How Cells Read the Genome: From DNA to Protein

Pathway from DNA to Protein

Overview of the Central Dogma

The central dogma of molecular biology describes the flow of genetic information within a biological system. It outlines how genetic information stored in DNA is transcribed into RNA and then translated into proteins, which perform most cellular functions.

• DNA replication: The process by which DNA makes a copy of itself during cell division.

• Transcription: The synthesis of RNA from a DNA template.

• Translation: The synthesis of proteins from an RNA template.

Key Equation:

$\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$

The Genome and Genes

Structure and Function of the Genome

The genome is the complete set of genetic material in an organism. In humans, only a small fraction of the genome encodes proteins. Genes are specific sequences of DNA that code for functional products, usually proteins.

• Gene mutations: Changes in the DNA sequence of a gene can lead to diseases. For example, mutation in the PLP1 gene causes demyelination disorders, and mutations in the Factor VIII gene cause hemophilia A.

• Protein-coding genes: Not all DNA sequences are genes; only certain regions encode proteins.

Transcription and Translation

Gene Expression: From DNA to RNA to Protein

Gene expression involves two main steps: transcription and translation. Each gene can be transcribed into multiple RNA molecules, which are then translated into proteins.

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

• Translation: The process by which ribosomes synthesize proteins using the sequence encoded in mRNA.

• One gene–one protein: Each gene typically encodes a single protein, but alternative splicing and other mechanisms can increase protein diversity.

RNA: Structure and Types

Properties of RNA

RNA (ribonucleic acid) is a nucleic acid similar to DNA but with several key differences.

• Ribose sugar: RNA contains ribose, whereas DNA contains deoxyribose.

• Uracil: RNA uses uracil (U) instead of thymine (T), which pairs with adenine (A).

• Single-stranded: RNA is usually single-stranded, allowing it to fold into complex shapes.

• Shorter than DNA: RNA molecules are typically much shorter than DNA molecules.

Diagram: The structure of RNA includes a ribose sugar and the base uracil, distinguishing it from DNA.

Comparison of Ribose and Deoxyribose; Uracil and Thymine

• Ribose vs. Deoxyribose: Ribose has a hydroxyl group (-OH) at the 2' carbon, while deoxyribose has a hydrogen (-H) at the same position.

• Uracil vs. Thymine: Uracil lacks the methyl group present in thymine.

Sugar	Used in	Structure
Ribose	RNA	Has -OH at 2' carbon
Deoxyribose	DNA	Has -H at 2' carbon

Base	Used in	Structure
Uracil	RNA	No methyl group
Thymine	DNA	Has methyl group

Summary Table: DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Strandedness	Double-stranded	Single-stranded
Function	Genetic storage	Information transfer, catalysis

Key Terms and Concepts

• Central Dogma: The flow of genetic information from DNA to RNA to protein.

• Gene: A segment of DNA that encodes a functional product, usually a protein.

• Transcription: The process of synthesizing RNA from a DNA template.

• Translation: The process of synthesizing a protein from an mRNA template.

• Codon: A sequence of three nucleotides in mRNA that specifies an amino acid.

• Mutation: A change in the DNA sequence that can affect gene function.

Example: Start Codon

• AUG: The codon for methionine, which also serves as the start signal for translation.

Additional info: The notes above are based on the provided textbook slides and expanded with standard academic context to ensure completeness and clarity for college-level cell biology students.