Ch 6. Molecular Basis of Inheritance (stack 3) Flashcards
Write any two differences between prokaryotic and eukaryotic transcription unit
Prokaryotic
- It is polycistronic
- Structural gene is uninterrupted
Eukaryotic
- It is monocistronic
- Structural gene is interrupted
Differentiate between intrans and exons
Intrans - They do not code for any protein. Intrans or intervening sequences do not appear in mature or processed RNA.
Exons - The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequence that appear in mature or processed RNA.
Write the coding strand and the sequence of base on mRNA synthesized by DNA template with the sequence 3’-ATGCATAGCAT-5’.
Coding strand- 5’ -TACGTATCGTA - 3’
mRNA- 5’ - UACGTUTCGTU - 3’
Write a note on the role of sigma factor and the rho factor in transcription in prokaryotes.
The sigma (σ) factor) binds to the RNA Polymerase to form the holoenzyme. It is responsible for promoter recognition and subsequent initiation of transcription of each bacterial gene.
Rho factor is a protein that recognizes and binds preferably to C-rich sites in the mRNA. It is required for the termination of transcription by an RNA polymerase and is essential for the viability of the cell.
In bacteria, translation can begin much before the mRNA is fully transcribed. Justify with two reasons.
In bacteria, since the mRNA does not require any processing to become active, and also since transcription and translation take place in the same compartment (there is no separation of cytosol and nucleus in bacteria), many times the translation can begin much before the mRNA is fully transcribed.
RNA polymerases in eukaryotes show a clear cut division of labour
- The RNA polymerase I transcribes rRNAs (28S, 18S, and 5.8S),
- RNA polymerase III is responsible for the transcription of tRNA, Ssr RNA, and snRNAs (small nuclear . RNAs).
- The RNA polymerase II transcribes the precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).
Explain the function of the following:
(a) Promoter
(b) tRNA
(c) Exons
It is a DNA sequence that provides a binding site for RNA polymerase.
Transfer amino acids from the cellular pool to the place of protein synthesis
Expressed sequences or coding sequences in matured mRNA
Define genetic code
The sequence of nucleotides on DNA/mRNA specifying the sequence of amino acids in protein is called genetic code
Name the Severo Ochoa enzyme
Polynucleotide phosphorylase
What is the special property of Severo Ochoa enzyme (polynucleotide phosphorylase
Helpful in polymerising RNA with defined sequences in a template independent manner.
Name the initiator codon
AUG
What other function the initiator codon performs in addition to initiating translation?
It codes for the amino acid methionine
Mention terminator codons
UAA, UAG and UGA
Why UAA is considered as terminator or stop codon
Because it does not code for any amino acid and the translation will end at this codon.
Why genetic code is said to be universal?
Because, the codons which specify the amino acids is same in all living organisms.
Why genetic code is said to be unambiguous or specific
Because, a particular codon will code for a specific amino acid
What is point mutation?
Point mutation is a type of mutation caused by the substitution of a nucleotide by another nucleotide, or the deletion or insertion of a nucleotide into the DNA resulting in a change from the normal or wild type gene sequence.
What is frame shift insertion mutation?
Shifting of reading frame one or two steps forward due to addition of one or two nucleotides
What is frame shift deletion mutation?
Shifting of reading frame one or two steps backwards due to deletion of one or two nucleotides
Mention an example of a genetic disorder that is a result of point mutation.
Sickle cell anaemia
Name Severo Ochoa enzyme. Mention its function
Severo Ochoa enzyme - Polynucleotide phosphorylase.
It was helpful in polymerising RNA with defined sequences in a template-independent manner (enzymatic synthesis of RNA).
Explain any two properties of genetic code
- The codon is triplet. 61 codons code for amino acids and 3 codons do not code for any amino acids, hence they function as stop codons.
- One codon codes for only one amino acid, hence, it is unambiguous and specific
Mention the initiator and terminator codons
AUG - Initiator codon
UAA, UAG and UGA - Terminator codon
“Codon AUG has dual function”. Justify the statement
AUG has dual functions. It codes for Methionine.(met), and it also act as initiator codon
Define translation.
The process of polymerisation of amino acids to form a polypeptide as defined by the sequence of codons on mRNA is called translation.
Name the cellular factory responsible for synthesizing proteins
Ribosomes
What do you mean by charging of tRNA with respect to translation
Linking of a specific amino acid to a specific tRNAin the presence of ATP energy is called charging of tRNA
What do you mean by aminoacylation of tRNA with respect to translation
Linking of a specific amino acid to a specific tRNA in the presence of ATP energy is called charging of tRNA
What is the function of ibosome during chain elongation of translation
Ribosomes acts as catalysts for linking the amino acids by peptide bonds.
Which type of rRNA acts as ribozyme for the formation of peptide bonds during translation in bacteria
23S rRNA
Mention the type of RNA that has anticodon
tRNA
Expand UTR with reference to mRNA
Untranslated region
What is an operon?
A group of genes clustered under common promoter, operator and reg ula to r gene is called operon.
What is lac operon?
A group of genes involving in lactose metabolism clustered under common promoter, operator and regulator gene is called lac operon.
Name the protein produced by lac ‘i’ gene
Repressor protein
What is the function of regulatory gene of Lac-operon?
It codes for repressor protein.
Why transcription in E.coli does not occur in the absence of lactose in the medium?
Because, the repressor protein binds to the operator region in the absence of lactose and prevents binding of RNA polymerase to the promoter region.
How does repressor protein prevent the transcription of strnctural genes
The repressor protein binds to operator region in the absence of lactose and prevents binding of RNA polymerase to promoter region
What is the function of- galactosidase in E.coli
Breaking lactose into glucose and galactose
Mention the function of permease in E.coli
Transport lactose into the cells from outside medium
What is the importance of operator in Lac-operon?
It provides site for binding of repressor protein
Mention the inducer that inactivates Lac repressor protein
lactose
Why lactose is termed as inducer with reference to Lac-operon?
Because, it induces the expression of lac- operon by binding to repressor protein
What is negative regulation
Regulation of lac operon by repressor protein is referred to as negative regulation
