Biology Chapter 2 Notes: Life and the Cell
Biology Chapter 2 Notes: Life and the Cell Bio 190
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This 6 page Class Notes was uploaded by Anna Stidham on Tuesday February 9, 2016. The Class Notes belongs to Bio 190 at Towson University taught by Joseph Velenovsky in Fall 2015. Since its upload, it has received 17 views. For similar materials see Intro Biology for Health Professions in Biology at Towson University.
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Date Created: 02/09/16
UNIT 2 NOTES: Life and Cells 1.1All forms of life share common properties Biology: scientific study of life Properties of life: 1. Order: living cells are the basis of complex organization 2. Reproduction: organisms reproduce their own kind 3. Growth and Development: inherited information in the form of DNA controls the pattern of growth + development of all organisms 4. Energy Processing: chemical energy and reactions occur 5. Response to environment: all organisms respond to environment stimuli 6. Regulation: many types of mechanisms regulate an organism’s internal environment, keeping it within limits that sustain life 7. Evolutionary adaptations: adaptations that evolve over many generations as individuals with traits best suited to their environment have greater reproductive success and pass their traits to offspring 1.2In life’s hierarchy of organization, new properties emerge at each level Levels: Biosphere: all of the environments on Earth that support life Ecosystem: all organisms living in a particular area and physical components like air, soil, water Community: entire array of organisms in an ecosystem Population: all individuals of a species in an area Organism: an individual living thing Organ System: system of several organs that cooperate in a specific function Organ: specialized structure consisting of tissues Tissue: integrated group of cells with a common function Cell: fundamental unit of life Organelle: membrane-enclosed structure Molecule: cluster of small chemical units Atom: the smallest unit of matter that retains the properties of an element Emergent Properties: new properties that arise with every step upward in the hierarchy of life, owing to the arrangement and interactions of parts as complexity increases 4.1 Microscopes reveal the world of the cell Light microscopes: first microscopes, visible light is passed through a specimen and a glass lenses, magnifies about 1,000x. Magnification: increase in apparent size of an object Micrograph: photograph taken through a microscope Resolution: measured clarity of an image Cell theory: all living things are composed of cells and that all cells come from other cells Electron Microscope: focuses a beam of electrons through a specimen or onto its surface Scanning Electron Microscope: study the detailed architecture of cell surfaces Transmission Electron Microscope: study details of internal cell structures 4.2 The small size of cells relates to the need to exchange materials across the plasma membrane Cell must be large enough to house enough DNA, protein molecules, and structures to survive and reproduce Large cells have more surface area than small cells, but much less surface area relative to their volume Plasma membrane: forms a flexible boundary between the living cell and its surroundings Phospholipid hydrophilic heads face into the cell exposed to the aqueous solutions on both sides of the membrane and out of the cell while hydrophobic tails point inward mingling together and shielding from water Nonpolar Molecules (O ,2CO )2easily move across membrane Ions and Polar Molecules need help getting across. Some proteins form channels so the polar molecules can get through the membrane 4.3 Prokaryotic cells are structurally simpler than Eukaryotic cells Prokaryotic cells: Bacteria and Archae Eukaryotic cells: all others forms of life including protists, fungi, animals, and plants. They all have membrane-enclosed nucleus and organelles All cells have: Plasma membranes Chromosomes: carrying genes made of DNA Ribosomes: tiny structures made of proteins Cytoplasm: interior of cell Just Prokaryotic cell: All DNA is coiled into nucleoid Ribosomes are smaller Outside is a rigid cell wall which protects cell and helps keep its shape Some have sticky outer coat: capsule Some have flagella- large projections that propel a cell through liquid environments 4.4 Eukaryotic cells are partitioned into functional compartments Nucleus and ribosomes: genetic control Organelles (bound by a membrane): perform specific functions in the cell; manufacture, distribute, and breakdown molecules including ER, Golgi apparatus, lysosomes, vacuoles, peroxisomes Mitochondria: energy processing Cytoskeleton, plasma membrane, and plant cell wall: structural support, movement, and communication between cells Cellular metabolism: chemical activities of cell; occur in organelles Almost all structures of Animals are in plants Only in Animals: lysosomes and centrioles Only in Plants: rigid cell wall made of cellulose and that contain plasmodesmata that are cytoplasmic channels through cell walls that connect adjacent cells. 4.16 The cell’s internal skeleton helps organize its structure and activities Cytoskeleton-a network of protein fibers in the cytoplasm of a eukaryotic cell; includes microfilaments, intermediate filaments, and microtubules Cell motility includes internal movement of cell parts and locomotion of the cell Three main kinds of fibers: 1. Microfilaments (actin filaments)- thinnest fibers are solid rods composed mainly of globular proteins called actin, arranged in a twisted double chain; they support cell shape and help in muscle contraction and Amoeba’s “crawling” movements 2. Intermediate filaments- made of various fibrous proteins that supercoil into thicker cables; they serve mainly to reinforce cell shape and to anchor certain organelles (especially nucleus) 3. Microtubules- straight, hollow tubes composed of globular proteins called tubulins; in animals, microtubules grow out from places near the nucleus. Where a pair of centrioles are located (a structure in an animal cell composed of cylinders of microtubule triplets). They shape and support the cell and are “tracks” along which organelles move and guide movement of chromosomes during cell division. 4.19 The extracellular matrix of animal cells functions in support and regulation Animal cells produce an elaborate extracellular matrix- a layer outside of the plasma membrane that helps hold cells together in tissues and protects and supports the plasma membrane. The main components are glycoproteins, proteins bonded to carbs. Complexes form when hundreds of small glycoproteins attach to long polysaccharide molecule). Most abundant is collagen- which forms strong fibers outside the cell. Integrins- transmembrane protein that interconnect (transmit signals between) the extracellular matrix and the cytoplasm 4.20 Three types of cell junctions are found in animal tissues 1. Tight junctions- plasma membranes of neighboring cells are tightly pressed against each other and knit together by proteins. They prevent leakage of fluid across a layer of cells 2. Anchoring junctions- fasten cells together in strong sheets, intermediate filaments anchor junctions in cytoplasm. Common in tissues subject to stretching or mechanical stress like skin and heart 3. Gap junctions-communicating junctions, channels that allows small molecules to flow through protein-lined pores between cells. 4.21 Cell Walls enclose and support plant cells Cell wall-rigid extracellular structure that protects plant cells and provides skeletal support that keeps them up right; they consist of fibers of cellulose; and many layers make up the cell wall and are joined together by sticky polysaccharides called pectins To function as part of a tissue, cells must have cell junctions that connect them to other cells and in adjacent plant cells the channels are called plasmodesmata (where water, nourishment, and chemical messages can be shared between cells. 5.1 Membranes are fluid mosaics of lipids and proteins with many functions Fluid Mosaic- describes plasma membrane (composed of phospholipids with embedded and attached proteins). Fluid-components able to drift about, cholesterol helps maintain fluidity. Mosaic- having diverse protein molecules in the framework and all of them have various functions. Protein functions-maintain cell shape and coordinate changes inside and outside cell through ECM, receptors for chemical messengers, some are enzymes that carry out steps of a metabolic pathway, membrane glycoproteins that are involved in cell-cell recognition, membrane proteins participate in intercellular junctions that attach adjacent cells, and transporting ions and molecules. Selective Permeability- (membranes exhibit) they allow some substances to cross more easily then others; many essential ions and polar molecules require transport proteins to help them cross membrane 5.2 Membranes form spontaneously, a critical step in the origin of life Phospholipids spontaneously self-assemble into simple membranes. The formation of membrane-enclosed collections of molecules was probably a critical step in evolution of first cells. All cells’ plasma membrane is similar in structure and function 5.3 Passive transport is diffusion across a membrane with no energy investment Diffusion: tendency for particles of any kind to spread out evenly in an available space; molecules in a fluid are constantly in motion and they collide with each other and bounce off others and spread into open space. If the membrane is permeable to a molecule—the molecule can easily pass through membrane Equilibrium: when the number of molecules moving in one direction is equal to the number of molecules moving in the opposite direction. Concentration Gradient: substances tend to move from areas of high concentration (where a ton of molecules are) to areas of less concentration (where fewer are) Passive Transport- diffusion across a membrane that requires no energy (O 2 and CO d2ffuse easily) 5.4 Osmosis is the diffusion of water across a membrane Osmosis- diffusion of water across a selectively-permeable membrane Water molecules readily pass through the cell membrane even though they are polar because protein channels Water diffuses across a membrane from regions of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides; solute gets dissolved in water; low solute- high free water, high solute-low free water 5.5 Water balance between cells and their surroundings is crucial to organisms Tonicity- ability of a surrounding solution to cause a cell to gain or lose water Isotonic- solute concentration in cell is equal to concentration in the isotonic environment (loses water at same rate as it gains) Hypotonic- solution has less solute concentration than the cell does (gains water at a fast rate) Hypertonic- solution has higher solute concentration than cell (loses waste at a fast rate) Osmoregulation- control of water balance to prevent excessive intake or loss (fish gills&kidneys) 5.6 Transport Proteins can facilitate diffusion across membranes Facilitated Diffusion- passage of a substance through a specific transport protein across a biological membrane down its concentration gradient. Transport proteins help substances that do not diffuse freely across membrane, without them certain substances wouldn’t be able to cross membrane or would take too long & wouldn’t be useful; t.proteins are specific for the substance they help No energy is used because it is a type of passive transport and works with the concentration gradient Polar molecules and ions use facilitated diffusion Aquaporin- the transport protein that helps move water across membrane b/c water is polar 5.7 Research on another membrane protein led to the discovery of aquaporins Dr. Peter Agre talks about aquaporins being hourglass shaped and they allow about 3 bill water molecules in and out of cell membranes 5.8 Cells expend energy in the active transport of a solute Active Transport- energy (ATP) must be expended to move a solute against its concentration gradient (toward the side where the solute is more concentrated) 1. Solute Binding- solute on the cytoplasmic side of the plasma membrane attaches to a specific binding site on the transport protein 2. Phosphate Attaching (Phosporylation)- ATP transfers one of its phosphate groups to the transport protein 3. Transport- Protein changes shape in such a way that the solute goes through and is released on the other side of the membrane 4. Protein reversion- Phosphate group detaches and transport protein returns to its original shape 5.9 Exocytosis and endocytosis transport large molecules across membranes Exocytosis- export bulky materials ex. Proteins and polysaccharides Transport vesicle filled with macromolecules buds from Golgi goes to plasma membrane then vesicles fuse with membrane and vesicle’s contents spill out of cell. Tears are when salty solutions get exported through exocytosis. Endocytosis- cell takes in large molecules Depression in the plasma membrane pinches in and forms a vesicle enclosing material that had been outside the cell Three kinds: Phagocytosis: “cellular eating”, cell engulfs a particle by wrapping extensions called pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be called a vacuole Pinocytosis- “cellular drinking”, cell gulps droplets of fluid into tiny vesicles; not specific (any and all solutes dissolved in the droplets) Receptor-mediated endocytosis- highly selective; receptor proteins for specific molecules are embedded in regions of the membrane that are lined by a layer of coat proteins; take cholesterol from blood for synthesis of membranes and steroids 11.10 Signal transduction pathways convert messages received at the cell surface to response within the cell Signal Transduction pathway- a series of molecular changes that converts a signal on a target cell’s surface to a specific response inside the cell 1. Signaling cell secretes a signaling molecule 2. This molecule binds to a receptor protein embedded in the target cell’s plasma membrane 3. The binding activates the first in a series of relay proteins within the target cell 4. The last relay molecule in the series activates a transcription factor 5. The factor triggers transcription of a specific gene 6. Translation of the mRNA produces a protein
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