Students who have fully met the prescribed learning outcomes (PLO’s) are able to:
B9. Analyze the structure and function of the cell membrane.
apply knowledge of organic molecules – including phospholipids, proteins, glycoproteins, glycolipids, carbohydrates, and cholesterol – to explain the structure and function of the fluid-mosaic membrane model.
Analyze the structure and function of the cell membrane. (continued)
identify the hydrophobic and hydrophilic regions of the phospholipid bilayer.
explain why the cell membrane is described as “selectively permeable”.
describe passive transport processes including diffusion, osmosis, and facilitated transport.
explain factors that affect the rate of diffusion across a cell membrane (e.g., temperature, size of molecule, charge of molecule, concentration gradient, pressure gradient).
predict the effects of hypertonic, isotonic, and hypertonic environments on osmosis in animal cells.
http://sps.k12.ar.us/massengale/biology%20class%20notes2.htm (A terrific site with animations, self-quiz, notes etc. Click on the various notes for Effect of Solutions on Cells, Web Tutorials on Passive & Active Transport, Scientific Method, and Designing an Experiment )
http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm (Animation of Cell Transport)
http://curriculum.calstatela.edu/courses/builders/lessons/less/les4/cellsize.html (Limits to Cell Size)
The ‘fluid-mosaic model’ is a model that describes the structures of the CM, i.e. a fluid lipid layer in a mosaic made up of many different types of molecules. Cell membranes include a flexible bilayer of phospholipids interspersed with large protein molecules that aid in membrane transport and cholesterol for rigidity.
Some act as carriers bringing amino acids , ions , and glucose in/out, e.g. Na+/K+ pump in nerve transmission; protein carriers bringing in glucose for RBC’s; or concentrating molecules/ions inside or outside of cell, e.g. nerve cells actively pumping Na+ & K+ or thyroid cells concentrating iodine.
Some have channels/gates/pores to allow passage of H 2 O, dissolved ions, and small molecules.
Some are receptors that a specific molecule can bind to, e.g. hormones such as insulin, thyroxin, aldosterone, estrogen, testosterone etc. or neurotransmitters such as acetylcholine (ACh), norepinephrine (NE). http://www.mhhe.com/biosci/genbio/espv2/data/cells/003/index.html
Note: Cytoskeleton (Recall Unit B1) is an internal framework of protein fibres that gives the cytoplasm strength and flexibility and provides movement of organelles. Some protein filaments attaches to the integral proteins of the CM. Attachment of the Cytoskeleton
Summary of Cell Membrane Structures and Functions Amino acids Allows/selects certain molecules in/out of cell through channels/gates/pores . E.g. H 2 O, O 2 , CO 2 , ions. Carries molecules selectively in/out of cell by carriers. E.g. Na + , K + , C 6 H 12 O 6 , áá’s, HCO 3 - , Ca 2+ . Proteins Unit molecules Functions Molecules
Catalyzes reactions on cell surface by enzymatic proteins. E.g. Enzymes for ATP metabolism or breakdown of ATP for Na+ transport.
Provides receptor sites by receptor proteins. E.g. Hormones having the same shape as receptor proteins to bind to it.
Backbone of 4 fused C-H rings Stiffen CM and provide flexibility Cholesterol Chains of carbohydrates attached to lipid or protein (a) Used in cell identification . (b) Glycoproteins can form a carbohydrate coat that envelops the cell membrane (glycocalyx). Glycolipids and Glycoproteins 2 fatty acids (saturated/ unsaturated) & 1 glycerol, N and phosphate group (a) Allows for diffusion of lipid soluble molecules. E.g. O 2 , CO 2 , and alcohol. (b) Allows for flexibility & fluidity of cell membrane. E.g. Vesicle formation. (c) Excludes H 2 O and ions. (d) Acts as a boundary keeping organelles within the cell. Phospholipids
Isotonic If the concentration of solute (salt) is equal on both sides, water will move back in forth but it won't have any result on the overall amount of water on either side. " ISO " means the same.
Hypotonic " HYPO " means less. There are less solute (salt) molecules outside the cell, which causes water to move into the cell by osmosis (high to low). The cell will gain water & grow larger. In plant cells, the central vacuole will fill and the plant becomes stiff and rigid, i.e. turgor. The cell wall keeps the plant from bursting. In human animal cells, the cell is in danger of lysis or bursting.
" HYPER " means more. There are more solute (salt) molecules outside the cell, which causes the water to leave the cell by osmosis (high to low).
In plant cells, the central vacuole loses water; the cells shrink, i.e. plasmolysis causing wilting.
In animal cells, the cells also shrink. In both cases, the cell may die.
It is dangerous to drink sea water. People marooned at sea will speed up dehydration (and death) by drinking sea water. This is also why "salting fields" was a common tactic during war, it would kill the crops, thus causing food shortages.
E.g. Thyroid gland cells accumulates iodine from the blood against a [gradient] OR cells in intestine absorbing C 6 H 12 O 6 and concentrating in the blood against a [gradient] OR amino acids entering the blood from specific cells of the nephron OR cells of the nephron absorbing Na+ from the filtrate.
E.g. Na+/K+ pumps in neurons. Protein ‘pumps’ Na+ across cell membrane against [gradient] and also moves K+ across cell membrane against [gradient], and thus maintains the resting potential and recovery during nerve transmission (See C11).
Active transport also involves the movement of materials into/out of the cell using ATP, BUT do not cross through the lipid bilayer. Instead, portions of the lipid bilayer membrane engulf items being moved into or fuse with a membrane-bound sac to get out of the cell.
ATP energy is used to alter the shape of the membrane surface.
Movement of particles/macromolecules into the cell. The cell membrane invaginates around the particles, pinches off forming a membrane-bound vesicle; requires ATP .
E.g. Removal of worn out red blood cells from blood, or invading microbes etc. or cholesterol synthesized in the liver are packaged as LDL’s (low density lipoproteins + cholesterol/’bad cholesterol’), get released into the blood and then re-enter body cells by endocytosis .
Movement of macromolecules out the cell. Membrane-bound vesicles move to the cell membrane, fuse and discharges the molecules; requires ATP .
E.g. Secretory vesicle containing insulin (hormone) OR a protein from Golgi apparatus fusing with the cell membrane OR salivary amyl ase made in salivary glands act in the mouth and pancreatic enzymes act in the small intestine OR neuron cells secreting noradrenaline (neurotransmitter) into the synaptic cleft (See C11).
Ions, sugars, and amino acids. Carrier protein and ATP energy towards higher concentration active Active Transport Water 0nly. Concentration gradient, channel proteins optional towards lower concentration passive Osmosis Water, glucose, and amino acids. Concentration gradient, plus channel or carrier proteins towards lower concentration passive Facilitated Diffusion Water, gases (0 2 and CO 2 ), and steroid hormones. Concentration gradient towards lower concentration passive Diffusion Examples Conditions Direction of Movement Type of Transport Name Comparison of the ways molecules move into & out of cells.
B9 - Factors Which Affect Movement of Molecules
-Increase of temperature increases the speed of molecules/molecular movement.
-Decrease of temperature decreases the speed of molecules/molecular movement.
2.) Molecular size/mass
Larger molecules move slower because of molecular weight.
The greater number of protein pores and carriers allows faster and more numerous molecular movements.
9.) Chemical and Physical Properties of CM
Permeability of molecules is affected by the hydrophobic and hydrophilic properties of the phospholipid bilayer and the scattered proteins.
10.) Electrical Charge
Ions or molecules with a charge cannot pass through the lipid bilayer by diffusion. Other mechanisms involving protein carriers and ATP energy are required, e.g. the Na+/K+ ion pump transport mechanism.
(c) Facilitated transport of C 6 H 12 O 6 & amino acids entering quickly from [high] to [low] using protein carriers.
Some use protein carriers, channel proteins
Moves with the [gradient].
Movement of lipid soluble molecules, gases, & H 2 0.
Endo/exocytosis of macromolecules using vesicles.
Phago/pinocytosis using vesicles.-
Requires ATP to form vesicle.
Uses protein carriers.
Moves against the [gradient] & requires ATP.
Movement of ions, large molecules, cells, molecules in fluid via vesicles.
Devise an Experiment Using the Scientific Method and Interpreting Data and Graphs
See provincial diagrams, data, graphs, “Potato lab”, class worksheets AND web link resources.
Note: The Potato Lab/Solute Concentration of Potato Cells will be performed over 1.5 days and a lab report (includes data sheet, graphs, questions & conclusion) will be evaluated. It is expected that you review the Scientific Method in order to understand the sequential steps of this controlled experiment. See text…..p. 10-13.
Demonstrating your comprehension of Experimental Design is covered in detail in A1. This is a new unit! You can preview this at:
The specific number of the group or groups (plants, animals, bacteria etc.) being studied. Generally, the larger the sample size, the more reliable the study results , and the more likely it is that the results can be applied to larger groups of people.
When a variable is manipulated by an experimenter.
In this study, 19-month old rats (equivalent to 60-year old humans) were fed either a standard diet or a diet supplemented by either blueberry, strawberry, or spinach powder. After eight weeks, the rats were given memory and motor tests. Although all supplemented rats showed improvement, those supplemented with blueberry powder showed the most notable improvement.
cell size affects the SA/V . As a cell grows larger, its rate of producing wastes and requiring nutrients increases faster than the surface area through which molecules must exit and enter. Volume increases by the cube, while surface area increases by the square. As a cell grows larger, its surface area becomes too small to maintain life functions. Cells remain small and therefore maintain a large surface-area-to volume ratio
Note: As the cell increases in size, the SA/V ratio decreases (the V ↑ faster than the SA, i.e. cubed function vs. squared function). There is less surface (CM) to meet the needs of the volume (chemical activity within the cytoplasm & organelles). If chemical reactions within the cytoplasm cannot be supplied with nutrients or remove wastes, the cell will die OR it can divide into two cells and thus obtain a favourable, i.e. large SA/V ratio .
In summary, increasing cell size results in a decrease in the SA/V ratio for the cell. This reduction in the SA/V ratio combined with the increased distance to the cell center makes diffusion of materials into & out of the cell less efficient.
Note: Some cells have unique shapes & structures to overcome SA/V ratio. E.g. intestinal epithelial cells on villi contain microvilli (a “brush border”) to ↑ SA for diffusion of nutrients; RBC’s are biconcave shape to ↑ SA/V ratio for more efficient gas diffusion (See C1 and C6).