Macromolecules in Human Physiology: Proteins and Nucleic Acids

Macromolecules: Proteins and Nucleic Acids

Introduction

Macromolecules are large, complex molecules essential for life. In human physiology, proteins and nucleic acids play critical roles in cellular structure, function, and information storage. This guide covers their structure, function, and the processes by which they are synthesized and broken down.

Proteins

Structure and Function of Proteins

Proteins are polymers made from amino acid monomers. Their structure determines their diverse functions in the body, including catalysis, signaling, structural support, and immune defense.

• Monomers: Amino acids (contain C, H, O, N)

• Peptide: Short chain of amino acids linked together

• Polypeptide: Longer chain of amino acids

• Oligopeptide: Short polypeptide (few amino acids)

• Protein: Polypeptide that folds into a specific 3D shape

Proteins serve as:

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

• Enzymes: Catalyze biochemical reactions (e.g., DNA polymerase)

• Contractile proteins: Enable muscle contraction (e.g., troponin)

• Communication proteins: Transmit signals (e.g., hormones)

• Defensive proteins: Fight infections (e.g., immunoglobulins/antibodies)

Amino Acids: Structure and Types

Amino acids are the building blocks of proteins. Each amino acid has a central carbon atom bonded to:

• Amine group: (-NH2)

• Carboxyl group: (-COOH)

• R group: Side chain that determines the identity and properties of the amino acid

• Hydrogen atom

There are 20 common amino acids, each with a unique R group. Some are essential amino acids that must be obtained from the diet.

Table: Classification of Amino Acids

Type	Examples	Properties
Nonpolar	Alanine, Valine	Hydrophobic
Polar	Serine, Threonine	Hydrophilic
Acidic	Aspartic acid, Glutamic acid	Negatively charged
Basic	Lysine, Arginine	Positively charged
Sulfur-containing	Cysteine, Methionine	Disulfide bonds

Peptide Bond Formation and Breakdown

Amino acids are linked by peptide bonds formed through dehydration synthesis:

• Dehydration synthesis: The carboxyl group of one amino acid bonds to the amine group of another, releasing a water molecule.

Equation:

$ext{Amino acid}_1 + ext{Amino acid}_2 ightarrow ext{Dipeptide} + H_2O$

• Hydrolysis: Peptide bonds are broken by adding water, releasing individual amino acids.

Equation:

$ext{Dipeptide} + H_2O ightarrow ext{Amino acid}_1 + ext{Amino acid}_2$

Levels of Protein Structure

• Primary structure: Sequence of amino acids

• Secondary structure: Folding into alpha helices or beta sheets via hydrogen bonding

• Tertiary structure: 3D folding due to interactions among R groups

• Quaternary structure: Multiple polypeptide chains assembled together (e.g., hemoglobin)

Nucleic Acids

Structure and Function of Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

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

• RNA (Ribonucleic acid): Transfers genetic information and helps synthesize proteins

Nucleotide Structure

Each nucleotide consists of:

• Pentose sugar: Deoxyribose (DNA) or ribose (RNA)

• Phosphate group

• Nitrogenous base: Adenine (A), Guanine (G), Cytosine (C), Thymine (T, DNA only), Uracil (U, RNA only)

DNA vs. RNA: Comparison

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Double-stranded (double helix)	Single-stranded
Bases	A, T, G, C	A, U, G, C
Location	Mainly nucleus	Mainly cytoplasm
Function	Genetic blueprint	Protein synthesis

Base Pairing Rules

• DNA: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C)

• RNA: Adenine (A) pairs with Uracil (U); Guanine (G) pairs with Cytosine (C)

Base pairing occurs via hydrogen bonds, ensuring accurate replication and transcription.

Types of RNA and Their Functions

• mRNA (messenger RNA): Carries genetic code from DNA to ribosomes

• tRNA (transfer RNA): Brings amino acids to ribosomes during translation

• rRNA (ribosomal RNA): Forms part of the ribosome structure

ATP: The Energy Currency

Structure and Function of ATP

Adenosine triphosphate (ATP) is the primary energy carrier in cells. It consists of:

• Adenine (nitrogenous base)

• Ribose (sugar)

• Three phosphate groups

Energy is stored in the bonds between phosphate groups. When a phosphate bond is broken, energy is released for cellular processes.

Equation:

$ext{ATP} ightarrow ext{ADP} + ext{P}_i + ext{energy}$

• Functions: Powers active transport, muscle contraction, and biosynthetic reactions

Summary Table: Key Macromolecules

Macromolecule	Monomer	Main Function
Protein	Amino acid	Structure, enzymes, defense, signaling
DNA	Nucleotide	Genetic information storage
RNA	Nucleotide	Protein synthesis
ATP	Nucleotide (modified)	Energy transfer

Applications and Examples

• Protein synthesis: DNA is transcribed to mRNA, which is translated into a polypeptide chain that folds into a functional protein.

• Enzyme activity: Enzymes lower activation energy, speeding up chemical reactions in the body.

• Energy use: ATP is consumed during muscle contraction and active transport across membranes.

Additional info: The notes infer the importance of protein folding, the role of essential amino acids, and the centrality of ATP in cellular metabolism.