Cell Structure and Function Chapter 6and 7 AP Biology
Cell Theory • All living things are made of cells. • Cells are the basic unit of structure and function in living things. • All cells come from pre-existing cells.
Eukaryotic vs. Prokaryotic Cells • Eukaryotic cells contain DNA in the nucleus. Prokaryotic cells contain DNA in a concentrated region called the nucleoid.
The Plasma Membrane • Plasma Membrane- a selective barrier (semipermeable) that allows passage of enough oxygen, nutrients, and wastes to and from the cell. • The plasma membrane is a lipid bilayer embedded with diverse proteins.
Surface Area to Volume Ratio • As you ___________ the cell size, you ____________ the surface area to volume ratio, which ___________ the efficiency of transport across the cell membrane.
Animal Cell Plant Cell
Nucleus: Information Central • Nucleus- contains cellular DNA which includes most of the genes in the cell. The nucleus is surrounded by the nuclear envelope. • The nuclear envelope is a double membrane made of 2 lipid bilayers. Includes pore structures that help regulate things entering and exiting the nucleus. • Nuclear Lamina- a net of protein filaments that maintain shape of nucleus and support nuclear envelope.
Nucleus: Information Central • Chromosomes- structures that carry genetic information (DNA). Each chromosome contains one long DNA molecule. • Each eukaryotic species has a distinct number of chromosomes. • Chromatin- the complex of DNA and protein making up chromosomes. • Nucleolus- helps synthesize rRNA (ribosomal RNA) and ribosomes.
Ribosomes: Protein Factory • Ribosomes- made of rRNA and proteins- carry out protein synthesis. • Ribosomes exist as either free ribosomes (suspended in cytosol) or bound ribosomes (attached to the Rough ER or nuclear envelope)
Endoplasmic Reticulum: Biological Factory • Endoplasmic Reticulum- consists of membranous tubules, and sacs, called cisternae. • Smooth ER- lacks ribosomes. Functions lipid synthesis, detoxification, and storing calcium ions. • Rough ER- has ribosomes on surface. Continuous with the nuclear envelope. Synthesizes glycoproteins and other secretory proteins.
Golgi Apparatus: Shipping and Receiving • Golgi Apparatus- made of flattened membranous sacs called cisternae. Has 2 sides the cis face (receiving) and the trans face (shipping).
Lysosomes: Digestive Compartments • Lysosome- contains hydrolytic enzymes used to digest molecules. • Phagocytosis- “cell eating”- lysosome digesting food • Autophagy- lysosome breaking down damaged organelles.
Vacuoles: Storage Centers • Vacuole- functions vary depending on cell type. • Food Vacuole • Contractile Vacuole • Central Vacuole
Mitochondria: Chemical Energy Supercenter • Mitochondria- site of cellular respiration. • Cellular Respiration- the process that uses O2 to generate ATP by extracting energy from sugars, fats, and other fuels.
Chloroplast: Light Energy Capturer • Chloroplast- found in plants and algae- the site of photosynthesis. Contain the green pigment chlorophyll. • Is a member of the plastid family- a group of plant organelles.
Peroxisomes: Oxidation • Peroxisomes- contain enzymes that remove hydrogen atoms and transfer them to oxygen, producing hydrogen peroxide (H2O2).
Cytoskeleton • Cytoskeleton- a network of fibers extending throughout the cytoplasm- plays a major role in organizing the structure and activities of the cells. • Motor Proteins- allows for cell movement.
Cytoskeleton • Microtubules- the thickest cytoskeletal fiber, provide a track that organelles with motor proteins can move along. Help separate chromosomes during mitosis. Form flagella and cilia. • Centrosome- region where microtubules are organized. Contains a pair of centrioles. Only in animal cells.
Cytoskeleton • Microfilaments- the thinnest fiber. Actin and myosin filaments help muscle cells contract. Aide in pseudopodia movement by converting cytoplasm from a liquid to a gel. • Cytoplasmic Streaming- circular flow of cytoplasm within cells. Speeds distribution of cell materials.
Cytoskeleton • Intermediate Filaments- more permanent fixtures, fix the position of organelles and shape of the cell. Include keratin proteins.
Cell Wall • Cell Wall- extracellular structure of plant cells. Protects the cell, maintains its shape, and prevents excessive uptake of water. Holds the plant up against gravity. • Primary Cell Wall, Middle Lamella, Secondary Cell Wall • Plasmodesmata-perforations in the plant cell wall that allows cytoplasm to be continuous between neighboring plant cells.
Extracellular Matrix • Extracellular Matrix (ECM)- glycoproteins, carbohydrates and proteoglycans that form strong fibers outside of cells.
Warm Up Exercise • What are the three components of the cytoskeleton? • Which cytoskeletal component provides tracks for motor proteins to move along within the cell? • Which cytoskeletal structure helps muscles contract? • Which cytoskeletal component helps form cilia and flagella?
Fluid Mosaic Model • Fluid Mosaic Model- membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a phospholipid bilayer. (lipids and proteins are amphipathic)
Membrane Proteins • Integral Proteins- penetrate the hydrophobic interior of he lipid bilayer. (Ex: integrins) • Most of these are transmembrane proteins which span the entire membrane. • Peripheral Proteins- loosely bound to the surface of the membrane. Not embedded at all.
Functions of Membrane Proteins • Transport • Enzymatic Activity • Signal Transduction • Cell to Cell Recognition • Intercellular Joining • Attachment to Cytoskeleton and ECM
Membrane Fluidity • Membranes are held together by weak hydrophobic interactions.
Membrane Fluidity • Membrane remains fluid as temperature decreases, until phospholipids pack so closely together that the membrane solidifies. • Cholesterol reduces membrane fluidity at high temperatures by reducing movement. It also prevents packing, slowing solidification at low temperatures.
Membrane Permeability • Transport Proteins • Channel Proteins- provide a channel for hydrophilic molecules to move through. • Aquaporins- allow water to pass through the cell membrane quickly. • Carrier Proteins- bind to molecules and shuttle them across the membrane.
Diffusion • Diffusion- movement of molecules of any substance until they spread out evenly in the available space. (equilibrium). • Diffusion is a spontaneous process, needing no energy input. • Rule of Diffusion: in the absence of a force, a substance will diffuse from high concentration to low concentration.
Diffusion • A substance diffuses down its own concentration gradient, unaffected by the concentration of other substances. • Diffusion is a form of passive transport- movement that does not require the cell to use energy.
Osmosis • Osmosis- the diffusion of water. Water diffuses from the region of lower solute concentration (higher free water concentration) to the area of higher solute concentration (lower free water concentration)- until equilibrium is reached. • Osmosis is a method of passive transport
Osmosis • Tonicity- the ability of a surrounding solution to cause a cell to gain or lose water. • Hypertonic- concentration of solution is more than the cell. Cell will lose water, shrivel, and probably die. • Hypotonic- concentration of solution is less than the cell. Water will enter the cell and the cell will swell and lyse (burst). • Isotonic- concentration of solutions is the same on both sides of the membrane. No net movement of water = stable volume.
Osmosis • Osmoregulation- the control of solute concentrations and water balance. • Less permeable membrane, contractile vacuole, etc.
Facilitated Diffusion • Facilitated Diffusion- passive transport aided by proteins. • Frequently involves polar molecules. • Ion Channels- channel proteins that transport ions down the concentration gradient. No energy required. • Gated Channels- open or close in response to a stimulus.
Active Transport • Active Transport- moves solute from low to high concentration. Requires energy (usually ATP). Uses carrier proteins. • Active transport allows a cell to have an internal concentration different from its surroundings. • Sodium-Potassium Pump- an example of active transport that exchanges Na+ for K+ across the plasma membrane.
Active Transport • Membrane Potential – the difference in voltage across the cell membrane. (ranges from -50 to -200 mV) • The inside of the cell is negative relative to the outside. • This favors transport of cations into the cell and anions out of the cell. • Electrochemical Gradient- the combination of the membrane potential (electrical force) and concentration gradient (chemical force). • Ions diffuse not only down their concentration gradient, but down its electrochemical gradient.
Active Transport • Electrogenic Pump- a transport protein that generates voltages across a cell membrane by maintaining a membrane potential. • Ex. Sodium-potassium pump in animals and proton pump in plants, fungi and bacteria
Cotransport • Cotransport- active transport driven by a concentration gradient.
Endocytosis/Exocytosis • Exocytosis- the secretion of large molecules by the fusion of vesicles with the plasma membrane. Requires energy. • Endocytosis- cell takes in molecules by forming new vesicles from the plasma membrane. • Phagocytosis- cell eating • Pinocytosis- cell drinking • Receptor-Mediated Endocytosis