Biology 255 - THOUGHT QUESTIONS  
      Thought questions on Cell and Molecular Biology topics
    which are designed to make you think, They are structured
    to help you understand a concept, topic, or paradigm better.

       Using your prior knowledge and your comprehension of a topic
    you should be able to explain or clarify through multiple avenues
    an answer that predicts or expresses insight into a better
   understanding of a topic or concept.		 collabarative thoughts
       You may collaborative with your neighbor and exchange ideas
    to come to a conclusion that you believe will support your hypothesis. 		  
    There are generally no right or wrong answers, just a thought process
    that can lead to a viable conclusion.     		  
  ..    
    Good luck   
   
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An A-T base pair is stabilized by only two hydrogen bonds. Hydrogen-bonding schemes of very similar strengths can also be drawn between other base combinations that normally do not occur in DNA molecules, such as the A-C and the A-G pairs. What would happen if these pairs formed during DNA replication and the inappropriate bases were incorporated? Discuss why this does not often happen.  
mismatched base pairing
     Answer

 

 

 

 

 

 

 

 

 

 

 

 

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If the wrong bases were frequently incorporated during DNA replication, genetic information could not be inherited accurately. Life, as we know it, could not exist. Although the bases can form hydrogen-bonded pairs as indicated, these do not fit into the structure of the double helix. The angle with which the A residue is attached to the sugar–phosphate backbone is very different in the A-C pair, and the spacing between the two sugar–phosphate strands is considerably increased in the A-G pair, where two large purine rings interact. Consequently, it is energetically unfavorable to incorporate a wrong base in DNA, and such errors occur only very rarely.
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Homopolymers are polymers made by joining together monomers of the same 
     chemical composition or structure, a polymer consisting of all the same monomer.
Heteropolymers are polymers composed of more than one kind of monomer.

Homochiral polymers are polymers made by joining together same enantiomer
      all D or all L optical isomers: 
                    ex -  biological proteins are all L-amino acids.
                         -  starch (amylose) is a polymer of D-glucose units
Heterochiral polymers are polymers composed of a mix of enantiomers
      and are found with a few D-amino acids in proteins as peptidoglycan. 

Homochiral polymers take less energy to form than heterochiral polymers
       and likely might need more that one enzyme to polymerize the monomers.    
              chiral conformers
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   The two electron micrographs show nuclei of two different cell types. Can you tell from these pictures which of the two cells is transcribing more of its genes? Explain how you arrived at your answer.

 

 cells gene expression
       answer   

 

 

 

 

 

 

 

 

 

 

 

 

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   In the electron micrographs, you can detect chromatin regions of two different densities; the densely stained regions correspond to heterochromatin, while less condensed chromatin is more lightly stained. The chromatin in A is mostly in the form of condensed, transcriptionally inactive heterochromatin, whereas most of the chromatin in B is decondensed and therefore potentially transcriptionally active.
   The nucleus in A is from a reticulocyte, a red blood cell precursor, which is largely devoted to making a single protein, hemoglobin. The nucleus in B is from a lymphocyte, which is active in transcribing many different genes.



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 cells