Biology Practice Test: DNA Replication and Protein Synthesis

Each original strand serves as a template for a new strand. So both new DNA molecules keep one old strand and gain one newly made strand.

Helicase opens the double helix at the replication fork. DNA polymerase then adds nucleotides to build the new strands.

DNA ligase seals the gaps in the sugar-phosphate backbone between Okazaki fragments. Helicase unwinds DNA but does not join fragments.

The two strands are held together by hydrogen bonds between base pairs, which are weak enough to break during replication and transcription. The strong covalent backbone of each strand stays intact.

RNA uses uracil in place of thymine. Adenine and guanine are found in both DNA and RNA.

G pairs with C, C with G, and A with U, giving CGU. The option CGT contains thymine, which is found in DNA, not in tRNA.

Each codon is three nucleotides and codes for one amino acid, so 300 ÷ 3 = 100. Multiplying by 3 instead of dividing gives the trap answer 900.

Introns are noncoding sections that are cut out during splicing. The exons that remain are joined to form the mature mRNA, which then goes to the ribosomes.

DNA is transcribed into mRNA, and mRNA is translated into protein. This one-way flow is known as the central dogma of molecular biology.

Because the genetic code has several codons for most amino acids, this change is a silent mutation. The protein's amino acid sequence does not change.