Question

1. Consider the following in light of the concept of levels of structure (primary, secondary, tertiary, quarternary) as defined for proteins.

- what level is shown by double-stranded DNA?

- what level is shown by tRNA?

- what level is shown by mRNA?

2. give the name of the base, the ribonucleoside or deoxyribonucleoside, and the ribonucleoside triphosphate for A, G, C, T, and U.

3. which of the following statements are true?

- bacterial ribosomes consist of 40 S and 60 S subunits.

- prokaryotic DNA is normally complexed with histones.

- prokaryotic DNA normally exists as a closed circle.

- Circular DNA is super coiled.

4. How do the major and minor grooves in B-DNA compared to those in A-DNA

5. define super coiling, positive super coil, topoisomerase, and a negative super coil

6. if circular b-DNA is positively super coiled, then will these super coils be left or right handed?

7. what is the complete base composition of a double-stranded eukaryotic DNA that contains 22% guanine

8. why does DNA with a high A-T content have a lower transition temperature then DNA with a high G-C content?

9 what is the purpose of small nuclear RNA? What is an snRNP?

10. which type of RNA is the biggest? Which is the smallest?

11. which type of RNA has the least amount of secondary structure?

12. why does the absorbance increase when a DNA sample unwinds?

13. would you expect mRNA or rRNA to be to grade more quickly in the cell? Why?

14. which would be more harmful to a cell, a mutation in DNA or a transcription mistake that leads to an incorrect mRNA? Why?

15. explain briefly what happens to eukaryotic mRNA before it can be translated to protein.

16. explain why a 50 S ribosomal subunits and a 30 S ribosomal subunits combine to form a 70 S subunit, instead of an 80 S subunit

Answer 1

1. a) double stranded usually considered as thought as secondary structure unless we consider its supercoiling then its structure is tertiary and if they associated with proteins then its structure is quarternary.

b) tRNA structure has many folds and twists in 3D so its level shown is tertiary.

c) mRNA shown the level of primary structure

2) A - adenine ,adenosine oe deoxyadenosine , adenosine triphosphate

G- guanine,guanosine,deoxyguanosine, guanosine triphosphate

C-cytosine,cytidine or deoxycytidine,cytidine triphosphate

T- thymine,deoxythymidine,deoxythymidine triphosphate

U-uracil,uridine, uridine triphosphate.

3)  prokaryotic DNA normally exists as a closed circle and Circular DNA is super coiled. these two statements are true.

4) the major groove and minor groove in B-DNA have very different dimension in terms of width and those in A-DNA are much closer in width.

5) supercoiling- supercoling refers to twist in DNA over and above those of the double helix.

positive super coiling - it refers to the extra twist in DNA caused by the overwinding of the helix before sealing the ends to produce circular DNA.

topoisomerase - it refer as an enzyme that induces a single stranded break in super coiled DNA,relax the supercoiling and reseals the break.

negative supercoiling- it refers as unwinding of the double helix before sealing the ends to produce circular DNA.

6) then it will be left handed.

7) G= C and A=T, so 28% of A and T each,44% of GC content and 56% of AT content.

8) AT base has two hydrogen bond whereas GC base has three hydrogen bond.it takes more energy and higher temperature to disrupt the structure of DNA rich in GC base.

9) snRNA is found in eukaryotic nucleus and is involved in splicing reactions of other DNA types. an snRNP is a small nuclear ribonucleprotein particle.a complex of small nuclear RNA and protein catalyzes splicing of RNA.

10) rRNA is largest and tRNA is smallest.

11) mRNA is having least amount of secondary structure.