Cell Physiology PDF

Cell Physiology Dr. Giam Vega-Meléndez August 2024 Term 2025-11 Body Levels of Organization  The Cell Basic unit of life The cell is a sum of its parts: PLASMA MEMBRANE (CELL WALL) CYTOSOL ORGANELLES...

Cell Physiology Dr. Giam Vega-Meléndez August 2024 Term 2025-11 Body Levels of Organization  The Cell Basic unit of life The cell is a sum of its parts: PLASMA MEMBRANE (CELL WALL) CYTOSOL ORGANELLES INCLUSIONS  Plasma Membrane Cell boundary 7-10 nm thick Functions: – Cell to cell recognition – Protection – Signaling pathways Complex structure composed of: – Lipids – Proteins – Carbohydrates  Plasma Membrane Lipid bilayer (fluid mosaic model) PHOSPHOLIPIDS 75% CHOLESTEROL 20% GLYCOLIPIDS 5% Phospholipids: Amphipathic molecule with a: Polar head phosphate head (hydrophilic) Amphipathic fatty acid tail (hydrophobic) molecule Glycolipids: Nonpolar tails Lipid molecule with a sugar side chain Cholesterol: Found ONLY in eukaryotic cells  Proteins Classified according to their position in the plasma membrane (PM) Integral- proteins that cross the membrane. Functions: structural, receptors and as channels Peripheral- proteins found on the outer surface of the PM Functions: hormone receptors, cell surface markers (antigens, for the immunological recognition)  Intracellular Environment Intracellular compartment: – Consists mostly of water – Separated form extracellular compartment by a cell membrane – Comprised of all intracellular organelles – Main electrolyte is K+  Extracellular Environment Extracellular compartment: – Divided into two parts: blood plasma and interstitial fluid – Communicates with intracellular compartment via movement of molecules and ions through the cell membrane – Main electrolyte is Na+  Intra and Extracellular Homeostasis is maintained by the ATPase MEMBRANE PERMEABILITY (selective permeability) LIPID SOLUBLE It depends on: Size Charge Channels or Transporters  Cell transport mechanisms Passive process Depend on pressure or concentration differences and diffusion 1. Simple diffusion 2. Osmosis 3. Bulk flow 4. Facilitated diffusion  SIMPLE DIFFUSION Process of random mixture of particles in a solution achieving equilibrium WITHOUT USING CELLULAR ENERGY (eg. O2, CO2, small COH, H2O, lipid soluble vitamins) Factors that influence diffusion Concentration gradient Temperature Mass of diffusion substance Surface area Diffusion distance  Osmosis – Diffusion of a solvent through a selective membrane. – It is determined by the osmotic pressure defined as the pressure required to stop the net movement of pure water through a selective membrane – Aquaporin: Integral protein that act as a canal for water movement. BULK FLOW Movement of large volume of particles dissolved or carried in a medium (eg. air flow, capillary blood flow (filtration) FACILITATED DIFFUSION (transport) Movement of molecules through a selective membrane aided by specific membrane proteins that serve as channels or transporters. (eg. glucose vitamins, ions)  Active transport Energy spending process for the movement of a molecule against a concentration gradient Primary Active Transport Movement of molecules across a selective membrane from a lower to a higher concentration area by pump proteins using energy released by splitting ATP (eg. Ions Na+, K+, Cl-, H+)  Secondary active transport Indirectly uses ATP Uses gradient derived from primary active transport (usually Na/K pump) to transport two or more ions Two types: – Co-transport: both ions are moved in the same direction – Counter-transport: move ions in opposite directions  Vesicular transport Process through which small vesicles bud from a cell membrane to bring in or out material. Phagocytosis (cell eating) Endocytosis Pinocytosis (cell drinking) Exocytosis (eg. neurotransmitters) Process for exporting substances from the cell (neurotransmitters, hormones, digestive enzymes)  Cytoplasm 1. Cytosol Gel like fluid in which the cell metabolic reactions occur. Contains suspended particles, minute filaments and tubules. 75 - 90% H2O Proteins Colloids – (large organic compounds eg. glycogen) Lipids 2. Organelles: Specialized structures related to cell growth, repair and maintenance.  Cytoskeleton Internal network of proteins inside the cytoplasm involved in locomotion, phagocytosis and cell wall strength. Made up of: Microfilaments Microtubules Intermediate filaments (connect the nuclear membrane with the cellular membrane) Microfilament Rod like structure composed of actin filaments that provides support and movement assisting in cell shape. (microvilli) Microtubules Largest of the cytoskeletal components cylindrical structure consists of tubulin major function is assembly of centromere during cell division. Provide motility.  Flagella and Cilia Mainly composed of microtubules. Both structures are motile, but only the flagella allows for locomotion.  Nucleus Largest organelle. It is enclosed in a bi-layer membrane continuous with the endoplasmic reticulum. Houses genetic information of the cell (DNA/Cromosomes) – DNA replication – mRNA transcription – rRNA transcription  Number or Nucleus Most cells are unicellular Binuclear: hepatocytes, cardiac muscle, epithelial cells of urinary tract Multinuclear: osteoclast and skeletal muscle cells RBCs only cell in the body anuclear  Nucleolus Region within the nucleus Responsible for the production of rRNA Endoplasmic reticulum: Membrane bound network of channels providing surface area for chemical reactions Smooth ER: Related with synthesis of lipids and detoxification of lipid soluble drugs Without ribosomes Rough ER: Synthesis for proteins to be exported Contain ribosomes  Ribosomes: Cytoplasmic site for protein translation and assembly. Some are free in the cytoplasm while others are attached to the endoplasmic reticulum. 2 Sub-units Large 60’S Small 40’S  DNA is copied during a process called replication The flow of genetic information in cells is as follows: DNA--->messenger RNA---->protein RNA has 3 functions: 1) carry genetic information in the form of a message (mRNA); 2) to the ribosomes (made of ribosomal RNA); 3) in order for transfer RNA (tRNA) to deliver the correct amino acid needed to build a specific protein DNA is converted into messenger RNA during a process called transcription mRNA is converted into proteins during a process called translation  In Eukaryotic cells, DNA replication and transcription occur in the nucleus and translation occurs in the cytoplasm – Fungi, animals, plants In Prokaryotic cells, DNA replication, transcription and translation occur in the cytoplasm – bacterial cells  Membrane enclosed Golgi cisternae where proteins complex and lipids are packaged into secretory vesicles for export or insertion into the cell membrane.  CIS FACE GC RER TRANS FACE Medial cysternae Secretory Add CHO and lipids vesicle to proteins  Lysosomes Specialized vesicles which contain digestive enzymes for breakdown of nutrients and foreign bodies Primary lysosomes (with enzymes) Secondary lysosomes (with a phagocytic vacuole)  Lysosomes clinical implication Secondary lysosomes are exocytosed out of the cell Cherry red macula in or undergo partial 90% of the cases degradation forming residual bodies. Tay Sach’s Disease is an accummulation of residual bodies – Autosomal recessive disorder – Present first year of life – Dead usually age 2 Mitochondria Organelle in which energy is produced during cellular respiration. Mitochondrial DNA is transmitted through maternal inheritance Mitochondria clinical implication Leber’s Hereditary Optic Neuropathy (LHON) – Rare optic nerve diseases that is the result of maternal mitochondrial DNA mutations – Central visual loss