animals and humans.  Comparison between prokaryotes and eukaryotes Prokaryotes Eukaryotes 1- Cell size 0.1- 5 micrometer 10-100 micrometer Present with true nuclear 2- Nucleus absent envelope Present such as 3- Membranous mitochondria, Golgi absent organelles apparatus, endoplasmic reticulum…….. - Single and circular - Linear 4-DNA - Not complexed with - Highly condensed with histones histones 5-Ribosomes Smaller in size Larger in size The human body is composed of: Cells Tissues Organs Systems Structural Formed of Composed Group of and similar tissues to organs functional cells perform a perform units of all performing specific interrelated living a specific function function organisms function e.g. e.g. stomach digestive system There are 4 basic tissues Epithelial Nervous tissue Connective tissue Muscular tissue tissue  How to study cells? Because of the small size of cells, we use microscopes for magnification and resolution. Units of magnifications Types of microscopes: 1 cm = 10 millimeters (mm) 1- Light microscope. 1 mm = 1000 micrometers (µm) 2- Electron microscope. 1 µm = 1000 nanometer (nm) Light microscope (LM) Electron microscope (EM) Staining for light microscopy Tissues and their components are colorless Need to be stained Stains color different components with different colors  Hematoxylin and Eosin Stain (H & E) Is the commonly used stain in routine histological examination (the ordinary stain) 1. Hematoxylin (H): Acidophilic It is a basic stain with a blue color. cytoplasm Binds to acidic components of the cell e.g nucleic acids. Nuclei Structures that accept the blue color of hematoxylin are called basophilic. Basophilic cytoplasm  Hematoxylin and Eosin Stain (H & E) 2. Eosin (E): Acidophilic It is an acidic stain with a red color. cytoplasm Binds to basic components of the cell. Structures that accept the red color of eosin are called acidophilic. Nuclei N.B. Nucleus is basophilic Cytoplasm may be basophilic or Basophilic acidophilic cytoplasm  Electron microscope (EM) ▪ Allows more magnification for more details ▪ Structures seen by EM appear either: Grey to Black (electron-dense) White (electron-lucent)  General structure of eukaryotic animal cells Cells are of variablein shapes and sizes. Each animal cell is composed of two main parts: 1. The cytoplasm. 2. The nucleus. Cytoplasm consists of: Organelles Inclusions Cytosol Living structures Nonliving structures Viscous fluid containing Essential for life of each Not essential for life of enzymes, ions, O2, CO2, cell cells metabolites. Metabolically Metabolically inert Support organelles active  Organelles They are classified according to the presence or absence of membrane into: Membranous Non-membranous organelles organelles ✓ Ribosomes ✓ Cell membrane ✓ Microtubules ✓ Mitochondria ✓ Microfilaments ✓ Endoplasmic reticulum ✓ Intermediate ✓ Golgi apparatus filaments ✓ Lysosomes ✓ Centrioles ✓ Peroxisomes ✓ Cilia ✓ Flagella  Membranous Cell Organelles - Definition - Structure (LM & EM) 1- The cell membrane - Function (plasma membrane or plasmalemma) Definition: It is the membrane that envelops the cell. Structure: By L.M.: ▪ It is difficult to be seen (Why??) ▪ The cell membrane is only 7.5 - 10 nm thick and thus, it is too thin to be seen with L.M. By E.M.: ▪ At low magnification: it appears as a single electron dense line. 2 electron dense ▪ At high magnification: Electron lucent layer layers ✓ It appears as a trilaminar membrane Glycocalyx (trilamellar or unit membrane), formed of two electron dense layers separated by an electron lucent intermediate layer. ✓ The outer surface of the cell membrane is covered by the cell coat (glycocalyx) (has a fuzzy appearance). Molecular structure of the cell membrane Lipids Proteins Carbohydrates Phospholipids Cholesterol Integral Peripheral Glycoproteins Glycolipids 1- Lipid component: includes a) Phospholipid molecules ▪ They are arranged into 2 layers (lipid bilayer). ▪ Each molecule has a polar and a non-polar end: The polar end (phosphate heads): It is hydrophilic and directed towards aqueous solution. So, the heads are found on the outer and the inner (cytoplasmic) surfaces of the cell membrane. The non-polar end (fatty acid tails): It is hydrophobic and directed inwards (away from aqueous solutions). b) Cholesterol molecules: They are inserted among the hydrophobic fatty acid tails, restricting their movement. They regulate membrane fluidity. 2- Protein component There are two types of protein molecules in cell membrane: Integral proteins a) The integral (intrinsic) membrane proteins; i- Some of them are extending all the way from one side of the membrane to the other side. They are called transmembrane proteins. Peripheral ii- Others are only partially embedded in the lipid proteins bilayer. b) The peripheral (extrinsic) membrane proteins; They are bound mainly to the cytoplasmic side of the lipid bilayer. Integral membrane proteins act as: channels, carriers, receptors and enzymes.  3- Carbohydrate component ▪ Sugar chains are linked to proteins of cell membrane forming glycoproteins and to lipids forming glycolipids. ▪ Found at the external surface of the cell membrane. ▪ Glycoprotein and glycolipid form cell coat (glycocalyx).  Glycolipid Glycoprotein Phosphate head Phospholipid molecule Fatty acid tail Cholesterol molecule Peripheral protein Integral protein Integral protein (Partly embedded protein) (Transmembrane protein)  Glycocalyx Glycocalyx ▪ It is formed of glycoproteins and glycolipids. ▪ Has a fuzzy appearance by EM. ▪ Function: Cell recognition Intercellular adhesions Include digestive enzymes (as in small intestine).  Functions of cell membrane 1- It maintains the structural integrity of the cell. 2- It controls movement of substances into and out of the cell through establishing a transport system (selective permeability). Transport across cell membrane Passive transport Active transport Vesicular transport  Simple ▪ Movement of molecules e.g. O2 & CO2 diffusion down the concentration I- Passive transport gradient. Through transporter ▪ Does not need energy Facilitated (carrier) proteins e.g. diffusion transport of glucose  ▪ Movement of molecules against the concentration gradient II- Active transport ▪ Needs energy ▪ e.g. sodium potassium pump  III- Vesicular transport Transport of large molecules by formation of vesicles It includes Endocytosis Exocytosis Phagocytosis Receptor-mediated endocytosis Pinocytosis  Endocytosis It is the uptake of materials across the cell membrane into the cytoplasm of the cell.  Endocytosis includes 3 forms: 1- Phagocytosis (cell eating) ▪ Uptake of solid materials e.g. bacteria in the form of phagocytic vesicles (phagosomes). ▪ It involves extension of folds called pseudopodia to engulf the solid particle. ▪ The phagosome fuses with a lysosome for degradation of its contents. ▪ Some cells, such as macrophages and neutrophils, are specialized for phagocytosis. 2- Pinocytosis (cell drinking) Uptake of fluid materials in the form of pinocytotic vesicles. The resulting pinocytotic vesicles either fuse with lysosomes or move to the opposite side of the cell membrane to release their contents outside the cell in a process celled transcytosis. Transcytosis 3- Receptor-mediated endocytosis Ligand (Clathrin dependent endocytosis) Ligand-receptor It includes integral membrane proteins called receptors that bind specific molecules called ligands (as low-density lipoproteins and protein hormones). Binding of the ligand to its receptor causes their accumulation in a cell membrane region called coated pit. Coating on the cytoplasmic surface of the pit is composed of many proteins mainly clathrin.  The coated pit invaginates and is Ligand Ligand-receptor pinched off in the cytoplasm as a coated vesicle. So, the coated vesicle carries the ligand & its receptor into the cell. The clathrin molecules separate from the coated vesicles & recycle back to the cell membrane for formation of new coated pits.  The vesicle ,after losing their coat, fuse with the endosome that separate the receptor form the ligand. The receptors return to the cell membrane for reusing. The remaining vesicle that contains the ligand may fuse with the lysosome for degradation or move to the opposite side of the cell membrane to release their contents outside the cell (transcytosis). The endosome is a membranous organelle. Its lumen has acidic pH that allow dissociation of receptor and ligand.  Exocytosis It is the release of substances across the cell membrane outside the cell e.g., release of secretory proteins as pancreatic enzymes. Which of the following is characteristic to the structure of cell membrane? A- It is 2 to 3 nm in thickness B- It is lined from inside by glycocalyx C- Appears bilayer by EM high magnification D- Its phospholipids are arranged in 2 rows Which of the following cellular processes describes the uptake of extracellular fluids by the cell? A- Autophagy B- Exocytosis C- Phagocytosis D- Pinocytosis 49