Nucleic Acids & The Flow of Genetic Information: Protein Synthesis

Nucleic Acids & The Flow of Genetic Information

Introduction

Nucleic acids are essential biomolecules responsible for the storage, transmission, and expression of genetic information in all living organisms. The flow of genetic information, often referred to as the "central dogma" of molecular biology, describes how genetic information is transferred from DNA to RNA to protein, ultimately determining cellular structure and function.

4 Main Classes of Biomolecules

Overview of Biomolecules

• Carbohydrates: Serve as energy sources and structural components. Some are polymers (e.g., starch), composed of monosaccharide monomers.

• Lipids: Primarily non-polymeric molecules involved in energy storage, membrane structure, and signaling. No true monomer.

• Proteins: Polymers made of amino acid monomers. Function as enzymes, structural elements, and signaling molecules.

• Nucleic Acids: Polymers composed of nucleotide monomers. Store and transmit genetic information.

Class	Polymer?	Monomer
Carbohydrates	SOME	Monosaccharides
Lipids	NO	N/A
Proteins	ALL	Amino acids
Nucleic Acids	ALL	Nucleotides

Nucleic Acids

Functions of Nucleic Acids

• Storage of genetic information: DNA stores hereditary information in the form of genes.

• Transmission of genetic information: DNA is replicated and passed to offspring.

• Expression of genetic information: RNA molecules help translate genetic code into proteins.

• Energy transfer: Nucleotides such as ATP act as cellular energy currency.

Types of Nucleic Acids

• Deoxyribonucleic Acid (DNA): Double-stranded polymer that stores genetic information.

• Ribonucleic Acid (RNA): Single-stranded polymer involved in protein synthesis and gene regulation.

Organization of Nucleotides & Nucleic Acids

• Nucleotide: The monomer of nucleic acids, composed of three parts:

  • Nitrogenous base (adenine, guanine, cytosine, thymine/uracil)

  • Pentose sugar (deoxyribose in DNA, ribose in RNA)

  • Phosphate group

• Nucleic acids: Polymers made of nucleotide monomers linked by phosphodiester bonds.

• ATP (Adenosine Triphosphate): A nucleotide that serves as the primary energy carrier in cells.

DNA vs RNA

Structural and Functional Differences

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, G, C, T	A, G, C, U
Strands	Double-stranded (double helix)	Single-stranded
Function	Stores genetic information	Various roles in gene expression and protein synthesis

DNA Structure

• Double helix held together by hydrogen bonds between complementary bases.

• Base pairing rules:

  • Adenine (A) pairs with Thymine (T)

  • Guanine (G) pairs with Cytosine (C)

• Backbone consists of alternating sugar and phosphate groups.

RNA Structure

• Single-stranded, but can fold into complex 3D shapes.

• Contains uracil (U) instead of thymine (T).

• Functions include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

The Flow of Genetic Information: Protein Synthesis

Overview

The process by which genetic information is used to synthesize proteins involves two main steps: transcription and translation. This flow is often summarized as "DNA → RNA → Protein." Each step is essential for the accurate expression of genetic information.

Step 1: Transcription

• Genetic information is transferred from DNA to messenger RNA (mRNA).

• Occurs in the nucleus (in eukaryotes).

• Only one DNA strand (the template strand) is used to synthesize a complementary mRNA strand.

• Base pairing rules for transcription:

  • A (DNA) pairs with U (RNA)

  • T (DNA) pairs with A (RNA)

  • G (DNA) pairs with C (RNA)

  • C (DNA) pairs with G (RNA)

• Example: DNA sequence: TAC GCT CAA TGG GTC GAG CCT ATT mRNA sequence: AUG CGA GUU ACC CAG CUC GGA UAA

Step 2: Translation

• mRNA is decoded to build a polypeptide (protein) at the ribosome.

• Occurs in the cytoplasm.

• mRNA codons (groups of three nucleotides) specify amino acids.

• Transfer RNA (tRNA) molecules bring amino acids to the ribosome, matching their anticodon to the mRNA codon.

• Ribosomes catalyze the formation of peptide bonds between amino acids.

• Translation continues until a stop codon (UAA, UAG, UGA) is reached.

• Example: mRNA codons: AUG CGA GUU ACC CAG CUC GGA UAA Amino acid sequence: Met - Arg - Val - Thr - Gln - Leu - Gly

Types of RNA and Their Functions

Type	Function
mRNA (Messenger RNA)	Encodes the sequence of amino acids in a protein
tRNA (Transfer RNA)	Carries specific amino acids to the ribosome; matches anticodon to mRNA codon
rRNA (Ribosomal RNA)	Forms the core of the ribosome and catalyzes peptide bond formation

Protein Structure and Function

Importance of Protein Shape

• The sequence of DNA determines the sequence of amino acids in a protein.

• The sequence of amino acids determines the protein's 3D shape.

• The shape of a protein determines its function (e.g., enzymes, antibodies, hormones, hemoglobin).

Mutations and Disease

• Mutation: A change in the genetic code (DNA sequence) that can alter the amino acid sequence of a protein.

• Mutations may change protein shape and disrupt normal function, potentially leading to disease (e.g., sickle-cell anemia).

Applications: Gene Therapy and mRNA Vaccines

• Gene therapy: Introducing a functional gene to replace a mutated or missing gene, often using viral vectors.

• mRNA vaccines: Provide instructions for cells to produce a viral protein, stimulating an immune response.

Summary Table: Key Concepts

Concept	Description
DNA	Stores and transmits genetic information
RNA	Transmits and translates genetic information
Nucleotide	Monomer of nucleic acids (phosphate, sugar, base)
Transcription	DNA → mRNA
Translation	mRNA → Protein
Mutation	Change in DNA sequence

Key Equations and Rules

• Base Pairing (DNA): $A = T$ $G = C$

• Base Pairing (RNA): $A = U$ $G = C$

• Central Dogma: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Additional info: The notes also reference the importance of protein folding, the consequences of mutations, and modern applications such as gene therapy and mRNA vaccines, which are highly relevant to current biomedical science.