Question

19 multiple choice 1 point
thymine dimers are formed due to exposure to
ultraviolet radiation
free radical damage
preservatives
genetically modified foods
20 multiple choice 1 point
which type of enzyme can repair dna errors during replication in eukaryotes?
dna polymerase
dna ligase
phosphodiesterase
rna primase

Explanation:

• Question 19: Thymine dimers are formed when adjacent thymine bases in DNA are covalently linked due to exposure to ultraviolet (UV) radiation. UV radiation can cause this type of DNA damage. Free radical damage can cause various types of DNA damage (e.g., base oxidation), but not specifically thymine dimers. Preservatives and genetically modified foods are not the cause of thymine dimer formation.
• Question 20: DNA polymerase has a proof - reading activity. During DNA replication in eukaryotes, when an incorrect nucleotide is added, DNA polymerase can recognize the mis - pair (using its 3' - 5' exonuclease activity) and remove the incorrect nucleotide. DNA ligase is involved in joining Okazaki fragments (in lagging strand synthesis) by forming phosphodiester bonds between adjacent nucleotides. Phosphodiesterase breaks phosphodiester bonds (e.g., in cAMP breakdown). RNA primase is involved in synthesizing RNA primers for DNA replication initiation.

Answer:

1. ultraviolet radiation
2. DNA polymerase