Chapter 17: gene->protein Flashcards
gene expression
process of DNA -> protein
Archibald Garrod
hypothesized that genes control phenotypes through enzymes that catalyze specific reactions
- ex: alkaptonuria (lacks enzyme so urine is black)
Beadle and Tatum
one-gene one-enzyme hypothesis
experiment: bombarded neurospora crassa (bread mold) with X rays to cause genetic changes and found mutants that could not survive on minimal medium.
- discovered mutants were defective in single genes that made them unable to synthesize specific nutrients
transcription
synthesis of RNA using DNA. occurs in nucleus
mRNA
RNA synthesized during transcription used to make proteins
translation
synthesis of polypeptide using mRNA. occurs in cytoplasm
ribosomes
sites of translation
primary transcript
initial unedited RNA transcript from a gene
triplet code
one amino acid determined by sequence of 3 RNA nucleotides
template strand
strand of DNA that is transcribed in transcription. same strand used as template for a given gene
codons
mRNA nucleotide triplets. written in 5-3 direction
reading frame
correct groupings of triplet code
RNA polymerase
untwists DNA apart and joins complementary RNA nucleotides
promoter
DNA sequence where RNA polymerase attaches and initiates transcription
terminator
sequence signaling end of transcription
transcription unit
stretch of DNA transcribed into RNA molecule
start point
nucleotide where RNA synthesis actually begins. located in promoter
RNA polymerase 2
used in mRNA synthesis
transcription factors
mediate binding of RNA polymerase and initiation of transcription
transcription initiation complex
complex of transcription factors and RNA polymerase 2 bound to the promoter
TATA box
important promoter DNA sequence in eukaryotes
polyadenylation signal
sequence (AAUAAA) signaling end of transcription in eukaryotes. 10-35 nucleotides down RNA transcript cut from DNA.
RNA processing
enzymes in eukaryotic nucleus modify pre-mRNA. both ends of transcript altered
5’ cap
modified guanine nucleotide added onto 5’ end on RNA transcript
poly A tail
chain of 50-250 adenine nucleotides added onto 3’ end of RNA transcript
RNA splicing
stage in RNA processing when large portions of RNA molecule is removed
introns
regions of noncoding mRNA in RNA transcript
exons
regions of RNA transcript that are expressed
snRNP
particles that recognize splice sites in RNA. made of snRNA, 150 nucleotides long.
spliceosome
assembly of snRNPs that cuts out intron and joins together exons
ribozymes
RNA molecules that function as enzymes
- single-stranded so it can base pair with itself to make 3D shape
-some bases in RNA have functional groups that can help in catalysis
- RNA can hydrogen bond with other nucleic enzymes
alternative RNA splicing
different segments of RNA can be treated as exons. increases number of protein products for smaller amounts of DNA
mains
discrete structural and functional regions of protein
tRNA
transfers amino acids from cytoplasm to polypeptide in ribosome. made in nucleus and transported to cytoplasm
anticodon
nucleotide triplet on tRNA that base-pairs with complementary mRNA codon
aminoacyl-tRNA synthetase
enzymes that match up tRNA with matching mRNA. (20 types)
1. active site binds amino acid and ATP
2. ATP loses 2 P and binds to amino acid as AMP
3. tRNA covalently binds to amino acid, displacing AMP
4. tRNA charged with amino acid released
wobble
flexible base pairing at 3rd nucleotide of codon and anticodon (less synthetases than codons)
rRNA
makes up ribosomes
large subunit
has P, A, and E site and exit tunnel.
small subunit
has mRNA binding site
P site
holds tRNA with growing polypeptide chain
A site
holds tRNA with the next amino acid
E site
where discharged tRNAs leave ribosome
translation initiation
- small subunit with initiator tRNA binds at 5’ cap of mRNA and shifts until it binds with start codon
- large subunit joins with small subunit using GTP hydrolysis and initiation factors.
translation elongation
- anticodon of tRNA base pairs with mRNA codon at A site. uses GTP hydrolysis
- rRNA catalyzes peptide bond between amino acid in A site and amino acid in P site. polypeptide shifts from P site to A site.
- tRNA in P site moves to E site and exits. tRNA in A site moves to P site.
translation initiation complex
small subunit and large subunit combined with iniator tRNA, mRNA, amino acid
translation termination
stop codon in mRNA reaches A site of ribosome. translation assembly disassociates
release factor
protein shaped like aminoacyl tRNA. binds to stop codon and causes addition of water molecule instead of amino acid to polypeptide. breakdown of translation complex needs 2+ GTP
polyribosomes
strings of ribosome making one protein
signal peptide
marks polypeptides of proteins for endomembrane system or secretion
signal-recognition particle
protein RNA complex that brings signal peptide marked ribosome to ER membrane.
translocation complex
membrane pore and signal-cleaving receptor protein in ER. polypeptide translocated through pore into ER and after termination signal-cleaving enzyme cuts off signal polypeptide.
mutations
changes in DNA
point mutations
small mutations in single nucleotide pair of a gene
nucleotide-pair substitution
replacement one nucleotide and its partner with another pair of nucleotides
silent mutation
no observable effect on phenotype
missense substitution
changes one amino acid to another one
nonsense mutation
changes codon to stop codon
insertion
addition of nucleotide pair
deletion
loss of nucleotide pair
frameshift mutation
changes triplet grouping of nucleotides on mRNA read during translation
mutagenes
physical/chemical agents interacting with DNA and causes mutation
