A level Biology: Post your doubts here!

[rz123]

another question i am unable to answer!!

View attachment 5601
please give me the answer to this question
i mean does mRNA have stages after it leaves the nucleus and enters the cytoplasm of a cell????

ok this will cover up protein synthesis i.e transcription and translation which includes the role of mRNA as well.

In the nucleus part of a DNA molecule unwinds and unzips as the hydrogen bonds between the bases break. free activitated RNA nucleotides pair up with the exposed bases of one strand only. as the RNA nucleotides pair up with their complementary ones, their sugar phosphate groups are bonded together to form a sugar phosphate backbone. the new single stranded molecule which has formed is called messenger RNA. it leaves the nucleus via a pore in the nuclear envelope.
in the cytoplasm there are free amino acids and transfer RNA molecules. at one end of each tRNA molecule is a site to which an amino acid can bind. at the other end are three unpaired bases. the base triplet is called an anti codon. each tRNA molecule bonds with a particular amino acid, under the control of a specific enzyme and with energy from atp.
meanwhile, also in the cytoplasm, the mRNA molecule attaches to a ribosome. ribosome are made of ribosomal RNA and protein and contain a small and large subunit. the mRNA binds to the small subunit. six bases at a time are exposed to the large subunit.
the first three exposed bases, or codons are always AUG. A tRNA molecule with the complementary anticodon, UAC, forms hydrogen bonds with this codon.

a second trna molecule bonds with the next three exposed bases. this one brings a different amino aicd. the two amino acids are held closelty together, and a peptide bond is formed between them. this reaction is catalysed by the enzyme peptidyl transferase, which is found in the small subunit of the ribosome.

the ribosome now moves along the mRNA reading the next three bases on the ribosome. a third tRNA molecule brings a third amino acid, which joins to the second one. the first tRNA leaves.

the polypeptide chain continues to grow like a good baby until a stop codon is exposed on the ribosome. this is UAA, UAC OR UGA. reference to this info is from mary jones book.

 

[nano9595]

could u guys pls help me
define substrate level phosphorylation
pls help me i m desperate thnx in advance

 

[bia awan]

Umm which tissues in da roots are called root tubers?

 

[rz123]

Umm which tissues in da roots are called root tubers?

don't know much, but they r the storage tissue, they store starch in POTATO!!!

 

[Amy Bloom]

thank you!!!!
very much!!
people over here are kind and willing to help

i too love the subject biology, but am not very good at tweaking the information i study
i mean i can only write what i study....

for example the mRNA question i posted i have the notes about the topic under which it comes but i donno how to answer using the ,,, i mean the info is scattered ....

do you have any ideas on how to customize the notes which i study and make it applicable for exam??????

The most important thing is to understand what you are reading (i'm referring to the notes) and extract what is required.
For such concepts, like the mRNA - it is better you draw up a diagram/schematic diagram by yourself using the notes and write few and concise notes on the diagram itself - try this, it might help you [sometimes i even draw cartoons to understand ].

Read your question, see the glossary of terms in your syllabus if you want to know the significance of what the examiner is telling you (E.g. Explain, why, describe...).
If you have understood what's going on, you can easily tell the examiner, in your own words the events that occur.

 

[Gogo]

could u guys pls help me
define substrate level phosphorylation
pls help me i m desperate thnx in advance

well according to Wikipedia its "Substrate-level phosphorylation is a type of metabolism that results in the formation and creation of adenosine triphosphate (ATP) or guanosine triphosphate (GTP) by the direct transfer and donation of a phosphoryl (PO3) group to adenosine diphosphate (ADP) or guanosine diphosphate (GDP) from a phosphorylated reactive intermediate. Note that the phosphate group does not have to directly come from the substrate. By convention, the phosphoryl group that is transferred is referred to as a phosphate group." Hope It helps

 

[hassam]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_qp_4.pdf Q7 last part why urea more conc. in urine than in filtrate??? plx explain....i want to test my concept

 

[bia awan]

What agar jelly actually is?

 

[rz123]

What agar jelly actually is?

http://www.google.com.pk/search?ix=sea&sourceid=chrome&ie=UTF-8&q=agar+jelly

 

[princesszahra]

agar = colloidal solution!!
basically a semisolid!

 

[XPFMember]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_qp_4.pdf Q7 last part why urea more conc. in urine than in filtrate??? plx explain....i want to test my concept

Assalamoalaikum !
may be this'll help: http://www.xtremepapers.com/community/threads/biology-post-your-doubts-here.9858/page-2#post-131264

 

[smartangel]

can some one please help me out with November o6 paper 4 Q2. i dont get how do we calculate the ratios for each!
thanks in advance!

 

[samwickz]

Re: Stuck in Biology?? Post your doubts here!!

How does anyone remember photosynthesis n respiration processes? It's pretty complicated, too many details to memorise!

go check u get owsome youtube videos

 

[melly713]

can some1 send me a link to
AS bio pp1 s02 and
w11 pp1 , 2 and 3 plz thankyou!

 

[melly713]

does any1 have AS bio and chem papers from 1990's and can u send me a link plz ty!

 

[Hazirah Mn]

Assalamualaikum friends

I need help in searching for images of the human reproductive system, e.g. the structure of testis, and the labellings for the Graafian follicle as these questions usually come out during the A level examination..

Does anyone have a good website to recommend?

Thanks in advance!

 

[farhan143]

i donot understand how the length of scale bar is 200000 ?



some one explain this thankyou!!!

 

[farhan143]

Did you measure the length of the chloroplast?

well yes i did but in no way am i getting the answer according to the question
they asked to measure the scale bar .... I get 23mm and basically that will be 23000_micrometer not 200000_micrometer

 

[farhan143]

just help me out please!

 

[Amy Bloom]

just help me out please!

Well, i tried to do it my way.
First, you measure the length of the scale bar with ur ruler. say x mm.
So, x mm is equivalent to 2 micrometres
Then measure the length of the chloroplast using your ruler. Say y mm.
By proportion, y mm = (2 * y)/x micrometres. Say it is t micrometres
That's the size of the object (actual size)

Then see y mm is equivalent to how many micrometres. Say its z micrometres. This is the size of image
Magnification = size of image/actual size = t/z times

Try it and see if you got the answer.