Gene Expression; from Gene to Protein Flashcards
1
Q
Gene Expression
A
he process by which DNA directs protein synthesis, includes two stages
2
Q
The two stages of Gene Expression
A
transcription and translation
3
Q
Central Dogma of Molecular Biology
A
describes the flow of information from DNA to mRNA to protein.
4
Q
What does the Central Dogma state?
A
It states that genes specify the sequence of mRNA which specifies the sequence of proteins
5
Q
RNA is the bridge between what?
A
Genes and the proteins that they code
6
Q
Transcription
A
The synthesis of RNA using information in DNA, producing mRNA.
7
Q
Translation
A
The synthesis of a polypeptide, using information in the mRNA, with ribosomes being the sites of translation
8
Q
Prokaryote Transcription and Translation
A
translation of mRNA can begin before transcription has finished. Transcription & translation are coupled in prokaryotes.
9
Q
Eukaryotic Transcription and Translation
A
the nuclear envelope separates transcription from translation;Transcription & translation are not coupled.
10
Q
Eukaryotic RNA transcripts are …
A
modified through RNA processing to yield the finished mRNA
11
Q
How many amino acids are there?
A
20
12
Q
How many nucleotide bases in DNA are there?
A
4
13
Q
What is a Triplet Codon
A
A series of non-overlapping, three-nucleotide words. The words of a gene are transcribed into complementary non-overlapping three-nucleotide words of mRNA
14
Q
After genes are transcribed into mRNA, what happens next?
A
These words are then translated into a chain of amino acids, forming a polypeptide
15
Q
What is a Template Strand?
A
During transcription, one of the two DNA strands, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript.
16
Q
Is the template strand always the same strand for a given gene?
A
Yes
17
Q
What is the process called from DNA to Pre-mRNA?
A
Transcription
18
Q
What is the process called from Pre-mRNA to mRNA?
A
RNA Processing
19
Q
What is the Process called from mRNA to Ribosome?
A
Translation
20
Q
What comes out of a Ribosome?
A
Polypeptide
21
Q
In a Bacterial Cell; What happens from DNA to mRNA?
A
Transcription
22
Q
In a Bacterial Cell; what happens from mRNA to Ribosome?
A
Translation
23
Q
What are codons?
A
mRNA base triplets
24
Q
During translation, the mRNA base triplets are read in what direction?
A
5’ –> 3’ Direction
25
What is the job of the codon?
To specify the amino acid to be placed at the corresponding position along a polypeptide
26
The genetic code is ___
Redundant ; more than one codon may specify a particular amino acid
27
Of the 64 triplets, how many codes are for amino acids?
61 Codes
28
Of the 64 triplets, how many codes are for "stop" signals to end translation
3 (UAA, UGA, UAG)
29
Of the 64 triplets, how many codes are TO START CODON?
1; AUG
30
Where is non-universal genetic code located?
Found in the Mitochondria and Protists
31
What are the three stages of transcription?
Initiation, Elongation, Termination
32
What is RNA Polymerase
RNA synthesis is catalyzed by this, which pries the DNA strands apart and joins together the RNA nucleotides.
33
What is a Promoter
The DNA sequence that RNA polymerase attaches to
34
What is a transcription unit?
The stretch of DNA that is transcribed
35
Does RNA Polymerase need a Primer??
No
36
How do Promoters start the process?
signal the transcriptional start point and usually extend several dozen nucleotide pairs upstream of the start point
37
What are Transcription Factors?
They mediate the binding of RNA polymerase and the initiation of transcription.
38
What is a Transcription Initiation Complex?
The completed assembly of transcription factors and RNA polymerase II bound to a promoter
39
What is a TATA box?
A promoter, that is crucial in forming the initiation complex in eukaryotes
40
As RNA polymerase move along the DNA, how many does it untwist?
10-20 bases at a time
41
Transcription progresses at a rate of..
40 nucleotides/sec in eukkaryotes
42
Which end are Nuceotides added to?
They are added to the 3' end
43
Termination of Transcription; Bacteria
the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification
44
Termination of Transcription; Ekaryotes
RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
45
When do enzymes in the eukaryotic nucleus modify pre-mrna?
Before the genetic messages are dispatched to the cytoplasm
46
During RNA processing, what is usually altered?
Both ends of the primary transcript
47
Usually, what sections are cut out and the remaining spliced together?
Introns are cut out, and exons are spliced together
48
Pre-mRNA molecule is modified with the 5' and 3' end recieving what?
The 5' end receives a modified nucleotide 5' cap (Guanine) and the 3' gets a poly-A tail
49
Why do both the 5' and 3' get modified?
They seem to facilitate the export of mRNA to the cytoplasm
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5′ end
50
What are Introns?
They are noncoding regions; where NA transcripts have long noncoding stretches of nucleotides that lie between coding regions
51
What are Exons?
They are eventually expressed, usually translated into amino acid sequences
52
What does RNA cutting & splicing do?
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
53
In some cases, what is RNA splicing carried out by?
Spliceosomes
54
What are spliceosomes
consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites.
55
What are Ribozymes?
are catalytic RNA molecules that function as enzymes & can splice RNA.
56
Property of RNA that enables it to function as an enzyme (1)
It can form a three-dimensional structure because of its ability to base-pair with itself
57
Property of RNA that enables it to function as an enzyme (2)
Some bases in RNA contain functional groupsthat may participate in catalysis
58
Property of RNA that enables it to function as an enzyme (3)
RNA may hydrogen-bond with other nucleicacid molecules
59
Importance of Introns?
Some introns contain sequences that may regulate gene expression
Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during ,splicing, also known as alternative RNA splicing
60
What are domains?
Proteins often have a modular architecture consisting of discrete regions
61
Why might exon shuffling happen?
As a result in the evolution of new proteins
62
Information and Translation
Genetic information flows from mRNA to protein through Translation
63
How does cell translate an mRNA message into a protein'?
With the help of transfer RNA (tRNA)
64
tRNAs transfer what?
Transfer amino acids to the growing polypeptide in a ribosome
65
tRNA carries___
one specific amino acid on one end
66
On the other end of a tRNA, there is...
an anticodon. The anticodon base-pairs with a complementary codon on mRNA
67
tRNA consists of a single RNA strand that is how long?
80 nucleotides long
68
What does a tRNA look like?
A cloverleaf
69
Translation requires how many steps?
Two
70
Translation Step 1
a correct match between a tRNA & an amino acid, done by the enzyme aminoacyl-tRNA synthetase
71
Translation Step 2
a correct match between the tRNA anticodon & an mRNA codon
72
What is a wobble?
Flexible pairing at the third base of a codon that allows some tRNAs to bind to more than one codon
73
Ribosomes facilitate specific coupling of
tRNA anticodons with mRNA codons in protein synthesis
74
Two ribosomal subunits are made of
ribosomal proteins (~ 80) and ribosomal RNAs (18S, 5S, 5.8S, 28S)
75
Ribosome has how many binding sites for tRNA?
Three
76
What are the three binding sites that a ribosome has for tRNA?
P, A, and E site
77
P Site
holds the tRNA that carries the growing polypeptide chain
78
A Site
holds the tRNA that carries the next amino acid to be added to the chain
79
E Site
is the exit site, where discharged tRNAs leave the ribosome
80
Three stages of Translation?
Initation, Elongation, Termination
81
Translation ; Initation brings together..
mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
82
What happens first in Initation in Translation?
a small ribosomal subunit binds with mRNA and a special initiator tRNA (met) Then the small subunit moves along the mRNA until it reaches the start codon (AUG)
83
Proteins called initation factors bring...
in the large subunit that completes the translation initiation complex
84
Translation; During Elongation..
amino acids are added oneby one to the C-terminus of the growing chain
85
Translation; Elongation; Each addition invovles proteins called
elongation factors and occurs in 3 steps: codon recognition, peptide bond formation, and translocation
86
When does energy expenditure occur in Elongation (Translation?
During Codon Recognition and Translocation
87
Translation proceeds along the mRNA in a
5' --> 3' direction
88
Termination; Translation
Occurs when a stop codon in the mRNA reaches the A site of the ribosome
89
(Termination; Translation) A site accepts..
A protein called a release factor
90
(Termination; Translation) Release factor causes..
the addition of a water molecule instead of an amino acid
91
(Termination; Translation) The release factor reaction
releases the polypeptide, and the translation assembly comes apart
92
IS translation suffcient to make a functional protein?
Often times no
93
Polypeptide chains are modified after..
translation or targeted to specific sites in the cell
94
Post-Translational Modification, During Synthesis, polypeptide chain begins to..
coil & fold spontaneously to form a protein with a specific 3-D/4-D structure
95
Post-Translational Modifications may be required before...
the protein can begin doing its particular job in the cell
96
What two populations of ribosomes are evident in cells?
Free Ribosomes (Cytosol) and Bound Ribosomes (Attached to ER)
97
Free ribosomes mostly..
synthesize proteins that function in the cytosol
98
Bound ribosomes make..
proteins of the endomembrane system and proteins that are secreted from the cell
99
Ribosomes are identical and..
can switch from free to bound
100
Where does polypeptide synthesis always begin?
In the cytosol
101
Synthesis finishes in ___ unless _______
the cytosol unless the polypeptide signals the ribosome to attach to the ER
102
Polypeptides are destined for
the ER or for secretion are marked by a signal peptide
103
A Signal-Recognition Particle (SRP)
binds to the signal peptide
104
SRP brings...
the signal peptide and its ribosome to the ER
105
Polypeptide Formation (1)
Polypeptide synthesis begins
106
Polypeptide Formation (2)
SRP bings to signal peptide
107
Polypeptide Formation (3)
SRP binds to receptor protein
108
Polypeptide Formation (4)
SRP detaches and polypeptide synthesis resumes
109
Polypeptide Formation (5)
Signal-cleaving enzyme cuts off signal peptide
110
Polypeptide Formation (6)
Completed polypeptide folds into final conformation
111
How is a polyribosome (or polysome) formed?
Multiple ribosomes can translate a singla mRNA simultaneously to form this
112
Polyribosomes enable a cell to..
make many copies of a polypeptide very quickly
113
A bacterial cell ensures astreamlined process by...
coupling transcription and translation
114
What are mutations?
changes in the genetic material of a cell or virus
115
What are point mutations?
chemical changes in just 1 base pair of a gene
116
Change in a single nucleotide in a DNA template strand can lead to..
PRoduction of an abnormal protein (sickle cell anemia)
117
Two categories of Point Mutations
Nucleotide-Pair Substitutions
| One or more nucleotide-pair insertions or deletions
118
Nucleotide-Pair Substitution
replaces one nucleotide and its partner with another pair of nucleotides
119
Silent Mutations
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
120
Missense Mutations
still code for an amino acid, but not the correct amino acid
121
Nonsense Mutations
change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
122
What are insertions and deletions?
Are additions or losses of nucleotide pairs in a gene
123
Frameshift Mutation
Result after the Insertion or deletion of nucleotides may alter the reading frame,
124
What are Mutagens?
Physical or chemical agents that can cause mutations
125
Structural Gene
a region of DNA that can be expressed to produce a final functional product (part of a physical structure within cell) that is either a polypeptide or an RNA molecule (rRNA, tRNA).
126
Regulatory Gene
regulates the expression of one or more structural genes by regulating the production of a protein which regulates the rate of transcription.
