Unit 6 AP Biology Gene Expression and Regulation

Enzymes responsible for synthesis of new DNA

• Helicase

• Ligase

• Polymerase

• Topoisomerase

Answer explanation

DNA polymerase synthesizes the new DNA strand. It will bind to an open 3’ end to add the next nucleotide to the polynucleotide strand. Recall, enzymes tell you what they do… DNA polymerase makes a DNA polymer.

How is DNA replicated?

• Conservative

• Dispersive

• Lagging

• Semiconservative

Answer explanation

The parent strand of DNA separates to provide a template strand for base pairing. The two separate strands base pair to synthesize the daughter strand. Each daughter strand has one parent strand (old) and one daughter strand (new) so the original sequence is conserved. 

DNA polymerase can start replication independently 

• True

• False

Answer explanation

DNA polymerase requires an open 3’ end for synthesis. Primase will synthesize an RNA primer of 5-10 RNA nucleotides before the DNA strand.

Which direction is DNA synthesized?

• 3’ to 5’

• 5’ to 3’

• Right to Left

• Left to Right

Answer explanation

DNA is antiparallel, so it is synthesized 5' -> 3’ and read 3' -> 5’. Recall the 5’ end is the phosphate group and the 3’ end is the hydroxyl of the deoxyribose.

Which RNA has the codons sequence for translation?

• mRNA

• rRNA

• tRNA

Answer explanation

mRNA is the messenger RNA. It is a transcript of the DNA to carry to message to the ribosome for protein synthesis. The triplet code of nucleotides on the mRNA is called a codon.

Which bases are pyrimidines?

• Adenine and Cytosine

• Adenine and Guanine

• Cytosine and Guanine

• Cytosine and Thymine

Answer explanation

Nucleotides are made up of pentose sugar, nitrogenous base, and phosphate group. There are two types of nitrogenous bases: purine (double-ring) and pyrimidine (single-ring). Adenine & Guanine are Purines and Cytosine, Uracil, and Thymine are Pyrimidines.

Which enzyme is responsible for transcription?

• Ligase

• Primase

• RNA Polymerase

• Transcriptase

Answer explanation

RNA Polymerase is an enzyme that binds to the DNA and synthesizes a RNA strand. Remember: enzymes tell you what they do. RNA Polymerase makes an RNA polymer.

Which strand is read for transcription?

• 3’ to 5’ coding strand

• 5’ to 3’ coding strand

• 3’ to 5’ noncoding strand

• 5’ to 3’ noncoding strand

Answer explanation

DNA and RNA are antiparallel, so the DNA is read 5’ to 3’ and the RNA is synthesized 3’ to 5’. Note: the DNA template strand can be called 4 different names: noncoding strand, minus strand, or antisense strand.

Contrast amount of DNA between prokaryotes and eukaryotes.

• Eukaryotes have multiple DNA strands while prokaryotes have one DNA strand

• Prokaryotes have multiple DNA strands while eukaryotes have one DNA strand

Answer explanation

The DNA structure differs between prokaryotes and eukaryotes. Prokaryotes have a single circular DNA strand while eukaryotes have multiple linear DNA strands. Prokaryotes store theirs in the nucleoid while eukaryotes store theirs in the nucleus.

Which strand is formed continuously into the replication fork?

• Lagging strand

• Leading strand

Answer explanation

The leading strand is synthesized continuously. This strand is synthesized towards the replication fork. DNA is antiparallel so moving in one direction, one strand will be in the correct orientation of 3’ to 5’ while the other strand will be "backwards" in the 5’ to 3’ orientation.