SS BIS II PQs #7 11
7. Describe 4 key features that are found in a eukaryote such as Danio rerio (zebrafish) that are not
found in E. coli.
a.
b.
c.
d.
linear chromosomes
membrane bound organelles (nucleus; mitochondria; etc)
cytosol compartmentalized by membranes
extensive cytoskeleton (MTs, MFs, IFs)
Describe 4 features that are found in both of these species.
a.
b.
c.
d.
Genetic information encoded in DNA using identical code
Shared metabolic pathways
Plasma membrane of similar construction
Similar mechanisms for transcribing mRNA
See Chapter 1, Table 1.1 for all possible answers.
8. Proof of a scientific hypothesis is convincing only if supported by a diverse series of experimental
evidence. Your suggested reading Rules of Evidence I, describes three types of evidence:
Experiments that establish (1) plausibility, (2) necessity, or (3) sufficiency.
a. Define each of these three experimental criteria (one sentence each).
(1) Plausibility: Observations or measurements that lead to a correlation in time and space
between two events or agents. It is relatively weak, suggestive evidence that does not provide direct
proof of a relationship.
(2) Necessity: This category of evidence is obtained through loss-of-function type experiments
where a single suspected causative agent is blocked or inhibited, and its effect on normal activity is
determined.
(3) Sufficiency: This category of evidence comes from experiments in which the variable of
interest is artificially introduced into an experimental system. The system is then monitored to see if
there is a gain of function due to the activity or presence of the single variable.
b. Which of the above three criteria provides the weakest type of evidence?
Plausibility
c. Which provides the strongest?
Sufficiency
9. In a truly rigorous scientific investigation, experiments designed to test a hypothesis must be
accompanied by appropriate controls.
a. Why are control experiments necessary for the proper interpretation of experimental results?
Controls a necessary to rule out alternative for the cause of an observed result. For each variable
that is introduced into an experimental procedure, a control must be performed to make sure that a
particular variable did not contribute to the observed result.
b. What is the difference between a positive and a negative control? That is, what is the definition of a
positive control? The definition of a negative control?
Negative controls are experiments that are designed to specifically rule out the of
extraneous contribution variable. That is, to determine what is not the cause of the result.
Positive controls are experiments that verify that the experimental techniques actually work they
way they are supposed to , and to reassure investigators that they are measuring exactly what they think
they are measuring.
10. Phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE), and
phosphatidylinositol (PI) are the four most prevalent phospholipids that contribute to membrane
structure and function. One of their most significant shared properties is that they are all amphipathic.
Attempt to pronounce amphipathic.
What determines whether or not a molecule is classified as being amphipathic?
A molecule that is amphipathic has both hydrophobic and hydrophilic regions, thus giving it a
dual nature and influencing how it reacts in an aqueous environment.
How does being amphipathic influence the way that phospholipids behave in an aqueous solution?
The amphipathic phospholipids will arrange themselves in a aqueous solvent so that their polar
head groups will maximize their exposure to the solvent, while the hydrophobic fatty acid tails will
group together internally to minimize exposure to the solvent.
11. Discuss the various factors that have an influence on the fluidity / viscosity of biomembranes. In
your discussion, include the following factors:
lipid composition; lipid structure; cholesterol; temperature; lipid rafts
lipid composition: Fluidity of a membrane is dependent on the types of lipids that make up that
particular membrane; the relative proportions of the different lipid types determine the fluidity.
Lipid structure: lipid structure itself plays a ole since longer chain Fas and saturated Fas favor
membrane viscosity, whereas short chains and unsaturated Fas favor fluidity. The chain length and
degree of saturation mainly affect the packing arrangement of the bilayer.
Cholesterol: Cholesterol tends to toughen and ad make a membrane less fluid (also less permeable)
Cholesterol also stabilizes a membrane against subtle temperature changes; it acts as a buffer to broaden
the transition temperature so a membrane can remain functional over a broader temp range.
Temperature: Biomembranes tend to become more viscous as temp is lowered, and more fluid at higher
temps.
Lipid rafts: Lipid rafts, because they are composed of relatively large integral membrane proteins,
sphingomyelin, and cholesterol, tend to create micro-domains of relatively low fluidity.