Chapter 3 Review Introduction to Organic Compounds Water and the Fitness of the Environment

a protein's functional shape results from four levels of structure.

. A protein's primary structure is the sequence of amino acids in its polypeptide chain. Its secondary structure is the coiling or folding of the chain, stabilized by hydrogen bonds. The tertiary structure is the overall three-dimensional shape of a polypeptide, resulting from interactions among R groups. Proteins made of more than one polypeptide have quaternary structure.

Given that the function of egg yolk is to nourish and support the developing chick, explain why egg yolks are so high in fat, protein, and cholesterol.

A developing chick is growing rapidly, increasing its number of cells. To build new cells it needs large stores of cell membrane components, including cholesterol and lipids, and amino acids for building its proteins. It also requires energy to fuel all this construction, and that is available in the form of fats, as fat molecules can be broken down to yield a lot of energy.

Monosaccharides are the simplest carbohydrates.

A monosaccharide has a formula that is a multiple of CH2O and contains hydroxyl groups and a carbonyl group.

What are the two types of secondary structures found in polypeptides, and what maintains them? What stabilizes the tertiary structure of a polypeptide?

Alpha helices and beta pleated sheets, the secondary structures of a polypeptide, are maintained by hydrogen bonds between oxygen and hydrogen atoms of the polypeptide backbone. The tertiary structure is formed by interactions among the R groups of constituent amino acids and stabilized by hydrogen bonds, ionic bonds, clustering of hydrophobic R groups, and covalent bonds between sulfur atoms of some amino acids.

Most proteins are soluble in the aqueous environment of a cell. Knowing that, where in the overall three-dimensional shape of a protein would you expect to find amino acids with hydrophobic R groups?

Amino acids with hydrophobic R groups are most likely to be found clustered together in the interior of a protein, sheltered from the surrounding water.

The diversity of life is staggering. Yet the molecular logic of life is simple and elegant: Small molecules common to all organisms are ordered into unique macromolecules. Explain why carbon is central to this diversity of organic molecules. How do carbon skeletons, chemical groups, monomers, and polymers relate to this molecular logic of life?

Carbon forms four covalent bonds, either with other carbon atoms, producing chains or rings of various lengths and shapes, or with other atoms, such as characteristic chemical groups that confer specific properties on a molecule. This bonding capability is the basis for the incredible diversity of organic compounds. Organisms can link a small number of monomers into different arrangements to produce a huge variety of polymers.

Life's molecular diversity is based on the properties of carbon.

Carbon's ability to bond with four other atoms is the basis for building large and diverse organic compounds. Hydrocarbons are composed of only carbon and hydrogen. Isomers have the same molecular formula but different structures.

Circle and name the functional groups in this organic molecule. What type of compound is this? For which class of macromolecules is it a monomer?

Circle NH2, an amino group; COOH, a carboxyl group; and OH, a hydroxyl group on the R group. This is an amino acid, a monomer of proteins. The OH group makes it a polar amino acid.

Lactose tolerance is a recent event in human evolution.

Different mutations in DNA have led to lactose tolerance in several human groups whose ancestors raised dairy cattle.

a few chemical groups are key to the functioning of biological molecules

Hydrophilic functional groups give organic molecules specific chemical properties.

Fats are lipids that are mostly energy-storage molecules.

Lipids are diverse, hydrophobic compounds composed largely of carbon and hydrogen. Fats (triglycerides) consist of glycerol linked to three fatty acids. Saturated fatty acids are found in animal fats; unsaturated fatty acids are typical of plant oils.

The nucleic acids dNa and RNa are information-rich polymers of nucleotides.

Nucleotides are composed of a sugar, a phosphate group, and a nitrogenous base. DNA is a double helix; RNA is a single polynucleotide chain. DNA and RNA serve as the blueprints for proteins and thus control the life of a cell. DNA is the molecule of inheritance.

Phospholipids and steroids are important lipids with a variety of functions.

Phospholipids are components of cell membranes. Steroids include cholesterol and some hormones.

Proteins are made from amino acids linked by peptide bond

Protein diversity is based on different sequences of amino acids, monomers that contain an amino group, a carboxyl group, an H atom, and an R group, all attached to a central carbon. The R groups distinguish 20 amino acids, each with specific properties.

Proteins have a wide range of functions and structures.

Proteins are involved in almost all of a cell's activities; as enzymes, they regulate chemical reactions.

Polysaccharides are long chains of sugar units.

Starch and glycogen are storage polysaccharides; cellulose is structural, found in plant cell walls. Chitin is a component of insect exoskeletons and fungal cell walls.

How can a cell make many different kinds of proteins out of only 20 amino acids? Of the myriad possibilities, how does the cell "know" which proteins to make?

The 20 amino acids that are found in proteins can be arranged in many different sequences into chains of many different lengths. The sequences of DNA nucleotides in the genes of a cell dictate the amino acid sequences of its polypeptide chains.

are we eating too much sugar?

The FDA recommends that only 10% of daily calories come from added sugar. Research supports the correlation between high sugar intake and adverse health effects.

Explain the role of complementary base pairing in the functions of nucleic acids.

The complementary base pairing of the two strands of DNA makes possible the precise copying of DNA every time a cell divides, ensuring that genetic information is faithfully transmitted. Complementary base pairing is involved in transferring information from DNA to RNA to specify the order of amino acids in a polypeptide. In some types of RNA, complementary base pairing enables RNA molecules to assume specific three- dimensional shapes that facilitate diverse functions.

Another aspect of the Nurses' Health Study introduced in Module 3.9 looked at the percentage of change in the risk of coronary heart disease associated with substituting one dietary component for another. These results estimated that replacement of 5% of energy from saturated fat in the diet with unsaturated fats would reduce the risk of heart disease by 42%, and that the replacement of 2% of energy from trans fat with unsaturated fats would reduce the risk by 53%. Explain what these numbers mean.

These results indicate that replacing either saturated or trans fats in the diet with unsaturated fats reduces the risk of coronary heart disease. The benefit is greater (risk reduced the most) when trans fats are replaced, even though the quantity of energy in the diet replaced was only 2% rather than the 5% of saturated fats replaced.

Sucrose is broken down in your intestine to the monosaccharides glucose and fructose, which are then absorbed into your blood. What is the name of this type of reaction? Using this diagram of sucrose, show how this would occur.

This is a hydrolysis reaction, which consumes water. It is essentially the reverse of the diagram in Figure 3.5, except that fructose has a different shape than glucose

Enzymes usually function best at an optimal pH and temperature. The following graph shows the effectiveness of two enzymes at various temperatures.

a. A: at about 37°C; B: at about 78°C b. A: from humans (human body temperature is about 37°C); B: from thermophilic bacteria c. Above 40°C, the human enzyme denatures and loses its shape and thus its function. The increased thermal energy disrupts the weak bonds that maintain secondary and tertiary structure in an enzyme.

A shortage of phosphorus in the soil would make it especially difficult for a plant to manufacture a. DNA. b. proteins. c. cellulose. d. sucrose

a. DNA.

Complete the following table to help you review the structures and functions of the four classes of organic molecules.

a. glucose; b. energy storage; c. cellulose; d. fats; e. cell membrane component; f. steroids; g. amino group; h. carboxyl group; i. R group; j. enzyme; k. structural proteins; l. movement; m. membrane transport protein; n. defense; o. phosphate group; p. nitrogenous base; q. ribose or deoxyribose; r. DNA; s. code for proteins

Unsaturated fats a. have double bonds in their fatty acid chains. b. have fewer fatty acid molecules per fat molecule. c. are associated with greater health risks than are saturated fats. d. are more common in animals than in plants.

a. have double bonds in their fatty acid chains.

Which structural level of a protein would be least affected by a disruption in hydrogen bonding? a. primary structure b. secondary structure c. tertiary structure d. quaternary structure

a. primary structure

What makes a fatty acid an acid? a. It does not dissolve in water. b. It is capable of bonding with other molecules to form a fat. c. It has a carboxyl group that can donate an H+ to a solution. d. It contains only two oxygen atoms.

c. It has a carboxyl group that can donate an H+ to a solution

Cows can derive nutrients from cellulose because a. they produce enzymes that recognize the shape of the glucose-glucose bonds and hydrolyze them. b. they re-chew their cud to break down cellulose fibers. c. their digestive tract contains microorganisms that can hydrolyze the bonds of cellulose. d. they convert cellulose to starch and can digest starch.

c. their digestive tract contains microorganisms that can hydrolyze the bonds of cellulose.

A glucose molecule is to starch as (Explain your answer.) a. a steroid is to a lipid. b. a protein is to an amino acid. c. a nucleic acid is to a polypeptide. d. a nucleotide is to a nucleic acid.

d. a nucleotide is to a nucleic acid

Of the following functional groups, which is/are polar, tending to make organic compounds hydrophilic? a. carbonyl b. amino c. hydroxyl d. all of the above

d. all of the above

Which of the following substances is a major component of the cell membrane of a fungus? a. cellulose b. chitin c. cholesterol d. phospholipids

d. phospholipids

anabolic steroids

pose health risks.

scientific studies document

the health risks of trans fats.

Two monosaccharides are linked

to form a disaccharide.