Ch 17 Flashcards
How does DNA lead to specific traits?
It dictates the synthesis of proteins
gene expression
the process by which DNA directs the synthesis of proteins or RNAs
stages of gene expression
transcription and translation
The hypothesis of Beadle and Tatum
one gene, one enzyme: The function of a gene is to dictate the production of a specific enzyme
Describe Beadle and Tatum’s experiment
They bombarded a bread mold with x-rays to create mutants, and then they tested supplements to find what each mutant needed, which identified the defective pathway and step.
Srb and Horowitz
They distinguished three types of arginine-requiring mutants, each mutated at a different gene; each lacked a different enzyme to catalyze a different blocked step.
define RNA
the nucleic acid that is the bridge between DNA and protein synthesis
How does RNA differ from DNA?
- ribose instead of deoxyribose
- uracil instead of thymine
- single strand
define transciption
synthesis of mRNA using information in the DNA
Where does transcription occur?
in the nucleus
define translation
synthesis of a polypeptide using the information in the mRNA
Where does translation occur?
in cytoplasm (at the ribosomes)
ribosomes
complex particles that facilitate the orderly linking of amino acids into polypeptide chains
mRNA
messenger RNA, carries a coded genetic instructions from the DNA to the protein-synthesizing machinery of the cell
primary transcript
initial RNA transcript from any gene which requires further processing
other name for primary transcript
pre-mRNA
central dogma
directional flow of genetic info
DNA -> RNA -> Protein
What is the main difference between prokaryotic and eukaryotic transcription?
Prokaryotes lack the compartmentalization of the nucleus. Translation begins while transcription is still ongoing.
nucleotide bases code for ## amino acids.
4, 20
reading frame
the groupings of three that the code is read in
triplet code
genetic info written as a series of nonoverlapping, three-nucleotide words
template strand
the DNA strand that is transcribed
The ____ strand is transcribed every time for a specific gene
same
codons
mRNA nucleotide triplets
The mRNA strand forms…
antiparallel in the 5’ to 3’ direction
start codon
AUG, methionine
stop codons
UAA, UAG, UGA
What does RNA polymerase do?
pries DNA strands apart and joins together complementary RNA nucleotides
RNA polymerase does not need:
a primer
There are three stages to both transcription and translation. What are they?
- initiation
- elongation
- termination
define transcription unit
the stretch of DNA that is transcribed into an RNA molecule
promoter
DNA sequence where RNA polymerase attaches and initiates transcription
TATA box
DNA sequence containing TATA where transcription initiation complex binds and forms
transcription initiation complex
group of transcription factors and RNA polymerase II bound to the promoter.
Why the TATA box?
Only 2 hydrogen bonds join A and T, so it is easy to break the strands apart
start point
nucleotide where RNA synthesis actually begins
terminator
signals end
RNA processing
enzymes in the eukaryotic nucleus modify pre-mRNA before it is sent to the cytoplasm
other name for RNA processing
post-transcriptional modification
Through RNA processing, the _____ _____ becomes the _____ ______.
primary transcript -> mature transcript
Parts of RNA processing
alteration of ends
RNA splicing
5’ cap
modified form of G added to 5’ end
poly-A tail
50 to 250 As added to 3’ end
RNA splicing
cut out large portions of the primary transcript and splice together the remaining parts
introns
intervening noncoding segments
exons
expressed segments, coding regions
spliceosome
assembly of snRNPs and proteins that does the splicing
ribozymes
RNA that functions as enzymes
alternative RNA splicing
a gene can give rise to more than one kind of polypeptide depending on which segments are treated as exons
Alternative splicing and evolution
Might result in beneficial proteins with new structure and/or function
tRNA
translator of mRNA to build a polypeptide by transferring amino acids from the cytoplasm to the growing polypeptide in the ribosome
anticodon
nucleotide triplet on the end of tRNA that is complementary to an mRNA codon
What holds together the polypeptide chain?
peptide bonds
aminoacyl-tRNA synthetases
enzymes that correctly match up tRNA and amino acid
Why are proteins important?
as enzymes or structural proteins
UTR
untranslated region
open reading frame
part of the strand that becomes a polypeptide
mutation
change to genetic info
point mutations
change in single nucleotide pair
nucleotide-pair substitution
replacement of one pair with another pair
silent mutation
no observable effect on phenotype
missense mutation
substitutions that change one amino acid to another
repressor protein
doorstop that prevents RNA polymerase from moving along strand
Repressor proteins disengage when… and reengage when…
a specific substance binds to it, the substance is no longer present
repressible system
gene is always on and a repressor protein can’t bind until the substance is present
sense strand
same sequence as mRNA, coding strand
antisense strand
template strand
nonsense mutation
changes a codon into a stop codon, premature termination
insertion
addition of nucleotide
deletion
removal of nucleotide
frameshift mutation
triplet groupings change due to insertion or deletion
mutagen
physical or chemical agents that cause mutations
