Chapter 5 - Cells: The Working Units of Life PDF

Chapter 5 Cells: The Working Units of Life Cells Are the Fundamental Units of Life Key Concept #1 5.1 Cells Are the Fundamental Units of Life The Cell Theory an important unifying principle of biology first stated in 1838 three tenets: C...

Chapter 5 Cells: The Working Units of Life Cells Are the Fundamental Units of Life Key Concept #1 5.1 Cells Are the Fundamental Units of Life The Cell Theory an important unifying principle of biology first stated in 1838 three tenets: Cells are the fundamental units of life. All organisms are composed of one or more cells. All cells come from preexisting cells. It is also now recognized that: Modern cells evolved from a common ancestor. 5.1 Cells Are the Fundamental Units of Life Common Characteristics of ALL Cells plasma (cell) membrane: the outer boundary that surrounds the cell consisting of a phospholipid bilayer with embedded proteins acts as a selectively permeable barrier allows for a relatively constant internal environment to be maintained important in communicating with adjacent cells and receiving signals from the extracellular environment contains proteins responsible for binding and adhering to adjacent cells plays an important structural role and contributes to cell shape cytoplasm: everything inside the cell except for the nucleus; cytosol: the fluid cytoplasm not contained inside another compartment region of DNA: (nucleoid in prokaryotes; nucleus in eukaryotes) ribosomes: sites of protein synthesis 5.1 Cells Are the Fundamental Units of Life Cell size is limited by the surface area-to-volume ratio. The surface area of a cell determines the amount of substance that can enter it and the amount of waste products that can exit it. As a living cell grows larger, its chemical activities (and thus its need for resources and its rate of waste production) increase. Because cells are small, they can maintain a large surface area-to-volume ratio. This allows them to exchange adequate quantities of materials with their environment. Substances must move from one site to another within the cell; the smaller the cell, the more easily this is accomplished.  5.1 Cells Are the Fundamental Units of Life Two types of cells: Prokaryotic Bacteria and Archaea have no membrane-enclosed internal compartments Eukaryotic Eukarya have membrane-enclosed organelles in which different functions occur Prokaryotic Cells Are the Simplest Cells Key Concept #2 5.2 Prokaryotic Cells Are the Simplest Cells 5.2 Prokaryotic Cells Are the Simplest Cells capsule outside the cell wall slimy; made of polysaccharides protects WBC attack; retains moisture; helps in attaching to other cells outer membrane encloses the peptidoglycan layer of the cell wall cell wall (most prokaryotes have this structure) outside the cell membrane rigid; contains peptidoglycan supports the cell and gives it shape flagella help in swimming pili project from the cell surface; hair-like help in adhering to other cells; help in the movement of genetic material from one cell to another cytoskeleton system of protein filaments maintain cell shape; plays roles in cell movement and cell division Eukaryotic Cells Contain Organelles Key Concept #3 5.3 Eukaryotic Cells Contain Organelles Eukaryotic cells are about 10 times larger than prokaryotes. They have membrane-enclosed organelles that carry out specific functions; similar in all. 5.3 Eukaryotic Cells Contain Organelles ribosomes: sites of protein synthesis have similar structure in prokaryotes and eukaryotes consist of ribosomal RNA (rRNA) and more than 50 different protein molecules 5.3 Eukaryotic Cells Contain Organelles nucleus: usually the largest organelle contains most of the cell’s DNA site of DNA replication assembly of ribosomes begins in a region called the nucleolus surrounded by the nuclear envelope, a double membrane Nuclear pores in the envelope control movement of molecules across the envelope. 5.3 Eukaryotic Cells Contain Organelles endomembrane system: Interconnected system of membrane-enclosed compartments. Tiny, membrane-surrounded vesicles shuttle substances between the various components. In the living cell, the membranes and the materials they contain are in constant motion. 5.3 Eukaryotic Cells Contain Organelles endoplasmic reticulum (ER): network of membranes in the cytoplasm; large surface area rough endoplasmic reticulum (RER): ribosomes are attached newly made proteins enter the RER lumen and are modified, folded, and transported to other regions smooth endoplasmic reticulum (SER): no ribosomes chemically modifies small molecules such as drugs and pesticides site of glycogen degradation in animal cells synthesis of lipids and steroids 5.3 Eukaryotic Cells Contain Organelles 5.3 Eukaryotic Cells Contain Organelles Golgi apparatus: flattened sacs (cisternae) and small vesicles receives proteins from the RER—can further modify them concentrates, packages, sorts proteins in plant cells, polysaccharides for cell walls are synthesized here lysosomes: contain digestive enzymes that hydrolyze macromolecules into monomers primary lysosomes originate from the Golgi apparatus. Food molecules enter the cell by phagocytosis—a phagosome is formed. Phagosomes fuse with primary lysosomes to form secondary lysosomes. Enzymes hydrolyze the food molecules. Wastes are ejected by exocytosis. 5.3 Eukaryotic Cells Contain Organelles 5.3 Eukaryotic Cells Contain Organelles mitochondria: energy in fuel molecules such as glucose is transformed to the bonds of energy-rich ATP (cellular respiration) Cells that require a lot of energy have many mitochondria. They can reproduce and divide independently of the nucleus. Mitochondria have two membranes. outer membrane inner membrane folds inward to form cristae—creates large surface area for the embedded proteins involved in cellular respiration Mitochondrial matrix contains enzymes, DNA, and ribosomes to make the proteins needed for cellular respiration. 5.3 Eukaryotic Cells Contain Organelles plastids: occur only in plants, some protists; many types & functions chloroplasts (chloro = green): site of photosynthesis; have a double membrane; can divide independently of the nucleus inner membrane forms thylakoids which contain chlorophyll and other pigments that harvest light energy chromoplasts (chromo = color): contain red, orange, and yellow pigments—give color to flowers leucoplasts: store starches and fats 5.3 Eukaryotic Cells Contain Organelles 5.3 Eukaryotic Cells Contain Organelles Plant and protist cells have vacuoles: provide structure for plant cells— water enters the vacuole by osmosis, creating turgor pressure store pigments in flowers and fruits—these colors attract pollinators may also store digestive enzymes, waste products and toxic compounds to deter herbivores 5.3 Eukaryotic Cells Contain Organelles cytoskeleton: supports and maintains cell shape holds organelles in position moves organelles involved in cytoplasmic streaming interacts with extracellular structures to hold cell in place composed of three types of filaments 5.3 Eukaryotic Cells Contain Organelles Three components of the cytoskeleton: microfilaments: help a cell or parts of a cell move; determine cell shape; formation of pseudopodia intermediate filaments: anchor cell structures in place; many kinds microtubules: long, hollow cylinders; form rigid internal skeleton in some cells Cilia and eukaryotic flagella are made of microtubules in “9 + 2” array. cilia—short, hundreds on one cell, move stiffly to propel the cell or move fluid over a cell flagella—longer, usually one or two present, movement is snakelike Extracellular Materials Provide Support Key Concept #4 5.4 Extracellular Materials Provide Structure extracellular structures important for protection, support, and interacting with other cells secreted to the outside of the cell membrane consist of macromolecules embedded in a gel-like medium (eukaryotes) 5.4 Extracellular Materials Provide Structure plant cell wall: cellulose fibers are embedded in other complex polysaccharides and proteins; provide rigid yet flexible support for the plant, are a barrier to disease organisms adjacent plant cells are connected by cell membrane-lined channels called plasmodesmata (permit movement of water, ions, small molecules, RNA and proteins) 5.4 Extracellular Structures Have Important Roles Many animal cells are surrounded by an extracellular matrix: composed of fibrous proteins such as collagen, gel-like proteoglycans and other proteins holds cells together in tissues contributes to properties of bone, cartilage, skin, etc. filters materials passing between different tissues orients cell movements in development and tissue repair plays a role in chemical signaling Eukaryotic Cells Evolved in Several Steps Key Concept #5 5.5 Eukaryotic Cells Evolved in Several Steps Evidence of the first eukaryotes appears in the fossil record 2.7 billion years ago. The advent of compartmentalization and evolution of eukaryotic cells was a major event in the history of life. The nucleus and endomembrane system may have originated from the inward folds of the cell membrane in prokaryotes. Enclosed compartments would be advantageous: chemicals could be concentrated and chemical reactions would proceed more efficiently. Some organelles arose by symbiosis. The theory of endosymbiosis proposes that mitochondria and plastids (chloroplasts) arose when one cell engulfed another cell. Many of the ingested cell’s genes were transferred to the host’s DNA but the symbionts retained specialized functions.