Thinking and Texting

Facts,Truth and Method

An especially apt characterization of science fact was made by Lynn white .JrWhite wrote that ,to a scientist,truth is not a citadel of certainty to be defended against error,it is a shady spot where one eats lunch before tramping on. 1.make initial observation

2.Formulate a testable hypothesis 3.collect data 4.Interpret results

5.Draw reasonable conclusions

The Second Week

Friedrich Miescher, Gregor Mendel,Louis Pasteur,and Rudolf Virchow were European scientistswhose most important discoveries were made in the 20-year period from 1855 to 1875.Assume that the four man met at a scientific conference in 1875to discuss their respective contributions to biology.

（1）What might the four scientists have found they had in common.

The Third Week

You just developed an autoradiography after a two-week exposure. You had incubated your protein with a cell-cyte kinase. You see the hint of a band on the gel at the right position, but it is just too faint to be convincing. You show your result to your advisor and tell him that you have put the blot against a flesh sheet of him, which you plan to expose for a longer period of time. He gives you a sideways look and tells you to do the experiment over again and use more radioactivity.

The Forth Week

Gonter and Grendel revisited.

Gonter and Grendel’s classic conduction that the plasma membrane of the human erythrocyte consists of a lipid bilayer was based on the following observation.

(1) The lipids that they extract with acetone from 4.74*109 erythrocytes formed monolayer

0.89m2 in area when spread out on a water surface.

(2) And the surface area of one erythrocyte was about 100μm2 according to their measurements.

We now know that the surface area of a human erythrocyte is about 145μm2. Explain how Gonter and Grendel could have come to the right conclusion.

The Fifth Week

You are studying the binding of proteins to the cytoplasmic face of cultured neuroblastomes（神经母细胞瘤） cells and have found a method that gives a good yield of inside-out vesicles from the plasma membrane. Unfortunately, your preparations are contaminated with variable amounts of right-side out vesicles. Nothing you have tried avoids this variable contamination.

A friend suggest that you pass your vesicles over an affinity column made of lectin coupled to solid beads.

The Sixth Week

Proteins that span a membrane as an α Helix have a characteristic structure in the region of the bilayer which of the three 20-amino acid sequences listed below is the most likely candidate for such a transmembrane segment? Explain the reasons for your choice.

The Seventh Week

Mutations in the genes encoding collagens often have detriment a consequences resulting in severely crippling diseases. Particularly devastating are mutations that change glycine resides which are required at every third position in the protein chain so that it can assemble into the characteristic triple-helical rod.

The Eighth Week

Working out the order in which the individual components in a signaling pathway act is an essential step in defining the pathway. Image that two protein kinases. PK1 and PK2, actsequentially in an intracellular signaling pathway. When either kinase is completely inactivated, cells do not respond to the normal extracellular signal. By contrast, cells containing a mutant from of PK1 that is permanently active respond even in the absence of an extracellular signal. Doubly mutant cells that contain inactivated PK2 and permanently active PK1 respond in the absence of a single.

Given the numerous processes inside cells that are regulated by changes in Ca2+-dependent cell-cell adhesions are also regulated by changes in Ca2+ concentration.

The Ninth Week

1.Currently, there are about 150a protein-coupled receptor proteins whose ligands and functions are unknown. What research approaches have been used to discover the signaling molecules associated with these “orphan GPCR’s”?

2.Describe the experimental evidence that the intrinsic GTPase activity for the Gα subunit is important for terminating effector activation.

3.All the following statements describe biomembranes except:

a, different biomembranes may contain different proportions of the same phospholipids.

b, the two leaflets of a biomembrane may contain different phospholipids. c. some biomembranes have free edges.

d. some phospholipids and cholesterol may duster to form lipid rafts.

4.All small intracellular mediators are water soluble and diffuse freely through the cytosol. (F)

The Tenth Week

1When the antibiotic valinomyein is added to actively respiring mitochondria,several things happen:the yield of ATP decreases,the rate of O2 consumption increases,heat is reteased,and the PH gradient across the inner mitochondrial membrane increases.Does valinomyein act as an unconpler or an inhibitor of oxidative phosphorylation?

2Although both ADP and Pi are required for the synthesis of ATP, the rate of synthesis depends mainly on the concentration of ADP,not Pi,why?

The Eleventh Week

1Describe in a general way how you might use radiolabled proteins and proteases to study import processes in isolated,intact mitochondria.What sorts of experimental controls might you include to ensure that the results you obtain mean what you think they do?

2All new phospholipids are added to the cytoplasmic leaflet of the ER membrane,yet the ER membrane has a symmetrical distribution of different phospholipids in its two leaflets.By contrast,the plasma membranes,which receives all its membrane components ultimately from the ER,has a very asymmetrical distribution of phospholipids in the two leaflets of its lipid bilayer.How is asymmetry generated in the plasma membrane?