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Transcript
The Nature of Life Chapter 2 Outline Attributes of Living Organisms Chemical and Physical Bases of Life • The Elements: Units of Matter • Molecules • Valence, Bonds and Ions • Acids, Bases and Salts • Energy • Chemical Components of Cells • Monomers and Polymers – – – – Carbohydrates Lipids Proteins Nucleic Acids Attributes of Living Organisms Composition and Structure • Cells - structural units of organisms – Cytoplasm - interior cell matrix o Nucleus - houses genetic material (DNA) suspended in cytoplasm – Cell Wall - bounds cytoplasm Attributes of Living Organisms Growth • Increase in mass accompanied by an increase in volume – Results from production of new cells and includes variation in form – Controlled by genetic make up and environment Reproduction • Production of offspring – Offspring always resemble parents Attributes of Living Organisms Response to Stimuli • Plants respond to stimuli • What types of stimuli do plants respond to? Light, gravity, injury, temperature Attributes of Living Organisms Metabolism • Collective product of all biochemical reactions in an organism – Respiration - energy release – Photosynthesis - energy harnessing – Digestion - conversion of large insoluble food molecules to smaller soluble molecules – Assimilation - conversion of raw materials into cell substances Attributes of Living Organisms Movement • Occurs at all levels of organization – Usually slow and imperceptible – Mostly related to growth phenomena – Cytoplasmic streaming = movement at cellular level Attributes of Living Organisms Complexity of Organization • Molecules organized into compartments, membranes and other structures within cells • Arrangements of molecules highly structured and complex Environmental Adaptation • Living organisms respond to their environment • Natural selection adapts organisms to their environment Chemical and Physical Bases of Life The Elements: Units of Matter Matter • Three states: solid, liquid, gas • Occupies space • Has mass • Composed of elements Chemical and Physical Bases of Life The Elements: Units of Matter Atoms - smallest stable subdivision of element • Nucleus - center of an atom – Protons - positively charged particles – Neutrons - neutral particles Model of an oxygen atom Chemical and Physical Bases of Life The Elements: Units of Matter • Atomic Number - number of protons – Cannot change within an element • Atomic Mass - combined number of protons and neutrons Chemical and Physical Bases of Life The Elements: Units of Matter Electrons - negative electric charges circling nucleus • Paths of electrons guided by protons • Orbitals - volume of space where electron occurs 90% of time Models of orbitals Chemical and Physical Bases of Life The Elements: Units of Matter Electron’s distance from nucleus depends on energy level • Electron Shells – Energy levels of atom – Associated with orbitals – Outermost shell determines atom’s reactivity Energy levels of electrons Chemical and Physical Bases of Life The Elements: Units of Matter Isotope - form of element varying in number of neutrons and atomic weight • Radioactive isotopes unstable and spontaneously split into smaller parts, releasing great amounts of energy. Oxygen isotopes Chemical and Physical Bases of Life Molecules Compound - two or more elements united in definite ratio by chemical bonds Molecule - two or more atoms bound together • Smallest independently existing particle of a compound or element • In constant motion Chemical and Physical Bases of Life Molecules Random collisions between molecules capable of sharing electrons are basis for all chemical reactions • Often results in formation of new molecules • Usually controlled by specific enzymes (catalyst) – Catalyst - speeds up reaction without being used up in reaction Chemical and Physical Bases of Life Molecules To form a water molecule: two hydrogen atoms attach to an oxygen atom • Electrons shared and form electron cloud – Gives molecule asymmetrical shape • Asymmetrical shape and unequal sharing of electrons make it polar Water molecule Chemical and Physical Bases of Life Molecules Water molecules form cohesive network • Cohesion - attraction of similar molecules – Capillary movement in plants • Adhesion - attraction of dissimilar molecules Cohesion of water molecules Chemical and Physical Bases of Life Valence, Bonds, and Ions Valence - combining capacity of atom or ion based on electron number Bonds - forces that form molecules by attracting and holding atoms together • Number of electrons in atom’s outermost orbital determines number of chemical bonds formed • Formed by losing, gaining or sharing electrons • What are the 3 types of bonds? covalent bonds, ionic bonds and hydrogen bonds Chemical and Physical Bases of Life Valence, Bonds, and Ions Covalent Bonds • Form when two atoms share pair of electrons • Nonpolar - electrons shared equally • Polar - electrons shared unequally (like water) Covalent bond between two oxygen atoms Chemical and Physical Bases of Life Valence, Bonds, and Ions Ionic Bonds • Electrons in outermost orbital removed from one atom and transferred to another atom. – Ions - formed when molecules lose or gain electrons • Form when oppositely charged ions come into contact Chemical and Physical Bases of Life Valence, Bonds, and Ions Hydrogen Bonds • Form from attraction between positively charged hydrogen atoms in polar molecules and negatively charged atoms in other polar molecules – Only have 7–10% strength of covalent bonds Chemical and Physical Bases of Life Acids and Bases Acids - chemicals that release hydrogen atoms (H+) when dissolved in water Bases (alkaline compounds) - compounds that release hydroxyl ions (OH-) when dissolved in water. Chemical and Physical Bases of Life Acids and Bases • pH scale represents measurement of H+ ion concentration 7 = Neutral (H+ and OH- are same concentration) <7 = Acidic (lower number = higher acidity) >7 = Alkaline (higher number = higher alkalinity) Chemical and Physical Bases of Life Energy Energy - capacity to perform work Thermodynamics - study of energy and its conversions from one form to another • First Law: Energy is constant. It cannot be gained or lost, only converted from one form to another. • Second Law: When energy is converted to another form, it flows from a high energy state to a low energy state and releases energy during the conversion. Chemical and Physical Bases of Life Energy Forms of energy include kinetic and potential energy • Potential Energy - capacity to do work owing to position or state of particle Where are electrons with the least potential energy located? The most potential energy? the inner shell; the outermost shell Chemical and Physical Bases of Life Chemical Components of Cells Living substance of cells includes cytoplasm and structures within it About 96% of cell composed of carbon, hydrogen, oxygen, and nitrogen Simple molecules and ions converted to large, complex molecules through cell metabolism Chemical and Physical Bases of Life Monomers and Polymers Polymers (macromolecules) - “many units” • Formed when two or more small units called monomers (“single units”) bond together Bonding between monomers occurs by dehydration synthesis reactions • Dehydration synthesis - Removal of water in the formation of a bond Chemical and Physical Bases of Life Monomers and Polymers Bonds between monomers broken by hydrolysis • Hydrolysis - occurs when hydrogen becomes attached to one monomer and hydroxyl group to the other • Energy is released, may be stored temporarily or used in manufacture or renewal of cell components Polymers include carbohydrates, lipids, proteins, and nucleic acids. Carbohydrates Carbohydrates - most abundant organic compounds in nature • Contain carbon, hydrogen and oxygen in ratio of CH2O • 3 basic kinds of carbohydrates: monosaccharides, disaccharides, and polysaccharides. Monosaccharides - simple sugars with backbones of 3-7 C (glucose and fructose) Carbohydrates Disaccharides - 2 monosaccharides bonded together (sucrose) Polysaccharides - several to many monosaccharides bonded together • Can be in long branched or unbranched chains, or in coils of monosaccharides – Starch = coils of glucose molecules o main carbohydrate reserve of plants – Cellulose = unbranched chain of glucose molecules o main structural polymer in plant cell walls Lipids Lipids - fatty or oily substances mostly insoluble in water (fats and oils) • Typically store twice energy as carbohydrates • Long term energy reserves and structural components of cells • Contain C, H, and O, but have proportionately less O than carbohydrates Lipids Fats and oils produced from one glycerol molecule and three fatty acid molecules • Most fatty acids consist of chain with 16–18 C – Saturated - H attached to every available bonding site on C of fatty acid, and with no double bonds – Unsaturated - with fewer H and with at least one double bond between C atoms Structure of a fat molecule Lipids Waxes - lipids consisting of long-chain fatty acids bonded to long chain alcohol, instead of glycerol • Surfaces of leaves and stems Phospholipids - constructed like fats, but one fatty acid usually replaced by phosphate group • Important components of membranes Proteins, Polypeptides, and Amino Acids Proteins regulate chemical reactions in cells, usually very large and consist of one or more polypeptide chains • Polypeptides - composed of chains of amino acids – – Amino acid composed of: o Amino group (-NH2) o Carboxyl group (-COOH) o R group - can vary from one hydrogen to a complex ring R groups distinctive for each of 20 amino acids Structure of amino acid, glycine Proteins, Polypeptides, and Amino Acids Polypeptide Structure • Primary Structure – Sequence of amino acids fastened together by peptide bonds • Secondary Structure – Formation of alpha helix or pleated sheets due to hydrogen bonding Proteins, Polypeptides, and Amino Acids Polypeptide Structure • Tertiary Structure – Coiling or folding maintained by interactions among R groups • Quaternary Structure – Association of more than one polypeptide to form single functional protein Storage Proteins Some plant food-storage organs store small amounts of proteins as well as large amounts of carbohydrates • Ex. potato tubers and onion bulbs Seeds contain proportionately larger amounts of proteins in addition to complement of carbohydrates • Get used during germination and during seedling development • Important sources of nutrition for humans and animals Enzymes Enzymes - large, complex proteins functioning as organic catalysts under specific conditions • Break bonds and allow new bonds to form, facilitating chemical reactions • Increase reaction rates • Lower the energy of activation – Energy of activation - minimal amount of energy needed to cause molecules to react with one another Enzymes Enzymes temporarily bond with substrate • Substrate fits into active site of enzyme • Reaction occurs rapidly and products released • Enzyme remains unchanged and capable of catalyzing another reaction Mode of action of an enzyme Nucleic Acids Nucleic acids - very large, complex polymers • Vital to internal communication and cell functioning • What are the two types? – Deoxyribonucleic Acid (DNA) – Ribonucleic Acid (RNA) Nucleotide structure DNA - double helix of repeating subunits of 4 kinds of nucleotides • Nucleotides composed of nitrogenous base, five- C sugar and phosphate Nucleic Acids DNA contains genes encoding information determining form and structure of organism Can be passed from generation to generation without change RNA differs from DNA in its sugar and one of its nucleotide components Occurs as single strand and involved in protein synthesis Outline Attributes of Living Organisms Chemical and Physical Bases of Life • The Elements: Units of Matter • Molecules • Valence, Bonds and Ions • Acids, Bases and Salts • Energy • Chemical Components of Cells • Monomers and Polymers – – – – Carbohydrates Lipids Proteins Nucleic Acids