i want 25 multiple choice questions  with theri model answer below each question about all the following inforamtion : Rna structure
RNA structure
RNA V/S DNA
Cute
RNA (Ribonucleic acid)
ORNA is a polymer of ribonucleotides linked together by 3'-5' phosphodiester linkage
The of
Quanne
A
A
M
Thymine
faucleobases
RNA
DNA
Types of RNA
In all prokaryotic and eukaryotic organisms, three main classes of RNA
molecules exist-
1) Messenger RNA(m RNA)
2) Transfer RNA (t RNA)
3) Ribosomal RNA (r RNA)
The other are -
• small nuclear RNA (SnRNA), micro RNA(mi RNA) and
o small interfering RNA(Si RNA) and
⚫ heterogeneous nuclear RNA (hnRNA).
Eukaryotic rRNA
Ribosomal RNA (rRNA)
The functions of the ribosomal RNA molecules in the ribosomal particle are not fully understood, but they are necessary for ribosomal assembly and seem to play key roles in the binding of mRNA to ribosomes and its translation
Recent studies suggest that an rRNA component performs the peptidyl transferase activity and thus is an enzyme (a ribozyme).
Transfer RNA (t- RNA)
Transfer RNA are the smallest of three major species of RNA molecules
They have 74-95 nucleotide residues
They are synthesized by the nuclear processing of a precursor molecule
rRNA make up 80% of the total RNA in the cell.
2053
28S
Ribosome
5S
25.05 5.8S
183
They transfer the amino acids from cytoplasm to the protein synthesizing machinery, hence the name t RNA.
They are easily soluble, hence called "Soluble RNA or s RNA
They are also called Adapter molecules, since they act as adapters for the translation of the sequence of nucleotides of the m RNA in to specific amino acids
There are at least 20 species of t RNA one corresponding to each of the 20 amino acids required for protein synthesis.
Secondary st ure of t-RNA
Ester band-
Messenger RNA (m-RNA)
ONA
000000000
Amino act
IRNA molecule
pairing
Anticodon
RA
GCC Codoe
The carboxyl group of amino acid is attached to 3'OH group of Adenine nucleotide of the acceptor arm. The anticodon arm base pairs with the codon present on the m- RNA
Structural Characteristics of m-RNA
Eukaryotic mRNA molecule
5 Cap
AUG
UAG
Poly (A) 3
Leader
Coding sequence
Trailer
5-cap-AGGAUUAUGCCUGGACUGAGCGCUUAGAUAUAUAAAAAAAAAAA
Stat
Sop
5' cap and 3' tail impart stability to m RNA by protecting from specific exo nucleases.
Heterogeneous nuclear RNA (hnRNA)
In mammalian nuclei, hnRNA is the immediate product of gene transcription
The nuclear product is heterogeneous in size (Variable) and is very large.
Molecular weight may be more than 10 while the molecular weight of m RNA is less than 2x 106 75% of hnRNA is degraded in the nucleus, only 25% is processed to mature m RNA
Cell Nucleus
Protein tamino acid chain)
Cytoplasm
Ribosome
Comprises only 5% of the RNA in the cell
Most heterogeneous in size and base sequence
All members of the class function as messengers carrying the information in a gene to the protein synthesizing machinery
Suches for Medes
Structural Characteristics of m-RNA(Contd.)
The m- RNA molecules are formed with the help of DNA template during the process of transcription.
The sequence of nucleotides in m RNA is complementary to the sequence of nucleotides on template DNA.
The sequence carried on m -RNA is read in the form of codons.
A codon is made up of 3 nucleotides
The m-RNA is formed after processing of heterogeneous nuclear RNA
Small Nuclear RNAs (snRNAs)
snRNAs, a subset of the small RNAs, are significantly involved in mRNA processing and gene regulation
Of the several snRNAs, U1, U2, U4, US, and U6 are involved in intron removal and the processing of hnRNA into mRNA
The U7 snRNA is involved in production of the correct 3' ends of histone mRNA-which lacks a poly(A) tail.
Micro RNAs, miRNAs, and Small Interfering RNAs, siRNAs
These two classes of RNAs represent a subset of small RNAs; both play important roles in gene regulation.
miRNAs and siRNAs cause inhibition of gene expression by decreasing specific protein production albeit apparently via distinct mechanisms
Transcription (RNA biosynthesis)
Transcription
The synthesis of RNA molecules using DNA strands as the templates so that the genetic information can be transferred from DNA to RNA.
Central Dogma?
• Central dogma of molecular biology proposes a unidirectional or one way flow of information from DNA to RNA (transcription) and from RNA to protein (translation).
The concept was given by Watson and Crick
Transcription
DNA
RNA
Protein
Replication
Translation
RNA polymerase
Start of transcription
Direction of transcription
Nantemplate strand
Promoter
RNA/DNA hybrid
Template DNA strand
Similarity between replication and transcription
• Both processes use DNA as the template.
• Phosphodiester bonds are formed in both cases.
• Both synthesis directions are from 5 to 3.
Differences between replication and transcription
template
substrate
primer
Enzyme
product
base pair
replication
double strands
dNTP
yes
DNA polymerase
dsDNA
A-T, G-C
transcription
single strand
NTP
no
RNA polymerase
SSRNA
A-U, T-A, G-C
The whole genome of DNA needs to be replicated, but only small portion of genome is transcribed in response to the development requirement, physiological need and environmental changes.
The template strand is the strand from which the RNA is actually transcribed. It is also termed as antisense strand.
The coding strand is the strand whose base sequence specifies the amino acid sequence of the encoded protein. Therefore, it is also called as sense strand.
5
GCAGTACATGTC 3
coding strand
• DNA regions that can be transcribed into RNA are called structural genes.
transcription
template strand
CGTCATGTACAG 5'
RNA
SGCAGUACAUGUC 3
RNA Polymerase
• The enzyme responsible for the RNA synthesis is DNA-dependent RNA polymerase.
The prokaryotic RNA polymerase is a multiple-subunit protein of -480kD.
- Eukaryotic systems have three kinds of RNA polymerases, each of which is a multiple-subunit protein and responsible for transcription of different RNAs.
RNA-pol of E. Coli
The holoenzyme of RNA-pol in E.coli consists of 5 different subunits: α β β' ωσ.
subunit
α
MW
36512
Determine the DNA to be transcribed
150618
Catalyze polymerization
155613
Bind & open DNA template
Recognize the promoter for synthesis initiation
β΄
σ
70263
function
β
The dissociable sigma subunit gives promoter specificity to prokaryotic RNA polymerase (RNAP)
Care enzyme
Holaenzyme
Transcription Process
No specific promoter binding tight non-specific DNA binding 510M)
Specific promoter binding, weak non-specific DNA binding (K 10M): finds promoter 10,000 times faster.
General concepts
• Three phases: initiation, elongation, and termination.
• The prokaryotic RNA-pol can bind to the DNA template directly in the transcription process.
• The eukaryotic RNA-pol requires co- factors to bind to the DNA template
Transcription of Prokaryotes
• Initiation phase: RNA-pol recognizes the promoter and starts the transcription.
• Elongation phase: the RNA strand is continuously growing.
• Termination phase: the RNA-pol stops sunthesis and the nascent RNA is
General concepts
• Three phases: initiation, elongation, and termination.
• The prokaryotic RNA-pol can bind to the DNA template directly in the transcription process.
• The eukaryotic RNA-pol requires co- factors to bind to the DNA template together in the transcription process.
Recognition of Origins
• Each transcriptable region is called operon.
• One operon includes several structural genes and upstream regulatory sequences (or regulatory regions).
• The promoter is the DNA sequence that RNA-pol can bind. It is the key point for the transcription control.
. Rifampicin, a therapeutic drug for tuberculosis treatment, can bind specifically to the ẞ subunit of RNA-pol, and inhibit the RNA synthesis.
. RNA-pol of other prokaryotic systems is similar to that of E. coli in structure and functions.
iption of Prokaryotes
• Initiation phase: RNA-pol recognizes the promoter and starts the transcription.
Elongation phase: the RNA strand is continuously growing.
• Termination phase: the RNA-pol stops synthesis and the nascent RNA is separated from the DNA template.
Prokaryotic promotor
Sequences within the prokaryotic promoter region that are recognind by the ANA polymerase hokoenzyme
Sequence
TTGACA
-10 base pairs
Pribnow box
7 base pairs
DNA
-35
-20
TATAAT
Start of transcription
Figure 31.7 Structure of the prokaryotic promoter region. T = thymine; G = guanine; A = adenine; C = cytosine.
β΄
Rifampin
RNA polymerase with distorted conformation
Rifampin binds to RNA polymerase and prevents chain growth beyond three nucleotides. Eukaryotic RNA polymerases do not bind rifampin, and transcription is unaffected.