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MSI Unit I > 1-26 Protein Synthesis > Flashcards

1-26 Protein Synthesis Flashcards

1
Q

Start codon for translation

A

AUG

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2
Q

what does “the code is degenerate” mean?

A

there are more codons than amino acids, several codons can code for the same amino acids

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3
Q

translation of mRNA goes from

A

5’ to 3’

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4
Q

Codon table trends

A

right - hydrophobic
charged - left/lower left

middle - polar

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5
Q

what does the start codon do

A

AUG - indicates where synthesis will start and establishes the reading frame

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6
Q

silent mutations

A

does not change the actual amino acid, generally a change in the third letter

however, this mutation can effect the rate of translation, which alters polypeptide folding, leading to proteins with different 3d structure.

this can change the properties of the protein

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7
Q

transcription

A

segment of DNA is transcribed into an mRNA by RNA polymerase

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8
Q

Translation

A

mRNA is decoded at/by ribosome to create polypeptides to form protein

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9
Q

describe tRNA structure

A

cloverleaf stabalized by watson crick pairing

base pairing between 5’3 forms the acceptor

anticodon loop in middle interacts with codon of mRNA

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10
Q

aminoacyl tRNA synthetase

A

enzyme that charges tRNA to amino acid with high energy bond.

uses ATP which gets hydrolyzed to AMP

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11
Q

ribosomes are comprised of

A

a large and small subunit

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12
Q

how many binding sites does the ribosome have for tRNA

where?

A

3

Exit, Peptidyl, Aminoacyl

at the interface of the small and large subunit

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13
Q

how do bacteria know which AUG to use?

A

the shine-delagno sequence just upstream (g-rich) of the correct AUG.

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14
Q

how do eukaryotes know which AUG to usee?

A

eukaryotic mRNA has a 5’ cap in the 5’ UTR, this tells ribosome that downstream is the correct AUG

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15
Q

how is mRNA read in bacteria and eukaryotes?

A

bacteria - linearly

eukaryotes - read in circle. Poly A- tail binds to 5’ cap during reading. can be read by several at the same time, increasing efficiency.

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16
Q

what additional factors help transcription?

A

Initiation factors (IF), elongation factors (Ef-), and Termination/release factors (RF-)

eurkaryotes have an “e” before.
eIF, eEF, eRF ad more of them

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17
Q

initiation (Genera)

A
  1. mRNA binds to small ribosomal subunit and is aligned with correct reading frame
  2. initiator amino-acyl tRNA binds
  3. ribosome assembles from small and large subunits
18
Q

the 30s initiation complex

A

eIF-2-GTP initiator tRNA binds to small subunit

circular mRNA binds, ribosome searches for start codon

GTP hydrolyzed, releases the initiation factors

large subunit binds, leaving the initator tRNA in P site

19
Q

elongation

A
  1. aminoacyl tRNA binds and checks codon-anticodon match
  2. new peptide bond Is formed.
  3. Growing chain is translocated from A site to P side, mRNA pulled so next codon is exposed to A site. 4.

Catalytic rRNA of the ribosome creates the peptide bond, no additonal energy needed.

tRNA comes in, peptide bond formed (transpeptidation), mRNA gets pulled so next codon exposed to A site, shifted by one.

20
Q

describe transpeptidation

A

does not require additional energy, uses the energy from the high energy amino acyl tRNA.

Reaction is catalyzed by the ribosome itself (ribozyme activity).

21
Q

the growing chain is translocated from

A

the A site to the P site

22
Q

where is the peptide bond formed?

A

to the c-terminus of the growing chain

23
Q

Termination

A
  1. stop codon in A site
  2. release factor binds A site
  3. release factor brings in water to hydrolyze peptide chain and released. (the water mimics an incoming amino acid)
  4. the complex dissociates
24
Q

rate of translation in eurkayotes vs bacteria?

A

rate faster in bacteria

25
Q

rate limiting step?

A

hydrolysis of GTP bound to Elongation factor (Ef-Tu)

as well as proofreading

26
Q

describe the high energy cost of protein syntehsis

A

Charging tRNA takes ATP
Initiation takes one GTP and unknown ATP
Elongation takes two GTP per amino acid incorporated
Termination takes one GTP to release
Unknown amount for proofreading/proper folding

27
Q

describe a major way that protein syntehsis is regulated

minor way?

A

the lifetime of mRNA

at the level of translation

28
Q

what can inhibit protein synthesis?

A

toxins

29
Q

two cases where protein synthesis is regulated at the level of translation

A
  • at translation initiation controlling the phosphorylation of elongation factor 2 (heme and HCI inhibitor)
  • sequence elements within the mRNA structure - enzymes will chew on poly-a tail. once the tail is degraded, in eukaryotes it will come apart from the 5’cap and the mrna will quickly be degraded
30
Q

since protein synthesis is so expensive, its generally controlled at the

A

initiation step, ussually by regulating the availabilty of eIF-2. when phosphorylated by specific kinases, decreases the rate of synthesis.

31
Q

Ferritin/transferrin is an example of

A

regulatory elements within the structure of the eukaryotic mRNA

32
Q

interferons

A

viruses produce dsRNA, which is not normally present in cells. this signals the cell that it is infected and induces secretion of IFN’s.

IFN’s bind to surfaces of other cells and induce expression of two new enzymes that when in the precense of dsRNA, inhibit protein synthesis.

33
Q

What happens when eIF-2 is phosphorylated?

A

Inhibition of translation

34
Q

The _______ of an mRNA usually contains elements that influence translational efficiency, whereas the _____ usually affects mRNA stability.

A

5’ UTR = translational efficiency (shine delgano, etc..)

3’UTR - mRNA stability (poly a tail)

35
Q

All mature tRNA molecules have a CCA sequence at their 3’-ends. t/f?

A

t

36
Q

During protein synthesis, the newly synthesized peptide is covalently bound to

A

tRNA

37
Q

If you were developing a new antibiotic that specifically targeted bacterial protein synthesis and did not affect eukaryotic protein synthesis, which of the following enzymes, structures, or molecules would be good targets?

A

an enzyme that formylates the initiator methionine

38
Q

Activation of an amino acid prior to its incorporation into a polypeptide chain

A

C. involves transient formation of an aminoacyl-AMP intermediate before the amino acid is transferred to tRNA.

39
Q

GTP, which is used during the translation process,

A

D. is hydrolyzed to GDP, which causes a conformational change of translation factors¸ usually allowing them to dissociate from the ribosome.

40
Q

Interferons cause decreased synthesis of viral proteins by which of the following mechanisms?

A

D. inhibition of translation of both host and viral proteins by phosphorylation of eIF-2

41
Q

codons are read

A

5-3

42
Q

anticodons are read

A

3-5

MSI Unit I (52 decks)

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