3.2 Organic Molecules

10/10/2012 § Leave a comment

Is it just me or are we zooming by this unit? Like, does anyone feel like they’re trapped in a state of vertigo after today’s lecture? And since when was I dropped back into Chemistry 101? Goodness.

I mentioned in the previous blog that a lot of living things are based off of the element of carbon. Usually, a molecule that has carbon in it is defined as organic but there are a few exceptions that are not categorized as organic, including CO, CO2, and HCO3-. The term “organic” used to link directly to “living” organisms but this is not the case – many inorganic substances are important to life, including the other three fundamental elements (nitrogen, oxygen, hydrogen). Similarly, there are organic chemicals like plastics and petrol that are found in non-living things. So technically, “organic” can’t be completely synonymous with “living” and that’s totally fine – we’ll just have to remember all the exceptions.

Subunits of Organic Macromolecules

Organic compounds are made of large molecules called macromolecules that are long chains of repeating subunits, also known as monomers. Some macromolecules are: ribose and glucose (monosaccharides), fatty acids and amino acids. The two structures below are of glucose and of a fatty acid.

Carbohydrates

Carbohydrates are made up of carbon, hydrogen, and oxygen. The hydrogen and oxygen molecules are present as water – H2O. The subunits (monomers!) of carbohydrates are monosaccharides, which include ribose, fructose, and glucose, two of which were previously mentioned.

Other monomers include maltose (a disaccharide made up of two glucose molecules), sucrose (made up of one glucose and one fructose molecule), and lactose (made up of one glucose and one galactose molecule). Carbohydrates can have many monomers and are then called polysaccharides, examples of which include starch, glycogen and cellulose.

Carbohydrates have multiple functions, which include the following:

  • glucose – is an energy source in animal cells
  • fructose – is a component of flower nectar that helps to attract animals
  • lactose – is the sugar in milk that provides energy to young mammals
  • sucrose – carried by the phloem, can transport energy to cells in a plant
  • glycogen – is a short-term energy storage in liver and muscles
  • cellulose – makes strong fibbers that construct the cell wall of a plant

Condensation and Hydrolysis

These two are like a pair – they come hand in hand, or at least they’re strongly linked to the other. When subunits combine to form polysaccharides, polypeptides, and nucleic acids, they do so by condensation, a reaction where two molecules join together to form a larger molecule, resulting in the formation of a macromolecule and a water molecule.

Between two subunits, the new bond formed after condensation is called a peptide linkage. More and more condensation reactions can add more amino acids to the previously created peptide molecule – a long chain of many amino acids is called a polypeptide.

Condensation can also build up carbohydrates and lipids. In this case, two monosaccharides are linked to form a disaccharide (di = two) and the addition of more monosaccharides will create a large molecule of many saccharides, eventually forming a polysaccharide (poly = many). Fatty acids can be linked to glycerol, too, to produce glycerides (a type of lipid). Only three fatty acids can be linked to a glycerol – that’s the maximum – and can create a triglyceride molecule.

The opposite of condensation is the breaking down of these molecules – hydrolysis, the opposite of condensation. Hydrolysis is when water is used to split the bonds previously formed by condensation. The addition of water will break up the bond previously created by condensation, thus breaking down the molecule.

Lipids

There are many kinds of lipids; lipids are kind of like a wide range of molecules that can include steroids, waxes, fatty acids and triglycerides. The functions of lipids, however include the following:

  • energy storage – lipids can store energy in the form of fat on animals and oil in plants
  • heat insulation – heat loss is reduced because of the fat (lipids) under skin
  • buoyancy – can help animals to float because lipids are less dense than water

Both carbohydrates and lipids can store energy but do so differently. Lipids, for example, store energy for long periods of time, while carbohydrates are better for storing energy for short periods of time. Other advantages include:

  • lipids: can contain more energy per gram [than carbohydrates] so are lighter than carbohydrates
  • lipids: insoluble in water and don’t meddle with osmosis while carbohydrates do
  • carbohydrates: digested more easily [than lipids] therefore can release energy more rapidly
  • carbohydrates: soluble in water and are easier to transport [than lipids]

 

Essay Questions

  1. Outline the thermal, cohesive, and solvent properties of water. (5 marks)
  2. Describe the significance of water to living organisms. (6 marks)
  3. Describe the use of carbohydrates and lipids for energy storage in animals. (5 marks)
  4. List three functions of lipids. (3 marks)
  5. Describe the significance of polar and non-polar amino acids. (5 marks)
  6. Outline the role of condensation and hydrolysis in the relationship between amino acids and dipeptides. (4 marks)
  7. Describe the structure of proteins. (9 marks)
  8. List four functions of proteins, giving an example of each. (4 marks)
  9. Distinguish between fibrous and globular proteins with reference to one example of each protein type. (6 marks)
  10. option i – Lactase is widely used in food processing. Explain three reasons for converting lactose to glucose and galactose during food processing (3 marks)
    option ii – Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of reaction is highest at 48°C. In food processing, lactase is used at a much lower temperature, often at 5°C. Suggest reasons for using lactase at relatively low temperatures. (2 marks)
  11. Outline how enzymes catalyze reactions. (7 marks)
  12. Explain the effect of pH on enzyme activity. (3 marks)
  13. Compare the induced fit model of enzyme activity with the lock and key model. (4 marks)
  14. Draw graphs to show the effect of enzymes on the activation energy of chemical reactions. (5 marks)
  15. Explain, using one named example, the effect of a competitive inhibitor on enzyme activity. (6 marks)

I was able to italicize two more of the essay questions after this reading, the 3-mark question on lipids and the 4-mark question on hydrolysis and condensation. That’s a grand total of 5 italicized items, which leaves us with ten more to learn. Not too bad. I… guess.

 

DATA BASED QUESTIONS

Page 50 emperor penguins

a. Calculate the total mass loss for each group of birds.

i) wild —> 38.6 kg (before) – 22.4 kg (after) = 16.2 kg lost

ii) captive —> 37.2 kg (before) – 23.9 kg (after) = 13.3 kg lost

b. Compare the changes in lipid content of the captive birds with those of the birds living free in the colony.

Both groups started off with around the same amount of lipids in their body composition, about 11.8 kg or 12 kg. After the 14 weeks, the wild group of penguins were left with 2.2 kg while the captive were left with 0.8 kg. The wild group of penguins lost a grand total of 9.6 kg of lipids while the captive birds lost a grand total of 11.2 kg. 

c. Besides being used as an energy source, state another function of lipid which might be important for penguin survival.

Other than storing energy, the ability to keep warm (heat insulation) is vastly important for the lifestyle of the male penguin, especially during the winter season. They need to keep not only themselves warm or the entire flock warm, but also the eggs that they are left to incubate.

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