1.3 Cell membrane structure and function IB Biology

I can understand that… Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules. Membrane proteins are diverse in terms of structure, position in the membrane, and function. Cholesterol is a component of animal cell membranes.

Prison fence? How does that relate? Entry-way only accessible to the special guards Outside fence Inside fence Outside environment

Biological membranes Separate the cell from the environment Allows some substances to move across more easily than others Has 2 layers (bilayer) Helps maintain homeostasis Protective Barrier Allows cell recognition Provides binding sites for enzymes Bind cells together in interlocking junctions Contains cytoplasm

Cell membrane Phospholipid bilayer ~8 nm thick Selectively permeable Flexible Fluid Mosaic Model

Structure of the cell membrane: phospholipid bilayer

Amphipathic phospholipid layers Amphipathic (adj.): Pertains to a molecule containing both polar (water-soluble) and nonpolar (not water-soluble) portions in its structure. (biology-online.org)

Phospholipids Made up of: Glycerol 3-carbon compound Water soluble Phosphate group 2 fatty acid chains Not water soluble because they are non-polar Hydrophilic Head Water Loving Hydrophobic Tail Water Fearing The hydrophobic and hydrophilic regions make the phospholipids line up as a bilayer

Models of the cell membrane Davson-Danielli Model: Singer-Nicolson “Fluid Mosaic Model”

Fluidity of the membrane Cholesterol in the tail-region of membrane Stabilizes fluidity, which changes with temperature Less fluid in warmer temperature by restraining phospholipid movement More fluid in colder temp by preventing close packing of phospholipids Flip-Flop and Lateral Movement of phospholipids in the membrane Flippase? Unsaturated (kinks) enhance fluidity Saturated phospholipids make membrane easier to solidify

Proteins of the membrane Integral Proteins: Have an amphipathic character Completely penetrate the lipid bilayer Control the entry and removal of specific molecules from the cell

Proteins of the membrane Peripheral Proteins: Remain bound to the surface of the membrane They are often anchored to an integral protein

Selective permeability Some non-polar substances are transported directly through the lipid bilayer. Smaller non-polar molecules move faster than larger ones. Some polar substances, particularly ions and carbohydrates, are transported across the membrane via the channel proteins. Some smaller, uncharged polar substances go right between the phospholipids into the cell. https://www.youtube.com/watch?v=5jZXCDcM14g Selective Permeability

Functions of membrane proteins Pumps for active and passive transport Cell adhesion Enzymatic action Cell-to-cell communication Sites for hormone binding

Transport proteins + Passive transport

Questions? Answer the following questions in your notes guide then share with a partner: Explain the orientation of the bilayer of phospholipid molecules in the plasma membrane using the terms ”hydrophobic” and “hydrophilic”. Draw a sketch of the bilayer. What type of properties do amphipathic phospholipids have? What types of substances can pass directly through the membrane. What is the function of cholesterol in the plasma membrane? 1.Hydrophilic heads and hydrophobic tails in a bilayer. 2. Both hydrophobic and hydrophilic regions. 3. Non polar substances 4. Helps stabilize the membrane, without cholesterol the membrane would be too fluid and let too many substances through.

I understand that… Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules. Membrane proteins are diverse in terms of structure, position in the membrane, and function. Cholesterol is a component of animal cell membranes.

Source Damon, Alan, Randy McGonegal, Patricia Tosto, and William Ward. "1.3 and 1.4." Higher Level Biology. 2nd ed. N.p.: Pearson Education Limited, n.d. N. Print.