C4,16,17 Central Dogma of Molecular Biology: DNA, RNA, and Protein Synthesis

Unit 2: Central Dogma and Regulation

Central Dogma of Molecular Biology

The central dogma of molecular biology describes the flow of genetic information within a biological system. It explains how genetic information is transferred from DNA to RNA and then to proteins, which ultimately determine the phenotype of an organism.

• DNA (Deoxyribonucleic Acid): Stores genetic information in the nucleus.

• RNA (Ribonucleic Acid): Acts as a messenger, carrying instructions from DNA for protein synthesis.

• Proteins: Functional molecules that perform a wide range of biological activities and determine phenotype.

Summary of the Central Dogma:

• DNA → RNA → Protein

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• Translation: mRNA is translated into a polypeptide (protein) at the ribosome.

Nucleic Acids: DNA and RNA

Nucleic acids are polymers made up of nucleotide monomers. There are two main types: DNA and RNA.

• Nucleotides: The building blocks of nucleic acids, each consisting of a phosphate group, a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

• DNA: Double-stranded, contains the bases adenine (A), thymine (T), cytosine (C), and guanine (G).

• RNA: Single-stranded, contains the bases adenine (A), uracil (U), cytosine (C), and guanine (G).

Example: The phosphate group (PO43−) is a key component of the nucleotide structure, linking the sugars of adjacent nucleotides to form the backbone of DNA and RNA.

From DNA to Protein: The Flow of Genetic Information

Genetic information is stored in the DNA within the nucleus. This information is transcribed into mRNA, which exits the nucleus and is translated by ribosomes in the cytoplasm to synthesize proteins.

• Transcription: The process by which a segment of DNA is copied into mRNA by the enzyme RNA polymerase.

• Translation: The process by which ribosomes read the mRNA sequence and assemble the corresponding amino acids into a polypeptide chain (protein).

• Ribosome: The molecular machine in the cytoplasm where protein synthesis occurs.

Example: In eukaryotic cells, DNA is found in the nucleus. mRNA is synthesized in the nucleus and then transported to the cytoplasm, where ribosomes translate the mRNA into protein.

Polypeptides and Proteins

Polypeptides are chains of amino acids linked by peptide bonds. When one or more polypeptides fold into a specific three-dimensional structure, they form a functional protein.

• Amino Acids: The monomers that make up polypeptides and proteins. There are 20 standard amino acids, each with a unique side chain (R group).

• Peptide Bond: A covalent bond formed between the amino group of one amino acid and the carboxyl group of another.

• Proteins: Perform a variety of functions, including catalysis (enzymes), structural support, transport, and regulation.

Example: Hemoglobin is a protein composed of four polypeptide subunits, each containing an iron atom that binds oxygen for transport in the blood.

Relationship to Phenotype

The sequence of nucleotides in DNA determines the sequence of amino acids in proteins, which in turn determines the structure and function of those proteins. The collective activities of proteins in a cell or organism result in the observable characteristics, or phenotype.

• Genotype: The genetic makeup of an organism (DNA sequence).

• Phenotype: The observable traits or characteristics of an organism, resulting from the interaction of its genotype with the environment.

Example: A mutation in the DNA sequence can lead to a change in the amino acid sequence of a protein, potentially altering its function and affecting the phenotype.