Molecular and Cellular Bases of Physiology L01 - Summer 24 PDF

Molecular and Cellular Bases 1. The cell Andre Azevedo, DVM, MSc Visiting Professor of Veterinary Physiology [email protected] Learning objectives for this lecture Describe the 5 substances that make up the cell and their functions Describe cell membrane composition and functions De...

Molecular and Cellular Bases 1. The cell Andre Azevedo, DVM, MSc Visiting Professor of Veterinary Physiology [email protected] Learning objectives for this lecture Describe the 5 substances that make up the cell and their functions Describe cell membrane composition and functions Describe cytoplasmic organelles and their function List the components and functions of the cytoskeleton Describe the structure of the nucleus and its function The cell video https://www.youtube.com/watch?v=URUJD5NEXC8 Eukaryotic cell Eukaryotic vs prokaryotic 2 major parts Cytoplasm – separated from the surrounding fluid (external environment) by a plasma membrane Nucleus – separated from the cytoplasm by a nuclear membrane Cell substances The different substances that make up the cell are: Water Ions Proteins Lipids Carbohydrates Water The main fluid medium for most cells Cellular chemicals are dissolved in water or suspended as solid particles Chemical reactions take place: Among dissolved chemicals At the surface of the suspended particles In the membranes Polar molecule except for fat cells (95% is fat) The composition of a bacterial cell Most of a cell is water (70%). The remaining 30% contains varying proportions of structural and functional molecules. © 2010 Nature Education All rights reserved. View Terms of Use Ions Higher quantities (inside cell) Potassium, magnesium, phosphate, sulfate, bicarbonate Smaller quantities (inside cell) Sodium, chloride, calcium Charged molecules get along well with water (hydrophilic) Provide inorganic chemicals for cellular reactions Necessary for the operation of some of the cellular mechanisms I.e., transmission of electrochemical impulses in nerve and muscle cells ECF vs ICF – chemical composition THE UNEVEN DISTRIBUTION OF IONS BETWEEN THE OPPOSING SIDES OF THE CELL MEMBRANE LEADS TO A VOLTAGE DIFFERENCE CALLED MEMBRANE POTENTIAL Proteins Second most abundant substance in the cell (after water) The 3-dimentional shape of a protein determines its function Can bind to other molecules very specifically (lock-and-key) Can change shape and alter binding properties and function All physiological changes are mediated by proteins Can be STRUCTURAL (i.e., cytoskeleton) or FUNCTIONAL (i.e., enzymes, transport proteins, signaling proteins) Lipids Key components of the cells Plasma membrane, nuclear membrane, endoplasmic reticulum, Golgi apparatus, endosomes, lysosomes The diversity of lipids in on the same level as that of proteins But lipids have not been as well studied as proteins Poorer understanding of their functions Lipids Phospholipids and cholesterol are especially important Insoluble in water – they form the cell membrane and intracellular membrane barriers that separate the different cell compartments Cholesterol and cell membrane video: https://www.youtube.com/watch?v=5Q-Tz30pz18 Lipids Phospholipids spontaneously form bilayers when in aqueous solution When mixed with phospholipids, cholesterol enhances the barrier properties of the lipid bilayer, also turning it more stable Lipids Triglycerides are also found in some cells Most cells store the excess of lipids in lipid droplets Can be used for membrane synthesis or food source Adipocytes are specialized for lipid storage 95% of the adipocyte mass is TRIGLYCERIDES Body’s main storehouse of energy-giving nutrients Carbohydrates Little structural function In combination with proteins and lipids Play a major role as a source of energy Small amounts stored inside the cells Can be stored as glycogen Glucose from the ECF is readily available to cells The cell membrane The plasma membrane is composed almost entirely of lipids and proteins Intrinsic membrane proteins embedded in the lipid bilayer The outer surface contains carbohydrates in combination with lipids and proteins Impermeable to water-soluble substances The cell membrane Lipids in the cell membrane: Phospholipids Most abundant, attach to one another in the middle of the membrane Sphingolipids Small amounts, especially in nerve cells Cholesterol Control fluidity and permeability The cell membrane Proteins in the cell membrane: INTEGRAL PROTEINS Permanently attached Both structurally and functionally integral components of a membrane Usually are transmembrane proteins Act as channels, transporters, and receptors PERIPHERAL PROTEINS Are attached only to one surface of the membrane and do not penetrate all the way through Often attached to the integral proteins Act as enzymes or as controllers of the channels The cell membrane Functions of biological membranes Compartmentalization Selective transport Information processing and transmission Organizing biochemical reactions in the space The cell membrane Membrane potential exists across the membrane of virtually all cells Difference in electrical potential between the interior and the exterior Membrane potential has 2 basic functions Allows the cell to function as a battery, generating an electrical charge that can control/influence the activity of various 'molecular devices' embedded in the membrane, such as ion channels and pumps In electrically excitable cells, it is used for transmitting signals between different parts of a cell Cytoplasm/cytosol Cytoplasm is the space between the nucleus and the plasma membrane Consists of organelles and cytosol Cytosol is the fluid in which organelles of the cell reside Contains mainly water, dissolved proteins, electrolytes, and glucose Organelles – endoplasmic reticulum Organized into a netlike labyrinth of branching tubules and flattened sacs that extends throughout the cytosol ER lumen or ER cisternal space Their membrane is continuous with the outer nuclear membrane Central role: lipids and proteins biosynthesis Synthesis of membrane proteins and proteins that will be secreted to the exterior Synthesis of membrane lipids for plasma membrane and organelles Also serve as an intracellular calcium store for signaling pathways Organelles – endoplasmic reticulum GRANULAR ER or ROUGH ER Has RIBOSOMES attached to it Composed of a mixture of RNA and proteins Responsible for synthesizing new protein molecules AGRANULAR ER or SMOOTH ER No attached ribosomes Synthesize lipids Bigger in cells that produce lipids Organelles – Golgi apparatus Collection of flattened, membrane-enclosed compartments called cisternae “stack of pita bread” Closely related to ER Small vesicles pinch off from ER and fuse with Golgi Golgi process and form Lysosomes Secretory vesicles Other cytoplasmic components Organelles – Lysosomes Main site of intracellular digestion Vesicular organelles full of digestive enzymes (hydrolases) that break down: Damaged cellular structures Food particles ingested by the cell Unwanted matter, such as bacteria Organelles – Peroxisomes Vesicular organelle similar to lysosomes Formed by self-replication or from ER Contain at least 50 different enzymes Mostly OXIDASES capable to combine O2 with hydrogen ions to form H2O2 Also carries CATALASE that decomposes hydrogen peroxide Oxidated compounds include amino acids and fatty acids Also involved in lipid biosynthesis Ex: In liver cells, peroxisomes are involved in the synthesis of bile acids Organelles – Mitochondria Powerhouses of the cell Burn food molecules (glucose, AA, FA) to produce ATP by oxidative phosphorylation Self replicative Tissues that need more energy have more mitochondria Cytoskeleton Network of fibrillar proteins organized into filaments or tubules Microfilaments Microtubules Intermediate filaments Functions: Cell shape Cell division Movement Track-line system to the movement of molecules/organelles Mechanical strength Nucleus Control center of the cell Contains: Nuclear membrane or envelope Continuous with ER Penetrated by several pores Nucleolus Accumulation of large amounts of RNA and proteins Help to synthesize ribosomes Genetic material DNA (Chromosomes and chromatin) Control cellular growth, maturation, division and death From DNA to protein video https://www.youtube.com/watch?v=gG7uCskUOrA Questions?