Biochemistry Chapter 3

Water Sec 3-1

Polarity (1) Many of water’s biological functions stem from its chemical structure. The hydrogen and oxygen atoms share electrons to form covalent bonds.

Polarity (2) The oxygen atom pulls the shared electrons toward its nucleus away from the hydrogen nucleus, so the electrical charge is unevenly distributed. Because of this uneven pattern of charge, water is called a polar compound.

Polarity (3) The polar nature of water makes water very effective in dissolving many other substances. Water dissolves other polar substances, including sugars and some proteins, as well as ionic compounds.

Hydrogen Bonding (1) The polar nature of water also causes water molecules to be attracted to one another. The type of attraction that holds two water molecules together is called a hydrogen bond.

Hydrogen Bonding (2) A hydrogen bond tends to form between a hydrogen atom in one molecule and the region of negative charge on another molecule. A hydrogen bond is a weak bond that can easily be broken.

Hydrogen Bonds (3) The hydrogen bonds in water exert a significant attractive force, causing water to cling to itself and to other substances. An attractive force between particles of the same kind is known as cohesion. Adhesion is the attractive force between unlike substances.

Hydrogen Bonding (4) Water must gain or lose a relatively large amount of energy for its temperature to change its state. When water is heated, most of the thermal energy that the water initially absorbs breaks the hydrogen bonds.

Complete Reading Guide and Review 3-1

Carbon Compounds Sec 3-2

Compounds of Life Organic compounds contain carbon atoms that are covalently bonded to other carbon atoms and to other elements. Inorganic compounds are the compounds used to create organic compounds and don’t contain carbon, except carbon dioxide.

Carbon Bonding (1) A carbon atom has four electrons in its outermost energy level. A carbon atom readily forms four covalent bonds with other elements as well as with other carbon atoms.

Carbon Bonding (2) The tendency of carbon to bond with itself results in an enormous variety of organic compounds in many different shape, including straight chains, branched chains, and rings These structures form the backbone of many different kinds of organic molecules.

Functional Groups In most organic compounds, clusters of atoms, called functional groups, influence the properties of the molecules they compose. The functional group is the structural building block that determines the characteristics of the compound.

Large Carbon Molecules (1) In many carbon compounds, the molecules are built up form smaller, simpler molecules known as monomers. Monomers can bond to one another to form complex molecules known as polymers. Large polymers are called macromolecules.

Large Carbon Molecules (2) Monomers link to form polymers through a chemical reaction called a condensation reaction or dehydration synthesis.

Large Carbon Molecules (3) The breakdown of some complex molecules, such as polymers, occurs through a process known as hydrolysis.

Energy Currency (1) Life process require a constant supply of energy. Most cellular energy is stored in a chemical compound known as adenosine triphosphate, more commonly abbreviated as ATP.

Energy Currency (2) The covalent bond that holds the last phosphate group to the rest of the molecule is easily broken. When this bond is broken, much more energy is released than was required to break the bond This conversion of energy is used by the cell to drive the chemical reactions that enable an organism to function.

Complete Reading Guide and Review 3-2

Molecules of Life Sec 3-3

Organic Compounds There are four main classes of organic compounds are essential to life processes. Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates (1) Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen The ratio of hydrogen to oxygen is 2:1 The monomer of a carbohydrates is a monosaccharide.

Carbohydrates (2) The general formula for a monosaccharide is written as (CH2O)n, where n is any whole number from 3 to 8. The most common monosaccharides are glucose, fructose, and galactose.

Carbohydrate (3) Glucose, fructose, and galactose have the same molecular formula, C6H12O6 but they have different structures and different properties. Compounds like these sugars, with a single chemical formula but different forms, are called isomers.

Carbohydrates (4) Two monosaccharides can combine in a condensation reaction to form a double sugar, or disaccharide. A polysaccharide is a complex molecule composed of three or more monosaccharides.

Proteins (1) Proteins are organic compounds mainly composed mainly of carbon, hydrogen, oxygen, and nitrogen. Proteins are made up of the monomers of amino acids.

Proteins (2) There are 20 different amino acids. Amino acids all have the same basic structure; a central carbon atom covalently bonded to four other atoms or functional groups. A single hydrogen atom, a carboxyl group, an amino group and a functional group called the R group The main difference between the amino acids is the difference in the R-group.

Proteins (3) In a condensation reaction, two amino acids form a covalent bond, called a peptide bond to form a dipeptide. Amino acids can bond to each other one at a time, forming a very long chain called a polypeptide.

Proteins (4) Proteins are composed of one or more polypeptides. Protein shape can also be influenced by conditions such as temperatures or the type of solvent in which the protein is dissolved.

Proteins (5) Most enzymes are proteins. Enzyme reactions depend on a physical fit between the enzyme molecule and its substrate, the reactant being catalyzed. The enzyme and substrate have shapes that allow them to fit together like a lock and key.

Lipids (1) Lipids are large, nonpolar organic molecules that do not dissolve in water. Lipid molecules have a higher ratio of carbon and hydrogen atoms to oxygen atoms than carbohydrates.

Lipids (2) Lipids store energy efficiently. Lipid molecules have large numbers of carbon-hydrogen bonds, which store more energy than the carbon-oxygen bonds common in other organic compounds.

Lipids (3) Fatty acids are unbranched carbon chains that make up most lipids. A fatty acid contains a long, straight carbon chain with a carboxyl group attached to one end.

Lipids (4) The two ends of the fatty-acid molecule have very different properties. The carboxyl end is polar and is attracted to water molecules so it is said to be hydrophilic which means “water loving”. The hydrocarbon end of the fatty-acid molecule is nonpolar does not interact with water molecules and is said to be hydrophobic, or “water fearing”.

Lipids (5) Lipids are divided into categories according to their structure. (a) A triglyceride is composed of three molecules of fatty acid joined to one molecule of the alcohol glycerol.

Lipids (6) (b) Phospholipids have two, rather than three, fatty acids joined by a molecule of glycerol. The cell membrane is composed of two layers of phospholipids, which are referred to as the lipid bilayer. The inability of lipids to dissolve in water allows the membrane to form a barrier between the inside and outside the cell.

Lipids (7) (c) A wax is a type of structural lipid. A wax molecule consists of a long fatty-acid chain joined to a long alcohol chain. Waxes are highly waterproof, and in plants, wax forms a protective coating on the outer surfaces.

Lipids (8) Unlike most other lipids steroid molecules are composed of four fused carbon rings with various functional groups attached to them. Many animal hormones, such as the male hormone testosterone, are steroid compounds. One of the most familiar steroids in humans is cholesterol.

Nucleic Acids (1) Nucleic acids are very large and complex organic molecules that store important information in the cell. Nucleic acids use a system of four compounds to store hereditary information.

Nucleic Acids (2) Deoxyribonucleic acid, or DNA, contains information that is essential for almost all cell activities, including cell division. Ribonucleic acid, or RNA, stores and transfers information that is essential for the manufacturing of proteins.

Nucleic Acids (3) Both DNA and RNA are polymers, composed of thousands of linked monomers called nucleotides. Each nucleotide is made up of a phosphate group, a five-carbon sugar, a ring-shaped nitrogen base.

Complete Reading Guide and Review 3-3