8.2 Structure and Function of Biomolecules

Carbohydrates and lipids are essential biomolecules with diverse structures and functions. Carbs provide energy and structural support, while lipids form cell membranes and store energy. Both play crucial roles in biological systems.

Proteins and nucleic acids are fundamental to life processes. Proteins perform various functions, from catalyzing reactions to defending against pathogens. Nucleic acids store and transmit genetic information, enabling replication, transcription, and translation.

Carbohydrates and Lipids

Structure and function of carbohydrates

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• Carbohydrates form organic compounds composed of carbon, hydrogen, and oxygen with general formula $C_n(H_2O)_n$
• Monosaccharides represent simplest carbohydrates (glucose, fructose, galactose)
  • Exist in linear and ring forms
  • Classified as aldoses (aldehyde group) or ketoses (ketone group)
  • Provide energy source for cells and serve as building blocks for larger carbohydrates
• Disaccharides consist of two monosaccharides joined by glycosidic bond (sucrose, lactose, maltose)
  • Transport and store energy in organisms
• Polysaccharides form long chains of monosaccharides (starch, cellulose, glycogen)
  • Store energy in plants (starch) and animals (glycogen)
  • Provide structural support in plants (cellulose)

Lipids in biological systems

• Lipids comprise hydrophobic molecules with diverse structures and functions
• Fatty acids contain long hydrocarbon chains with carboxyl group
  • Saturated fatty acids lack double bonds
  • Unsaturated fatty acids contain one or more double bonds
  • Store energy and form cell membrane components
• Triglycerides consist of three fatty acids attached to glycerol backbone
  • Store energy in adipose tissue
• Phospholipids contain two fatty acids and phosphate group attached to glycerol backbone
  • Exhibit amphipathic nature with hydrophilic head and hydrophobic tails
  • Form main component of cell membranes
• Other lipids include steroids (cholesterol) and waxes
  • Act as hormone precursors
  • Provide waterproofing and insulation

Proteins and Nucleic Acids

Protein structure and function

• Amino acids serve as building blocks of proteins
  • Central carbon atom bonds to amino group, carboxyl group, hydrogen, and R-group
  • 20 standard amino acids differ in R-group structure
• Peptide bonds form covalent links between amino group of one amino acid and carboxyl group of another
  • Create polypeptide chains
• Protein structure levels organize hierarchically:
  1. Primary structure defines amino acid sequence
  2. Secondary structure forms local folding patterns (α-helices, β-sheets)
  3. Tertiary structure determines overall 3D shape of single polypeptide
  4. Quaternary structure involves multiple polypeptide subunits
• Protein folding occurs through hydrophobic interactions, hydrogen bonds, and ionic interactions
  • Chaperone proteins assist in folding process
• Proteins perform diverse functions:
  • Catalyze reactions as enzymes
  • Provide structural support (collagen)
  • Transport molecules (hemoglobin)
  • Transmit signals (hormones)
  • Defend against pathogens (antibodies)

Nucleic acids: DNA and RNA

• Nucleic acids form polymers of nucleotides to store and transmit genetic information
• Nucleotides consist of sugar (deoxyribose in DNA, ribose in RNA), phosphate group, and nitrogenous base
• DNA (Deoxyribonucleic acid) adopts double-helix structure
  • Contains bases adenine, thymine, cytosine, guanine
  • Forms base pairs A-T and C-G
  • Stores genetic information
  • Serves as template for replication and transcription
• RNA (Ribonucleic acid) typically exists as single-stranded molecule
  • Incorporates bases adenine, uracil, cytosine, guanine
  • Includes types mRNA, tRNA, rRNA
  • Facilitates transcription and translation of genetic information
  • Performs catalytic activities as ribozymes
• Nucleic acids participate in genetic processes:
  1. Replication duplicates DNA
  2. Transcription produces RNA from DNA template
  3. Translation synthesizes proteins using mRNA code