Ecologist Robert Macarthur observed that five species of similar warblers coexisted on spruce trees because they

#Question id: 10857

#Unit 10. Ecological Principles

Cowbirds never make nests, never incubate their eggs, and never care for their young. Instead they lay their eggs in the nests of host species, which either reject the egg or care for it and the young that hatches as their own. The cowbird is an example of a(n)

#Question id: 13117

#Unit 2. Cellular Organization

#Question id: 7766

#Unit 5. Developmental Biology

The relationship between shortened telomeres and stem cell depletion has been seen in degenerative diseases such as mouse muscular dystrophy,

I) When____ is activated by damaged telomeres, DNA replication halts, and if the repair doesn’t work, apoptosis is initiated. If the cell is a stem cell or some other rapidly replicating cell, this will reduce the numbers of cells produced, and the lack of stem cells will produce an “aged” phenotype.

 II) When ____ is activated by damaged telomeres, DNA replication halts, repair do its work, apoptosis is inhibited. If the cell is a stem cell or some other rapidly replicating cell, this will increase the numbers of cells produced, and then these cells will produce an “aged” phenotype.

 Choose correct gene name with right statement

#Question id: 21283

#Unit 12. Applied Biology

#Question id: 723

#Unit 1. Molecules and their Interaction Relevant to Biology

Common structural elements in proteins such as α-helices or β-sheets are characterized by uniformly repeating, energetically favorable main chain conformations which additionally exhibit a completely saturated hydrogen-bonding network of the main chain NH and CO groups. Although polyproline or polyglycine type II helices (PPII or PGII ) are frequently found in proteins, they are not considered as equivalent secondary structure elements. Which of the following statements are correct about PP and PGs.

A. PGII -like helices form hexagonal bundles which appear to fulfill the criterion of a (largely) saturated hydrogen-bonding network of the main-chain groups

B. main chain NH and CO groups of the central PGII -helix are saturated by either intra- or intermolecular hydrogen-bonds, resulting in a self-contained hydrogen-bonding network

C. The formation of the right-handed PPI helix is possible only with proline residues because of the required cis conformation. 

D. PPII helices seem to be stabilized by main chain-water hydrogen bonds (in the absence of main chain- main chain H-bonds), and tend to have a regular pattern of hydrogen bonds with water. After this, it is not surprising, that PPII helices are found mostly on the protein surface.