MCAT BIO CH. 4 PART 2 Flashcards
1
Q
How is sickle-cell anemia caused?
A
By a mutation in the gene for hemoglobin (Hb)
2
Q
What does the mutation of sickle-cell anemia cause?
A
Allows deoxygenated Hb to dimeric and form long chais which distorts the red blood cell shape
3
Q
What happens to the deformed cells in sickle cell anemia?
A
Cannot function, destroyed prematurely; leads to anemia
4
Q
Why is having sickle cell anemia positive?
A
This is common in area where malaria is prevalent; important benefit
5
Q
What is the purpose of the 32 bp deletion in gene called CCR5?
A
Deletion confers HIV resistance to homozygotes and delays AIDS onset in heterozygotes
6
Q
What is a historical reason of the 32 bp deletion in gene CCR5?
A
May have conferred resistance to diseases in the past
7
Q
What are two types of disease causing mutations?
A
- Inborn errors of metabolism
2. Cancer
8
Q
What do inborn errors of metabolism includes?
A
Involve disorders of metabolism
9
Q
What are most inborn errors of metabolism due to?
A
Single mutation in a single gene that codes for some sort of metabolic enzyme
10
Q
What are the symptoms of inborn errors of metabolism caused by?
A
- Build-up of toxic compound
2. Deficiency of an essential molecule unable to be synthesized
11
Q
Tumor mutations in cancer are often in…?
A
Oncogenes and tumor suppressors
12
Q
What is an oncogene?
A
A gene that can cause cancer when it is mutated or expressed at high levels
13
Q
What are tumor suppressors?
A
Their deletion can cause cancer
14
Q
What is direct reversal?
A
A few DNA damage can be reversed
15
Q
What is photo reactivation?
A
Enzymes that repair UV-induced pyrimidine photodimers using visible light
16
Q
What is the most common type of mechanism repair in humans based on direct reversal?
A
Nucleotide excision repair
17
Q
If lead unprepared, what can pyrimidine dimers cause?
A
May lead to melanoma, a type of very dangerous and malignant skin tumor
18
Q
What is homology-dependent repair pathways?
A
Using the undamaged complementary information on the other strand to repair the damaged strand
19
Q
What can homology-dependent repairs be divided in?
A
- Excision repair
2. Post-replication repair
20
Q
What does excision repair involve?
A
Involves removing defective bases nucleotides and replicating them
21
Q
What does the mismatch repair pathway target?
A
Targets mismatched bps that were not repaired by DNA poly proofreading during replication
22
Q
What do bacterias use when needing to know which mispaired base should be fixed?
A
Genome methylation to help differentiate between the old DNA template stranding the newly synthesized daughter strand
23
Q
What is methylated and what isn’t, based on genome methylation in bacteria?
A
Parental bases have methylates bases and new daughter strand doesn’t
24
Q
What recognization pattern do prokaryotes and eukaryotes use?
A
- Newly synthesized strand is recognized by the free 3’-terminus on the leading strand
- Gaps b/n Okazaki segments
25
What are the two pathways to help with double-strand repair break?
1. Homologous recombination
| 2. Nonhomologous end-joining
26
If DSB is done incorrectly, what can occur?
Deletions or translocations
27
What is homologous recombination?
One sister chromatid can help repair a DSB in the other
28
Why can one sister chromatid help repair the other based on DSB?
Because after DNA replication, the genome contains identical sister chromatids
29
On which end is the DSB trimmed?
5' end to generate single stranded DNA
30
How is the DSB trimmed? (By the help of which enzymes)
1. Nucleases
| 2. Helicases
31
What do the nucleases do?
Break the phosphodiester bonds
32
What do the help of multiple proteins aid with?
Bind these ends and start a search of the genome to find sister chromatid region that is complementary to the single-strand DNA
33
What enzymes help to build a corrected DNA strand?
DNA poly and ligase
34
What is the purpose of the joint molecule?
Damaged and undamaged sister chromatids crossover
35
When is non-homologous end joining used?
When there are no backup chromosome to use
36
What happens during non-homologous end joining?
1. Broken ends are stabilized
| 2. DNA ligase connects the fragments
37
What can be the outcome of non-homogolous end joining?
Base pairs being lost or chromosomes being connected in an abnormal way
38
What is another word for gene expression?
Transcription
39
What is gene expression?
Information contained in genes being to have effects in the cell
40
What are the three unique facts about RNA?
1. Single-stranded
2. Uracil
3. Ribose
41
Which RNA is the only type of coding RNA?
mRNA
42
Which region of the mRNA is not translated into protein and what is it called?
5' untranslated region or 5' UTR
43
What is the open reading frame?
Region that codes for a protein
44
The 3' end of the mRNA is translated into the protein. T/F
False: after stop codon; is not translated
45
If the 3' end of the mRNA is not translated into the protein, what its purpose?
Contains regulatory regions that influence post-transcriptional gene expression
46
What does monocistronic mean?
Each piece of mRNA encodes only one polypeptide
47
What does polycistronic mean?
mRNA codes for more than one polypeptide
48
Which type of mRNA is monocistronic?
Eukaryotic mRNA
49
Which type of mRNA is polycistronic?
Prokaryotic mRNA
50
In prokaryotic mRNAs, what can be found between ORFs?
Translation termination and initiation sequences
51
What is the name of the first RNA transcribed from DNA and why?
Heterogeneous nuclear RNA (hnRNA) - precursor to mRNA
52
What events are required to mature hnRNA?
Addition of cap and tail, splicing introns
53
hnRNA is only found in......? Why?
Eukaryotes; because prokaryotes do not process their primary transcripts
54
What is a non-coding RNA (ncRNA)?
RNA not translated into a protein
55
What are the two major types of ncRNAs?
tRNA and rRNA (transfer and ribosomal)
56
What is tRNA?
Responsible for translating genetic code
57
What does tRNA do?
Carriers amino acid from cytoplasm to the ribosome to add to the growing protein
58
How many types of rRNAs do humans have?
4 types: 18S, 5.8S, 28S and 5S
59
What is the purpose of rRNA?
Provides catalytic function of the ribosome
60
What are ribozymes?
Catalytic RNAs
61
Why are catalytic RNAs called ribozymes?
Can perform specific biochemical reactions similar to protein enzymes
62
What are four rare types of ncRNAs?
1. snRNA
2. miRNA and siRNA
3. piRNA
4. Long ncRNAs
63
What are snRNAs?
Small nuclear RNAs that associate with proteins to form snRNP complexes in the spliceosome
64
What does snRNP stand for?
Small unclear ribonucleic particles
65
What does miRNA stand for? What does siRNA stand for?
MicroRNA and small interfering RNA
66
What do miRNA and siRNA function in?
Function in RNA interference (RNAi)
67
What is RNAi
A form of postranscriptional regulation of gene expression
68
What can both miRNA and siRNA do?
Bind to specific mRNA molecules to increase or decrease translation
69
What does piRNAs stand for?
PIWI-interacting RNAs
70
How is the structure piRNAs?
Single stranded and short (typically b/n 23 to 21 nucleotides in length)
71
What is the function of piRNAs?
Work with a class of regulatory proteins called PIWI proteins to prevent transposons from mobilizing
72
What's the structure of long ncRNAs?
Longer than 200 nucleotides
73
What do the long ncRNAs help with?
Control basal transcription level in a cell
74
How do Long ncRNAs help with controlling basal transcription levels?
By regulating initiation complex assembly on promoters
75
What can Long ncRNAs control?
Control splicing and translation, imprinting and X-chromosome inactivate
76
What do both transcription and replication involve?
template-driven polymerization
77
The RNA transcript produced in transcription is.... to DNA?
Complementary
78
What is the driving force for both replication and transcription?
Removal and subsequent hydrolysis of pyrophosphate from each nucleotide added to the chain (existing chain is nucleophile)
79
Do the polymerase enzymes in both replication and transcription require a primer?
No, RNA pol does not require a primer
80
What does RNA poly lack?
exonuclease activity
81
Which process has a lower fidelity process? Transcription or replication....
Transcription
82
What is the name of the start site where transcription begins? What is the name of the start site where replication begins?
1. Start site
| 2. Origin
83
What is the promotor based on the transcription process?
The sequence of nucleotides on a chromosome that activates RNA polymerase to begin the process
84
What is the name of the strand which is actually being transcribed?
Template, non-coding, transcribed antisense strand
85
What is the DNA strand called, the one not being used for transcription?
Coding or sense strand
86
What does downstream mean?
Towards the 3' end of the coding strand and transcript
87
What does upstream mean?
Towards the 5' end of the coding strand, beyond the 5; end of the transcript
88
Upstream nucleotide sequences are referred to using ______? Downstream nucleotide sequences are referred to using _______?
1. Negative
| 2. Positive
89
The first nucleotide on the template strand which is actually transcribed is called.....
Start site
90
The first nucleotide on the coding strand is given....
Number +1
91
What is the structure of prokaryotic RNA poly?
Large enzyme complex consisting of five subunits
92
What are the five subunits of the prokaryotic RNA poly?
Two alpha subunits, beta subunit, a beta' subunit and an omega subunits
93
What are the prokaryotic RNA poly subunits referred to and what are they important for?
Core enzymes; responsive for rapid elongation of the transcript
94
The core enzyme on its own can start the transcription process. T/F
False: Additional subunit termed the sigma factor is required to form the holoenzyme
95
What are the three stages of transcription? (prokaryotes)
1. Initial
2 Elongation
3. termination
96
When does initiation of transcription occur? (in prokaryotes)
1. RNA polymerase holoenzyme binds to a promoter
97
What type of sequences does the bacterial promoter contain?
Two primary sequences: the Pribnow box at -10 and the -35 sequence
98
What do holoenzyme to once they arrive near the chromosome?
Scan along the chromosome like a train on railroad track
99
What happens when the holoenzyme recognizes a promoter?
Stops, forms a closed complex
100
After the holoenzyme forms a closed complex to the promoter, which enzyme must act next?
RNA polymerase: must unbind portion of DNA double helix before it can begin to synthesize RNA
101
What is the open complex?
RNA poly bound to the promoter with a single stranded DNA
102
How does the sigma factor help for the polymerase to find promoters?
1. Help RNA poly recognize promoters
| 2. Decrease nonspecific affinity of holoenzyme for DNA
103
When is the sigma factor no longer necessary and what does it do?
When the open complex and phosphodiester bonds have been formed; leaves the RNA poly complex
104
How does the core enzyme elongate the RNA chain?
Processively with one polymerase complex synthesizing entire RNA molecule
105
What is the transcription bubble?
Region of the DNA double helix unwound to allow polymerase to access the complementary DNA template
106
What happens when the termination signal is detected?
With sometimes the help of rho, RNA poly falls off, RNA released and transcription bubble closes
107
What are the four major differences in eukaryotic vs prokaryotic transcription?
1. Location
2. RNa polymerases
3. Primary transcripts
4. Regulation of transcription
108
Based on location, what does eukaryotic mean? What does prokaryotic mean?
Eukaryotic: True-kernelled
Prokaryotic: Before-the-kernel
109
What is the karyon (kernel)?
The nucleus
110
Based on prokaryotic meaning before-the-kernel, what does that mean about its transcription?
No nucleus means transcription occurs free in the cytoplasm
111
Because the processes for prokaryotic cells occur in the same compartment, it means that transcription and translation can occur....?
Simultaneously
112
Because the processes for eukaryotic cells occur in different compartment, it means that translation and transcription can....
NOT occur simultaneously
113
What is the different in transcription b/n prokaryotic and eukaryotic cells based on their RNA product after transcription?
Prokaryotes: mRNA can be translated right away
Eukaryotes: hnRNA made by RNA pol II needs to be modified before translation
114
What is the most important example of a modification that needs to occur on the pre-mRNA (hnRNA) before translation in eukaryotic organisms?
Splicing
115
What are introns?
Non-coding sequences intervening between the segments that actually code for proteins
116
Sometimes these introns can contain what?
Contain enhancers or other regulatory sequences
117
What is the average size of an intron?
2000 nucleotides
118
What are exons?
Protein-coding regions of the RNA
119
What is splicing?
Removing introns and joining the exons
120
What is splicing mediated by?
Spliceosome
121
What is the structural composition of a spliceosome?
Complex containing 100 proteins and 5 small nuclear RNA molecules (snRNA)
122
How are snRNPs formed?
Half the proteins from the spliceosome stably bind snRNAs and these form three small nuclear ribonucleic particles (snRNPs)
123
What are snRNPs made up of?
Proteins and snRNAs
124
The spicleosome is preassembled in our nucleus. T/F
Falsee: it assembles around each intron that needs to be removed
125
What do the snRNPs do to start the catalytic activity of the splicing reaction?
snRNPs recognize and hydrogen bond to conserved nucleotides in the intron
126
What is the conserved nucleotide sequence in the intron?
GU at the 5', AG at the 3' end and adenine 15-45 bases upstream of the 3' splice site
127
How many reactions are catalyzed by the spliceosome?
Two
128
What is the first reaction catalyzed by the spliceosome?
1. Attach one end of the intron to the conserved adenine causing the intron to form a loop structure
129
What is the second reaction catalyzed by the spliceosome?
2. Joining he two exons and releasing the loop
130
What are the five conserved nucleotides necessary for the splicing reaction?
GU, A and AG
131
What is alternative splicing?
Different options or patterns of splicing
132
What is a way of increasing the complexity gene expression?
Shuffling exons
133
After the splicing reaction, how is eukaryotic hnRNA modified to be able to go through translation?
5' cap and 3' poly-A tail
134
What is the 5' cap?
Methylated guanine nucleotide stuck on 5' end
135
What is the poly-A-tail?
String of several hundred adenine nucleotides
136
Why are the 5' cap and 3' poly-A tail important for the hnRNA?
Preventing digestion of the mRNA by exonucleases that are free in the cell
137
In prokaryotes, all RNA is made by the....?
α2ββ'σ RNA polymerase complex
138
What is α2ββ'σ RNA polymerase complex again?
Core enzyme responsible for rapid elongation of transcript
139
In eukaryotes, what are the different types or RNA polymerases?
1. RNA poly I
2. RNA poly II
3. RNA poly III
140
What is the purpose of RNA poly I in eukaryotes?
Transcribes most rRNA
141
What is the purpose of RNA poly II in eukaryotes?
Transcribes hnRNA, most snRNA and some miRNA
142
What is the purpose of RNA poly III in eukaryotes?
Transcribes tRNA, long ncRNA, siRNA, miRNA and some rRNAs
143
There are many DNA polymerases for which type of cell?
Prokaryotes
144
What is translation?
Synthesis of polypeptides according to the amino acid sequence from by the sequence of codons in mRNA
145
What does the mRNA molecule do during translation?
Attaches to a ribosome at a specific codon and the appropriate amino acid is delivered by a tRNA molecule
146
What happens when the mRNA attaches to the ribosome?
The second amino acid is delivered by another tRNA
147
What does the ribosome do when the two amino acids are added by the tRNA?
The ribosome binds the two amino acids together, creating a dipeptide
148
What is tRNA composed of?
A single transcript produced by RNA poly III
149
What is the tertiary structure of every tRNA molecule?
tRNAs have a stem-and-loop structure
150
What is the tRNA stem-and-loop structure stabilized by?
Stabilized by hydrogen bonds b/tn bases on neighboring segments of the RNA chain
151
What is the anticodon?
A sequence of 3 ribonucleotides which is complementary to the mRNA codon the tRNA translates
152
What is a key step in translation?
Specific base pairing b/n the tRNA anticodon and the mRNA codon
153
What is the amino acid acceptor site based on tRNA?
Where the amino acid is attached to the tRNA
154
Since there is a tRNA for each codon.....
Each tRNA is specific for one amino acid while each amino acid may have several tRNAs
155
How would a tRNA for valine be written?
tRNA subscript val
156
When the amino acid is attached, the tRNA is written in what way?
Val-tRNA subscript Val
157
What type of bases do tRNA molecules contain?
Contain nitrogenous bases in many positions that have been covalently modified
158
Base methylation is particular common in what?
tRNA molecules
159
What are specific examples of nitrogenous bases contained in tRNA molecules?
1. Inosine (derived from adenine)
2. Pseudorine (derived from uracil)
3. Lysidine (derived from cytosine)
160
What does inosine play a role in?
Wobble base pairing
161
How many tRNAs do most organisms have and what does that mean?
45 types of tRNAs; some anticodon must pair with more than one codon
162
What is the Wobble Hypothesis?
The first two codon-anticodon pairs obey normal base pairing rules but the third position is more flexible
163
What are the three 5' base in anticodon (tRNA) that can wobble?
1. G
2. U
3. I
164
What can G pair with, if its apart of the 5' base in anticodon (tRNA)?
C or U (wobble base)
165
What can U pair with, if its apart of the 5' base in anticodon (tRNA)?
A or G (wobble base)
166
What can G pair with, if its apart of the 5' base in anticodon (tRNA)?
A, U or C (all wobble bases)
167
What are the most common wobble base pairs?
1. Guanine-uracil
2. Inosine-uracil
3. Inosine-adenine
4. Inosine-cytosine
168
The thermodynamics stabilities are greater for the normal watson-crick base pair rather than the wobble base pair. T/F
False: have similar thermodynamics stabilities
169
How is the thermodynamics and kinetic of peptide bond formation?
Unfavourable and slow kinetics
170
Because the peptide bond formation is unfavorable and slow, what is used to power the process?
Coupling
171
What is used to energize the peptide bond formation in amino acid activation?
Two high-energy phosphate bonds are hydrolyzed to provide the energy to attach an amino acid to its tRNA molecule
172
What is tRNA loading or amino acid?
Two high-energy phosphate bonds are hydrolyzed to provide the energy to attach an amino acid to its tRNA molecule
173
Why is tRNA loading useful?
Breaking the aminoacyl-tRNA bond will drive peptide bond formation forwards
174
What are the three steps to amino acid activation?
1. aminoacyl AMP formation
2. Orthophosphates
3. Destruction of aminoacyl-AMP
175
What is the first step, AMP attachment, of the amino acid activation?
An amino acid is attached to AMP to form aminoacyl AMP.
176
What's the nucleophile and the leaving group in the formation of aminoacyl AMP?
Nucleophile: Acidic oxygen of the AA
| Leaving group: PPi
177
What is the second step, Orthophosphates, of the amino acid activation?
The pyrophosphate leaving group is hydrolyzed to 2 orthophosphates
178
How is the thermodynamics of the hydrolization of 2 orthophosphates?
Highly favorable ΔG <<< 0
179
What is the third step, Destruction of aminoacyl-AMP, of the amino acid activation?
tRNA loading is driven forward by the destruction of the highly-energy aminoacyl-AMP bond created in Step 1
180
What does amino acid activation requires in energy? How do we know that?
2 ATP equivalents; it uses two high-energy bonds
181
What is an ATP equivalent?
A single high-energy phosphate bond
182
How can you get 2 ATP equivalents?
1. Hydrolyzing 2 ATP to 2 ADP + 2 Pi
| 2. Hydrolyzing 1 ATP to AMP + 2 Pi
183
What happens after step 3 of the amino acid activation?
Bond between amino acid and the tRNA molecule will be broken
184
What does the hydrolysis of the bond b/n AA and the tRNA molecule cause?
Powers the peptide bond formation
185
How does the peptide bond occur, based on nucleophiles present?
The nitrogen of another AA will nucleophilically attack carbon carbon of this amino acid and tRNA will be the leaving group
186
Which enzyme is used to confirm the attachment of the appropriate amino acid to each tRNA molecule accomplished?
Aminoacyl-tRNA synthétase enzymes
187
How do Aminoacyl-tRNA synthetase enzymes knows which AA to choose? (It is specific....?)
Specific to each AA and there is at least one aminoacyl-tRNA synthétase for every AA
188
How does the Aminoacyl-tRNA synthetase enzymes recognize the tRNA and the AA?
Based on their 3D structures
189
How is the error rate of Aminoacyl-tRNA synthetase enzymes?
Low error rate
190
What is the two most important functions of the amino acid activation?
1. Specific and accurate AA delivery
| 2. Thermodynamic activation of amino acid
191
What is the ribosome composed of?
Many polypeptide and tRNA chains
192
In the ribosomes, how are many polypeptides and tRNA chains held together?
Massive quaternary structures
193
What is the unit of measurements for ribosome?
Svedberg (S)
194
What type of rate is the Svedberg rate?
A sedimentation rate; how quickly something will sink in a gradient during centrifugation
195
The Svedberg rate is additive. T/F
False: it is not additive
196
The prokaryotic ribosome sediments at a rate of...? What is it referred to?
70S ; 70S ribosome
197
What is the 70S ribosome composed of in prokaryotes?
A 30S small subunit and a 50S large subunit
198
What is the small 30S subunit ribosome made of in prokaryotes?
16s RNA and 21 peptides
199
What is the large 50S subunit ribosome made of in prokaryotes?
2 rRNAs (23Sand 5S) and 31 peptides
200
How does the prokaryotic ribosome and eukaryotic ribosome differ?
Eukaryotic ribosomes have an 80s ribosome, prokaryotes have 70S
201
What is the 80S ribosome in eukaryotes composed of?
Large 60S subunit and a small 40S subunit
202
What is the large 60S subunit ribosome made of in eukaryotes?
Three rRNA molecules and 46 peptides
203
What are the sediment rates of the three rRNA molecules in the 60S large ribosome subunit in eukaryotes?
5S, 5.8S and 28S
204
What is the small 40S subunit ribosome made of in eukaryotes?
33 peptides and 1 rRNA 9(18S)
205
Which rRNAs have ribozyme function in eukaryotes and prokaryotes?
23S rRNA in proka. and 28S rRNA euka.
206
What is the ribozyme function of the 23S rRNA and 28 s rRNA?
Link amino acids during protein synthesis via peptidyl transferase activity
207
The ribozymic activity of the ribosome is found in ......
The large subunit of both prokaryotic and eukaryotes ribosomes
208
What are the three special binding sites of the complete ribosome?
1. A site
2. P site
3. E site
209
What is the A site? What is its purpose?
1. aminoacyl-tRNA site
| 2. Where each new tRNA delivers its AA
210
What is the P site? What is its purpose?
1. Peptidyl-tRNA
| 2. Where the growing polypeptide chain, still attached to. tRNA
211
What is the E site? What is its purpose?
1. exit-tRNA site
| 2. Where a now-empty tRNA sits prior to its release
212
What is polyribosome? In which type of cells are they used during translation?
1. Several ribosomes
| 2. Prokaryotes: many ribosomes attach and begin translating mRNA while its being made
213
Where are polyribosomes found? (Which type of cells)
Prokaryotes and eukaryotes
214
What is an important fact about prokaryotes mRNA?
Polycistronic
215
Because prokaryotes have polycistronic mRNAs.....?
Their ribosomes can start translation in the middle of the chain
216
Where are termination and initiation sequences found, based on the prokaryote mRNAs?
Between each ORF
217
What is the Shine-Dalgarno sequence?
The "promoter" for prokaryotic translation called ribosome binding site
218
Where is Shine-Dalgarno located?
-10 (ten ribonucleotides upstream or on the 5' side of the start codon)
219
What is the Shine-Dalgarno complementary to? What does that aid?
1. Complementary to a pyrimidine-rich region
| 2. Helps position the initiation machinery on the transcript
220
What are the stages of translation in prokaryotic cells?
Initiation, elongation, termination
221
What is the first step in the initiation for prokaryotic cells translation?
Small 30S binding two initiation proteins called IF1 and IF3
222
What complex ends to the mRNA, based on the initiation step?
The Small 30S subunit and IF1, IF3 proteins
223
What is the second step in initiation for prokaryotic cells? (What happens after the 30S, IF1 and IF3)?
The first aminoacyl-tRNA joins with third initiation factor IF2
224
What is the IF2 bound to?
A GTP
225
What is the third step in initiation for prokaryotic cells? (What happens after aminoactyl-tRNA, GTP and IF2)?
50S subunit completes the complex
226
What is the 50S binding at the end powered by, based on the prokaryotic cells translation?
Powered by the hydrolysis of one GTP molecule
227
What is the fMet-tRNA?
The first aminoacyl-tRNA, the initiator tRNA
228
What does the fMet in fMet-tRNA stands for?
fMet stands for formylmethionine
229
What is formylmethionine?
Modified methionine used as the first amino acid in all prokaryotic proteins
230
What happens when fMET is found by our immune system?
They release cytotoxins because its a sign that bacteria are busily translating
231
Where does the initiator tRNA sit?
In the P site the 70S ribosome, hydrogen-bonded with the start codon
232
Where is the start codon of the prokaryotic cell translation?
initiator tRNA hydrogen bonded with the start codon
233
Before elongation, what happens to the initiation factors?
Dissociate from the complex
234
How many steps in the elongation cycle for prokaryotic translation?
Three step cycle
235
What are the three steps of the elongation of prokaryotic translation?
1. 2nd aminoacyl-tRNA entrance
2. Peptidyl transferase activity
3. Translocation
236
What does the second aminoacyl-tRNA do during the first step?
Enters the A site and hydrogen bonds with the second codon
237
What is required in the first step, for the second aa-tRNA to bin to the second codon?
Hydrolysis of one phosphate from GTP
238
What is the hydrolysis of the one phosphate from GTP processed by? Based on the first step of elongation in prokaryotic cells?
1. Elongation factor called Tu (EF-TU)
| 2. Elongation factor called EE-Ts
239
What does elongation factor Tu (EF-Tu) does?
It is a GTPase
240
What does elongation factor EE-Ts does?
Removes the remaining GDP from EF-TU and helps it reset
241
What subunit acts during the second step of elongation in prokaryotic cells?
The peptide transferase activity of the large ribosomal subunit (the 23S rRNA)
242
What does the large ribosomal subunit do during the second step?
Catalyzes the formation of a peptide bond between fMet and the second amino acid
243
What happens between the fMET and the second amino acid, during second step of translation in prokaryotes?
Amino group of AA #2 acts as a nucleophile and tRNAfMet is the leaving group
244
What is the direction of translation from the point of view of the polypeptide?
N to C; since the N AA #2 binds to the C #1
245
What is occurring between tRNA #1 and tRNA #2?
Dipeptide attaches
246
What is the third step of prokaryotic translation?
Translocation
247
What happens at the beginning of the third step, translation?
The empty tRNA 1 moves to the E site
248
What is occurring with tRNA 2 during the third step, translocation?
tRNA 2holding the growing peptide moves into the P site and the next codon to be translated move into the A site
249
What's the purpose of Elongation factor G?
Elongation factor G (EF-G) helps with translocation
250
What does the translocation process require?
One GTP
251
What is EF-G sometimes called and why?
Translocase because of its function during the third step
252
Disruption of tRNA binding to the E site results in what?
An increase in the number of frameshift mutations in the resulting protein
253
What does EF-Tu help with during the last step of elongation?
Remove the tRNA from the E site
