Mastering Biology Chapter 3

What are characteristics of a protein's secondary structure?

Alpha helices and beta pleated sheets

Which part of an amino acid is always acidic?

Carboxyl functional group (The carboxyl group (COOH) contains two oxygen atoms that tend to pull electrons away from the hydrogen atom, so this group tends to lose a proton and is acidic.)

Which of the functional groups behaves as an acid?

Carboxyl; By donating hydrogen ions, carboxyl groups act as an acid.

What type of bond joins the monomers in a protein's primary structure?

peptide (The amino acids of a protein are linked by peptide bonds.)

A nucleotide is composed of a(n) _________________.

phosphate group, a nitrogen-containing base, and a five-carbon sugar

Phosphate Group

(PO4) A chemical group consisting of a phosphorus atom bonded to four oxygen atoms; important in energy transfer.

_________ is the most abundant organic compound on Earth.

Cellulose (Cellulose, a component of plant cell walls, is the most abundant organic compound found on earth.)

Carboxyl Group

(-COOH) A carbon atom both double bonded to an oxygen and single bonded to the oxygen of a hydroxyl group, found in organic acids.

Hydroxyl Group

(-OH) a hydrogen atom bonded to an oxygen, which in turn is bonded to a carbon skeleton

Carbonyl Group

(C=O) A carbon atom linked by a double bond to an oxygen atom.

Amino Group

(NH2) a nitrogen atom bonded to two hydrogen atoms, covalently linked to the central carbon atom of an amino acid.

If a strand of DNA has the nitrogen base sequence 5'-ATTTGC-3', what will be the sequence of the matching strand?

3'-TAAACG-5' (Adenine pairs with thymine and guanine pairs with cytosine.)

If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain?

75 (100 nucleotide pairs are a total of 200 nucleotides. Because of base pairing, if there are 25 adenine there must also be 25 thymine. This leaves 200-50 = 150 nucleotides to be divided evenly between guanine and cytosine.)

Which of the functional groups behaves as a base?

Amino; The electronegativity of nitrogen means that amino groups tend to pick up hydrogen ions.

Which of the following is not attached to the central carbon atom in an amino acid?

An oxygen (The central carbon atom in an amino acid is bonded to an amino functional group, a carboxyl functional group, a side chain, and hydrogen.)

Which of the functional groups is a characteristic of a ketone?

Carbonyl; A carbon group in the middle of a carbon skeleton characterizes ketones.

Which of the following best summarizes the relationship between dehydration reactions and hydrolysis?

Dehydration reactions assemble polymers; hydrolysis reactions break polymers apart.

Which functional group is a characteristic of alcohol?

Hydroxyl

Which monomers make up RNA?

Nucleotides (Nucleotide monomers make up nucleic acids.)

Which of the functional groups plays a major role in energy transfer?

Phosphate; Phosphate groups are a component of ATP.

Which polymers are composed of amino acids?

Proteins (Proteins are composed of amino acids joined together)

The four levels of protein structure are primary, secondary, tertiary, and quaternary structure. Which level of protein structure is a characteristic of some, but not all, proteins?

Quaternary level of protein structure (Quaternary structure results from the aggregation of two or more polypeptide subunits, and not all proteins are composed of more than one polypeptide.)

Which of the functional groups is a characteristic of thiols?

Sulfhydryl; Thiols are characterized by the presence of a sulfhydryl group.

How are genes used by cells to build proteins?

The genes in DNA direct the synthesis of an RNA molecule, which is used to build a protein.

True or false? Enzymes in the digestive tract catalyze hydrolysis reactions.

True (Enzymes in the digestive tract break down food molecules, which is a process that occurs by hydrolysis.)

Phospholipids are composed of

a phosphate group, a glycerol, and fatty acids.

Glycogen is ________________________________.

a polysaccharide found in animals (Animals store energy in the form of glycogen.)

Which of the following statements about the formation of polypeptides from amino acids is true? a. A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid. b. The reaction occurs through the addition of a water molecule to the amino acids. c. Polypeptides form by condensation or hydrolysis reactions. d. A bond can form between any carbon and nitrogen atom in the two amino acids being joined.

a. A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid. (A hydroxyl group is removed from the carboxyl group of one amino acid and hydrogen is removed from the amino group of the other amino acid, allowing a bond to form between the two groups.)

Select the hydrocarbon from the following choices. a. C3H8 b. CO2 c. H2CO3 d. C6H12O6

a. C3H8 (This is a typical hydrocarbon with single bonds; the number of hydrogen atoms is equal to two times the number of carbon atoms plus 2.)

Which of the following statements regarding nucleotides is false? a. Nucleotides contain lipids. b. Nucleotides contain sugar molecules. c. Nucleotides contain nitrogenous bases. d. Nucleotides can be linked together to form nucleic acids.

a. Nucleotides contain lipids.

Which of these is NOT a lipid? a. RNA b. wax c. cholesterol d. steroids e. phospholipid

a. RNA (RNA is a nucleic acid.)

Organic compounds

always contain carbon.

Proteins are polymers of ___________.

amino acids

Steroids are considered to be lipids because they ________________________.

are not soluble in water

A function of cholesterol that does not harm health is its role ______________________________________.

as a component of animal cell membranes

Which of the following statements about hydrocarbons is false? a. Hydrocarbons can form straight, branched, or ringed structures. b. Hydrocarbons are inorganic compounds. c. Hydrocarbons contain only carbon and hydrogen atoms. d. Hydrocarbons consist of atoms linked by single or double bonds.

b. Hydrocarbons are inorganic compounds.

Which of these is a polysaccharide? a. sucrose b. cellulose c. glucose d. galactose e. lactose

cellulose (Cellulose is a carbohydrate composed of many monomers.)

Which of these functional groups is found in all amino acids? a. -OH b. =O c. -PO4^2- d. -NH2

d. -NH2 (This is an amino group, which is attached to the central carbon of all twenty different amino acids.)

Which of these is a source of lactose? a. sugar cane b. potatoes c. sugar beets d. milk e. starch

d. milk (Lactose is the sugar found in milk.)

Which of these is rich in unsaturated fats? a. beef fat b. lard c. a fat that is solid at room temperature d. olive oil e. butter

d. olive oil (Olive oil is a plant oil, and most plant oils are rich in unsaturated fats.)

Tertiary structure is NOT directly dependent on _____________. a. bonds between sulfur atoms b. ionic bonds c. hydrogen bonds d. peptide bonds e. hydrophobic interactions

d. peptide bonds (Peptide bonds link together the amino acids of a protein's primary structure.)

The secondary structure of a protein results from ______________.

hydrogen bonds (Electronegative oxygen and nitrogen atoms leave hydrogen atoms with partial positive charges.)

The two strands of a DNA double helix are held together by ______________ that form between pairs of nitrogenous bases.

hydrogen bonds (Nitrogenous base pairs are joined by hydrogen bonds.)

glucose + glucose —> _____________ by _________________.

maltose + water ... dehydration synthesis

A molecule with the chemical formula C6H12O6 is probably a _____________.

monosaccharide

Propanol and isopropanol are isomers. This means that they have

the same molecular formula but different structural arrangements.