Flashcards in Gene Expression; from Gene to Protein Deck (126):
he process by which DNA directs protein synthesis, includes two stages
The two stages of Gene Expression
transcription and translation
Central Dogma of Molecular Biology
describes the flow of information from DNA to mRNA to protein.
What does the Central Dogma state?
It states that genes specify the sequence of mRNA which specifies the sequence of proteins
RNA is the bridge between what?
Genes and the proteins that they code
The synthesis of RNA using information in DNA, producing mRNA.
The synthesis of a polypeptide, using information in the mRNA, with ribosomes being the sites of translation
Prokaryote Transcription and Translation
translation of mRNA can begin before transcription has finished. Transcription & translation are coupled in prokaryotes.
Eukaryotic Transcription and Translation
the nuclear envelope separates transcription from translation;Transcription & translation are not coupled.
Eukaryotic RNA transcripts are ...
modified through RNA processing to yield the finished mRNA
How many amino acids are there?
How many nucleotide bases in DNA are there?
What is a Triplet Codon
A series of non-overlapping, three-nucleotide words. The words of a gene are transcribed into complementary non-overlapping three-nucleotide words of mRNA
After genes are transcribed into mRNA, what happens next?
These words are then translated into a chain of amino acids, forming a polypeptide
What is a Template Strand?
During transcription, one of the two DNA strands, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript.
Is the template strand always the same strand for a given gene?
What is the process called from DNA to Pre-mRNA?
What is the process called from Pre-mRNA to mRNA?
What is the Process called from mRNA to Ribosome?
What comes out of a Ribosome?
In a Bacterial Cell; What happens from DNA to mRNA?
In a Bacterial Cell; what happens from mRNA to Ribosome?
What are codons?
mRNA base triplets
During translation, the mRNA base triplets are read in what direction?
5' --> 3' Direction
What is the job of the codon?
To specify the amino acid to be placed at the corresponding position along a polypeptide
The genetic code is ___
Redundant ; more than one codon may specify a particular amino acid
Of the 64 triplets, how many codes are for amino acids?
Of the 64 triplets, how many codes are for "stop" signals to end translation
3 (UAA, UGA, UAG)
Of the 64 triplets, how many codes are TO START CODON?
Where is non-universal genetic code located?
Found in the Mitochondria and Protists
What are the three stages of transcription?
Initiation, Elongation, Termination
What is RNA Polymerase
RNA synthesis is catalyzed by this, which pries the DNA strands apart and joins together the RNA nucleotides.
What is a Promoter
The DNA sequence that RNA polymerase attaches to
What is a transcription unit?
The stretch of DNA that is transcribed
Does RNA Polymerase need a Primer??
How do Promoters start the process?
signal the transcriptional start point and usually extend several dozen nucleotide pairs upstream of the start point
What are Transcription Factors?
They mediate the binding of RNA polymerase and the initiation of transcription.
What is a Transcription Initiation Complex?
The completed assembly of transcription factors and RNA polymerase II bound to a promoter
What is a TATA box?
A promoter, that is crucial in forming the initiation complex in eukaryotes
As RNA polymerase move along the DNA, how many does it untwist?
10-20 bases at a time
Transcription progresses at a rate of..
40 nucleotides/sec in eukkaryotes
Which end are Nuceotides added to?
They are added to the 3' end
Termination of Transcription; Bacteria
the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification
Termination of Transcription; Ekaryotes
RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
When do enzymes in the eukaryotic nucleus modify pre-mrna?
Before the genetic messages are dispatched to the cytoplasm
During RNA processing, what is usually altered?
Both ends of the primary transcript
Usually, what sections are cut out and the remaining spliced together?
Introns are cut out, and exons are spliced together
Pre-mRNA molecule is modified with the 5' and 3' end recieving what?
The 5' end receives a modified nucleotide 5' cap (Guanine) and the 3' gets a poly-A tail
Why do both the 5' and 3' get modified?
They seem to facilitate the export of mRNA to the cytoplasm
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5′ end
What are Introns?
They are noncoding regions; where NA transcripts have long noncoding stretches of nucleotides that lie between coding regions
What are Exons?
They are eventually expressed, usually translated into amino acid sequences
What does RNA cutting & splicing do?
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
In some cases, what is RNA splicing carried out by?
What are spliceosomes
consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites.
What are Ribozymes?
are catalytic RNA molecules that function as enzymes & can splice RNA.
Property of RNA that enables it to function as an enzyme (1)
It can form a three-dimensional structure because of its ability to base-pair with itself
Property of RNA that enables it to function as an enzyme (2)
Some bases in RNA contain functional groupsthat may participate in catalysis
Property of RNA that enables it to function as an enzyme (3)
RNA may hydrogen-bond with other nucleicacid molecules
Importance of Introns?
Some introns contain sequences that may regulate gene expression
Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during ,splicing, also known as alternative RNA splicing
What are domains?
Proteins often have a modular architecture consisting of discrete regions
Why might exon shuffling happen?
As a result in the evolution of new proteins
Information and Translation
Genetic information flows from mRNA to protein through Translation
How does cell translate an mRNA message into a protein'?
With the help of transfer RNA (tRNA)
tRNAs transfer what?
Transfer amino acids to the growing polypeptide in a ribosome
one specific amino acid on one end
On the other end of a tRNA, there is...
an anticodon. The anticodon base-pairs with a complementary codon on mRNA
tRNA consists of a single RNA strand that is how long?
80 nucleotides long
What does a tRNA look like?
Translation requires how many steps?
Translation Step 1
a correct match between a tRNA & an amino acid, done by the enzyme aminoacyl-tRNA synthetase
Translation Step 2
a correct match between the tRNA anticodon & an mRNA codon
What is a wobble?
Flexible pairing at the third base of a codon that allows some tRNAs to bind to more than one codon
Ribosomes facilitate specific coupling of
tRNA anticodons with mRNA codons in protein synthesis
Two ribosomal subunits are made of
ribosomal proteins (~ 80) and ribosomal RNAs (18S, 5S, 5.8S, 28S)
Ribosome has how many binding sites for tRNA?
What are the three binding sites that a ribosome has for tRNA?
P, A, and E site
holds the tRNA that carries the growing polypeptide chain
holds the tRNA that carries the next amino acid to be added to the chain
is the exit site, where discharged tRNAs leave the ribosome
Three stages of Translation?
Initation, Elongation, Termination
Translation ; Initation brings together..
mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
What happens first in Initation in Translation?
a small ribosomal subunit binds with mRNA and a special initiator tRNA (met) Then the small subunit moves along the mRNA until it reaches the start codon (AUG)
Proteins called initation factors bring...
in the large subunit that completes the translation initiation complex
Translation; During Elongation..
amino acids are added oneby one to the C-terminus of the growing chain
Translation; Elongation; Each addition invovles proteins called
elongation factors and occurs in 3 steps: codon recognition, peptide bond formation, and translocation
When does energy expenditure occur in Elongation (Translation?
During Codon Recognition and Translocation
Translation proceeds along the mRNA in a
5' --> 3' direction
Occurs when a stop codon in the mRNA reaches the A site of the ribosome
(Termination; Translation) A site accepts..
A protein called a release factor
(Termination; Translation) Release factor causes..
the addition of a water molecule instead of an amino acid
(Termination; Translation) The release factor reaction
releases the polypeptide, and the translation assembly comes apart
IS translation suffcient to make a functional protein?
Often times no
Polypeptide chains are modified after..
translation or targeted to specific sites in the cell
Post-Translational Modification, During Synthesis, polypeptide chain begins to..
coil & fold spontaneously to form a protein with a specific 3-D/4-D structure
Post-Translational Modifications may be required before...
the protein can begin doing its particular job in the cell
What two populations of ribosomes are evident in cells?
Free Ribosomes (Cytosol) and Bound Ribosomes (Attached to ER)
Free ribosomes mostly..
synthesize proteins that function in the cytosol
Bound ribosomes make..
proteins of the endomembrane system and proteins that are secreted from the cell
Ribosomes are identical and..
can switch from free to bound
Where does polypeptide synthesis always begin?
In the cytosol
Synthesis finishes in ___ unless _______
the cytosol unless the polypeptide signals the ribosome to attach to the ER
Polypeptides are destined for
the ER or for secretion are marked by a signal peptide
A Signal-Recognition Particle (SRP)
binds to the signal peptide
the signal peptide and its ribosome to the ER
Polypeptide Formation (1)
Polypeptide synthesis begins
Polypeptide Formation (2)
SRP bings to signal peptide
Polypeptide Formation (3)
SRP binds to receptor protein
Polypeptide Formation (4)
SRP detaches and polypeptide synthesis resumes
Polypeptide Formation (5)
Signal-cleaving enzyme cuts off signal peptide
Polypeptide Formation (6)
Completed polypeptide folds into final conformation
How is a polyribosome (or polysome) formed?
Multiple ribosomes can translate a singla mRNA simultaneously to form this
Polyribosomes enable a cell to..
make many copies of a polypeptide very quickly
A bacterial cell ensures astreamlined process by...
coupling transcription and translation
What are mutations?
changes in the genetic material of a cell or virus
What are point mutations?
chemical changes in just 1 base pair of a gene
Change in a single nucleotide in a DNA template strand can lead to..
PRoduction of an abnormal protein (sickle cell anemia)
Two categories of Point Mutations
One or more nucleotide-pair insertions or deletions
replaces one nucleotide and its partner with another pair of nucleotides
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
still code for an amino acid, but not the correct amino acid
change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
What are insertions and deletions?
Are additions or losses of nucleotide pairs in a gene
Result after the Insertion or deletion of nucleotides may alter the reading frame,
What are Mutagens?
Physical or chemical agents that can cause mutations
a region of DNA that can be expressed to produce a final functional product (part of a physical structure within cell) that is either a polypeptide or an RNA molecule (rRNA, tRNA).