7.3 Translation Flashcards
1
Q
What are ribosomes made of?
A
Proteins and ribosomal RNA
2
Q
Why are ribosomes made of proteins?
A
For stability
3
Q
Why are ribosomes made of ribosomal RNA?
A
For catalytic activity
4
Q
What do ribosomes consist of?
A
A large and small subunit
5
Q
What does the small ribosome subunit consist of?
A
An mRNA binding site
6
Q
What does the large ribosomal subunit consist of?
A
Three tRNA binding sites
7
Q
What are the three binding sites on the large subunit called?
A
Aminoacyl (A) site
Peptidyl (P) site
Exit (E) site
8
Q
Where can ribosomes be found?
A
Freely floating in the cytosol or bound to the rough ER
9
Q
What are the two sizes of ribosomes?
A
Prokaryotes = 70S
Eukaryotes = 80S
10
Q
What is the structure of the tRNA molecule?
A
A cloverleaf structure with four regions
11
Q
What are the four regions of the tRNA molecules?
A
The acceptor stem
The anticodon
The T arm
The D arm
12
Q
What does the acceptor stem carries?
A
An amino acid
13
Q
What does the anticodon associate with?
A
The mRNA codon
14
Q
How does the anticodon associated with the mRNA codon?
A
Via complementary base pairing
15
Q
What does the T arm associate with?
A
The ribosome
16
Q
How does the T arm associate with the ribosome?
A
Via the E, P and A binding sites
17
Q
What does the D arm associate with?
A
The tRNA activating enzyme
18
Q
What is the tRNA activating enzyme responsible for?
A
Adding the amino acid to the acceptor stem
19
Q
What does each tRNA molecule bind with?
A
A specific amino acid
20
Q
Where does the tRNA molecule bind with specific amino acids?
A
In the cytoplasm
21
Q
What catalyses the binding between tRNA molecule and amino acid?
A
A tRNA activating enzyme
22
Q
What is each amino acid recognised by?
A
A specific enzyme
23
Q
Why may the enzyme recognise multiple tRNA molecules?
A
Due to degeneracy
24
Q
What is the two step process of an amino acid binding to the tRNA acceptor stem?
A
The enzyme binds ATP to the amino acid to form an amino acid AMP complex
The amino acid is then coupled to tRNA and the AMP is released and the tRNA molecule is charged
25
What is the function of the ATP in tRNA activation?
To create a high energy bond that is transferred to the tRNA molecule
26
What does the stored energy do in tRNA activation?
Provides the majority of the energy required for peptide bond formation during translation
27
What does the initiation stage of involve?
The assembly of the three components that carry out the process (mRNA, tRNA, ribosome)
28
In initiation, where does the small ribosomal subunit bind to?
The 5’- end of the mRNA
29
In initiation, up until what point does the small ribosomal subunit move along the mRNA?
Until it reaches the start codon
30
In initiation, what happens when the small ribosomal unit reaches the start codon?
The appropriated tRNA molecule bind to the codon via its anticodon
31
How does te tRNA molecule bind to the codon via its anticodon?
Complementary base pairing
32
In initiation, where does the large ribosomal subunit aligns itself to the tRNA molecule?
At the P site
33
In initiation, what does the large subunit do once it is at the P site?
Forms a complex with the small subunit
34
In elongation, what does the second tRNA molecule do?
Pairs with the next codon
35
In elongation, where does the second tRNA molecule pair with the next codon?
At the A site
36
In Elongation, what happens to the amino acid in the P site?
It is covalently attached to the amino acid in the A site
37
In elongation, via what type of bond and reaction is the amino acid in the P site attached to the amino acid in the A site?
A peptide bond and condensation reaction
38
In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the P site?
It is now deacylated
39
What does deacylated mean?
No amino acid
40
In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the A site?
It carries the peptide chain
41
What is the first thing that happens in translocation?
The ribosome moves along the mRNA strand by one codon position
42
In what directions does the ribosome move along the mRNA strand in?
A 5’- 3’ direction
43
In translocation, what happens to the deacylated tRNA?
It moves to the E site and is released
44
In translocation, what happens to the tRNA molecule which is carrying the peptide chain?
It moves to the P site
45
In translocation, now that the A site is unoccupied happens?
Another tRNA molecule attaches to the next codon in the unoccupied A site and the process is repeated
46
What does termination involve?
The disassembly of the components and the release of a polypeptide chain
47
When do elongation and termination stop repeating?
When the ribosome reaches a stop codon
48
What do the stop codons recruit?
A release factor that signals for translation to stop
49
In termination what is released?
The polypeptide
50
In termination what does the ribosome disassemble back into?
It’s two independent subunits
51
What does initiation and elongation do until it reaches the stop codon?
Continues in a repeating cycle
52
In eukaryotes, what are the ribosomes separated from?
The genetic material
53
What separates the ribosomes from the genetic material?
The nucleus
54
After transcription, what must the mRNA transported from and how?
The nucleus via nuclear pores
55
After transcription, what must the mRNA be transported prior to?
Translation
56
What transports the mRNA from the nucleus after transcription?
The ribosome
57
What does the transport of the mRNA after transcription require?
Modification to the RNA construct
58
Why does transcription and translation need not to be separated in prokaryotes?
As they lack compartmentalised structures
59
When may ribosomes begin translating the mRNA molecule in prokaryotes?
While it is still being transcribed from the DNA template
60
Why is it possible for ribosomes to begin translating the mRNA molecule while it is still being transcribed from the DNA template?
Because both transcription and translation occur in a 5’ - 3’ direction
61
What is a polysome?
A group of two or more ribosomes translating an mRNA sequence simultaneously
62
How do polysomes appear?
As beads on a string
63
What are the beads?
Ribosomes
64
What is the string?
The mRNA strand
65
When may polysomes form in prokaryotes?
While the mRNA is still being transcribed from the DNA template
66
Ribosomes at which end of the polysome cluster will have a longer polypeptide chain?
The 3’ end
67
In eukaryotic cells, how are all proteins produced initially synthesised?
By ribosomes found freely circulating within the cytosol
68
When would the ribosome remain free and unattached?
If the protein is targeted for intracellular use within the cytosol
69
When would the ribosome become bound to the ER?
If the protein is targeted for secretion, membrane fixation or use in lysosomes
70
What determines protein destination?
The presence or absence of an initial signal sequence on a nascent polypeptide chain
71
What does SRP do?
Halts translation
72
What does the presence of the signal sequence that determines protein destination result in?
The recruitment of a SRP
73
Where does the SRP-ribosome complex dock?
At a receptor located on the ER membrane
74
What happens when the SRP ribosome complex docks on the ER membrane?
Translation is re-initiated and the polypeptide chain continues to grow
75
Once translation is re initiated, how does the polypeptide chain continue to grow?
Via a transport channel into the lumen of the ER
76
Once translation is re-initiated, where will the synthesised protein be transported and how?
To the Golgi complex or the lysosome via a vesicle
77
Once translation is re-initiated, where do the proteins targeted for membrane fixation get embedded?
Into the ER membrane
78
In protein destination, what happens once the polypeptide is completely synthesised within the ER?
The signal sequence is cleaved and the SRP is recycled
79
How many structures of protein are there?
Four
80
What is primary structure of protein?
The order/ sequence of amino acids which comprise the polypeptide chain
81
What forms the primary structure of protein?
Covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids
82
What does primary structure control?
All subsequent levels of protein organisation
83
Why does the primary protein structure determine all levels of protein organisation?
It determines the nature of the interactions between R groups of different amino acids
84
What is secondary protein structure?
The way a polypeptide folds in a repeating arrangement to form alpha helices and beta sheets
85
What causes the folding in secondary protein structure?
Hydrogen bonding between the amine and carboxyl groups of non adjacent amino acids
86
How will sequences that do not form either an alpha helix or beta pleated sheet exist?
As a random coil
87
What does secondary structure provide the polypeptides chain with?
A level of mechanical stability
88
Why does secondary structure provide a level of mechanical stability?
Due to the presence of hydrogen bonds
89
What is tertiary protein structure?
The way the polypeptide chain coils and turns to deform a complex molecular shape
90
What causes tertiary structure?
Interactions between R groups
91
What is examples of interactions between R groups?
Hydrogen bonds, disulfirame bridges, ionic bonds and hydrophobic interactions
92
What is important for tertiary structure?
Relative amino acid positions
93
What is tertiary structure important for?
The function of the protein
94
What is quarternary structure?
Multiple polypeptides or prosthetic groups may interact to form a single, larger, biologically active protein
95
What is a prosthetic group?
An inorganic compound involved in protein structure or function
96
What is a conjugate protein?
A protein containing a prosthetic group
97
What may hold quaternary structures together?
A variety of bonds
