Learning Objectives
1. Describe the general function of DNA.
DNA (Deoxyribonucleic Acid) functions as the genetic blueprint of living organisms, storing the information necessary for the construction, regulation, and inheritance of biological traits. It encodes instructions for synthesizing proteins and regulates various cellular processes.
2. Name the parts of a nucleotide.
A nucleotide, the basic unit of DNA, comprises three components: a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
3. Identify which parts of a nucleotide are involved in phosphodiester bonds & hydrogen bonds.
Phosphodiester bonds link the sugar of one nucleotide to the phosphate group of another, forming the DNA backbone. Hydrogen bonds occur between nitrogenous bases across opposite strands, connecting them (adenine to thymine and cytosine to guanine).
4. Use the sequence of one DNA strand to predict the sequence of its complementary strand.
Given the sequence of one DNA strand, the complementary strand can be determined using base-pairing rules: adenine pairs with thymine and cytosine pairs with guanine. For example, if one strand is 5’-AGTC-3’, the complement is 3’-TCAG-5’.
5. Name the functional groups found at the 5’ & 3’ ends of a DNA strand.
The 5’ end of a DNA strand contains a phosphate group attached to the 5’ carbon of the deoxyribose sugar. The 3’ end has a hydroxyl group (-OH) attached to the 3’ carbon of the sugar.
6. Explain the importance of the 3’ end of a DNA strand in the process of DNA replication.
During DNA replication, DNA polymerases can only add nucleotides to the 3’ end of a strand. This directionality (5’ to 3’ synthesis) is crucial for the accurate and efficient replication of the DNA molecule.
7. Explain what is meant by “semiconservative replication”.
Semiconservative replication refers to the process in which each strand of the original DNA molecule serves as a template for a new strand. As a result, each new DNA molecule consists of one original and one newly synthesized strand.
8. Describe the role of origins of replication, replication bubbles, and replication forks in the process of DNA replication.
DNA replication begins at specific locations called origins of replication. At these sites, the DNA unwinds, forming replication bubbles. Within each bubble, replication forks are the areas where the DNA strands are actively being separated and copied, moving outward as replication progresses.
9. Describe the role of each of the major enzymes involved in DNA replication.
- DNA Helicase: Unwinds the DNA double helix.
- Primase: Synthesizes RNA primers to initiate replication.
- DNA Polymerase III: Adds nucleotides to a growing DNA strand.
- DNA Polymerase I: Replaces RNA primers with DNA.
- Ligase: Joins Okazaki fragments on the lagging strand.
10. Explain why the leading strand of DNA is made continuously while the lagging strand is not.
The leading strand is synthesized continuously because it is oriented in the 5’ to 3’ direction, parallel to the replication fork movement. The lagging strand, oriented in the 3’ to 5’ direction, is synthesized in short segments called Okazaki fragments, as it runs opposite to the fork movement.
11. Describe the roles of DNA Polymerase III & nucleotide excision enzymes in ensuring the quality of copied DNA.
DNA Polymerase III synthesizes new DNA strands and has a proofreading function to correct errors. Nucleotide excision enzymes identify and remove damaged or erroneous sections of DNA, which are then accurately replaced by DNA polymerase, ensuring the integrity of the copied DNA.