ALL CIE BIOLOGY DOUBTS HERE !!!

[**RoRo**]

I dont think the first evidence is required but the second one about DNA replication and semi-conservative method is definitely needed.
I say, you check your syllabus.

Here's what the syllabus says:
(a) describe the structure of RNA and DNA and explain the importance of base pairing and hydrogen
bonding;
(b) explain how DNA replicates semi-conservatively during interphase;
(c) state that a gene is a sequence of nucleotides as part of a DNA molecule, which codes for a polypeptide;
(d) describe the way in which the nucleotide sequence codes for the amino acid sequence in a polypeptide
with reference to the nucleotide sequence for HbA (normal) and HbS (sickle cell) alleles of the gene for
the ?-haemoglobin polypeptide;
(e) describe how the information on DNA is used during transcription and translation to construct
polypeptides, including the role of messenger RNA (mRNA), transfer RNA (tRNA) and the ribosomes;
(f) explain that, as enzymes are proteins, their synthesis is controlled by DNA;
(g) use the knowledge gained in this section in new situations or to solve related problems.

It doesn't mention anything about it [evidence that DNA in the chromosome is the genetic material]

[Deadly_king]

Here's what the syllabus says:
(a) describe the structure of RNA and DNA and explain the importance of base pairing and hydrogen
bonding;
(b) explain how DNA replicates semi-conservatively during interphase;
(c) state that a gene is a sequence of nucleotides as part of a DNA molecule, which codes for a polypeptide;
(d) describe the way in which the nucleotide sequence codes for the amino acid sequence in a polypeptide
with reference to the nucleotide sequence for HbA (normal) and HbS (sickle cell) alleles of the gene for
the ?-haemoglobin polypeptide;
(e) describe how the information on DNA is used during transcription and translation to construct
polypeptides, including the role of messenger RNA (mRNA), transfer RNA (tRNA) and the ribosomes;
(f) explain that, as enzymes are proteins, their synthesis is controlled by DNA;
(g) use the knowledge gained in this section in new situations or to solve related problems.

It doesn't mention anything about it [evidence that DNA in the chromosome is the genetic material]

The evidence is not required. But you must only know that the DNA is actually the genetic material and not the protein.

The second one is essential as you must know the experiment using Nitrogen-14 and Nitrogen-15.

[**RoRo**]

The evidence is not required. But you must only know that the DNA is actually the genetic material and not the protein.

The second one is essential as you must know the experiment using Nitrogen-14 and Nitrogen-15.

Okay, thank you very much!!

[mdwael]

What the F**** does R-group mean, my stupid cie textbook keeps repeating this word in biological molecules without giving a definition of it, confusing me and not letting me understand anything!!!

[Master_Key]

What the F**** does R-group mean, my stupid cie textbook keeps repeating this word in biological molecules without giving a definition of it, confusing me and not letting me understand anything!!!

R-Groups are a specific groups in amino acids and they vary greatly between amino acids. For eg. Glycine would have different R-Group than Valine. You do not need to know the names R-Groups at A levels but you may find it if you are interested.

[**RoRo**]

Question... Explain why cells that are produced as a result of mitosis are genetically identical. [3 marks]

[ashish]

Question... Explain why cells that are produced as a result of mitosis are genetically identical. [3 marks]

during cell division, the DNA from the parent cell is taken as template. Both sister chromatids move to the opposite sides during metaphase and during interphase the chromatids replicate to form Chromosomes. since DNA is taken from a single parent cell they are genetically identical

[**RoRo**]

during cell division, the DNA from the parent cell is taken as template. Both sister chromatids move to the opposite sides during metaphase and during interphase the chromatids replicate to form Chromosomes. since DNA is taken from a single parent cell they are genetically identical

Thanks Ashish!!

[**RoRo**]

Okay, here's a couple of questions straight from the syllabus, I want to know what points should be mentioned under these questions:

1. Explain the importance of mitosis in growth, repair and asexual reproduction.

2. Explain the need for the production of genetically identical cells and fine control of replication.

3. Explain the need for meiosis prior to fertilization in sexual reproduction.

NOTE: They all belong to the chapter: Cell and Nuclear Division

Thanks a lot in advance!

[Deadly_king]

Okay, here's a couple of questions straight from the syllabus, I want to know what points should be mentioned under these questions:

1. Explain the importance of mitosis in growth, repair and asexual reproduction.

2. Explain the need for the production of genetically identical cells and fine control of replication.

3. Explain the need for meiosis prior to fertilization in sexual reproduction.

NOTE: They all belong to the chapter: Cell and Nuclear Division

Thanks a lot in advance!

1. Mitosis is important in these cases so as to replace dead cells with new identical ones which will carry out the same function as the others preceding it. Hence this is to ensure the survival of this particular species.

Example : (i) The body cells of a child undergoes mitosis for growth so that the child becomes bigger and have more developped organs which will be more efficient in their respective jobs.

2. Identical cells should be produced to ensure the survival of the respective species as well as the genes coding for it. If the cells are not identical the organism is going to be affected as the same genes will not be present and hence will not be able to carry out the wanted function.

3. Meiosis is required to half the number of chromosome in each gamete. This will ensure that upon fertilization the required number of chromosomes will be restored. In other words it prevents the number of chromosome to double each generation.

Example : (i) In man, we have 46 chromosome in each cell. Our body produces gamete with half the number of chromosome(23) such that at fertilization two gametes combine together to form one cell. Hence number of chromosome is restored. (23 + 23 = 46)

[**RoRo**]

1. Mitosis is important in these cases so as to replace dead cells with new identical ones which will carry out the same function as the others preceding it. Hence this is to ensure the survival of this particular species.

Example : (i) The body cells of a child undergoes mitosis for growth so that the child becomes bigger and have more developped organs which will be more efficient in their respective jobs.

2. Identical cells should be produced to ensure the survival of the respective species as well as the genes coding for it. If the cells are not identical the organism is going to be affected as the same genes will not be present and hence will not be able to carry out the wanted function.

3. Meiosis is required to half the number of chromosome in each gamete. This will ensure that upon fertilization the required number of chromosomes will be restored. In other words it prevents the number of chromosome to double each generation.

Example : (i) In man, we have 46 chromosome in each cell. Our body produces gamete with half the number of chromosome(23) such that at fertilization two gametes combine together to form one cell. Hence number of chromosome is restored. (23 + 23 = 46)

Finally someone replied!

THANK YOU VERY MUCH!!

I have another question:Can you please explain to me the experiment [evidence that DNA replicates by semi-conservative method]? I don't understand what this experiment is about and how is it conducted! :/

[Deadly_king]

Finally someone replied!

THANK YOU VERY MUCH!!

I have another question:Can you please explain to me the experiment [evidence that DNA replicates by semi-conservative method]? I don't understand what this experiment is about and how is it conducted! :/

Evidence for the semi-conservative replication of DNA.

In an experiment on e.coli(a bacteria) these were used to follow the DNA in the new cells every generation.

NOTE : Bacteria are used in this experiment since they replicate very rapidly causing this experiment not to last too long.(Generation time is about 50 minutes at 36^oC)

The bacteria were grown in a nutrient medium containing the heavy isotope of Nitrogen-15. This replaced the normal Nitrogen-14 in the DNA. The bacteria labelled with N-15 contained the original or parental DNA. These bacteria were then transferred in a medium containing N-14 and allowed to grow.

Other similar bacteria were left for their DNA to replicate 2 or 3 times. The DNA was then extracted and centrifuged. The heavier the DNA, the closer to the bottom of the tube it settles. The DNA appeared as bands in the tubes as shown.



As you can see only 50% of the original DNA is restored each generation. This is why it is called semi-conservative.

[**RoRo**]

Evidence for the semi-conservative replication of DNA.

In an experiment on e.coli(a bacteria) these were used to follow the DNA in the new cells every generation.

NOTE : Bacteria are used in this experiment since they replicate very rapidly causing this experiment not to last too long.(Generation time is about 50 minutes at 36^oC)

The bacteria were grown in a nutrient medium containing the heavy isotope of Nitrogen-15. This replaced the normal Nitrogen-14 in the DNA. The bacteria labelled with N-15 contained the original or parental DNA. These bacteria were then transferred in a medium containing N-14 and allowed to grow.

Other similar bacteria were left for their DNA to replicate 2 or 3 times. The DNA was then extracted and centrifuged. The heavier the DNA, the closer to the bottom of the tube it settles. The DNA appeared as bands in the tubes as shown.



As you can see only 50% of the original DNA is restored each generation. This is why it is called semi-conservative.

Thank you very very much! 

That was really simple, to the point and well-explained!!

[Deadly_king]

Thank you very very much! 

That was really simple, to the point and well-explained!!

Hehe.................anytime dude 

[mdwael]

Do plant cells have lysosome structure? In wikipedia it says they dont, only animals do. But I came across the Multiple choice question in which the answer says that they infact do have lysosome structure. The past paper is 2010 cie 9700 qp_11 summer question number 4.