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Biology > 7.3 > Flashcards

7.3 Flashcards

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1
Q

When does translation start

A

when mature mRNA binds to a small ribosomal subunit at the mRNA binding site

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2
Q

what is the initiation codon for mRNA

A

AUG (methionine) which can be like to the initiator tRNA

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3
Q

what happens when a tRNA molecule binds to its corresponding amino acid

A

it forms a complex called an aminoacyl- tRNA

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4
Q

what happens at initiation of translation

A

mRNA binds to a small ribosomal subunit

the anticodon of the initiator tRNA binds to the codon of the mRNA

finally, the large ribosomal subunit joins to complete the assembly o the translation complex

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5
Q

what are the three different sites

A

E P and A

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6
Q

what do the sites E P and A stand for

A

Exit

peptide - tRNA

Aminoacyl - tRNA binding site,

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7
Q

what is the E site

A

where the tRNA moves after transferring its amino acid to the growing polypeptide chain, ready to exit the ribosome

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8
Q

what is the A site

A

where the incoming tRNA with its attached amino acid binds, while the P site is where the tRNA from the A site moves after its amino acid forms a peptide bond with the growing polypeptide chain

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9
Q

What is the P site

A

where the TRNA from the A site moves after its amino acid forms a peptide bond with the growing polypeptide chain

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10
Q

where is the tRNA holding the growing polypeptide chain found

A

at the P site

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11
Q

what takes place during elongation

A

involves a repeated cyclic of events

a new aminoacyl tRNA comes in and binds to the A site. this carries a specific amino acid that matches to the codon on the mRNA and the anticodon on the rRNA

then the new amino acid is joined to the existing polypeptide chain by a peptide bond

the tRNA that was bound to the polypeptide chain is now ready to be recycled as it is no longer bound to an amino acid

the ribosome translocates the tRNA holding the growing amino acid chain from the A site to the P site, this shifts the empty tRNA to the E site where it can leave or be recycled and the process starts again until the ribosomes reaches the termination codons

UAG

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12
Q

what is the final stage of termination

A

a release factor binds in the A site and causes the disassembly of the components of the translation complex. all of these components can be reused for another translation complex,

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13
Q

What is the first event to take place in translation in eukaryotes?

A

The small subunit of the ribosome recognises and attaches to the initiator codon of mRNA

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14
Q

During which stage of translation does a release factor bind to the ribosome?

A

termination

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15
Q

what are ribosomes consisted of

A

a small and large subunit with three bindings sites for tRNA molecules

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16
Q

what is tRNA

A

a single stranded RNA molecule that folds on itself to form a cloverleaf shaped structure with double stranded regions and three hairpin loops.

one of the loops contains a sequence called the anticodon which binds to the mRNA conons.

each tRNA has a corresponding amino acid attached to the 3’ end of CCA.

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17
Q

what is found at the 3’ end of the tRNA

A

CCA

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18
Q

what bond forms between the amino acid and CCA

A

ester bond

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19
Q

The triplet of bases at the amino acid binding site of tRNA is:

A

5’ CCA 3’

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20
Q

How many permanent loops does a tRNA molecule have?v

A

3

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21
Q

What describes the subunits of eukaryotic ribosomes?

A

A small subunit which binds mRNA and a large subunit with three tRNA binding sites.

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22
Q

what is knowns as the tRNA activating enzyme

A

the enzyme aminoacyl tRNA synthetase

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23
Q

how many different tRNA activating enzymes are there

A

20 for each 20 different amino acids

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24
Q

how does the specificity of the tRNA and the matching anticodon happen

A

based on the match between the shape of the particular amino acid and the enzyme

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25
Q

Aminoacylation of a tRNA molecule

A

hydrolysis of an ATP molecule provides energy fro the reaction

ATP + H2O - AMP and PP (pyrophosphate)

when phosphates are removed from ATP molecules, energy is released for use by the cell

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26
Q

what is a tRNA called once is is attached to an amino acid

A

it is called a charged tRNA molecule

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27
Q

what are free ribosomes

A

produce proteins use mainly within the cell

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28
Q

what are bound ribosomes

A

synthesis proteins mainly meant for recreation or for use in lysosomes

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29
Q

where are proteins synthesized on the bound ribosomes usually found

A

in the ER, Golgi apparatus, lysosomes and plasma membrane

30
Q

when does translation start

A

once the mRNA attaches itself to the ribosome

31
Q

what recognizes the signal sequence

A

signal recognition particle (SRP)

32
Q

what does the SP do once recognizing the sequence

A

it binds to the SRP recognition protein on the endoplasmic reticulum

allowing the polypeptide to enter the rough ER as it grows in length

33
Q

what happens when translation ends

A

the translation complex disassembles, the whole polypeptide is taken into the RER

34
Q

where does post translational modifications take place

A

in the lumen of the ER

35
Q

where are free ribosomes usually found or destined to function in

A

the mitcohondria, chloroplasts, cytoplasm, nucleus of the cell

36
Q

where do translation and transcription take place in bacteria

A

in the same place due to the absence fo a nuclear membrane.

37
Q

what is a polysome

A

a structure formed where multiple ribosomes can attach to the same mRNA to produce proteins at a faster rate

38
Q

What is a function of the signal recognition particle (SRP)?

A

To help translocate polypeptides across the ER membrane

39
Q

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by:

A

A signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane

40
Q

Actin and myosin are proteins found in muscle cells. Where would they be synthesised?

A

Free ribosomes in cytoplasm of muscle cells

41
Q

how many different amino acids make up a polypeptide

A

around 20

42
Q

what is the primary structure of a protein

A

the sequence and the number of amino acids in the polypeptide

43
Q

what is the primary structure of a protein

A

the sequence and the number of amino acids in the polypeptide

44
Q

what bonds form between amino acids in poly peptides in the primer structure

A

peptide bonds

45
Q

what is the secondary structure

A

formed when the polypeptide chain folds back on itself into a helices or b pleated sheets

46
Q

how are secondary structures stabilized

A

by hydrogen bonds between the -NH groups) and the - C=O groups

47
Q

what is the tertiary structure

A

further folding, forming a 3 dimensional shape

48
Q

how is the tertiary structure stabilized

A

by interactions between the R groups

49
Q

what r groups will associate together

A

polar as they are all hydrophilic

non polar as they are hydrophobic

50
Q

what types of interactions happen between polar R groups

A

ionic interactions between acidic and basic R groups or hydrogen bonds

51
Q

what bonds form between r groups that contain sulfur

A

covalent bond

also known as

disulfide bridges

52
Q

what amino acids contain sulphur in their r groups

A

cysteine and methionine

53
Q

where would covalent bonds form in amino acids

A

between r groups that contain sulphur

54
Q

where are the hydrophilic amino acids located in tertiary structures

A

located on the outside of the protein and the hydrophobic amino acids are located in the center of the protein away from the watery cytoplasm

55
Q

what is an example of a tertiary strcucture

A

lysozyme

56
Q

what bonds appear when the r group contains sulfur

A

disulfide bonds

57
Q

what are quaternary structures

A

more than one polypeptide chains,

58
Q

example of quaternary structure

A

hemoglobin - 2 a chains, 2 b pleated chains and four heme groups

59
Q

what is attached to quaternary proteins

A

non protein units called a co factor that is tightly attached,

60
Q

what is the co-factor in hemoglobin

A

heme - the iron containing prosthetic group

61
Q

what is a conjugated protein

A

a protein with a prosthetic groups attached

62
Q

What aspects of protein structure are stabilised or assisted by hydrogen bonds?

A

secondary , tertiary and quaternary

63
Q

Tertiary structure of proteins depends primarily on which structural component of amino acids?

A

r groups

64
Q

what is said about termination codons found on mRNA

A

there are no anticodons that complement termination codons found on mRNA

65
Q

how many nucleotides code for one specific amino acid

A

3

66
Q

where is initiator tRNA never found in translation

A

at the A binding site

67
Q

whats to tRNA activating enzymes do

A

they bind to the amino acid to the corresponding tRNA by hydrolysis of ATP and gaining one phosphate molecule. The phosphate molecule is released from App through hydrolysis and then added to the enzyme

68
Q

What does charging tRNAs involve

A

it is accompanied by pyrophosphate release during the charging cycle

69
Q

where are amino acids joined together during translation

A

at the P site by a peptide bond

70
Q

where does the second tRNA pair with the next codon

A

at the A site

Biology (51 decks)

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