Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOL 200 - Molecular Biology > Lecture 28 - Protein Synthesis I > Flashcards

Lecture 28 - Protein Synthesis I Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Which critical quality control mechanism takes place once the mRNA has passed through the NPC?

A

Pioneer Round (of Transcription)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What response do premature stop codons trigger?

A

Non-Sense Mediated Decay Response (NMD)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What type of RNA constitutes the largest proportion of total RNA in the cell? What percent is it?

A

rRNA (80%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are pre-rRNA transcription units arranged in?

A

Repetitive Clusters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What can be said about the structure of the ribosome between different organims?

A

It is highly conserved.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How big are the large and small ribosomal subunits (in S)?

A

60S and 40S respectively

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which ribosomal subunit contains the 28S rRNA and the 5S rRNA?

A

Large Subunit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Which ribosomal subunit consists of proteins associated with 18S rRNA?

A

Small Subunit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the only difference between the 80S eukaryotic ribosome and prokaryotic ribosomes?

A

The only difference is the sizes of some of the subunits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What do Svedburg units (S) describe?

A

They describe where proteins sediment in a centrifugal gradient.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What type of secondary structure does rRNA take on?

A

It folds into conserved and complex stem-loop secondary structures.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the importance of tRNA?

A

It acts as the bridge between the mRNA sequence and the amino acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the stem-loop at the bottom of a tRNA called?

A

Anticodon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the amino acid attachement site of tRNA?

A

It is the site where the CCA trinucleotide is added to the 3’ end of the tRNA. It is where the amino acid is attached.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the role of the anticodon?

A

Its job is to recognize the codon in the mRNA through antisense recognition and Watson-Crick base pairing.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does aminoacyl-tRNA synthetase do and how does it do it?

A

It attaches the amino acid to the 3’ adenosine on the tRNA. It does so by bring the right amino acid in proximity to the appropriate tRNA by interacting with its anticodon and regions along the stem, catalyzing a high-energy an ester bond at either the 2’ or 3’ site on that 3’ end of the tRNA (the added CCA trinucleotide). As a result, you end up with a bound tRNA: a charged or activated tRNA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How many aminoacyl-tRNA synthetases are there?

A

20

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How many possible codons are there?

A

64

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How many stop codons are there?

A

3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Which tRNA initiates translation?

A

tRNAiMet

21
Q

What is different about tRNAiMet?

A

It has a formyl group attached to it.

22
Q

What are the three sites of the ribosome?

A

A (aminoacyl site), P (peptidyl transferase site) and E (exit site)

23
Q

What class of proteins are needed for the initiation of protein synthesis?

A

Eukaryotic Initiation Factors (eIF)

24
Q

Which eukaryotic initation factors are associated with the small 40S subunit?

A

eIF1, eIF1a, and eIF3

25
Q

How is the preinitation complex for protein synthesis set up? What is this regulated by?

A

eIF2 in its GTp bound state binds to the tRNAiMet to form a complex. These with another initating factor (eIF5) will interact with the small 40S ribosomal subunit (already bound by eIF1, eIF1a, and eIF3). All together, they will form the 43S preinitation complex. This is regulated by the phosphorylation of eIF2.

26
Q

What do starved cells do to eIF2? What does this lead to? Why does the cell do this?

A

Starved cells provide a signal to eIF2 by phosphorylating its serine 51 residue. This phosphorylation on eIF2 blocks its ability to maintain a GTP-bound state making it unable

to interact with tRNAiMet to make the first step in protein synthesis happen. The cell does this because the last thing it would want to do when starved is use energy to make proteins.

27
Q

How does the 5’ cap contribute to translational initation?

A

The 7-methylguanylate cap at the 5’ end of the mRNA serves to stabilize and protect the mRNA from degradation. It is a tag for critical proteins that are required for translation.

28
Q

How was it proven that a protein binds specifically to the 7mGDP cap on mRNA?

A

Sonenberg performed purification of proteins that interacted with the cap structure by covalently linking proteins onto beads and doing SDS-page. He found things that interact specifically to the 7mGDP cap on the mRNA. Addition of this purified protein to capped mRNAs in translation reaction (in vitro) enhanced the efficiency of translation.

29
Q

What did Sonenberg demonstrate?

A

Sonenberg demonstrated the important of the cap-binding protein as well as the proteins involved in its regulation and their importance in maintaining normal cellular homeostasis.

30
Q

In which complex is cap-binding protein found?

A

eIF4

31
Q

What task does eIF4 perform?

A

eIF4 is instrumental in recruiting an mRNA to the preinitiation complex.

32
Q

What is eIF4 made up of?

A

eIF4E (cap-binding protein), eIF4A (RNA helicase), eIF4G (acts as a scaffold), and eIF4B (stabilizes the structure and enhances eIF4A helicase activity)

33
Q

How does eIF4 form a stable complex with the mRNA?

A

It forms a complex through the interaction between eIF4E and the 5’ cap of mRNA.

34
Q

What does the 5’ end of mRNA do after binding eIF4?

A

It interacts with the 3’ end of the mRNA through cytoplasmic proteins that bind to the poly A tail, the poly A binding proteins C (PABPC).

35
Q

Why is mRNA forming loops advantageous?

A

The loops maintain the efficiency of translation due to the proximity of the factors; it facilitates the restarting of translation.

36
Q

Why can mRNA loops with a lot of adenosine maintain their circular structures longer?

A

It takes more time for the deadenylase complex to degrade/chew up enough adenosine to reach the threshold point.

37
Q

What happens when a poly A tail is degraded past its threshold point?

A

A smaller number of PABPCs will not allow for sufficient interactions with the 3’ poly A tail of mRNA meaning no loops will be formed with the 5’ end. The 5’ end of the mRNA will then become vulnerable to decapping and degrading proteins in a 5’ to 3’ manner.

38
Q

What is being formed while eIF4 is interacting with the 5’ end of the mRNA?

A

The 43S Preinitation Complex

39
Q

How does the 43S preinitiation complex attach to the mRNA?

A

The complex attaches to the 5’ end of the mRNA by an interaction between eIF3 and eIF4G.

40
Q

When does the RNA helicase activity of eIF4A become active?

A

It becomes active when the 43S preinitiation complex attaches to the 5’ end of the mRNA.

41
Q

Which eIF removes any secondary structures from the UTR in the 5’ end of the mRNA?

A

eIF4A

42
Q

What is the sequence of the start codon?

A

UAG

43
Q

What does the pairing of the Shine-Galgarno box and the 16S rRNA result in?

A

It results in a match of the AUG codon with the initator tRNA in bacteria.

44
Q

What conserved sequence around the start codon in mammals helps the scanning complex recognize that start codon?

A

KOZAK Sequence (ACCAUGG)

45
Q

What conformational change occurs when the scanning complex finds the start codon? What does this give rise to?

A

eIF2 changes conformation due to GTP hydrolysis. With its conformational change, eIF2 will give rise to the dissociation of almost all initation factors from the 48S initation complex.

46
Q

What interacts with the 48S intiation complex after eIF2’s conformation changes due to GTP hydrolysis?

A

The Large Ribosomal Subunit

47
Q

What is the ribosomal complex referred to as when eIF1A and eIF5B leave the complex?

A

80S Initation Complex

48
Q

What ribosomal complex will switch from an initation to an elongation phase?

A

80S Initation Complex

BIOL 200 - Molecular Biology (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions