Section 7: Gene Expression Flashcard

One Gene-One Poypeptide
oversimplification;idea that each gene in the genome encodes only a single polypeptide–that there is a one-to-one correspondence between genes and polypeptides
transcription
process of copying information in a DNA sequence (a gene) into a coimplementary RNA sequence
translation
process of creating the amino sequence of a polypeptide from the RNA sequence of transcription
messenger RNA
(mRNA)
travels from the nucleus to the cytoplasm, where it is translated into a polypeptide
ribosomal RNA
(rRNA)
catalyzes peptide bond formation between amino acids to form a polypeptide
transfer RNA
(tRNA)
can bind a specific amino acid and can recognize a specific sequence of nucleotides in mRNA through complementary base pairing
*recognizes which amino acid should be added to a growing polypeptide chain next
transcription requires…
a) DNA template for complementary base pairing
b) appropriate nucleoside triphosphates (ATP GTP, CTP, UTP)to act as substrates
c) RNA polymerase enzyme
RNA polymerase
catalyze the synthesis of RNA from DNA template
*only one kind in bacteria and archea
*several kinds in eukaryotes
common structure of RNA polymerase
processive; single enzyme–template binding event results in the polymerization of hundreds of RNA nucleotides
*DO NOT REQUIRE A PRIMER
promoter
special DNA sequence to which RNA polymerase binds very tightly
*”tell” RNA polyermase where to start transcription and which of the two DNA strands to transcribe
transcription initiation site
(transcription start site-TSS)
where transcription begins
*located on the promoter
elongation
process of RNA polymerase unwinding the DNA and reading the template strand in the 3′-to-5′ direction
termination
particular base sequences specify transcription termination
coding regions
sequences within a DNA molecule that are expressed as proteins
introns
noncoding sequences of a gene
*intervening regions;interrupt coding region
exons
expressed regions interspersed with the introns
pre-mRNA
primary mRNA transcript
*where introns and exons appear
*introns are removed by the time the mature mRNA leaves the nucleus
pre-mRNA processing
involvies cutting introns out of the pre-mRNA transcript and splicing together the exon transcripts
nucleic acid hybridization
methoed that originally revealed the existence of introns
involves 2 steps:
a) DNA to be analyzed is denatured by heat to break hudrogen bonds btwn base pairs and separate 2 strands
b) singled stranded nucleic acid from other source(probe) is incubated with denatured DNA; if probe has similar DNA sequence, it will form double helix by hydrogen bonding the bases
RNA splicing
removes introns and splices exons together
consensus sequences
short stretches of DNA that appear with little variation (“consensus”) in many different genes
small nuclear ribonucleoprotein particles
(snRNP)
complex of an enzyme and a small nuclear RNA molecule, functioning in RNA splicing
*bind consensus sequences in RNA splicing
spliceosome
large RNA-protein complex; cuts pre-mRNA, releases introns, and joins exons together to produce mature mRNA
ribonucleases
enzymes that break down RNAs in a 5’cap
codon
each sequence of 3 nucleotide bases along the mRNA polynucleotide chain
*specifies a particular amino acid
*each in mRNA is complementary to corresponding triplet of bases in DNA from which it was transcribed
start codon
initiation signal for translation
stop codon
termination signals for translation; when translation machinery reaches one of these codons, translation stops and the polypeptide is released from translation complex
*UAA, UAG, UGA
anticodon
3 nucleotides in tRNA that pair with a complementary triplet (a codon) in mRNA;
located about midpoint on tRNA polynucleotide chain; triplet of bases; complementary to mRNA codon for particular amino acid that tRNA carries
A (amino acid) Site
where the charged tRNA anticodon binds to the mRNA codon, lining up the correct amino acid to be added to teh growing polypeptide chain
P (polypeptide) Site
where the tRNA adds its amino acid to the polypeptide chain
E (exit) Site
where the rRNA, having given uup its amino acid, resides before being release from the ribosome and going back to the cytosol to pick up another amino acid and begin the process again
ribosome fidelity function
ensures that a charged tRNA with the correct anticodon binds to the appropriate codon in the mRNA
polyribosome
(polysome)
assemblage consisting of a strand of mRNA with its beadlike ribosomes and their growing polypeptide chains
protein synthesis always begins…
on free ribosomes floating in the cytoplasm
*”default” location for protein is cytosol
signal sequence
(signal peptide)
short stretch of amino acids that indicates where in the cell the polypeptide belongs
*directs the protein to a particular organelle
*proteins destined for different locations have different signals
*binds to specific receptor protein at surface of organelle
polyproteins
long polypeptides containing the primary sequences of multople distinct proteins
gene
unit of hereditary;
used as the unit of genetic function which carries the info for a polypeptide or RNA
gene expression
process by which information from a gene is used in the synthesis of a functional gene product
central dogma of molecular biology
gene expression;
describes the way genetic information is expected to be transferred in a single direction through a biological system
transcription
process of creating a complementary RNA copy of a sequence of DNA
reading frame
3′-5′
*builds 5′-3′
transcription factor
(sometimes called a sequence-specific DNA-binding factor)
*protein that binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to mRNA
polyadenylation
addition of a poly(A) tail to an RNA molecule
primary transcript
(pre-mRNA)
initial gene transcript before it is modified to produce functional mRNA
mature mRNA
transcript of a region of one of the strands of DNA; carries info(as a sequence of codons) for the synthesis of one or more proteins
mRNA splicing
primary transcript contains both introns and exons
splicing removes introns
the exons are then joined together in a continusous coding sequence of nucleotides
alternative splicing
process of generating different mature mRNAs from a single gene by splicing together different sets of exons during RNA processing
spliceosome
RNA-protein complex that splices out introns from eukaryotic pre-mRNAs
charging reaction
process of loading tRNA with the amino acid
*aminoacyl-tRNA synthetase
aminoacyl-tRNA synthetase
enzyme that catalyzes the esterification of a specific amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl-tRNA
*simply attaches the accurate amino acid onto the corresponding tRNA
ribosome
small particle in the cell that is the site of protein synthesis
peptidyl transferase
catalytic function of large ribosomal subunit
consists of 2 rxns:
a)breaking bond btwn an AA and its rRNA in P site
b)forming peptide bond btwn that AA and AA attached to tRNA in A site
release factor
protein that allows for the termination of translation by recognizing the termination codon or stop codon in a mRNA sequence
wobble
(wobble pairing)
phenomenon that the cell gets by with about 2/3 of the total 61 different tRNA species becuase the specificity for the base at the 3′ end of the codon (and the 5′ end of the anticodon) is not always strictly observed
silent mutation
change in a gene’s sequence that has no effect on the amino acid sequence of of a protein becuase it occurs in noncoding DNA or because it does not change the amino acid specified by the corresponding codon
mutation
change in the genetic material not caused by recombination
missense mutation
change in a gene’s sequence that changes the amino acid at that site in the encoded protein
nonsense mutation
change in a gene’s sequence that prematurely terminates translation by changing one of its codons to a stop codon
frameshift mutation
addition or deletion of a single or two adjacent nucleotides in a gene’s sequence
*results in the misreading of mRNA during translation and the production of a nonfunctional protein
Insertion
addition of one or more nucleotide base pairs into a DNA sequence
Deletion
part of a chromosome or a sequence of DNA is missing
*loss of genetic material
*any number of nucleotides can be deleted, from a single base to an entire piece of chromosome

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