SCI260 – Introduction to Biochemistry Lesson #9 (1) Which of the double-stranded DNA sequences below will require more heat to separate the two strands (select Option A or Option B)? (2) Why is more heat is required to separate the strands? Option A 5’-GGACTCCCGGGTGAG-3’ 3’-CCTGAGGGCCCACTC-5’ Option B 5’-AACTGTTTAAAGACA-3’ 3’-TTGACAAATTTCTGT-5’ (3) What will be the mRNA sequence that is produced during the transcription of the DNA sequence below? Hint: As we discussed in class, there is a slight difference in the nucleotides used in DNA vs RNA. 5’-ACGTCAGGTTTCCGT-3’ (4) Based on what was discussed in Lecture 9, name four (4) enzymes/proteins that play a role in human DNA replication, and briefly describe the specific role each plays during human DNA replication. You may use the internet and/or your textbook to assist you. Each answer is worth 25 points (be sure to answer ALL four questions) giving you a maximum total of 100 points for this assignment. Please DO NOT copy your answers directly from the textbook or the internet.

According to the double-stranded DNA sequences provided, Option A (5’-GGACTCCCGGGTGAG-3’ and 3’-CCTGAGGGCCCACTC-5’) will require more heat to separate the two strands compared to Option B (5’-AACTGTTTAAAGACA-3’ and 3’-TTGACAAATTTCTGT-5’).

The reason more heat is required to separate the strands in Option A is due to the presence of a higher number of guanine (G) and cytosine (C) base pairs in Option A compared to Option B. G-C base pairs have three hydrogen bonds, whereas adenine (A) and thymine (T) base pairs only have two hydrogen bonds. The higher number of G-C base pairs in Option A makes the hydrogen bonds between the strands stronger, requiring more heat energy to break them and separate the strands. Therefore, the presence of more G-C base pairs in Option A increases the stability of the DNA helix, leading to higher heat requirements for strand separation.

The mRNA sequence that will be produced during the transcription of the DNA sequence 5’-ACGTCAGGTTTCCGT-3’ can be determined by replacing each DNA nucleotide with its complementary RNA nucleotide. In RNA, uracil (U) replaces thymine (T). Thus, the mRNA sequence would be 3’-UGCAGUCCAAAAGCA-5’.

Four enzymes/proteins that play a role in human DNA replication are DNA polymerase, primase, helicase, and ligase.

1. DNA polymerase: DNA polymerase is responsible for synthesizing a new complementary DNA strand during replication. It uses the existing DNA strand as a template and adds complementary nucleotides to the growing DNA chain. DNA polymerase also proofreads the newly synthesized DNA strand to ensure accuracy.

2. Primase: Primase is an enzyme that synthesizes RNA primers during DNA replication. These RNA primers serve as a starting point for DNA polymerase to begin synthesizing the new DNA strand.

3. Helicase: Helicase is responsible for unwinding and separating the DNA strands at the replication fork. It breaks the hydrogen bonds between the base pairs, allowing DNA polymerase to access the template strand and synthesize a new complementary strand.

4. Ligase: Ligase is an enzyme that joins the Okazaki fragments on the lagging strand during DNA replication. The lagging strand is synthesized in short segments called Okazaki fragments, and ligase helps to seal the gaps between these fragments, creating a continuous DNA strand.

In summary, DNA polymerase is responsible for synthesizing a new DNA strand, primase synthesizes RNA primers, helicase unwinds the DNA strands, and ligase joins the Okazaki fragments. These enzymes play crucial roles in the replication of human DNA.

In order to answer these questions, it is important to understand the concepts of DNA replication, transcription, and base pairing in DNA and RNA. Additionally, knowledge of the specific functions of enzymes involved in DNA replication is required.