Chapter 3

______________ are hydrophobic molecules composed mainly of hydrogen and carbon atoms, and some oxygen. The defining feature of lipids is that they are nonpolar and therefore insoluble in water. Lipids account for about 40% of the organic matter in the average human body and include fats, phospholipids, steroids, and waxes.

lipids

Alternatively, some fatty acids contain one or more C=C double bonds. These fatty acids are known as ________________________ The C=C double bond introduces a kink into the linear shape of a fatty acid. Because of kinks in their chains, unsaturated fatty acids do not pack together as tightly as saturated fatty acids. A fatty acid with one C=C bond is a monounsaturated fatty acid, whereas a fatty acid with two or more C=C bonds is a polyunsaturated fatty acid.

unsaturated fatty acids

Macromolecules

carbohydrates, lipids, proteins, nucleic acids

Nucleic acids

A nucleic acid is a linear sequence of nucleotides; DNA is double-stranded DNA stores genetic information in units called genes. RNA is made from DNA and provides access to that information DNA and RNA

Proteins

A polypeptide is a structural unit composed of a linear sequence of amino acids. A protein is a functional unit composed of one or more polypeptides. Proteins play a key role in cell structure and carry out a diverse array of cellular functions; for example, there are proteins involved with gene expression and regulation, motor proteins, defense proteins, cell-signaling proteins, metabolic enzymes, structural proteins, and transporters.

Other polysaccharides provide a structural role, rather than storing energy. For example, cellulose is a major constituent of plant cell. ___________________ is a polymer of β-d-glucose, with a linear arrangement of carbon-carbon bonds and no branching (see Figure 3.7). Each glucose monomer in cellulose is in an opposite orientation from its adjacent monomers ("flipped over"), forming long chains of several thousand glucose monomers.

Cellulose

Monosaccharides can join together by dehydration to form larger carbohydrates. _______________ are carbohydrates composed of two monosaccharides. A familiar disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose Sucrose is the major transport form of sugar in plants. The linking together of most monosaccharides involves the removal of a hydroxyl group from one monosaccharide and a hydrogen atom from the other, giving rise to a molecule of water and covalently bonding the two sugars together through an oxygen atom. The bond formed between two sugar molecules by such a dehydration reaction is called a __________________

Disaccharides (meaning two sugars) - blank glycosidic linkage - second blank

______________________ are large polysaccharides that play a structural role in animals. For example, they are abundantly found in cartilage, the tough, fibrous material found in joints and other animal structures. Glycosaminoglycans are also abundant in the extracellular matrix that provides a structural framework surrounding many of the cells in an animal's body

Glycosaminoglycans

Motor proteins

Initiate movement

Lipids

Lipids are nonpolar molecules that are primarily composed of carbon and hydrogen, with some oxygen. Lipids are a key part of cell membranes and also function as hormones and in energy storage; in animals, they act as insulators and shock absorbers. Phospholipids, estrogen, testosterone, triglycerides

Proteins involved in gene expression and regulation

Make mRNA from a DNA template; synthesize polypeptides from mRNA; regulate genes

___________________, another class of lipids, are similar in structure to triglycerides but with one important difference. The third hydroxyl group of glycerol is linked to a phosphate group instead of a fatty acid. In most phospholipids, a small polar or charged nitrogen-containing molecule is attached to this phosphate (Figure 3.11a). The glycerol backbone, phosphate group, and a charged molecule (in this case, choline) constitute a hydrophilic head at one end of the phospholipid, whereas the fatty acid chains are hydrophobic tails at the opposite end. Recall from Chapter 2 that molecules with polar and nonpolar regions are called amphipathic molecules.

Phospholipids,

Transporters

Promote movement of solutes across membranes

_____________ are composed of carbon, hydrogen, oxygen, nitrogen, and small amounts of other elements, notably sulfur. The monomers of proteins are amino acids, compounds with a structure in which a carbon atom, called the α-carbon, is linked to an amino group (—NH2) and a carboxyl group (—COOH). The α-carbon also is linked to a hydrogen atom and a side chain, designated with the letter R. Proteins are polymers of amino acids. When an amino acid is dissolved in water at neutral pH, the amino group accepts a hydrogen ion and is positively charged, whereas the carboxyl group loses a hydrogen ion and is negatively charged. The term amino acid is the name given to such molecules because they have an amino group and also a carboxyl group that acts as an acid.

Proteins

Carbohydrates

The general formula is Cn(H20)n, where n is a whole number Simple carbohydrates are broken down to make ATP, which is used as a source of energy. Larger carbohydrates store energy or may play a structural role, as in plant cell walls. Some carbohydrates function as molecular tags allowing recognition of specific cells and molecules. Simple sugars, such as glucose; larger polymers, such as starch and cellulose

_________________________ (often called fats) are formed by bonding glycerol to three fatty acids Glycerol is a three-carbon molecule with one hydroxyl group (—OH) bonded to each carbon A _______________ is a chain of carbon and hydrogen atoms with a carboxyl group (— COOH) at one end. Each of the hydroxyl groups in glycerol is linked to the carboxyl group of a fatty acid by the removal of a molecule of water by a dehydration reaction. The resulting bond is an ester bond.

Triglycerides fatty acids

Enzymes

are molecules that catalyze (speed up) the rates of many biologically important chemical reactions. An enzyme that recognizes one enantiomer usually does not recognize the other

What occurs in all chemical reactions

chemical bonds are formed or broken

Other polysaccharides also play structural roles. ________________ a tough, structural polysaccharide, forms the external skeleton of insects and crustaceans (shrimp and lobsters) as well as the cell walls of fungi The sugar monomers within chitin have nitrogen-containing groups attached to them.

chitin

cis-trans isomers

cis is next to each other whereas trans is across from each other

When a polymer is formed, two smaller molecules combine by a ______________ reaction, which produces a larger organic molecule plus a water molecule. This specific type of condensation reaction is also called a __________________ reaction, because a molecule of water is removed when a monomer is added to a growing polymer.

condensation - first bank dehydration - second blank

structural isomers

contain the same atoms but in different bonding relationships Urea and ammonium cyanate fall into this category. A simpler example of structural isomers (isopropyl alcohol and propyl alcohol)

Cell-signaling proteins

enable cells to communicate with each other and with the environment

Functional Group

group of atoms with characteristic chemical features and properties are called

Stereoisomers

have identical bonding relationships but a different spatial arrangement of atoms Two types of stereoisomers are cis-trans isomers and enantiomers In cis-trans isomers, like those shown in Figure 3.3b, the two hydrogen atoms linked to the two carbons of a C=C double bond may be on the same side of the carbons, in which case the C=C bond is called a cis double bond. If the hydrogens are on opposite sides, it is a trans double bond. A second type of stereoisomer, called an enantiomer, exists as a pair of molecules that are mirror images. Four different atoms can bind to a single carbon atom in two possible ways, designated a left-handed and a right-handed structure. The resulting structures are not identical, but instead are mirror images of each other

Metabolic enzymes

increase rates of chemical reactions

Two molecules with an identical chemical formula but different structures and characteristics are called

isomers Wöhler was surprised to discover that urea ((NH2)2CO) and ammonium cyanate (NH4OCN) contained the exact same ratio of carbon,Page 46 nitrogen, hydrogen, and oxygen atoms, yet they were different molecules with distinct chemical and biological properties.

Hydrocarbons

molecules with a high amount of hydrogen-carbon bonds. are hydrophobic and poorly soluble in water. In contrast, when carbon forms polar covalent bonds with more electronegative atoms, such as oxygen or nitrogen, the molecule is much more soluble in water due to the electrical attraction of polar water molecules. Carbon can form both nonpolar and polar bonds, and both single and double bonds, as shown here for the molecule propionic acid, a common food preservative.

However, some organic molecules are extremely large macromolecules composed of thousands or even millions of atoms. Such large molecules are formed by linking together many smaller molecules called_________________ and are known as _________________________.

monomers (meaning one part) - first blank polymers (meaning many parts) - second blank

The simplest sugars are monomers known as

monosaccharides The most common types contain either five carbons (pentoses) or six carbons (hexoses). Important pentoses are ribose (C5H10O5) and the closely related deoxyribose (C5H10O4), which are part of RNA and DNA molecules, respectively, and are described later in this chapter. The most common hexose is glucose (C6H12O6) Like other monosaccharides, glucose is very water-soluble and circulates in the blood or fluids of animals, where it can be transported across cell membranes. Once inside a cell, enzymes can break down glucose into smaller molecules, releasing energy that was stored in the chemical bonds of glucose. This energy is then stored in the bonds of another molecule, called adenosine triphosphate, or ATP

Carbohydrates

monosaccharides, polysaccharides, disaccharides

carbon containing molecules

organic molecules

When many monosaccharides are linked together to form long polymers, _____________________ are made. Starch, found in plant cells, and glycogen, in animal cells, are examples of polysaccharides . The bonds that connect the monomers are very specific. In starch and glycogen, the bonds form between carbons 1 and 4 and between carbons 1 and 6. The high degree of branching in glycogen contributes to its solubility in animal tissues, such as muscle tissue, because the extensive branching creates a more open structure in which many hydrophilic hydroxyl (—OH) side groups have access to water and can hydrogen-bond with it. Starch is less branched and less soluble, which contributes to the properties of plant structures (think of a potato or a kernel of corn).

polysaccharides (meaning many sugars)

Defense proteins

protection against disease

When all of the carbons in a fatty acid are linked by single covalent bonds, the fatty acid is said to be a ___________________ because all of the carbons are saturated with covalently bound hydrogen.

saturated fatty acid

Structural proteins

support and strengthen structures

Vitalism

the idea that there is a force in life that is distinct from physical entities

organic chemistry

the study of compounds containing carbon