Chapter 15 and 16 Flashcards
Archibald Garrod
1902
Genes dictate phenotypes
phenotype requires enzyme
mutations cause faulty protein
Beadle and Ephrussi
1930s
posed the actual hypothesis
linked enzymes to metabolic pathways
a faulty enzyme affects reaction
1941
mutated specific nutritional enzymes
observed by modifying nutrients
one-gene-one protein hypothesis
not all proteins are enzymes
one-gene-one protein hypothesis
quaternary proteins and subunits
hemoglobin with 4 subunits
Ribonucleic acids
mRNA
tRNA
rRNA
tRNA and rRNA do not equal protein
Template strand
holds directions for proteins
reported for each gene
3’ -> 5’
mRNA
Equivalent to coding strand
except T -> U
ribose instead of deoxyribose
complementary to template
primary transcript
result of transcription
mRNA (prokaryotes)
pre-mRNA (eukaryotes)
Codon
triplet code
3 nucleotides
Reading frame
degenerate/redundant
unambiguous
non overlapping
must be read 5’ -> 3’
steps of Transcription
Initiation -> Elongation -> Termination
Promotor region
specific region on DNA (transcription)
TATA box (start)
polymerase may bind
Transcription unit
promotor -> terminator
transcribed into mRNA
RNA polymerase II
Similar to DNA poly
no primer needed
no 3’ to add onto
Initiation Pro
no transcription factors
promotor + start site
Elongation Pro
only RNA polymerase II
also codes for RNA
Termination Pro
Rho protein collides with RNA pol
RNA folds back on itself
signals to stop and detach
no post transcription (mRNA ready for translation)
Initiation Euk
Requires transcription factors
transcription initial complex
bind to specific location (TATA)
Elongation Euk
many RNA polymerases
RNA polymerase II -> pre-mRNA
40 nucleotides/sec
Termination Euk
polyadenylation signal
transcribed onto mRNA
AAUAAA sequence
bound by proteins
cut pre-mRNA and release
post transcription occurs
post transcription
pre mRNA produces
untranslated region
polyadenylation signal
protein and coding segment (Exons and Introns)
start and stop codons
mRNA leaves nucleus
Exons
expressed or exits nucleus
codes for protein or domain
Introns
Intervening sequence
between exons, regulatory
RNA splicing
splicesome (protein and ribozymes)
exons combined and introns removes
alternative RNA splicing (order of exons)
Where translation occurs
cytoplasm
anticodon
sequence of nucleotides in RNA (3)
complementary to codon
tRNA
wobble = flexibility
rRNA
ribosomal RNA
transcribed separately
catalyze formation of polypeptide
adds AA to carboxylic ends
most common cellular RNA
Ribosomes
site of translation
produced by nucleolus
protein subunits and rRNAs
sandwich with mRNA
binding site for tRNA
Initiation
factors bring all components together
mRNA, tRNA, ribosomes
Translation initiation complex
small subunit with initiator tRNA
binds to mRNA w/ 5’ cap
scans downstream until AUG (start)
initiator tRNA H bonds to AUG
signals reading frame
large subunit binds and requires E (GTP)
Elongation
formation of polypeptides
require elongation factors
3 stops require GTP
add new AA to carboxylic ends
Elongation steps
- new tRNA arrives
binds with A site uses GTP
increases specificity - polypeptide bonds
large subunit catalyzes
peptide bond with new AA
uses residual energy from 3
new tRNA in A site - translocation
A site -> P site
requires GTP
P site -> E site and expelled
Ribosome moves forward
next codon to A site
repeat
Termination
release factor signals disassembly, binds with stop codon, A site of ribosome
Steps of terminaiton
reaches stop codon on mRNA
release factor binds
cleaves polypeptide from tRNA
via hydrolysis using H2O
release polypeptide
through funnel on large subunit
ribosomal subunits dissociates
2 GTP required for breakdown
Protein folding and modification
begins folding as synthesized
post-translation modifications
AA chemically modified
AAs removed
polypeptide cleaved
subunits come together
Free ribosomes
proteins stay/functional in cytosol
Bound ribosomes
endomembrane proteins
those packaged for secretion
silent mutation
change has no affect
redundancy of codons
translation -> correct AAs
missense mutation
1 AA -> diff AA
similar AA -> no effect
diff. -> sickle cell
still codes for AA
nonsense mutation
change does not code for AA
translation terminated
polypeptide is shorter
usually non-functional
Frameshift mutations
insertion and deletion
immediate nonsense
noticeable missense
3 nucleotide deletion
Insertion and deletion
causes a frame shift
when not multiple of 3
often leads to nonsense
Immediate nonsense
mutation -> stop codon
noticeable missense
multiple incorrect AA’s
3 nucleotide deletion
one AA missing
Gene mutations
permanent change
DNA base sequences
autosomal trait
germ or somatic cells
will affect protein activity
added to 5’ end of pre-mRNA
G-Cap
added to 3’ end of pre-mRNA
poly A tail
How are anticodons reported
3’ to 5’
aminoacyl-tRNA
adds AA to complementary tRNA
Wobble
3rd nucleotide not rigid, if 3rd nucleotide changes AA doesn’t necessarily change
Initiation factors
bring mRNA, tRNA, and ribosomes together
P site
where initiator tRNA binds, gets polypeptide from A site
A site
empty at beginning, polypeptide binds with AA, moves next codon to P site (translocation)
E site
passed tRNA from P site and expels
Steps of elongation that require GTP
- new tRNA arrives and binds to A site
- translocation (A to P to E)
Step of elongation that uses GTP from translocation
- peptide bonds with new AA and new tRNA in A site
Release factor binds to
stop codon and cleaves polypeptide from tRNA
how do release factors cleave polypeptide from tRNA
hydrolysis
how many GTP does it take to dissociate ribosomal subunits
2
Polyribosomes
rapidly produce multiple polypeptides
