Question

How is genetic information encoded in a DNA molecule?

Short answer

Short Answer: Genetic information is encoded in a DNA molecule through the linear sequence of nucleotide bases (A, T, C, G). This sequence determines the genetic code, with each set of three nucleotides (codon) corresponding to a specific amino acid. The information in the DNA is first transcribed into mRNA and then translated into proteins by matching codons to anticodons of tRNA molecules, ensuring the correct sequence of amino acids in the resulting protein.

Step-by-step solution

Understand the Structure of a DNA Molecule

A DNA molecule is a long, double-stranded molecule made up of smaller units called nucleotides. Each nucleotide consists of three parts: a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base. There are four different bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These bases pair up in specific ways - A with T and C with G - forming base pairs which make up the "rungs" of the DNA double helix.

Explain How Genetic Information is Encoded in the Sequence of Nucleotides

The genetic information in a DNA molecule is encoded within the linear sequence of nucleotides. The order of the bases (A, T, C, G) in a DNA molecule determines the specific genetic code. Each set of three nucleotides, called a codon, corresponds to a particular amino acid. For example, the codon ATG codes for the amino acid methionine.

Describe the Process of Transcription

In order for genetic information to be used for protein synthesis, the information encoded in the DNA must first be copied, or transcribed, into a molecule of messenger RNA (mRNA). During transcription, one strand of the DNA (the template strand) is used as a template to create a complementary mRNA molecule in a process that is catalyzed by the enzyme RNA polymerase.

Explain the Process of Translation

After transcription, the mRNA molecule leaves the cell nucleus and goes to the cytoplasm, where it binds to a ribosome. Here, the genetic information in the mRNA is translated into a sequence of amino acids, which are then assembled into a protein. During translation, transfer RNA (tRNA) molecules carry specific amino acids to the ribosome. Each tRNA molecule has a specific anticodon that matches a codon on the mRNA, ensuring that the correct amino acid is added to the growing protein chain. In summary, genetic information is encoded in a DNA molecule as a linear sequence of nucleotide bases. This information is then transcribed into mRNA and finally translated into proteins through the processes of transcription and translation.

Key concepts

DNA Structure

DNA, or deoxyribonucleic acid, is the blueprint for all living organisms. It is composed of two strands that wind around each other, forming the iconic double helix. Imagine twisting a ladder until it spirals; that's what the DNA structure looks like. Each 'rung' of this spiral staircase is made up of a pair of nucleotides.

Each nucleotide in the DNA structure includes a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base. Four types of nitrogenous bases are present in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases form pairs - A with T and C with G - creating a strict pairing rule due to their specific chemical structure. This pairing is the critical aspect of DNA's function in encoding genetic information, as the sequence of these bases holds the instructions for building and maintaining an organism.

Nucleotide Sequence

The nucleotide sequence is the order of the nitrogenous bases along a DNA strand, and it's akin to the letters forming sentences in a book. The 'language' of DNA is comprised of only four 'letters': A, T, C, and G. These letters combine in various ways to encode genetic instructions. Each group of three bases, or a codon, specifies a particular amino acid—the building block of proteins. For instance, the codon ATG is a command for the amino acid methionine. This language, read in groups of three, dictates how amino acids should be assembled to create proteins that perform critical functions. Genetic information is effectively written in this concise genetic code within the long DNA molecules found in every cell.

Transcription

Transcription is the first step in the journey from DNA to proteins. It's like copying a critical page out of an extensive archive so that it can be used. During transcription, an enzyme called RNA polymerase reads one strand of the DNA, known as the template strand, and synthesizes a complementary strand of messenger RNA (mRNA).

As the enzyme moves along the DNA, it unwinds the double helix and composes a strand of mRNA by matching each DNA base with its counterpart - except in RNA, uracil (U) replaces thymine. This mRNA strand then detaches from the DNA once the gene is fully transcribed, leaving the DNA intact and ready to be transcribed again whenever the cell needs more of the encoded protein.

Translation

In translation, the cell interprets the genetic 'sentences' composed during transcription and uses them to assemble amino acids into proteins. This takes place in the cell's cytoplasm, where ribosomes act as microscopic factories.

Transfer RNA (tRNA) molecules transport specific amino acids to the ribosome. Each tRNA has an anticodon that pairs with a corresponding codon on the mRNA strand. When a tRNA anticodon and an mRNA codon form base pairs, the tRNA deposits its amino acid, which is linked to create a protein chain. This process continues until a stop codon is reached, signaling the end of protein synthesis. The resulting chain of amino acids then folds into a three-dimensional shape to function as a completed protein.