- Understanding: A mutation leads to a change in amino acid from serine, an amino acid with a polar side
chain, to alanine, an amino acid with a nonpolar side chain Do you think that the following levels of protein
structure change? If so how and why? If not, why not. Please frame your answer in terms of chemical bonds
and interactions.
Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure
Analyzing: The enzyme lysozyme catalyzes the hydrolysis of glycosidic bonds of peptidoglycans, a molecule
found in the cell wall of some bacteria. Consider the three-dimensional model of the tertiary structure enzyme
lysozyme (A) and a map of the primary structure of lysozyme showing the location amino acids that participate
in binding and catalysis at the active site (B) and answer the following questions.
three dimensional structure of lysozyme
Lysozyme catalyzes the hydrolysis of glycosidic bonds from peptidoglycans but does not catalyze the
hydrolysis of glycosidic bonds in glycogen. Why?
Research has shown that amino acid 35 (yellow), a glutamic acid, an amino acid with a negatively-charged
side chain, is critical for catalysis. Other studies have found that amino acids 62 (pink) and 63 (purple), both
tryptophan, an amino acid with a positively-charged side chain, are critical for substrate binding. Use this
information and figure 4.2 in your book to answer the following questions: Do you think changing amino acid 35
from glutamic acid to a lysine, an amino acid with a positively-charged side chain will affect substrate binding,
catalysis, both, or neither? Explain your answer
Applying: Refer to the Lac operon to answer the questions below
lac operon diagram
How does the presence or absence of different carbon sources affect the expression of genes in the Lac
operon? The first row is filled out as an example:
Carbon source
Lac repressor
Expression of genes in Lac operon
Glucose
Bound to DNA
Repressed
Glucose + lactose
Lactose
You isolate a mutant that produces the repressor protein but also produces B-galactosidase whether or not
lactose is present. In which gene would you expect to find that mutation to be and why?
You isolate a mutant strain with a mutation in lacP (promotor) that prevents RNA polymerase from binding.
When would expect this strain to produce B-galactosidase: all the time, only in the presence of lactose, or
never? Explain your reasoning.
Analyzing Mini-case study: Researcher studying epigenetic changes induced by exercise had participants
pedal a stationary bicycle with only one leg for 45 minutes a day, 4 times a week for 3 months. They then took
muscle biopsies from both legs (the one that exercised and the one did not) and compared DNA to look for
epigenetic changes induced by exercise. They found over 5,000 sites on the genome where methylation
patterns differed between the DNA isolated from the exercised leg and DNA isolated from the non-exercised
leg.
A. How would you predict these changes would affect transcription and translation? Is there other information
you need to know to feel confident in your prediction?
B. Would these changes be passed down to the participants’ offspring? Why or why not?
C. Why did they have all participants exercise only one leg rather than having two groups- one who exercised
and one who did not?
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