Chapter 13 The Genetic Code and Transcription Flashcards
1
Q
The genetic code is…
A
written
2
Q
mRNA molecules act as …
A
letters
They have complementary bases
3
Q
Triplet codons…
A
specify one amino acid (mRNA)
4
Q
Unambiguous
A
triplet= 1 amino acid
5
Q
Degenerate
A
amino acid specified by more than 1 triplet
“start” and “stop” signals
6
Q
The genetic code is…
A
unambiguous degenerate one start and three stop nonoverlapping nearly universal
7
Q
Jacob and Monad-
Early studies establishing basic operational patterns of the genetic code
A
1961- hypothesized mRNA
8
Q
What is mRNA?
A
intermediate in transferring genetic information
9
Q
How can 4 nucleotides encode 20 amino acids?
A
triplet code
10
Q
Triplet nature of the code…
A
64 codons specify 20 amino acids
11
Q
Reading frame…
A
sequence of nucleotides encoding a polypeptide
12
Q
Crick and colleagues:
A
acridine dye- induce DNA mutations into a T4 phage
13
Q
Frameshift mutations…
A
change reading frame
14
Q
Brenner and colleagues - nonoverlapping code
A
-genetic code reads 3 nucleotides at a time in a continuous, linear manner
15
Q
During translation, the genetic code is…
A
nonoverlapping
16
Q
Nirenberg and Matthei
A
characterize coding sequences
17
Q
Nirenberg and Matthei utilized…
A
- in vitro protein synthesizing system
- polynucleotide phosphorylase- enzyme- artificial synthesis of RNA templates- does not require DNA template
18
Q
RNA homopolymer
A
one type of mRNA
used UUUU…., AAAA…., CCCC…., or GGG to determine which amino acids were incorporated into the proteins
19
Q
Attached _____ to a different amino acid in each experiment
A
14C
20
Q
GGG is a …
A
non funcional template
21
Q
In mixed copolymers the proportion known, could predict…
A
the frequency of possible triplets
22
Q
mixed copolymers predict…
A
composition of triplets
23
Q
Triplet binding assay consists of…
Nirenberg and Leder
A
- Ribosomes (bind to single codon of 3 nucleotides)
- codon
- complementary amino acid- charged tRNA (radioactive) termed anticodon
24
Q
Triplet binding assay…
Incubate what???
A
- radioactive tRNA
- RNA triplet
- nitrocellulose filter with ribosomes
25
If the paper is NOT radioactive???
incorrect AA was tested; repeat experiment
26
If the paper is radioactive???
tRNA bound to RNA triplet associated with ribosome
| A specific codon assignment is made
27
What are repeating copolymers?
1. chemically synthesized long RNA's
2. short repeating sequences enzymatically joined short sequences together, which made long RNA's
3. used for in vitro translation to determine more codon assignments
28
Repeating copolymers are dependent on...
initiation point
29
Coding Dictionary is ___________ meaning many amino acids are specified by more than one codon
degenerate
30
How many termination signals are there?
3
| UAA UGA UAG
31
how many triplet codons are there for amino acids
61
32
What is the Wobble hypothesis
The first 2 ribonucleotides of triplet codes are more critical than the 3rd because the third position is less spatially constrained.
H bonding is more relaxed at the 3rd position
anticodon pair with more than one mRNA triplet
33
Ordered nature of code
similar AA often share middle bases in the coding triplets
34
In translation initiation, the initial __ is incorporated
AA
35
what is the initial AA?
modified form of methionine- N- formylmethionine (fmet)
36
What is the codon?
AUG
37
internally in mRNA, __________ methionine is inserted
unformylated
38
What are termination codons?
UAG UAA UGA
39
The termination codons are not recognized by ____ molecule
tRNA
40
What does termination end?
translation
41
what is a nonsense mutation?
mutation to stop codon internally in a gene may lead to early termination
This causes a partial peptide
42
codon UGA normally specifies termination, but in mtDNA, UGA codon encodes_________ in yeast and humans
tryptophan
43
codon UAU normally specifies isoleucine, but in human mitochondria it encodes internal insertion of ______________
methionine
44
Different initiation points creates __________ genes
overlapping
45
ORF (open reading frame(overlapping genes))???
DNA sequence produces RNA with start and stop
| Series of triplet codons specify amino acids to make polypeptides
46
In some viruses, initiation at different AUG positions out of frame with another leads to distinct____________________
polypeptides
Ex: X174- expected 1795 aa; 9 proteins
(where there would have only been 3, there are now 7)
47
Transcription Synthesis; RNA on a DNA template
| 4 things...
1. Where is DNA? Where is protein synthesis?
2. List commonalities between DNA and RNA.
3. After RNA synthesis, it migrates to cytoplasm
4. #RNA is generally proportional to # protein in a cell
48
RNA serves as an _______________ molecule between DNA and proteins
intermediate
49
RNA is synthesized on a ___ template
DNA
50
RNA polymerase directs RNA synthesis using a ___ template
DNA
51
RNA polymerase directs RNA synthesis with/ without a primer???
without
52
RNA polymerase uses __________________ instead of deoxyribonucleotides
ribonucleotides
53
Reaction for RNA synthesis can be expressed as...
nNTP+NTP-----DNA-----(NMP)n+n(PPi)
54
What are the e coli subunits for RNA polymerase?
alpha, beta, beta prime, and sigma
55
Which e coli subunits are the active sites for transcription?
beta and beta prime
56
what is the sigma factor?
regulatory function in the initiation of RNA transcription
57
In transcription, RNA polymerase binds to a __________________
promotor
58
Which subunit is responsible for promotor recognition?
sigma
59
Where does transcription begin?
transcription start site
60
The DNA is __________ to make the template strand accessible
unwound
61
Promotors have 2 consensus sequences. What are they?
TTGACA
| TATAAT
62
Where are the 2 consensus sequences positioned?
-35 and -10 to the initiation site
63
Mutations? Increase or decrease?
decrease
64
cis- acting elements are... _________________ to start site
adjacent
65
In transcription chain elongation _-_ nucleotides are synthesized, and sigma subunit_______________
8-9
| dissociates
66
____________ proceeds with the core enzyme
elongation
67
continues to transcribe until ______________
termination
68
In transcription termination, RNA hairpin formation is held by what bonds?
hydrogen
69
Can depend on the rho (p) termination factor... what is this?
large hexameric protein that interacts with RNA
70
Transcribed RNA is ______________. It is complementary to DNA, yet will contain _ instead of T.
released
| U
71
Eukaryotic vs. Prokaryotic transcription:
| Eukaryotes: occurs in the _________ and is not coupled to translation (move to cytoplasm)
nucleus
72
Eukaryotic vs. prokaryotic transcription:
| chromatin _______________
remodeling
73
eukaryotic vs. prokaryotic transcription:
| involves __________
enhancers
74
eukaryotic vs. prokaryotic transcription:
| mRNAs require processing 5' _______ and 3' ________
cap
| tail
75
RNA polymerase in eukaryotes:
Form: 1
Product: _______
Location: nucleolus
rRNA
76
RNA polymerase in eukaryotes:
Form: 2
Product: ____, _______
Location: nucleoplasm
mRNA, snRNA
77
RNA polymerase in eukaryotes:
Form: 3
Product: _______,_____________
Location: nucleoplasm
5S rRNA, tRNA
78
RNA polymerase 2 promoters contain:
| 2 things
- a core promoter element where protein binds and transcription begins
- promoter and enhancer elements that determine rate of transcription
79
What is a TATA box? (Goldberg- Hogness)
- core promoter element
- (-30) TATA A/T AAR (A or T in 5th position)
- TATA binding protein (TBP)
- start site of transcription
80
What is the CAAT box in RNA polymerase 2?
upstream and part of eukaryotic promoter
81
enhancers and silencers are found ____, ________, or ____________ of a gene
upstream
within
downstream
82
enhancers ________ transcription levels, silencers ________ them
increase
| decrease
83
enhancers and silencers _______ transcription from a distance
modulate
84
enhancers and silencers act to ________ or ________ transcription in response to cell's requirement for ____ product
increase
decrease
gene
85
Transcription factors facilitate _____ binding and __________ of transcription
RNAP 2
| initiation
86
General transcription factors are ________ for all RNAP 2 mediated transcription
required
87
Transcription activators and repressors...
influence efficiency or rate of RNAP2 transcription initiation
88
RNA PROCESSING:
| 5' cap protects from _________, helps transport across nuclear membrane into _________.
nucleases
| cytoplasm
89
RNA PROCESSING
| The RNA tail is the _________ cap. The 3' region is _______ in UAUCAA region, then polyadenylation occurs
following
| cleaved
90
What are intervening sequences?
introns and exons
91
What is an intron?
an intervening sequence where regions of initial RNA transcript is not expressed in amino acid sequence of protein
DNA sequences are not represented in final mRNA product
92
What is an exon?
an intervening sequence where the sequence in retained and expressed.
93
What is a heteroduplex?
introns present in DNA but not mRNA that loop out
94
introns are removed by ________
splicing
95
exons are joined together and called ______ mRNA
mature
96
SPLICEOSOME
| splices out pre- ____ introns
mRNA
97
What is essential for the spliceosome?
small nuclear ribonucleoproteins (snRNP's)
98
what is the donor sequence?
GU
99
what is the acceptor sequence?
AG
100
The "loop" is called a ______ structure
lariat
101
There are ___ transesterfication reactions
2
102
At the end... the exons are _______
ligated
103
What is substitution editing?
identities of individual nucleotide bases are altered; prevalent in mitochiondria and chloroplasts RNA derived in plants
104
What is insertion/ deletion editing?
nucleotides are added/ deleted from total number of bases
| prevalent in mitochondrial and chloroplast RNA's
