SDS PAGE

Describe the purpose and process of SDS PAGE. (10 marks)


The purpose of the SDS PAGE is to separate proteins according to their size.
In order to prepare the SDS PAGE, we must firstly add the protein into the SDS using the pipette. The SDS solution is also known as Sodium dodecyl sulfate for its full name. Its function is to make the secondary or teritary structure of the protein to primary structure, and it becomes a linear strand. After putting into the SDS, the protein will be covered with many negative charges. The reason is because before it gets break down into primary structure, it has positive and negative charges. After soaking into the SDS, it becomes negative charges.
After the protein is being inserted into the well, the electric charges will flow through it by opening the switch. The proteins will flow from the negative electrode to the positive electrode. The reason is because the proteins have strong negativity, and it will therefore get attracted to the positive sides.
After some time, the proteins with different sizes will get stuck at the different locations, therefore we are able to determine the size of it, and telling which is larger and which is smaller.

献媚之行， 奢求之为

品读三国

（一）邓艾破蜀，遣人赴洛阳报捷，修书司马昭：“今可封刘禅为扶风王，赐以资财，供其左右，以显归命之宠。”司马昭览毕，深疑邓艾有自专之心，乃发手书告知：“此事须候奏报，不可辄行。”邓艾忿忿回书：“吾既奉诏专征，当权宜行事，如何阻挡？”司马昭不悦，用计杀邓艾。　　“无规矩不成方圆”，该你干的事你去干，不该你干的事就别去干，有些事最好想都不要想，中国人就认这个理。可怜邓艾一介武夫，不懂这个道理，居然把司马昭的“奉诏专征”当成回事，居大功而不得善终。　　宋朝有个叫曹彬的将军，能征善战。有一次奉命攻城，敌兵将败，曹彬却突然下令停止进攻，诸将不解。他的意思是：之前圣上屡攻此城而不下，我等今日一举拿下，岂不是自己找死。于是，曹彬上奏，皇帝御驾亲征，结果顷刻破城，万民欢腾，龙颜大悦。　　曹彬没有邓艾的功勋大，可他的结果比邓艾好多了，因为他懂规矩。（二）曹操攻徐州，俘吕布。吕布献媚：“布今愿降明公，公为大将，布副之，何愁天下不定？”时刘备在侧，吕布哀求：“公为座上客，布为阶下囚，何不发一言而相救乎？”吕布军中大将张辽怒斥：“吕布匹夫，大丈夫死则死耳，何惧之有。”　　自古以来流传着两句话，“知遇之恩”和“士为知己者死”，可见要想遇一个英明的主子是多么的不易。张辽是个视死如归的汉子，却跟了吕布这么一个贪生怕死的家伙，连死都没有骨气(张辽最后并没被杀，曹操感其人品，收为大将)。　　汉文帝时，晁错忠心耿耿，怀才抱负，堪称一代贤臣，而当吴楚七国向朝廷发难之时，汉文帝却把他给卖了。五代十国，当北汉大将杨继业正与宋军苦战，他的主子北汉王却怀揣着宋朝的官印，前来劝他投降。　　我们有着太多“不遇”的悲哀。所以我们把“知遇”当成了一种奢求，一旦得遇明主，便要肝脑涂地，甚至以死相报。　　一页页史书翻过，我一声声叹息。

奢求 she1 qiu2

过高而难以实现的要求。

献媚 xiàn mèi

为讨好别人而做出使人欢心的姿态、举动。



老爷翰苑蜚声，素羨风流太守；贱妾平康献媚，自惭窈窕佳人。　　明 陈汝元《金莲记·湖赏》

有欲私其仆妇者，仆固黠，令其妻献媚勾引，而终不一任缱绻，主急甚。　　清 采蘅子《虫鸣漫录》

卷二她不想用鲜花向主人献媚，遍身披上刺刀。　　流沙河《草木篇》诗

operon

The lac-operon consists of a operator, gene Z, gene Y, and Gene A.

The repressor protein will be able to bind onto the operator side. After binding onto the operator side, the RNA polymerase will not be able to proceed to read the DNA, and therefore, the DNA will not be transcripted.

In order for the RNA polymerase to be able to transcript the DNA, the lactose will bind onto the repressor, and therefore changing the shape of the repressor, and it will no longer be able to fit onto the operator.

After that, the RNA polymerase is able to proceed into transcripting the DNA without any obstacle blocking.

After transcription, it will form mRNA, and then it will form protein. The gene A codes for beta-galactosidase, which is able to break down lactose to form glucose.

MCB Quiz problem 7

The following reaction involving the breakdown of sugar A occurs in a bacterial cell. The gene that codes for the enzyme is part of an operon.
In an experiment, some of the bacterial cells were cultured in three flasks with 100 mg/ml of sugar A added. In flasks 1 and 2, compounds L and M were added respectively. Nothing was added to flask 3. The following results were obtained.


Concentration of B (mg/ml)

Flask 1
Flask 2
Flask 3

Addition of…
L
M
(nothing)
At 0 minutes

0
0
0
At 40 minutes

110
2
98
At 80 minutes

201
3
100
At 120 minutes

250
5
100



a) Which of the compounds (L or M) might be a gene repressor? Explain your answer. (5 marks)


M. The reason is because the function of the repressor is to stop the DNA from getting transcripted. If the concentration of the B is very less, this means that there are very less proteins present inside the cell, and this could be due to the large amount of repressor. The reason is because large amount of repressor will slow down the transcription process. The DNA will be transcripted to produce the enzymes, and therefore the sugar will be able to break down. Lesser amount of B means that there are also not enough amount of enzymes for breaking, and this shows that the transcription process is being slowed down by the repressor, therefore the translation process is also being slowed down, therefore, the proteins being produced are also lesser, therefore, the amount of B is less.

b) Suggest with explanations what compound L might be. (5 marks)

Compound L increases the production of the B, therefore, it could be the enzyme that breaks down the sugar A.
It can also be a inductor which is able to bind with the repressor, and therefore preventing the repressor from binding onto the operator of the DNA, and therefore, it is able to go through more transcription, and therefore going through more translation, and then, it will be able to produce more enzymes that is able to break down the sugar A into B and C, and therefore, the concentration of B increases.