Dna

Question 1

Basics of dna and rna

Answer 1

Nucleic acids are a group of the most important molecules of which the best known are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
DNA carries genetic information.

Question 2

Nucleotide structure

Answer 2

pentose sugar (so called because it has five carbon atoms)
• a phosphate group
• a nitrogen-containing organic base. These are: cytosine C, thymine
T, Uracil U, adenine A and guanine G.
The pentose sugar, phosphate group and organic base are joined, as a result of condensation reactions, to form a single nucleotide. Two nucleotides may, in turn, be joined as a result of a condensation reaction between the deoxyribose sugar of one mononucleotide and the phosphate group of another. The bond formed between them is called a phosphodiester bond. The new structure is called a dinucleotide.

Question 3

Ribonucleic acid

Answer 3

Ribonucleic acid is a polymer made up of nucleotides. It is a single, relatively short, polynucleotide chain in which the pentose sugar is always ribose and the organic bases are adenine, guanine, cytosine and uracil. One type of RNA transfers genetic information from DNA to the ribosomes. The ribosomes themselves are made up of proteins and another type of RNA. A third type of RNA is involved in protein synthesis.

Question 4

DNA structure

Answer 4

In DNA the pentose sugar is deoxyribose and the organic bases are adenine, thymine, guanine and cytosine. DNA is made up of two strands of nucleotides Each of the two strands is extremely long, and they are joined together by hydrogen bonds formed between certain bases.

Question 5

Base pairing

Answer 5

• Adenine always pairs with thymine
• Guanine always pairs with cytosine
As a result of these pairings, adenine is said to be complementary to thymine and guanine is said to be complementary to cytosine.
It follows that the quantities of adenine and thymine in
DNA are always the same, and so are the quantities of guanine and cytosine. However, the ratio of adenine and thymine to guanine and cytosine varies from species to species.

Question 6

Double helix

Answer 6

the uprights of phosphate and deoxyribose wind around one another to form a double helix. They form the structural backbone of the DNA molecule.

Question 7

Stability or DNA

Answer 7

DNA is a stable molecule because:
• The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
• Hydrogen bonds link the organic base pairs forming bridges (rungs) between the phosphodiester uprights. As there are three hydrogen bonds between cytosine and guanine, the higher the proportion of CG pairings, the more stable the DNA molecule.

Question 8

Function of DNA

Answer 8

DNA is the hereditary material responsible for passing genetic information from cell to cell and generation to generation. In total, there are around 3.2 billion base pairs in the DNA of a typical mammalian cell. This vast number means that there is an almost infinite variety of sequences of bases along the length of a DNA molecule. It is this variety that provides the genetic diversity within living organisms.

Question 9

How is DNA adapted to carry out functions

Answer 9

It is a very stable structure which normally passes from generation to generation without significant change. Most mutations are repaired, so persistent mutations are rare.
• Its two separate strands are joined only with hydrogen bond s, which allow them to separate during DNA replication) and protein synthesis.
• It is an extremely large molecule and therefore carries an immense amount of genetic information.
• By having the base pairs within the helical cylinder of the deoxyribose-phosphate backbone, the genetic information is to some extent protected from being corrupted by outside chemical and physical forces.
• Base pairing leads to DNA being able to replicate and to transfer information as mRNA.