AP Bio Insta-Review Topic 1.2

What is at the 5' end of a nucleic acid?

• Carbon

• Hydroxyl

• Nitrogenous Base 

• Phosphate 

Answer explanation

Nucleotides are made of a pentose sugar. Each carbon is numbered, and we use the different numbers to identify the functional groups. 1’ is the nitrogenous base, 3’ is the hydroxyl of the sugar, and 5’ is the phosphate group.

What is at the 3' end of a nucleic acid?

• Carbon

• Hydroxyl

• Nitrogenous Base 

• Phosphate 

Answer explanation

Nucleotides are made of a pentose sugar. Each carbon is numbered, and we use the different numbers to identify the functional groups. 1’ is the nitrogenous base, 3’ is the hydroxyl of the sugar, and 5’ is the phosphate group.

What is the direction of DNA synthesis?

• 3' to 5’

• 5' to 3’

• It's anti-parallel so either direction is correct

Answer explanation

DNA polymerase is the enzyme responsible for DNA synthesis. The enzyme is only able to add to an open 3’ end. This means that it will assemble the new DNA strand in the 5’ to 3’ direction.

What does antiparallel mean in terms of the nucleic acids?

Answer explanation

Antiparallel describes the directionality of the two strands that are complementary base paired. The strands are equidistant (parallel) and in opposite directions (anti). This means that the 5' end is across from a 3' end.

What type of bond is between nitrogenous bases?

• Covalent

• Hydrogen

• Ionic

• Van der Waals

Answer explanation

Hydrogen bonds are between the nitrogenous bases. There are 2 hydrogen bonds between adenine and thymine. There are 3 hydrogen bonds between cytosine and guanine.

Why would a strand with more G/C bonding be more stable than A/T bonding?

Answer explanation

There are 3 hydrogen bonds between G & C while there are 2 hydrogen bonds between A & T. So, if there are more G/C bonding there will be more hydrogen bonds between the nitrogenous bases than if there were more A/T bonding.

Where are new bonds formed in a growing polypeptide?

• Amine group

• Carboxyl group

• Hydrogen

• R-group

Answer explanation

There is an N terminus (amine group) and a C terminus (carboxyl group). The polypeptide is synthesized in the N terminus to C terminus direction. The new bonds will be formed at the C terminus binding to amine group of next amino acid.

What is the bond between amino acids called?

• Ester linkage

• Glycosidic linkage

• Peptide bond

• Phosphodiester linkage

Answer explanation

Peptide bonds are specific covalent bonds between amino acids. This forms between the carboxyl group of one amino acid and the amine group of the next amino acid.

Describe the orientation of the amino acids that form the peptide bond

Answer explanation

The amine group of one amino acid is bonded with a carboxyl group of the next amino acid. The formed bond will look like bond between a carbon double bonded to an oxygen (carboxyl) and to a nitrogen (amine).

What level of protein structure of is described as hydrogen bonds between backbone?

• Primary

• Secondary

• Tertiary

• Quaternary

Answer explanation

Secondary structure is described as the alpha helix or beta pleated sheets resulting from the hydrogen bonds between the backbone of the polypeptide.