jimtrue.com : school : BSC2010 : CH 05: Structure and Function of Macromolecules

Posted by Jim True on January 26, 2004 6:52 AM. Last Updated October 22, 2006 9:23 PM

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CH 05: Structure and Function of Macromolecules

Macromolecules

• The term macromolecules simply means "large" molecules, molecules that may incorporate hundreds or thousands of atoms and many different elements.
• All of the major groups of organic molecules in living things, often called biomolecules, are macromolecules.
• The four main biomolecular groups are:
  1. Carbohydrates -- sugars and starches.
  2. Lipids -- fats, oils, steroids.
  3. Proteins -- include enzymes. Hair, nails, muscle, hemoglobin, all proteins.
  4. Nucleic Acids -- RNA, DNA.
• All of the groups except lipids are formed of repeating chains of smaller molecules. These large chains are called polymers ("poly" -- many; "mer" -- part).
• The individual or smallest subunits that are connected to form polymers are known as monomers ("mono" - one).
• All monomers have specific functional groups associated with them, and thus are different for each of the biomolecular groups. Will have different monomers for different biomolecular groups.
• The construction of polymers is a process known as polymerization.
• The polymerization processes for the construction and breakdown of polymers, as well as all lipids, is the same REGARDLESS OF THE BIOMOLECULAR CATEGORY OR FUNCTIONAL GROUP!
• Dehydration synthesis ("dehydrate" - loss of water, "syn" - together, "thesis" - arranging). The specific type of polymerization reaction that forms biomolecules. Just ONE specific type of polymerization; this is just the one specific to biomolecules. Taking the water away, leaves open bonds with a charge allowing the bonds to join; concentrate on the 'synthesis'.
• During D.S. (also known as a condensation reaction), monomers or smaller molecules are linked together at their functional groups. When you condense something, you PACK something together.
• One functional group loses a single H, the other an O and an H (--OH) during this link, thus, each new link is formed with the loss of 1 H₂O molecule per link.
• Dehydration synthesis is the the CONSTRUCTION reaction for ALL biomolecules. When connecting 8 monomers in a chain, remove 7 water links. To create a ring, need 8 water links to be removed. (See figure 5.2, p 63).
• Hydrolysis ("hydro" - water, "lys" - to loose [as in break apart], "sis" - the act of, a process) -- The breakdown of biomolecules into smaller molecules by the addition of H₂O.
• Each break requires one H₂O molecule PER break.
• The "breaks" occur at the functional group sites. One functional group accepts an H from H₂O, the other an O and an H. Food began hydrolizing the instant it hit your mouth (hydrolitic reactions from salivary enzymes). (See figure 5.2, p 63)

Carbohydrates

• Carbohydrates (CHO's) - the monomer is called a simple sugar or monosaccharide ("mono" - one, "sacchar" - sugar) and the functional groups are multiple hydroxyls (--OH), and either an internal or terminal carbonyl (>C=O).
• These contain C, Hk, and O in a fixed ratio (CH₂O)_n. One Carbon to a molecule of water; "hydrated carbon". 3 Tri, 4 Tetra, etc. Simple sugar ends in -ose.
• Monosaccharides have 3 to 7 C's. six carbons (hexoses) and five carbon sugars (pentoses) are the most important, with glucose (6C) the most abundant of all.
• Depending on the position of the carbonyl group, sugars are either aldoses (terminal carbonyl) or ketoses (internal carbonyl).
• The names of most monosaccharides (AKA single or simple sugars) end in -- ose, e.g. glucose, fructose).
• Monosaccharides in solution typically form ring compounds which can bind with others to form a huge variety of carbohydrates. (See figure 5.3, p 64). Easiest ones to broke down are carbs; assuming they haven't been epoxied together.
• Monosaccharides, especially glucose, are a major energy source for cells, and also serve as the framework for constructing other monomers such as amino and fatty acids.
• If not immediately used, monosaccharides can be linked by DS to to form disaccharides ("di" - two) or larger molecules. Cells will immediately convert glucose to energy.
• Disaccharides -- Two monosaccharides (double sugars) linked by D.S. Important group because they can easily be broken into monosaccharides, but if not immediately needed, can be transported to other locations in organism.
• Examples include maltose (common plant sugar) (glucose + glucose) and sucrose (table sugar) (glucose + fructose) in plants and lactose (glucose + galactose) in animals. Mother's milk is lactose, and only form of energy for newborn mammals. (See figure 5.5, p 65)
• Polysaccharides -- repeating polymer of monosaccharides, usually glucose.
• Depending on how the molecular structure is arranged, these can form either energy storage or structural types:
• Energy storage -- can be broken down to monomers if needed. These are starches, known as amylose in plants, glycogen in animals. These "energy storage" structural types are built so they CAN be disassembled. When eating amylose, the amylase in your saliva will start to break down the amylose into glucose so it can be converted in an animal system to glycogen. Substance used to thicken jelly is pectin; amylopectin.
• Structural -- The molecules are "glued" together. the molecules differ in structure and cannot be broken down (except by a very few types of organisms), and so are used to provide actual physical structure in many organisms.
• The structural polysaccharide in plants is cellulose (the most abundant organic compound on the planet!), in animals and fungi it is chitin. Cellulose is in cardboard, celery stalks, stems and plant structures. Chitin is the shells of shellfish, and the exoskeleton of insects. Termites have a tiny unicellular organism in their intestines to digest cellulose. Wings of the butterflies are pure chitin. (See figures 5.8 & 5.9, p.68)
• CHO's are linked by glycoside (glycosidic) linkages. H₂O is removed during each link, leaving a single O ("oxygen bridge").

Lipids

• Lipids ("lip" - fat) -- Composed of C, H and O, but fewer O's than in CHO's.
• Includes a wide variety of molecules that are typically nonpolar and so are poorly soluble or insoluble in water.
• Main portion of the molecular structure is formed by hydrocarbons.
• Some major groups include neutral fats (fats and oils), phospholipids, steroids, and a number of pigments. The major groups we're going to look at are triglycerides (neutral fats) and phospholipids, and briefly steroids and pigments.
• Neutral Fats -- the most abundant lipids and are mainly used for energy storage.
  • Neutral fats have the HIGHEST energy content of any of the biomolecular groups.
  • Two types of monomers form neutral fats, one molecule of glycerol bonded to one (monoglyceride), two (diglyceride) or three (triglyceride) fatty acids. A hydrocarbon with a carboxyl acid functional group.
  • About 30 different fatty acids known with 4-18 (usually 16-18) C's in "backbone". Average between 16 and 18 Carbons. The Fatty acids are so called because the backbone is a hydrocarbon with a 'carboxylic acid' function group. All three can be the same, two can be the same, with one different, or all three can be different. Another term for them is a triaglycerol. (figure 5.10, p.69)
  • Functional Groups are hydroxyls (glycerol) and carboxyls (-COOH) on the fatty acids.
  • Saturated fat -- except for carbon-carbon and carbon-functional group bonds, all other available bonds are filled with H's.
  • Saturated fats tend to be solid at room temperature (fats). Difficult to break down because the chemical bonds are strong.
  • Unsaturated fats -- One or more carbon-carbon bonds are double bonds.
  • Molecule is weaker, and more easily broken (the chain is kinked).
  • Unsaturated fats tend to be liquid at room temperature (oils). Polyunsaturated fats have multiple carbon-carbon double bonds. (figure 5.11, p.69)
  • Like CHO's, neutral fats are left with an oxygen bridge between monomers. the specific type of linkage is called an ester linkage.
• Phospholipids -- Formed by a glycerol, two fatty acids, plus a third functional group, the phosphate group (so we have P in addition to C, H, and O), and a charged portion containing a nitrogen compound.
  • The fatty acid end of the molecule is insoluble in water (nonpolar); it is hydrophobic.
  • The phosphate end of the molecule is polar and attracted to water; it is hydrophilic.
  • The unusual nature of phospholipids make them critically important in some structures like the cell membrane. Two layers of phospholipids create the cell membranes. (figures 5.12 & 5.13, p.70)
• Steroids -- Lipid molecules formed by four interlocking rings of C. Very important in regulating metabolic functions (bile salts, cortisol) and cell membrane structure (cholesterol). Most organic steroids created in the body are created by cholesterol. (figure 5.14, p.70)
• Pigments -- Substances that absorb certain wavelengths of light and reflect others. A number of pigments used for photosynthesis and vision are lipid-based, e.g. beta carotene. Lipid based pigments; not all pigments are lipid based. Beta carotene is the color in a carrot; converted to beta carotene are critical in the eye and add to or replace pigments in the eye for light detection. (Figure 10.9, p.184)

Proteins

• Proteins ("proteios" - first place). Contain C, H, O, plus N (and sometimes S). What differentiates organisms is the types and quantities of proteins they contain.
• Their name origin is in reference to the fact that this is an extremely important group with enormous diversity in shapes and functions. Most abundant biomolecules and their diversity and variety dictate organic structures.
• As we will see, proteins provide most of the structure and functions for the cell. It is the diversity of proteins that forms the diversity of life!
• Most living organisms possess similar CHO's, lipids and nucleic acids. Glucose is the most abundant carbohydrate on earth.
• Differences and similarites between and among different species of organisms are mainly based on protein content.
• Monomer of all proteins is the amino acid.
• There are 20 known amino acids. All have the same basic construction:
  • a single central C bonded to one H.
  • a carboxyl functional group on one side of the central C.
  • an aminefunctional group (--NH₂) on the other side of the central C.
  • An "R" group attached to the central C gives the amino acid its characteristics and ranges from a single H (glycine) to an elaborate organic molecule(tryptophan).
• Essential amino acids -- Even though an organism may need many of the amino acids for survival, it may not be able to synthesize all of them within itself. Of the 20 needed for human life, 10 of them are provided outside the human body. Without those essential nutrients, you suffer dietary deficiencies. (See figure 5.15, pp 72-73)
• Essential amino acids must be obtained from outside source (diet).
• Ten essential amino acids for humans.
• Amino acids are linked together by D.S. and the linkage is called a peptide bond. Amino end (N-terminus), Carboxyl end (C-terminus).
• Two amino acids joined together form a dipeptide, three a tripeptide, and more than three, a polypeptide.
• Proteins are formed by multiple polypeptide chains connected together. (See figure 5.16, p.73)
• Proteins are arranged in an enormous variety of complex shapes. The shapes are so complex that they are assigned to one of four different levels of complexity. One very special groups of proteins are the enzymes.
• There are a tremendous number of different types of enzymes. (See figure 5.18, p.75; 5.19, p.76; 5.22, p.77; 5.23, p.78)
• Their overall function is to speed up the rate of chemical reactions, and they are dispensable to life. "Organic catalysts"; enzymes can speed chemical reactions from 100,000 to a billion times faster.
• Will examine these when we get to Chapter 6.

Nucleic Acids

• Nucleic Acids -- Contain C, H, O, N, P.
• The monomer is a nucleotide. This is itself a very large molecule composed of three parts:
  • Pentose -- One five carbon sugar (ribose in RiboNucleicAcid, deoxyribose in DeoxyriboNucleicAcid).
  • Phosphate functional group.
  • Nitrogenous base -- a ring compound containing N. The one variable are the nitrogenous base: adenine, guanine, cytosine, thymine and uracil. (These are the pyrimidines and Purines) One additional oxygen in Deoxyribonucleic acid. (See figure 5.29, p.83)
• Nucleotides have two functional groups, the phosphate group and the hydroxyl on the pentose.
• The link formed between nucleotides is called the phosphodiester bond. We'll discuss its nature in Chapter 16.
• The two important nucleic acids are RNA and DNA. Will discuss in detail in Chapters 16 & 17.
• ATP - Adenosine Triphosphate.

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