2.3 Organic Compounds: Carbohydrates, Lipids, Proteins, and Nucleic Acids
5 min read•august 7, 2024
Organic compounds are the building blocks of life. Carbohydrates, lipids, proteins, and nucleic acids play crucial roles in energy storage, cell structure, and genetic information. These molecules form the foundation of biochemistry and are essential for all living organisms.
Understanding these compounds is key to grasping how life works at the molecular level. From powering our cells to storing our genetic code, these molecules are the basis for all biological processes and structures in living things.
Carbohydrates
Monosaccharides and Polysaccharides
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- Carbohydrates consist of carbon, hydrogen, and oxygen atoms, usually in a 1:2:1 ratio (CH2O)n
- are simple sugars that serve as the building blocks of carbohydrates (glucose, , )
- Monosaccharides can be linked together by to form (, , ) and
- Polysaccharides are complex carbohydrates composed of long chains of monosaccharides
- Polysaccharides can serve as energy storage molecules ( in plants, in animals) or structural components ( in plant cell walls, in insect exoskeletons)
Functions and Importance of Carbohydrates
- Carbohydrates are the primary source of energy for living organisms
- Glucose is the most common monosaccharide used for energy production through cellular respiration
- Carbohydrates play a crucial role in various biological processes, such as cell signaling, cell recognition, and immune system function
- Carbohydrates are essential components of nucleic acids (DNA and ), where they form the backbone of the molecule ( in DNA, in RNA)
Lipids
Structure and Types of Lipids
- Lipids are a diverse group of hydrophobic organic molecules that are insoluble in water but soluble in nonpolar solvents
- are long hydrocarbon chains with a carboxyl group (COOH) at one end, serving as the building blocks of many lipids
- Fatty acids can be saturated (single bonds between carbon atoms) or unsaturated (one or more double bonds between carbon atoms)
- are the most common type of lipid, consisting of three fatty acid molecules attached to a backbone
- Triglycerides serve as energy storage molecules in animals (fat) and plants (oils)
- are composed of two fatty acid molecules and a phosphate group attached to a glycerol backbone
- Phospholipids are the primary components of cell membranes, forming a bilayer structure with their hydrophobic tails facing inward and hydrophilic heads facing outward
Functions and Importance of Lipids
- Lipids play a vital role in energy storage, providing a highly concentrated source of energy (9 kcal/g compared to 4 kcal/g for carbohydrates and proteins)
- Lipids are essential components of cell membranes, regulating the movement of molecules in and out of cells and maintaining cell structure and integrity
- Lipids serve as signaling molecules (hormones like steroids and eicosanoids) and are involved in various physiological processes (inflammation, blood clotting, immune response)
- Some lipids, such as cholesterol, are precursors for the synthesis of steroid hormones (testosterone, estrogen) and bile acids
Proteins
Amino Acids and Peptide Bonds
- Proteins are large, complex molecules composed of one or more chains of
- Amino acids are the building blocks of proteins, consisting of a central carbon atom (α-carbon) bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain (R group)
- There are 20 different amino acids found in proteins, each with a unique R group that determines its chemical properties and interactions
- Amino acids are linked together by , which are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another
- Peptide bonds have a partial double bond character, resulting in a planar and rigid structure that contributes to the secondary structure of proteins (α-helices and β-sheets)
Protein Structure and Function
- Proteins have four levels of structure: primary (amino acid sequence), secondary (local folding patterns like α-helices and β-sheets), tertiary (overall 3D shape), and quaternary (multiple polypeptide chains)
- The unique sequence of amino acids and the resulting structure determine a protein's specific function
- Proteins perform a wide variety of functions in living organisms, including:
- that catalyze biochemical reactions (digestive enzymes, metabolic enzymes)
- Structural proteins that provide support and shape to cells and tissues (, )
- Transport proteins that move molecules within and between cells (, ion channels)
- Signaling proteins that transmit messages between cells (hormones, neurotransmitters)
- Defensive proteins that protect against pathogens (, complement proteins)
Nucleic Acids
Nucleotides and Nucleic Acid Structure
- Nucleic acids are large biomolecules that store and transmit genetic information in living organisms
- are the building blocks of nucleic acids, consisting of three components: a nitrogenous base, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group
- There are five nitrogenous bases found in nucleic acids: (A), (G), (C), (T) in DNA, and (U) in RNA
- Nucleotides are linked together by between the phosphate group of one nucleotide and the sugar of another, forming a long polynucleotide chain
- The sequence of nucleotides in a nucleic acid molecule determines the genetic information it encodes
DNA and RNA Structure and Function
- DNA (deoxyribonucleic acid) is a double-stranded molecule that stores genetic information in the form of a double helix
- The two strands of DNA are held together by between complementary base pairs: A with T and G with C
- DNA replication occurs during cell division, ensuring that each daughter cell receives an identical copy of the genetic material
- RNA (ribonucleic acid) is a single-stranded molecule that plays a crucial role in gene expression and protein synthesis
- There are three main types of RNA: messenger RNA (), transfer RNA (), and ribosomal RNA ()
- mRNA carries the genetic information from DNA to ribosomes, where it is translated into a protein sequence
- tRNA molecules transport amino acids to the ribosomes and recognize the corresponding codons on the mRNA
- rRNA is a component of ribosomes, the cellular machinery responsible for protein synthesis
Key Terms to Review (43)
Adenine: Adenine is one of the four primary nitrogenous bases found in nucleic acids, specifically DNA and RNA. It plays a crucial role in various biological processes, including energy transfer and the synthesis of nucleotides. As a purine base, adenine pairs with thymine in DNA and with uracil in RNA, forming essential components of the genetic code that dictate cellular function and heredity.
Amino Acids: Amino acids are organic compounds that serve as the building blocks of proteins, consisting of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) unique to each amino acid. They play crucial roles not only in protein synthesis but also in metabolic processes, influencing cellular functions and energy production.
Antibodies: Antibodies are specialized proteins produced by the immune system to identify and neutralize foreign objects like bacteria, viruses, and toxins. These proteins play a crucial role in the body's defense mechanism by binding to specific antigens, which are substances that provoke an immune response, leading to their destruction or inactivation. They are a key feature of the adaptive immune response and are primarily made of proteins, connecting them to other organic compounds that serve essential functions in biological systems.
Cellulose: Cellulose is a complex carbohydrate, or polysaccharide, that forms the structural component of plant cell walls. It consists of long chains of glucose molecules linked by β-1,4-glycosidic bonds, providing rigidity and strength to plant structures. This unique arrangement makes cellulose indigestible to most organisms, serving as a crucial source of dietary fiber for herbivores and playing a significant role in the ecosystem as a primary structural component of plants.
Chitin: Chitin is a long-chain polymer of N-acetylglucosamine, which is a derivative of glucose, and serves as a structural component in the exoskeletons of arthropods and the cell walls of fungi. This organic compound is a key example of a carbohydrate that provides rigidity and protection, highlighting the importance of polysaccharides in various biological structures and functions.
Collagen: Collagen is a structural protein that is a major component of connective tissues in the body, providing strength, elasticity, and support to various structures including skin, bones, tendons, and ligaments. It plays a crucial role in maintaining the integrity and function of tissues, making it an essential organic compound that relates closely to proteins in the body.
Cytosine: Cytosine is one of the four main bases found in DNA and RNA, classified as a pyrimidine. It pairs specifically with guanine in DNA and RNA through hydrogen bonding, playing a crucial role in the encoding of genetic information. Its presence and sequence in nucleic acids are essential for proper gene expression and protein synthesis.
Deoxyribose: Deoxyribose is a five-carbon sugar molecule that is a key component of DNA, the hereditary material in all living organisms. It differs from ribose, another sugar found in RNA, by lacking an oxygen atom at the 2' position, which helps form the stable structure of DNA. This sugar is essential for the formation of the nucleotides that make up the DNA backbone and plays a critical role in genetic encoding and transmission.
Disaccharides: Disaccharides are carbohydrates formed by the combination of two monosaccharide molecules through a glycosidic bond. These sugars serve as important energy sources and are vital in various biological processes, acting as building blocks for more complex carbohydrates and influencing metabolic pathways.
DNA: DNA, or deoxyribonucleic acid, is the hereditary material in nearly all living organisms, containing the instructions necessary for development, functioning, growth, and reproduction. This molecule is composed of two long strands that form a double helix, held together by base pairs of nucleotides. It serves as a blueprint for biological structures and processes, connecting it to other organic compounds like proteins and nucleic acids that play vital roles in life.
Enzymes: Enzymes are biological catalysts that speed up chemical reactions in living organisms by lowering the activation energy required for those reactions to occur. They are essential for various biological processes, including metabolism, digestion, and DNA replication. Enzymes are typically proteins, but some ribonucleic acid molecules can also function as enzymes, known as ribozymes.
Fatty Acids: Fatty acids are long hydrocarbon chains that are key components of lipids, characterized by their carboxylic acid group at one end. They play crucial roles in energy storage, cell membrane structure, and signaling pathways within organisms. As essential building blocks of lipids like triglycerides and phospholipids, fatty acids contribute to the diversity and functionality of biological membranes and are also involved in metabolic processes such as cellular respiration and photosynthesis.
Fructose: Fructose is a simple sugar, or monosaccharide, that is found naturally in many fruits, vegetables, and honey. It is one of the primary components of sucrose, commonly known as table sugar, along with glucose. As a carbohydrate, fructose plays an important role in providing energy to living organisms and serves as a key building block for more complex carbohydrates.
Galactose: Galactose is a monosaccharide sugar that is an important component of lactose, the sugar found in milk. It plays a crucial role in energy metabolism and is a vital building block for complex carbohydrates, which are essential for various biological functions.
Glucose: Glucose is a simple sugar and essential carbohydrate that serves as a primary source of energy for living organisms. It is a monosaccharide that plays a crucial role in cellular respiration, where it is broken down to produce ATP, the energy currency of cells, and also serves as a key substrate in photosynthesis for plants.
Glycerol: Glycerol is a simple polyol compound that serves as a backbone for triglycerides and phospholipids, playing a vital role in lipid metabolism. It is a three-carbon molecule with hydroxyl groups attached to each carbon, which allows it to interact with fatty acids to form esters, essential for creating fats and oils in living organisms. This connectivity makes glycerol significant in biological processes, especially in the formation of lipids that store energy and form cellular membranes.
Glycogen: Glycogen is a multi-branched polysaccharide that serves as a form of energy storage in animals and fungi, primarily found in the liver and muscle tissues. It acts as a crucial carbohydrate reserve that the body can quickly mobilize when energy is needed, linking it closely to metabolism and energy management.
Glycosidic bonds: Glycosidic bonds are covalent linkages formed between two monosaccharides through a dehydration reaction, resulting in the creation of disaccharides or polysaccharides. These bonds are essential in carbohydrate chemistry, as they connect sugar units and determine the structure and properties of carbohydrates such as starch, glycogen, and cellulose.
Guanine: Guanine is one of the four main nitrogenous bases found in DNA and RNA, classified as a purine. It plays a critical role in the encoding of genetic information, pairing specifically with cytosine in the structure of nucleic acids. This base is essential for the formation of nucleotides, which are the building blocks of DNA and RNA, thus linking it to other organic compounds like carbohydrates, lipids, and proteins through its role in cellular function and heredity.
Hemoglobin: Hemoglobin is a protein found in red blood cells that is responsible for transporting oxygen from the lungs to the rest of the body and returning carbon dioxide from the body back to the lungs. This vital protein consists of four subunits, each containing an iron atom that binds to oxygen, making it crucial for cellular respiration and overall metabolism.
Hydrogen Bonds: Hydrogen bonds are weak attractions that occur between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. These interactions are essential for stabilizing the structures of various organic compounds, influencing properties like solubility and melting points. Hydrogen bonds play a critical role in determining the three-dimensional shape of proteins and the double-helix structure of nucleic acids.
Keratin: Keratin is a fibrous structural protein that plays a critical role in the composition of hair, nails, and the outer layer of skin. It provides strength and resilience to these tissues, making them durable and protective against environmental damage. Keratin is a key component of various biological structures, forming the basis for many types of epithelial cells.
Lactose: Lactose is a disaccharide sugar composed of two monosaccharides, glucose and galactose, and is primarily found in milk and dairy products. It plays a vital role as an energy source, especially for infants, and is important for understanding how carbohydrates function within biological systems. The ability to digest lactose depends on the presence of the enzyme lactase, which breaks down lactose into its constituent sugars.
Maltose: Maltose is a disaccharide sugar formed from two glucose molecules linked together by a glycosidic bond. It plays a crucial role in the metabolism of carbohydrates and is often found in various food sources, particularly in malted foods and beverages. As an important carbohydrate, maltose is involved in energy production within living organisms and serves as a building block for more complex carbohydrates.
Monosaccharides: Monosaccharides are the simplest form of carbohydrates, consisting of single sugar molecules that serve as the building blocks for more complex carbohydrates. They are crucial for energy production and are involved in various biological processes, acting as fundamental units that can be linked to form disaccharides and polysaccharides.
MRNA: mRNA, or messenger RNA, is a single-stranded molecule that carries genetic information from DNA to the ribosome, where proteins are synthesized. This process is crucial as it translates the genetic code into functional proteins, which are essential for numerous biological functions and processes.
Nucleotides: Nucleotides are the building blocks of nucleic acids, which include DNA and RNA. Each nucleotide consists of three components: a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. These components link together to form the long chains that encode genetic information and play critical roles in cellular processes like protein synthesis.
Peptide bonds: Peptide bonds are covalent bonds that link amino acids together in proteins. They form through a dehydration reaction between the amino group of one amino acid and the carboxyl group of another, releasing a molecule of water. This process is fundamental for building polypeptides, which fold into specific shapes to create functional proteins that play crucial roles in biological processes.
Phosphodiester Bonds: Phosphodiester bonds are covalent linkages that form between the phosphate group of one nucleotide and the hydroxyl group on the sugar of another nucleotide, creating a backbone for nucleic acids like DNA and RNA. These bonds are crucial because they connect nucleotides together, allowing for the formation of long chains that carry genetic information and play vital roles in cellular functions.
Phospholipid bilayer: The phospholipid bilayer is a fundamental structure of cell membranes, composed of two layers of phospholipids arranged tail-to-tail. This arrangement creates a semi-permeable barrier that separates the internal environment of the cell from the external surroundings, facilitating selective transport and communication. The unique properties of phospholipids, including their hydrophilic heads and hydrophobic tails, play a crucial role in maintaining cellular integrity and function.
Phospholipids: Phospholipids are a class of lipids that are essential components of cell membranes, consisting of two fatty acid tails and a phosphate group attached to a glycerol backbone. Their unique structure allows them to form bilayers in an aqueous environment, making them critical for creating the semi-permeable barriers that separate the interior of cells from their external surroundings and facilitating various cellular functions.
Polysaccharides: Polysaccharides are complex carbohydrates formed by long chains of monosaccharide units linked together by glycosidic bonds. They play critical roles in living organisms, primarily serving as energy storage and structural components, which are fundamental to the biology of both plants and animals.
Ribose: Ribose is a five-carbon sugar (pentose) that plays a crucial role in the formation of nucleotides, which are the building blocks of nucleic acids like DNA and RNA. It is essential for cellular processes, particularly in energy transfer and genetic information storage, linking it closely to the functions of carbohydrates and nucleic acids.
RNA: RNA, or ribonucleic acid, is a vital macromolecule that plays a key role in the synthesis of proteins within cells. It acts as a messenger carrying instructions from DNA to the ribosomes, where proteins are produced. RNA is essential for various biological processes and is classified into different types, each serving unique functions in gene expression and regulation.
RRNA: Ribosomal RNA (rRNA) is a type of RNA that is a fundamental component of ribosomes, which are the cellular structures responsible for protein synthesis. rRNA plays a crucial role in translating messenger RNA (mRNA) into proteins by facilitating the binding of transfer RNA (tRNA) and catalyzing the formation of peptide bonds between amino acids, thus linking it to the larger framework of nucleic acids and proteins in living organisms.
Saturated Fats: Saturated fats are a type of fat molecule characterized by having no double bonds between carbon atoms in their fatty acid chains, resulting in a solid state at room temperature. These fats are primarily found in animal products, such as meat and dairy, as well as some plant oils. Their structure allows for a higher density of hydrogen atoms, which contributes to their solid form and impacts various health considerations.
Starch: Starch is a polysaccharide carbohydrate consisting of a large number of glucose units joined by glycosidic bonds, primarily serving as an energy storage molecule in plants. It plays a crucial role in the metabolic processes of living organisms, providing energy and supporting cellular functions. Starch is made up of two components: amylose, which is linear, and amylopectin, which is branched, making it an essential biomolecule for energy storage and release.
Sucrose: Sucrose is a disaccharide composed of one glucose molecule and one fructose molecule, commonly known as table sugar. It plays an essential role in providing energy for living organisms and is a key component of the carbohydrate category, which includes sugars and starches.
Thymine: Thymine is one of the four main nitrogenous bases found in nucleic acids, specifically DNA. It pairs with adenine through hydrogen bonds and plays a crucial role in the structure of DNA, which is essential for genetic information storage and transmission. This base is integral to the formation of the genetic code, influencing protein synthesis and cellular functions.
Triglycerides: Triglycerides are a type of lipid made up of one glycerol molecule bonded to three fatty acids. They serve as the main form of stored energy in the body and play crucial roles in cellular structure and function. As a major class of lipids, triglycerides are also significant in the context of energy metabolism, contributing to both short-term and long-term energy needs.
TRNA: tRNA, or transfer RNA, is a type of RNA molecule that plays a crucial role in translating genetic information from messenger RNA (mRNA) into proteins. Each tRNA carries a specific amino acid to the ribosome during protein synthesis, ensuring that the correct building blocks are assembled in the right order as dictated by the mRNA sequence. This process connects the flow of genetic information from nucleic acids to proteins, highlighting the relationship between nucleic acids and proteins in cellular functions.
Unsaturated fats: Unsaturated fats are types of fats that contain one or more double bonds in their fatty acid chains, which makes them liquid at room temperature. They are generally considered healthier than saturated fats due to their ability to improve cholesterol levels and provide essential fatty acids that the body cannot produce on its own. Unsaturated fats play a critical role in cellular function and are a key component of many lipids.
Uracil: Uracil is a nitrogenous base found in RNA that pairs with adenine during the processes of transcription and translation. It plays a critical role in the structure and function of nucleic acids, helping to store and transmit genetic information. Unlike its DNA counterpart thymine, uracil is essential for RNA's unique properties and functions.