Ch 6. Molecular Basis of Inheritance (stack 2) Flashcards
Mention any two criteria that a molecule must full fill to act as genetic material.
- It should be able to generate its replica (Replication).
- It should chemically and structurally be stable.
DNA is a better genetic material than RNA. Justify with two reasons
- DNA chemically is less reactive and structurally more stable when compared to RNA.
- The presence of thymine at the place of uracil also confers additional stability to DNA.
List any three criteria that a molecule has to fulfil to act as a genetic material
- It should be able to generate its replica (Replication).
- It should chemically and structurally be stable.
- It should provide the scope for slow changes (mutation) that are required for evolution.
Why is DNA molecule a more stable genetic material than RNA? Explain
- DNA is structurally more stable because of its double-stranded nature.
- 2’-0 H group present at every nucleotide in RNA is a reactive group and makes RNA labile and easily degradable. RNA is also now known to be catalytic, hence reactive. Therefore, DNA chemically is less reactive and structurally more stable when compared to RNA.
- The presence of thymine at the place of uracil also confers additional stability to DNA
- Define replication.
The process of synthesis of two new DNA from a parental DNA is called replication.
Why replication in DNA is referred to as semi-conservative replication?
It is because , in the resulting daughter DNA only one strand is newly synthesised and the other strand is from the parental DNA conserved as it is.
Name the enzyme involved in the polymerization of nucleotides during DNA replication.
DNA polymerase
Mention the template polarity on which replication occurs continuously
3’ → 5
Mention the template polarity on which replication occurs discontinuously.
5’ → 3’
Name the enzyme which joins discontinuously synthesized fragments of DNA during DNA replication
DNA ligase
What is origin of replication?
A definite region in DNA, where replication begins
In which phase of the cell cycle DNA replication occurs?
S-Phase
Mention the functions of DNA polymerase and DNA ligase during replication
DNA polymerase - Catalyse polymerisation of a large number of nucleotides in a very short time.
DNA ligase - The discontinuously synthesised fragments lagging strand are later joined.
Draw a labelled diagram of replication fork
Explain the role of enzymes involved in DNA replication.
Unwindase/ Helicase - Unwinding of DNA double helix
Topoisomerase/gyrase-Reduces the strain between two strands of DNA
DNA polymerase - Synthesis of new strand by linking nucleotides
DNA ligase - joining of fragments in the lagging strand
Define transcription
” Both the strands of DNA do not act as templates during transcription”. Justify with a reason
Both the strands of DNA do not act as templates during transcription because:
- If both strands act as a template, they would code for two different proteins, and this would complicate the genetic information transfer machinery.
- The two RNA molecules if produced simultaneously would be complementary to each other, hence would form a double stranded RNA. This would prevent RNA from being translated into protein .
Name the enzyme involved in polymerization of nucleotides during transcription
RNA polymerase
What is a ‘coding strand’ with respect to transcription?
The DNA strand with 5’ → 3’ polarity and the sequence same as RNA (except thymine at the place of uracil) is called coding strand.
What is ‘template strand’ with respect to transcription?
The DNA strand with 3’ → 5’ polarity and acts as template for the synthesis of RNA is called template strand.
What is the significance of promoter site on a transcription unit
The promoter site is a DNA sequence that provides binding site for RNA polymers and its presence defines the template and coding stand.
What is a cistron
A segment of DNA coding for a polypeptide
What do you mean by monocistronic transcriptional unit
A transcription unit coding for a single polypeptide.
What is polycistronic transcriptional unit?
A transcription unit coding for more than one polypeptide
What are exons
The coding sequences or expressed sequences in eukaryotic gene are called exons.
What are intrans
The non-coding or intervening sequences in eukaryotic gene are called intrans.
What are split genes
The gene in which expressed sequences are interrupted by intervening sequences or intrans are called split genes.
Mention the function of mRNA
It carries coded information in the form of codons to synthesis a polypeptide.
Mention the function of tRNA
It transfers amino acid from cellular pool to the site of protein synthesis.
Mention the function of rRNA
It is part of ribosomes and provide site for protein synthesis.
Why tRNA is called an adaptor molecule
Because, it will read the code on one hand -and on the other hand would bind to specific amino acids.
Mention the factor that temporarily associate with RNA polymerase during initiation of transcription in prokaryotes
Sigma factor
Mention the factors that temporarily associate with RNA polymerase during termination of transcription in prokaryotes.
Rho factor
Mention the enzyme that transcribes mRNA in prokaryotes
RNA polymerase
In bacteria, translation can begin much before mRNA is fully transcribed. Give one reason
Since transcription and translation occurs in the same compartment, many times the translation can begin much before the mRNA is fully transcribed.
Mention the enzyme that transcribes hnRNA in eukaryotes.
RNA polymerase II
Which enzyme is involved in transcription of tRNA in eukaryotes
RNA polymerase III
Which enzyme is involved in transcription of 28SrRNA in eukaryotes
RNA polymerase I
What is hnRNA?
Heterogeneous nuclear RNA - precursor of mRNA
What is ‘capping’ with reference to post-transcriptional stage in eukaryotes?
Addition of an unusual nucleotide (methyl guanosine triphosphate) to the 5’ - end of hnRNA.
What is ‘ tailing’ with reference to post-transcriptional stage in eukaryotes?
Addition of adenylate residues (200-300) to the 3’ - end of hnRNA.
- Define ‘ splicing’ with respect to post-transcriptional stage in eukaryotes.
Removal of introns and joining of adjacent exons in a defined order is called splicing.
