Question

Explain how complementary base pairing is responsible for a. the structure of the DNA double helix. b. DNA replication. c. transcription of RNA from DNA. d. the attachment of mRNA to a ribosome. e. codon/anticodon pairing. f. tRNA conformation.

Short answer

Complementary base pairing is crucial for the basic processes of genetics. It forms the basis of DNA's double-helical structure, enables the creation of identical DNA copies during replication, and allows the transcription of RNA from DNA. During protein synthesis, mRNA binds to ribosomes and tRNA molecules interpret the mRNA's codons through complementary anticodon pairing, resulting in the formation of a specific peptide chain. The structure of the tRNA molecule is also a result of specific internal base pairing.

Step-by-step solution

Understand the role in DNA structure

Due to the base pairing rules, Adenine (A) always pairs with Thymine (T) and Cytosine (C) with Guanine (G) in DNA. So, the two strands of the DNA molecule are held together by these complementary base pairs, which form hydrogen bonds. It's this specific pairing that causes the double helix structure.

Examine DNA replication

During DNA replication, the double-helix molecule unwinds and the two strands separate. Each original strand serves as a template for a new strand. The new strand is formed by adding nucleotides that are complementary to the template strand, demonstrating the role of base pairing in DNA replication.

Discuss the process of transcription

Transcription is the process of creating an RNA molecule from a DNA template. The complementary base pairing allows RNA polymerase to match Adenine (A) with Uracil (U) and Guanine (G) with Cytosine (C), creating a messenger RNA (mRNA) which is a complementary copy of the DNA strand.

Relation to mRNA and ribosome interaction

During protein synthesis, mRNA attaches to the ribosome. Each codon (triplet of nucleotides) on the mRNA molecule is recognized by its complementary anticodon on a transfer RNA (tRNA) molecule. This shows how complementary base pairing is responsible for mRNA-ribosome interaction.

Explain codon/anticodon pairing

Each codon in the mRNA molecule pairs with its complementary anticodon in the tRNA molecule during protein synthesis. This means each amino acid brought to the ribosome by tRNA is specifically selected according to this codon/anticodon complementary base pairing.

Justify tRNA conformation

In tRNA, specific bases complement and bind to each other, this allows the tRNA strand to fold in a specific 'cloverleaf' shape necessary for its function. The correct structure is achieved and maintained through this base complementarity, which dictates the tRNA conformation, thereby enabling the attachment of a specific amino acid and the anticodon recognition of mRNA codons.

Key concepts

DNA Structure

DNA, or deoxyribonucleic acid, forms the blueprint for all living organisms. At the heart of DNA's structure is complementary base pairing, a concept crucial for its iconic double helix shape.
Within this double helix, the two DNA strands run in opposite directions and are held together by hydrogen bonds. These bonds occur between specific pairs of nitrogenous bases: adenine (A) paired with thymine (T) and cytosine (C) with guanine (G).

• This pairing is complementary because of the specific shape and hydrogen binding potential of each base.
• This specificity ensures that the two strands of DNA are mirrored in terms of base pairing, maintaining a consistent width of the helix.

The specific order of these bases along a DNA strand constitutes the genetic code, enabling the storage of information necessary for life.

DNA Replication

DNA replication is the process through which a cell copies its DNA before cell division, ensuring each new cell has a complete set of genetic instructions.
Complementary base pairing plays a fundamental role in this process.

• It begins with the unwinding of the double helix, separating the two strands.
• Each original strand serves as a template for the creation of a new complementary strand.

New nucleotides are added by DNA polymerase, matching adenine to thymine and cytosine to guanine, faithfully replicating the original DNA sequence.
This ensures that each new DNA molecule is a perfect copy of the original, maintaining genetic consistency.

Transcription

Transcription is the process of creating an RNA molecule from a DNA template, a critical step in expressing genes. During transcription, an enzyme called RNA polymerase plays a major role.

• It separates a section of the DNA to access the template strand.
• RNA polymerase then matches RNA nucleotides with their complementary DNA bases.

Adenine (A) pairs with uracil (U) in RNA (instead of thymine), and cytosine continues to pair with guanine. The result is a single-stranded messenger RNA (mRNA) molecule, comprising a sequence complementary to the DNA template.
This RNA will exit the nucleus to guide protein synthesis in the process called translation.

Codon-Anticodon Interaction

Protein synthesis requires precise interpretation of mRNA, which is accomplished through codon-anticodon interactions.
Each sequence of three bases on mRNA, called a codon, is matched with an anticodon on transfer RNA (tRNA).

• tRNA molecules each carry specific amino acids, which they bring to the growing protein chain at the ribosome.
• These anticodons are complementary to the mRNA codons, ensuring precise pairing.

This base pairing dictates the sequence of amino acids in the protein, cementing the importance of accurate codon-anticodon interactions in protein synthesis.

tRNA Conformation

tRNAs are small RNA molecules that assist in translating genetic code into proteins by carrying amino acids.
Their conformation is crucial for their function: they must fit into ribosomes and bind correctly to mRNA.

• Complementary base pairing within the tRNA itself helps it fold into its functional 'cloverleaf' shape.
• This shape is stabilized by hydrogen bonds between bases at various points along the tRNA molecule.

The specific folding also positions the anticodon so it can effectively pair with mRNA codons, and aligns the amino acid for incorporation into a growing protein chain.
This conformation is key to the tRNA's role in protein synthesis, demonstrating the importance of internal base pairing.