Biology Unit 3 Questions Megathread

[HERculina]

I looked in my text and i don't actually know where Kreb's cycle occurs.

I think Biozone has some nice spreads on these details

yup biozone is really good for c.respiration/photosynthesis. also nelson textbook is great at explaining the steps/processes, but it has nothing on limiting factors for photosynthesis! 

[poojas73]

is the cell wall permeable to everything?

[HERculina]

What is the name of the fine structure that can only be seen using an electron microscope where carbon fixation takes place?

[Inside Out]

ribosomes

[vexx]

What is the name of the fine structure that can only be seen using an electron microscope where carbon fixation takes place?

in photosynthesis, carbon fixation occurs in the chloroplast during the Calvin Cycle..

[HERculina]

hm but i thought chloroplasts were visible under light microscopes.
and im not entirely sure about ribosomes. i noe that chloroplasts have their own ribosomes but i cant relate this to carbon fixation...
and the q. says fine structure - it sounds like thylakiod membranes but only light dependent state happens here :/
any other suggestions?

[simpak]

Chloroplasts can be seen under a light microscope.  I honestly don't know the answer.

[HERculina]

o the question must be wrong or something. it was from the 2008 Lisachem topic test 1 :|

[dooodyo]

happen to have a copy to post pleeeeaasse?

[HERculina]

i wrote on it already. but here is 2011

[HERculina]

more

[HERculina]

last pages

[WhoTookMyUsername]

Can organisms compensate for the lack of enzymes in a biochemical pathway by using a different biochemical pathway?


This is a question from STAV 2008

Question 5

A section of nucleic acid taken from a human cell has the following base sequence

UCUUCAUAA

It is reasonable to conclude that:


B. This base sequence codes for 3 different amino acids

D. Template base sequence would be AGAAGTATT

i answered D, which is the answer,
but
is the reason it can't  be B because, may not code for 3 different amino acids, or/and may be 'junk dna'?

[shinny]

Can organisms compensate for the lack of enzymes in a biochemical pathway by using a different biochemical pathway?

Yep, of course. It's not really a case of 'can', but it's a natural thing that will be enforced. If A can be turned into B and C via certain enzymes, and the enzyme to catalyse the conversion to B is screwed up, then consequently A will naturally increase and the increase in substrate will be shunted into the C pathway, leading to more C.

As for Q5, note the presence of uracil. If there is uracil, it is a strand of mRNA. Hence, it cannot be junk DNA because it's already been transcribed. However, look in your databook and translate that strand; it actually becomes Ser-Ser-STOP. Hence, only two amino acids. However, if it was a DNA strand, then it could have been a non-coding sequence (hesitant to use the term 'junk DNA').

[WhoTookMyUsername]

ah okay thankyou, so STOP is not an amino acid? like methionine is a 'start?"

Also for chemical pathways if

A->B -> C is the reaction
but A - B enzyme is messed up, how does the body get past this? I'm not sure if in your answer you meant

A->B or A -> C
I'm not sure exactly how it works

is it just by chance that there is another enzyme that turns it into the product? or does every product have more than 1 possible pathway?