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Protein synthesis begins when the gene encoding a protein is

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Protein synthesis begins when the gene encoding a protein is [#permalink] New post 25 Jun 2013, 08:32
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Protein synthesis begins when the gene encoding a protein is activated. The gene’s sequence of nucleotides is transcribed into a molecule of messenger RNA (mRNA), which reproduces the information contained in that sequence. Transported outside the nucleus to the cytoplasm, the mRNA is translated into the protein it encodes by an organelle known as a ribosome, which strings together amino acids in the order specified by the sequence of elements in the mRNA molecule. Since the amount of mRNA in a cell determines the amount of the corresponding protein, factors affecting the abundance of mRNA’s play a major part in the normal functioning of a cell by appropriately regulating protein synthesis. For example, an excess of certain proteins can cause cells to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes.

Biologists once assumed that the variable rates at which cells synthesize different mRNA’s determine the quantities of mRNA’s and their corresponding proteins in a cell. However, recent investigations have shown that the concentrations of most mRNA’s correlate best, not with their synthesis rate, but rather with the equally variable rates at which cells degrade the different mRNA’s in their cytoplasm. If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNA’s will accumulate to high levels.

An important example of this phenomenon is the development of red blood cells from their unspecialized parent cells in bone marrow. For red blood cells to accumulate sufficient concentrations of hemoglobin (which transports oxygen) to carry out their main function, the cells’ parent cells must simultaneously produce more of the constituent proteins of hemoglobin and less of most other proteins. To do this, the parent cells halt synthesis of non-hemoglobin mRNA’s in the nucleus and rapidly degrade copies of the non-hemoglobin mRNA’s remaining in the cytoplasm. Halting synthesis of mRNA alone would not affect the quantities of proteins synthesized by the mRNA’s still existing in the cytoplasm. Biologists now believe that most cells can regulate protein production most efficiently by varying both mRNA synthesis and degradation, as developing red cells do, rather than by just varying one or the other.
1. The passage is primarily concerned with discussing the
(A) influence of mRNA concentrations on the development of red blood cells
(B) role of the synthesis and degradation of mRNA in cell functioning
(C) mechanism by which genes are transcribed into mRNA
(D) differences in mRNA concentrations in cell nuclei and in the cytoplasm
(E) way in which mRNA synthesis contributes to the onset of diabetes
[Reveal] Spoiler:
B


2. The passage suggests that a biologist who held the view described in the first sentence of the second paragraph would most probably also have believed which of the following?
(A) The rate of degradation of specific mRNA’s has little effect on protein concentrations.
(B) The rate of degradation of specific mRNA’s should be studied intensively.
(C) The rates of synthesis and degradation for any given mRNA are normally equal.
(D) Different mRNA’s undergo degradation at widely varying rates.
(E) Most mRNA’s degrade very rapidly.
[Reveal] Spoiler:
A


3. Which of the following best describes the relationship between the second and third paragraphs of the passage?
(A) The second paragraph presents arguments in support of a new theory and the third paragraph presents arguments against that same theory.
(B) The second paragraph describes a traditional view and the third paragraph describes the view that has replaced it on the basis of recent investigations.
(C) The third paragraph describes a specific case of a phenomenon that is described generally in the second paragraph.
(D) The third paragraph describes an investigation that was undertaken to resolve problems raised by phenomena described in the second paragraph.
(E) Both paragraphs describe in detail specific examples of the phenomenon that is introduced in the first paragraph.
[Reveal] Spoiler:
C


4. The accumulation of concentrations of hemoglobin in red blood cells is mentioned in the passage as an example of which of the following?
(A) The effectiveness of simultaneous variation of the rates of synthesis and degradation of mRNA
(B) The role of the ribosome in enabling a parent cell to develop properly into a more specialized form
(C) The importance of activating the genes for particular proteins at the correct moment
(D) The abnormal proliferation of a protein that threatens to make the cell cancerous
(E) The kind of evidence that biologists relied on for support of a view of mRNA synthesis that is now considered obsolete
[Reveal] Spoiler:
A


5. To begin to control a disease caused by a protein deficiency, the passage suggests that a promising experimental treatment would be to administer a drug that would reduce
(A) only the degradation rate for the mRNA of the protein involved
(B) only the synthesis rate for the mRNA of the protein involved
(C) both the synthesis and degradation rates for the mRNA of the protein involved
(D) the incidence of errors in the transcription of mRNA’s from genetic nucleotide sequences
(E) the rate of activity of ribosomes in the cytoplasm of most cells
[Reveal] Spoiler:
A


6. According to the passage, which of the following best describes the current view on the relationship between the synthesis and the degradation of mRNA in regulating protein synthesis?
(A) Biologists have recently become convinced that the ribosome controls the rates of synthesis and degradation of mRNA.
(B) There is no consensus among biologists as to the significance of mRNA degradation in regulating protein synthesis.
(C) The concept of mRNA degradation is so new that most biologists still believe that the vital role in protein regulation belongs to mRNA synthesis.
(D) Degradation of mRNA is now considered to be the key process and mRNA synthesis is no longer believed to play a significant role.
(E) Degradation of mRNA is now considered to be as important as mRNA synthesis has been, and still is, believed to be.
[Reveal] Spoiler:
E


7. According to the passage, which of the following can happen when protein synthesis is not appropriately regulated?
(A) Diabetes can result from errors that occur when the ribosomes translate mRNA into protein.
(B) Cancer can result from an excess of certain proteins and diabetes can result from an insulin deficiency.
(C) A deficiency of red blood cells can occur if bone marrow cells produce too much hemoglobin.
(D) Cancer can be caused by excessively rapid degradation of certain amino acids in the cytoplasm of cells.
(E) Excessive synthesis of one protein can trigger increased degradation of mRNA’s for other proteins and create severe protein imbalances.
[Reveal] Spoiler:
B


8. The passage suggests that a biologist who detected high levels of two proteins in a certain type of cell would be likely to consider which of the following as a possible explanation?
(A) The rate of mRNA degradation for one of the proteins increases as this type of cell develops a more specialized function.
(B) The two proteins are most likely constituents of a complex substance supporting the cells’ specialized function.
(C) The cells are likely to proliferate abnormally and possibly become cancerous due to the levels of these proteins.
(D) The mRNA’s for both proteins are being degraded at a low rate in that type of cell.
(E) The mRNA’s for the two proteins are being synthesized at identical rates in that type of cell.
[Reveal] Spoiler:
D




I always get lost in the details in such passages and hence make mistakes in inference questions.
Could anyone help me how can we attempt these kind of passages.

Below are some specific doubts.

Question 5 -

I marked C as the answer but the correct answer is not that.
While we talk about protein deficiency in the last line of first passage but we are nowhere talking about how to overcome that.
Also in the passage we are talking about varying the synthesis as well as degradation rate and hence I selected Option C.
Could anyone explain this answer and also the flaw in my reasoning.

Question 7 and 8.

I got these two question also incorrect.
Can anyone explain me each answer choice.

Thanks

Last edited by fameatop on 25 Jul 2013, 23:03, edited 1 time in total.
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Re: Detailed Biology Passage - Need Help [#permalink] New post 26 Jun 2013, 01:58
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[quote="anukrati"]

I always get lost in the details in such passages and hence make mistakes in inference questions.
Could anyone help me how can we attempt these kind of passages.

Below are some specific doubts.
HI ,
IT IS LIKE THIS :
CELLS synthesize mRNA==>mRNA produces protein in cell.
now in second paragraph if you read the highlited part:


Biologists once assumed that the variable rates at which cells synthesize different mRNA’s determine the quantities of mRNA’s and their corresponding proteins in a cell. However, recent investigations have shown that the concentrations of most mRNA’s correlate best, not with their synthesis rate, but rather with the equally variable rates at which cells degrade the different mRNA’s in their cytoplasm. If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNA’s will accumulate to high levels.

so its saying if you want to increase level of mRNA the cell should degrade it slowly.
if degradation is slow==>more mRNA will accumulate and hence more protein will develop.
so as in question 5 ==>there is a protein deficincy ..and that can be improved only by reducing the degradation rate.....hence A
.

QUESTION 7 has answer in the last line of the first paragraph:
an excess of certain proteins can cause cells to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes. ===>hence B

QUESTION 8:
AGAIN FOR THIS AS WE KNOW IF THERE IS EXCESS LEVEL OF SOMETHING THEN DEGRADATION WILL BE LOW AS STATED IN THE HIGHLITED AREA OF SECOND PARAGRAPH.
HENCE D

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Re: Detailed Biology Passage - Need Help [#permalink] New post 28 Jun 2013, 10:54
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#7 "According to the passage..."

So using the GMATPill RC technique, you want to find instances in the passage that talk about the relevant topic, then dive further for detailed information. Using that detailed information, try to answer the question.

GMATPill Tip: So we know we have to find instances where they talk about the relevant topic - "when protein synthesis is not appropriately regulated"

Well we have a keyword phrase:
"Since the amount of mRNA in a cell determines the amount of the corresponding protein" -- well this is a hint as to protein production -- which is relevant to "protein synthesis" in the question stem.

So what happens when protein production/synthesis is not regulated? Well if we read on a little bit here since they are talking about protein production and the question stem is about protein production...

...we'll see that the rest of the sentence talks about "appropriately regulating protein synthesis".

Great, we're still on the same topic.

The sentence following that talks about "an excess of certain proteins" -- BINGO. This keyword "excess" is synonymous to "not appropriately regulated". What happens in this case? The last sentence of the first paragraph:

"an excess of certain proteins can cause cells to proliferate abnormally and become cancerous; a lack of the protein insulin results in diabetes." -- the first part of that sentence is important. "Not appropriately regulated" leads to "cancerous".

Answer choice (B) says "cancer can result from an excess of certain proteins and diabetes can result from an insulin deficiency..." -- that's the answer. It's worded exactly as we see it in the last sentence of paragraph 1.


7. According to the passage, which of the following can happen when protein synthesis is not appropriately regulated?
(A) Diabetes can result from errors that occur when the ribosomes translate mRNA into protein.
(B) Cancer can result from an excess of certain proteins and diabetes can result from an insulin deficiency.
(C) A deficiency of red blood cells can occur if bone marrow cells produce too much hemoglobin.
(D) Cancer can be caused by excessively rapid degradation of certain amino acids in the cytoplasm of cells.
(E) Excessive synthesis of one protein can trigger increased degradation of mRNA’s for other proteins and create severe protein imbalances.


Answer choice (A) might get you tricked up. Itsays "diabetes can result..." -- yes that's one of the side effects of "excess proteins" but the details are not right. "Diabetes can result from errors that occur when the ribosomes translate mRNA into protein." -- well the last sentence of paragraph 1 does not talk about errors occurring from translation so this is not directly supported. Diabetes resulting from insulin deficiency is supported but NOT the diabetes resulting from translation errors. So you can just jump to the answer choice once you see something your recognize "diabetes" -- instead you have to read the whole answer choice and the check the reasoning. Make sure it is fully supported by information in the specific area of the passage that you are reading.
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Re: Detailed Biology Passage - Need Help [#permalink] New post 25 Jun 2013, 21:35
If a cell degrades both a rapidly and a slowly synthesized mRNA slowly, both mRNA’s will accumulate to high levels.

Answer to eigth... got 5 and 7 wrong... need to figure out...
Re: Detailed Biology Passage - Need Help   [#permalink] 25 Jun 2013, 21:35
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