RNA Structure and Function Flashcards
What are the types of RNA?
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Messenger RNA (mRNA)
Noncoding RNA (which edits mRNA to alter gene expression)
Prevalence of each RNA type in the cell
80% rRNA
15% tRNA
5% mRNA
The start of the RNA molecule is the ____ end and the termination is the ____ end
__5’__
__3’__
How are ribosomes formed?
rRNA + Proteins
rRNA
Prokaryotic rRNA has ____ different sizes of RNA
3
rRNA
Eukaryotic rRNA has ____ different sizes of RNA
4
rRNA
Prokaryotic rRNA sizes
23S
16S
5S
rRNA
Eukaryotic rRNA sizes
28S
18S
5.8S
5S
rRNA
Process of primary transcript conversion to rRNA in eukaryotes
Primary transcript processed into 28S, 18S, 5.8S and 5S rRNAs
rRNA
Components of large ribosomal subunit formation in eukaryotes
28S, 5.8S and 5S rRNAs + Ribosomal Protein
rRNA
Size of large ribosomal subunit (rRNA and proteins) in eukaryotes
60S
rRNA
Process of small ribosomal subunit formation in eukaryotes
18S associates + Ribosomal Proteins
rRNA
Size of small ribosomal subunit (rRNA and proteins) in eukaryotes
40S
rRNA
Size of Eukaryotic Ribosome
80S
tRNA
Characteristics
Exhibit extensive secondary structure
Contain several modified ribonucleotides
tRNA
How are modified ribonucleotides formed?
Derived from four normal ribonucleotides
tRNA
Names of hairpin-turn loops
TψC Loop
Anticodon Loop
D Loop
tRNA
Modified bases of the D loop
Methylated Cytosine
Dihydrouridine
tRNA
Function of the anticodon loop
Recognition of complementary mRNA codons
tRNA
Modified bases of the TψC loop
Pseudouridine (ψ)
tRNA
Structure of Acceptor Stem
5’ - … CCA-3’
tRNA
Function of Acceptor Stem
Ester bond forms between 3’-OH group of Adenosine of tRNA and carboxyl group of amino acid
mRNA
Difference in prokaryotic and eukaryotic mRNA processes
Compartmentalization of transcription and translation
Protection at their 5’ and 3’ ends
Processing of mRNAs
Prokaryotic mRNAs are polycistronic and eukaryotic mRNAs are monocistronic
mRNA
Compartmentalization of transcription and translation in prokaryotes and eukaryotes
Prokaryotes synthesize RNA and proteins in cytoplasm
Eukaryotes separate transcription and translation in nucleus and cytoplasm
mRNA
Protection at the 5’ and 3’ ends of eukaryotes
Eukaryotic mRNA have 5’ cap and 3’ poly(A) tail
mRNA
Processing of mRNA in prokaryotes and eukaryotes
Prokaryotic mRNA is not processed
Eukaryotic mRNA has introns which are spliced out
mRNA
Monocistronic vs Polycistronic
Prokaryotes have Polycistronic mRNA (multiple proteins from one mRNA)
Eukaryotes have Monocistronic mRNA (one protein formed from each mRNA)
Noncoding RNA
Types
lncRNAs
miRNAs
siRNAs
Noncoding RNA: lncRNA
Length
> 200 nucleotides long
Noncoding RNA: lncRNA
Function
Affects gene regulation by binding to DNA, RNA and proteins
Mediates developmental inactivation of duplicated X chromosomes
Noncoding RNA: miRNAs
Length
21-25 nucleotides
Noncoding RNA: miRNA
Formation
Pri-miRNAs transcribed by RNA Polymerase II from noncoding genome segment
Noncoding RNA: miRNA
Function
Loaded into silencing complex which scans and cleaves mRNA
Noncoding RNA: miRNA
Why is mRNA cleaved by miRNA?
To downregulate gene expression
Noncoding RNA: siRNA
Formation
Processed from double-stranded RNAs in the cytoplasm
Noncoding RNA: siRNA
Origin of double stranded RNA in cytoplasm
Viral RNAs
Part of innate cellular immunity
Noncoding RNA: siRNA
Purpose of siRNA
RNA intereference (RNAi)
Noncoding RNA: siRNA
What is RNA interference?
siRNA binds to the mRNA to stop translation
What are ribozymes?
RNA molecules acting as enzymes
Example of ribozymes
Large ribosomal subunit (23S in prokaryotes and 28S in eukaryotes)
Ribonuclease P (essential endonuclease)
Spliceosome (converts primary transcript to mature mRNA)
Introns
