WK 2- The Cell Building Blocks of Cell PDF

The cell Lecture 1: Overall function other cell is essential for biosynthesis Chemical analysis – enzymes Information to guide all activities Energy to drive the various reactions and processes that are essential to life and biological function Cell Membrane: Pho...

The cell Lecture 1: Overall function other cell is essential for biosynthesis Chemical analysis – enzymes Information to guide all activities Energy to drive the various reactions and processes that are essential to life and biological function Cell Membrane: Phospholipid bilayer Embedded proteins Carbohydrates Cholesterol Fluid Mosaic model: - Lipid bilayer: proteins embedded in - Fluid Part: lipid - Main components of membrane mosaic models -mainly contains proteins Structure of fluid mosaic Model:  - Has cell adhesion molecules allow cells to identify and interact for immune response - Structural proteins attached to microfilaments in cytoskeleton= stability - Membrane enzymes – substances for cell function - Membrane receptor – proteins serve as connection between cells internal and external environments - Transport proteins to play vital role maintenance of concentrations of ions KEY: HEAD – HYDROPHOLLIC TAIL- HYDROPHOBIC Membrane Lipids: Lipid bilayer ( fluid state of membrane ) Allows nuclear transfer during cloning – the fluid nature of the plasma membrane. Contains the following: Phosphoglycerides  Sphingolipids Sterols ( Phospholipids ) ( Glycolipids and Sterols ) Glycolipids – Monosaccharides attached to glycerol Sterol – multi ring Molecules related to cholesterol Terpenes – Aromatic compounds in plants Phospholipid and lipid Bilayers: Phospholipid – 2 fatty acid with glycerol backbone associated with glycerol backbone associated with modified phosphate group with simple organic molecules ( e.g. Choline ) Amphipathic lipid with phosphate based head group and 2 pronged hydrophobic tail. Movement of phospholipid molecules within membranes: Rotation on long axis Lateral diffusion by exchanging places within neighbouring monolayer Transverse diffusion – from one monolayer to the other Proteins – Mosaic Part of fluid Model: The membrane grouped based on nature and association with lipid bilayer:  Integral proteins: embedded in lipid bilayer, they are in place by affinity of hydrophobic segments and the protein hydrophobic interior of lipid bilayer Peripheral Proteins: are hydrophilic – located surface on membrane and linked noncovalently to polar heads to phospholipids Lipid-anchored Proteins: - hydrophilic proteins reside membrane surfaces – covalently attached to lipid and embedded in bilayer Main classes of Membrane Proteins: Myelin Plasma membrane Energy transduction membranes Main functions of Membrane Proteins: They regulate molecular ionic compositions of cellular compartments Control flow of info between cells Proteins embedded in lipid layers – specific to substance and transport Production of proteins activated via signalling pathways- their expression regulated differential transcription of genes. Overall function of cell membrane:  Dependent on lipid and proteins Each organelle has own distntive membrane bound proteins The function of membrane protein – reflected on its protein associated with lipid bilayer – e.g protein function only one side of membrane likely to be peripherial protein or lipid anchored protein on specific side. Enzymes - Localization of specific function to specific membranes – aid to identify specific organelle Electron transport proteins – cytochromes and iron sulphur proteins involved energy production in mitochondria etc Solute transport across membranes – hydrophilic/hydrophobic passageways allows transport of nutrients Receptors – chemical signals Intercellular communication – binding of hormone/signal molecule appropriate protein receptor surface triggers an intracellular response Properties of Cell Membrane: Overall dynamic structure not fixid or rigid – ions and organic molecules allows flexibility fluidity. A vesicle: Structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the plasma membrane. Dynamism: Fatty acid composition can change, the unsaturated fatty acids and chain length etc. Selective permeability of membrane: Via Homeostasis – crucial for proper functioning of cell/organelle to overcome the permeability of barriers.  thickness – proportion of each substances wavy arrows and curved is its permeability substance can move through membrane Membrane Transport: Solutes higher conc inside organelle than outside Major aspect is transport of ions and organic molecules 1- Permeability of molecule bilipid layer 2- Availability of an energy source 2 – secondary Active transporters – gradient power of the formation of another not directly driven by hydrolysis of ATP Overall carrier proteins via uniport transportation, transport a membrane protein solute across membrane – and also Coupled transport – simultaneously moves 2 solutes same directions or opposite Receptors: Bind signalling molecules outside cell and initiate physiological response Transmembrane proteins – different types cell receptors 3 major classes:  - Ion channel receptors - G- protein coupled receptors - Enzyme linked receptors Ion Channel receptors: Multimeric proteins arranged to form passageway through membrane Individual ion channels – specific to particular ions Ion channels open and close in response to chemical mechanical signals G- Protein coupled receptors: - Specialised proteins – alpha subunit binds to GTP or GDP depends on activation - Subunits dissociate into 2 parts – GTP bound alpha subunit and beta gamma dimer - Both remain anchored to plasma membrane and diffuse laterally to interact with other membrane bound proteins. Enzyme-linked receptors: Receptor tyrosine Kinases ( RTKs ) make up largest class enzyme- linked receptors RTK phosphorylation – regulated by protein tyrosine phosphate ( PTP ), removing phosphates and deactivating the receptor following ligand release upon returning to resting state. Enzyme-lined receptors:  - Membrane bound enzymes perform the same function as those in cytoplasm, catalysing the information of molecules into other forms Anchor: - Link intracellular and extracellular structures - E.g actin filaments to extracellular matrix proteins Cell – cell recognition and adhesion: - Carbohydrate layer protects cell from mechanical and chemical damage Intracellular Transport: - Gap junctions – composed of connexion protein molecules – interact from small amino acids and lined pores between cells - Tight junctions – define apical and basolateral plasma membrane domains in polarised epithelial cells and control the flow of solutes between cells in epithelial sheet Cell membrane channels and pumps: Importance of cell membrane in health and disease: