Cell Biology Lecture Notes PDF

Presented by Dr. Marwa Ashraf Essa Lecturer of Biochemistry - Faculty of Pharmacy - O6U 1  What is this course about? Its importance? This course is the basic science for several future courses in several departments, namely: Biochemistry, Microbiology, Pharmacology, and...

Presented by Dr. Marwa Ashraf Essa Lecturer of Biochemistry - Faculty of Pharmacy - O6U 1  What is this course about? Its importance? This course is the basic science for several future courses in several departments, namely: Biochemistry, Microbiology, Pharmacology, and Pharmacognosy. CELL BIOLOGY is essential for understanding how the cell work and behave in health and disease, how drugs interact with cells, how antibiotics target bacterial cells, etc.. The course is divided between 2 departments: Biochemistry & Microbiology Starting by the Biochemistry part,,, you will learn about structure, function and behavior of the eukaryotic cells. 2  Cell discovery It paralleled the development of microscope in the seventeenth-century. Hooke was the first to observe and record cells. He described the cella (open spaces) of plant tissues. Later, the “cell theory” was proposed by the botanist Schleiden and the zoologist Schwann Cell theory All living organisms are composed of cells. 3  Cell Diversity Cell size is measured in micrometers (μm) (1 μm = 10-6 m). 1. Size Unicellular as bacteria. Multicellular as humans, animals, plants, fungi. 2. Number Cells have different shapes according to their function. 3. Morphology 4. Function Cell functions are extremely complex and diverse, for example, food digestion (by gastrointestinal tract), detoxification (by liver), movement (by muscle cells), reproduction (by germ cells), support (by bone), defense against pathogens (by lymphocytes), and those related to thinking, emotions or consciousness (by neurons). 4  Cell classification Presence or absence of a nucleus is used for the classification of all living things: Prokaryotes Eukaryotes Organisms whose cells lack a nucleus. Organisms whose cells have a nucleus. Pro, means “before” & karyon, a “nucleus”. Eu, means “truly,” & karyon, a “nucleus”. 5  Biological membranes 6  Biomembranes are selectively-permeable membranes, that separate cells from each other → maintain differences in composition between the inside and outside of the cell OR create intracellular compartments → maintain differences in composition inside different cell organelles. Membrane structure Biomembranes are composed of: Carbohydrates Lipids Proteins 7 ✓ Carbohydrates form a small proportion of the membrane, as glycolipids or glycoproteins, present only in the outer leaflet. * Protein to lipid ratio differs in each membrane according to its function: Most plasma membranes are composed of 50% protein: 50% lipid. Inner mitochondrial membrane is composed of 75% protein: 25% lipid. WHY? Due to its many biological functions. In the nervous system, the myelin sheath is composed of 20% protein: 80% lipid. WHY? To provide a thick permeability barrier for ions to insulate the axon and it has much less biological functions. 8  Membrane LIPIDS Phospholipids Phosphoglycerides: glycerol is the alcohol backbone. Ex.: phosphatidyl -ethanolamine, -choline, -serine, - glycerol, or -inositol. Sphingomyelins: sphingosine is the alcohol backbone. Fatty acids are hydrophobic. -3 Amphipathic PO4 & Alcohol are hydrophilic. WHY?? Because PO4-3 & alcohol carry negative charges. 9  Membrane LIPIDS (cont’d) Glycosphingolipids sugar-containing lipids e.g. cerebrosides & gangliosides Also contains sphingosine as the alcohol backbone. Cholesterol intercalates among the phospholipids of the membrane. 10  Membrane Lipids form Bilayers Plasma membrane forms a sheet in which the hydrophobic regions (FATTY ACIDS) of the phospholipids are protected from the aqueous environment, while the hydrophilic regions (PO4-3 & Alcohol) are immersed in water. 11  Membrane Fluidity It is determined by the relative movement of lipids within the membrane. Movement is determined by the strength of intermolecular interactions between the lipids. STRONGER interactions → ↑ RIGID membrane. weaker interactions → ↑ fluid membrane. 12 ❑Strength of intermolecular interactions depends on: 1) Length of fatty acid chains: LONGER → ↓ fluidity. 2) Degree of unsaturation: ↑ → ↓ the compactness of the side chain packing → ↑ fluidity. 3) Concentration of cholesterol: has BUFFERing action!!! At ↓ temp.→ lipids cluster together, but cholesterol fill in between the phospholipids → disrupt their intermolecular interactions → ↑ fluidity. At ↑ temp.→ lipids are apart, but cholesterol pulls phospholipids together → ↑ intermolecular forces → ↓ fluidity. 13 Membrane PROTEINS are attached to the LIPID bilayer 14  Cell Adhesion is the process by which cells interact and attach to neighboring cells. It is mediated by “Cell adhesion molecules”. Direct contact: Types of Indirect contact: Immediate contact with connection Cells adhere to the nearby neighboring cell extracellular matrix → Cell-Cell adhesion → Cell-Matrix adhesion eg.: Cadheren (Ca+2 eg.: Integrin dependent adhesion) 15  Train your brain: (T or F & correct the F) 1. Cell membranes are freely-permeable membranes. 2. Most cell membranes are formed of 70% lipids and 30% proteins. 3. Phosphatidyl part of the phospholipid is formed of glycerol backbone with 2 fatty acids and phosphate group. 4. Cerebroside is an example of phospholipids. 5. Cell membrane forms bilayer, where the hydrophilic heads of phospholipids are present in the outer layer of both sides of the sheet. 6. Fluidity of the cell membrane is determined by the strength of intramolecular interactions between the phospholipids. 7. The kink in phospholipids is caused by the double bond in the fatty acid. 8. Cholesterol increases cell membrane fluidity in hot weather. 9. The cell membrane is rigid if its fatty acids are short. 10.The cell membrane protein “integrin” adheres a cell to its neighboring cell. 16 Thank you 17