Biochemistry

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GRE Subject Test: Chemistry › Biochemistry

Questions 1 - 10
1

How many water molecules are lost from the condensation of 100 amino acids into a polypeptide?

Explanation

A peptide bond is formed via the condensation of one amino acid's alpha-carboxy group with the alpha-amino group of another amino acid. Thus, the joining together of two amino acids results in the loss of one water molecule. Likewise, joining three amino acids together results in the loss of two water molecules. Following this pattern, we can conclude that the number of water molecules lost is equal to the number of amino acids joined together, minus 1. Therefore, the joining together of 100 amino acids results in the loss of 99 water molecules.

2

How many water molecules are lost from the condensation of 100 amino acids into a polypeptide?

Explanation

A peptide bond is formed via the condensation of one amino acid's alpha-carboxy group with the alpha-amino group of another amino acid. Thus, the joining together of two amino acids results in the loss of one water molecule. Likewise, joining three amino acids together results in the loss of two water molecules. Following this pattern, we can conclude that the number of water molecules lost is equal to the number of amino acids joined together, minus 1. Therefore, the joining together of 100 amino acids results in the loss of 99 water molecules.

3

Which type of bond is created between carbohydrates and the sidechain amine of select asparagine residues in proteins?

N-glycosidic

O-glycosidic

Both are correct

Neither is correct

Explanation

A glycosidic bond covalently joins a carbohydrate molecule to another molecule. An O-glycosidic bond is a covalent linkage between a carbohydrate and a protein, joining a serine or threonine hydroxyl side chain and a sugar (oxygen in the bond yields "O"). An N-glycosidic linkage involves bonding of a carbohydrate and a protein, joining an asparagine side chain amide and a sugar (nitrogen in the bond yields "N"). Thus, N-glycosidic is the correct answer.

4

Which type of bond is created between carbohydrates and the sidechain amine of select asparagine residues in proteins?

N-glycosidic

O-glycosidic

Both are correct

Neither is correct

Explanation

A glycosidic bond covalently joins a carbohydrate molecule to another molecule. An O-glycosidic bond is a covalent linkage between a carbohydrate and a protein, joining a serine or threonine hydroxyl side chain and a sugar (oxygen in the bond yields "O"). An N-glycosidic linkage involves bonding of a carbohydrate and a protein, joining an asparagine side chain amide and a sugar (nitrogen in the bond yields "N"). Thus, N-glycosidic is the correct answer.

5

Which of the following will you most likely find in a steroid molecule?

Cyclohexane ring

Phosphate group

Pentose sugar

Nitrogenous base

Explanation

Steroids are a type of lipid that are characterized by their four-ring molecular structure. The four rings consist of three six-membered rings and one five-membered ring. Recall that six-membered rings are called cyclohexanes and five-membered rings are called cyclopentanes; therefore, you will most likely find a cyclohexane in a steroid.

Phosphate groups, pentose sugars, and nitrogenous bases are found in nucleotides, which are monomers that make up nucleic acids. Steroids are a type of lipid; therefore, you will most likely not find these substances in a steroid.

6

Which of the following will you most likely find in a steroid molecule?

Cyclohexane ring

Phosphate group

Pentose sugar

Nitrogenous base

Explanation

Steroids are a type of lipid that are characterized by their four-ring molecular structure. The four rings consist of three six-membered rings and one five-membered ring. Recall that six-membered rings are called cyclohexanes and five-membered rings are called cyclopentanes; therefore, you will most likely find a cyclohexane in a steroid.

Phosphate groups, pentose sugars, and nitrogenous bases are found in nucleotides, which are monomers that make up nucleic acids. Steroids are a type of lipid; therefore, you will most likely not find these substances in a steroid.

7

Of the following groups of nitrogenous bases, which does not contain a purine?

Cytosine, thymine, uracil

Thymine, adenine, cytosine

Adenine, guanine, thymine

Guanine, uracil, adenine

Cytosine, thymine, guanine

Explanation

We can use the mnemonic "PurAG" to remember that the purines are adenine and guanine. The only choice that does not contain a purine, therefore, is "cytosine, thymine, and uracil." Remember, pyrimidines contain a single ring, while purines have two.

8

Of the following groups of nitrogenous bases, which does not contain a purine?

Cytosine, thymine, uracil

Thymine, adenine, cytosine

Adenine, guanine, thymine

Guanine, uracil, adenine

Cytosine, thymine, guanine

Explanation

We can use the mnemonic "PurAG" to remember that the purines are adenine and guanine. The only choice that does not contain a purine, therefore, is "cytosine, thymine, and uracil." Remember, pyrimidines contain a single ring, while purines have two.

9

Cellulose is a polymer that is composed of what monomer?

Glucose

Fructose

Galactose

Glycerol

Glycogen

Explanation

Cellulose is a polysaccharide (a sugar). Glucose is the monosaccharide used to generate the structure of cellulose via linkages. Cellulose is composed of several hundred glucose molecules bound in this chain. Due to the nature of the beta linkage, humans cannot digest cellulose.

10

Cellulose is a polymer that is composed of what monomer?

Glucose

Fructose

Galactose

Glycerol

Glycogen

Explanation

Cellulose is a polysaccharide (a sugar). Glucose is the monosaccharide used to generate the structure of cellulose via linkages. Cellulose is composed of several hundred glucose molecules bound in this chain. Due to the nature of the beta linkage, humans cannot digest cellulose.

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