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TLS Online TPP Program

#Question id: 1387

The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes. Microinjection into the cytoplasm of a wild. type cell of a solution of a synthetic peptide possessing the same sequence as the integrin beta subunit cytoplasmic domain would be expected to yield an average fibroblast-cell migration rat

Fibroblast Phenotype

Level of Integrin Heterodimer at the Cell Surface (percent of wild type)

Rate of Cell Migration (pm/min) 

1. Wild type

100

2

2. Overexpression of the wild-type integrin alpha subunit

104

2

3. Overexpression of an integrin beta subunit lacking the cytoplasmic domain

96

0.6

4. Overexpression of the soluble cytoplasmic domain of an integrin beta subunit

98

0.6

5. Absence of the integrin alpha subunit

Less than 1

0.05

#Unit 4. Cell Communication and Cell Signaling

  1. 4 microm/min

  2. 2 microm/min

  3. 0.6 microm/min

  4. 0.05 microm/min

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TLS Online TPP Program

#Question id: 731

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following structure is mentioned in the given Ramachandran plot
TLS Online TPP Program

#Question id: 729

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following is correct about the collagen triple-helix domain

a. is rich in glycine.                             b. is rich in proline.

c. is rich in hydroxyproline.                d. is an alpha helix.
TLS Online TPP Program

#Question id: 728

#Unit 1. Molecules and their Interaction Relevant to Biology

Match the following tile peaks with corresponding circular dichroism spectra

A. Alpha helixI. negative bands at 222 nm and 208 nm and a positive one at 190 nm.
B. Beta sheetII. negative band at 218 nm and a positive one at 196 nm.
C. Random coilIII. positive band at 212 nm and a negative one around 195 nm.
TLS Online TPP Program

#Question id: 727

#Unit 1. Molecules and their Interaction Relevant to Biology

26-residue peptide composed of alanine and leucine shows a circular dichroism (CD) spectrum characteristic of α-helix at 50°C in 5 mM phosphate buffer at pH 7.4. When the peptide solution is cooled gradually to 25°C, and the CD spectra are recorded at different temperatures, the most likely observation will be that
TLS Online TPP Program

#Question id: 726

#Unit 1. Molecules and their Interaction Relevant to Biology

The structure of a protein is known from X-ray diffraction studies which gave 30% - helix, 50% -sheet and 20% random coil. Circular dichroism (CD) measurements gave 50% -helix, 40% -sheet and 10% random coil. What could not be a possible explanation for these observations.
TLS Online TPP Program

#Question id: 725

#Unit 1. Molecules and their Interaction Relevant to Biology

At 25°C values of [θ]222, the mean residue ellipticity at 222 nm, are - 33,000 and -3,000 deg cm2 dmol-1 for a polypeptide existing in α- helical (α) and β-structure (β), respectively. If this polypeptide undergoes a two-state heat-induced α-β transition, and a value of [θ]222 =  -15,000 deg cm2 dmol-1 is observed at 60°C, then this observation leads to the conclusion that the α helix conversion to β- structure is: