Chapter 2 The Chemistry of Life Part 2

Carbohydrates are Polymers of Monosaccharides

TABLE 2.4 REVIEW OF SOME COMMON CARBOHYDRATES

Three different ways to represent a monosaccharide FIGURE 2.14 Monosaccharides are simple sugars, generally having a backbone of three to six carbon atoms. Many of these carbon atoms are also bonded to hydrogen (H) and a hydroxyl group (OH). In the fluid within our cells, the carbon backbone usually forms a ring like structure. Here, three representations of the monosaccharide glucose (C6H12O6) are shown.

Carbohydrates Carbohydrates are sugars and starches and provide fuel for the body. Sucrose and lactose are examples of disaccharides or double sugars.

(Dehydration) Synthesis of a Disaccharide FIGURE 2.15 Disaccharides are built from two monosaccharides. Here, a molecule of glucose and one of fructose combine to form sucrose.

Polysaccharides Polysaccharides: thousands of monosaccharides joined in chains and branches Starch: made in plants; stores energy Glycogen: made in animals; stores energy Cellulose: indigestible polysaccharide made in plants for structural support

FIGURE 2.16b Polysaccharides may function in storage (as in glycogen) or provide structure (as in cellulose).

Lipids Lipids are water-insoluble molecules that store long-term energy, and form cell membranes

Lipids Fats and oils are examples of triglycerides, a polymer made of one molecule of glycerol and three fatty acids

Lipids The fatty acids bond to glycerol through dehydration synthesis

FIGURE 2.17a Triglycerides are composed of a molecule of glycerol joined to three fatty acids.

Lipids If there are no double bonds between carbon atoms and fatty acids triglycerides are classified as saturated Solid at room temperature If there are double bonds they are called unsaturated Liquid at room temp

FIGURE 2.17b Triglycerides are composed of a molecule of glycerol joined to three fatty acids.

Oleic acid: a cis unsaturted fat

Elaidic acid: a trans unsaturated fat Trans fats are artificial unsaturated fats that are not “kinked” and therefore are not soluble at room temperature Elaidic acid: a trans unsaturated fat

Phospholipids Components of cell membranes Warm-blooded animals have saturated Cold-blooded and plants have more unsaturated

Phospholipids Phospholipid molecules have a Glycerol head that is polar and water soluble (hydrophilic) and a Fatty acid tail that is nonpolar and water insoluble (hydrophobic) Phospholipids function as essential structural components of membranes

FIGURE 2.18a Structure of a phospholipid. Phospholipids are the main components of the plasma membrane encasing a cell and separating its internal and external watery environments.

Phospholipids Phospholipids are arranged in a bilayer with the hydrophilic heads of each layer facing the aqueous side of the memb.

FIGURE 2.18b Structure of a phospholipid. Phospholipids are the main components of the plasma membrane encasing a cell and separating its internal and external watery environments.

Steroids Cholesterol and Hormones Estrogens and testosterone are examples of steroids

FIGURE 2.19 The steroid cholesterol is a component of cell membranes and is the substance from which steroid hormones such as estrogen and testosterone are made. All steroids have a structure consisting of four carbon rings. Steroids differ in the groups attached to these rings.

Proteins Amino acids consist of a central carbon atom bound to a hydrogen (H) atom, an amino group (NH2), and a carboxyl group (COOH) in addition to a unique side chain called a radical (R)

FIGURE 2.20 Structure of an amino acid. Amino acids differ from one another in the type of R group (side chain) they contain.

FIGURE 2.21 Formation of a peptide bond between two amino acids through dehydration synthesis. The carboxyl group (COOH) of one amino acid bonds to the amino group (NH2) of the adjacent amino acid, releasing water.

Proteins Proteins have four distinct levels of structure—primary, secondary, tertiary and quaternary—that affect their function in the body

Proteins Changes in the chemical environment of a protein can cause it to lose its structure (called denaturation) resulting in a loss of function

FIGURE 2.22 Levels of protein structure.

Proteins A special group of proteins are called enzymes and they serve as catalysts for chemical reactions

FIGURE 2.23a The working cycle of an enzyme.

FIGURE 2.23b The working cycle of an enzyme.

Characteristics of Enzymes Biological catalysts Make chemical reactions go fast (very) Active Site has affinity for its substrate Each enzyme is specific for a substrate

Nucleic acids include DNA and RNA Functions Store genetic information Provide information used in making proteins

Nucleic Acids Genes are segments of polymers called deoxyribonucleic acid (DNA)

Nucleic Acids DNA and ribonucleic acid (RNA) are the two types of nucleic acids and both are polymers of smaller units called nucleotides

Nucleic Acids A nucleotide is made up of: One five-carbon sugar bonded to One of five nitrogen-containing bases and One phosphate group

FIGURE 2.24 Structure of a nucleotide. Nucleotides consist of a five-carbon (pentose) sugar bonded to a phosphate molecule and one of five nitrogencontaining bases. Nucleotides are the building blocks of nucleic acids.

Nucleic Acids The sequence of the nucleotides in DNA and RNA determine the sequence of amino acids in protein (i.e., primary structure of the protein)

Nucleic Acids RNA and DNA have structural differences related to sugar, bases, and number of strands

TABLE 2.5 REVIEW OF THE STRUCTURAL DIFFERENCES BETWEEN RNA AND DNA

Nucleic Acids RNA is single-stranded

RNA FIGURE 2.25 RNA is a single-stranded nucleic acid. It is formed by the linking together of nucleotides composed of the sugar ribose, a phosphate group, and the nitrogen-containing bases cytosine (C), adenine (A), guanine (G), and uracil (U).

RNA

Nucleic Acids DNA has two strands to form a distinctive double helix

DNA (double stranded) FIGURE 2.26 DNA is a nucleic acid in which two chains of nucleotides twist around one another to form a double helix. The two chains are held together by hydrogen bonds between the nitrogen-containing bases. Each nucleotide of DNA contains the pentose sugar deoxyribose, a phosphate group, and one of the following four nitrogen-containing bases: adenine (A), thymine (T), cytosine (C), and guanine (G).

Adenosine Triphosphate (ATP) Adenosine triphosphate (ATP) is a special nucleotide ATP molecule is capable of storing energy in its phosphate-to-phosphate bonds

ATP molecule stores energy in its phosphate-to-phosphate bonds FIGURE 2.27 Structure and function of adenosine triphosphate (ATP). This nucleotide consists of the sugar ribose, the base adenine, and three phosphate groups. The phosphate bonds of ATP are unstable. When cells need energy, the last phosphate bond is broken, yielding adenosine diphosphate (ADP), a phosphate molecule, and energy.

ATP All energy from the breakdown of molecules such as glucose must be captured in ATP before the body can use it. It is often described as the energy currency of cells