1. MEMBRANES
Topic 2.4
IB Biology
Miss Werba

2. 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
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3. 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
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4. 2.4.1
MEMBRANE STRUCTURE
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5. 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
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6. 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)
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7. 2.4.3
MEMBRANE PROTEINS
Remember: TRACIE
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8. 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)
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9. 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
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10. 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
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11. OSMOSIS Command term = DEFINE
2.4.4
OSMOSIS Command term = DEFINE
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12. 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
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13. 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+
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14. 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
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15. 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
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16. 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.
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17. 2.4.7
VESICULAR TRANSPORT
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18. 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
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19. 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!
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20. 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
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21. 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”
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22. 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
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23. 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
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24. 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
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25. 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]
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26. 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
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