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TLS Online TPP Program

#Question id: 720

How would a homopolymer of alanine be more likely to form an alpha helix in water or in a hydrophobic medium?

#Unit 1. Molecules and their Interaction Relevant to Biology

  1. In an aqueous environment, the formation of intrachain hydrogen bonds stabilizes the amide hydrogen atoms and carbonyl oxygen atoms of the polypeptide chain, and so an alpha helix forms. In an hydrophobic environment, these groups are stabilized by interaction with water, and so there is no energetic reason to form an a helix. Thus, the alpha helix would be more likely to form in a aqueous environment.

  2. In a hydrophobic environment, the formation of intrachain hydrogen bonds stabilizes the amide hydrogen atoms and carbonyl oxygen atoms of the polypeptide chain, and so an alpha helix forms. In an aqueous environment, these groups are stabilized by interaction with water, and so there is no energetic reason to form an alpha helix. Thus, the alpha helix would be more likely to form in a hydrophobic environment.

  3. In both hydrophobic environment as well as aqueous environment, the formation of intrachain hydrogen bonds stabilizes the amide hydrogen atoms and carbonyl oxygen atoms of the polypeptide chain, and so an alpha helix forms.

  4. In a aqueous environment, the formation of interchain hydrogen bonds stabilizes the amide hydrogen atoms and carbonyl oxygen atoms of the polypeptide chain, and so an alpha helix forms. In an hydrophobic environment, these groups are stabilized by interaction with water, and so there is no energetic reason to form an alpha helix. Thus, the alpha helix would be more likely to form in a aqueous environment.

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TLS Online TPP Program

#Question id: 13187

#Unit 10. Ecological Principles

The following figure is a model of seedling establishment as a function of distance from a parent tree. Initial seed density measures the number of seeds falling to the ground. Seed survivorship measures the proportion of seeds that survive to the adult stage at each distance


Which of the following factors is most likely to generate the seed density curve shown? 
TLS Online TPP Program

#Question id: 13186

#Unit 10. Ecological Principles

The following figure is a model of seedling establishment as a function of distance from a parent tree. Initial seed density measures the number of seeds falling to the ground. Seed survivorship measures the proportion of seeds that survive to the adult stage at each distance

This model predicts that recruitment of new individuals into the population should be
TLS Online TPP Program

#Question id: 13185

#Unit 10. Ecological Principles

If a drop in sea level led Island 1 to double in area, the MacArthur-Wilson model predicts that the number of bird species found there would
TLS Online TPP Program

#Question id: 13184

#Unit 10. Ecological Principles

The MacArthur-Wilson equilibrium model of island biogeography predicts the number of species found on islands. The figure below depicts two volcanic islands located off a section of mainland coast.

According to  the  MacArthur-Wilson model, the  number of  bird  species present on  Island 2  at  any  one  time is  a function of the relative rates of
TLS Online TPP Program

#Question id: 13183

#Unit 10. Ecological Principles

The MacArthur-Wilson equilibrium model of island biogeography predicts the number of species found on islands. The figure below depicts two volcanic islands located off a section of mainland coast.


According to the MacArthur-Wilson model, how would the number of bird species change from the time of an island's formation (assuming it remains constant in size and isolation)?
TLS Online TPP Program

#Question id: 13182

#Unit 10. Ecological Principles

The MacArthur-Wilson equilibrium model of island biogeography predicts the number of species found on islands. The figure below depicts two volcanic islands located off a section of mainland coast.

The MacArthur-Wilson model predicts that the relative numbers of bird species on the mainland and two islands would be