chapter 03

Bio1100 Chapter 3

Molecules of life

Four classes of macromolecules are important to life.
- Carbohydrates
  - Carbohydrates (carbon and water) are made of C, H, and O, and are the main source of energy for life.
    Like water, these molecules are polar and are "hydrophilic" (water-loving).
    The simplest carbohydrates (simple sugars) are monosaccharides.
    Larger carbohydrates (complex sugars) are polysaccharides linked by glucose subunits.
    In addition to starch, polysaccharides include cellulose and glycogen.
    Glucose is the building block of most carbohydrates.
  - The simplest sugars (monosaccharides) are composed of one ring of carbohydrates, and can provide quick energy.
    Examples include glucose, fructose, and galactose.
  - Complex sugars (polysaccharides) are made of multiple monosaccharides.
    The shortest polysaccharides are disaccharides such as sucrose (table sugar).
    Starch is an example of a longer, larger polysaccharides that is easily digestible.
    The strong covalent bonds between the simple sugars can be broken down by digestion for energy.
  - The polysaccharide cellulose is a major component of plant cells.
    Hydrogen bonds between parallel chains of linked glucose subunits provide strong support in trees.
    Cellulose is indigestible for humans, but moderate amounts in our diet (fiber) is beneficial.
  - Glycogen is a polysaccharide composed of linked glucose subunits.
    Some excess glucose is converted into Glycogen and stored in muscles and liver of animals for short-term energy needs.
  - Glucose is the most important sugar for life.
    Polysaccharides are digested into glucose, which is used as a source of energy.
    Some excess glucose is stored in muscles and liver of animals as the polysaccharide glycogen, which can be broken down to glucose for energy needs.
    Additional excess glucose is converted into fat for long-term energy storage.
- Lipids
  - Lipids comprise 3 major types.
    - fats
      Fats can be saturated or unsaturated.
    - sterols
    - phospholipids
  - Fat molecules are triglycerides, each containing a glycerol head attached to 3 fatty acid tails.
    A fatty acid is a long chain of carbon and hydrogen atoms (hydrocarbon).
    The nonpolar hydrocarbons are hydrophobic ("afraid" of water) and are insoluble in water.
    The dense covalent bonds make fats ideal for long-term energy storage; many animals develop a taste for sweet and fatty foods.
  - Saturated fats contain only single bonds between carbon and hydrogen atoms in the hydrocarbon tails.
    Saturated fats tend to be solid at room temperature; they can accumulate in your blood, contributing to heart disease.
    Unsaturated fats contain at least one double bond, and tend to be liquid at room temperature.
  - Hydrogenation (adding hydrogen atoms) of an unsaturated fat makes it more saturated.
    Some of the resulting unsaturated hydrocarbon tails contain double bonds that may be in a trans form.
    The trans fats can also accumulate in your blood vessels and contribute to heart disease.
  - Sterols are lipids with 4 carbon rings.
    - Cholesterol is an important component of animal cell membranes, and is also required to synthesize steroid hormones.
    - Steroid hormones such as estrogen and testosterone are built through chemical modifications to cholesterol precursor molecules.
  - A phospholipid is similar to a fat molecule except it has:
    - a hydrophilic (polar) phosphate group
    - 2 hydrophobic (nonpolar) fatty acid tails
    Phospholipids are major components of cell membranes.
- Proteins
  - Proteins are made from 20 different kinds of subunits called amino acids.
    Amino acids are composed of a central carbon joined to
    - an amino group which often loses an electron.
    - a carboxyl group which often gains an electron.
    - a side chain unique to each of 20 different kinds of amino acids.
    The polar amino acids are linked by covalent bonds to form polypeptide chains called proteins.
    Many proteins are enzymes that play a critical role in biological reactions.
  - Proteins serve a wide diversity of functions in living organisms.
    Weak hydrogen bonds fold each protein into a unique 3-dimensional shape that determine its function.
  - Enzymes such as lactase help speed up chemical reactions.
    1. An active site on the protein's surface binds a particular substrate such as lactose.
    2. The tight fit allows the enzyme to break the covalent bond between the simple sugars.
    3. The products of the reaction are the 2 sugars, which are released.
    Factors such as temperature and pH can affect an enzyme's activity by altering its shape, thus how well it binds the substrate to the active site.
    Review:
- Nucleic acids
- Nucleic acids
  (DNA and RNA) are made of nucleotide subunits.
  Nucleotides are composed of a five-carbon sugar, a phosphate group, and 4 different types of nitrogen-containing base.
  This diagram illustrates DNA (Deoxyribonucleic Acid).
  RNA (Ribonucleic Acid) is similar with minor differences.
- Differences between DNA and RNA
  - The sugar found in DNA (Deoxyribonucleic Acid) is deoxyribose (missing an oxygen), as opposed to ribose (has an extra oxygen) that is found in RNA (Ribonucleic Acid).
  - Four different nitrogen-containing bases are found in DNA: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
    In RNA, Uracil (U) takes the place of Thymine (T).