The Molecules of Life [Ch. 3]

     Four major groups of macromolecules are essential for the life of the cell: carbohydrates, lipids, proteins and nucleic acids. These four categories of molecules consist of very large organic compounds with an enormous variety in terms of function. Fortunately, the basic concept of their structure is a simple one: a large number of building blocks (monomers) are joined together with covalent bonds to form larger molecules (polymers). Their unique structures give them a variety of different functions within living systems. Natural selection and the process of evolution is the source of variety in structure and function in these molecules.

Review Questions: [continue to the links or the outline]
  1. It is often stated that life is made of organic compounds. What exactly is meant by that statement?
  2. The carbon atoms and other elements are joined to form different functional groups. How does different functional groups affect the different properties (charged, non-charged, bulky, small, polar, non-polar etc.) of a molecule?
  3. How do monomers form polymers via dehydration synthesis?
  4. How are polymers broken down to monomers via hydrolysis?
  5. Note: You need to be able to recognize different types of monomers and polymers. E.g. assume the test has a figure of fructose. You should be able to recognize it as a type of monosaccharide (simple sugar). A figure of any of the twenty amino acids should be recognized as an amino acid and so on.
  6. What is a monosaccharide? Give examples of, and recognize figures of,  monosaccharides (simple sugars).
  7. What is a disaccharide? Examples?
  8. Understand the concept of polysaccharides. Describe the following three examples of polysaccharides (including their source and function): Starch, glycogen and cellulose.
  9. What is a lipid (definition)?
  10. How do hydrophobic and hydrophilic compounds differ from each other?
  11. What is the function of fats and oils in living organisms?
  12. Do animals use fats differently? E.g. compare a seal, a marmot and a fox in terms of how they use their adipose (fat) tissues.
  13. Animals often use fat as a way to store energy. Why do animals not typically store energy in the form of carbohydrates?
  14. Fats are often referred to as triglycerides. Describe the basic components of a triglyceride.
  15. What is the difference between unsaturated and saturated fatty acids?
  16. Can you give examples of where one can expect to find unsaturated and saturated fats? Is there a reason for why either of these fats/oils dominate in those organisms?
  17. There are other types of lipids than triglycerides. Some examples are phospholipids, waxes and steroids. Briefly describe how these differ from each other as well as their function in biological systems.
  18. Give examples of different kinds of steroids.
  19. What is an anabolic steroid?
  20. Proteins are very important macromolecules. Give six examples of the different functions proteins can have within an organism.
  21. Are proteins important? Why?
  22. What are the building blocks for proteins? How many different kinds of these building blocks are available for human proteins?
  23. Sketch an amino acid. Would you recognize it on a test?
  24. How are amino acids joined together to form a peptide?
  25. What is the connection between the shape of a protein and its function?
  26. What is denaturation? What causes denaturation? How does the process of denaturation affect the function of a protein?
  27. Define the primary structure of a protein.
  28. Define the secondary structure of a protein (local folding into a helix or a sheet).
  29. Define the tertiary structure of a protein. It is crucial that you understand how the shape of a protein determines its function.
  30. Define the quaternary structure of a protein (more than one polypeptide unite to form the protein e.g. hemoglobin). Do all proteins have a quaternary structure?
  31. Who is Linus Pauling? How did he contribute to our knowledge of macromolecules?
  32. What is the role of nucleic acids in living organisms?
  33. There are two different types of nucleic acids in a cell. What are they and how do they differ from each other in structure and function?
  34. What is adenosine triphosphate (ATP)?
  35. What is the function of DNA?
  36. What are the building blocks of nucleic acids?
  37. Describe how the building blocks (nucleotides) are joined together with covalent bonds to form a macromolecule (nucleic acids).
  38. Know the general structure of the double helix and the concept of base pairing (A with T, G with C).
  39. What is the complementary sequence to the following DNA sequence: ATC CTA AAC GTA?
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Lecture Outline
Macromolecules: We will look at four major groups of macromolecules: carbohydrates/ lipids/ proteins and nucleic acids. These very large molecules fulfill important roles in the cellular realm.
The building blocks of macromolecules are referred to as monomers. The macromolecule itself is a polymer.
The process by which the monomers are joined together to form the polymer is called a condensation reaction.
The breakdown of the polymer to form the monomers is called hydrolysis.

"Carbon water"  - since they are formed by the elements C, H and O. If these atoms are counted in a sugar molecule they will form a multiple of C and H2O. All the molecules in this group (from the small sugar molecules to the enormous starch molecules (macromolecule)) are referred to as carbohydrates.
The building blocks of carbohydrates are referred to as monosaccharides (or simple sugars). Examples of such sugars are glucose, fructose and galactose.
Glucose - an example of a monosaccharide
Disaccharides are two monosaccharides joined together (e.g. sucrose, lactose or maltose)
Monosaccharides and disaccharides are joined together to form polysaccharides.
Polysaccharides: large polymers of simple sugars connected with covalent bonds
  • starch (storage of energy in plants)
  • glycogen (storage of energy in animals [liver, muscle] (remember that most of the energy in animals is stored in the form of fat [triglycerides]); branched structure for faster access)
  • cellulose (structural carbohydrates in plants and algae in their cell walls) [all of the three carbohydrates above are made of glucose units as monomers]
  • chitin (structural component of fungi (cell walls) and in exoskeletons of arthropods [e.g. insects and crustaceans]
Starch - an example of a polysaccharide
starch (energy storage in plants)
   glycogen (energy storage in animals esp in muscle tissue and the liver)
Cellulose - an example of polysaccharide
cellulose (structural component in plants (cell walls))

A group of several types of molecules. They are all referred to as lipids since they cannot be dissolved in water. They are hydrophobic ("water fearing").
In contrast a hydrophilic ("water loving") compound is attracted to water.
Understand the difference between hydrophobic versus hydrophilic characteristics in a molecule.
We are studying A. Fats, B. Phospholipids and C. Steroids in this section.
  A. Triglycerides or Fats/oils (components: glycerol + three fatty acids)
   There are two major types of fatty acids: unsaturated versus saturated fatty acids; these are the building blocks of fats.
   The presence of double bonds in an otherwise uniforms chain of carbon and hydrogen atoms cause kinks in the molecular structure. 
    Unsaturated fatty acids are prominent in triglycerides with an origin from plants. 
FATS: (glycerol + three fatty acids) [triglycerides] (to the right)
Biological roles: 
  • energy storage (2x  energy/weight compared to carbohydrates). It is not surprising that animals were selected for using fat for energy storage since it is an efficient form of storing energy relative to its weight. Plants tend to use starch instead for storing energy. Why do you think that is?
  • insulation: especially prominent in some mammals and birds. Recall the example from class (penguins and seals).
  • padding (some organs have extra padding of fat)
The diagram to the right compares a saturated versus an unsaturated fat molecule. Notice the "bulky" aspect of the unsaturated fat. What do you think are some possible consequences of this "bulkiness"? In which organisms do you tend to find unsaturated fats? Why do you think that is?
Triglycerides aka fats - a saturated and unsaturated fat molecule

  B. Phospholipids (glycerol + two fatty acids + phosphate group [polar])

   the molecules form a bilayer in water. One part of the molecule is hydrophobic while the other is hydrophilic (this is often referred to as amphipathic).

   Phospholipids is a basic structural component of the cell membrane. You will learn more about membranes later. They serve as selective barriers.
  C. Steroids
Steroids - testosterone
   Some hormones are steroids (estrogen/ testosterone)
   Another example is cholesterol is an important structural componment of cell membranes in animals (it stabilizes the fluidity of the membrane).

  Crucial functions in the organism 
  • structural proteins (e.g. keratin in hair, nails and skin)
  • enzymes (e.g. amylase that breaks down starch to maltose)
  • antibodies (immunoglobulins [Ig])
  • hormones (not all) (e.g. insulin and human growth hormone)
  • clotting factors in blood
  • transport proteins (e.g. hemoglobin transporting oxygen)
  • membrane proteins



An amino acid (the R group varies - see below)

    Amino acids are the building blocks of proteins.
The figure above shows the basic structure of an amino acid 
(R is the variable side chain that strongly influences the property of 
the amino acids (see below))
There are 20 different kinds of amino acids in the human species 
(you do not need to memorize them!).
      Each amino acid has different chemical properties
(large vs small, hydrophobic vs hydrophilic)

The twenty different kinds of amino acids

  The amino acids are joined by peptide bonds (a type of covalent bond) to form a polypeptide.
The amino acid sequence will determine the three-dimensional structure of the protein which ultimately is linked to its function. Since life is waterbased their behavior relative to water is very important. The protein folds into a unique structure as it is exposed to a water environment.
  The structure of proteins can be viewed as primary, secondary, tertiary and quaternary structure

Proteins - primary, secondary, tertiary and quaternary structure
  The three dimensional shape of the protein very important for its function.

  This shape is influenced by the solvent (water) as well as surrounding solutes, pH and temperature. Even physical pressure can affect the shape. This is not something that is critical for us as humans, but for deep sea fish species it is a critical issue.
Denaturation of proteins (caused by temperature or chemicals) may inactivate the protein (this may be irreversible) by changing its tertiary structure.

Nucleic acids
  function: information carriers and information storage
  deoxyribonucleic acid (DNA)
  ribonucleic acid (RNA)
  building block: nucleotides (a 5-carbon sugar + a phosphate + a nitrogenous base)
  4 bases in DNA: adenine, thymine, guanine, cytosine (A T G and C)
  4 bases in RNA: adenine, uracil, guanine, cytosine (A U G and C)
  link the nucleotides to form a polynucleotide (a nucleic acid)
Nucleotides - the building blocks of nucleic acids

DNA: double helix made of two chains of polynucleotides

  Watson and Crick determined the structure of DNA in 1953
  the bases face inwards and pair up ( A with T / G with C)
  the pairing is a weak interaction: hydrogen bonds
  the pairing gave Watson and Crick the firs clues in regards to  how the DNA double helix replicates.

Base pairing in DNA The two strands wrap around each other as the bases pair up The DNA double helix

 After reading these chapters you will have the fundamental knowledge to approach biology on a cellular level. Remember to not be intimidated by complex terminology. You are learning a lot of new concepts and structures. It is necessary to use labels to be able to study the cellular realm and journey further into the field of biology.

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Page created by: Peter Svensson
Updated: February 17, 2010