SBU1053 Chapter 3 Part I PDF - Cell Structures

CHAPTER 3: CELL STRUCTURES DR. AZI AZEYANTY BT JAMALUDIN  Plasma Membrane ✘ The pla sm a m em bra ne sepa ra t es t he int erna l environm ent of t he cell from it s ext erna l environm ent. ✘ Ma rks t he bounda ry bet ween t he out side &inside of a cell....

CHAPTER 3: CELL STRUCTURES DR. AZI AZEYANTY BT JAMALUDIN  Plasma Membrane ✘ The pla sm a m em bra ne sepa ra t es t he int erna l environm ent of t he cell from it s ext erna l environm ent. ✘ Ma rks t he bounda ry bet ween t he out side &inside of a cell. ✘ It regula t es t he ent ra nce a nd exit of m olecules int o a nd out of t he cell. ✘ The st ea dy int erna l environm ent m a int a ined is ca lled hom eost a sis. ✘ In proka ryot ic &euka ryot ic cell, t he pla sm a m em bra ne is a phospholipid bila yer. ✘ The fluid m osa ic m odel st a t es t ha t t he prot ein m olecules em b edded in t he m em bra ne ha ve a pa t t ern (a m osa ic) wit hin t he phospholipid bila yer. ✘ The pa t t ern va ries a ccording t o t he t ype of cell (sa m e m em bra ne but a t different t im e). A model of the plasma membrane composed of a phospholipid bilayer ✘ Phospholipidbilayer with embedded proteins. ✗ Hydrophilic (water - loving) polar heads Face inside and outside of cell (water present) ✗ Hydrophobic (water - fearing) nonpolar tails Face each other, away from water ✗ Cholesterol (animal cells) controls excessfluidity ✘ Membrane proteins throughout membrane may be: ✗ Peripheral proteins – associated with only one side of membrane ✗ Integral proteins – span the membrane Canprotrude from one or both sides Embeddedwithin the membrane Able to move laterally ✘ Both phospholipids and protein can have attached carbohydrate chains. ✘ Glycolipidsare lipids attached to carbohydrates. ✘ Glycoproteins are proteins attached to carbohydrates. Functions of Membrane Proteins The protein that occur within a membrane have varied, specific function:  Cha nnel prot ein  Ca rrier prot ein  Cell recognit ion prot ein  Recept or prot ein  Enzym a t ic prot ein  Junct ion prot ein / Adhesion prot ein  Channel protein ✘ Are simple protein pores. ✘ Form a tunnel for specific molecules across the entire membrane. ✘ Allow substances to move across the membrane freely (allowing only one /a few types of specific molecule to simply move across the membrane channel.  Carrier protein @ Transport protein  Combine wit h subst a nces t o a ssist t heir m ovem ent a cross m em bra nes.  Involved in pa ssa ge of m olecules & ions t hrough m em bra ne, som et im es requiring input of energy (ATP).  Eg: carnitine, to carry fatty acid into mitochondria  Cell recognition protein (Crp) Crp are glycoproteins Crp enable our body to distinguish between our own cells and cells of other organisms These proteins help the body recognize when it is being invaded by pathogens. Eg: MHC glycoprotein for immune system.  Receptor protein ✘ Have a shape that can only bind specific molecule (called a signal molecules). ✘ The binding of a signal molecule cause the receptor protein to change its shape & thereby bring cellular to bind causing a cellular response ✘ Eg: insulin receptor- inducing glucose uptake.  Enzymatic protein  Membrane proteins t ha t ca t a lyze (ca rry out ) specific chem ica l rea ct ions.  Direct ly pa rt icipa t e in m et a bolic rea ct ions.  Ca rry out m et a bolic rea ct ions direct ly.  Wit hout enzym e a cell would be never a ble t o perform t he m et a bolic rea ct ions t ha t a re im port a nt t o it s funct ion.  Eg: hydrolase enzyme- catalyze hydrolysis  Junction protein /Adhesion protein  Connect cells to each other and allow t hem t o com m unica t e.  Prot ein t ha t a re involved in form ing va rious t ypes of junct ion bet ween cells.  Form junct ions bet ween cells.  Cell- t o- cell a dhesion a nd com m unica t ion  Tight junctions (blue dots) between cells are connected areas of the plasma membrane that st it ch cells t oget her.  Adherens junct ions (red dot s) join t he a ct in fila m ent s of neighbouring cells t oget her.  Desm osom es a re even st ronger connect ions t ha t join t he int erm edia t e fila m ent s of neighbouring cells.  Hem idesm osomes (light blue) connect int erm edia t e fila m ent s of a cell t o t he ba sa l la m ina , a com bina t ion of ext ra cellula r m olecules on ot her cell surfa ces.  Ga p junct ions (yellow) a re clust ers of cha nnels t ha t form t unnels of a queous connect ivit y bet ween cells.  The Permeability of the Plasma Membrane ✘ The plasma membrane ✘ Small, uncharged molecules freely cross ✘ Water which is polar would not be expected to readily cross the ✗ can regulate the membrane Examples: CO2, O2, glycerol, and membrane. ✘ passage of molecules ✗ into and out of the cell alcohol Aquaporins are special channels because it is selectively Slip in between the hydrophilic that allow water to cross the permeable. heads and pass through membrane. ✘ Meaning that certain ✗ hydrophobic tails Driven by the concentration ✘ Aquaporins are present in the substances can across majority of cells. ✘ gradient the membrane while ✘ Large molecules, ions, and charged ✗ Concentration gradient other cannot. molecules are unable to freely More of a substance on one side of ✘ cross the membrane, but can ✗ Which molecules can the membrane cross the membrane via ✘ freely cross the Going “down” a concentration membrane and which gradient from an area of higher to Channel proteins forming a pore ✗ may require carrier lower concentration through the membrane proteins and/or energy depends on Going “up” a concentration gradient from an area of lower to ✘ Carrier proteins that are specific ✗ for substance they transport ✘ higher concentration, requires Size ✗ input of energy Vesicle formation in endocytosis Nature of or exocytosis molecule – polarity, charge 15 Passage of Molecules Into and Out of the Cell VIDEO: membrane transport animation: Detail: https://www.youtube.com/watch?v=WvpiLINjv_E  Movement of molecules: Diffusion ✗ Movement of molecules from an area of higher (going “down” to lower concentration Downa concent ra t ion gra dient Occurs unt il equilibrium is rea ched For exa m ple, when a cryst a l of dye is pla ced in wa t er t he dye a nd wa t er m olecules m ove a bout unt il equilibrium occurs. ✗Solut ion cont a ins a solute (solid) a nd a solvent (liquid) Once t he solut e a nd solvent a re evenly dist ribut ed, t heir m olecules cont inue t o m ove a bout , but t here is no net m ovem ent of eit her one in a ny direct ion.  O2 O2 O2 O2 O2 O2 O2 oxygen ✘ O2 O2 Gases can diffuse through O2 O2 a membrane ✘ O2 bronchiole Oxygen and carbon alveolus capillary dioxide enter and exit this way  Movement of molecules: Osmosis  The diffusion of water across a differentially (selectively) permeable membrane, due to concentration differences is called osmosis  Diffusion always occurs from higher to lower concentration.  Osmotic pressureis the pressure that develops in a system due to osmosis.  The greater the possible osmotic pressure, the more likely it is that water will diffuse in that direction. * Water (a solvent) more across the membrane into the area of lower water (or higher solute) less water (higher more water (lower percentage of solute) percentage of solute) < 10% 10% water solute more water (lower 5% thistle > 5% less water (higher percentage of solute) tube percentage of solute) a. c. differentially permeable membrane beaker ✘ b. ✘ Membrane is not permeable to solute ✘ Isotonic: the solute concentration is equal inside and outside of a cell ✘ Hypotonic: a solution has a lower solute concentration than the inside of a cell Hypertonic: a solution has a higher solute concentration than the inside of a cell  Animal cells plasma 6.6 µm 6.6 µm 6.6 µm nucleus membrane In an isotonic solution, there is no net In a hypotonic solution, water enters the cell, In a hypertonic solution, water leaves the ✘ movement of water. which may burst (lysis). cell, which shrivels (crenation). Isotonic ✗ No net ga in or loss of wa t er ✗ 0.9% Na Cl ✘ Hypot onic ✗ Cell ga ins wa t er ✗ Cyt olysis – hem olysis ✘ Hypert onic ✗ Cell loses wa t er ✗ Crena t ion Plant cells nucleus cell wall central plasma vacuole membrane chloroplast 25 µm 25 µm 40 µm In an isotonic solution, there is no In a hypotonic solution, the central vacuole In a hypertonic solution, the central vacuole loses net movement of water. fills with water, turgor pressure develops, and water, the cytoplasm shrinks (plasmolysis), and ✘ chloroplasts are seen next to the cell wall. chloroplasts are seen in the center of the cell. Isotonic ✗ No net ga in or loss of wa t er ✘ Hypot onic ✗ Cell ga ins wa t er ✗ Turgor pressure keeps pla nt erect – cell wa ll ✘ Hypert onic ✗ Cell loses wa t er ✗ Pla sm olysis  Animal cells 6.6 µm 6.6 µm 6.6 µm plasma nucleus membrane In an isotonic solution, there is no net In a hypotonic solution, water enters the cell, In a hypertonic solution, water leaves the movement of water. which may burst (lysis). cell, which shrivels (crenation). Plant cells nucleus cell wall plasma central vacuole membrane chloroplast 25 µm 25 µm 40 µm In an isotonic solution, there is no In a hypotonic solution, the central vacuole In a hypertonic solution, the central vacuole loses net movement of water. fills with water , turgor pressure develops, and water, the cytoplasm shrinks (plasmolysis), and chloroplasts are seen next to the cell wall. chloroplasts are seen in the center of the cell. Osmosis video ✘ ht t ps:/ / www.yout ube.com / wa t ch?v=SSS3Et KAzYc (egg experim ent ) ✘ ht t ps:/ / www.yout ube.com / wa t ch?v=Ia Z8Mt F3C6M (osm osis exa m ples)  Movement of molecules: Transport by Carrier Proteins ✘ The plasma membrane prevent/delay the passage of all but few substances. ✘ Substances enter or exit cells because of carrier proteins. ✘ Carrier proteins are specific. ✗ Combine with a molecule or ionto be transported across the membrane ✗ Change shapeto move molecules across membranes ✘ Carrier proteins are required for ✗ Facilitated Transport (passive transport) ✗ Active Transport  Facilitated Transport ✘ Facilitated transport explains the passage of molecules such as glucose or amino acids. ✗ Neither molecule is lipid- soluble. ✗ Reversible combination and transport occurs. ✗ Like diffusion,ATP is not requiredbecause molecules are transported down their concentration gradient. Small molecules that are not lipid- soluble. Moleculesfollow the concentration gradient. Energy is not required  Active Transport ✘ Moleculesor ions combine with carrier proteins. ✗ Often called pumps ✘ Molecules moveagainst the concentration gradient ✗ Entering or leaving cell ✗ Accumulate either inside or outside the cell ✘ Energy and carrier proteins are required. ✗ Usually ATPis used ✘ Eg: Na+/K+ pump is especially important for nerve and muscle cells–it moves Na+ out and K+ into cells. ✘ The carrier changes shape after phosphate attaches, and then again after it detaches. ✘ This process is responsible for maintaining the large excess of Na + outside the cell and the large excess of K+ ions on the inside (eg important for action potential). This figure shows the mechanism action of sodium potassium pump. carrier K+ Outside protein K+ K+ K+ K+ K+ K+ K+ K+ K+ Inside 1. Carrier has a shape that allows it to take up 3 Na+. P K+ K+ ATP ADP 6. Change in shape results and 2. ATP is split, and phosphate causes carrier to release 2 K + group attaches to carrier. inside the cell. K+ K+ K+ K+ K+ K+ K+ K+ K+ P K+ P K+ K+ 5. Phosphate group is released 3. Change in shape results and from carrier. causes carrier to release 3 Na + outside the cell. P 4. Carrier has a shape that allows it to take up 2 K+. Movement of molecules: Bulk Transport ✘ Macromolecules are transported into or out of cells by vesicle formation. ✗ Macromolecules are too large to be transported by carrier proteins. ✗ Energy is required to form vesicles. ✗ Vesicle formation is called membrane- assisted transport. Exocyt osis – exit from cell Endocyt osis – ent er int o cell  Exocytosis ✘ The vesicle fuses with plasma membrane as secretion occurs. ✘ The vesicle membrane becomes part of plasma membrane. ✘ Cells of particular organs are specialized to produce and export molecules. ✗ Pancreatic cells release insulin or enzymes. ✗ Anterior pituitary cells release growth hormone.  Endocytosis ✘ Cellstake in substances by vesicle formation. ✗ Part of the plasma membrane invaginates to envelop the substance. ✗ The membrane then pinches off to form an intracellular vesicle. ✘ 3 types of endocytosis ✗ Phagocytosis ✗ Pinocytosis ✗ Receptor- mediated endocytosis  Endocytosis Phagocytosis: large, particulate matter such as “food” m olecules or viruses or whole cells Am oeba a nd m a cropha ges ✘ Pinocytosis: liquids a nd sm a ll pa rt icles dissolved in liquid ✗ Cert a in blood cells or pla nt root cells ✘ Receptor Mediated Endocytosis: a t ype of pinocyt osis t ha t involves a coa t ed pit ✗ Cert a in pla cent a l cells  plasma membrane paramecium pseudopod of amoeba vacuole forming vacuole a. Phagocytosis 399.9 µm vesicles forming solute vesicle b. Pinocytosis 0.5 µm receptor protein coated coated solute pit vesicle coated vesicle coated pit c. Receptor- mediated endocytosis