Membrane Structure and Function

1. Membrane Structure and Function

2. 4.1 The Nature of Membranes The primary substance of all membranes is a phospholipidbilayer The arrangement of the phospholipids provides the outer edges of the membrane with a polar surface This helps cells mix freely with environmental water on the outside and watery cytoplasm on the inside

4. PhospholipidBilayer The specific nature of the interior is somewhat variable due to a phospholipids variety Interiors have the consistency of light oil which stops water from passing freely through the membrane Proteins in the bilayer provide the membrane with its specific regularity capabilities and functions

5. Proteins in the Bilayer Proteins that are a site for envoronmental molecules to attach and impact a cell, like neurotransmitters or hormones, are called surface receptor sites Transmembrane proteins provide the mechanisms for lipid insoluble materials to cross the membrane

7. Water is an example of a molecule that passes through the 3D polar routes called protein channels This sometimes requires the expenditure of ATP The variations in protein structures found in membranes contribute to the differences in their permeability and their regulatory nature

8. Outer surface has two types of oligosaccharide attachments If they are attached to phospholipids, they are called glycolipids If they are attached to proteins, they are called glycoproteins These function as markers for the identification of cell types

9. A blood antigen is a glycoprotein for a red blood cell Different antigens contribute to the differences in blood type The membrane has been given the name selectively permeable because it can select (or neglect) substances that are able to move through them

11. Transport Across Membranes Diffusion Osmosis Protein Assisted Transport Transport involving Vesicles

12. 4.2 Diffussion Diffusion is the random movement of particles due to concentration differences This process is considered to be passive A membrane is not even needed for diffusion to occur

13. Factors that affect the rate of diffusion Concentration: the difference in solute concentration (concentration gradient) causes diffusion Temperature: the increase of temperature increases the kinetic energy of the particles which increases the motion and thus the diffusion rate Size and Shape: smaller, more streamlined substances will diffuse more rapidly

14. IonicCharge: Could be attracted or repelled Viscosity: The lower the viscosity, the faster a substance will diffuse through it. Movement of the Medium: currents will aid diffusion (cytoplasmic streaming in cells) A particle’s solubility and polarity also affect it’s ability to pass freely through a membrane

15. Review The fluid mosaic model describes membranes having A set of protein channels separated by phospholipids A bilayer of phospholipids in which specialized proteins are embedded Two sheets of protein with a layer of phospholipids sandwiched between them

16. The fluid mosaic model describes membranes having A set of protein channels separated by phospholipids A bilayer of phospholipids in which specialized proteins are embedded Two sheets of protein with a layer of phospholipids sandwiched between them

17. The fact that lipids move relatively easily through cell membranes is due to Osmosis Their size Active transport Their chemical composition

18. The fact that lipids move relatively easily through cell membranes is due to Osmosis Their size Active transport Their chemical composition

19. Proteins do not pass freely through membranes because They contain nitrogen They would get denatured They are very large molecules Membranes, themselves, are made of protein

20. Proteins do not pass freely through membranes because They contain nitrogen They would get denatured They are very large molecules Membranes, themselves, are made of protein

21. Which of the following is absolutely necessary for diffusion to occur? A living cell. A true solution. A concentration difference. A selectively permeable membrane.

22. Which of the following is absolutely necessary for diffusion to occur? A living cell. A true solution. A concentration difference. A selectively permeable membrane.

23. The difference in solute concentration between two areas/regions is called hypotonic. hypertonic. absolute difference. concentration gradient.

24. The difference in solute concentration between two areas/regions is called hypotonic. hypertonic. absolute difference. concentration gradient.

25. 4.3 Osmosis The diffusion of water is known as osmosis Water moves to areas with greater solute concentrations Solutions with equal solute concentrations are termed isotonic

26. Osmotic pressure is a measure of collisions that water molecules make against the membrane surface (the greater the concentrations difference, the greater the osmotic pressure) Turgot pressure (turgitidy) is the force the cytoplasm exerts against the inside of the cell membrane

27. 3 Environment Types Hypertonic environments have a higher concentration outside the cell. Hypotonic environments have a lower concentration outside the cell Isotonic environments have no change in concentration inside or outside of the cell.

29. The Shriveling of the cell is known as plasmolysis The expanding is known as deplasmolysis Too much exposure to deplasmolysis can cause the cell to burst, this is called lysis

30. 4.4 Protein Assisted Transport

31. Surface regions are sensitive to the presence of specific solute particles which contributes to the membranes selective nature When particles attach, they change to proteins shape which allows the particle to be propelled through

32. Two Variations • Facilitated transport: substances are transported according to the laws of diffusion (concentration, no energy requires) • Active transport: substances are transported against the laws of diffusion (ATP is required)

33. 4.5 Transport Involving Vesicles The largest substances that must exit or enter a cell do so through membranous vesicles

34. Phagocytosis is the process of ingesting food via endocytosis Pinocytosis is the process of smaller objects, or fluids entering the cell in the form of a vesicle instead of a food vacuole via endocytosis

35. Review Which of the following transportation mechanisms does NOT obey the “laws of diffusion”? Osmosis Diffusion Active transport Facilitated transport

36. A cell in a hypotonic solution loses water gains water neither loses or gains water gains and loses water equally

37. Which of the following crosses a cell membrane by active transport? Water Oxygen Sodium ions Carbon dioxide

38. Osmotic pressure is BEST described as the measure of the Force of water against a membrane Amount of water crossing a membrane Size of water compared to solute particles Movement of water to higher solute concentrations

39. 4.6 Requirements of Cells Cells exist individually, or in clusters forming tissues, organs, and eventually organisms Size is an important factor for their survival and function As a cell grows due to one of the transport mechanisms mentioned above, the normal surface area/volume ratio is lost

40. Apart from dying, the cell may change by • Altering shape • Altering function • Dividing

41. Unfortunately specialized cells, as well as with those of multicellular organisms, cannot do any of these Hence if conditions are too extreme and too long lasting, these cells will die