CH_11 Flashcards
To learn and retain information from CH 11 from the course Cell Biology (88 cards)
1
Q
Transcription
A
The process by which an RNA is synthesized from a DNA template in the nucleus
2
Q
Translation
A
The process by which proteins are synthesized from an mRNA template in the cytoplasm
3
Q
Messenger RNA (mRNA)
A
An intermediate between a gene (DNA) and a polypeptide (Protein)
4
Q
What are mRNA assembled as?
A
A complementary copy of one of the two DNA strands that make up the gene
5
Q
Fucntions of mRNA
A
Allows the cell to separate information storage from information utilization
Allows a cell to greatly amplify
6
Q
What are RNA polymerase responsible for?
A
Transcription in both prokaryotes and eukaryotes
7
Q
What are RNA polymerase capable of doing?
A
Incorporate nucleotides one at a time, into a strand of RNA from a DNA template
8
Q
What do RNA polymerase require the help of?
A
Require the help of transcription factors to recognize the promter
9
Q
What does the RNA polymerase bind the DNA template to?
A
The promoter
10
Q
What is a promoter?
A
A region of DNA that locates prior to the transcription start site of a gene
11
Q
What are the functions of the promoter?
A
- Contains information that determines which of the two DNA strands will be used as the template and where transcription will begin
- Initiates transcription
12
Q
What direction does the newly synthesized RNA chain grow?
A
5’ to 3’ direction, antiparallel to the DNA template
13
Q
What does the RNA polymerase establish during transcription?
A
The transcription bubble
14
Q
What happens to the DNA after RNA polymerase passes?
A
DNA double helix re-forms
15
Q
What happens to newly synthesized RNA ?
A
It dissociates with DNA template
16
Q
How long is the DNA-RNA hybird?
A
About 9 base pairs long
17
Q
What are properties of RNA polymerase?
A
RNA polymerase must be processiv–remain attached to DNA over long stretches
RNA polymerase must be able to move from nucleotide to nucleotide.
18
Q
What are Ribonucleoside triphosphates substrates (NTPs) cleaved to?
A
Nucleoside monophosphates as tthey are polymerized into RNA chain
19
Q
What rule are NTPs incorporated to?
A
The Watson-Crick base pairing rule
20
Q
How many RNA polymerase are in prokaryotes?
A
One
21
Q
Composed of _____ subunits named as the _______________
A
five, core enzyme
22
Q
Where does the core enzyme bind?
A
It binds randomly
23
Q
What does the sigma factor do?
A
Biding to the core enzyme to facilitate interaction with DNA at specific promoter sites
24
Q
What RNA polymerase is used in eukaryotes?
A
RNA polymerase II
25
What is needed to recognize the promoter?
Transcription factors
26
What is the name for the initially synthesized RNA
Primary transcript
27
What will the primary transcript be processed to become?
Mature RNA or mRNA
28
What is a transcription unit?
The DNA segment corresponding to a primary transcript
29
What are properties of mRNA
They each code for a specific polypeptide
They are found in the cytoplasm
They are attached to ribosomes when translated
Most have a noncoding segment
Eukaryotic mRNAs possess specific modifications at their 5’ and 3’ end
5’: methylated guanosine cap
3’: poly(A) tail, composed of 50-250 adenosine residues
30
Function of the 5' cap
Prevents the 5’-end of mRNA from being digested by enzymes
Aids in transport of the mRNA out of the nucleus
Plays an important role in the initiation of translation
31
Function of the 3' poly (A) tails
All mRNAs possess a string of adenosines (50-250) at their 3’end
Protect the mRNA from premature degradation by enzymes
32
What synthesizes all eukaryotic mRNA precursors?
RNA polymerase in the nuclues
33
What does RNA polymerase associate with?
General transcription factors (GTFs) to form the preinitation complex (PIC)
34
What does the PIC assemble?
The critical portion of the promoter, it lies 24-32 bases upstream (5' - 3') to the iniation site and its called the TATA box (5'- TATAAA- 3')
35
What does the TFIIH do?
Possess enzymatic activites
36
What does the protein kinase do?
Phosphorylate RNA polymerase II
37
What does the helicase?
Unwinding DNA double helix to generate the transcription bubble
38
What is an Exon?
Parts contribute to the mature RNA
39
What is an Intron?
Intervening sequences, which are excluded from the mature RNA
40
How are Pre-mRNA transcripts processed?
Cotranscriptionally
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What happens to RNA transcripts as they are synthesized?
They be come associated with ribonucleoproteins
42
What happens to RNA transcripts as they are processed?
A 5' methyguanosine cap and 3' poly (A) tail are added
43
What happens to the introns and exons?
Introns are removed and exons are connected by RNA splicing
44
What is RNA splicing?
A modification process of the nascent pre-messenger RNA (pre-mRNA) transcript in which introns are removed and exons are joined to produce the mRNA
45
What are splice sites?
Jucntions between introns and exons
46
What is GU?
The 5' splice site of intron
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What is AG?
The 3' splice site
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What tracts near the 3' splice site?
Polypyrimidine
49
Where do splice sites get assistance from?
Exon splicing enhancers (ESEs) situated in the exon
50
Is Pre-mRNA self-splicing?
No they require help from small nuclear RNAs (snRNAs) and their associated proteins
51
What does the intron become associated with?
A complex called spliceosome
52
What is the splicesome consisted of?
The spliceosome consists of small nuclearribonucleoproteins(snRNPs)
- snRNA + specific proteins
- U1, U2, U5, and U4/U6 snRNPsare required
53
What is Alternative splicing?
A regulated process during gene expression that results in a gene coding for multiple proteins
54
How is information stored in a gene?
Stored in a gene in the form of a genetic code, named codons
55
What are the properties of codons?
Triplets of nucleotides
non-overlapping
Degenerate
o some of the amino acids are specified by more than one codon
56
Do the first two codon bases for an amino acid change?
No, the first two are invariant, whereas the thrid may vary
57
How are codons for specicfic and smilar amino acids?
They tend to be clustered
58
What are the types of nucleotide mutations?
Synonymous- does change the amino acid sequence
Non-synonymous- causes an amino acid substitution
Nonsense- creates a premature termination codon
59
How many nucleotides does an insertion or deletion mutation add/ delete?
One or more
60
What is a frameshift DNA mutation?
Alters the normal reading frame of the mRNA
61
What is the role of tRNA?
tRNA translate a sequence of mRNA codons into a sequence of amino acid residues
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What does tRNA transfer?
Appropriate amino acid to specific codons
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What is the length of tRNAs?
73 to 93 nucleotides
64
What is the structure of tRNA?
All tRNAhad a significant percentage of unusual bases
All tRNAs have sequences of nucleotides in one part of the molecule complementary to sequences located in other part of the same molecule, forming stem of the cloverleaf
All mature tRNAs ended in CCA at their 3’ end
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What is an Anticodon?
A stretch of three sequential nucleotides reisde in tRNA that decode codon information through formation of complementary base pairs between codons on mRNA transcript
66
What is the wobble hypothesis?
A tRNA can recognize codons with variable third bases
3rd position: U with A or G (codon); G with U or C (codon); I with U, C, or A (codon)
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What do aminoacyl-tRNA synthetases (aaRS) do?
Link amino acids with their respective tRNAs
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How aaRS exist?
There are 20 different that exist in an organism
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What is the small and large ribosomal subunit?
40S and 60S
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What is the purpose of Ribosomal RNAs (rRNA)?
Structural support
Catalyze the chemical reaction in which amino acids are covalently linked to one another
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What is the purpose of Transfer RNAs (tRNA)
Required to translate the information in the mRNA nucleotide code into the amino acid
72
How many binding sites to tRNA have?
3 binding tRNA binding sites:
A (aminoacyl) site
P (peptidyl) site
E (exit) site
73
What is the 1st Step of Translation?
43S complex binds to the 5’ end of mRNA complex and scan for the AUG start codon
74
What are the components of 43S complex?
Ribosomal 40S subunit
Initiator tRNAlinked to a methionine
eIFs: eIF2-GTP
75
What are the components of mRNA complex?
mRNA
eIF4E: binding to 5’-cap
eIF4A: remove double stranded structure
eIF4G: linked 5’ and 3’ end
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What is the 2nd Step of Translation?
Large subunit (60S) joins the complex after 43S complex reaches the appropriate AUG codon
77
What happens after the 2nd Step of Translation?
Complete assemble of 80S ribosome
All eIFsare released
Initiator tRNAbinds to the P site of the ribosome
78
What are the properties of elongation?
The elongation cycle is the process of adding each subsequent amino acid to the growing polypeptide chain.
Specific proteins will be required, referred as “elongation factors(eEFs)”
2 GTPs are required for each cycle of elongation
79
What are the major steps of elongation?
Step_1: Aminoacyl-tRNAselection
Step_2: Peptide bond formation
Step_3:Translocation
Step_4: Releasing the deacylatedtRNA
80
What happens during the first step of elongation: Aminoacyl-tRNA selection
With the charged amino acid in the P site, the next aminoacyl-tRNAbinds to the vacant A site is the first step for elongation
Any aminoacyl-tRNAcan enter the A site, but ONLY the one with complementary anticodon can trigger the conformational change of ribosome
81
What happens during the second step of elongation: Peptide bond formation
Catalyzed by peptidyl transferase
Amine nitrogen of the amino acid bound to the A site tRNAlinked to carboxyl carbon of the amino acid bound to the P site tRNAfor the formation of peptide bond
Result in a dipeptide bound to the tRNAat A site, and tRNAat P site is deacylated
82
What happens during the third step of elongation: Translocation
Translocation refers to the procedure that ribosome moves three nucleotides (one codon) in the 5’ to 3’ direction on the mRNA molecule
Accompanied with the movement of:
- The dipeptidyl-tRNAfrom the A site to the P site of the ribosome
- Deacylated tRNA from the P site to the E site
83
What happens during the fourth step of elongation: Releasing the deacylated tRNA
The deacylatedtRNAleaves the ribosome and empty the E site of the ribosome
84
What three stop codons cause termination?
UAA, UAG, or UGA
85
What does termination require?
Release factors, which recognize stop codons
86
What type of release factor do eukaryotic cells have?
eRF1, they recognize all the stop codons
87
What does termination accompany?
Accompanied by dissociation of the mRNA from the ribosome and the disassembly of the ribosome
88
What is a polyribosome?
A polyribosome (or polysome) is a complex of mulitple ribosomes on mRNA, allowing simultaneous translation, they increase the rate of protein synthesis
