2.4 Biological Macromolecules

Biological macromolecules are the building blocks of life. Carbohydrates, lipids, proteins, and nucleic acids work together to power cells, form structures, and store genetic info. They're essential for all living things.

These molecules are made of smaller units called monomers. How they're put together determines their function. Understanding macromolecules is key to grasping how life works at the molecular level.

Biological Macromolecules: Classes and Functions

Four Main Classes of Biological Macromolecules

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• Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms, typically in a 1:2:1 ratio
  • Serve as a primary energy source (glucose) and structural components (cellulose) in living organisms
• Lipids are a diverse group of hydrophobic molecules that include fats, oils, waxes, and steroids
  • Function in energy storage (triglycerides), cell membrane structure (phospholipids), and signaling (hormones)
• Proteins are complex macromolecules composed of amino acids linked by peptide bonds
  • Play crucial roles in cell structure, function, and regulation, serving as enzymes, transporters, and signaling molecules (insulin)
• Nucleic acids, DNA and RNA, are polymers of nucleotides that store and transmit genetic information
  • DNA is the hereditary material, while RNA is involved in protein synthesis and gene regulation

Functions of Biological Macromolecules

• Carbohydrates provide energy for cellular processes through glycolysis and the citric acid cycle
  • Serve as structural components in cell walls (cellulose) and exoskeletons (chitin)
• Lipids form cell membranes, which regulate the passage of molecules in and out of cells
  • Serve as energy reserves (triglycerides) and signaling molecules (steroid hormones)
• Proteins catalyze biochemical reactions as enzymes, transport molecules across membranes, and provide structural support
  • Participate in cell signaling (receptors) and regulation (transcription factors)
• Nucleic acids store and transmit genetic information, directing the synthesis of proteins
  • Enable the inheritance of traits from one generation to the next through DNA replication

Structure and Function of Macromolecules

Carbohydrate Structure and Function

• Carbohydrates are composed of monosaccharides, which can be linked to form disaccharides and polysaccharides
  • Monosaccharides, such as glucose and fructose, serve as energy sources
  • Polysaccharides like starch and glycogen store energy in plants and animals, respectively
  • Structural polysaccharides, such as cellulose and chitin, provide support and protection in cell walls and exoskeletons
• The specific arrangement of monosaccharides determines the properties and functions of carbohydrates
  • Glycosidic bonds link monosaccharides to form complex carbohydrates (sucrose, lactose)

Lipid Structure and Function

• Lipids are composed of a hydrophobic hydrocarbon chain and a hydrophilic head group
  • Triglycerides, made of glycerol and three fatty acids, store energy in adipose tissue
  • Phospholipids, with a hydrophilic head and two hydrophobic tails, form cell membranes and enable selective permeability
  • Steroids, such as cholesterol, play roles in cell membrane fluidity and serve as precursors for hormones (testosterone, estrogen)
• The hydrophobic nature of lipids allows them to form barriers and compartments in cells
  • Lipid bilayers create selectively permeable membranes that regulate cellular processes

Protein Structure and Function

• Proteins are made of amino acids linked by peptide bonds, forming polypeptide chains
  • The sequence of amino acids determines the protein's primary structure, which folds into secondary structures (α-helices and β-sheets) and tertiary structures
  • Quaternary structure involves the interaction of multiple polypeptide chains (hemoglobin)
• Protein function depends on its specific three-dimensional shape, which is determined by its amino acid sequence
  • Enzymes catalyze biochemical reactions by lowering activation energy (ATP synthase)
  • Transport proteins move molecules across membranes (sodium-potassium pump)
  • Structural proteins provide support and shape to cells and tissues (collagen, keratin)

Nucleic Acid Structure and Function

• Nucleic acids are composed of nucleotides, each containing a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil), a pentose sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group
  • DNA is a double-stranded helix, with complementary base pairing (A-T, G-C)
  • RNA is single-stranded and exists in various forms (mRNA, tRNA, rRNA)
• The sequence of nucleotides in DNA encodes genetic information, which is transcribed into RNA and translated into proteins
  • DNA replication ensures the accurate transmission of genetic information during cell division
  • Transcription produces mRNA, which is then translated into proteins by ribosomes

Monomers and Polymers in Macromolecules

Building Blocks and Bonds

• Monomers are the basic building blocks of macromolecules, while polymers are larger molecules formed by the covalent bonding of multiple monomers
  • Carbohydrate monomers are monosaccharides, which can be linked by glycosidic bonds to form disaccharides and polysaccharides
  • Amino acids are the monomers of proteins, linked by peptide bonds to form polypeptide chains
  • Nucleotides are the monomers of nucleic acids, connected by phosphodiester bonds to form polynucleotide chains (DNA and RNA)
• The specific sequence and arrangement of monomers determine the structure and function of the resulting macromolecule
  • The order of amino acids in a protein's primary structure dictates its folding and ultimate function
  • The sequence of nucleotides in DNA encodes the genetic information necessary for an organism's development and function

Polymer Formation and Diversity

• Dehydration synthesis reactions join monomers together, releasing a water molecule and forming a covalent bond
  • Glycosidic bonds form between monosaccharides, peptide bonds between amino acids, and phosphodiester bonds between nucleotides
• Hydrolysis reactions break down polymers into their constituent monomers by adding a water molecule
  • Enzymes such as amylases, proteases, and nucleases catalyze the hydrolysis of macromolecules
• The diversity of macromolecules arises from the variety of monomers and the numerous ways in which they can be combined
  • Different combinations of monosaccharides lead to a wide range of carbohydrates with distinct properties (starch, cellulose, chitin)
  • The 20 different amino acids can be arranged in countless ways to produce proteins with unique structures and functions (enzymes, antibodies, hormones)

Importance of Macromolecules for Life

Cellular Processes and Interactions

• The interactions between macromolecules form the basis of complex biological processes, such as metabolism, cell division, and gene expression
  • Enzymes (proteins) catalyze metabolic reactions, such as the breakdown of glucose in glycolysis
  • DNA replication and cell division require the coordinated action of numerous proteins and enzymes
  • Gene expression involves the transcription of DNA into RNA and the translation of mRNA into proteins
• Macromolecules work together to maintain cellular homeostasis and enable organisms to respond to their environment
  • Cell signaling pathways rely on the interactions between proteins, lipids, and small molecules (hormones, neurotransmitters)
  • The immune system uses antibodies (proteins) to recognize and neutralize foreign substances

Organismal Development and Function

• Macromolecules are essential for the development and function of organisms at all levels of organization
  • Carbohydrates provide energy for growth and development and serve as structural components in plants and fungi
  • Lipids insulate and protect organs, serve as energy reserves, and are involved in hormone production
  • Proteins are the main functional molecules in cells, enabling movement, transport, catalysis, and regulation
  • Nucleic acids store and transmit the genetic information necessary for an organism's development and reproduction
• The proper functioning of macromolecules is crucial for maintaining the health and survival of organisms
  • Mutations in DNA can lead to altered protein function and the development of genetic disorders (sickle cell anemia, cystic fibrosis)
  • Disruptions in macromolecular interactions can result in diseases such as diabetes, cancer, and neurodegenerative disorders (Alzheimer's, Parkinson's)