DNA Replication and Key Enzymes

DNA Replication & Key Enzymes

• DNA Polymerase III is the primary enzyme for adding nucleotides in the 5' to 3' direction during DNA replication.
• DNA Polymerase I removes RNA primers and replaces them with DNA nucleotides, and also corrects errors via proofreading.
• Nuclease removes damaged or incorrect nucleotides from DNA, playing a role in proofreading and repair.
• Helicase unzips DNA by breaking hydrogen bonds between base pairs, creating a replication fork.
• DNA Ligase seals gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds, ensuring a continuous strand.
• Primase synthesizes short RNA primers, which act as starting points for DNA Polymerase III.
• Topoisomerase prevents DNA from supercoiling ahead of the replication fork by cutting and rejoining DNA strands.

Matching a DNA Sequence in the 5' to 3' Direction

• Adenine (A) pairs with Thymine (T).
• Cytosine (C) pairs with Guanine (G).
• Original strand (3' → 5'): TACGGCAT.
• Complementary strand (5' → 3'): ATGCCGTA.

DNA Structure

• DNA has a double helix structure with two nucleotide strands twisted around each other.
• Nucleotides consist of a phosphate group, a deoxyribose sugar (5-carbon sugar), and a nitrogenous base (A, T, C, or G).
• Phosphodiester bonds link the 5' carbon of one nucleotide's sugar to the 3' carbon of the next.
• Hydrogen bonds hold base pairs together; A-T has 2 bonds and C-G has 3 bonds.

Virus Reproduction: Lytic vs. Lysogenic Cycle

• The lytic cycle is fast and destructive.
• The Lytic Cycle involves the virus injecting DNA into the host, the host replicating viral DNA, new viruses assembling, and the host cell lysing (bursting).
• Examples of viruses that reproduce via the lytic cycle: Influenza and COVID-19
• The lysogenic cycle is hidden and long-term.
• The Lysogenic Cycle involves viral DNA integrating into the host genome (becoming a prophage) and remaining dormant until triggered to enter the lytic cycle.
• Examples of viruses that reproduce via the lysogenic cycle: HIV and Herpes

Graphing Viral/Bacterial Growth

• Viruses and bacteria exhibit exponential growth through rapid reproduction.
• The rate of reproduction is represented by the slope of the growth graph.
• Bacterial growth phases: Lag Phase → Exponential Phase → Stationary Phase → Death Phase.