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Transcript
Elements in Cells • The living substance of cells is made up of cytoplasm and the structures within it. • About 96% of cytoplasm and its included structures are composed of the elements carbon, hydrogen, oxygen, and nitrogen. ▫ 3% from phosphorus, potassium and sulfur ▫ 1% from calcium, iron, magnesium, sodium, chlorine, copper, manganese, cobalt, zinc and minute quantities of other elements Elements in Cells • When a plant first absorbs these elements from the soil or atmosphere, or when it breaks down products within the cell, the elements are in the form of simple molecules or ions. • These simple forms may be converted to very large, complex molecules through the metabolism of the cells. • The large molecules have “backbones” of carbon atoms within them and are said to be organic. • The countless number of chemical reactions of living organisms is based on organic compounds. Carbon-organic Compounds • In their outer shells, carbon atoms have four electrons that can bond with other atoms. • When carbon is bonded to hydrogen, which is common in organic molecules, the carbon atom shares an electron with hydrogen, and hydrogen likewise share an electron with carbon. • Carbon-hydrogen molecules are referred to as hydrocarbons. • Nitrogen, sulfur, and oxygen also are often joined to carbon in living organisms. Building Cells from Four Types of Molecules • The cells of all living things, including plant cells, are primarily made of four types of big molecules, called macromolecules: Carbohydrates Lipids Proteins Nucleic acids Carbohydrates • Carbohydrates, commonly called sugars, are the most abundant organic compounds in nature. • Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1C:2H:1O. • The formula can be multiplied, for example, glucose has the formula C6H12O6. The basic ratio is the same. • Cells use carbohydrates for: ▫ Storing energy and ▫ Building materials and ▫ To provide structure to the cell. Carbohydrates • Monosaccharides - Simple sugars with backbones of three to seven carbon atoms. (Glucose and Fructose) • Glucose fast source of energy Carbohydrates • Monosaccharides may form bonds with each other to form larger structures. ▫ Disaccharides - Formed when two monosaccharides (simple sugars) bond together by dehydration synthesis. (glucose + fructose = sucrose) ▫ Polysaccharides - Formed when several to many (some thousands) of monosaccharides bond together. (Cellulose) Carbohydrates • Carbohydrates are in nearly every food, not just bread and pasta, which are know for “carbo loading.” • Fruits, vegetables, and meats also contain carbohydrates. • Any food that contains sugars contains carbohydrates. • Most foods are converted to sugars when they are digested. • Plants and animals both store sugars. In animals it is glycogen • The storage form of glucose in plants is starch. Lipids • Lipids are fatty or oily substances that are mostly insoluble in water. (Fats and Oils) • Glycerol (or other alcohol) + three fatty acids ▫ Typically store twice as much energy as carbohydrates. Most consist of chain with 16-18 carbon atoms. Saturated - No double bonds, H atoms attached to every available bond of their C atoms Unsaturated - At least one double bond between carbon atoms. Glycerol (or other alcohol) + three fatty acids Saturated - No double bonds, H atoms attached to every available bond of their C atoms Unsaturated - At least one double bond between carbon atoms. Lipids • Lipids serve many important functions. ▫ Store energy ▫ Protection against dehydration and pathogens ▫ Carry electrons and absorb light ▫ Contribute to structure of membranes ▫ Agricultural commodities important to the food, medical, and manufacturing industry Lipids • Because plants can’t control their temperatures, they contain much more oil than fats. • Waxes - Lipids consisting of long-chain fatty acids bonded to long chain alcohol other than glycerol. ▫ Example: In plants, waxes, cutin, and suberin protect against dehydration and pathogens. • Phospholipids - Constructed like fats, but one of the fatty acids is usually replaced by a phosphate group. ▫ Example: found in cell membranes Proteins, Polypeptides, and Amino Acids • Proteins perform essential jobs in cells. ▫ Help chemical reactions ▫ Support the cell ▫ Move materials around ▫ Control information flow ▫ Send signals Proteins, Polypeptides, and Amino Acids • Proteins are usually very large and consist of one or more polypeptide chains. ▫ Polypeptides are chains of amino acids. ▫ 20 different amino acids. Each amino acid has two functional groups plus an R group. Amino group (-NH2) Carboxyl group (-COOH) Proteins, Polypeptides, and Amino Acids Proteins, Polypeptides, and Amino Acids • Polypeptide Structure- To make a protein amino acids bond with covalent bonds called peptide bonds ▫ Primary Structure - A sequence of amino acids fastened together by peptide bonds. ▫ Secondary Structure - Coiling of polypeptide chains. ▫ Tertiary Structure - Maintained by coils between R groups. ▫ Quaternary Structure - Occurs when a protein has more than one kind of polypeptide. Proteins, Polypeptides, and Amino Acids • Structural proteins support the cell. ▫ Cytoskeletal proteins provide supportive scaffolding from the inside of the cell. ▫ Outside the cell, proteins are woven into the cell wall, a protective layer that encases a plant cell. Proteins, Polypeptides, and Amino Acids • Transport proteins move materials into and within plant cells. • Proteins located at the boundary of the cell help create passageways for materials. • Inside the cells, structures may use cytoskeletal proteins as tracks that allow them to move around the cell. Proteins, Polypeptides, and Amino Acids • Enzymes are proteins that speed up chemical reactions. • Enzymes are mostly large, complex proteins that function as organic catalysts under specific conditions. ▫ Work by lowering energy of activation. Temporarily bonds with potentially reactive molecules at a surface site. Names end in =ase. Nucleic Acids • Nucleic acids are very large, complex polymers. ▫ Vital to internal communication and cell functioning. ▫ Two types of nucleic acids. Deoxyribonucleic Acid (DNA) and ribonucleic acid (RNA) are composed of nucleotides. Three parts- nitrogenous base, five-carbon sugar, and a phosphate. DNA does not leave the nucleus of the cell. Nucleic Acids • DNA stores the information that determines the structure and function of all cells on earth. • DNA determines the traits of plants. • When cells reproduce, they copy their DNA molecules and pass them on to the new cells. • RNA is similar to DNA in structure, but more flexible in its functions. Different types perform different functions. • Some carry information around the cell. • Some help build proteins. • Some control when proteins are made. • RNAs contain information, but they can move around and cause things to happen. Review • Attributes of Living Organisms • Chemical and Physical Bases of Life • Molecules • Bonds and Ions • Acids and Bases • Carbohydrates, Lipids, Proteins • Enzymes • Nucleic Acids Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display