H2 Biology Questions

Zqhtr

12 Apr 09, 09:31

Hi all

How to do these questions? Many thanks in advance!

Question 1

In tomato plants, ‘purple pigment’ and ‘hairy stems’ are genetically determined and the genes are tightly linked. Pure breeding, purple, hairy plants crossed with pure breeding, green, hairless plants produced only purple, hairy plants in the F₁generation. These F₁plants were then crossed to produce the F₂generation. Which phenotypic ratio would be expected in the F₂generation?
	Purple, hairy	Purple, hairless	Green, hairy	Green, hairless
A	1	1	1	1
B	3	0	0	1
C	3	3	1	1
D	9	7	0	0

Question 2

In E. coli, the production of enzymes for tryptophan synthesis is carefully controlled according to the organism’s metabolic needs. A mutation in the gene encoding the tryptophan repressor has occured, such that the repressor can bind DNA without the co-repressor. What effect on enzyme production can be expected under this condition?
A	Constitutive, high-level enzyme production
B	No enzyme production in the absence of tryptophan, high-level activity in the presence of tryptophan
C	High-level enzyme production in the absence of tryptophan, no activity in the presence of tryptophan
D	No enzyme production under any conditions

Question 3

d3sT1nY

12 Apr 09, 12:22

Laughing

Zqhtr

12 Apr 09, 12:36

Hi all

Sorry for the mess up there. Here is a repost of the questions.

Question 1

A student performed the following steps in a Southern blot experiment to determine the number of copies of a particular gene that has been inserted in a genetically modified organism.
i - Transfer of DNA to nitrocellulose membrane
ii - Restriction digestion of genomic DNA

iii - Cleaved DNA separated using gel electrophoresis

iv - Create radioactive probe

v. Incubate probe and membrane

Which is the correct sequence to the above steps?

A - ii , iii, i , iv, v

B - ii , iii , i , v , iv

C - iv , v , i , ii , iii

D - v , iv , iii , ii , i

Question 2

20% of the purines in a DNA molecule consist of guanine. The total percentage of thymine nucleotides in this DNA is

A - 20%

B - 40%

C - 80%

D - Cannot be determined

Question 3

Which choice presents items in the proper order (earliest to latest) in which they would be used in the process of gene expression resulting in the formation of a protein?

A - polyribosome, promoter, spliceosome, primary transcript

B - spliceosome, promoter, primary transcript, polyribosome

C - promoter, primary transcript, spliceosome, polyribosome

D - primary transcript, spliceosome, promoter, polyribosome

That's it. Thanks all!

d3sT1nY

12 Apr 09, 15:31

Originally posted by Zqhtr:

Hi all

Sorry for the mess up there. Here is a repost of the questions.

Question 2

20% of the purines in a DNA molecule consist of guanine. The total percentage of thymine nucleotides in this DNA is

A - 20%

B - 40%

C - 80%

D - Cannot be determined

Question 3

Which choice presents items in the proper order (earliest to latest) in which they would be used in the process of gene expression resulting in the formation of a protein?

A - polyribosome, promoter, spliceosome, primary transcript

B - spliceosome, promoter, primary transcript, polyribosome

C - promoter, primary transcript, spliceosome, polyribosome

D - primary transcript, spliceosome, promoter, polyribosome

That's it. Thanks all!

Question 2:

Edited: Misinterpreted the question.

20% of purine is guanine, means 80% will be adenine.

Therefore 80% of pyrimidine will be thymine since adenine base pair with thymine.

Doing some simple math, 80/200 = 40% of nucleotides will be thymine.

UltimaOnline

12 Apr 09, 23:13

Originally posted by Zqhtr:

Hi all

Sorry for the mess up there. Here is a repost of the questions.

Question 1

A student performed the following steps in a Southern blot experiment to determine the number of copies of a particular gene that has been inserted in a genetically modified organism.
i - Transfer of DNA to nitrocellulose membrane
ii - Restriction digestion of genomic DNA

iii - Cleaved DNA separated using gel electrophoresis

iv - Create radioactive probe

v. Incubate probe and membrane

Which is the correct sequence to the above steps?

A - ii , iii, i , iv, v

B - ii , iii , i , v , iv

C - iv , v , i , ii , iii

D - v , iv , iii , ii , i

Question 2

20% of the purines in a DNA molecule consist of guanine. The total percentage of thymine nucleotides in this DNA is

A - 20%

B - 40%

C - 80%

D - Cannot be determined

Question 3

Which choice presents items in the proper order (earliest to latest) in which they would be used in the process of gene expression resulting in the formation of a protein?

A - polyribosome, promoter, spliceosome, primary transcript

B - spliceosome, promoter, primary transcript, polyribosome

C - promoter, primary transcript, spliceosome, polyribosome

D - primary transcript, spliceosome, promoter, polyribosome

That's it. Thanks all!

d3sT1nY has already addressed Q2.

For Q1, Wikipedia is your best friend.

http://en.wikipedia.org/wiki/Southern_blot

For Q3, ask yourself,

does the promoter come before transcription, after transcription, before translation, or after translation?

does the primary transcript come before transcription, after transcription, before translation, or after translation?

does the spliceosome come before transcription, after transcription, before translation, or after translation?

does the polyribosome come before transcription, after transcription, before translation, or after translation?