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INVERTEBRATE ZOOLOGY, BIOLOGY 03050 WEEK 15: CHEMISTRY OF LIFE

Text (7th ed.): Ch. 1, pp. 5-11; Ch. 2, pp. 39-40; Appendix, pp. 691-697 12/6/99

Dr. W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)

possible web site: http://esg-www.mit.edu:8001/esgbio/chem/chemdir.html

(MIT Biology Hypertext chapter that reviews chemistry for biology)

1. Chemistry, the science of the composition of substances, underlies biology. This week, we will highlight some important aspects. Atoms combine to form molecules. When atoms interact chemically to form molecules, they are held together by bonds.

2. There are three types of bonds important in biology: 1) covalent, in which electrons are shared (single, double, triple bonds). If the electrons are shared equally, e.g., H2, the bond is nonpolar, and if the electrons spend more time around one of the atoms, e.g., H2O, it is polar. 2) hydrogen bonds, as in water, where there is a weak attraction between the slightly positive and slightly negative regions of different molecules. 3) ionic bonds, where an atom (or molecule) has gained or lost an electron (a charged atom or molecule is an ion), and has an attraction to an atom of opposite charge, e.g., Na+Cl-, table salt.

3. An acid is a substance that releases H+ when dissolved in water, and a base releases OH-. pH is a scale of acidity and alkalinity, running from 0 to 14, with 7 at neutral. Acidic solutions are 6.9 and less, and alkaline are 7.1 and up. The pH scale is logarithmic, so that a pH acid of 3 is 10 more acid than pH 4, because: pH=-log[H+]. Buffers are substances that help to maintain neutrality, near where most animal cell activity takes place.

4. Water is the most important molecule to life, as it covers 75% of the world's surface and makes up anywhere from 50% to 99% of an animal. Water is polar and has lots of hydrogen bonds. It is therefore a universal solvent and has a high boiling point, a high capacity to absorb heat, and lower density as a solid than as a liquid. Water is a good evaporative coolant, and water also shows adhesion and cohesion. Can you think of examples why these characteristics are important for living organisms?

5. Organic molecules contain the element carbon, inorganic molecules do not. Carbohydrates contain carbon, hydrogen, and oxygen in a 1:2:1 ratio. Types of carbohydrates are monosaccharides (example of glucose), disaccharides (sucrose, table sugar), and polysaccharides (glycogen and chitin). Disaccharides and polysaccharides are made of linked simple sugars.

6. Lipids are nonpolar, are made of carbon, hydrogen, and oxygen, but with much less oxygen. Fats contain a glycerol and fatty acids off of that. If they have all single bonds in the fatty acids, they are saturated. If they have one or more double bonds, they are unsaturated. Why are unsaturated fats often oils and saturated fats solids at room temperature? The double bonds act as kinks and therefore the unsaturated fat molecules cannot be as close to one another.

7. Proteins are a major structural material in animals (just think of your last steak) and are made up units called amino acids, which contain a -NH2 group, a -COOH group, and a -H off of a C. Proteins are joined by a peptide bond, so as to make dipeptides, tripeptides, all the way up to polypeptides. One can consider the protein to have several layers of structure. The primary structure is the linear sequence of amino acids. The secondary structure is a repeating pattern of bonds among the amino acids. The tertiary structure is the three dimensional aspect of shape.

The quaternary structure is the link of two protein links into a whole.

8. Nucleic acids are made of sugar, phosphate (-PO4), and organic bases in repeating units called nucleotides. Remember their function from last week? DNA and RNA are deoxyribonucleic acid and ribonucleic acid, respectively. DNA can replicate itself and is present in the nucleus of a cell, and RNA is a carrier of information between DNA and the sites of protein synthesis.

ENERGY ISSUES:

9. The rest of this course will be about energy and how animals obtain and use it. Ultimately, photosythetic plants capture light energy and store it in the form of the carbohydrates, fats, and proteins discussed above. Harking back to the food chain concept discussed in week 2 in the ecology lecture, we can call plants producers as a result. A primary consumer is a plant-eating animal, and a secondary consumer eats these primary consumers. Decomposers can work at each of these levels. Underlying this food chain is a flow of energy in the form of nutrients from one to another. Metabolism is the sum of all chemical reactions occurring in an animal's cells, both breaking down processes (catabolism) and building up processes (anabolism).

10. Energy and useful terms. Energy is the capacity to do work. Work is the transfer of energy. Energy can be in different states. Kinetic energy is the energy of motion, and potential energy is stored, like in a gallon of gas. The science of energy is called thermodynamics, since it's easiest to measure energy by the amount of heat used or created. Heat is measured in kilocalories (kcal), or Calories, the amount of heat necessary to raise 1 kg of water 1o C. These are the"calories" of a diet.

Thermodynamics: the study of energy and its transformations into different forms

First law of thermodynamics: energy cannot be created or destroyed, but it can be transformed from one form to another. Hence, plants use the sun's energy for photosynthesis and to make chemical bonds in food molecules, which animals can then eat and break the chemical bonds for their energy needs.

Second law of thermodynamics: energy, when it is converted, is in some way partially lost as a less useful form, usually heat. Hence, when an animal eats a plant, some of that energy within the plant material is lost.

After some thinking, you should realize how these two laws of thermodynamics affect the makeup of food chains, e.g., why there are more plants than herbivores, or more herbivores than carnivores.

11. Chemical reactions fall into two categories:

a) those that have a net release of energy (exergonic)

b) those that need more energy put in than they release (endergonic)

As we will see, cells use energy-releasing (exergonic) reactions to drive energy-requiring (endergonic) reactions. Often, especially with biological reactions, one needs an activation energy to start the process. A catalyst is a substance that accelerates the rate of a chemical reaction by lowering this activation energy, and is unaltered in the process. Hence, a catalyst can be used over and over. An enzyme is a protein catalyst (name ends in -ase). Many of the proteins that a cell makes are therefore enzymes for many cell reactions.


|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|

 


Please send comments and questions to: cronewil@hvcc.edu

 

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This page updated on November 22, 1999