生物讨论专区

silent91

原帖由 星座小王子 于 1-6-2009 03:31 PM 发表


有问题多问哦。。。

尽量，大家研究研究咯～

白羊座aries

Describe the DNA replication, your answer should including all the enzyme involved . [15]

谢谢各位热心帮忙下

jenyeh90

Describe the DNA replication, your answer should including all the enzyme involved . (15)

-double helix of DNA unwind,starting frm one end.
-H bonds between DNA bases breaks,double helix of DNA start to separate frm one end.
-DNA helicase enzyme catalyzes the unwinding and also the separation of the double helix.
-both strands of DNA act as template for the formation of the new DNA strand
-free nucleotides pair with the exposed bases of both template strands.
-base pairing is exact that is between A with T and G with C.
-nucleotides are then linked together to form the new DNA strand.Process catalyzed by DNA polymerase.
-DNA polymerase synthesized the new strand of DNA in the direction of 5' to 3'.
-DNA helicase move along the DNA until the double helix of the DNA completely separates.
-because the synthesis of new strand of DNA is in the direction of 3',only one new strand is systhesis continuously by the DNA polymerase.
-the other new strand is synthesized in fragments called Okazaki fragments.
-the Okazaki fragments are the linked together by DNA ligase enzyme.
-when replication is completed,2 new DNA molecules identical to the DNA parent molecule is produced.
-the accuracy of replication is the result of exact base pairing between bases,ie,A with T and G with C.
-DNA replication in all organism is semi-conservative.The new DNA possess one parental strand and one new strand.


这是1992年 STPM Bio 的 SKEMA

白羊座aries

原帖由 jenyeh90 于 7-9-2009 04:25 PM 发表
Describe the DNA replication, your answer should including all the enzyme involved . (15)

-double helix of DNA unwind,starting frm one end.
-H bonds between DNA bases breaks,double helix of DNA st ...

哈哈,谢谢你的热心帮忙,但是你答案的sequence好像乱了,对吧..

[ 本帖最后由 白羊座aries 于 7-9-2009 06:37 PM 编辑 ]

jenyeh90

恩，你是说那里呢？呵呵

白羊座aries

原帖由 jenyeh90 于 7-9-2009 07:00 PM 发表
恩，你是说那里呢？呵呵

-the accuracy of replication is the result of exact base pairing between bases,ie,A with T and G with C.

base pairing is exact that is between A with T and G with C.

为什么有两个一样的point??但是位置不一样就有分?

jenyeh90

一样么？

-when replication is completed,2 new DNA molecules identical to the DNA parent molecule is produced.
-the accuracy of replication is the result of exact base pairing between bases,ie,A with T and G with C.
-DNA replication in all organism is semi-conservative.The new DNA possess one parental strand and one new strand.

这3句可以说是SUMMARY DNA replication process，所以不一样point吧？

白羊座aries

原帖由 jenyeh90 于 8-9-2009 06:30 PM 发表
一样么？

-when replication is completed,2 new DNA molecules identical to the DNA parent molecule is produced.
-the accuracy of replication is the result of exact base pairing between bases,ie,A wi ...

是咩我觉得很乱下咯

白羊座aries

为什么没有RNA primase?
RNA primase synthesis RNA primer to enable DNA polymerize 3 elongate嘛...

道信

可以问关于experiment的事情吗？
我对soil analysis，抓insect和plants的不是很了解！

白羊座aries

Explain the role of NAD and oxygen in oxidative phosphorylation.   [7]

我只是知道NAD去oxidative phosphorylation会得到3ATP by pumping 3 times hydrogen to the complex protein molecule .

oxygen act as final receptor ,如果没有oxygen,整个kreb cycle会停下来,但是问题是这样是得不到7分,要怎样写才可以拿到7分

darksider

原帖由 jenyeh90 于 2009/9/7 04:25 PM 发表
Describe the DNA replication, your answer should including all the enzyme involved . (15)

-double helix of DNA unwind,starting frm one end.
-H bonds between DNA bases breaks,double helix of DNA st ...

需要mention的有
-DNA helicase unwinds the double-helix strands
-Both strands are stabilised by single-stranded binding protein
-RNA primase attaches RNA primer (a short RNA polynucleotides) to the bottom DNA template (3' to 5').
-Free DNA nucleotides that are complementary to the bottom template are added by DNA polymerase III in the direction 5' to 3' continuously as it follows the direction of replication fork, forming the leading strands.
-RNA primase also attaches RNA primer to the top DNA template (5' to 3'). However, the strands elongate discontinuously because free DNA nucleotides can only be added in the direction 5' to 3'. As a result, okazaki fragment is formed. Since it doesn't follow the direction of replication fork, it is called lagging strand.
-The DNA nucleotides base pair with the nucleotide base in the DNA template with Adenine (A) pairing to Thymine(T) and Guanine (G) pairing with Cytosine(C) by hydrogen bond.
-When elongation of both strands complete, DNA polymerase I replaces the RNA nucleotides found in RNA primer with DNA nucleotides and then the okazaki fragments are covalent-bonded to each other by DNA ligase.
-Then, the leading strand and lagging strand is completely formed. They detaches from the DNA templates and wind with each other to form double-helix structure through hydrogen bonding.

*Remember to mention DNA nucleotides instead of only free nucleotides.
In actual fact, we should use DNA nucleosides triphosphates. Addition of nucleotides is possible due to the energy released when two phosphate groups are broken down from the DNA nucleosides triphosphates.

Enzymes involved in DNA replication
-RNA primase & RNA polymerase (add nucleotides to form RNA primer)
-Topoisomerase (reduce strain caused by supercoiling at the replication fork)
-Single-stranded binding protein - stabilise the unwound DNA strands so that they can be used as template
-DNA polymerase III - add DNA nucleotides to the RNA primer in the direction 5' to 3' to form leading and lagging strand.
-DNA polymerase I - replaces all the RNA nucleotides with DNA nucleotides
-DNA ligase - connects okazaki fragments together and  also connect the replaced part of the RNA primer by covalent bonding.

[ 本帖最后由 darksider 于 24-10-2009 10:11 AM 编辑 ]

darksider

原帖由 白羊座aries 于 2009/10/24 07:34 AM 发表
Explain the role of NAD and oxygen in oxidative phosphorylation.   [7]

我只是知道NAD去oxidative phosphorylation会得到3ATP by pumping 3 times hydrogen to the complex protein molecule .

oxygen act ...

The role of NAD in oxidative phosphorylation is such that it is the first electron acceptor in Electron Transport System(ETS). Its role is to accept electrons from molecules such as NADPH + H(+) to be oxidised into NADPH+ H(+).

The energy released when NADH + H(+), the primary electron acceptor, is oxidised into NAD+ is sufficient for oxidative phosphorylation to occur in which ATP is formed from ADP and Pi.  

According to chemiosmosis theory,the oxidation of NADH + H(+) to NAD+ when it passes electrons to flavoprotein will pump H+ ions into the intermembranous space of mitochondria which then creates a concentration gradient. The energy released when H+ return to the mitochondria is used in oxidative phosphorylation.

Oxygen acts as the final electron acceptor in ETS. Its main role is to accept electrons and hydrogen ions from the cytochrome oxidase to be reduced into water molecules. Without oxygen as the final electron acceptor, the oxidation phosphorylation cannot be carried out. Consequently, anaerobiosis occurs in the absence of oxygen.


Hence, if there is no oxygen, NADPH + H(+) produced in Kreb's cycle, glycolysis and link's reaction and FADH2 produced in Kreb's cycle cannot be used up in the Electron Transport System and hence, no ATP can be produced by oxidative phosphorylation.
If cyanide is introduced to the bodies, it will inhibit the activity of cytochrome oxidase which results in no electrons being transported to the oxygen molecules. Therefore, oxidation phosphorylation is not carried if cyanide is introduced as it prevents electrons from being transported to oxygen, the final electron acceptor.

*If you want to add more, you can mention the following
- NADH + H(+) is the reduced form of NAD. It is produced in glycolysis, link's reaction and kreb's cycle.
The NADH + H(+) produced in glycolysis will enter the Electron Transport System (ETS) in mitochondria and pass its electron to NAD+, the first electron acceptor to be oxidised into NAD+ itself and then the electrons are passed to subsequent electron acceptors until it is passed to the final electron acceptor oxygen, through a series of redox reactions.
-The energy released from the oxidation of NADH + H(+) and subsequent electron acceptors in ETS is sufficent to make 3 ATP molecules through oxidative phosphorylation.

[ 本帖最后由 darksider 于 24-10-2009 10:04 AM 编辑 ]

bell_25

想问一下。。
cistron和gene有什么分别？还是两个都是同样的东西？
DNA里的gene是不是就是triplet genetic code 或 codon呢？
谢谢

darksider

原帖由 bell_25 于 2009/11/2 12:21 AM 发表
想问一下。。
cistron和gene有什么分别？还是两个都是同样的东西？
DNA里的gene是不是就是triplet genetic code 或 codon呢？
谢谢

cistron 的意思就是gene.It is a section of DNA that codes for polypeptide/protein. Operon的structural genes are arranged in polycistronic arrangement.意思是他们都是在同一个chromosome而且也是连续的。

Codon是triplet code。在mRNA，我们称呼它为codon，在tRNA我们称呼为anticodon.

白羊座aries

问下ATP synthetase 和 整个oxidative phosphorylation 是怎样操作的?为什么没有oxygen就没有kreb cycle?就因为oxygen是act as final acceptor for oxidative phosphorylation,所以没有O2就没有kreb cycle?没有oxidative phosphorylation而已,关kreb cycle什么事?

四月一日的小皮

原帖由 白羊座aries 于 2-11-2009 02:17 PM 发表
问下ATP synthetase 和 整个oxidative phosphorylation 是怎样操作的?为什么没有oxygen就没有kreb cycle?就因为oxygen是act as final acceptor for oxidative phosphorylation,所以没有O2就没有kreb cycle?没有oxida ...

yup,oxygen is needed during electron transport chain.it react with proton to form water.without it,the electron are accumulated at the cytochrome oxidase.this is then prevent the NADH and FADH2 to oxidise back to NAD+ and FAD+.there is no free NAD+ and FAD+ for glycolysis,link reaction and also  Kreb's cycle.

bell_25

哦。。谢谢。。
可是。。我还是很疑惑。。
书本里写the instruction for making proteins comes from the genes。。这个genes是不是refer to triplet code in DNA?

bell_25

想问你们。。
你们同意一下的statement吗？

Dark reaction is the stage of photosynthesis that does not need light.
It could occur in light or in the dark.

谢谢。。

darksider

原帖由 bell_25 于 2009/11/2 04:50 PM 发表
哦。。谢谢。。
可是。。我还是很疑惑。。
书本里写the instruction for making proteins comes from the genes。。这个genes是不是refer to triplet code in DNA?

Gene is a section in DNA which codes for a protein/polypeptide. Remember Beadle and Tatum hypothesis - One gene one polypeptide?

Codon is just a triplet code found in DNA that codes for a certain amino acid.

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Dark reaction is the light independent reaction in photosynthesis.