7.3 Translation Flashcards

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1
Q

What are ribosomes made of?

A

Proteins and ribosomal RNA

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2
Q

Why are ribosomes made of proteins?

A

For stability

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3
Q

Why are ribosomes made of ribosomal RNA?

A

For catalytic activity

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4
Q

What do ribosomes consist of?

A

A large and small subunit

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5
Q

What does the small ribosome subunit consist of?

A

An mRNA binding site

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6
Q

What does the large ribosomal subunit consist of?

A

Three tRNA binding sites

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7
Q

What are the three binding sites on the large subunit called?

A

Aminoacyl (A) site
Peptidyl (P) site
Exit (E) site

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8
Q

Where can ribosomes be found?

A

Freely floating in the cytosol or bound to the rough ER

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9
Q

What are the two sizes of ribosomes?

A

Prokaryotes = 70S
Eukaryotes = 80S

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10
Q

What is the structure of the tRNA molecule?

A

A cloverleaf structure with four regions

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11
Q

What are the four regions of the tRNA molecules?

A

The acceptor stem
The anticodon
The T arm
The D arm

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12
Q

What does the acceptor stem carries?

A

An amino acid

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13
Q

What does the anticodon associate with?

A

The mRNA codon

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14
Q

How does the anticodon associated with the mRNA codon?

A

Via complementary base pairing

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15
Q

What does the T arm associate with?

A

The ribosome

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16
Q

How does the T arm associate with the ribosome?

A

Via the E, P and A binding sites

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17
Q

What does the D arm associate with?

A

The tRNA activating enzyme

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18
Q

What is the tRNA activating enzyme responsible for?

A

Adding the amino acid to the acceptor stem

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19
Q

What does each tRNA molecule bind with?

A

A specific amino acid

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20
Q

Where does the tRNA molecule bind with specific amino acids?

A

In the cytoplasm

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21
Q

What catalyses the binding between tRNA molecule and amino acid?

A

A tRNA activating enzyme

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22
Q

What is each amino acid recognised by?

A

A specific enzyme

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23
Q

Why may the enzyme recognise multiple tRNA molecules?

A

Due to degeneracy

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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

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25
Q

What is the function of the ATP in tRNA activation?

A

To create a high energy bond that is transferred to the tRNA molecule

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26
Q

What does the stored energy do in tRNA activation?

A

Provides the majority of the energy required for peptide bond formation during translation

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27
Q

What does the initiation stage of involve?

A

The assembly of the three components that carry out the process (mRNA, tRNA, ribosome)

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28
Q

In initiation, where does the small ribosomal subunit bind to?

A

The 5’- end of the mRNA

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29
Q

In initiation, up until what point does the small ribosomal subunit move along the mRNA?

A

Until it reaches the start codon

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30
Q

In initiation, what happens when the small ribosomal unit reaches the start codon?

A

The appropriated tRNA molecule bind to the codon via its anticodon

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31
Q

How does te tRNA molecule bind to the codon via its anticodon?

A

Complementary base pairing

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32
Q

In initiation, where does the large ribosomal subunit aligns itself to the tRNA molecule?

A

At the P site

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33
Q

In initiation, what does the large subunit do once it is at the P site?

A

Forms a complex with the small subunit

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34
Q

In elongation, what does the second tRNA molecule do?

A

Pairs with the next codon

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35
Q

In elongation, where does the second tRNA molecule pair with the next codon?

A

At the A site

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36
Q

In Elongation, what happens to the amino acid in the P site?

A

It is covalently attached to the amino acid in the A site

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37
Q

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

A peptide bond and condensation reaction

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38
Q

In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the P site?

A

It is now deacylated

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39
Q

What does deacylated mean?

A

No amino acid

40
Q

In elongation, after the tRNA in the p site attaches to the A site, what happens to the tRNA in the A site?

A

It carries the peptide chain

41
Q

What is the first thing that happens in translocation?

A

The ribosome moves along the mRNA strand by one codon position

42
Q

In what directions does the ribosome move along the mRNA strand in?

A

A 5’- 3’ direction

43
Q

In translocation, what happens to the deacylated tRNA?

A

It moves to the E site and is released

44
Q

In translocation, what happens to the tRNA molecule which is carrying the peptide chain?

A

It moves to the P site

45
Q

In translocation, now that the A site is unoccupied happens?

A

Another tRNA molecule attaches to the next codon in the unoccupied A site and the process is repeated

46
Q

What does termination involve?

A

The disassembly of the components and the release of a polypeptide chain

47
Q

When do elongation and termination stop repeating?

A

When the ribosome reaches a stop codon

48
Q

What do the stop codons recruit?

A

A release factor that signals for translation to stop

49
Q

In termination what is released?

A

The polypeptide

50
Q

In termination what does the ribosome disassemble back into?

A

It’s two independent subunits

51
Q

What does initiation and elongation do until it reaches the stop codon?

A

Continues in a repeating cycle

52
Q

In eukaryotes, what are the ribosomes separated from?

A

The genetic material

53
Q

What separates the ribosomes from the genetic material?

A

The nucleus

54
Q

After transcription, what must the mRNA transported from and how?

A

The nucleus via nuclear pores

55
Q

After transcription, what must the mRNA be transported prior to?

A

Translation

56
Q

What transports the mRNA from the nucleus after transcription?

A

The ribosome

57
Q

What does the transport of the mRNA after transcription require?

A

Modification to the RNA construct

58
Q

Why does transcription and translation need not to be separated in prokaryotes?

A

As they lack compartmentalised structures

59
Q

When may ribosomes begin translating the mRNA molecule in prokaryotes?

A

While it is still being transcribed from the DNA template

60
Q

Why is it possible for ribosomes to begin translating the mRNA molecule while it is still being transcribed from the DNA template?

A

Because both transcription and translation occur in a 5’ - 3’ direction

61
Q

What is a polysome?

A

A group of two or more ribosomes translating an mRNA sequence simultaneously

62
Q

How do polysomes appear?

A

As beads on a string

63
Q

What are the beads?

A

Ribosomes

64
Q

What is the string?

A

The mRNA strand

65
Q

When may polysomes form in prokaryotes?

A

While the mRNA is still being transcribed from the DNA template

66
Q

Ribosomes at which end of the polysome cluster will have a longer polypeptide chain?

A

The 3’ end

67
Q

In eukaryotic cells, how are all proteins produced initially synthesised?

A

By ribosomes found freely circulating within the cytosol

68
Q

When would the ribosome remain free and unattached?

A

If the protein is targeted for intracellular use within the cytosol

69
Q

When would the ribosome become bound to the ER?

A

If the protein is targeted for secretion, membrane fixation or use in lysosomes

70
Q

What determines protein destination?

A

The presence or absence of an initial signal sequence on a nascent polypeptide chain

71
Q

What does SRP do?

A

Halts translation

72
Q

What does the presence of the signal sequence that determines protein destination result in?

A

The recruitment of a SRP

73
Q

Where does the SRP-ribosome complex dock?

A

At a receptor located on the ER membrane

74
Q

What happens when the SRP ribosome complex docks on the ER membrane?

A

Translation is re-initiated and the polypeptide chain continues to grow

75
Q

Once translation is re initiated, how does the polypeptide chain continue to grow?

A

Via a transport channel into the lumen of the ER

76
Q

Once translation is re-initiated, where will the synthesised protein be transported and how?

A

To the Golgi complex or the lysosome via a vesicle

77
Q

Once translation is re-initiated, where do the proteins targeted for membrane fixation get embedded?

A

Into the ER membrane

78
Q

In protein destination, what happens once the polypeptide is completely synthesised within the ER?

A

The signal sequence is cleaved and the SRP is recycled

79
Q

How many structures of protein are there?

A

Four

80
Q

What is primary structure of protein?

A

The order/ sequence of amino acids which comprise the polypeptide chain

81
Q

What forms the primary structure of protein?

A

Covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids

82
Q

What does primary structure control?

A

All subsequent levels of protein organisation

83
Q

Why does the primary protein structure determine all levels of protein organisation?

A

It determines the nature of the interactions between R groups of different amino acids

84
Q

What is secondary protein structure?

A

The way a polypeptide folds in a repeating arrangement to form alpha helices and beta sheets

85
Q

What causes the folding in secondary protein structure?

A

Hydrogen bonding between the amine and carboxyl groups of non adjacent amino acids

86
Q

How will sequences that do not form either an alpha helix or beta pleated sheet exist?

A

As a random coil

87
Q

What does secondary structure provide the polypeptides chain with?

A

A level of mechanical stability

88
Q

Why does secondary structure provide a level of mechanical stability?

A

Due to the presence of hydrogen bonds

89
Q

What is tertiary protein structure?

A

The way the polypeptide chain coils and turns to deform a complex molecular shape

90
Q

What causes tertiary structure?

A

Interactions between R groups

91
Q

What is examples of interactions between R groups?

A

Hydrogen bonds, disulfirame bridges, ionic bonds and hydrophobic interactions

92
Q

What is important for tertiary structure?

A

Relative amino acid positions

93
Q

What is tertiary structure important for?

A

The function of the protein

94
Q

What is quarternary structure?

A

Multiple polypeptides or prosthetic groups may interact to form a single, larger, biologically active protein

95
Q

What is a prosthetic group?

A

An inorganic compound involved in protein structure or function

96
Q

What is a conjugate protein?

A

A protein containing a prosthetic group

97
Q

What may hold quaternary structures together?

A

A variety of bonds