Key Concepts from Chapter 9: What Genes Are

DNA Structure

• Definition of DNA: Deoxyribonucleic acid, a molecule that carries genetic information.

• Structure:

  • Composed of two parallel strands made up of repeating units called nucleotides.

  • Each nucleotide consists of:

  • Sugar: Deoxyribose

  • Phosphate group

  • Base: One of four types—Adenine (A), Cytosine (C), Guanine (G), Thymine (T).

• Connection:

  • Strands linked by strong covalent bonds between nucleotides.

  • Bases on opposite strands connected by weak hydrogen bonds, allowing strands to separate during replication.

Base-Pairing Rules

• Complementary Base-Pairing:

  • A pairs with T

  • C pairs with G

• Importance:

  • Given one strand's nucleotide sequence, the complementary strand can be determined.

DNA Double Helix

• Shape: Twisted ladder known as the double helix.

  • Ladder Rungs: Base pairs

  • Ladder Sides: Sugar-phosphate backbone

DNA Replication

• Definition: The process of duplicating a DNA molecule.

• Steps:

  1. Unwinding: Special proteins bind to replication origins, unwind the DNA, and break hydrogen bonds.

  2. Synthesis: DNA polymerase constructs a new strand using the original strand as a template; primer is required to start the replication.

  3. Completion: Result is two identical DNA molecules, embodying the concept of semiconservative replication (one old strand and one new strand in each helix).

PCR (Polymerase Chain Reaction)

• Definition: A technique for producing millions of DNA copies quickly.

• Mechanism:

  • Utilizes heat to separate DNA strands.

  • Targeted primers initiate replication at specified locations.

• Result: Amplifies a specific DNA sequence significantly, useful in genetic analysis.

CRISPR-Cas9 Genome Editing Tool

• Definition: A genome-editing technology enabling precise modifications in an organism’s DNA.

• Components:

  • Guide RNA: Directs Cas9 protein to specific DNA sequences.

  • Cas9 Protein: Cuts DNA at targeted locations.

• Applications:

  • Potential to create organ sources for transplantation (e.g., modifying pigs for human compatibility).

  • Ability to inactivate harmful viral DNA, like PERVs in pig cells, allowing safer organ transplants.

Mutations and Repair

• Definition: A mutation is a change in nucleotide sequence that can alter gene function.

• Types of Mutations:

  • Point mutation: Changes in a single nucleotide; can result from substitution, insertion, or deletion.

• Repair Mechanism:

  • DNA polymerase proofreading minimizes errors during replication.

  • Errors, though rare (about one mistake in every billion nucleotides), can occur and may have consequences, such as diseases (e.g., sickle cell disease).

Applications in Medicine

• Xenotransplantation: Transplanting pig organs into humans to solve organ shortages, underpinned by CRISPR technology to ensure organ compatibility and safety by eliminating PERVs.

• Ethical Considerations: The engineering of human organs in pigs raises various bioethical questions and possible implications in genetic research.