The hormone adrenaline interacts with proteins located on the surface of cells and down not
cross the cell membrane. However, larger steroid molecules, such as estrone, cross cell
membranes and interact with proteins located in the call nucleus. Why is a large steroid
molecule able to cross the cell membrane when a smaller molecule such as adrenaline cannot?
- Answer The ability of a molecule to cross the fatty cell membrane has little to do with its size,
but more with its hydrophobic character.
Estrone is more hydrophobic than adrenaline since it has a larger carbon skeleton and only two
polar functional groups. Thus, the molecule is hydrophobic in character and can dissolve
through the fatty cell membrane.
Adrenaline has four polar functional groups and a much smaller carbon skeleton. Thus the polar
functional groups dominate in determining the character of the molecule making it very polar
and unlikely to pass through the cell membrane.
Valinomycin is an antibiotic which is able to transport ions across cell membranes and disrupt
the ionic balance of the cell. Find out the structure of valinomycin and explain why it is able to
carry out this task. - Answer outside is hydrophobic and inside is hydrophilic. as a result, it can
easily pass through the cell membrane and encapsulate polar ions;
Archea are microorganisms that can survive in extreme environments, such as high
temperatures, low pH, or high salt concentrations. It is observed that the cell membrane
phospholipids in these organisms are markedly different from those in eukaryotic membranes.
What differences are present and what function might they serve? - Answer The alkyl chains
are linked to the glycerol skeleton by ether linkages rather than by ester linkages. Ethers are
chemically more stable than esters to extreme conditions.
The long alkyl chains are also branched, unlike those in eukaryotic cell membranes. Branching
makes the chains more resistant to oxidation.
Teicoplanin is an antibiotic which 'caps' the building blocks used in the construction of the
bacterial cell wall such that cannot be linked up. The call wall barrier surrounding the bacterial
cell membrane and the building blocks are anchored to the outside of this cell membrane prior
to their incorporation into the cell wall. Teicoplanin contains a very long alkyl substituent which
plays no role in the capping mechanism. However, if this substituent is absent, activity drops.
What role do you think this alkyl substituent may serve? - Answer The alkyl group is
hydrophobic and is embedded into the cell membrane. As a result, the drug is anchored to the
cell membrane and is located on its outer surface such that it is ideally located to interfere with
cell wall synthesis.
The Rao protein is an important protein in signaling processes within the cell. It exists freely in
the cell cytoplasm, but must become anchored to the inner surface pf the cell membrane in
order to carry out its function. What kind of modification to the protein might take place to
, Cholesterol is an important constituent of eukaryotic cell membranes and affects the fluidity of
the membrane. Consider the structure of cholesterol and suggest how it might be oriented in
the membrane. - Answer Cholesterol has one polar group - the alcohol group. This can form a
H-bond to the polar head group of phospholipids. The rest of the molecule is hydrophobic and
will sink into the cell membrane to form hydrophobic interactions with the alkyl side chains of
the phospholipids.
Most unsaturated alkyl chains in phospholipids are cis rather than trans. Consider the cis-
unsaturated alkyl chain in the phospholipid shown in Fig. 1. 2. Redraw this chain to give a better
representation of its shape and compare it with the shape of the trans isomer. What conclusions
can you make regarding the packing of such chains in the cell membrane and the effect of the
membrane fluidity? - Answer Phospholipids are an amphipathic molecules, therefore they
have both hydrophobic and hydrophilic ends. The main components are unsaturated alkyl
chains and proteins. The main reason for the dominance of cis over trans is that it increases the
fluidity of the cell membrane by adding a kink to the chain. This kink results in the hindrance of
the hydrophobic interaction, thereby, increase the fluidity of the cell membrane.
cis-double bonds introduce a kink into the chain which will hinder the regular packing of the
hydrophobic chains. This increases the fluidity of the cell membrane.
The relative strength of carbonyl oxygens as hydrogen bond acceptors is shown in Fig. 1. 12.
Suggest why order is as shown. - Answer This reflects the fact that the greater the electron
density on the carbonyl oxygen, the stronger it will act as a hydrogen bond acceptor.
The carboxylate group is the strongest hydrogen bond acceptor since a full negative charge is
shared between both oxygens.
The carbonyl oxygen of the amide will also act as a good hydrogen bond acceptor since the lone
pair of electrons on nitrogen can interact with the carbonyl group to increase electron density
on the carbonyl oxygen as shown below.
No such interaction occurs for the ketone or ester carbonyl groups, but the carbonyl groups are
still polarised resulting in the oxygen having a slightly negative charge. Consequently it can still
act as a hydrogen bond acceptor, but less strongly.
Consider the structure of adrenaline, estrone, and cholesterol and suggest what kind of
intermolecular interactions are possible for these molecules and where they occur. - Answer
What is unique about glycine compared with other naturally-occuring amino acids? - Answer
cross the cell membrane. However, larger steroid molecules, such as estrone, cross cell
membranes and interact with proteins located in the call nucleus. Why is a large steroid
molecule able to cross the cell membrane when a smaller molecule such as adrenaline cannot?
- Answer The ability of a molecule to cross the fatty cell membrane has little to do with its size,
but more with its hydrophobic character.
Estrone is more hydrophobic than adrenaline since it has a larger carbon skeleton and only two
polar functional groups. Thus, the molecule is hydrophobic in character and can dissolve
through the fatty cell membrane.
Adrenaline has four polar functional groups and a much smaller carbon skeleton. Thus the polar
functional groups dominate in determining the character of the molecule making it very polar
and unlikely to pass through the cell membrane.
Valinomycin is an antibiotic which is able to transport ions across cell membranes and disrupt
the ionic balance of the cell. Find out the structure of valinomycin and explain why it is able to
carry out this task. - Answer outside is hydrophobic and inside is hydrophilic. as a result, it can
easily pass through the cell membrane and encapsulate polar ions;
Archea are microorganisms that can survive in extreme environments, such as high
temperatures, low pH, or high salt concentrations. It is observed that the cell membrane
phospholipids in these organisms are markedly different from those in eukaryotic membranes.
What differences are present and what function might they serve? - Answer The alkyl chains
are linked to the glycerol skeleton by ether linkages rather than by ester linkages. Ethers are
chemically more stable than esters to extreme conditions.
The long alkyl chains are also branched, unlike those in eukaryotic cell membranes. Branching
makes the chains more resistant to oxidation.
Teicoplanin is an antibiotic which 'caps' the building blocks used in the construction of the
bacterial cell wall such that cannot be linked up. The call wall barrier surrounding the bacterial
cell membrane and the building blocks are anchored to the outside of this cell membrane prior
to their incorporation into the cell wall. Teicoplanin contains a very long alkyl substituent which
plays no role in the capping mechanism. However, if this substituent is absent, activity drops.
What role do you think this alkyl substituent may serve? - Answer The alkyl group is
hydrophobic and is embedded into the cell membrane. As a result, the drug is anchored to the
cell membrane and is located on its outer surface such that it is ideally located to interfere with
cell wall synthesis.
The Rao protein is an important protein in signaling processes within the cell. It exists freely in
the cell cytoplasm, but must become anchored to the inner surface pf the cell membrane in
order to carry out its function. What kind of modification to the protein might take place to
, Cholesterol is an important constituent of eukaryotic cell membranes and affects the fluidity of
the membrane. Consider the structure of cholesterol and suggest how it might be oriented in
the membrane. - Answer Cholesterol has one polar group - the alcohol group. This can form a
H-bond to the polar head group of phospholipids. The rest of the molecule is hydrophobic and
will sink into the cell membrane to form hydrophobic interactions with the alkyl side chains of
the phospholipids.
Most unsaturated alkyl chains in phospholipids are cis rather than trans. Consider the cis-
unsaturated alkyl chain in the phospholipid shown in Fig. 1. 2. Redraw this chain to give a better
representation of its shape and compare it with the shape of the trans isomer. What conclusions
can you make regarding the packing of such chains in the cell membrane and the effect of the
membrane fluidity? - Answer Phospholipids are an amphipathic molecules, therefore they
have both hydrophobic and hydrophilic ends. The main components are unsaturated alkyl
chains and proteins. The main reason for the dominance of cis over trans is that it increases the
fluidity of the cell membrane by adding a kink to the chain. This kink results in the hindrance of
the hydrophobic interaction, thereby, increase the fluidity of the cell membrane.
cis-double bonds introduce a kink into the chain which will hinder the regular packing of the
hydrophobic chains. This increases the fluidity of the cell membrane.
The relative strength of carbonyl oxygens as hydrogen bond acceptors is shown in Fig. 1. 12.
Suggest why order is as shown. - Answer This reflects the fact that the greater the electron
density on the carbonyl oxygen, the stronger it will act as a hydrogen bond acceptor.
The carboxylate group is the strongest hydrogen bond acceptor since a full negative charge is
shared between both oxygens.
The carbonyl oxygen of the amide will also act as a good hydrogen bond acceptor since the lone
pair of electrons on nitrogen can interact with the carbonyl group to increase electron density
on the carbonyl oxygen as shown below.
No such interaction occurs for the ketone or ester carbonyl groups, but the carbonyl groups are
still polarised resulting in the oxygen having a slightly negative charge. Consequently it can still
act as a hydrogen bond acceptor, but less strongly.
Consider the structure of adrenaline, estrone, and cholesterol and suggest what kind of
intermolecular interactions are possible for these molecules and where they occur. - Answer
What is unique about glycine compared with other naturally-occuring amino acids? - Answer
