MEMBRANES Topic 2.4 IB Biology Miss Werba

TOPIC 2 - CELLS 2.1 CELL THEORY 2.2 2.5 CELL DIVISION PROKARYOTIC CELLS 2.3 EUKARYOTIC CELLS 2.4 MEMBRANES 2.5 CELL DIVISION J WERBA – IB BIOLOGY 2

THINGS TO COVER Structure of membranes Hydrophobic & hydrophilic properties of membranes Membrane proteins: structure & function Diffusion & osmosis Passive transport: simple & facilitated diffusion Active transport Vesicles, endocytosis & exocytosis J WERBA – IB BIOLOGY 3

2.4.1 MEMBRANE STRUCTURE J WERBA – IB BIOLOGY 4

2.4.2 PHOSPHOLIPIDS Consist of a polar head (hydrophilic) made from glycerol and phosphate Consist of two non-polar fatty acid tails (hydrophobic) Phospholipids arrange in a bilayer Hydrophobic tail regions face inwards The two hydrophilic head regions associate with the cytosolic and extracellular environments respectively J WERBA – IB BIOLOGY 5

2.4.2 PHOSPHOLIPIDS Phospholipids are held together by hydrophobic interactions (weak associations) Hydrophilic / hydrophobic layers restrict entry and exit of substances Phospholipids allow for membrane fluidity / flexibility (important for functionality) Fluidity allows for the breaking / remaking of membranes (exocytosis / endocytosis) J WERBA – IB BIOLOGY 6

2.4.3 MEMBRANE PROTEINS Remember: TRACIE J WERBA – IB BIOLOGY 7

MEMBRANE PROTEINS Remember: TRACIE 2.4.3 MEMBRANE PROTEINS Remember: TRACIE Transport: Protein channels and protein pumps (eg. Na+/K+ Pump) Receptors: Peptide-based hormones (insulin, glucagon, etc.) Anchorage: Cytoskeleton attachments and extracellular matrix Cell recognition: MHC proteins and antigens Intercellular joinings: Tight junctions and plasmodesmata Enzymatic activity: Metabolic pathways (e.g. ETC in cellular respiration) J WERBA – IB BIOLOGY 8

DIFFUSION Command term = DEFINE 2.4.4 DIFFUSION Command term = DEFINE The net movement of particles from a region of high concentration to a region of low concentration, along the gradient, across a semi-permeable membrane J WERBA – IB BIOLOGY 9

OSMOSIS Command term = DEFINE 2.4.4 OSMOSIS Command term = DEFINE The net movement of water molecules from a region of low solute concentration to a region of high solute concentration , along the gradient, across a semi- permeable membrane J WERBA – IB BIOLOGY 10

OSMOSIS Command term = DEFINE 2.4.4 OSMOSIS Command term = DEFINE J WERBA – IB BIOLOGY 11

PASSIVE TRANSPORT Does not require energy 2.4.5 PASSIVE TRANSPORT Does not require energy Movement of substances is along the concentration gradient (high  low) 2 types of passive transport: Simple diffusion (inc. osmosis) Facilitated diffusion J WERBA – IB BIOLOGY 12

PASSIVE TRANSPORT Simple diffusion: Facilitated diffusion: 2.4.5 PASSIVE TRANSPORT Simple diffusion: Small, non-polar molecules can freely diffuse across the membrane eg. O2, CO2, H2, H2O, glycerol Facilitated diffusion: Larger, polar substances cannot freely diffuse Require the transport proteins to facilitate their movement eg. glucose, sucrose, Cl-, Na+, K+ J WERBA – IB BIOLOGY 13

ACTIVE TRANSPORT Does require energy 2.4.6 ACTIVE TRANSPORT Does require energy Movement of substances is against the concentration gradient (low  high) Will only occur in the presence of ATP eg. Na+/K+ Pump vesicular transport J WERBA – IB BIOLOGY 14

2.4.6 ACTIVE TRANSPORT They use the energy from ATP to translocate the molecules against the gradient The hydrolysis of ATP to ADP causes a the protein pump to change shape, resulting in the forced movement of the substance Protein pumps are specific for a given molecule J WERBA – IB BIOLOGY 15

2.4.7 VESICULAR TRANSPORT Proteins destined for secretion are directed to the endoplasmic reticulum The protein is transferred to the golgi apparatus via a vesicle, which forms from the budding of the membrane The protein moves via vesicles from one side of the golgi to the other and may be modified along the way (eg. glycosylated, truncated, etc.) The protein is transferred via a vesicle to the plasma membrane, whereby it is either immediately released or stored for a delayed release. J WERBA – IB BIOLOGY 16

2.4.7 VESICULAR TRANSPORT J WERBA – IB BIOLOGY 17

VESICULAR TRANSPORT Vesicular transport is possible b/c: 2.4.7 VESICULAR TRANSPORT Vesicular transport is possible b/c: Membrane has some fluidity Small amounts can be added or removed without tearing the membrane (endo- & exo- cytosis) Membranes of all organisms are the same J WERBA – IB BIOLOGY 18

VESICULAR TRANSPORT Exocytosis 2.4.8 VESICULAR TRANSPORT Exocytosis Rough ER produces proteins intended for export Golgi apparatus prepares substances for exocytosis Transport vesicle formed from a section of membrane from the Golgi apparatus This membrane then joins the cell surface membrane Exocytosis requires energy! J WERBA – IB BIOLOGY 19

VESICULAR TRANSPORT Endocytosis 2.4.8 VESICULAR TRANSPORT Endocytosis Transport vesicle formed from a section of the cell membrane This process requires energy too! Used to take up substances that are too large and/or highly polar and cant enter on their own Requires recognition of the substance by a membrane receptor protein J WERBA – IB BIOLOGY 20

VESICULAR TRANSPORT Endocytosis 2.4.8 VESICULAR TRANSPORT Endocytosis Two types of endocytosis : Pinocytosis when the substance is fluid “cell-drinking” Phagocytosis when the substance is solid “cell-eating” J WERBA – IB BIOLOGY 21

SUMMARY of CELLULAR TRANSPORT 2.4 SUMMARY of CELLULAR TRANSPORT ATP required Concentration gradient Diffusion no down Facilitated diffusion Osmosis Active transport with carrier proteins yes against if possible Endocytosis J WERBA – IB BIOLOGY 22

MEMBRANES Sample question 2.4 MEMBRANES Sample question Q: What do diffusion and osmosis have in common? A: Both are forms of passive transport Both move substances along a concentration gradient Both transport substances across a semi-permeable membrane J WERBA – IB BIOLOGY 23

MEMBRANES Sample question 2.4 MEMBRANES Sample question Describe the movement of water across membranes. [2] Osmosis / passive transport Moves from regions of low solute concentration to high solute concentration or high water concentration to low water concentration passes through protein channels (or aquaporins) in a semi-permeable membrane J WERBA – IB BIOLOGY 24

MEMBRANES Sample question 2.4 MEMBRANES Sample question Draw a labelled diagram to show the fluid mosaic structure of a plasma membrane, indicating the hydrophilic and hydrophobic regions. [5] J WERBA – IB BIOLOGY 25

MEMBRANES Sample question 2.4 MEMBRANES Sample question DISTINGUISH between active and passive movements of materials across plasma membranes, using named examples. [5] Hint: Use a table! Passive Active Diffusion / osmosis / facilitated diffusion active transport / ion pumps / exocytosis / pinocytosis / phagocytosis a second passive method (from above) a second active method; (from above) does not require energy requires energy/ATP; down concentration gradient against concentration gradient no pumps needed requires protein pumps oxygen across alveoli / other example glucose absorption in ileum / other example J WERBA – IB BIOLOGY 26