1|Page
Chem 153A - Midterm 1 Exam With Complete
Solutions 100% 2026||Verified Exam!!!
What does the z axis on the diagram represent? -
Answers-Free energy
What does N mean on the diagram? - Answers-'N' refers
to the native state of the protein. It's meaningful that N is
lower in the energy landscape because it asserts that the
native state is the thermodynamic minimum, aka the most
thermodynamically stable state
Describe the physical process(es) associated with Region
1. Include relevant thermodynamic details in your
description. - Answers-This is hydrophobic collapse, the
rapid aggregation of nonpolar residues so as to increase
the entropy of the surrounding water. This forms a molten
globule state of the protein, an early intermediate in the
folding process.
Describe the physical process(es) associated with Region
2. Include relevant thermodynamic details in your
description. - Answers-The molten globule starts forming
new interactions such as hydrogen bonds in the peptide
,2|Page
backbone that create secondary structure, as well as a
number of interactions between R groups (hydrogen
bonds, electrostatic interactions, and disulfide bridges) - all
of which lower enthalpy. The folding also causes the
polypeptide chain to become more ordered, decreasing
entropy. As the structure works towards a thermodynamic
minimum (i.e. the native state) these opposing factors
create the observed 'jagged path'.
What is Levinthal's paradox and how does the diagram
address it? - Answers-Levinthal's paradox discusses how
a protein, if forming conformations randomly, would take
an impossibly long time to fold into the one, correct state.
The diagram addresses Levinthal's paradox by showing
that, instead of a countless number of equally energetic
states, the peptide can follow a series of favorable folding
decisions that lead it down a probable path.
Why is proline not good for secondary structure? -
Answers-Would destabilize secondary structure due to
constrained bond angles, would create a kink in β-sheet or
α-helix
One particularly old-school member of your team starts
isolating xeno-proteins and attempting to denature them to
, 3|Page
learn more about their structures. Urea is effective at
denaturing the xeno-proteins but all of the samples they've
exposed to 2-mercaptoethanol haven't been impacted in
any way. What do both of these pieces of data imply about
protein structure on Trappist-1d? - Answers-Urea being
effective at denaturing the xeno-proteins means the
peptide backbone is much the same as Earth's and that
hydrogen bonding between peptide chains is vital to xeno-
protein structure.
2-mercaptoethanol being ineffective at denaturation
means that life on Trappist-1d has no cysteines/disulfide
bonds!
Why do parallel and antiparallel β-sheets differ in stability?
- Answers-Antiparallel beta sheets are more stable
because their H-bonds are straighter and shorter
Function of His F8 Proximal - Answers-His F8 acts as a
coordination site for the central Fe2+ atom, holding the
heme in place
Function of His E7 Distal - Answers-Stabilizes O2 binding
and promotes specificity
Chem 153A - Midterm 1 Exam With Complete
Solutions 100% 2026||Verified Exam!!!
What does the z axis on the diagram represent? -
Answers-Free energy
What does N mean on the diagram? - Answers-'N' refers
to the native state of the protein. It's meaningful that N is
lower in the energy landscape because it asserts that the
native state is the thermodynamic minimum, aka the most
thermodynamically stable state
Describe the physical process(es) associated with Region
1. Include relevant thermodynamic details in your
description. - Answers-This is hydrophobic collapse, the
rapid aggregation of nonpolar residues so as to increase
the entropy of the surrounding water. This forms a molten
globule state of the protein, an early intermediate in the
folding process.
Describe the physical process(es) associated with Region
2. Include relevant thermodynamic details in your
description. - Answers-The molten globule starts forming
new interactions such as hydrogen bonds in the peptide
,2|Page
backbone that create secondary structure, as well as a
number of interactions between R groups (hydrogen
bonds, electrostatic interactions, and disulfide bridges) - all
of which lower enthalpy. The folding also causes the
polypeptide chain to become more ordered, decreasing
entropy. As the structure works towards a thermodynamic
minimum (i.e. the native state) these opposing factors
create the observed 'jagged path'.
What is Levinthal's paradox and how does the diagram
address it? - Answers-Levinthal's paradox discusses how
a protein, if forming conformations randomly, would take
an impossibly long time to fold into the one, correct state.
The diagram addresses Levinthal's paradox by showing
that, instead of a countless number of equally energetic
states, the peptide can follow a series of favorable folding
decisions that lead it down a probable path.
Why is proline not good for secondary structure? -
Answers-Would destabilize secondary structure due to
constrained bond angles, would create a kink in β-sheet or
α-helix
One particularly old-school member of your team starts
isolating xeno-proteins and attempting to denature them to
, 3|Page
learn more about their structures. Urea is effective at
denaturing the xeno-proteins but all of the samples they've
exposed to 2-mercaptoethanol haven't been impacted in
any way. What do both of these pieces of data imply about
protein structure on Trappist-1d? - Answers-Urea being
effective at denaturing the xeno-proteins means the
peptide backbone is much the same as Earth's and that
hydrogen bonding between peptide chains is vital to xeno-
protein structure.
2-mercaptoethanol being ineffective at denaturation
means that life on Trappist-1d has no cysteines/disulfide
bonds!
Why do parallel and antiparallel β-sheets differ in stability?
- Answers-Antiparallel beta sheets are more stable
because their H-bonds are straighter and shorter
Function of His F8 Proximal - Answers-His F8 acts as a
coordination site for the central Fe2+ atom, holding the
heme in place
Function of His E7 Distal - Answers-Stabilizes O2 binding
and promotes specificity
