Lecture 14 - RNA structure and gene expression Flashcards
RNA world hypothesis steps
- RNA forms
- Ribozyme catalyzes RNA replication
- RNA catalyzes protein synthesis
- RNA encodes both DNA and protein
- Proteins catalyze cell activities
Reverse transcriptase is a
polymerase
Information encoded in a DNA molecule is transcribed via
synthesis of an RNA molecule
Polymerase
An enzyme that brings about the formation of a particular polymer, especially DNA or RNA
Messenger RNA is a
copy (transcription) of DNA and the template for protein synthesis (translation)
Cistronic gene expression
one mRNA molecule is usually produced for a whole group of genes (in prokaryotes)
Alternative splicing
A single distinct mRNA is produced for each gene (in eukaryotes)
mRNA adopts _________ structures such as stem-loops
secondary
RNA chains are produced by
copying of template DNA strands
The base sequence of mRNA is the complement of
the DNA template strand
The strand besides the mRNA and DNA template strand is the
coding strand
The coding strand has the
same sequence as RNA transcript except T is replaced by U
mRNA in eukaryotes is modified after
transcription
A nucleotide cap is added to the 5’ end and signals
the docking of ribosomes
The docking of ribosomes initiates
protein synthesis
A poly (A) tail is added to the 3’ end to
prevent digestion of mRNA by exonucleases in the cytosol
The 5’ UTRs in mRNA typically contain
regions of RNA that determine translational control (initiation)
Transfer RNA (tRNA) is
a ribonucleic acid that carries a specific amino acid to the site of protein synthesis in ribosomes.
There is at least one kind of tRNA for
each of the 20 amino acids
Transfer RNA adopts a specific secondary structure of loops resembling a
clover leaf
The adaptors in protein synthesis are
transfer RNAs
A mature tRNA is about ________ amino acids long
75
tRNAs contain
an amino acid attachment site and a template-recognition site
a tRNA molecule carries
one specific amino acid in an activated form to the ribosome (site of protein synthesis)
The anticodon of tRNAs recognize
a complementary sequence of three bases on mRNA called a codon
In tRNA, the amino acid is attached by
esterification of the carboxyl group of the amino acid to the 3’- or 2’-hydroxyl group of the ribose unit at the 3’ end of the tRNA chain
Amino acids attaching to tRNA is catalyzed by the enzyme
aminoacyl-tRNA synthetase
Amino acids attaching to tRNA is driven by the
hydrolysis of ATP
A tRNA molecule attached to an amino acid is called
an aminoacyl-tRNA
mRNAs carry ________ signals for protein synthesis
start and stop
In prokaryotes, the initial N-terminal amino acid in translation is
N-formylmethionine (fmet)
The initiator tRNA carries
fmet which recognizes the codon AUG (start)
Ribosomal RNA (rRNA) is the major component of
ribosomes
In prokaryotes, the three kinds of rRNA are named ____________
23s, 16s, and 5s due to their sedimentation
In eukaryotes, the four kinds of rRNA are named _____________
28s, 18s, 5.8s, and 5s
rRNA functions as the catalyst in
protein synthesis
Ribosomes are referred to as ribozymes because
most catalytic reactions in cells are carried out by enzymes
The ribosome from E. coli consists of what two subunits
50S and 30s (form 70s)
The 30S subunit in E. coli contains
21 different proteins and one 16s RNA molecule
The 50S subunit in E. coli contains
31 different proteins and two RNA molecules (23S and 5S)
The ribosome has three tRNA binding sites called
A site (aminoacyl)
P site (peptidyl)
E site (exit)
Small nuclear RNA (snRNA) is found in
the nucleus of eukaryotic cells
snRNA complexes with proteins to form
small nuclear ribonculeoprotein particles (snRNPs)
snRNPs help with
mRNA processing to splice introns from the precursor mRNA to yield mature mRNA
Splicing is done by a large complex called the
spliceosome
The spliceosome consists of
RNAs and proteins
In eukaryotes, the vast majority of RNA is processed immediately after
transcription
Primary transcripts (pre-mRNA) acquire a
5’ cap and a 3’ poly(A) tail
Almost all pre-mRNAs are
spliced
Introns are _______ and exons are _______ to form mature mRNAs
excised; joined
The pattern of splicing is regulated to
match the requirements of the cell
Alternative splicing enlarges
the repertoire of proteins in eukaryotes
Which is more complex, the proteome, or the genome?
proteome
Micro RNA (miRNA) is
a class of small 21-oligonucleotides that serve as an inhibitor for translation by binding to the complementary mRNA
Small interfering RNA (siRNA) is
a class of small RNA molecules that bind to mRNA and facilitate its degradation
