Macromolecules and Polymers

• Macromolecules are large carbohydrates, proteins, and nucleic acids.
• They are polymers composed of similar or identical building blocks linked by covalent bonds.
• The repeating units of polymers are called monomers.

Synthesis and Breakdown of Polymers

• Condensation reaction is the covalent bonding of two molecules with the loss of a small molecule.
• If a water molecule is lost, this is called a dehydration reaction.
• Protein polymers are synthesized by dehydration reactions.
• Hydrolysis converts polymers to monomers; it's the reverse of dehydration.
• In hydrolysis, the bond between monomers is broken with the addition of a water molecule.

Carbohydrates

• Carbohydrates include sugars and polymers of sugars.
• Monosaccharides are the simplest carbohydrates, also known as simple sugars.
• Disaccharides are double sugars, two monosaccharides joined by a covalent bond.
• Poylsaccharides are polymers composed of many sugar molecules, making up a large carbohydrate molecule.

Monosaccharides

• Monosaccharides have molecular formulas that are multiples of the unit CH₂O (Formaldehyde).
• A monosaccharide is either an aldose (aldehyde sugar) or a ketose (ketone sugar), depending on the location of the carbonyl group.
• Glucose (C6H12O6) is the most common monosaccharide, of central importance in the chemistry of life.
• Fructose is a ketose, while glucose is an aldose.
• The way their parts are arranged spatially around asymmetric carbons is another way simple sugars are diverse.
• Asymmetric carbon is a carbon attached to four different atoms or groups of atoms
• Even small structural differences can give sugars different shapes, binding activities, and behaviors.

Glucose

• Glucose (C6H12O6) is the most common monosaccharide, a major nutrient for cells.
• During cellular respiration, cells extract energy from glucose.

Disaccharides

• A disaccharide consists of two monosaccharides joined by a glycosidic linkage.
• Maltose is a disaccharide formed by two molecules of glucose and the malt sugar, an ingredient used in brewing beer.
• Sucrose (table sugar) is a disaccharide, and its two monomers are glucose and fructose.
• Lactose, present in milk, is a disaccharide of a glucose molecule joined by galactose.

Sugar Usage

• Disaccharides must be broken down into monosaccharides to be used for energy in organisms.
• Lactose intolerance is a common condition in humans lacking lactase, the enzyme that breaks down lactose.
• In individuals with lactose intolerance, the sugar is instead broken down by intestinal bacteria, causing gas and cramping.
• Lactose intolerance may be avoided by taking lactase when eating or drinking dairy products treated with lactase.

Polysaccharides

• Polysaccharides are macromolecules with a few hundred to a few thousand monosaccharides joined by glycosidic linkages.
• Storage polysaccharides can be hydrolyzed as needed to provide monosaccharides for cells.
• Starch is a polymer of glucose monomers in plants (for example, potato tubers and grains).
• Most animals, including humans, have enzymes that can hydrolyze plant starch, making glucose.
• Animals store glycogen, a polysaccharide, a polymer of glucose.
• Vertebrates store glycogen mainly in liver and muscle cells.
• The breakdown of glycogen in these cells releases glucose when the demand for energy increases.

Structural Polysaccharides

• Organisms build strong materials from structural polysaccharides.
• Cellulose is a major component of plant cell walls, a polymer of glucose with 1–4 glycosidic linkages.
• Cellulose molecules are straight and have no branches.
• Almost all animals, including humans, lack cellulose-digesting enzymes.
• Some microorganisms can digest cellulose, breaking it down into glucose monomers.
• Cows harbor cellulose-digesting prokaryotes and protists in their guts.
• Chitin is another important structural polysaccharide, and used by arthropods to build their exoskeletons.
• Chitin becomes a rigid structure by combining with proteins or calcium (insects, crab).

Lipids

• Lipids are a diverse group of hydrophobic molecules, one of the classes of large biological molecules.
• Lipids are hydrophobic, meaning they don't mix well with water.
• Biologically important lipids include fats, phospholipids, and steroids.

Fats

• Fats are formed from small molecules by dehydration reactions.
• A fat consists of a glycerol molecule and three fatty acids.

Saturated and Unsaturated Fats

• Saturated fats are solid at room temperature.
• Unsaturated fats are liquid at room temperature.

Phospholipids

• Phospholipids are essential for cells because they are major components of cell membranes.
• A phospholipid is similar to a fat molecule but has only two fatty acids attached to glycerol.

Steroids

• Steroids are lipids characterized by a carbon skeleton with four fused rings.
• Cholesterol, a steroid type, is a crucial molecule in animals.
• Cholesterol is a common component of animal cell membranes.
• In vertebrates, the liver synthesizes cholesterol, which is also obtained from the diet.

Proteins

• Proteins have diverse structures, resulting in a wide range of functions.
• Proteins speed up chemical reactions (enzymes), play roles in defense, storage, transport, cellular communication, movement, and structural support.
• Humans have tens of thousands of different proteins, each with a specific structure and function.
• Proteins are constructed from the same set of 20 amino acids.
• A polypeptide is a polymer of amino acids, and the bonds between those acids are called piptide bonds.
• A protein is a biologically functional molecule of one or more polypeptides folded and coiled into a specific three-dimensional structure.

Amino Acids

• An amino acid is an organic molecule containing an amino group and a carboxyl group.
• The general formula includes a side chain (R group), an alpha (a) carbon, an amino group, a carboxyl group, and hydrogen.
• The unique characteristics of a particular amino acid are determined by the physical and chemical properties of its side chain, which affects its functional role in a polypeptide.

Polypeptides

• A peptide bond forms between the carboxyl group of one amino acid and the amino group of another through dehydration reaction, removing a water molecule.
• Polypeptides range in length from a few amino acids to 1,000 or more, each with a unique linear sequence.
• The chemical nature of the molecule as a whole is determined by the kind and sequence of the side chains, which determine how a polypeptide folds, it's final shape, and it's chemical characteristics.

Protein Structure and Function

• The specific activities of proteins are maintained by their three-dimensional shape and their amino acid (aa) sequence.
• A functional protein is one or more polypeptides precisely twisted, folded, and coiled into a unique shape.
• The amino acid sequence of each polypeptide is is what determines what three-dimensional structure the protein will have under normal cellular conditions.
• This 3-D shape is achieved by formation of chamical bonds which depend of the sequence of amino acids.
• Many proteins are roughly spherical (globular), while others are shaped like long fibers (fibrous).

Protein Structure

• Proteins share three superimposed levels of structure: the primary, secondary, and tertiary.
• Quaternary structure arises when a protein consists of two or more polypeptide chains.
• The primary structure of a protein is its sequence of amino acids.
• Transthyretin, a globular blood protein, transports vitamin A and one of the thyroid hormones, and is composed of four identical polypeptide chains, each with 127 amino acids.
• Hydrogen bonds between atoms of the polypeptide backbone, form secondary structure.
• α-helices and β-pleated sheets form the secondary structure.
• Tertiary structure results from interactions between the side chains (R groups), including hydrophobic interactions, van der Waals interactions, and disulfide bridges.

Structure Determination

• Physical and chemical conditions influence the structure of a protein.
• pH, salt concentration, and temperature are all factors.
• The weak chemical bonds and interactions within a protein may be destroyed by denaturation, causing the protein to lose its native shape.
• Denatured proteins are biologically inactive.
• When a protein has been denatured by heat or chemicals, it can sometimes return to its functional shape once the denaturing agent has been removed.

Nucleic Acids

• Nucleic acids store, transmit, and help express hereditary information.
• The two types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• Nucleic acids enable living organisms to reproduce their complex components from one generation to the next.
• DNA directs its own replication and also synthesis of RNA.
• From RNA, proteins are synthesized in a process called gene expression.
• DNA is the genetic material that organisms inherit from their parents.
• Each chromosome contains one long DNA molecule, usually carrying several hundred or more genes.