Membrane Structure Assignment

Membrane Structure Phospholipids Draw the structure of a phospholipid and identify its properties Phospholipids consist of: ………………………………………………………………………………………... Phosphate hydrophilic • Phosphate head (hydrophilic = water loving) ………………………………………………………………………………………... • 2 x Fatty acid tails (hydrophobic = water hating) ………………………………………………………………………………………... Fatty acids hydrophobic The phosphate group is connected to the fatty acid tails via ………………………………………………………………………………………... a glycerol group ………………………………………………………………………………………... Explain how the properties of phospholipids help to maintain the structure of cell membranes The phospholipids form a phospholipid BILAYER ………………………………………………………………………………………………………………………………………………….......... The hydrophilic phosphate heads face outwards into the aqueous solutions (intracellular and extracellular) ………………………………………………………………………………………………………………………………………………….......... The hydrophobic fatty acid tails face inwards and are held in place by weak hydrophobic associations ………………………………………………………………………………………………………………………………………………….......... Because the associations are weak, phospholipids are able to move within the bilayer (membrane fluidity) ………………………………………………………………………………………………………………………………………………….......... Identify and describe the two main models for membrane structure based on the diagrams below Model A: Davson-Danielli Model Model B: Nicolson-Singer Model According to this model: According to this model: …………………………………………………………………………. …………………………………………………………………………. Two layers of protein flank a central phospholipid Transmembrane proteins are embedded within a …………………………………………………………………………. …………………………………………………………………………. bilayer phospholipid bilayer This model is also referred to as a ‘lipo-protein This model is also referred to as the ‘fluid-mosaic sandwich’ model’ …………………………………………………………………………. …………………………………………………………………………. …………………………………………………………………………. …………………………………………………………………………. …………………………………………………………………………. …………………………………………………………………………. Describe how the following electron micrograph supports the structure of model A Cell 1 Cell 2 The micrograph shows a trilaminar (three layer) structure: 2 dark outer layers and a light inner layer ………………………………………………………………………………………………………………………………………………….......... This supports the idea of two layers of protein (dark) flanking a central phospholipid bilayer (light) ………………………………………………………………………………………………………………………………………………….......... However this interpretation is incorrect ………………………………………………………………………………………………………………………………………………….......... Outline the evidence that lead to the falsification of model A and acceptance of model B BIOCHEMICAL EVIDENCE: ………………………………………………………………………………………………………………………………………………….......... Not all membranes have a constant ratio of lipid:protein (precludes ‘sandwich’ model) ………………………………………………………………………………………………………………………………………………….......... Membrane proteins vary in size and are insoluble in water (can’t form an outer layer) ………………………………………………………………………………………………………………………………………………….......... FLUORESCENT ANTIBODY TAGGING: ………………………………………………………………………………………………………………………………………………….......... Membrane proteins are mobile and are not fixed in place (do not form a static layer) ………………………………………………………………………………………………………………………………………………….......... FREEZE FRACTURING: ………………………………………………………………………………………………………………………………………………….......... Fracturing the membrane reveals a rough and irregular internal surface ………………………………………………………………………………………………………………………………………………….......... These irregularities are interpreted as transmembrane proteins ………………………………………………………………………………………………………………………………………………….......... Cholesterol Explain what is meant by the term ‘membrane fluidity’ Membrane fluidity means that the bilayer is not static and membrane components (such as proteins) can ………………………………………………………………………………………………………………………………………………….......... move positions (allows membranes to change shape and to break and reform) ………………………………………………………………………………………………………………………………………………….......... Outline the role of cholesterol in animal cell membranes Cholesterol interacts with phospholipids to moderate membrane properties: ………………………………………………………………………………………………………………………………………………….......... • It reduces membrane fluidity (immobilises phospholipids at higher temperatures) ………………………………………………………………………………………………………………………………………………….......... • It also reduces membrane permeability (to hydrophilic ions) ………………………………………………………………………………………………………………………………………………….......... • It prevents crystallisation (increase flexibility at lower temperatures) ………………………………………………………………………………………………………………………………………………….......... • It helps secure peripheral proteins by forming high density lipid rafts capable of anchoring the protein ………………………………………………………………………………………………………………………………………………….......... Membrane Proteins Differentiate between integral and peripheral membrane proteins • Integral proteins are permanently attached to the membrane and are typically transmembrane ………………………………………………………………………………………………………………………………………………….......... (they span across the bilayer and may contain hydrophilic pores to mediate material transfer) ………………………………………………………………………………………………………………………………………………….......... • Peripheral proteins are temporarily attached by non-covalent interactions and associate with ………………………………………………………………………………………………………………………………………………….......... only one surface of the membrane ………………………………………………………………………………………………………………………………………………….......... List the functions of membrane proteins Junctions – Serve to connect and join two cells together J …………………………………………………………………………………………………………… – Fixing to membranes localises metabolic pathways E Enzymes …………………………………………………………………………………………………………… – Responsible for facilitated diffusion and active transport T Transport …………………………………………………………………………………………………………… – May function as markers for cellular identification R Recognition …………………………………………………………………………………………………………… – Attachment points for cytoskeleton and extracellular matrix A Anchorage …………………………………………………………………………………………………………… – Function as receptors for peptide hormones T Transduction …………………………………………………………………………………………………………… Label the following diagram of a plasma membrane 2 4 1 5 3 Cholesterol (animal cell membrane) Glycoprotein (receptor molecule) 4. ………………………………………………………………… Integral protein (transmembrane) Phospholipid (part of a bilayer) 5. ………………………………………………………………… 1. ………………………………………………………………… 2. ………………………………………………………………… Peripheral Protein 3. …………………………………………………………………