Chemistry in Biology 6

The Big Idea

Atoms are the foundation of biological

chemistry and the building blocks of all

living things.

Main Idea #1Matter is composed of tiny particles called

atoms.

Atoms

• Chemistry is the study of matter. Matter is anything that takes up space and has mass.

• Matter is composed of atoms.

• Even though there are many types of atoms, they all have the same basic structure.

• Neutrons and protons fill the nucleus, while electrons circle outside the nucleus in energy shells.

Atoms (continued...)• Neutrons are particles that have no charge, and protons are

positively charged.

• Electrons have a negative charge.

• Under normal circumstances, the number of electrons equals the number of protons keeping the atom neutral in charge.

Elements• An element is a pure substance that cannot be broken down

into other substances by physical or chemical means.

• There are over 100 known elements, 92 of which occur naturally.

• Each element has a unique name and symbol.

• The four most important elements to living things are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Together, these four compose over 90% of the mass of living matter..

Periodic Table

• The atomic number of an element is equal to the number of protons it contains. This usually appears on the periodic table just above the chemical symbol.

• The atomic mass of an element is equal to the number of protons plus the number of neutrons. This is located under the element’s name on the periodic table.

The Periodic Table

Isotopes

• Atoms of the same element that have the same number of protons and electrons but have a different number of neutrons are called isotopes.

Radioactive Isotopes

• When a nucleus breaks apart, it gives off radiation that can be detected and used for many applications.

Compounds

• A compound is a pure substance formed when two or more different elements combine.

• Compounds are always formed from a specific combination of elements in a fixed ratio.

• Compounds cannot be broken down into simpler compounds or elements by physical means.

Chemical Bonds

• Covalent Bonds - chemical bond that forms when electrons are shared

• A molecule is a compound in which the atoms are held together by covalent bonds.

Chemical Bonds• Ionic Bonds - Electrical attraction between two

oppositely charged atoms or groups of atoms

• Most ionic compounds are crystalline at room temperature and have higher melting points than molecular compounds formed by covalent bonds.

Chemical Bonds

• Some atoms tend to donate or accept electrons more easily than other atoms.

• The elements identified as metals tend to donate electrons.

• The elements identified as nonmetals tend to accept electrons.

van der Waals Forces

• When molecules come close together, the attractive forces between slightly positive and negative regions pull on the molecules and hold them together.

• The strength of the attraction depends on the size of the molecule, its shape, and its ability to attract electrons.

Main Idea #2Chemical reactions allow living things to grow,

develop, reproduce, and adapt.

Chemical Reactions

• A chemical reaction is the process by which atoms or groups of atoms in substances are reorganized into different substances.

• Clues that a chemical reaction has taken place include the production of heat or light, and formation of a gas, liquid, or solid.

Chemical Equations

• Chemical formulas describe the substances in the reaction and arrows indicate the process of change.

• Reactants are the starting substances, on the left side of the arrow.

• Products are the substances formed during the reaction, on the right side of the arrow.

Chemical Equations

• Glucose and oxygen react to form carbon dioxide and water.

• Is this equation written correctly?

Balancing Equations• The law of conservation of mass states

matter cannot be created or destroyed.

• The number of atoms of each element on the reactant side must equal the number of atoms of the same element on the product side.

Energy of Reactions

• The activation energy is the minimum amount of energy needed for reactants to form products in a chemical reaction.

Energy of Reactions

• This reaction is exothermic and released heat energy.

• The energy of the product is lower than the energy of the reactants.

Energy of Reactions

• This reaction is endothermic and absorbed heat energy.

• The energy of the products is higher than the energy of the reactants.

Enzymes

• A catalyst is a substance that lowers the activation energy needed to start a chemical reaction.

• It does not increase how much product is made and it does not get used up in the reaction.

• Enzymes are biological catalysts.

Enzymes

• The reactants that bind to the enzyme are called substrates.

• The specific location where a substrate binds on an enzyme is called the active site.

• The active site changes shape and forms the enzyme-substrate complex, which helps chemical bonds in the reactants to be broken and new bonds to form.

Enzymes• To sum it up:

1. Enzyme and substrate link together.

2. Chemical reaction occurs

3. Substrate becomes something new and the enzyme is let go.

4. The enzyme can be reused.

Enzymes

• Factors such as pH, temperature, and other chemicals affect enzyme activity.

• When enzymes are exposed to one of these factors, they may become denatured.

• Denaturing causes the enzyme to not be as effective or possibly quit working altogether.

Main Idea #3The properties of water make it well suited to help maintain homeostasis in an organism.

Water’s Polarity• Molecules that have an unequal distribution of

charges are called polar molecules.

• Polarity is the property of having two opposite poles.

• A hydrogen bond is a weak interaction involving a hydrogen atom and a fluorine, oxygen, or nitrogen atom.

Cohesion and Adhesion

• Cohesion is the attractive force between particles of the same kind. This property allows water to bulge from the top of a filled glass without spilling over.

• Adhesion is the attractive force between unlike substances.

• Together these properties make it possible for water to move upwards against the force of gravity in a narrow tube.

• This phenomenon is called capillarity.

Homogenous Mixtures

• A homogenous mixture is one that has a uniform composition throughout.

• A solvent is a substance in which another substance is dissolved.

• A solute is the substance that is dissolved in the solvent.

Food coloring dissolved in water forms a homogenous mixture.

Heterogenous Mixtures• In a heterogeneous mixture,

the components remain distinct.

• In a suspension, the components will eventually settle to the bottom.

• In a colloid, the particles will not settle over time. Examples include fog, smoke, butter, mayonnaise, milk, paint, and ink.

Acids and Bases• Substances that release hydrogen ions

(H+) when dissolved in water are called acids.

• Substances that release hydroxide ions (OH–) when dissolved in water are called bases.

The pH Scale• The measure of

concentration of H+ in a solution is called pH.

• Acidic solutions have pH values lower than 7.

• Basic solutions have pH values higher than 7.

• Buffers are mixtures that can react with acids or bases to keep the pH within a particular range.

Main Idea #4Organisms are made up of carbon-based

molecules.

Why is Carbon Important?

• The element carbon is a component of almost all biological molecules.

Why is Carbon Important?

• Carbon has four electrons in its outermost energy level.

• One carbon atom can form four covalent bonds with other atoms.

• Carbon compounds can be in the shape of straight chains, branched chains, and rings.

Why is Carbon Important?

• Carbon atoms can be joined to form carbon molecules.

• Macromolecules are large molecules formed by joining smaller organic molecules together.

• Polymers are molecules made from repeating units of identical or nearly identical compounds linked together by a series of covalent bonds.

Making or Breaking Molecules• Condensation Reaction - process of combining small

molecules to form large molecules, and in the process, create water; also called dehydration synthesis

1. One molecule releases H+ and the other molecule releases OH-.

2. The two molecules become joined by a C-O-C bridge.

3. The H+ and the OH- combine to form water (H2O).

Making or Breaking Molecules

• Hydrolysis - process that breaks down large molecules by using water

1. Opposite of a condensation reaction

2. Water is added to complex molecules to break the bonds that hold them together.

Molecules of Life

• There are four main classes of organic compounds that are needed for living things:

1. Carbohydrates

2. Proteins

3. Lipids

4. Nucleic acids

• All of these are mainly composed of carbon, hydrogen, oxygen, and nitrogen.

Carbohydrates

• Carbohydrates are composed of C, H, and O in a 1:2:1 ratio for each carbon atom—(CH2O)n.

• They can exist as monosaccharides, disaccharides, or polysaccharides.

• Ex.’s sugar, pasta, potatoes

Carbohydrates• Monosaccharides are more commonly called “simple

sugars.”

• Common monosaccharides are: glucose, fructose, and galactose

• These monosaccharides have the same chemical formula, C6H12O6, but they have very different structures.

• Compounds like these structures, having the same chemical formula but different forms, are called isomers.

Carbohydrates• When two monosaccharides combine in a condensation

reaction, a disaccharide is formed.

GLUCOSE + FRUCTOSE = SUCROSE

• When you combine three or more monosaccharides, a polysaccharide is formed.

• Animals store glucose in the form of the polysaccharide glycogen. It is hundreds of glucose molecules stuck together.

• Plants store glucose in the polysaccharide form of starch.

Lipids• Lipids are molecules made mostly of carbon and

hydrogen.

• Lipids are made up of building blocks called fatty acids.

• One end of the fatty acid is hydrophilic (water loving) while the other end is hydrophobic (water fearing).

• Saturated fats contain only single bonds (C-C).

• Unsaturated fats contain at least one double bond (C=C).

• Ex.’s oils, fats, steroids, waxes

Lipids

• A triglyceride is a fat if it is solid at room temperature and an oil if it is liquid at room temperature.

• Cell membranes are primarily composed of a lipid called a phospholipid.

• Other examples of lipids include waxes and steroids.

Proteins• A protein is a compound made of small carbon compounds

called amino acids. Ex.’s meat, beans, eggs

• Amino acids are small compounds that are made of carbon, nitrogen, oxygen, hydrogen, and sometimes sulfur.

• Amino acids have a central carbon atom.

• One of the four carbon bonds is with hydrogen.

• The other three bonds are with an amino group (–NH2), a carboxyl group (–COOH), and a variable group (–R).

Proteins• Dipeptides are formed when two amino acids join

together.

• The bond that holds them together is called a peptide bond.

• Long chains of amino acids are called polypeptides.

• Proteins are made up of one or more polypeptides.

Nucleic Acids• Nucleic acids are complex macromolecules that store

and transmit genetic information.

• DNA (deoxyribonucleic acid) contains information that is essential for almost all cell activities, including cell division.

• RNA (ribonucleic acid) stores and transfers information that is essential for the manufacturing of proteins.

• Both DNA and RNA are composed of thousands of nucleotides.

• Each nucleotide is composed of a phosphate group, a 5-carbon sugar, and a ring-shaped nitrogen base.