Nucleic acids

Do you know that DNA is like the boss of RNA. While DNA stays in it's office (Nucleus), it sends RNA to the workstations (Cytoplasm) with its messages.

Guess who?

WATSON CRICK

discovered the structure of the DNA molecule

awarded the Nobel

Prize

D Deoxyribo :the pentose does not have any oxygen in position 2.

N Nucleic: these molecules were first found in the nucleus of the cell , before being found in mitochondria, chloroplasts (of plant cells), and in the cytoplasm of prokaryotes

A Acid: only two of the three acid groups of the phosphoric acid are used to form the DNA chain. The third one gives the phosphoribo-backbone an acidic property.

This is the IIry structure of DNA

DNA double helix

Synthesis of mRNA

rRNA

rRNA

QUESTIONS

X

Y

1. Identify X and Y ;

2. name the components that make up X

3. Which two components make a nucleoside? a&b / a&c / b&c

a

b

c

nX = Y

Regarding components of DNA

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4. Identify the two types of bases and give examples

X Y

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5. What is “base pairing” in DNA ?

6. What are the bases involved in DNA base pairing shown in figure 1 & 2?

Figure: 1 Figure: 2

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7.The structure shown on to your right is the (Iry / IIry / IIIry) structure of DNA

8.Fill in the blanks in relation to areas labeled ‘a’ and ‘b’

8.1 ‘sugar phosphate backbone’ is indicated by area ……..

8.2 Area……... shows hydrophobic properties where as area…… shows hydrophilic properties.

9.Which one of the following is indicated by ‘c’

a. covalent hydrogen bondb. non covalent hydrogen bondc. di-sulfide bond

a b

c

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A B

C

D

E10. Identify the components A - D

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x11. Identify the components

labeled x,y& z that make up RNA nucleotide

Give examples for Z

x

yz

12. What are the 3 major types of RNA? List their functions

13. What are the other types of RNA that are present in cells?

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14. What are the differences between DNA and RNA structures?

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15. What is the process shown below16. List the factors that will enable process A.

A

B

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17. What information is coded into DNA?

18. What is a "codon"?

19. What are the four pairs of DNA bases that form in the double helix?

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20. How can A distinguish T from C?

21. Which DNA double helix do you think would be harder to separate into two strands: DNA composed predominantly of AT base pairs, or of GC base pairs? Why?

22. The DNA double helix looks like a twisted ladder. What makes up each rung of the ladder? What holds the rungs together at the sides?

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23. Is there mostly empty space between the atoms in a DNA double helix?

24. In a DNA double helix, why doesn't an A or T form two hydrogen bonds (out of the three possible) with C or G?

25. How many kinds of 5-membered rings are in DNA?

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•DNA : some facts... • The Watson and Crick model of a double helix structure provides an answer to the

regularity of the composition in bases and its physiological properties (replication in the cell). It is confirmed by diffraction data. Models using beads are useful to handle the concept.

• E. coli has a single circular DNA molecule of 4,600,000 base pairs. The total length is 1.4 mm.

• In addition to functioning as building blocks of nucleic acids, nucleotides are important because they are used to store and transfer chemical energy (e.g. ATP).

• In man, the DNA molecule in a diploid cell, if fully extended, would have a total length of 1.7 metres. If you unwrap all the DNA you have in all your cells, you could reach the moon ...6000 times!

• a branched DNA assay is a test for specific nucleic acid chains typically used to detect Reverse transcriptase viruses such as HIV. In the assay, Branched DNA is mixed with a sample to be tested. If the branched DNA binds to viral RNA, then the luminescent compound will react, and the result can be measured via luminometer

RNA: Some facts

• Approximately, 5-10% of total weight of a cell is RNA (compare with only about 1% DNA!).

• The extra hydroxyl group in RNA makes it more susceptible to damage by hydrolysis; that's why DNA is the ultimate repository of genetic information.

• RNA is the genetic material (like DNA for other organisms) in some viruses (which don't have DNA).

• RNA is found in the nucleus and in the cytoplasm but DNA is found only in nucleus.

• DNA is capable of self-replication, but only when assisted or catalysed by proteins (enzymes) but RNA is capable of both self replication and catalysis.

•  "RNA World hypothesis" states that before the emergence of the first

cell, RNA was  the dominant and probably the only form of life.

ANSWERS

1. X – Nucleotide

Y – Polynucleotide

2. a – phosphate;

b – base; c –deoxyribose sugar

3. b and c

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4. X – Purine

(Adenine, Guanine)

Y – Pyrimidine

(Cytosine, Guanine, Uracil)

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5. Binding of a Purine with its respective Pyrimidine

6. Figure 1 – Adenine and Thyamine

Figure 2 – Cytosine and Guanine

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7. Iry

8. 8.1 a

8.2 b

9. b non covalent hydrogen bond

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10. a – chromosomeb. protein scaffoldc - super coild –Nucleosomee – DNA double helix

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11 – X phosphatey – ribose sugarz – base (Adenine, Guanine, Uracil, Cytosine )

 12.

messengerRNA (mRNA): Carries the genetic information out of the nucleus into cytoplasm for protein synthesis.

transferRNA (tRNA): Decodes the information in mRNA.

ribosomalRNA (rRNA): Makes up ribosome, constitutes 50% of a ribosome, which is a molecular assembly involved in protein synthesis.

13. a.catalyticRNAs (cRNA) ; b.Small Nuclear RNA (snRNA)

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14.

1 Characters DNA RNA

2 Molecule Double stranded, helical

Single stranded, straight or variously folded and twisted.

3 Pentose sugar Deoxyribose Ribose

4 Pyrimidine base Thymine Uracil

5 Complementary base pairing

Always present and exists between A = T and G = C

Normally absent, but may be present in twisted segments of a molecule. If present, pairing is between A = U and G = C

6 Ratio of Purines: Pyrimidines

Always 1:1 Not necessarily 1:1

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15. A - Denaturation B – Renaturaton

16. extreme pH, low ionic strength heat

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17.

The DNA in each organism (for example tree, insect, person, dog, or bacterium) contains plans for making all of its proteins. There are many thousands of kinds of proteins in each organism. Proteins are chains of building blocks called amino acids. The DNA specifies the order or sequence in which the amino acids must be hooked together for each protein. The complete DNA sequence for each protein is called a "gene".

 

18.

A codon is three consecutive bases in a gene. Each codon codes for one amino acid in a protein.

19.

AT, CG, GC, and TA.

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20.

On the basis of the number and direction of hydrogen bonds T or C can form with A. Each base can form either two or three hydrogen bonds in a matched pair. The AT pair forms two, and the GC pair, three. However, when C is lined up against A, no hydrogen bonds can be formed (because donors do not line up with acceptors

21.

GC, because it has one more hydrogen bond per base pair

22.

Each rung is made of a base pair. and their attached sugar (deoxyribose) rings. The rungs are held together by the phosphates and sugars that make up the DNA "backbone".

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23.

No.

The "thin" and "thick" renderings show covalent bonds. These renderings hide the atoms so you can see the bonds clearly, and get a sense of the skeletal layout of DNA. In contrast, the "space fill" rendering shows the way the atoms of DNA occupy space.

24.

The middle hydrogen bonds run in opposite directions. In the middle bond, T donates a hydrogen to an acceptor on A. C does not have a hydrogen to donate in the middle position; rather, it accepts a hydrogen from G's middle position. The same is true of the "third hydrogen bond" (the one that is absent in an A-T pair). T has no hydrogen to donate to the acceptor on G in the third position.

 

25. Three: the pentose ring, and the two 5-membered rings in the purines.

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