May 8, 2009
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Most cell divisions proceed in a three-step cycle: division, growth, and DNA replication. However, embryonic cells skip the growth phase during cleavage. All of the following would be found in abundance during early cleavage cycles EXCEPT:

A. newly-transcribed RNA.
B. chromosomal proteins.
C. microtubules
D. lysosomes

The answer is A but that doesn't make sense... How can you have chromosomal proteins in abundance but not have new transcribed RNA in abundance????
 

RogueUnicorn

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NEWLY transcribed RNA would mean the DNA was in a resting state so that it could be transcribed. embryonic chromosomal proteins are NOT transcribed from the embryonic genome - rather, it is in the beginning inherited from the gametes (i.e. parental). also, the questions specifically states ABUNDANCE, and it should be clear that there is simply no time during cleavage to produce an abundance of new mRNA
 
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NEWLY transcribed RNA would mean the DNA was in a resting state so that it could be transcribed. embryonic chromosomal proteins are NOT transcribed from the embryonic genome - rather, it is in the beginning inherited from the gametes (i.e. parental). also, the questions specifically states ABUNDANCE, and it should be clear that there is simply no time during cleavage to produce an abundance of new mRNA
didn't know the chromosomal proteins are inherited from gametes.
 

RogueUnicorn

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didn't know the chromosomal proteins are inherited from gametes.
at least initially, EVERYTHING comes from gametes, right? that's essentially what i meant. to be honest with you i'm not sure whether histones are translated from maternal mRNA or embyronic mRNA, though my gut tells me the former is likely true. in either case, new mRNA would not be abundant regardless, as any and all transcription would be kept de minimus
 

Zona Pellucida

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This is an odd question. I probably would have gotten this wrong also. I would have picked MTs because the cell isn't expanding (which MTs aid in).

Oh well. Pretending I never saw this... cya!
 

RogueUnicorn

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This is an odd question. I probably would have gotten this wrong also. I would have picked MTs because the cell isn't expanding (which MTs aid in).

Oh well. Pretending I never saw this... cya!
MT is critical for chromosomal alignment and separation via the spindle apparatus, not to mention its cytoskeletal roles. without them you could not have mitosis
 

Zona Pellucida

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MT is critical for chromosomal alignment and separation via the spindle apparatus, not to mention its cytoskeletal roles. without them you could not have mitosis
Yeah, I completely understand that (took Cell). I just would have randomly picked MTs for that one reason. I don't really understand why it would be A but I might have to reread your answer a few more times.
 

Zona Pellucida

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So... the offspring doesn't use any of its own genome in the first few stages of life? It just undergoes cleavage for a while and then begins too? This is new to me
 

wanderer

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Most cell divisions proceed in a three-step cycle: division, growth, and DNA replication. However, embryonic cells skip the growth phase during cleavage. All of the following would be found in abundance during early cleavage cycles EXCEPT:

A. newly-transcribed RNA.
B. chromosomal proteins.
C. microtubules
D. lysosomes

The answer is A but that doesn't make sense... How can you have chromosomal proteins in abundance but not have new transcribed RNA in abundance????
During early cleavage cycles cells grow in number but not in size, meaning that little to no protein is being synthesized. If little to no protein is synthesized it would be very wasteful to produce lots of RNA. On the other hand chromosomal proteins are necessary. The reason you could have proteins in abundance without having RNA in abundance (ignoring the issue of where the actual proteins come from) is that ribosomes essentially amplify RNA by simultaneously translating many copies of the same mRNA.


edit: At least some of the microtubules come from the sperm cell's flagellum.
 
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RogueUnicorn

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During early cleavage cycles cells grow in number but not in size, meaning that little to no protein is being synthesized. If little to no protein is synthesized it would be very wasteful to produce lots of RNA. On the other hand chromosomal proteins are necessary. The reason you could have proteins in abundance without having RNA in abundance (ignoring the issue of where the actual proteins come from) is that ribosomes essentially amplify RNA by simultaneously translating many copies of the same mRNA.


edit: At least some of the microtubules come from the sperm cell's flagellum.
the centrosome in fact is an exclusively paternally donated organelle
 

wanderer

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the centrosome in fact is an exclusively paternally donated organelle
I know the centrosome for the first division is paternally derived, but at what point does the zygote begin to make its own centrosomes, and how are the centrosomes replicated?





Knowledge of this fact isn't necessary to answer the original question in any case.