3. Endomembrane System: It s all integrated!

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1 3. Endomembrane System: It s all integrated! 4. Vacuoles ii. Large Central Vacuole (Plants)! Fills up most of plant cell! Membrane bound (tonoplast)! Helps cell s water balance! Dump site for hazardous wastes! Vacuole fills with water & gives Turgor Pressure 1

2 5. Energy Related Organelles i. Mitochondria! Powerhouses in eukaryotic cells! Animals and Plants! ,000 per cell; highest numbers in muscle, brain, and eye cells! Surrounded with 2 membranes! inner membrane forms cristae (folds) 5. Energy Related Organelles i. Mitochondria 2

3 5. Energy Related Organelles i. Mitochondria!Semi-autonomous own DNA, circular, codes for ~15 genes own ribosomes however, dependent on proteins coded in the nucleus! Function: ATP (energy) synthesis through aerobic respiration; converts the energy stored in sugar to ATP ii. Chloroplasts! Site of photosynthesis uses the energy in sunlight to drive the production of ATP and simple sugars! Larger than mitochondria 3

4 ii. Chloroplasts! Plants and some protists!contain Thylakoids! Surrounded by 2 membranes organized into grana! s per cell chlorophyll (in membranes) Transfer Light E! ATP ii. Chloroplasts! contains DNA (circular)! codes for ~130 genes! however, like the mitochondria, dependent on proteins coded in the nucleus 4

5 iii. Endosymbiosis: living in close association!endosymbiotic theory: some modern organelles are the result of engulfed prokaryotes that provided their hosts with advantages associated with specialized metabolic activities.!origin of the Mitochondria and Chloroplast!Supported by a wealth of information number and structure of membranes size of structures is similar ribosomal makeup DNA: circular DNA: replicates in the same way 6. Cytoskeleton! Network of protein fibers that crisscrosses the cytoplasm of eukaryotic cells!supports cell shape, movement, and anchors organelles! It is a dynamic system, constantly forming and disassembling! Polymerization: the construction of long chains by the addition of identical protein subunits 5

6 i. Components Actin Filaments: Intermediate Filaments: Supports cell shape, movement reinforce cell, anchor organelles Microtubules: cell rigidity, anchor & tracks for organelles, major role in mitosis i. Components a. Actin Filaments! composed of two protein chains twined together! the subunits of the actin filament are the globular protein Actin! concentrated just inside the plasma membrane! rapid polymerization and depolymerization! contraction, crawling, pinching during cell division, cellular extensions 6

7 i. Components b. Microtubles Cilia! hollow tube! subunits are globular proteins that consist of dimers of alpha and beta tubulin! rapid polymerization and depolymerization! cellular movement, internal cellular movement, during cell division they move chromosomes [CLIP] i. Components c. Intermediate filaments! fibrous protein molecules twined together! subunits are fibers! tremendous strength! once formed they are stable! structural stability, constituents of hair and fingernails (Keratin) Rat epithelial cell 7

8 7. Cilia and flagella: made of microtubules in Eukaryotes i. Cilia: Short, numerous oars ii. Flagella Longer, fewer, with whip-like/ wave like motion 7. Cilia and flagella: made of microtubules Flagellum microtubules SEM 4,100! Plasma membrane TEM 206,500! TEM 206,500! LM 600! Arrangement: More complex than Prokaryotes 8

9 8. Cell Walls! plants, fungi, and most protists! prokaryotic! eukaryotic cell wall!protection & support!fungi: chitin! plants: cellulose! in plants it is thick, strong, and rigid! plants have a primary wall, a middle lamella, and may have a secondary cell wall 8. Cell Walls! plants, fungi, and most protists! prokaryotic! eukaryotic cell wall!protection & support!fungi: chitin! plants: cellulose! in plants it is thick, strong, and rigid! plants have a primary wall, a middle lamella, and may have a secondary cell wall 9

10 9. Extracellular Matrix Animal cells! Animal cells lack cell walls. form extracellular matrix support strength resilience binds cells together! Composed of an elaborate mixture of sticky glycoproteins (=proteins with short chains of sugars attached to them) REVIEW Eukaryotic organelles fall into 4 functional groups 1. Manufacture and transport dependent on network of membranes Nucleus Ribosomes Rough, smooth ER Golgi apparatus 2. Breakdown all single-membrane sacs Lysosomes (plants, animals, some protists) Peroxisomes Vacuoles (plants) 3. Energy Processing involves extensive membranes embedded with enzymes Chloroplasts Mitochondria 4. Support, Movement, Communication Cytoskeleton includes cilia, flagella, filaments, microtubules Cell walls Extracellular matrix Cell junctions 10

11 Chapter 5: Cell Membrane Structure and Function I. Phospholipid Bilayer & Fluid Mosaic Model II. Membrane Components III. Transport Mechanisms IV. Cell-Cell Interactions Fig. I. Phospholipid 6.3 (TEArt) Bilayer & Fluid Mosaic Model Polar hydrophilic heads Nonpolar hydrophobic tails Polar hydrophilic heads 11

12 Membrane structure is related to membrane function A. Membrane Structure= Fluid Mosaic Fluid = Membrane = phospholipid bilayer Mosaic = Proteins embedded in membrane Membrane is flexible, fluid Not rigid Proteins are embedded in the bilayer, but are free to move laterally I. Phospholipid Bilayer & Fluid Mosaic Model Membrane structure is related to membrane function A. Membrane Structure= Fluid Mosaic B. Function: Plasma membrane = gatekeeper Functions (For Cell): 1. Isolation- 2. Regulation- 3. Communication- selective from environment exchange of essential substances with other cells 12

13 Membrane structure is related to membrane function A. Membrane Structure= Fluid Mosaic Fluid = Membrane = phospholipid bilayer Mosaic = Proteins embedded in membrane Transport proteins: channels and carriers Receptor proteins: triggers and gates Recognition proteins: ID tags Membrane is flexible, fluid Not rigid Proteins are embedded in the bilayer, but may move laterally B. Transmembrane Proteins Anchoring Proteins in the Bilayer Nonpolar areas of protein Polar areas of protein i. Single-Pass Anchors Single non-polar segment anchored into the membrane ii. Multi-Pass Channels & Carriers Several non-polar!- helices form a channel in the membrane iii. Pores Several non-polar "- pleated sheets form a pore in the membrane 13

14 B. Transmembrane Proteins Anchoring Proteins in the Bilayer i. Single-Pass Anchors Single non-polar segment anchored into the membrane ii. Multi-Pass Channels & Carriers Several non-polar!- helices form a channel in the membrane iii. Pores Several non-polar "- pleated sheets form a pore in the membrane Membrane proteins have a variety of functions: Transporter Enzyme Cell Surface Receptor Cell Surface Identity Marker Cell-to-Cell Adhesion Attachment to the Cytoskeleton 14

15 III. Transport Mechanisms How particles get across cell membranes. Background: Two factors influence transport: 1) Hydrophilic/hydrophobic interactions 2) Concentration gradients a physical difference between 2 areas concentration (# molecules/unit volume) Molecules tend to move down a concentration gradient: High concentration Low concentration III. Transport Mechanisms Lipid bilayers are selectively permeable! some substances can readily pass from one side to the other, others only with great difficulty, and others not at all small hydrophobic substances pass through with ease some small hydrophyllic substances can pass (prob. negligible) large hydrophobic substances show minimal potential for crossing membranes are generally impermeable to proteins, amino acids, nucleic acids, & carbohydrates but permeable to lipids, lipid-like substances, and gasses 15

16 III. Transport Mechanisms Which molecules can cross the plasma membrane? Due to its polarity, water cannot cross the membrane freely. However, water flow is facilitated by Aquaporins (channel proteins). III. Transport Mechanisms A) Passive transport Follows concentration gradient Does not require energy Either direct or via channels or carriers 1) Diffusion 2) Osmosis B) Active Transport Against concentration gradient Requires energy (ATP) C) Bulk Transport Exocytosis, Endocytosis ATP 16

17 A. Types of Passive Transport 1. Diffusion All molecules constantly vibrating/moving Mixtures tend to become uniform Molecules move from high concentration! low concentration Down the gradient Doesn t require energy Time 0 Time 1 Time 2 Steep Concentration Gradient Reduced Concentration Gradient No Concentration Gradient 1. Diffusion (Types) i. Diffusion Across a Membrane: Small nonpolar (hydrophobic) molecules and gasses e.g. hydrocarbons Follows concentration gradient Does not show saturation Does not require energy Can occur either directly across a membrane (ex., O 2 ), or through Channel proteins. Channels are very specific for a particular ion (ex., Ca ++, Na + ) or molecule (ex., H 2 O). Channel proteins DO NOT bind to the solute, they are open passages. 17

18 1. Diffusion (Types) ii. Facilitated Diffusion: Uses Carrier proteins A given carrier is specific; it will only transport certain molecules or ions Transports polar (hydrophillic) molecules e.g. Sugars, amino acids, ions PHYSICALLY BINDS TO THE SOLUTE Follows concentration gradient, does not use energy Can saturate if all carriers are in use A. Types of Passive Transport 2. Osmosis Diffusion of water, but not solutes, across a selectively permeable membrane due to concentration differences EX: Net water movement toward sugar; Water follows concentration gradient, sugar cannot. Sugar molecule Semipermeable membrane Water molecules Net water movement toward regions of higher solute concentration! 18

19 salt 2. Osmosis: Water movement across membranes (other molecules cannot readily cross) Solution is HYPOTONIC to cell; (lower [solute] ) Solution = 5% salt Solution = 95% H 2 0 Where will water go? Cell =45% salt Cell = 55% H 2 0 salt 2. Osmosis: Water movement across membranes (other molecules cannot readily cross) Solution is HYPERTONIC to cell; (higher [solute] ) Solution = 40% salt Solution = 60% H 2 0 Where will water go? Cell = 5% salt Cell = 95% H

20 A. Types of Passive Transport 2. Osmosis: How animal & plant cells behave in different solutions Isotonic solution Hypotonic solution Hypertonic solution H 2 O H 2 O H 2 O H 2 O Animal cell (1) Normal (2) Lysed H 2 O H 2 O H 2 O (3) Shriveled Plasma membrane H 2 O Plant cell (4) Flaccid (5) Turgid (6) Plasmolysis (shriveled) B. Active Transport! Requires energy (ATP)! Moves molecules against concentration gradient! Pumped by conformational changes in transport protein 20

21 B. Active Transport: The Sodium-Potassium Pump Extracellular Intracellular Na + P ATP PPA 1. Protein in membrane binds intracellular sodium. K + P PPA ATP 2. ATP phosphorylates protein with bound sodium. P P PA ADP 3. Phosphorylation causes conformational change in protein, allowing sodium to leave. P P PA ADP 4. Extracellular potassium binds to exposed sites. P P PA ADP+P i 5. Binding of potassium causes dephosphorylation of protein. P PPA ATP 6. Dephosphorylation of protein triggers change back to original conformation, potassium moves into cell, and the cycle repeats. B. Active Transport: Coupled Transport 21

22 III. Transport Mechanisms C) Bulk transport 1) Endocytosis i. Phagocytosis: particulate matter ii. Pinocytosis: liquid iii. Receptor-mediated endocytosis 2) Exocytosis Phagocytosis of a bacterium by a mouse cell 1. Endocytosis: Processes to move large molecules, groups of molecules, or polar molecules into the cell. (Uses Vesicles) i. Phagocytosis! Macrophage: WBC 22

23 III. Transport Mechanisms 2. Exocytosis Secretes unwanted materials, materials for cell wall formation, hormones, digestive enzymes, etc. IV. Cell-Cell Interactions A. Membranes have important roles in cell signaling and cell-cell interactions A. Cells signal one another with chemicals B. Membrane proteins [and other proteins inside the cell] receive the signals C. Membrane proteins mediate cell-cell interactions 23

24 IV. Cell-Cell Interactions B. Cell Junctions 1. Gap Junctions: in Animal cells pairs of channel proteins to connect cytoplasm of cells 2. Plasmodesmata: in Plant cells Cytoplasmic bridges 24