DNA Structure and Replication

Nucleotides

• Nucleotides are the building blocks of DNA and RNA.
• They consist of a sugar, a phosphate group, and a nitrogenous base.

Complementary Base Pairing

• In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).
• This specific pairing is crucial for DNA replication and function.

DNA Helicase

• DNA helicase unwinds the DNA double helix, separating the two strands.

DNA Polymerase

• DNA polymerase synthesizes new DNA strands by adding nucleotides complementary to the template strand.

DNA Ligase

• DNA ligase joins the Okazaki fragments on the lagging strand during DNA replication.

Recombinant DNA

• Recombinant DNA is DNA that has been created by combining DNA from different sources.

DNA Replication

• DNA replication is the process of making a copy of a DNA molecule.

Semi-Conservative Replication

• DNA replication is semi-conservative because each new DNA molecule consists of one original strand (template) and one new strand.

Three Steps in Semi-Conservative Replication

• Initiation: DNA unwinds and separates into two strands.
• Elongation: New nucleotides are added to each template strand, forming new complementary strands.
• Termination: The process ends, resulting in two identical DNA molecules.

Purpose of DNA Replication

• DNA replication ensures that each daughter cell receives a complete and identical copy of the genetic material.

Site of DNA Replication

• DNA replication occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.

Description of Semi-Conservative DNA Replication

• A process where one original strand is conserved in the new molecule while creating a new strand using the original strand as a template.

Definition of Recombinant DNA

• DNA that has been engineered by combining DNA from different organisms or sources.

Enzymes Involved in Recombinant DNA Production (not exhaustive list)

• Restriction enzymes, DNA ligase, and possibly DNA polymerase.

How Recombinant DNA is Made:

• Detailed diagrams illustrating the creation of recombinant DNA are impractical to include in these study notes.

Amino Acid

• A molecule that is a basic building block for proteins.

Anti-codon

• A sequence of three nucleotides on a tRNA molecule that is complementary to a codon on mRNA.

Codon

• A sequence of three nucleotides on mRNA that codes for a specific amino acid.

DNA Sequence (Genetic Code)

• A sequence of nucleotides in DNA that determines the order of amino acids in proteins.

Elongation

• The process of adding amino acids to a growing polypeptide chain during protein synthesis.

Environmental Mutagen

• An environmental factor that causes changes in DNA.

Genetic Disorder

• An illness caused by mutations in genes.

Initiation

• The process that begins the synthesis of a polypeptide chain from mRNA.

Messenger RNA (mRNA)

• A molecule that carries the genetic code from DNA to the ribosome for protein synthesis.

Mutation

• A change in the DNA sequence that can result in changes in the protein sequence.

Polypeptide Chain

• A chain of amino acids linked together.

Ribosomes

• Cellular structures where proteins are synthesized.

Termination

• The process of ending the synthesis of a polypeptide chain.

Transcription

• The process of copying the genetic code from DNA to mRNA.

Transfer RNA (tRNA)

Translation

• The process of decoding the mRNA sequence into a polypeptide chain.

Three Uses for Recombinant DNA

• Producing pharmaceuticals (e.g., insulin).
• Improving crop yields.
• Preventing diseases.

Determining Amino Acid Sequence from DNA

• Use the genetic code table to convert each three-letter DNA sequence into an amino acid.

Degenerate and Universal Genetic Code

• The code is degenerate because multiple codons may code for the same amino acid, and universal because the same codons code for the same amino acids in almost all organisms.

Complementary Nature of mRNA Codon and tRNA Anti-codon

• The mRNA codon and tRNA anticodon are complementary to each other to ensure the correct amino acid is added to the polypeptide chain.

Examples of Environmental Mutagens

• Examples: Ultraviolet radiation and certain chemicals.

How Mutations Affect Amino Acid Sequence and Genetic Disorders

• Mutations in DNA can alter the sequence within the polypeptide chain and lead to changed protein structure and ultimately genetic disorders.