Home chapter 2. Matter—anything that has mass and takes up space. Elements—basic building blocks of matter; cannot be broken down by chemical means. •Over 90% of the human body is made up of only four elements: carbon (C), nitrogen (N), oxygen (O) and hydrogen (H). Atoms Atom—smallest unit of an element that retains its physical and chemical properties. •Atoms bond together to form molecules. •Parts of an atom (called subatomic particles): •Neutrons—neutral (uncharged). •Protons—positively charged. •Neutrons and protons make up the nucleus. •Electrons—negatively charged; orbit around the nucleus in electron shells. Loading… ©2020 McGraw-Hill Education ‹#› The Atomic Structure of Select Elements (Figure 2.2) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› The Periodic Table Atomic number—the number of protons. •Differs for every element. Mass number—sum of the number of protons and neutrons. •Protons and neutrons each have a mass equal to one atomic mass unit (AMU). •Electrons have a negligible mass. Atomic mass—the average AMU for all isotopes of that atom. Loading… ©2020 McGraw-Hill Education ‹#› Isotopes Isotopes—atoms of the same element (with the same atomic number) but a different number of neutrons. •They differ in their atomic mass. Radioisotopes—unstable isotopes; they emit energy called radiation. •Radiation can damage cells and cause cancer. •Useful for imaging the body, killing bacteria in food, sterilizing equipment and killing cancer cells. ©2020 McGraw-Hill Education ‹#› Molecules and Compounds Molecules—atoms bonded together. •Can be made of the same atom or different atoms. •That is, O2, H2O. Compounds—molecules made of different atoms. •That is, H2O (not O2). Two types of bonds join atoms: ionic bonds and covalent bonds. ©2020 McGraw-Hill Education ‹#› Ionic Bonding Atoms are most stable when their outer electron shell, the valence shell, is full. During an ionic reaction, atoms donate or take on electrons to fill their valence shell. •This results in the formation of positive or negative ions (charged particles). Ionic bond—the attraction between a positive and negative ion. ©2020 McGraw-Hill Education ‹#› Covalent Bonding Covalent bonds—atoms share electrons to fill their valence shells. •Each atom contributes one electron to the shared pair. •The electrons spend time in the valence shells of both atoms. •Double covalent bonds share two pairs of electrons; triple covalent bonds share three pairs. •Depicted by one, two, or three straight lines. ©2020 McGraw-Hill Education ‹#› Water and Life 2 Water is the most abundant molecule in organisms, making up about 70% of the total body weight. Water is a polar molecule. •Electrons spend more time around the oxygen than the hydrogens, creating a partial negative charge. ©2020 McGraw-Hill Education ‹#› Water (Figure 2.7a) Access the text alternative for these images Loading… ©2020 McGraw-Hill Education ‹#› Water is a Solvent 1 Properties of water, continued: •Water is a solvent (dissolves many substances). •Solution—water with dissolved solutes. •Salts dissociate, or separate, when dissolved in water, facilitating chemical reactions. ©2020 McGraw-Hill Education ‹#› Water is a Solvent 2 Properties of water, continued: •Water is a solvent, continued: •Polar molecules attract water, so are hydrophilic. •Hydrophobic molecules do not attract water; are nonpolar. •In nonpolar covalent bonds, the electrons are shared equally (no partial charges). •That is, vegetable oil is nonpolar, so won’t dissolve in water. ©2020 McGraw-Hill Education ‹#› Acids and Bases 1 Acids are substances that dissociate in water, releasing hydrogen ions (H+). •That is, hydrochloric acid (HCl) is produced by the stomach and aids in digestion. ©2020 McGraw-Hill Education ‹#› Acids and Bases 2 Bases are substances that take up hydrogen ions (H+) or release hydroxide ions (OH−). •That is, sodium hydroxide (NaOH) is a strong base. ©2020 McGraw-Hill Education ‹#› The pH Scale The pH scale is a measure of acidity or basicity (alkalinity) of a solution . •Ranges from 0 to 14. •7 is neutral; hydrogen ion (H+) concentration is equal to hydroxide (OH−) concentration. •A pH below 7 is acidic (H+ is greater than OH−) and above 7 is basic (OH− is greater than H+). •The concentration of hydrogen ions between each pH number changes by a factor of 10. ©2020 McGraw-Hill Education ‹#› The pH Scale (Figure 2.10) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Buffers Buffer—a solution that resists changes in pH when acids or bases are added to it. •Important within the body or in the ecosystem as a whole; pH values need to stay within a narrow range. •That is, carbonic acid and bicarbonate ions act as buffers in the blood; they absorb H+ and OH−produced by metabolism. •This prevents changes in pH. ©2020 McGraw-Hill Education ‹#› Molecules of Life 2 The four major organic molecules in the body: carbohydrates, lipids, proteins, and nucleic acids. •Organic molecules contain carbon and hydrogen and are associated with cells. •Each is composed of subunits. ©2020 McGraw-Hill Education ‹#› Molecules of Life 3 Dehydration reaction—a type of synthesis chemical reaction that removes water, linking subunits together into macromolecules (large molecules). Hydrolysis reaction—the addition of water to break macromolecules into their subunits. ©2020 McGraw-Hill Education ‹#› Carbohydrates 2 Carbohydrates •Used as an energy source. •In plants, can be structural. •Made of C, H, and O; the ratio of H:O is 2:1. ©2020 McGraw-Hill Education ‹#› Simple Carbohydrates: Monosaccharides Monosaccharides •Made of a single sugar molecule. •Has a carbon backbone of three to seven carbons. •That is, a pentose has five carbons. •That is, glucose is the most common and is used as an immediate energy source in the body. ©2020 McGraw-Hill Education ‹#› Glucose (Figure 2.12) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Disaccharides Disaccharides •Made of two monosaccharides joined by a dehydration reaction. •That is, sucrose is table sugar, lactose is milk sugar. •Lactose intolerance results if one can’t break down lactose. ©2020 McGraw-Hill Education ‹#› The Synthesis and Breakdown of a Disaccharide (Figure 2.13) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Complex Carbohydrates: Polysaccharides Polysaccharides (complex carbohydrates). •Long polymers of glucose subunits. •That is, starch—energy storage in plants. •That is, glycogen—energy storage in animals. •That is, cellulose—structural; in plant cell walls. •Can’t be digested; is called “fiber”. ©2020 McGraw-Hill Education ‹#› Starch is a Plant Complex Carbohydrate  (Figure 2.14) ©Jeremy Burgess/SPL/Science Source ©2020 McGraw-Hill Education ‹#› Glycogen is an Animal Complex Carbohydrate (Figure 2.15) ©Don W. Fawcett/Science Source ©2020 McGraw-Hill Education ‹#› Lipids 2 Lipids do not dissolve in water. •Lack hydrophilic polar groups. •Diverse in functions and forms. •Found in the form of triglycerides (fats and oils), phospholipids, and steroids. Loading… ©2020 McGraw-Hill Education ‹#› Triglycerides: Fats and Oils 1 Triglycerides: •Made of one glycerol and three fatty acids. •Function in energy storage, insulation, cushioning. •Come in two forms: fats and oils. •Fats. •Usually animal origin. •Solid at room temperature. •Oils. •Usually plant origin. •Liquid at room temperature. ©2020 McGraw-Hill Education ‹#› Triglycerides: Fats and Oils 2 Triglycerides, continued: •Triglycerides are hydrophobic, so will clump together in body fluids. •Emulsifiers are molecules that surround triglycerides and disperse, or emulsify, them. •That is, during digestion, this allows enzymes to fully break down triglycerides. •Waxes. •One fatty acid attached to an alcohol. •Prevent the loss of moisture from body surfaces. •That is, cerumen (ear wax). ©2020 McGraw-Hill Education ‹#› Phospholipids Phospholipids •Structure is similar to a triglyceride but one fatty acid is replaced by a polar phosphate group. •Have a polar, hydrophilic ‘head’ and nonpolar, hydrophobic ‘tails’. •Are the primary components of plasma membranes. •Form a bilayer; hydrophilic heads face the watery solutions in and around cells, and the hydrophobic tails face inward, away from water. ©2020 McGraw-Hill Education ‹#› Structure of a Phospholipid (Figure 2.19) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Steroids Steroids •Lipids made of four fused carbon rings. •Each type differs in the functional group attached to the rings. •That is, cholesterol. •Component of membranes and a precursor to other steroids like the sex hormones estrogen and testosterone. ©2020 McGraw-Hill Education ‹#› Examples of Steroids (Figure 2.20) (b): ©Purestock/Superstock; (c): ©Purestock/Superstock Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Protein Functions 1 Protein functions: •Support—that is, keratin forms hair and nails, collagen lends support to ligaments and skin. •Enzymes—speed chemical reactions. •Transport. •That is, channel and carrier proteins in cell membranes allow substances to leave and enter the cell. •That is, transport molecules in the blood. ©2020 McGraw-Hill Education ‹#› Protein Functions 2 Protein functions, continued: •Defense—antibodies are proteins that bind to foreign substances called antigens and disable them. •Hormones—chemical messengers. •Motion—contractile proteins allow parts of cells to move and muscles to contract. ©2020 McGraw-Hill Education ‹#› Amino Acids: Subunits of Proteins Amino acids—the subunits of proteins. •Components: an amino group, a carboxyl group and an R group. •Each amino acid differs in its R group. ©2020 McGraw-Hill Education ‹#› The Structure of Amino Acids (Figure 2.21) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Peptides Peptide bond •The polar covalent bond between two amino acids. Polypeptide •Three or more amino acids linked together. ©2020 McGraw-Hill Education ‹#› Synthesis and Breakdown of a Protein (Figure 2.22) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Shape of Proteins A protein’s 3-dimensional shape is closely linked to its function. Denaturation—the change in the shape of a protein; caused by extreme heat or pH. •Disrupts the protein’s function. ©2020 McGraw-Hill Education ‹#› Levels of Protein Organization 1 All proteins have primary, secondary, and tertiary levels of structure; only a few have quaternary structure. •Shapes are created by hydrogen bonding between amino acids. •Primary structure—the linear order of amino acids. •Secondary structure—localized folding. •Results in an alpha (α) helix or beta (β) pleated sheet. ©2020 McGraw-Hill Education ‹#› Levels of Protein Structure  (Figure 2.23 a-b) ©2020 McGraw-Hill Education ‹#› Levels of Protein Organization 2 Protein structure, continued. •Tertiary structure. •The 3-D shape of the entire protein. •Determined by all three bond types (ionic, covalent, hydrogen). •Quaternary structure—a combination of more than one polypeptide, each with its own primary, secondary, and tertiary structure. ©2020 McGraw-Hill Education ‹#› Levels of Protein Structure (Figure 2.23 c-d) ©2020 McGraw-Hill Education ‹#› Nucleic Acids 2 Nucleic acids •Polymers of nucleotides. •Components of a nucleotide: a phosphate, a 5-carbon sugar, and a nitrogenous base. •Functions: •Store information. •Contain the instructions for the activities essential to life. •Conduct chemical reactions. ©2020 McGraw-Hill Education ‹#› Structure of a Nucleotide (Figure 2.24) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› Nucleic Acids 3 Nucleic acids, concluded •That is, deoxyribonucleic acid (DNA). •Stores information on how to copy itself. •Specifies the order of amino acids in proteins. •That is, ribonucleic acid (RNA). •Various types, with many functions. •That is, some are components of coenzymes, which help regulate enzyme action . •That is, adenosine triphosphate (ATP), which stores energy. ©2020 McGraw-Hill Education ‹#› DNA Structure Compared to RNA Structure (Table 2.1) Table 2.1 DNA Structure Compared to RNA Structure. DNA RNA Sugar Deoxyribose Ribose Bases Adenine, guanine, thymine, cytosine Adenine, guanine,uracil, cytosine Strands Double-stranded with base pairing Single-stranded Helix Yes No ©2020 McGraw-Hill Education ‹#› DNA and RNA Structure 1 The backbone of DNA and some forms of RNA is alternating phosphate-sugar-phosphate-sugar. •The bases project to one side of the backbone. Nucleotides are commonly identified by their base, since that is the only component that differs within a nucleic acid. ©2020 McGraw-Hill Education ‹#› DNA and RNA Structure 2 DNA is double-stranded. •The two strands twist around each other in a double helix, held together by hydrogen bonds between the bases. •Complementary base pairing. •Adenine always binds to thymine. •Cytosine always binds to guanine. ©2020 McGraw-Hill Education ‹#› The Structures of DNA and RNA (Figure 2.25) Access the text alternative for these images ©2020 McGraw-Hill Education ‹#› ATP: An Energy Carrier ATP is a high-energy molecule. •Breaking of the bond between the 2nd and 3rdphosphates releases energy that can be used in other chemical reactions. •That is, synthesis of macromolecules, muscle contraction, nerve conduction. •Produces adenosine diphosphate (ADP), which is recycled