Biology Unit 4 Questions Megathread

[lexitu]

1) There's polyploidy which immediately comes to mind, and a quick search on my favourite source (wikipedia) says that speciation without geographic isolation is hotly debated.

2) Not exactly sure - but I'm guessing it would be a transition of wetness if that makes any sense at all. A lot of the surviving species of the past such as certain protists are still marine or freshwater organisms, or they at least rely on some sort of moist environment.

[Mr. Study]

Hello again.

My questions are:
1. What exactly are plasmids? (My definition is just a circular DNA). I have would love to get a little more indepth.
2. Clarfication: Biogeography is just the locations of different species around the world. True/False?

EDIT: Thank you very much!

[lexitu]

1. Extrachromosomal bits of DNA in a bacterial cell - the bacterium's chromosome is also circular so you need something else to differentiate it. They're much smaller than the chromosome too. (This is just talking about bacterial plasmids generally)
2. Basically, yes.

[omgwtf123]

Harro
1) plasmids are small, circular, Bacterial DNA molecules that are able to replicate fast and independantly from the Bacteria itself ( in other words, they can replicate independantly without the bacteria going into binary fission).
2) geographic location and distribution of living organisms around the world ( so you're are quite spot on

Hope i made no mistakes and hope this helps
damn beaten by lex >.<

[lexitu]

Haha, your definition for 2 was much better though

[omgwtf123]

but you're still more knowledgable lex xD

[Russ]

The key part of the definition of 1) is that they replicate independently of the bacterial chromosome

[WhoTookMyUsername]

Another definition question (sorry
Do silent mutations refer only to when a substitution in a DNA triplet still inserts the same amino acid, or can it also refer to substituting a very similar amino acid not affecting protein function in any way?

2) why is mRNA read from 5' to 3' by ribosomes?

3) upon transcription, is the region between th e stop codon and the stop transcription message in downstream region removed ( as introns are)?..

4) have conflicting usually reliable ( biozone and teacher ) sources in this matter
Ae there stop anticodons on tRNA , simply without an attached amino acid?


5) is it rna primase or rna polymerase that places primers in DNA replication ?

6) is it possible for two species that have diverged to fill similar niches to converge into the same species once re - introduced in a different place? (they are equally good at their nieche in this new place)

[lexitu]

AFAIK, anything that results in no change of AA sequence. Oh, and being really picky (won't matter), use polypeptide not protein

[WhoTookMyUsername]

Thanks lexitu
Couple more questions ( added to original post )
Thanks!

[scar]

Some Damn tricky questions.

2) why is mRNA read from 5' to 3' by ribosomes?


Not sure but considering the ribosome is partially made up of RNA  (rRNA = ribosomal RNA) it may have something to do with the ribose/ phosphate backbone  (I'm doubting that the nucleotides would face that way since they would cause conflicts unless matched to corresponding nucleotides)

4) have conflicting usually reliable ( biozone and teacher ) sources in this matter
Ae there stop anticodons on tRNA , simply without an attached amino acid?

There is no amino acid or tRNA for termination. When UAA, UAG or UGA enter the ribosome they bind with a 'protein release factor' that seperates the polypeptide chain and the last tRNA.   (LIFE - Science of Biology Pg 308)

6) is it possible for two species that have diverged to fill similar niches to converge into the same species once re - introduced in a different place? (they are equally good at their nieche in this new place)

No once they have become seperate species they cannot interbreed successfully - that's what defines them as belonging to different species rather than just geographical variation.

[lexitu]

5) Primase - but to explain the confusion, this is actually a type of polymerase (because it catalyses polymer synthesis)

[Russ]

I've said this before, but don't edit questions into a previously responded to post. It's confusing and annoying.

2) why is mRNA read from 5' to 3' by ribosomes?

It just is, there's no imperative for it to be read in that direction other than the fact we evolved that way. If we had evolved for the phosphate to be attached to the 3' carbon then we would be reading DNA in 3' -> 5' direction

3) upon transcription, is the region between th e stop codon and the stop transcription message in downstream region removed ( as introns are)?..

Probably varies. I imagine putting a splice site in wouldn't be too difficult but it doesn't strike me as particularly important because that area of DNA won't be translated. I also guess that, technically, that is an intron giving the definition of "transcribed but not translated".

[WhoTookMyUsername]

thanks for all the help.
The reason i edited (which i wont in the future) is because i have seen question 1) answered differently so many times so i wanted to take a larger sample size than just one answer

Couple more questions

-2) relating to an earlier question, is adaptive radiation t typically an example of non geographical isolation where an ancestor species moves into an isolated region where no competing species exist?

 -1) Is there a start transcription signal equivalent of the stop transcription signal (aattaa or something ? )

0) in a person with robertsonian translocation that results in 1 14 chromosome 1 14/21 chromosome and 1 21. Chromosome what are the possible gametes?
Is it:

14
14 + 14/21
21+ 14/21
21
14 + 21
?
( I ask this beuase I have not seen 14 + 14/21 anywhere

1) Just to confirm: Before cell division in eukaryotes, there are 2x(2n) number of DNA molecules, with each chromatid consisting of 1 DNA molecule (as per the answer for Q 4 VCAA 2007 MC)  ?


2)

Just wanted to clarify something.
MtDNA mutates more quickly than chromosomal DNA due to it's bacterial nature, but changes more slowly than DNA as it is inherited solely from the mother...

So this means the slow change allows easier tracing of maternal (and special) ancestry, and a faster mutation rate allows for greater distinctions between ages of evolutionary divergence?

3) Q6) SA
part b

answer states - large seeds proportionally more protein...
yet m. stipoides which is HALF the size of rice has MORE THAN twice the protein content...?
I am quite confuzzled

http://www.vcaa.vic.edu.au/vce/studies/biology/pastexams/2007/biol1_exam_2007.pdf

thanks again !

[jenerator]

this is a question from NOB. Would complete selection have a greater effect against a dominant trait in a population or a recessive trait? Explain.