Traci D.

asked • 12/09/13

What does a fertilized cell rely on for early developmental regulatory proteins

a) the cytosol of the egg
b) the DNA of the egg
c) the placenta
d) the uterus
e) none of these

L Jacque C.

What if you haven't mastered any of the material for this test? Use the process of elimination by relying on what is familiar to you.

This is a simple MEMORY question?

Biology Jargon or vocabulary

Ask yourself what are these terms?

Uterus  ?  (Just to let you know it’s a Reproductive ORGAN)

Placenta?  (Just to let you know it’s a Reproductive ORGAN)

Cytosol

DNA

None of the above

 

Test Taking skills

Let’s assume your teacher has just finished teaching about Eucaryotic and Procaryotic cells. These are the building blocks to multi-cellular organisms. So I will also assume that your teacher has not lectured on structures that groups of cells form (tissues) and structures that groups of tissues form (Organs) or groups of organs form (organ systems) and groups of organ system form THE ORGANISM. 

So you must identify the structures. If you have studied the cell and its structures you may say to yourself I don’t know anything about the choices Uterus or placenta.  If you haven’t missed class and you take great notes and read the chapter and you still don’t know what the Uterus and placenta are, you can exclude them as choices. 

Your teacher most likely has reviewed Mitosis, Meiosis, DNA and Cell organelles. But eliminating choice a) and b) of the five choices you have increased your chances of a correct guess in light of not actually knowing the answer from 1 in 5 (20% chance of getting it correct) to 1 in 3 (33% chance of getting correct).

Ok let’s move on, what is the Cytosol and DNA, ah, now those sound familiar, why? Your teacher lectured on them. Simple recognition and without knowing exactly what they are you know 100% that one of them is the answer. Well what does that mean, well you have excluded choice a) and b) and your chance at guessing correctly is now 33% but choice c) or d) is correct and that makes choice e) wrong. Now you are down to choice c) and d) and your chances of guessing correctly are now increased to 50%.

Now let’s say you studied well and are prepared. You would know that the subject of the question is the “Fertilized Cell” also known as a Zygote. The zygote will travel down the fallopian tube to eventually implant into the uterine wall and with time the placenta will form as the connection between the growing embryo.

What controls the growth and differentiation of the zygote, DNA or Cytosol? Well the Cytosol is a location in a cell where the cell does its business. DNA carries the genetic code that the cell depends for structural and functional proteins. Answer: DNA
Report

12/18/13

L Jacque C.

Thank you Dr. Naina for your Feedback I appreciate your time and input, I hope your holiday season is going well and I hope we can continue to exchange thoughts on Biology in the future. I would like to say testing students’ knowledge can be and is often a tricky endeavor. 

My response in short, the question very easily could have been constructed in a much clearer manner, I’ve been at fault in the past in constructing feeble test questions. Why? Two reasons; one, you want to challenge the student and two, time limitations. I concede that the professor’s question may be scored with the answer: Cytosol. But this is only in the case that a student did not consider the significance of the term “Egg” in choices a) and b). 

I believe the initial approach I used to arrive at the two final choices Cytosol and DNA you are in agreement. If not please share with me your reasoning. Although the question relates to a test of memory, either the process of building proteins which starts with DNA (my answer) or the source of proteins for early development of a zygote (your answer) can be reasoned; both can be correct!

I approached the question, most likely as you did, without access to the class notes or textbook of the student. The professor could have marked me down as an incorrect answer but I don’t think it would hold up.

My approach was to reason the answer based on the grammatical construct of the choices 1) and 2). Jumping ahead in the process if you Dr. Naina and I were studying this question prior to an upcoming examination, I may or may not provide a compelling argument to change your answer and we would likely go pay the professor a visit to find out what they were asking.

The question again, “What does a fertilized cell rely on for early developmental regulatory proteins“? It’s difficult but not impossible to rephrase the question, I would rephrase as; During early zygote development, what does the zygote rely for its source of Developmental regulatory proteins, or any protein for that matter? Ambiguity starts with the question root and the focus is on “fertilized cell”. No time line after fertilization is provided so a student taking the test could assume one second or 1 week. This point has a dramatic effect on the source of “early-Undefined term” used in the root question. 

Your explanation and knowledge of the supporting data is logical and sound and without a doubt shows that you are a very talented researcher. It’s been so long since I heard the word Drosophila I could have mistaken it for Dracula. The Zygote as you’ve outlined does utilize pre-formed proteins from the oocyte (Egg-maternal) cytoplasm (cytosol) as its source of regulatory proteins. However, during our study session I would pointed out the method in whichthe professor structured the final candidate answers a) the cytosol of the egg (oocyte) and b) the DNA of the egg (oocyte).

I reasoned that both choices refer to the maternal egg not the zygote which I argue destroys the symmetry of the question and makes this a poorly structured question as it is asking about the “Fertilized cell-zygote” and the choices reference the “Egg”. Egg (oocyte) ≠ Zygote I stated this for any student that my reference not you Doctor. 

Protein synthesis is, as you have stated, composed of transcription and translation material from the unfertilized cell. The reference again is to the choice of egg DNA (oocyte) vs. egg cytosol (cytoplasm) as being responsible for providing (producing) regulatory proteins in a fertilized cell. 

If the two choices where written as a) the cytosol of the zygote vs. b) the DNA of the zygote it would be clear that the professor wanted to know if I were aware that a zygotes cell cycle is quiet during Interphase of the zygote. However that not how the choices in the above question were composed, in this case the DNA of the oocyte (egg as stated in the choices) provides the regulatory proteins, notwithstanding the fact that without the eggs cytosol the regulatory proteins could not be stored in preparation for metabolism during embryogenesis. 

Again, I argue the answer is DNA not because cytosol is wrong but because DNA of the “Egg” as it is phrased is the reference point for the existence of the regulatory proteins for utilization later. If the two choices omitted the term “egg” or if you were to change the reference of the DNA and Cytosol to “Zygote” I would be willing to change the answer to Cytosol, reasoning as you have that the zygotes nuclear material is most likely in the G0 phase. 

If on the other hand the question were an essay and your description were provided it would be 100% correct as your answer would be based on the role of the cytosol’s importance during early development of the zygote and is unarguably correct! My essay answer would explain the importance of oocyte protein synthesis prior to fertilization and the DNA origin of the zygotes regulatory protein in the pre-cleavage stage of embryogenesis.

Answer: Poor question design and my answer is still DNA of the Egg not Cytosol of the Egg.

In response to your follow up I would also like to thank you for allowing me to do a little reading on the subject of embryogenesis, it’s been awhile. The description of Meiosis, Mitosis and fertilization did not change much since 1946 (Textbook: Arey Developmental Anatomy) through 1989 (Textbooks: Moore The Developing Human, Snyder Genetics and Nora/Fraser Medical Genetics). None of these references comment on the specific “Timing” and metabolic activity which occurs during Interphase of Mitosis in the immediate period post fertilization. Sorry these are probably much outdated texts.

I was able to find a publication on NIH’s website (stemcells.nih.gov/info/sciereport/pages/appendixa.aspx)

“. . . any maternal gene products in the zygote cytoplasm influence its first few divisions, called cleavages. Within several days, and after several cleavages, the genome (all the DNA or hereditary information in the cell's chromosomes) of the zygote becomes activated and controls subsequent embryonic development” [Gilbert 2000 Developmental Biology, Jones 2000 Human Embryonic stem cell technology]. . .

Any maternal (Egg) gene (DNA) products (Protein) in the zygote cytoplasm influence its first few divisions

It’s the maternal egg DNA that provides protein for the maternal egg cytosol that goes on to the zygote cytosol.
Report

12/20/13

2 Answers By Expert Tutors

By:

Naina B. answered • 12/09/13

Tutor
4.8 (155)

Naina, a versatile tutor

See tutors like this
See tutors like this
Dear Traci,
 
A fertilized cell is called zygote  and is formed by fertilization of a male and a female gamete. In mammals and  most vertebrates, the male gamete does not carry much cytoplasm that can store regulatory factors. In contrast, female gametes store regulatory factors that can turn on the transcription and translation machinery of the fertilized cell for its further development through cell-division and proliferation.
 
The DNA of the egg in contained in its chromosomes that pair with chromosomes of male gamete. Initially, DNA of fertilized egg is transcriptionally silent and therefore, it cannot produce regulatory proteins. So, b is not correct.
 
Placenta can only provide blood supply  to embryo/zygote when it is implanted in uterus. Fertilized zygote does not implant right away in uterus and therefore, c is not correct.
 
Uterus is home or  a chamber for embryo and fetus to grow, it does not provide regulatory proteins to embryo and therefore, d is incorrect.
 
Fertilized cell cannot divide and grow further without regulatory proteins, they have to come from somewhere and therefore, e is incorrect.
 
Maternal cytoplasm containing cytosol provides the regulatory proteins (transcription factors) for transcription of maternal mRNAs and their subsequent translation for cell-cycle regulatory proteins. Therefore, a is the correct answer.
 
Hope this helps.
Upvote • 1 Downvote
More
Report

Naina B.

I am sorry,  DNA here is not the correct answer. The question is about the reliance of fertilized cell on regulatory proteins in early development. In classical model eukaryote organisms ( C.elegans, Drosophila, Zebrafish, Xenopus, mice, rats and other mammals including humans), zygote is transcriptionally silent for first several hours after fertilization, its DNA  does not  transcribe mRNAs to produce regulatory proteins for early zygotic development. Fertilized cell or zygote relies on maternal regulatory proteins deposited in the cell by the mother for first several divisions and development. This classical view is supported in Genetics and Developmental Biology text books, there are hundreds of maternal effect mutations in Drosophila and zebrafish where mothers do not deposit correct regulatory proteins in eggs and the fertilized cell/zygote either develops abnormally or is arrested during development and becomes lethal. One can find this in Scott Gilbert's Developmental Biology (text book) as well as by searching journals like Genetics, Developmental Biology, Mechanisms of Development, Developmental Dynamics etc.
 
Dr. Naina B, PhD
Report

12/19/13

Naina B.

Dear Mr. Jaque,
 
Thank your for your response and comment. I shall interpret your following comment from NIH website:
 any maternal gene products in the zygote cytoplasm influence its first few divisions, called cleavages. Within several days, and after several cleavages, the genome (all the DNA or hereditary information in the cell's chromosomes) of the zygote becomes activated and controls subsequent embryonic development” [Gilbert 2000 Developmental Biology, Jones 2000 Human Embryonic stem cell technology]. . .
 
Maternal gene products in  cytoplasm of the zygote  are the regulatory factors/proteins that help in  early development, first several divisions  and not just one cell division and one interphase. This is what the quote says and that is true. Xenopus and Drosophila embryos undergo several cell divisions before the onset of transcription from fertilized cell/egg or zygote or in other words before activation of zygotic genome,  as the quote includes.
 
Technically, once the egg is fertilized, it has a zygotic genome or genome of fertilized cell.  It is no longer maternal or paternal genome/DNA. Haploid gametes fuse and form zygote, recombination might occur during chromosomal pairing and it is combined zygotic genome that is activated later in the development.
 
The question has two key components: early development and fertilized cell.
 
The answer has the choices of placenta, uterus, egg DNA and egg cytosol.
 
The answer does not include sperm or male gamete DNA and  sperm cytosol as choices.
 
As I have included in my answer,  the egg stores maternal regulatory  proteins that guide the activity of fertilized cell/zygote during early development, that is prior to the activation of zygotic genome.
 
I do not know what student's teacher has implied. I hope she will gain from this discussion and bring it to her teacher's attention seeking clarification and additional information.
Report

12/21/13

Sandra H. answered • 11/18/14

Tutor
5 (1)

Sandra H. A Patient, successful and effective professional.

See tutors like this
See tutors like this
What does a fertilized cell rely on for early developmental regulatory proteins
a) the cytosol of the egg
b) the DNA of the egg
c) the placenta
d) the uterus
e) none of these
 
The cytosol of the egg contains stored maternally deposited proteins for use during the early cell cycles.
In addition, the egg cytosol contains stored RNA molecules which can be quickly translated to protein.
It relies MUCH less so on DNA, since divisions are going so fast there is not really a G1 and G2 phase of the cell cycle (which is when most transcription of the DNA would occur).
 
So the answer is a
Upvote • 0 Downvote
More
Report

Still looking for help? Get the right answer, fast.

Ask a question for free

Get a free answer to a quick problem.
Most questions answered within 4 hours.

OR

Find an Online Tutor Now

Choose an expert and meet online. No packages or subscriptions, pay only for the time you need.