Special Sub-Topic: Genes and you Click Here To Play: Genes and you

Who proposed the double-helical model of the DNA?

Watson, Crick and Franklin. Griffith discovered transformation in bacterial cells, while Hershey and Chase, together with Avery, MacLeod and McCarty proved that DNA is the genetic material instead of proteins.

Nucleotides are monomers of DNA. What does each nucleotide consist of?

A nitrogenous base, a pentose sugar and a phosphate group. A nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group. For DNA, a hydrogen atom is attached to the 2' carbon of the pentose, hence deoxyribose. Whereas, in RNA, a hydroxyl group is attached to the 2' carbon, hence ribose.

True or false- Chargaff's rules states that the ratio of the purines to pyrimidines in the double-stranded DNA is always constant at 1.

t. Purines have 2-ring nitrogenous bases while pyrimidines single ring. Since purines pairs with pyrimidines in DNA, the ratio is always one. In DNA, purines adenine and guanine pairs with pyrimidines thymine and cytosine respectively.

Is RNA polymerase required for in vivo DNA replication?

y. Primase, a type of RNA polymerase is required for the synthesis of primers before deoxyribonucleotides are added to it by DNA polymerase. This is because DNA polymerase cannot initiate synthesis of a new polynucleotide strand complementary to the template strand.

What are Okazaki fragments?

short fragments of newly synthesized DNA. DNA replication takes place bidirectionally from the origin in 5' to 3' direction. Thus, only one strand will be continuous while the other strand growing in opposite direction will be in the form of Okazaki fragments. The fragments are then joined together by DNA ligase.

In eukaryotes, transcription of mRNA is 1)catalyzed by what type of enzyme 2)initiated by binding of transcription factors to which important promoter sequence?

RNA polymerase II ; TATA box. The TATA box is also known as the Goldberg-Hogness box. In eukaryotes, pre-mRNA is formed after transcription and undergoes some processing before becoming a mature mRNA molecule.

There are 20 essential amino acids in the human body. Using the triplet codon, theoretically, how many amino acids can be coded for?

64. There are four different nitrogenous base which codes for the different amino acids. Using a triplet code, where 3 bases code for one amino acid, we take 4 to the power of 3 giving 64.

Why does a single base substitution in DNA base sequence not necessary result in a malfunctional polypeptide?

All of the above. (Degeneracy of the triplet code., New amino acid is chemically equivalent., The substitution takes place at introns.). Base substitution is a type of gene mutation. However, for silent and neutral mutations, there is no change in the structure of polypeptide. Introns are non-coding segments of the DNA, thus no matter what mutation takes place, there is no effect on the polypeptide.

Translation requires the activation of amino acid into

aminoacyl tRNA. tRNA is an "adapter" molecule which has anticodon that recognises the codon on the mRNA, bringing in the appropriate amino acid attached to it, which forms aminoacyl tRNA. Aminoacyl adenylate is an amino acid with ATP, it is formed prior to the formation of aminoacyl tRNA.

Which molecule is not required during translation?

DNA. DNA is not directly involved in translation. It is involved in transcription. GTP is hydrolysed to release energy for codon recognition and translocation etc.

Bam HI restriction site is within tetracycline resistant gene. A foreign gene is inserted into a plasmid using Bam HI. When bacteria with the recombinant plasmid is grown in tetracylcine, will it die?

y. Introduction of foreign gene inbetween the tetracycline gene is similar to a frameshift mutation, and the bacteria will lose is resistance to tetracycline.

Name the enzyme that catalyzes formation of DNA from mRNA.

reverse transcriptase. Complementary DNA is formed. Benefits are that there are no introns present in the DNa strand.

Sickle cell anaemia is a disease resultant of missense mutation. What codon number in the DNA sequence does the mutation take place? What amino acid substituted the original glutamic acid? This mutation affects which protein chain in the hemoglobin?

6 ; valine ; beta hemoglobin. In fact, it is the second base pair of codon 6 that is altered from an adenine base to a thymine base, resulted in coding for a valine.

What are involved in removal of introns from the pre-mRNA?

spliceosomes. Spliceosomes consists of snRPS(small nuclear ribonucleoproteins) which in turn consists of snRNA(small nuclear RNA) and proteins. They recognise splice sites -- short nucelotide sequences at ends of introns and carry out excision.

What is the start codon in mRNA for protein synthesis?

AUG. The rest are actually stop codons.