Explain why DNA is said to have a structure that resembles a ladder. How is comp

Question

Explain why DNA is said to have a structure that resembles a ladder. How is complementary have pairing different when pairing DNA to DNA than when pairing DNA to mRNA? Explain why the genetic code is called a triplet code. What role does each of the following molecules play in protein synthesis? Which of the molecules listed in question 4 are involved in transcription? Which of the molecules listed in equation 4 are involved in translation? During the isolation of DNA what role was played by these substance? What is the purpose of gel electrophoresis? Why does sickle-cell hemoglobin (Hb^5) migrate slower than normal hemoglobin (Hb) during gel electrophoresis? Why are red blood cells sickle shaped in a person with sickle-cell disease?

Explanation / Answer

1- It has a double helical structure because there is interstrand base-pairing; according to Chargaff's rule- Adenine pairs with Thymine via 2 hydrogen bonds & Guanine pairs with Cytosine via three hydrogen bonds.

2- In mRNA, the base Thymine is replaced by Uracil; which pairs with Adenine via 2 Hydrogen bonds (when hybridized with complementary DNA; mRNA is generally made of a single strand of nucleotides.)

3- Because every three consecutive bases in the mRNA forms a triplet codon that corresponds to an amino acid during translation.

4- DNA- carries the gene for the protein

mRNA- carries the genetic information of the protein in a way that facilitates translation.

tRNA- carries the amino acids during translation.

Amino acids- they are the building blocks of protein; they are joined by peptide bonds to create the proteins.

5- DNA is transcribed to obtain mRNA.

6- mRNA, tRNA, amino acids.

7- Detergent- helps to dissolve the cell membrane.

Meat tenderizer- helps in extraction of DNA from tissue.

Ethanol- precipitates the DNA (when in 100% concentration); used to remove salts in the DNA pellet (when 70% concentration).

8- To separate molecules on the basis of charge in presence of an electric field.

9- In a gel electrophoresis (migration towards the anode), HbS travels slower because it is less negative than normal Hb.

10- The Glutamic acid (negatively charged at physiological pH) at the 6th position of Hb is replaced by valine (non-polar) in case of HbS. So this creates a sticky patch in the HbS- leading to sickling of the RBC & adhesion of RBCs in sickle cell anaemia.

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