Biology P22 Was Quiet Easy !!!!

[alisha]

oki its been 24hrs rite....those cells in the first question were small coz they were gaurd cells? and how about the question on how the ribosome activity is inhibited?

 

[bionology]

oki its been 24hrs rite....those cells in the first question were small coz they were gaurd cells? and how about the question on how the ribosome activity is inhibited?

eh....what? guard cells? in between? I doubt that.
I wrote might be because the mitosis has finished or not yet started. I guess both would be acceptable because every cell was in a different stage of mitosis

1 got my 1 point wrong from ribosomes but for the second i gave reference to non-competitive inhibition

what was the answer for the stupid red blood cell replacing the enzyme? why can't it?

 

[Anonymousx3]

oki its been 24hrs rite....those cells in the first question were small coz they were gaurd cells? and how about the question on how the ribosome activity is inhibited?

I said they were small 'cause they've just divided (gone through cytokinesis) so they've yet to go through interphase, which is where the cells grow to their proper size.

But I think I wrote prophase when I was meant to write interphase - ugh. D;

 

[Anonymousx3]

oki its been 24hrs rite....those cells in the first question were small coz they were gaurd cells? and how about the question on how the ribosome activity is inhibited?

eh....what? guard cells? in between? I doubt that.
I wrote might be because the mitosis has finished or not yet started. I guess both would be acceptable because every cell was in a different stage of mitosis

1 got my 1 point wrong from ribosomes but for the second i gave reference to non-competitive inhibition

what was the answer for the stupid red blood cell replacing the enzyme? why can't it?

RBCs don't have a nucleus - no DNA means no code for proteins (enzymes are proteins!). Replication and all that can't take place either. And there's no RER for protein synthesis and transport.

 

[bionology]

RBCs don't have a nucleus - no DNA means no code for proteins (enzymes are proteins!). Replication and all that can't take place either. And there's no RER for protein synthesis and transport.

i just misunderstood this one, i wrote that enzymes have active sites, rbc's don't and so thay can't replace them and perform their function

 

[aquariangurl]

Red Blood cell replacing the enzyme? Which component did you give?
Or is my memory very weak?

 

[new2sys]

salams guys,
i am unsure about the streptomycin question 2 (

from wikipedia:
"Streptomycin is a protein synthesis inhibitor. It binds to the S12 Protein of the 30S subunit of the bacterial ribosome, interfering with the binding of formyl-methionyl-tRNA to the 30S subunit.[4] This prevents initiation of protein synthesis and leads to death of microbial cells. Humans have structurally different ribosomes from bacteria, thereby allowing the selectivity of this antibiotic for bacteria. However at low concentrations Streptomycin only inhibits growth of the bacteria by inducing prokaryotic ribosomes to misread mRNA.[5] Streptomycin is an antibiotic that inhibits both Gram-positive and Gram-negative bacteria,[6] and is a therefore a useful broad spectrum antibiotic." http://en.wikipedia.org/wiki/Streptomycin

 

[Anonymousx3]

RBCs don't have a nucleus - no DNA means no code for proteins (enzymes are proteins!). Replication and all that can't take place either. And there's no RER for protein synthesis and transport.

i just misunderstood this one, i wrote that enzymes have active sites, rbc's don't and so thay can't replace them and perform their function

Oh well, it was only 2 marks or something.

 

[bionology]

i just hate CIE, 1 question makes so many senses !!! they should award accordingly!

 

[Anonymousx3]

Ha, I dunno, I think it's cool that they give questions that make you think.

 

[sakibfaiyaz]

Hey please tell me if my answers are right.
For Question 1(ii) i wrote: Because they have might not have begun with their new cell cycle, i.e they are still young in their life stages.

for (iii) I wrote: They are not in a "resting" stage because here they undergo DNA replication in the S stage of interphase and other synthetic reactions in G1 and G2 of interphase.

For the question about RBCs' inability to make new proteins, I wrote: Because they lack nucleus,ribosomes and ER-hence no protein synthesis. And they do not have Golgi apparatus so inevitably no final processing and packaging which are but essential to such globular proteins.
Hydrolysis of globins give AMINO ACIDS right? :S

For the question "why doesn't streptomycin affect mammals", I wrote: Because they affect 70s ribosomes not 80s as in eukaryotes.
I am very confused about the enzyme question, for the 4 mark question I wrote : Because lipase catalyses breakdown of triglycerides to glyerol and fatty acids. Fatty acids lower the pH. Since lipase works best in alkaline conditions, as the reaction proceeds the pH decreases, ionic bonds holding the tertiary structure break and it becomes increasingly unfavourable for lipase until when t=50 mins and the enzyme denatures completely.

 

[Anonymousx3]

Hey please tell me if my answers are right.
For Question 1(ii) i wrote: Because they have might not have begun with their new cell cycle, i.e they are still young in their life stages.

for (iii) I wrote: They are not in a "resting" stage because here they undergo DNA replication in the S stage of interphase and other synthetic reactions in G1 and G2 of interphase.

For the question about RBCs' inability to make new proteins, I wrote: Because they lack nucleus,ribosomes and ER-hence no protein synthesis. And they do not have Golgi apparatus so inevitably no final processing and packaging which are but essential to such globular proteins.
Hydrolysis of globins give AMINO ACIDS right? :S

For the question "why doesn't streptomycin affect mammals", I wrote: Because they affect 70s ribosomes not 80s as in eukaryotes.
I am very confused about the enzyme question, for the 4 mark question I wrote : Because lipase catalyses breakdown of triglycerides to glyerol and fatty acids. Fatty acids lower the pH. Since lipase works best in alkaline conditions, as the reaction proceeds the pH decreases, ionic bonds holding the tertiary structure break and it becomes increasingly unfavourable for lipase until when t=50 mins and the enzyme denatures completely.

I wrote more or less the same stuff - let's hope it's right!

 

[bionology]

well the ph was constant at 7, for that i wrote the substrate has finished. So no more enzyme reaction takes place and the ph is constant

for resting stage, yes DNA and the centrioles are replicating, so the cell is not in rest stage, the processes are going on



P.s, I dont the think so the paper was so easy. Have you ever read the mar schemes? they have very specific answers for their questions, and if you do not touch their criteria, they simply don't award u marks.
I must say that it was technical

 

[boy2011]

well the ph was constant at 7, for that i wrote the substrate has finished. So no more enzyme reaction takes place and the ph is constant

for resting stage, yes DNA and the centrioles are replicating, so the cell is not in rest stage, the processes are going on



P.s, I dont the think so the paper was so easy. Have you ever read the mar schemes? they have very specific answers for their questions, and if you do not touch their criteria, they simply don't award u marks.
I must say that it was technical

PH was not at 7 when it becomes constant it was like 6.sumthing soo i thnk enzyme got denatured as lipase works best in slightly alkaline conditions...

 

[oohlala]

i didnt mention anything about denaturation of lipase, its just that the ph value remains constant coz the reaction is complete...
and for that ribosomes inhibition qn. i wrote that it binds to r-RNA nd stops protien synthesis, is that right???

 

[bionology]

if 8 is the optimum temp, then it's slightly alkaline. I dont think so that very weak acidic conditions (near to 7) would denature it. The ph was constant because there was no more oil for hydrolysis, the reaction was complete! no more substrate was left for lipase to work on

 

[workinghard]

@sakib i also wrote almost xct ans as u!
fingers crossed dat u r rite!
n bout enxyme it leveled off at 6.45 or something and i wrote either da reac is finished or that the enxyme had denatured cux of the disruption of bonds ionic n h-bonds

 

[hassam]

it levelled off cos reaction was complete.....an pH decrease become less steeper b/c substrate conc. decreased with time thus leading to a decreasing no. of E-S complexes per unit time

 

[aquariangurl]

@working hard WHY wud you write that? The answer is simple that there was no more substrate left to break down..All was converted into products!

 

[hassam]

well that wiki guy......wikipedia tells wat actually does bt we were supposed to SUGGEST HOW it may act........so as fara as ur suggestions are maningful....they ll be correct