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Cell and Molecular Biology > Protein Synthesis > Flashcards

Protein Synthesis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

When and who provided evidence that DNA carries genetic information?

A

1994

Avery

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2
Q

What happened in 1966

A

Nirenberg, Ochoa, and Khorona elucidate the genetic code

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3
Q

Give the rules of the genetic code

A

1) Three bases encode one amino acid = codons
2) The code is non-overlapping
3) The code is degenerate ue some amino acids are specified by more than one codon

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4
Q

How many codons are there which code for amino acids?

A

61 codons for 21 amino acids

The others are stop codons

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5
Q

How many possible reading frames are there for one peice of DNA?

A

3

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6
Q

What is the start codon and which amino acid does it code for?

A

AUG = methionine

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7
Q

What are the three stop codons?

A

UAA
UAG
UGA

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8
Q

What do the tRNAs bind to?

A

One end base pairs with the codon = the anticodon loop

The other end (3’) end carries the amino acid

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9
Q

What gives tRNA its structure?

A

Intermolecular base pairing

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10
Q

Although tRNAs have a similar structure what varies?

A

The nucleotides vary, even with in the double stranded regions

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11
Q

Describe the structure of the tRNA molecules

A

Have a D loop, Anticodon loop and T loop

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12
Q

How are tRNAs modified?

A

Psuedouridine

Dihydrouridine

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13
Q

There are over 50 modifictions of tRNAs. What are their roles?

A

They affect the accuracy with which the tRNA is attached to the correct amino acid
They can facilitate the recognition of the appropriate mRNA codon by the tRNA molecule

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14
Q

True or false - there is a 1:1 ratio of tRNA per codon

A

FALSE

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15
Q

What allows the same tRNA anticodon to bind to more than one codon?

A

Wobble base pairing at position 3

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16
Q

Give one way that a wobble is made by modification

A

Deamination of A creates an inosine which can pair to U, C or A

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17
Q

How many tRNAs do bacteria have?

A

31

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18
Q

Coupling of the amino acid to tRNA is achieved by what?

A

Aminoacyl-tRNA synthetases

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19
Q

What are the steps of coupling amino acid to tRNA?

A

1) The amino acid is firstly activated by the linkage of AMP to the carboxyl group = adenylated amino acid
2) AMP linked carboxyl group is transferred to the hydroxyl group on the 3’ tRNA forming an ester linkage
This forms aminoacyl-tRNA

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20
Q

Aminoacyl tRNA is also known as what and why?

A

Charged tRNA

Because the energy of ATP hydrolysis is still contained in the ester linkage

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21
Q

Translation of mRNA to amino acids requires how many adapters?

A

2

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22
Q

What are the two adapters used?

A

1) Synthetase that pairs the correct amino acid to the correct RNA
2) tRNA that pairs the correct codon to the correct amino acid within the ribosome

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23
Q

Which terminus are new proteins added on to?

A

The C terminus

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24
Q

What are the two subunits of ribosomes?

A

The large subunit

The small subunit

25
Q

What is the role of the large subunit?

A

It catalyses polymerisation

26
Q

What is the role of the small subunit?

A

Facilitates tRNA/ mRNA interaction

27
Q

Why is the formation of each new peptide bond energetically favourable?

A

The growing C terminus has been activated by the covalent attachment of a tRNA molecule

28
Q

What are the sites of the large ribosomal sub unit?

A

E
P
A

29
Q

Where do charged tRNAs enter?

A

At the A site - they leave uncharged at the E site

30
Q

How many tRNAs are in the ribosome at any one time?

A

2

31
Q

Give the steps that occurs in translation at the ribosome

A

1) Charged tRNAs enter at the A site
2) Peptidyl transferase catalyses amino acid addition and conformational changes move the tRNAs the the E and P sites
3) Conformational changes move the small subunit three nucleotides a long
4) tRNA leaves the E site

32
Q

What are elongation factors?

A

They help translation and improve accuracy

33
Q

Once an anticodon is bound, how does EF-1 causes what two delays before peptidyl transferase can act?

A

1) First GT must be hydrolysed to GDP

2) Then it has to dissociate from the tRNA

34
Q

What are elongation factors called in eukaryotes and bacteria?

A 
Eukaryotes = EF-1 and EF -2 
Bacteria = EF-Tu and EF-G
35
Q

Why are the time lags important?

A

It gives time for incorrectly bound tRNAs to fall off

Some of the correct tRNAs may also fall off but at a slower rate

36
Q

The hydrolysis of GTP occurs more rapidly of what has happened?

A

If the codon and anticodon are incorrectly matched

37
Q

If synthesis occurs in the absence of EF-1 what happens?

A

There are more errors in the proteins sequence

38
Q

What is a ribozyme?

A

An RNA that catalyses a reaction

39
Q

Methionone tRNA assembles what?

A

The ribosome

40
Q

Only which tRNA with EiF-2 can bind to which subunit alone?

A

Met tRNA

41
Q

mRNA has a cap and a tail which are bound by what?

A

eIF-4G and eIF-4E

This forms a loop

42
Q

The loop formation is a checkpoint for what?

A

Broken mRNA

43
Q

How far apart are ribosomes spaced apart on a polysome?

A

80 nucleotides apart

44
Q

Stop codons are recognised by what?

A

Release factors

45
Q

What are release factors?

A

They look like charged tRNAs - molecular mimicry and enter the A site
This causes dissociation of the ribosome

46
Q

When does protein folding begin?

A

Immediately after leaving the ribosome

47
Q

Many proteins initially fold in to what?

A

The molten globule which is roughly the correct confirmation

48
Q

Misfolded proteins can lead to aggregation? How?

A

They have exposed hydrophobic regions that can lead to aggregation

49
Q

What are the two major classes of molecular chaperones?

A

hsp60

hsp70

50
Q

Why are they called heat shock proteins?

A

Their expression is elevated when the temperature is raised above the normal level

51
Q

Why do chaperones function during normal folding as well as when a cell has been heated?

A

Because at high temperatures the proteins denature

52
Q

How does the hsp70 class work?

A

Directly on proteins as they exit the ribosome binding to exposed hydrophobic amino acids

53
Q

What does the hsp60 family do?

A

Put misfolded proteins into isolation

54
Q

How does the HSP60 family work?

A

1) The hydrophobic entrance binds to the protein partially unfolding it
2) The GroES cap then seals the protein inside for about 15 seconds to allow refolding

55
Q

What is poluubiuitination?

A

Marks translation failures for destruction in the proteosome

56
Q

How many newly synthesised proteins are immediately recycled?

A

As much as 1/3 synthesised proteins

57
Q

Protein aggregated cause what and why?

A

Diseases and cell death

They are large and protease resistant, and can sometimes cause a chain reaction to misfold more proteins

58
Q

Give examples of diseases associated with protein aggregates

A

CJD
Huntingtons
Alzheimers

Cell and Molecular Biology (17 decks)

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