Cytoskeleton. Provide shape and support for the cell. Other functions of the cytoskeleton. Nucleolus. Nucleus

Transcription

1 Chapter 4: Cell Structure and Function Cytoskeleton The cytoskeleton is a network of fibers that organizes structures and activities in the cell. Microtubules (the largest) Intermediate fibers Microfilaments (the smallest) Think tube vs filaments tubes are always larger Provide shape and support for the cell MTs MFs IFs Other functions of the cytoskeleton Provide movement if the organism has flagellum or cilia Intracellular movement Transports organelles, proteins and other cell components along microtubule rails. Nucleus Only present in eukaryotic cells Location of the organism s genome DNA Nuclear envelope Membrane that surrounds the nucleus Nucleolus Darkly stained regions within the nucleus Ribosome assembly takes place in this organelle. Semipermeable does not allow DNA out, but messenger RNA does leave the nucleus. 1

2 Ribosomes Protein factories Ribosomes Synthesizes most proteins. Two types Free ribosomes Found in all cells Ribosomes attached to the endoplasmic reticulum (ER) Endoplasmic reticulum (ER) Smooth endoplasmic reticulum Lipid production, including steroids. In liver cells, it detoxify drugs and alcohol Also in liver cells, it breaks down Rough endoplasmic reticulum Place where most ribosomes attach Protein synthesis & transportation Golgi apparatus The warehouse of the cell Stores, sorts, and transports proteins and other molecules within the cell Directs transportation of proteins and other molecules to the outside of the cell. Also synthesizes cellulose and pectin (plants) Made by the golgi apparatus Lysosomes Highly acidic environments Due to digestive enzymes. Digest waste particles & malfunctioning organelles. Vacuoles Vacuoles Food vacuoles Transport food from cell membrane to other parts of the cell. This process is known as phagocytosis. 2

3 Contractile vacuoles Freshwater protists need these vacuoles to pump excess water out of the cell. Otherwise the cell continues to expand until it explodes. Found in plant cells Storage organelle Water Central vacuoles May store proteins and carbohydrates Provides turgor, giving plants strength Wilted plants have little turgor due to lack of water Paramecium Plant turgor Mitochondria & chloroplasts Mitochondria are the batteries of the cell. Produces a lot of ATP, the energy currency of most metabolic functions. Plant needs water to fill central vacuoles. Normal plant Chloroplasts Found only in plants and some protists Site of photosynthesis. Chapter 5: Membrane Structure and Function Plasma Membrane: Thin barrier separating inside of cell (cytoplasm) from outside environment Function: 1) Isolate cell s contents from outside environment 2) Regulate exchange of substances between inside and outside of cell 3) Communicate with other cells Note: Membranes also exist within cells forming various compartments where different biochemical processes occur 3

4 The Fluid Mosaic Model of Cellular Membranes: Phospholipid Bilayer: Double layer of phospholipids Hydrophilic ends form outer border Hydrophobic tails form inner layer Lipid tails of phospholipids are unsaturated (C = C) 1) Transport Proteins: Cell Membrane Proteins: Regulate movement of hydrophilic molecules through membrane 2) Receptor Proteins: A) Channel Proteins (form pores; e.g., Na + channels) B) Carrier Proteins (binding sites; e.g., glucose transporter) Trigger cell activity when molecule from outside environment binds to protein How are Substances Transported Across Membranes? Answer: Concentration Gradients Concentration = Number of molecules in a given unit of volume (e.g., grams / liter; moles / liter) Gradient = Difference between two regions of space such that molecules move from one region to the other 3) Recognition Proteins: Allow cells to recognize / attach to one another Glycoproteins: Proteins with attached carbohydrate groups Diffusion: Movement of molecules from an area of high concentration to an area of low concentration Types of Movement Across Membranes (Table 4.1): Requires no energy Substances move down concentration gradients A) Simple Diffusion Small molecules pass directly through the phospholipid bilayer (e.g., CO 2, H 2 O, O 2 ) Greater the concentration gradient, the faster diffusion occurs Diffusion will continue until gradient eliminated (dynamic equilibrium) Diffusion cannot move molecules rapidly over long distances Rate depends on: 1) Molecule size 2) Concentration gradient 3) Lipid solubility (Figure 4.3a) 4

5 Types of Movement Across Membranes: Requires no energy Substances move down concentration gradients B) Facilitated Diffusion Molecules need assistance of channel proteins or carrier proteins (e.g. ions, amino acids, sugars) Channel and Carrier proteins Channel Proteins (Figure 4.3b) Carrier Proteins (Figure 4.3c) Types of Movement Across Membranes: Requires no energy Substances move down concentration gradients C) Osmosis A) Simple Diffusion B) Facilitated Diffusion Movement of water from an area of high [water] to area of low [water] across semi-permeable membrane Osmosis: water water In which direction will there be a net osmotic movement of water? out of the cell into the cell neither In which direction will there be a net osmotic movement of water? out of the cell into the cell neither 0.05 M glucose Permeable only to water 0.02 M glucose 0.01 M sucrose 0.05 M glucose Permeable only to water 0.02 M glucose 0.03 M sucrose 5

6 Osmosis and Living Cells: Isotonic Solution: Outside of cell has same [solute] as inside of cell Iso = same. Isotonic = Same solute concentration inside and outside of the cell. Osmosis and Living Cells: Isotonic Solution: Outside of cell has same [solute] as inside of cell Hypertonic Solution: Outside of cell has higher [solute] than inside of cell Hyper = higher (no net water movement) (net water movement out of cell) Osmosis and Living Cells: Isotonic Solution: Outside of cell has same [solute] as inside of cell Hypertonic Solution: Outside of cell has higher [solute] than inside of cell Hypotonic Solution: Inside of cell has higher [solute] than outside of cell Hypo = lower Tonicity is relative to the inside of the cell Water balance in cells without walls Solution is: hypotonic isotonic hypertonic lyse normal shrivel (net water movement into cell) Water balance in cells with walls hypotonic isotonic hypertonic Types of Movement Across Membranes: 2) Active Transport (aka pumps) Requires energy (ATP) Substances move against concentration gradients turgid flaccid shriveled 6

7 Types of Movement Across Membranes: 2) Active Transport 3) Endocytosis Movement of large particles into cells (vesicle formation) 1) Pinocytosis ( cell drinking ) Uptake of fluid droplets 2) Receptor-mediated Endocytosis Uptake of specific molecules via coated pits 3) Phagocytosis ( cell eating ) Uptake of large particles (e.g. bacteria) (Figure 4.7) Types of Movement Across Membranes: 2) Active Transport 3) Endocytosis 4) Exocytosis Movement of large particles out of cells (e.g., hormones) (Figure 4.9) Exocytosis How are Cell Surfaces Specialized? Answer: Junctions allow cells to connect and communicate 1) Connection Junctions: A) Desmosomes: Hold cells together via protein filaments (Figure 4.10a) How are Cell Surfaces Specialized? Answer: Junctions allow cells to connect and communicate 1) Connection Junctions: B) Tight Junctions: Protein seals prevent leakage (cell cell) How are Cell Surfaces Specialized? Answer: Junctions allow cells to connect and communicate 2) Communication Junctions: A) Gap Junctions: Protein channels allowing for signals to pass between cells (animals) (Figure 4.10b) (Figure 4.11a) 7

8 How are Cell Surfaces Specialized? Answer: Junctions allow cells to connect and communicate 2) Communication Junctions: A) Plasmodesmata: Cytoplasmic bridges allowing for signals to pass between cells (plants) Cell Walls: How are Cell Surfaces Specialized? Answer: Cell walls offer support and protection Found in bacteria, plants, fungi, & some protists Composed of carbohydrates (e.g. cellulose, chitin), proteins, or inorganic molecules (e.g. silica) Produced by the cell it protects/supports (Figure 4.11b) Exam on Thursday! Bring scantrons and 2 pencils in case one breaks Covers Chapters 1 5. Will be multiple choice, short answer, and 1 or 2 essay questions. Study Chapter 3 particularly carefully, it s the biggest chapter! 8