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51 Cards in this Set

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one gene-one polypeptide hypothesis
discovered by Beadle and Tatum
-not all proteins are enzymes
- proteins are contructed from two ore more different polypeptide chains
-each polypeptide is specified by its own gene
transcription
synthesis of RNA under the direction of DNA
mRNA
messenger RNA
-carries a genetic message from DNA to the protein to be synthesized by the machinery of the cell
translation
synthesis of a polypeptide under the direction of mRNA
where does translation occur?
in the ribosomes
synthesis in prokaryotes
transcription and translation occur simulaneously
synthesis eukaryotes
nuclear envelopeps separates transcription from translation
primary transcript
initial RNA transcript
triplet code
the genetic insructions for polypeptide chain
- series of three nucleotides
template strand
- for each gene only one of the two DNA strands is transcribed
codons
mRNA base triplets that specify for an amino acid
AUG
methionine (Met)
initiation codon that signals the protein-synthesizing machine to begin translating the mRNA at the location
termination codons
signal the end of translation
redundancy but no ambiguity
-two codons may specify one amino acid
-neither of any two codons specifies any other amino acid
reading frame
reading the symbols in the correct sequence and groupings
RNA polymerase
pries the two strands of DNA apart and hooks together the RNA nucleotides as they base-[air along the DNA template
direction that RNA molecule elongates?
5'--> 3'
RNA polymerase II
type of RNA polymerase used for mRNA synthesis
three stages of transcription
initiation, elongation, and termination of the RNA chain
promoter
region of DNA where RNA polymerase attaches and initiates transcription
what are two functions of the promoter?
-determines where transcription starts.
- determines whihch of the two strands of the DNA helix is used as the template.
other (nontemplate strand)
provides the instructions for making a new template strand when the DNA replicates
transcription factors
collection of proteins in Eukaryotes which mediate the binding of RNA polymerase and the initiation of transcription
transcription initiation complex
completed assembly of transcription factors and RNA polymerase bound to the promoter
TATA box
promoter DNA sequence
- crucial in forming the iniation complex
RNA splicing
cut and paste job
introns
noncoding segments of nucleic acid that lie between coding regions
exons
regions of nucleic acd that are eventually expressed
snRPs
( small nuclear ribonucleic proteins)
signal RNA splicing
-located in the nucleus
-composed or RNA and protein molecules
-
snRNA
(small nuclea RNA)
the RNA in a snRNP particle
- 150 nucleotides long
spliceosome
an assembly of several additional proteins ( almost as big a ribosome)
- cuts at specidic points to release the intron, then immediately joins together the two exons that flanked the intron
ribozymes
RNA molecules that function as enzymes
structural domain
- structure that is self-stabilizing and often folds independently of the rest of the protein chain.
- classified into "folds
how are introns related to variety?
introns increase the opportunity for crossing over between two alleles of a gene, raising the probability that a crossover will switch one version of an exon for another version found on the homologous chromosome
tRNA
( transfer RNA)
transfers amino acids from the cytoplasm's amino acid pool to a ribosome
anticodon
nucleic triplet which binds according to base-pair rules to a complementary codon on mRNA
wobble
relaxation of base pair rules
ex: the bae U of a tRNA anticodon can pair with either Aor G in the third posistion of an mRNA codon
aminoacyl-tRNA
enzyme that joins each amino acid to the correct tRNA
-20 in each cell
number of amino acids in a cell
20
rRNA
(ribosomal RNA)
type of RNA that is the central component of the ribosome
P site
binding site for tRNA
- holds the tRNA carrying the growing polypeptide chain
A site
binding site for tRNA
- hold the tRNA carrying the 2nd anmino aicd to be added to the chain
E site
( exit site)
-site where discharged tRNAs leave the ribosome
initiation
brings together mRNA, a tRNA bearing the first amino acid of the polypeptide, and the two subunits of a ribosome
mutations
changes in the genetic information of a vell
base-pair substitution
replaces one nucelotide and it complementary partner with another pair of nucleotides
missense mutation
substitution that results in an incorrectly coded amino acid
Nonsense mutations
occur when the point mutation changes an amino acid codon into a stop codon
-halts translation early
frameshift mutatitions
-mutations that alter the reading frame
SRP
signal-recognition particle
-attaches the ribosome to a receptor protein
signal peptide
begins polypeptide chain destined to be for secretion