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This chapter covers the basics of chemistry in biology, including the structure of atoms, ions, molecules, and compounds. It also explores the properties of water and carbon-based molecules, such as carbohydrates, lipids, proteins, and nucleic acids. The role of enzymes as catalysts for biological reactions is also discussed.
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Chapter 2 notes: Chemistry of Life Biology Rainier Jr/Sr High School Mr. Taylor
Atoms, Ions, and Molecules • An atom is the smallest particle of an element. • An element is made of only one kind of atom and cannot be broken down further by ordinary chemical means. • Each atom of an element contains the same number of protons in its nucleus. • Carbon, Hydrogen, Oxygen, and Nitrogen compose 95% of the mass of humans ... and most other organisms are similar.
Atoms, Ions, and Molecules • A compound is two or more elements chemicallycombined. • The chemical formula for a compound tells what kind and how many atoms are present in the compound. • An atom that has gained or lost electrons is an electrically charged particle called an ion. • Compounds that are formed between charged particles are called ionic compounds. • Ions are important in the body and are often called electrolytes.
Atoms, Ions, and Molecules • Some atoms share electrons to form covalent bonds. • Covalent bonds tend to be stable. • Most of the compounds in organisms are covalently bonded.
Properties of Water • All the processes of living organisms take place in water. • Because of unequal sharing of electrons between hydrogen and oxygen, water has a very slight electrical charge. This allows water molecules to “stick” to each other and to other charged (polar) substances.
Properties of Water • Hydrogen bonding creates certain properties of water: • High specific heat: it takes a lot of energy to cause the molecules of water to separate. That means it takes a lot of energy to increase the temperature of water. (This stabilizes internal temperatures in cells.) • Cohesion: the molecules of water stick to each other. This causes surface tension of water drops. • Adhesion: the molecules of water stick to other charged substances. This helps plants transport water from roots to leaves.
Properties of Water • Water is often called the “universal solvent” because so many things will dissolve in it. • Water will dissolve other polar substances like salt and sugar. • Water will NOT dissolve non-polar substances like oils and fats. • Things that dissolve in water often change the pH (or acid-base balance). • pH measures Hydrogen ion concentrations • Lots of hydrogen ions results in an acid(pH = 1-7) • Few hydrogen ions present results in a base (or alkali) (pH = 7-14)
Carbon-Based Molecules • Carbon atoms form the “backbone” of almost all molecules made by organisms. • These substances are called organic molecules. • Carbon atoms have 4 electrons available for sharing. • Carbon atoms often join in long chains that can be straight or branched, or sometimes forms rings. • Carbon compounds can also form sub-units that can unite to form other substances • The single sub-unit is called a monomer. • The multiple-unit molecule is called a polymer.
Carbon-Based Molecules • There are 4 main types of polymers in organisms: • Carbohydrates • Are made of Carbon, Hydrogen, and Oxygen • Simple carbohydrates are sugars; sugars are monosaccharides (a monomer) • Complex carbohydrates are starches; starches are polysaccharides (a polymer) • Carbohydrates are excellent sources of energy. • Cellulose (a starch) makes up the cell walls of most plants.
Carbon-Based Molecules • There are 4 main types of polymers in organisms: 2. Lipids: non-polar molecules that make up fats, oils, and cholesterol. • The monomers of lipids are called fatty acids. • Fats and oils are usually made of three long chains of fatty acids held together by a molecule called glycerol. • Cholesterol is needed as part of your cell membranes and forms the basic structure of cortisones, estrogens, and testosterone.
Carbon-Based Molecules • There are 4 main types of polymers in organisms: 3. Proteins: these molecules form most of the structures and perform most of the work for organisms. • The monomers for proteins are amino acids. • Organisms use 20 different amino acids to make all proteins. • The amino acids are held together by a covalent bond called a peptide bond. Proteins are sometimes called polypeptides. • Because the amino acids that make up proteins have specific shapes, the resulting protein has a specific shape. It is the shapes that allow proteins to do all that they do for organisms.
Carbon-Based Molecules • There are 4 main types of polymers in organisms: 4. Nucleic acids: store the information to build proteins • The monomers for nucleic acids are called nucleotides. • There are two kinds of nucleic acids: DNA and RNA. These will be covered in more detail later this semester.
Enzymes • Enzymes are catalysts for reactions inside organisms. • A catalyst increases the speed at which a reaction occurs. • Enzymes basically work by holding two substances in the correct position so they can be linked together or broken apart. • Enzymes are usually proteins; it is their specific shapes that allow them to hold the correct substances in the correct position.
