The central dogma Flashcards
DNA-RNA-Proteins
what is gene expression
process by which information from a gene is used in the making of a functional gene product
what is transcription
process of making an RNA molecule complementary to a portion of a strand of DNA
what is a promotor and transcription unit
a TATA box located in front of the transcription start point
what are the steps of trancription
initiation, elongation, termination
what happens in initiation
transcription factor proteins bind to the promoter in the area of the TATA box and an RNA polymerase forming the transcription initiation complex
what happens in elongation
the DNA is copied to make RNA in complementary base pairs AU-GC
Elongation: how does a transcription bubble happen
as the RNA polymerase slides along the transcription unit separates the DNA strand creating a bubble
elongation: in what direction is DNA transcribed
5’ to 3’
transcribed antiparallel as well
what is different in the ribonuceloside triphosphate from RNA to DNA
RNA has a OH attached to the 2’ carbon instead of DNA’s H
elongation: what happens once the RNA polymerase has done its job
the DNA returns to it’s double helix
how does the RNA polymerase know when to stop transcribing
it hits a sequence of nucleotides that signal the stop of transcription
what is a codon
3 nucleotides in a row (sequence) on the mRNA (from transcription)
why are there more than one codon that give the same amino acid
so that in the unlikely case a mistake is made we still get the right amino acid to make the right protein
what is pre-mRNA
mRNA that is directly transcribed in the nucleus
what is mature mRNA
mRNA that has gone through processing
what makes an mRNA strand mature
a guanine cap, a poly(A) tail, removal of introns
what is a guanine cap and why is it important
G cap added to the 5’ end of a pre-mRNA that protects mRNA’s from being degraded by the cytosol, facilitates transport from the nucleus, the site where the ribosome attach in translation
what is a poly(A) tail and why is it important
an added 50-250 adenine nucleotides to the 3’ end of pre-mRNA
allows for export through the membrane, makes translation of mRNA into amino acids and proteins easier, and the longer the tail the more times mRNA can be translated before degradation
how does it know when to add the poly(A) tail
a polyadenylation signal
what are introns
non-coding sequences mixed with exons (coding sequences)
need to be removed so we are only left with coding exons in the mature mRNA
what is tRNA
transfer RNA, serves as code readers
what does tRNA carry
an amino acid and anticodons
what are anticodons
a sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA
how do we add amino acids to tRNA
through aminoacyl-tRNA synthetase enzyme in the cytosol that add the correct amino acid onto the tRNA with the correct anticodon
stages of translation
initiation, elongation, termiantion
what happens in the beginning of initiation in translation
we bind together an initiator tRNA with amino acid methionine (the singular start codon), the mRNA, and the small ribosomal subunit
why is it important that the initiator tRNA connects to the correct sequence of mRNA
establishes how it reads to codons
in the right way gets the right amino acids
what happens at the end of initiation in translation
the large ribosomal subunit binds to the small subunit creating three sites to accommodate tRNA’s
what are the three sites created for tRNA’s in translation
E- exit site
P- peptidyl site
A- aminoacyl site
what happens at the beginning of the elongation cycle in translation
tRNA attaches to the correct mRNA sequence (anticodon-codon) in the P site
what happens after a tRNA is in the P site
a new tRNA carryign another amino acid attaches to teh A site and peptidyl transferase occurs
what is peptidyl transferase
cataclyzes the formation of a peptide bond between amino acids held in the P and A sites
what happens after peptidyl transferase in translation
the tRNA’s shift to the next section
the one in P moves to E to exit, one in A moves to P, and a new tRNA moves into A
how is termination carried out
a stop codon in the mRNA and translation is terminated
how are the polypeptide chains released in termination (translation)
since there is no tRNA with an anticodon complementary to the stop codons it is recognized by the release factor proteins
what is the release factor proteins
something that binds to the stop codon and stimulates the release of the polypeptide chain from the ribosomal unit
what is a polysome
when an mRNA strand has multiple ribosome working along it creating the same polypeptide
can a functional protein be made up of more than one polypeptide and what happens to the expressed genes
yes, it can be made of 1 or more polypeptides, the more polypeptides the more genes are expressed
what is post-translational modification of proteins
when after they exit the ribosome they are somehow folded or modified (add another, fold, etc.)
what is the definition of a gene
a unit of heredity on a chromosome that contains the code for a protein molecule or the code for the functioning RNA molecules (tRNA, rRNA)
what is a mutation
a permanent heritable change in the genetic material on the large or small scale
what is a point mutation
where the mutation only affects one base pair of the DNA
what are four types of point mutations
missense, nonsense, silent, and frameshift mutations
what is a missense mutation
change in the DNA sequence causing a change in the sense codon (that specifies the amino acid needed) producing a different amino acid changing the function of the protein
what is a nonsense mutation
a change in the DNA sequence that causes a change in the nonsense (stop) codon making a shorter polypeptide chain
Very unlikely the polypeptide will be functional
what is a silent mutation
Change in the DNA sequence causes a change of a codon to a different sense codon but the new codon specifies the same amino acid as in the normal polypeptide
Function is unchanged
what is a frameshift mutation
Deletion or insertion in the DNA sequence that causes a change in the reading frame of the resulting mRNA
After the mutation point will produce a different amino acid sequence resulting in a non-functional polypeptide
