April 9, 2011 at 6:32 am #14790
i am here because i am doing Cell’s biology and so i got questions to ask
to start of with i am using the Campbell and Reece 8th edition textbook when studying for Cell’s biology
ok page 9
The sequence of nucleotides along a gene is transcribed into a RNA, which is then translated into a specific protein with a unique shape and function. In the translation process, all forms of life employ essentially the same genetic code. A particular sequence of nucleotides says the same thing to one organism as it does to another. Differences between organisms reflect differences between their nucleotide sequences.
i get the first sentence but i don’t get the others
April 9, 2011 at 8:07 am #104375
you should probably read a little bit more about the genetic code. I think there was a good chapter in Harper’s biochemistry.
Anyway, the point is, that the genetic code (i.e. what sequence in DNA/mRNA will be translated into which amino acid in protein) is universal. That is, we share this genetic code with all organisms including bacteria etc. Thus it doesn’t matter, whether one piece of mRNA will get human or E. coli, both will translate it into exactly the same protein.
Footnote for more advanced, you shouldn’t read this now.
Yes, I know there are exceptions as from everything and it’s not that simple.
April 9, 2011 at 11:10 pm #104386
thank you for the help
another quick question
"A prominent structure within the nondividing nucleus is the nucleolus …"
I thought all cells divide?
April 10, 2011 at 8:42 am #104389
they may be, but they are not dividing all the time. Even if so, there are the G1, S and G2 phases
April 12, 2011 at 6:21 am #104408
do prokaryotes have mitochondria??
because in the textbook (can’t remember the page no.) it says that prokaryotes do not have mitochondria
then how do bacteria have the energy to move if they don’t have mitochondria???
April 12, 2011 at 6:34 am #104409
no, bacteria have no organelles, either mitochondria, either plastids, either nucleus, either Golgi etc.
However, they have some similar membrane sacks on their plasma membrane, which function in energy gaining. Anyway, they are able to get energy without them. Even we are (for some time; look for fermentation)
April 12, 2011 at 10:54 am #104413
would mRNA be classify under in transcription or translation????
April 12, 2011 at 12:23 pm #104414
depends on what you’re interested in. It’s the product of transcription and template in translation. Isn’t there any chapter about nucleic acids?
April 17, 2011 at 4:42 am #104490
This is about the endomembrane system
Describe the route taken by a secreted protein, from synthesis to export and explain the importance of transport vesicles in this journey.
i couldn’t find the "importance of transport vesicles" in the textbook and so i am wondering if if you could tell me .
April 17, 2011 at 10:39 am #104491jwalinParticipant
If you must have noticed the proteins travel from one organelle to another. This transport is made possible by the vesicles. Now one can ask why does this have to be so? Its simple a protein needs to reach a specific place for its post translational modification and there must be something that must guide it to that place. But then a further question should be- why dont the proteins haev some sequence on them that will guide them to the particular place/ organelle- a few reasons. 1. the protein would get exposed to a different environment in the cytoplasm this would affect its str and func. 2. you would need to change all the proteins that need to be transferred and then once transferred a further change should be made (the signalling sequence would have to be removed) 3. its more efficient.
Hope that answers your question 🙂
April 17, 2011 at 11:45 am #104492
thank you for that
"We now have an explanation of why carbohydrates is always found on the outside surface of the plasma membrane. It is because the carbohydrate was originally added by enzymes in the lumen of the ER, and membrane asymmetry is preserved when budding or fusing occurs. If carbohydrate is on the inside of the ER membrane, it will also be on the inside of the ER membrane, it will also be on the inside of the vesicle and Golgi membrane, but it will be on the outside of the plasma membrane after exocytosis occurs.
Could you please explain what this means??
April 27, 2011 at 2:31 am #104649
i got a question
State where signal receptors may be located in target cells
April 27, 2011 at 11:10 am #104659quote Stephen1993:
Think about how are the membranes oriented 😉
Where would you expect receptors for extracellular molecules? 🙄
April 28, 2011 at 7:16 am #104681
About that question I know that the signal receptors would be on the outside of the plasma membrane but I wonder why it would be on the INSIDE of the ER membrane, vesicle and Golgi body- I mean how would the signal reach the receptor if they are on the INSIDE???
Or are the ER membrane, vesicle and Golgi body something to do with exocytosis???
April 28, 2011 at 7:23 am #104682
yes, they are the part of protein transport machinery.
And BTW, the receptors do not have to be on the outside of the cell 😉
April 28, 2011 at 12:28 pm #104688
"And BTW, the receptors do not have to be on the outside of the cell"
don’t you mean organelles instead of cell?
ok this is from pg 80 of the 8th edition biology book
"Sanger and his co-workers were able, after years of effort, to reconstruct the complete amino acid sequence of insulin. Since then, most of the steps involved in sequencing a polypeptide have been automated."
what does the last sentence mean?
April 29, 2011 at 8:33 am #104699
no, I meant on the outside of cells. Even you wrote that. You need to understand, which side is which on plasma membrane and organelle membrane 😉
The last sentence means, that we have machines, which are able to sequence proteins by themselves. You just add the sample (protein), solutions and turn it on 😉
April 29, 2011 at 8:48 am #104700
ok thank you
i want to clear up some things
So a gene is a length of sequence of the DNA molecule that codes for a particular trait.
DNA consists of a double helix which has a one strand and a complementary strand.
so a gene between the sequence of DNA strand as well as its complementary strand?
because in protein synthesis if DNA template strand number 1 is transcribed to mRNA then translated to a polypeptide number 1 from DNA template strand number 1
but what if you choose the other DNA complementary strand so the DNA template number 2 then transcribed to mRNA then translated to a polypeptide then wouldn’t this polypeptide different to the polypeptide number 1???
if they are different then how the definition of the gene works?
And you know we have alleles for a gene
If one allele is dominant to the other then how does it know which chromosome out of the homologous chromosome to transcribe and translate to a particular polypeptide?? because the dominant allele is express
what about the recessive allele? is it redundant i.e. not transcribed and translated to form a polypeptide?
April 29, 2011 at 10:10 am #104701
So a gene is a part of the DNA molecule that codes for a particular protein or RNA. (trait can be codšed by several genes).
Sure, DNA has two strand and both of them could and can be template for transcription. The promoter determines, where (AKA on which strand) will bind DNA Pol and what way will it go. And of course, if one piece of DNA was transcribed from both strand, different polypeptide would form.
Regarding the dominancy, that’s not that simple question. There can be several reasons for dominancy/recesivity. Either the gene can be silenced or mutated, so that the protein is not functional anymore. Or it is only partly functional (e.g. if you mutated one AA in the active side, so that the substrate would bind less efficiently)
April 29, 2011 at 1:05 pm #104703
so for a DNA molecule you got two strands
e.g. one strand might contain
then the other complementary strand must be
so if you transcribe and then translate each of them separately then the first strand will give a different polypeptide to the one made from the second strand
so polypeptide one may code for hair colour and the other different polypeptide may code for skin colour or something like that
is that right or is there something wrong because i though a gene is a sequence of DNA so that include both strands of the DNA sequence?? but both strands gives different polypeptides and so how does the definition of a gene works????????????????????????????
a bit confused
and about dominance and recessiveness of allele
were you telling me before that a recessive allele will give a non-functional protein and the dominant allele will give a functional protein and so is that why the dominant is expressed?
if an allele gives a partially functional protein just like what you have said before then do we have a situation of codominance and incomplete dominance???
thank you again
May 7, 2011 at 5:17 am #104802
i am wondering if there is anyone to help?
May 7, 2011 at 1:13 pm #104804
No, in general*, genes are not overlapping. Both strands can be transcribed because they carry genes, but for a given sequence only one of the strand will be transcribed. The other strand is there only to allow the replication of the DNA.
One of the obvious clue that it does not work like that is that the start codon is not just a stop codon in reverse. And conversely that stop codons in reverse code for perfectly legitimate aa
*In prokaryotes and viruses some genes can overlap on part of the sequence. But this is more an exception than the rule.
May 8, 2011 at 8:42 am #104821
thank you for that
Pg 81 of the textbook
Thus, the function of a protein- for instance, the ability of a receptor protein to bind to a particular pain-relieving signalling molecule- is an emergent property resulting from exquisite molecular order.
What does the last bit of the sentence mean especially ‘exquisite’.
May 11, 2011 at 8:50 am #104849
I would guess that the authors wanted to explicit, how beauty and complicated this order is. But I’m not native speaker
May 11, 2011 at 12:32 pm #104862
thank you for that
“The unwound sections of parental DNA strands are now available to serve as templates for the synthesis of a polynucleotide; they can only add nucleotides to the end of an already existing chain that is produced during DNA synthesis is actually a short stretch of RNA, not DNA”
What does the second part of the paragraph mean?
May 11, 2011 at 1:50 pm #104864
They describe the primers known as Okazaki fragments. The DNA polymerase can only extend a Nucleic acid chain, it cannot start it from scratch. Those bits of RNA serves as the starting block that are then extended by the polymerase.
May 12, 2011 at 8:48 am #104881
thank you for that
Why is DNA polymerase called DNA polymerase (III) which adds nucleotides to the RNA primer?? What is special about the number 3?
"After reaching the next RNA primer to the right, DNA pol (III) detaches."
how does the DNA pol (III) know when to detach?
May 12, 2011 at 8:55 am #104884
1) there are several DNA Pols, just by accident the major one is called Pol III, due to historical reasoning.
2) when it’s stuck
May 12, 2011 at 8:59 am #104885
wow thank you for the quick reply
Proofreading and repairing DNA
“We cannot attribute the accuracy of DNA replication solely to the specificity of base pairing.”
Just exactly what it means particular the word “attribute” used in this context?
Also following that:
“Although errors in the completed DNA molecule amount to only one in 10 billion nucleotides, initial pairing errors between incoming nucleotides and those in the template strand are 100,000 times more common- an error rate of one in 100,000 nucleotides.”
What does this mean????
May 12, 2011 at 9:44 am #104886
attribute means something like assign or credit
That means, that the base-pairing during DNA synthesis has mistake rate 1 in 100 000 nucleotides. But the final error rate is only 1 in 10 billions. Thus there must be some additional correcting mechanism
May 12, 2011 at 10:22 am #104887
thank you for that
In the table 16.1
“DNA pol 1- Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides.”
What does this mean?
May 12, 2011 at 10:45 am #104888
you don’t speak English? I’m sorry, but these are quite stupid questions about solitary senteces.
As canalon already told you and you have maybe read, the DNA replication starts from primers, which are RNA. But the DNA cannot contain pieces of RNA, because it’s unstable. Thus the primers must be replaced and they are replaced by DNA Pol I.
May 13, 2011 at 7:58 am #104895
thank you for that
well i find it pretty hard to learn this by myself because of the bad teacher i have so could you please bear with me?
The double helix …. … .. . "The helix is right-handed, curving up to the right"
what on earth does this mean- all i see is a spiral of DNA
May 14, 2011 at 3:01 am #104902
this refer to the sense of the rotation of the helix.
May 14, 2011 at 4:05 am #104905
thank you for that
The two liberated daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1um/min).
what does this mean?
May 15, 2011 at 6:35 pm #104920
the chromosomes consist of several parts, the chromatids and centromere. And the centromere is the place, where the microtubules attach and are pulled away, thus the chromosomes look like this
the centromere goes first and the chromatids are pulled behind 😉
May 16, 2011 at 7:06 am #104922
thank you for that
is there crossing over between the sex chromosomes? XX chromosomes in females and XY chromosomes in males?
Loss of cell cycle controls in cancer cells
"They may make a required growth factors themselves, or they may have an abnormality in the signalling pathway that conveys the growth factor’s signal to the cell cycle control system even in the absence of that factor."
What does the last part of the sentence mean?
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