The A&P of the Cell

1. The A&P of the Cell

2. The cell • The smallest living unit. • Your body consists of billions and billions of cell that are all working together to keep you alive.

3. *The cell theory* • 1. A cell is the simplest living unit. • 2. The activity of an organism depends on both the individual and collective activities of its cell. • 3. The biochemical activities of cells are dictated by the relative number of their specific subcellular structures. • 4. Continuity of life from one generation to another has a cellular basis.

4. The composite/generalized cell • All cells in the body have generally three main structures: • Cytoplasm • A plasma membrane • A nucleus • The exception to this rule is the fully matured red blood cell, which lacks a nucleus.

6. Cell Structures: The plasma membrane • The plasma membrane is the defining point of a cell. It separates the inside of the cell from the outside. • Another name for the plasma membrane is the phospholipid bilayer.

7. The phosopholipid bilayer • Let’s break down the phrase phospholipid bilayer. • Bilayer= • Bi=two • Bilayer= two layers • Phospho=phosphate • Lipid=fat

8. Has a “head” that contains the choline, a nutrient necessary for building a cell membrane, and phosphate that causes a change in polarity on the cell surface. The head is called “hydrophyllic” because it is designed to touch water.

9. Has a “tail” that is a chain of fatty acids that are insoluble in water. They are called hydrophobic because the fatty acids avoid water at all costs.

10. Phospholipid bilayer- a two layer lining of phospholipids that have hydrophyllic “heads” that touch the inside and outside of the cell, and a hydrophobic “tail” that creates a barrier that defines what stays inside and what stays outside the cell.

11. Fluid Mosaic model • Fluid- movable • Mosaic- Structure made up of many different parts. • Fluid Mosaic Model- a multitude of different proteins float in the fluid bilayer.

12. Membrane lipids • Glycolipids-lipids with carbohydrate sugars attached. Also act as a cell surface marker.

13. Transmembrane proteins: Proteins that are in or on the lipid bilayer. Allows the transport of substances and information across the membrane. • Interior protein network: provides structural support and helps give membrane its shape. • Cell surface marker: “self”-recognition. Creates glycoproteins and glycolipids that give the cell its own identity.

14. Transporters: selective; only lets certain substances through. • Enzymes: carries out chemical reactions inside the cell membrane. • Cell surface receptors: Picks up chemical messages outside of the cell. • Glycocalyx: Gives the cell its own “ID” tag. • Cell adhesion proteins: allows cells to stick together…literally. • Cytoskeletal attachments: surface proteins that interact with other cells are often anchored by the cytoskeleton by linking proteins.

15. Cholesterol • Cholesterol is a steroid found in the cell membrane of all animalcells. • Cholesterol is needed to maintain the cell membrane, and can be produced in our bodies, and retrieved in the food we eat.

16. No need to copy this down • Long hand: • (10R,​13R)-​10,​13-​dimethyl-​17-​(6-​methylheptan-​2-​yl)-​2,​3,​4,​7,​8,​9,​11,​12,​14,​15,​16,​17-​dodecahydro-​1H-​cyclopenta​[a]phenanthren-​3-​ol • IUPAC NAME: • (3β)-​cholest-​5-​en-​3-​ol

17. Membrane junctions • Although some cells are considered “free-floaters” inside the body (i.e. rbcs) most cells have some anchoring mechanism to bind themselves together and to other surfaces.

18. Three factors that can bind cells together. • 1. Glycoproteins in the glycocalyx act as an adhesive. (tight junctions) • 2. Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion. (Desmosomes) • 3. Special membrane junctions are formed. (Gap junctions)

19. Membrane Transport • Outside of each cell, there is a fluid that is called interstitial fluid. This fluid, derived from blood, acts as a nutrient rich soup.

20. Membrane Transport continued… • Although there is constantly information and materials moving back and forth to and from the cell by the access of a transmembrane protein, there are certain selective means by which these materials can enter the cell.

21. Methods of getting material through a membrane • Passive Processes • Diffusion • Filtration • Active Processes • Active • Vesicular trafficking • Endocytosis • Transcytosis • Phagocytosis

22. Passive Processes • Diffusion- the tendency of molecules and ions to move from areas of high concentration to areas of low concentration.

23. Simple diffusion • Nonpolar and lipid soluble substances diffuse directly through the lipid bilayer. Includes oxygen, carbon dioxide, and fat soluble vitamins. • Example: oxygen in blood cells

24. Facilitated diffusion • Some molecules are way too large to fit through a membrane. These molecules, like glucose, need to either be ferried across by a carrier molecule, or it needs to be dissolved in a solution, like water and brought through a channel.

25. Facilitated diffusion

26. Osmosis • The diffusion of water through a semipermeable membrane is called osmosis. • Water can freely move in and out of the cell through specialized channels called aquaporins.

27. It is all about homeostasis • If two solutions have different concentrations of solutes, then the one with the higher concentration of solutes is called hypertonic. • The solution with the lower amount of solutes is called hypotonic. • If the two solutions are equal in solutes, it is called isotonic.

29. Active Transport • Primary Active Transport- Sometimes, when we must maintain a certain concentration gradient of solutes regardless of the outside environment, we can expend ATP and use solute “pumps” to push a certain amount of solutes against a concentration gradient to maintain a particular level. • Example: sodium-potassium pumps

30. Primary active transport

31. Secondary active transport • As ions are built up inside a cell membrane, the ions that will eventually leak out can be used to facilitate transport. As these ions are leaking back down a concentration gradient, they can do work by taking other solutes with them.

33. Vesicular trafficking • Movement of large particles through the cell membrane through sacs called vesicles. • Exocytosis-shipping materials out of the cell. • Endocytosis- bringing materials from outside of the cell to inside the cell.

35. phagocytosis • Also known as “cell eating” • Phagocytosis is a type of endocytosis that brings in a large particle for digestion. These vesicles are usually brought to and combined with a lysosome that will release enzyme to break down the larger particle into smaller particles. Indigestible materials are then kicked out of the cell through exocytosis.

36. Pinocytosis • Pinocytosis is a process by which certain cells can engulf and incorporate droplets of fluid. This is a nonselective process. • i.e.- Cells of the small intestines

37. The plasma membrane: resting potential • Membrane potential= voltage • All body cells generate at least some resting potential inside the body. All cells are said to be polarized because of the -50 to -100 mV resting potential they have innately. • The negative sign means the voltage occurs inside the cell.

38. Resting potential • Diffusion causes ionic imbalances that polarize the membrane, and active transport maintains that membrane potential. • Typical ions that are associated with resting potential: Na+, K++

40. If you recall • Earlier we made mention in diffusion that solutes move down a concentration gradient. This is true for unpolarized particles and some ions, but not all ions. • Some ions can hinder diffusion due to the electrical differences in the potential of the ions and the membrane of the cell. • They can also move not only through a chemcial concentration gradient, but an electrical concentration gradient. • In conculsion, some ions are driven not only by chemical differences, but electrical differences in the membrane of the cell from which they diffused.

41. The plasma membrane’s interaction with the environment • The glycocalyx is a major player in the cell’s interaction with the outside. • Cell membrane can react with biochemicals and other hormones outside of the cell that may cause the cell to act or react to the outside environment differently.

42. Cell environment interactions • Cell adhesion molecules- also called CAMs. Allows cells to anchor themselves to other cells. (i.e. desmosones) CAMs act as: • Velcro like molecules that allow attachment to other cells • Act as an arm for migrating cells to cling to when moving through the body.

43. SOS signals that rally leukocytes when blood vessels are damaged. • Sensors that respond to cell tension synthesis or degradation of adhesive membrane junctions. • Intracellular signals that direct cell migration, proliferation (making others of it’s kind), and specialization.

44. Membrane receptors • Membrane receptors are integral proteins and glycoproteins that create binding sites on the cell’s surface. • Contact signaling- the actual touching of two cells. The signals given off by the cell tell the cells how to react with each other. *Vital for the immune system*

45. Chemical signaling- using the membrane receptors to pick up chemicals that bind specifically to said membrane receptor. These chemicals are called ligands. • Neurotransmitters • Hormones • Paracrines

46. G-protein linked receptors • Exert effects through a G-protein that usually acts as a middle man to signal the activation or deactivation of ion channels or enzymes. This usually causes a secondary messenger to activate to communicate with the cell’s metabolic machinery. • Secondary messengers • Cyclic AMP • Ionic calcium • Both are designed to transfer the phosphate groups of ATP to other molecules.

47. NO- Nitric oxide • Chemical that can cause an array of cell activities to occur. • Very tiny and thus can slip in and out of the cell very easily.

48. Cytoplasm • Cellular material between the plasma membrane and the nucleus. Contains three major pieces: • Cytosol • Cytoplasmic organelles • Inclusions

49. Cytosol • A viscous semitransparent fluid that suspends other cytoplasmic elements. (i.e. organelles, solutes, etc.)

50. Inclusions • Chemicals that may or may not be present depending on cell type. (Melanin, glycogen granules)