Exam 2: The Chemical Basis of Life

What is the maximum number of 100 amino acid long polypeptides that could be made?

What level of structure in proteins is held together by intermolecular R group interactions?

Red wine supposedly has health-related benefits.What antioxidant chemical is reputed to be responsible for these benefits? Where is this chemical normally found that explains its ending up in red wine? How is this chemical thought to exert its antioxidant effects?

You are working with an enzyme altase that you denature in the presence of urea.If altase were denatured no further by the addition of mercaptoethanol,what would that suggest to you about the enzyme?

What is some specific evidence that demonstrates the importance of superoxide dismutase in getting rid of superoxide free radicals?

You are studying a protein.It binds to elongating polypeptide chains as they emerge from an exit channel within the ribosome's large subunit.It appears to prevent partially formed or nascent polypeptides from binding to other proteins in the cytosol,which might cause them either to aggregate or misfold.What kind of proteins is this likely to be? Another protein you are studying picks up larger proteins from Hsp70 family proteins.It is a cylindrical protein complex that contains chambers in which newly synthesized polypeptides can fold without interference from other cellular macromolecules.What is this protein called?

An enzyme is placed in a solution containing urea.Assuming that this protein contains no disulfide linkages,is it reasonable to suspect that it will be totally denatured by the treatment? How could you know that the enzyme has,in fact,been denatured? Why does the urea denature the tertiary structure of the enzyme?

Since replication is a property characteristic of nucleic acids,how might a prion,which lacks nucleic acids,"replicate" itself?

Scientists have sequenced proteins by using specific proteases to "clip" a purified protein preparation between two specific amino acids,thus forming a number of moderately sized fragments;they have used acid hydrolysis to produce smaller fragments.Each fragment can then be sequenced by breaking the moderate fragments into dipeptides that are easily sequenced.The fragments below are obtained after the initial enzymatic cleavages.Can you deduce the sequence of the original polypeptide? (HINT: the original cleavages at specific locations differ depending on which proteolytic enzyme was used to create each fragment;this causes an overlap in the fragments' sequences. )The final polypeptide should have 18 amino acid residues.

A release of hydrogen ions to a solution would most likely ____________.

DNA is isolated from two different species.Both DNA samples are found to be the same size.One of the DNA samples has a G+C/A+T ratio of 2.0 and the other 2.5.Which DNA sample has a higher G+C content? Which sample contains the smallest number of H bonds between strands? Which DNA sample would be easiest to denature?

You are a crew member on the starship Enterprise.Your responsibilities include investigation of biological life forms.You take out your tricorder after landing on the planet Yamihere and find a number of organisms,all of which contain DNA that follows the nitrogenous base pairing rules you are familiar with on Earth.For one species,the following relationships hold for the organism's DNA. How many moles of guanine are present? How many moles of thymine are present? How many moles of uracil are present? You isolate DNA from another organism living on the surface of Yamihere and find that it contains all the bases normally found in DNA,but does not obey the pairing rules.Can you explain these strange results?

If people are kept on diets containing about 25% fewer calories than would be required to maintain their initial body weight,what happens?

In a living organism,where are ionic bonds most likely to be found?

You treat a partially purified preparation of protein with a reagent that breaks bonds between sulfur atoms.Which level(s)of protein structure are likely to be affected the most?

What kinds of conditions can cause free radicals?

How was it proved that CJD could be passed to another organism?

The most electronegative atoms typically present in biological molecules are ____ and ____.

What type of protein secondary structure is characterized as being highly extensible because of its coiled structure?

Why is hydrogen peroxide often used as a disinfectant and bleaching agent? How do cells generally rid themselves of hydrogen peroxide?