Modern Biology QUIZ #2 Answer Key
1. What are the functions of ribosomes, endoplasmic reticulum,
and golgi complex in the cell.
- Ribosomes: multiprotein complexes forming the site upon which protein synthesis takes place. ribosomes can be found associated with the endoplasmic reticulum or free in the cytoplasm. pages 96-97
- Endoplasmic Reticulum: an internal membrane system continuous with the outer nuclear membrane. The lumen of the ER contains many enzymes used in post-translational modification. This is the site for processing of proteins destined for the outside of the cell. Other functions are described on pages 97-99.
- Golgi Complex: Another self contained internal membrane systems. Several compartments are included in the golgi thus not representing a continuous membrane system. The lumen contains many enzymes used to process and package proteins especially glycosylation. see pages 99-100.
2. Describe the difference between the quaternary structure of
microfilaments and microtubules.
- Micofilaments: double strand of actin proteins in a twisted pair. Interaction of homologous subunits.
- Microtubules: interaction of alpha and beta tubulin molecules to form dimers which then associate in linear polar strands to form thirteen strands forming a tube. Dimers freely associate in reversible manner to form tubes.
3. Life is sometimes described as a struggle against the second
law of thermodynamics. Give one example where this would appear to be the
case. How do organisms succeed without violating the law.
The association of tubulin to form microtubules would appear to form
order spontaneously and thus violate the second law. However, in all cases
it is important to consider the universe in which the process is taking
place. Thus the assembly of the subunits may appear to violate the second
law but the disordering of molecules that had been associated with the surface
of the subunits is placing them in disorder and thus making the over all
process follow the second law.
4. Give two methods by which a non-spontaneous metabolic reaction
can be made to be spontaneous. (reversing the direction of the reaction
is not one of the ways.)
- One method is to couple the reaction with a spontaneous reaction such as the hydrolysis of ATP. Thus the free energy resulting from the hydrolysis of ATP can be coupled to the formation of glucose 6 phosphate from glucose and phosphate (a non-spontaneous process) yielding an overall spontaneous reaction. Free energies are additive.
- The second method involves overcoming a positive standard free energy by either increasing the amount of substrate or decreasing the amount of product.
5. Describe three methods by which the activity of an enzyme can
be controlled. pages 162-163.
(a) temperature
(b) pH
(c) substrate concentration
6. Using the solutions from questions 4 and 5, explain why anaerobic
glycolysis ends at lactic acid. Save this for this week!