Nucleic Acids

Introduction to Nucleic Acids

Nucleic acids are essential macromolecules that store and transmit genetic information in living organisms. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• DNA is found in various forms, including chromosomes and plasmids.

• RNA is involved in protein synthesis and gene regulation.

Biological Uses of Nucleic Acids

Nucleic acids play critical roles in the storage, transmission, and expression of genetic information.

• DNA stores genetic information and is found in chromosomes.

• RNA transmits genetic info and is involved in protein synthesis.

• Both DNA and RNA direct the creation of new proteins.

Polymer: Nucleic acids are polymers made of nucleotide monomers.

Monomer: Nucleotide

Three building blocks of nucleotides:

• Phosphate group

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

• Nitrogenous base

Nucleotide Structure

Nucleotides are the building blocks of nucleic acids, each consisting of three components:

• Phosphate group

• Pentose sugar (ribose or deoxyribose)

• Nitrogenous base (Adenine, Thymine, Cytosine, Guanine, Uracil)

Example: ATP (Adenosine Triphosphate) is a nucleotide with three phosphate groups, serving as an energy carrier in cells.

Components of Nucleotides

ATP and Energy

ATP is a multifunctional nucleotide that stores and releases energy for cellular processes.

• Energy is stored in the phosphate bonds.

• Hydrolysis of ATP releases energy:

Building Nucleic Acids

Nucleic acids are formed by joining nucleotides through covalent bonds between the phosphate group of one nucleotide and the sugar of the next.

• Phosphodiester bonds link nucleotides.

• DNA is typically double-stranded; RNA is usually single-stranded.

DNA Structure: The Double Helix

DNA consists of two antiparallel strands forming a double helix, stabilized by hydrogen bonds and base stacking interactions.

• Strands run in opposite directions (antiparallel).

• Complementary base pairing: Adenine pairs with Thymine, Cytosine pairs with Guanine.

• Hydrogen bonds hold the two strands together.

Properties of DNA Double Helix

• Strands are antiparallel.

• Base pairs are complementary.

• Base stacking interactions stabilize the helix.

• Hydrogen bonds between bases hold the strands together.

Types of RNA

There are three main types of RNA, each with distinct functions:

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

• rRNA (ribosomal RNA): Forms the core of ribosome structure and catalyzes protein synthesis.

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information in cells:

• DNA is transcribed into RNA.

• RNA is translated into protein.

Key processes: Transcription, Translation, Replication

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein.

• Involves transcription (DNA to RNA) and translation (RNA to protein).

• Proteins are folded into specific shapes to perform cellular functions.

Proteins

Protein Functions

Proteins are versatile macromolecules that perform a wide range of functions in cells.

• Enzymes: Catalyze biochemical reactions (e.g., digestive enzymes).

• Transport proteins: Move substances across membranes (e.g., hemoglobin).

• Storage proteins: Store amino acids or ions (e.g., ferritin).

• Structural proteins: Provide support and shape (e.g., collagen).

• Contractile and motor proteins: Enable movement (e.g., actin, myosin).

• Defensive proteins: Protect against disease (e.g., antibodies).

• Signal proteins: Coordinate cellular activities (e.g., hormones).

Polypeptides and Amino Acids

Proteins are polymers called polypeptides, made from amino acid monomers.

• There are 20 different amino acids, each with a unique side chain (R group).

• Amino acids are grouped as hydrophobic, hydrophilic, polar, or nonpolar based on their side chains.

• Essential amino acids cannot be synthesized by the body and must be obtained from the diet.

Peptide Bonds

Amino acids are linked by peptide bonds to form polypeptides.

• Peptide bond formation involves a dehydration reaction between the amino group of one amino acid and the carboxyl group of another.

• Polypeptides have an N-terminus (free amino group) and a C-terminus (free carboxyl group).

Levels of Protein Structure

Proteins have four levels of structure, each contributing to their function.

• Primary structure: Sequence of amino acids linked by covalent peptide bonds.

• Secondary structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape formed by interactions between R groups (side chains), including hydrophobic interactions, ionic bonds, and disulfide bridges.

• Quaternary structure: Association of multiple polypeptide chains to form a functional protein complex (e.g., hemoglobin).

Protein Denaturation

Proteins can lose their structure and function through denaturation, caused by changes in pH, temperature, or chemical exposure.

• Denaturation disrupts secondary, tertiary, and quaternary structures.

• Denatured proteins are often inactive.

Summary Table: Levels of Protein Structure

Vocabulary

• Genome

• Nucleic acid

• Deoxyribose

• Ribose

• Nucleotide

• Gene expression

• Transcription

• Translation

• Replication

• Polypeptide

• R group

• Peptide bond

• Chaperonin

• Denatured/Renatured

Additional info:

• Chaperonins are proteins that assist in the proper folding of other proteins.

• Protein misfolding can lead to diseases such as sickle-cell anemia.