Chapter 19, Problem 30P

Interpretation Introduction

(a)

Interpretation:

The performance of chloroplast ATP synthase in the presence of DDT alone and DDT+ with thioredoxin present should be monitored.

Concept introduction:

DDT stands for Dichlorodiphenyltrichloroethane. This prevents the complete repolarization of mitochondria. High concentrations of DDT leads to the destruction of the structural integrity of mitochondria.

Thioredoxin is a class of small redox proteins, which acts as a redox signal in organisms.

Answer to Problem 30P

Thioredoxin

Explanation of Solution

Thioredoxin is a class of small redox proteins known to be present in all organisms, including animals & plants. The major function of Thioredoxin is known to be redox signaling. Up to some extent it is understood that thioredoxin plays a central role in human response to reactive oxygen species (ROS). In plants, thioredoxins are responsible for the regulation of a wide range of functions including photosynthesis, growth, flowering and the development and germination of seeds.

The given graph shows ATPase activity under different conditions. The pink color graph is for the modified enzyme. The modified enzyme contains the Chloroplast subunit, which contains the chloroplast ATP synthase.

When the 2 pink color graphs are examined, it is obvious that the presence of thioredoxin has significantly increased the ATPase activity. So, it is clear that thioredoxin regulated the activity of chloroplast ATP synthase.

So thioredoxine act as a redox regulator for ATPsynthase.

Interpretation Introduction

(b)

Interpretation:

The graphical behavior of control enzyme and modified enzyme when DDT concentration increased along the x-axis should be monitored.

Concept introduction:

DDT which stands for Dithiothreitol is a reducing agent which is found in biological systems.

Explanation of Solution

The given graph shows the ATPase activity Vs. DDT amount under different conditions.

DDT is a reducing agent which is present in this medium. It has the ability to increase the redox power of the medium. So increasing the reducing power means increasing the DDT concentration. Therefore to determine the effect of increasing reducing power, the effect of increasing DDT concentration should be examined.

When considering the ATPase activity of control enzyme along the x-axis (increasing of DDT) it is clear that ATPase activity hasn’t been changed much. To observe this the 2 blue color graphs should be examined. So it is clear that the ATPase activity of control enzyme has no effect of DDT concentration.

But the activity of ATPase of the modified enzyme has been significantly increased when DDT concentration is increased. It should be obvious when comparing the behavior of the 2 pink graphs. In both pink color graphs in the initial part, the ATPase activity has been significantly increased, when DDT concentration is increased.

That means increasing of DDT concentration or increasing of reducing power has increased the ATPase activity of the modified enzyme.

Interpretation Introduction

(c)

Interpretation:

The graphical behavior of modified enzyme which thioredoxin present and absent should be observed.

Concept introduction:

Thioredoxin & DDT are reducing agents known to be present in biological organisms.

Explanation of Solution

Thioredoxin is a class of small redox proteins known to be present in all organisms including animals & plants. DDT is again a reducing agent which is found in biological systems.

When studying the 2 blue color graphs, which is for the control enzyme, it is clear that DDT / thioredoxin was not been able to make a significant impact on the ATPase activity.

When observing the pink color graphs, which are for the modified enzyme, it is obvious that DDT / thioredoxin has been able to make an impact on the ATPase activity.

Out of these 2 thioredoxin has been able to make a significant effect on the modified enzyme.This should be visible when monitoring pink colour graphs along the x axis & y axis.

So it is clear that thioredoxin has made a significant effect rather than DDT.

The reason should be the excess efficiency in thioredoxin compared to DDT to increase the ATPase activity of modified enzyme.

So adding thioredoxin to the system has made the redox power increased, hence the ATPase activity increased.

Interpretation Introduction

(d)

Interpretation:

Overall four graphs should be monitored.

Concept introduction:

This experiment is planned to determine the responsible sub unit for the difference in ATPase activity in Chloroplast & Mitochondria.

Answer to Problem 30P

Yes

Explanation of Solution

Consider the changes of the graph of the modified enzyme along x axis. When DDT concentration has been increased the ATPase activity has increased and then shows a zero slope.

When adding thioredoxin along with DDT the activity of ATPase has distinguishably increased. So, thioredoxin should be the major factor responsible for the redox regulation of chloroplast subunit.

The modified enzyme has $\gamma$ subunit replaced from a chloroplast. Therefore the region of gamma subunit where thioredoxin present should be responsible for the redox regulation.

Interpretation Introduction

(e)

Interpretation:

The biological process limited only to plants should be considered.

Concept introduction:

The biological process which is unique to plants is photosynthesis. It is the process of converting of the energy in sun light to chemical energy.

Answer to Problem 30P

Photosynthesis

Explanation of Solution

This thioredoxin use its reducing power to regulate high concentrations of reducing agents. Reducing agents are the chemical compounds who like to oxidize. This thioredoxin is present in the gamma sub unit of the modified enzyme. Gamma sub unit was originally taken from the chloroplast.

The particular biological process happens in chloroplast is photosynthesis. So photosynthesis, which is limited only to plant materials, should be the biological rationale of regulation of high concentrations ofreducing agents by producing thioredoxin.

Conclusion

Photosynthesis, which is unique to plant materials is the biological rationale of regulation of high concentrations of reducing agents by producing thioredoxin.

Interpretation Introduction

(f)

Interpretation:

For this part twenty amino acids with its structures should be considered.

Concept introduction:

Amino acid is the primary unit of protein. It has four groups as carbonyl group (- COOH), amine group (-NH₂), a hydrogen (-H) and R group. There are twenty different amino acids.

Answer to Problem 30P

Cysteine

Explanation of Solution

An amino acid has four groups as carbonyl group (- COOH), amine group (-NH₂), a hydrogen (-H) and R group.

Chemical formula of Cysteine: HS- C-H-(COOH)-NH₂ In Cysteine a SH group is present as the R group.

At the reducing conditions, oxidation is mostly prevented and reduction is encouraged. The Sylphydryl group of cysteine (-SH) is a very strong reducing factor. Cysteine is the only amino acid with −SH group.

So cysteine can be mostly affected by reducing conditions.

Conclusion

Cysteine can be mostly affected by reducing conditions.

Interpretation Introduction

(g)

Interpretation:

Experiments related to prove reducing ability of cysteine should be mentioned.

Concept introduction:

Reducing agents has the ability to reduce. It is the capability to capture electrons in the medium.

Answer to Problem 30P

Group specific modification and site specific modification of proteins

Explanation of Solution

Group and site specific modifications in amino acids enable to install pre- determined modifications on proteins. They will change the original nature and reactions of the amino acids.

Reducing ability of a compound is the ability to capture extra electrons from the medium in order to increase the negative charge. This is shown by the reducing agents.

The reducing nature of the cystine is mainly due to the −SH group present .Therefore several modification s on −SH group with allow to confirm that out of 20 amino acids cystine is the amino acid which can show remarkable affect due to the reducing conditions.

Conclusion

Group specific modification and site specific modification of cysteine will prove that out of 20 amino acids cysteine is the one which mostly affected by reducing conditions.