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MCAT BIOLOGY FLASHCARDS > MCAT BIO CH. 4 PART 2 > Flashcards

MCAT BIO CH. 4 PART 2 Flashcards

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1
Q

How is sickle-cell anemia caused?

A

By a mutation in the gene for hemoglobin (Hb)

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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

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3
Q

What happens to the deformed cells in sickle cell anemia?

A

Cannot function, destroyed prematurely; leads to anemia

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4
Q

Why is having sickle cell anemia positive?

A

This is common in area where malaria is prevalent; important benefit

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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

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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

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7
Q

What are two types of disease causing mutations?

A
  1. Inborn errors of metabolism

2. Cancer

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8
Q

What do inborn errors of metabolism includes?

A

Involve disorders of metabolism

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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

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10
Q

What are the symptoms of inborn errors of metabolism caused by?

A
  1. Build-up of toxic compound

2. Deficiency of an essential molecule unable to be synthesized

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11
Q

Tumor mutations in cancer are often in…?

A

Oncogenes and tumor suppressors

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12
Q

What is an oncogene?

A

A gene that can cause cancer when it is mutated or expressed at high levels

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13
Q

What are tumor suppressors?

A

Their deletion can cause cancer

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14
Q

What is direct reversal?

A

A few DNA damage can be reversed

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15
Q

What is photo reactivation?

A

Enzymes that repair UV-induced pyrimidine photodimers using visible light

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16
Q

What is the most common type of mechanism repair in humans based on direct reversal?

A

Nucleotide excision repair

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17
Q

If lead unprepared, what can pyrimidine dimers cause?

A

May lead to melanoma, a type of very dangerous and malignant skin tumor

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18
Q

What is homology-dependent repair pathways?

A

Using the undamaged complementary information on the other strand to repair the damaged strand

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19
Q

What can homology-dependent repairs be divided in?

A
  1. Excision repair

2. Post-replication repair

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20
Q

What does excision repair involve?

A

Involves removing defective bases nucleotides and replicating them

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21
Q

What does the mismatch repair pathway target?

A

Targets mismatched bps that were not repaired by DNA poly proofreading during replication

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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

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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

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24
Q

What recognization pattern do prokaryotes and eukaryotes use?

A
  1. Newly synthesized strand is recognized by the free 3’-terminus on the leading strand
  2. Gaps b/n Okazaki segments
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25
Q

What are the two pathways to help with double-strand repair break?

A
  1. Homologous recombination

2. Nonhomologous end-joining

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26
Q

If DSB is done incorrectly, what can occur?

A

Deletions or translocations

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27
Q

What is homologous recombination?

A

One sister chromatid can help repair a DSB in the other

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28
Q

Why can one sister chromatid help repair the other based on DSB?

A

Because after DNA replication, the genome contains identical sister chromatids

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29
Q

On which end is the DSB trimmed?

A

5’ end to generate single stranded DNA

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30
Q

How is the DSB trimmed? (By the help of which enzymes)

A
  1. Nucleases

2. Helicases

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31
Q

What do the nucleases do?

A

Break the phosphodiester bonds

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32
Q

What do the help of multiple proteins aid with?

A

Bind these ends and start a search of the genome to find sister chromatid region that is complementary to the single-strand DNA

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33
Q

What enzymes help to build a corrected DNA strand?

A

DNA poly and ligase

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34
Q

What is the purpose of the joint molecule?

A

Damaged and undamaged sister chromatids crossover

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35
Q

When is non-homologous end joining used?

A

When there are no backup chromosome to use

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36
Q

What happens during non-homologous end joining?

A
  1. Broken ends are stabilized

2. DNA ligase connects the fragments

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37
Q

What can be the outcome of non-homogolous end joining?

A

Base pairs being lost or chromosomes being connected in an abnormal way

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38
Q

What is another word for gene expression?

A

Transcription

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39
Q

What is gene expression?

A

Information contained in genes being to have effects in the cell

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40
Q

What are the three unique facts about RNA?

A
  1. Single-stranded
  2. Uracil
  3. Ribose
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41
Q

Which RNA is the only type of coding RNA?

A

mRNA

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42
Q

Which region of the mRNA is not translated into protein and what is it called?

A

5’ untranslated region or 5’ UTR

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43
Q

What is the open reading frame?

A

Region that codes for a protein

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44
Q

The 3’ end of the mRNA is translated into the protein. T/F

A

False: after stop codon; is not translated

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45
Q

If the 3’ end of the mRNA is not translated into the protein, what its purpose?

A

Contains regulatory regions that influence post-transcriptional gene expression

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46
Q

What does monocistronic mean?

A

Each piece of mRNA encodes only one polypeptide

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47
Q

What does polycistronic mean?

A

mRNA codes for more than one polypeptide

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48
Q

Which type of mRNA is monocistronic?

A

Eukaryotic mRNA

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49
Q

Which type of mRNA is polycistronic?

A

Prokaryotic mRNA

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50
Q

In prokaryotic mRNAs, what can be found between ORFs?

A

Translation termination and initiation sequences

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51
Q

What is the name of the first RNA transcribed from DNA and why?

A

Heterogeneous nuclear RNA (hnRNA) - precursor to mRNA

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52
Q

What events are required to mature hnRNA?

A

Addition of cap and tail, splicing introns

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53
Q

hnRNA is only found in……? Why?

A

Eukaryotes; because prokaryotes do not process their primary transcripts

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54
Q

What is a non-coding RNA (ncRNA)?

A

RNA not translated into a protein

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55
Q

What are the two major types of ncRNAs?

A

tRNA and rRNA (transfer and ribosomal)

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56
Q

What is tRNA?

A

Responsible for translating genetic code

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57
Q

What does tRNA do?

A

Carriers amino acid from cytoplasm to the ribosome to add to the growing protein

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58
Q

How many types of rRNAs do humans have?

A

4 types: 18S, 5.8S, 28S and 5S

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59
Q

What is the purpose of rRNA?

A

Provides catalytic function of the ribosome

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60
Q

What are ribozymes?

A

Catalytic RNAs

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61
Q

Why are catalytic RNAs called ribozymes?

A

Can perform specific biochemical reactions similar to protein enzymes

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62
Q

What are four rare types of ncRNAs?

A
  1. snRNA
  2. miRNA and siRNA
  3. piRNA
  4. Long ncRNAs
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63
Q

What are snRNAs?

A

Small nuclear RNAs that associate with proteins to form snRNP complexes in the spliceosome

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64
Q

What does snRNP stand for?

A

Small unclear ribonucleic particles

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65
Q

What does miRNA stand for? What does siRNA stand for?

A

MicroRNA and small interfering RNA

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66
Q

What do miRNA and siRNA function in?

A

Function in RNA interference (RNAi)

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67
Q

What is RNAi

A

A form of postranscriptional regulation of gene expression

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68
Q

What can both miRNA and siRNA do?

A

Bind to specific mRNA molecules to increase or decrease translation

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69
Q

What does piRNAs stand for?

A

PIWI-interacting RNAs

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70
Q

How is the structure piRNAs?

A

Single stranded and short (typically b/n 23 to 21 nucleotides in length)

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71
Q

What is the function of piRNAs?

A

Work with a class of regulatory proteins called PIWI proteins to prevent transposons from mobilizing

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72
Q

What’s the structure of long ncRNAs?

A

Longer than 200 nucleotides

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73
Q

What do the long ncRNAs help with?

A

Control basal transcription level in a cell

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74
Q

How do Long ncRNAs help with controlling basal transcription levels?

A

By regulating initiation complex assembly on promoters

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75
Q

What can Long ncRNAs control?

A

Control splicing and translation, imprinting and X-chromosome inactivate

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76
Q

What do both transcription and replication involve?

A

template-driven polymerization

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77
Q

The RNA transcript produced in transcription is…. to DNA?

A

Complementary

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78
Q

What is the driving force for both replication and transcription?

A

Removal and subsequent hydrolysis of pyrophosphate from each nucleotide added to the chain (existing chain is nucleophile)

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79
Q

Do the polymerase enzymes in both replication and transcription require a primer?

A

No, RNA pol does not require a primer

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80
Q

What does RNA poly lack?

A

exonuclease activity

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81
Q

Which process has a lower fidelity process? Transcription or replication….

A

Transcription

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82
Q

What is the name of the start site where transcription begins? What is the name of the start site where replication begins?

A
  1. Start site

2. Origin

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83
Q

What is the promotor based on the transcription process?

A

The sequence of nucleotides on a chromosome that activates RNA polymerase to begin the process

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84
Q

What is the name of the strand which is actually being transcribed?

A

Template, non-coding, transcribed antisense strand

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85
Q

What is the DNA strand called, the one not being used for transcription?

A

Coding or sense strand

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86
Q

What does downstream mean?

A

Towards the 3’ end of the coding strand and transcript

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87
Q

What does upstream mean?

A

Towards the 5’ end of the coding strand, beyond the 5; end of the transcript

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88
Q

Upstream nucleotide sequences are referred to using ______? Downstream nucleotide sequences are referred to using _______?

A
  1. Negative

2. Positive

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89
Q

The first nucleotide on the template strand which is actually transcribed is called…..

A

Start site

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90
Q

The first nucleotide on the coding strand is given….

A

Number +1

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91
Q

What is the structure of prokaryotic RNA poly?

A

Large enzyme complex consisting of five subunits

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92
Q

What are the five subunits of the prokaryotic RNA poly?

A

Two alpha subunits, beta subunit, a beta’ subunit and an omega subunits

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93
Q

What are the prokaryotic RNA poly subunits referred to and what are they important for?

A

Core enzymes; responsive for rapid elongation of the transcript

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94
Q

The core enzyme on its own can start the transcription process. T/F

A

False: Additional subunit termed the sigma factor is required to form the holoenzyme

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95
Q

What are the three stages of transcription? (prokaryotes)

A
  1. Initial
    2 Elongation
  2. termination
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96
Q

When does initiation of transcription occur? (in prokaryotes)

A
  1. RNA polymerase holoenzyme binds to a promoter
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97
Q

What type of sequences does the bacterial promoter contain?

A

Two primary sequences: the Pribnow box at -10 and the -35 sequence

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98
Q

What do holoenzyme to once they arrive near the chromosome?

A

Scan along the chromosome like a train on railroad track

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99
Q

What happens when the holoenzyme recognizes a promoter?

A

Stops, forms a closed complex

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100
Q

After the holoenzyme forms a closed complex to the promoter, which enzyme must act next?

A

RNA polymerase: must unbind portion of DNA double helix before it can begin to synthesize RNA

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101
Q

What is the open complex?

A

RNA poly bound to the promoter with a single stranded DNA

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102
Q

How does the sigma factor help for the polymerase to find promoters?

A
  1. Help RNA poly recognize promoters

2. Decrease nonspecific affinity of holoenzyme for DNA

103
Q

When is the sigma factor no longer necessary and what does it do?

A

When the open complex and phosphodiester bonds have been formed; leaves the RNA poly complex

104
Q

How does the core enzyme elongate the RNA chain?

A

Processively with one polymerase complex synthesizing entire RNA molecule

105
Q

What is the transcription bubble?

A

Region of the DNA double helix unwound to allow polymerase to access the complementary DNA template

106
Q

What happens when the termination signal is detected?

A

With sometimes the help of rho, RNA poly falls off, RNA released and transcription bubble closes

107
Q

What are the four major differences in eukaryotic vs prokaryotic transcription?

A
  1. Location
  2. RNa polymerases
  3. Primary transcripts
  4. Regulation of transcription
108
Q

Based on location, what does eukaryotic mean? What does prokaryotic mean?

A

Eukaryotic: True-kernelled
Prokaryotic: Before-the-kernel

109
Q

What is the karyon (kernel)?

A

The nucleus

110
Q

Based on prokaryotic meaning before-the-kernel, what does that mean about its transcription?

A

No nucleus means transcription occurs free in the cytoplasm

111
Q

Because the processes for prokaryotic cells occur in the same compartment, it means that transcription and translation can occur….?

A

Simultaneously

112
Q

Because the processes for eukaryotic cells occur in different compartment, it means that translation and transcription can….

A

NOT occur simultaneously

113
Q

What is the different in transcription b/n prokaryotic and eukaryotic cells based on their RNA product after transcription?

A

Prokaryotes: mRNA can be translated right away
Eukaryotes: hnRNA made by RNA pol II needs to be modified before translation

114
Q

What is the most important example of a modification that needs to occur on the pre-mRNA (hnRNA) before translation in eukaryotic organisms?

A

Splicing

115
Q

What are introns?

A

Non-coding sequences intervening between the segments that actually code for proteins

116
Q

Sometimes these introns can contain what?

A

Contain enhancers or other regulatory sequences

117
Q

What is the average size of an intron?

A

2000 nucleotides

118
Q

What are exons?

A

Protein-coding regions of the RNA

119
Q

What is splicing?

A

Removing introns and joining the exons

120
Q

What is splicing mediated by?

A

Spliceosome

121
Q

What is the structural composition of a spliceosome?

A

Complex containing 100 proteins and 5 small nuclear RNA molecules (snRNA)

122
Q

How are snRNPs formed?

A

Half the proteins from the spliceosome stably bind snRNAs and these form three small nuclear ribonucleic particles (snRNPs)

123
Q

What are snRNPs made up of?

A

Proteins and snRNAs

124
Q

The spicleosome is preassembled in our nucleus. T/F

A

Falsee: it assembles around each intron that needs to be removed

125
Q

What do the snRNPs do to start the catalytic activity of the splicing reaction?

A

snRNPs recognize and hydrogen bond to conserved nucleotides in the intron

126
Q

What is the conserved nucleotide sequence in the intron?

A

GU at the 5’, AG at the 3’ end and adenine 15-45 bases upstream of the 3’ splice site

127
Q

How many reactions are catalyzed by the spliceosome?

A

Two

128
Q

What is the first reaction catalyzed by the spliceosome?

A
  1. Attach one end of the intron to the conserved adenine causing the intron to form a loop structure
129
Q

What is the second reaction catalyzed by the spliceosome?

A
  1. Joining he two exons and releasing the loop
130
Q

What are the five conserved nucleotides necessary for the splicing reaction?

A

GU, A and AG

131
Q

What is alternative splicing?

A

Different options or patterns of splicing

132
Q

What is a way of increasing the complexity gene expression?

A

Shuffling exons

133
Q

After the splicing reaction, how is eukaryotic hnRNA modified to be able to go through translation?

A

5’ cap and 3’ poly-A tail

134
Q

What is the 5’ cap?

A

Methylated guanine nucleotide stuck on 5’ end

135
Q

What is the poly-A-tail?

A

String of several hundred adenine nucleotides

136
Q

Why are the 5’ cap and 3’ poly-A tail important for the hnRNA?

A

Preventing digestion of the mRNA by exonucleases that are free in the cell

137
Q

In prokaryotes, all RNA is made by the….?

A

α2ββ’σ RNA polymerase complex

138
Q

What is α2ββ’σ RNA polymerase complex again?

A

Core enzyme responsible for rapid elongation of transcript

139
Q

In eukaryotes, what are the different types or RNA polymerases?

A
  1. RNA poly I
  2. RNA poly II
  3. RNA poly III
140
Q

What is the purpose of RNA poly I in eukaryotes?

A

Transcribes most rRNA

141
Q

What is the purpose of RNA poly II in eukaryotes?

A

Transcribes hnRNA, most snRNA and some miRNA

142
Q

What is the purpose of RNA poly III in eukaryotes?

A

Transcribes tRNA, long ncRNA, siRNA, miRNA and some rRNAs

143
Q

There are many DNA polymerases for which type of cell?

A

Prokaryotes

144
Q

What is translation?

A

Synthesis of polypeptides according to the amino acid sequence from by the sequence of codons in mRNA

145
Q

What does the mRNA molecule do during translation?

A

Attaches to a ribosome at a specific codon and the appropriate amino acid is delivered by a tRNA molecule

146
Q

What happens when the mRNA attaches to the ribosome?

A

The second amino acid is delivered by another tRNA

147
Q

What does the ribosome do when the two amino acids are added by the tRNA?

A

The ribosome binds the two amino acids together, creating a dipeptide

148
Q

What is tRNA composed of?

A

A single transcript produced by RNA poly III

149
Q

What is the tertiary structure of every tRNA molecule?

A

tRNAs have a stem-and-loop structure

150
Q

What is the tRNA stem-and-loop structure stabilized by?

A

Stabilized by hydrogen bonds b/tn bases on neighboring segments of the RNA chain

151
Q

What is the anticodon?

A

A sequence of 3 ribonucleotides which is complementary to the mRNA codon the tRNA translates

152
Q

What is a key step in translation?

A

Specific base pairing b/n the tRNA anticodon and the mRNA codon

153
Q

What is the amino acid acceptor site based on tRNA?

A

Where the amino acid is attached to the tRNA

154
Q

Since there is a tRNA for each codon…..

A

Each tRNA is specific for one amino acid while each amino acid may have several tRNAs

155
Q

How would a tRNA for valine be written?

A

tRNA subscript val

156
Q

When the amino acid is attached, the tRNA is written in what way?

A

Val-tRNA subscript Val

157
Q

What type of bases do tRNA molecules contain?

A

Contain nitrogenous bases in many positions that have been covalently modified

158
Q

Base methylation is particular common in what?

A

tRNA molecules

159
Q

What are specific examples of nitrogenous bases contained in tRNA molecules?

A
  1. Inosine (derived from adenine)
  2. Pseudorine (derived from uracil)
  3. Lysidine (derived from cytosine)
160
Q

What does inosine play a role in?

A

Wobble base pairing

161
Q

How many tRNAs do most organisms have and what does that mean?

A

45 types of tRNAs; some anticodon must pair with more than one codon

162
Q

What is the Wobble Hypothesis?

A

The first two codon-anticodon pairs obey normal base pairing rules but the third position is more flexible

163
Q

What are the three 5’ base in anticodon (tRNA) that can wobble?

A
  1. G
  2. U
  3. I
164
Q

What can G pair with, if its apart of the 5’ base in anticodon (tRNA)?

A

C or U (wobble base)

165
Q

What can U pair with, if its apart of the 5’ base in anticodon (tRNA)?

A

A or G (wobble base)

166
Q

What can G pair with, if its apart of the 5’ base in anticodon (tRNA)?

A

A, U or C (all wobble bases)

167
Q

What are the most common wobble base pairs?

A
  1. Guanine-uracil
  2. Inosine-uracil
  3. Inosine-adenine
  4. Inosine-cytosine
168
Q

The thermodynamics stabilities are greater for the normal watson-crick base pair rather than the wobble base pair. T/F

A

False: have similar thermodynamics stabilities

169
Q

How is the thermodynamics and kinetic of peptide bond formation?

A

Unfavourable and slow kinetics

170
Q

Because the peptide bond formation is unfavorable and slow, what is used to power the process?

A

Coupling

171
Q

What is used to energize the peptide bond formation in amino acid activation?

A

Two high-energy phosphate bonds are hydrolyzed to provide the energy to attach an amino acid to its tRNA molecule

172
Q

What is tRNA loading or amino acid?

A

Two high-energy phosphate bonds are hydrolyzed to provide the energy to attach an amino acid to its tRNA molecule

173
Q

Why is tRNA loading useful?

A

Breaking the aminoacyl-tRNA bond will drive peptide bond formation forwards

174
Q

What are the three steps to amino acid activation?

A
  1. aminoacyl AMP formation
  2. Orthophosphates
  3. Destruction of aminoacyl-AMP
175
Q

What is the first step, AMP attachment, of the amino acid activation?

A

An amino acid is attached to AMP to form aminoacyl AMP.

176
Q

What’s the nucleophile and the leaving group in the formation of aminoacyl AMP?

A

Nucleophile: Acidic oxygen of the AA

Leaving group: PPi

177
Q

What is the second step, Orthophosphates, of the amino acid activation?

A

The pyrophosphate leaving group is hydrolyzed to 2 orthophosphates

178
Q

How is the thermodynamics of the hydrolization of 2 orthophosphates?

A

Highly favorable ΔG «< 0

179
Q

What is the third step, Destruction of aminoacyl-AMP, of the amino acid activation?

A

tRNA loading is driven forward by the destruction of the highly-energy aminoacyl-AMP bond created in Step 1

180
Q

What does amino acid activation requires in energy? How do we know that?

A

2 ATP equivalents; it uses two high-energy bonds

181
Q

What is an ATP equivalent?

A

A single high-energy phosphate bond

182
Q

How can you get 2 ATP equivalents?

A
  1. Hydrolyzing 2 ATP to 2 ADP + 2 Pi

2. Hydrolyzing 1 ATP to AMP + 2 Pi

183
Q

What happens after step 3 of the amino acid activation?

A

Bond between amino acid and the tRNA molecule will be broken

184
Q

What does the hydrolysis of the bond b/n AA and the tRNA molecule cause?

A

Powers the peptide bond formation

185
Q

How does the peptide bond occur, based on nucleophiles present?

A

The nitrogen of another AA will nucleophilically attack carbon carbon of this amino acid and tRNA will be the leaving group

186
Q

Which enzyme is used to confirm the attachment of the appropriate amino acid to each tRNA molecule accomplished?

A

Aminoacyl-tRNA synthétase enzymes

187
Q

How do Aminoacyl-tRNA synthetase enzymes knows which AA to choose? (It is specific….?)

A

Specific to each AA and there is at least one aminoacyl-tRNA synthétase for every AA

188
Q

How does the Aminoacyl-tRNA synthetase enzymes recognize the tRNA and the AA?

A

Based on their 3D structures

189
Q

How is the error rate of Aminoacyl-tRNA synthetase enzymes?

A

Low error rate

190
Q

What is the two most important functions of the amino acid activation?

A
  1. Specific and accurate AA delivery

2. Thermodynamic activation of amino acid

191
Q

What is the ribosome composed of?

A

Many polypeptide and tRNA chains

192
Q

In the ribosomes, how are many polypeptides and tRNA chains held together?

A

Massive quaternary structures

193
Q

What is the unit of measurements for ribosome?

A

Svedberg (S)

194
Q

What type of rate is the Svedberg rate?

A

A sedimentation rate; how quickly something will sink in a gradient during centrifugation

195
Q

The Svedberg rate is additive. T/F

A

False: it is not additive

196
Q

The prokaryotic ribosome sediments at a rate of…? What is it referred to?

A

70S ; 70S ribosome

197
Q

What is the 70S ribosome composed of in prokaryotes?

A

A 30S small subunit and a 50S large subunit

198
Q

What is the small 30S subunit ribosome made of in prokaryotes?

A

16s RNA and 21 peptides

199
Q

What is the large 50S subunit ribosome made of in prokaryotes?

A

2 rRNAs (23Sand 5S) and 31 peptides

200
Q

How does the prokaryotic ribosome and eukaryotic ribosome differ?

A

Eukaryotic ribosomes have an 80s ribosome, prokaryotes have 70S

201
Q

What is the 80S ribosome in eukaryotes composed of?

A

Large 60S subunit and a small 40S subunit

202
Q

What is the large 60S subunit ribosome made of in eukaryotes?

A

Three rRNA molecules and 46 peptides

203
Q

What are the sediment rates of the three rRNA molecules in the 60S large ribosome subunit in eukaryotes?

A

5S, 5.8S and 28S

204
Q

What is the small 40S subunit ribosome made of in eukaryotes?

A

33 peptides and 1 rRNA 9(18S)

205
Q

Which rRNAs have ribozyme function in eukaryotes and prokaryotes?

A

23S rRNA in proka. and 28S rRNA euka.

206
Q

What is the ribozyme function of the 23S rRNA and 28 s rRNA?

A

Link amino acids during protein synthesis via peptidyl transferase activity

207
Q

The ribozymic activity of the ribosome is found in ……

A

The large subunit of both prokaryotic and eukaryotes ribosomes

208
Q

What are the three special binding sites of the complete ribosome?

A
  1. A site
  2. P site
  3. E site
209
Q

What is the A site? What is its purpose?

A
  1. aminoacyl-tRNA site

2. Where each new tRNA delivers its AA

210
Q

What is the P site? What is its purpose?

A
  1. Peptidyl-tRNA

2. Where the growing polypeptide chain, still attached to. tRNA

211
Q

What is the E site? What is its purpose?

A
  1. exit-tRNA site

2. Where a now-empty tRNA sits prior to its release

212
Q

What is polyribosome? In which type of cells are they used during translation?

A
  1. Several ribosomes

2. Prokaryotes: many ribosomes attach and begin translating mRNA while its being made

213
Q

Where are polyribosomes found? (Which type of cells)

A

Prokaryotes and eukaryotes

214
Q

What is an important fact about prokaryotes mRNA?

A

Polycistronic

215
Q

Because prokaryotes have polycistronic mRNAs…..?

A

Their ribosomes can start translation in the middle of the chain

216
Q

Where are termination and initiation sequences found, based on the prokaryote mRNAs?

A

Between each ORF

217
Q

What is the Shine-Dalgarno sequence?

A

The “promoter” for prokaryotic translation called ribosome binding site

218
Q

Where is Shine-Dalgarno located?

A

-10 (ten ribonucleotides upstream or on the 5’ side of the start codon)

219
Q

What is the Shine-Dalgarno complementary to? What does that aid?

A
  1. Complementary to a pyrimidine-rich region

2. Helps position the initiation machinery on the transcript

220
Q

What are the stages of translation in prokaryotic cells?

A

Initiation, elongation, termination

221
Q

What is the first step in the initiation for prokaryotic cells translation?

A

Small 30S binding two initiation proteins called IF1 and IF3

222
Q

What complex ends to the mRNA, based on the initiation step?

A

The Small 30S subunit and IF1, IF3 proteins

223
Q

What is the second step in initiation for prokaryotic cells? (What happens after the 30S, IF1 and IF3)?

A

The first aminoacyl-tRNA joins with third initiation factor IF2

224
Q

What is the IF2 bound to?

A

A GTP

225
Q

What is the third step in initiation for prokaryotic cells? (What happens after aminoactyl-tRNA, GTP and IF2)?

A

50S subunit completes the complex

226
Q

What is the 50S binding at the end powered by, based on the prokaryotic cells translation?

A

Powered by the hydrolysis of one GTP molecule

227
Q

What is the fMet-tRNA?

A

The first aminoacyl-tRNA, the initiator tRNA

228
Q

What does the fMet in fMet-tRNA stands for?

A

fMet stands for formylmethionine

229
Q

What is formylmethionine?

A

Modified methionine used as the first amino acid in all prokaryotic proteins

230
Q

What happens when fMET is found by our immune system?

A

They release cytotoxins because its a sign that bacteria are busily translating

231
Q

Where does the initiator tRNA sit?

A

In the P site the 70S ribosome, hydrogen-bonded with the start codon

232
Q

Where is the start codon of the prokaryotic cell translation?

A

initiator tRNA hydrogen bonded with the start codon

233
Q

Before elongation, what happens to the initiation factors?

A

Dissociate from the complex

234
Q

How many steps in the elongation cycle for prokaryotic translation?

A

Three step cycle

235
Q

What are the three steps of the elongation of prokaryotic translation?

A
  1. 2nd aminoacyl-tRNA entrance
  2. Peptidyl transferase activity
  3. Translocation
236
Q

What does the second aminoacyl-tRNA do during the first step?

A

Enters the A site and hydrogen bonds with the second codon

237
Q

What is required in the first step, for the second aa-tRNA to bin to the second codon?

A

Hydrolysis of one phosphate from GTP

238
Q

What is the hydrolysis of the one phosphate from GTP processed by? Based on the first step of elongation in prokaryotic cells?

A
  1. Elongation factor called Tu (EF-TU)

2. Elongation factor called EE-Ts

239
Q

What does elongation factor Tu (EF-Tu) does?

A

It is a GTPase

240
Q

What does elongation factor EE-Ts does?

A

Removes the remaining GDP from EF-TU and helps it reset

241
Q

What subunit acts during the second step of elongation in prokaryotic cells?

A

The peptide transferase activity of the large ribosomal subunit (the 23S rRNA)

242
Q

What does the large ribosomal subunit do during the second step?

A

Catalyzes the formation of a peptide bond between fMet and the second amino acid

243
Q

What happens between the fMET and the second amino acid, during second step of translation in prokaryotes?

A

Amino group of AA #2 acts as a nucleophile and tRNAfMet is the leaving group

244
Q

What is the direction of translation from the point of view of the polypeptide?

A

N to C; since the N AA #2 binds to the C #1

245
Q

What is occurring between tRNA #1 and tRNA #2?

A

Dipeptide attaches

246
Q

What is the third step of prokaryotic translation?

A

Translocation

247
Q

What happens at the beginning of the third step, translation?

A

The empty tRNA 1 moves to the E site

248
Q

What is occurring with tRNA 2 during the third step, translocation?

A

tRNA 2holding the growing peptide moves into the P site and the next codon to be translated move into the A site

249
Q

What’s the purpose of Elongation factor G?

A

Elongation factor G (EF-G) helps with translocation

250
Q

What does the translocation process require?

A

One GTP

251
Q

What is EF-G sometimes called and why?

A

Translocase because of its function during the third step

252
Q

Disruption of tRNA binding to the E site results in what?

A

An increase in the number of frameshift mutations in the resulting protein

253
Q

What does EF-Tu help with during the last step of elongation?

A

Remove the tRNA from the E site

MCAT BIOLOGY FLASHCARDS (23 decks)

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