CH 21: Biosynthesis of Proteins (Translation)

Question 1

Translation

What is translation?

Answer 1

the RNA-directed process of protein synthesis

Question 2

Translation

What is the direction of translation of mRNA?

Answer 2

5’ –> 3’

Question 3

Translation

What is the direction of protein synthesis?

Answer 3

N –> C

Question 4

Genetic Code

What amount of nucleotides does the gentic code for proteins consist of?

Answer 4

Triplets of Nucleotides

Question 5

Gentic Code

How many codons are in the genetic code?

Answer 5

64

Question 6

Genetic Code

How many codons code for AA?

Answer 6

61

Question 7

Genetic Code

What are the 3 termination/stop codons?

Answer 7

UAA
UGA
UAG

Question 8

Genetic Code

What is the start/initiation codons?

Answer 8

AUG (Met)

Question 9

Genetic Code

What are the 3 characteristics of the genetic code?

Answer 9

Continuity: the genetic code reads as a long series of 3-letter codons that have no spaces or punctuation and never overlap

Redundancy: several different codons can code for the same AA. Only Met and Trp have single codons. However, no single codon can code for multiple AA

Universality: the genetic code is the same in almost all living organisms from bactera to mammals (with a few exceptions like mitrochondria which have have different codes)

Question 10

Transfer RNA

What does tRNA do?

Answer 10

acts as an adaptor to translate mRNA into protein

Question 11

Transfer RNA

What enzyme activates AA for synthesis by attachment to tRNA?

Answer 11

aminoacyl-tRNA synthetase

aminoacyl-tRNA is also called charged tRNA and is the AA ester of tRNA

Question 12

Transfer RNA

How many different aminoacyl-tRNA synthetases are there?

Answer 12

20, one for each AA

Question 13

Transfer RNA

Where do AA attach to on adenine residue of tRNA?

Answer 13

2’-hydroxyl for synthetase I

3’-hydroxyl for synthetase II

Question 14

Transfer RNA

What do most of the aminoacyl-tRNA synthetases have and what is the error frequency of protein synthesis?

Answer 14

Proofreading function, 10^-4

Question 15

Molecular Regocnition of COdons in mRNA by tRNA

What is the codon sequence complimentary with?

Answer 15

The anticodon sequence

Question 16

Molecular Regocnition of COdons in mRNA by tRNA

How does the codon in mRNA pair with the anticodon of tRNA?

Answer 16

using hydrogen bonding

Question 17

Molecular Regocnition of COdons in mRNA by tRNA

How are two RNA segments allined with each other?

Answer 17

antiparallel

Question 18

Molecular Regocnition of COdons in mRNA by tRNA

What are wobble hypothesis pairing in tRNA/mRNA?

Answer 18

Where non-canonical base pairs happen on the 3rd base due to alternate pairings.

Question 19

Ribosomes

Where does protein synthesis take place?

Answer 19

ribosomes

Question 20

Ribosomes

How many subunits do ribosomes have?

Answer 20

2: 1 large (catalyzes the peptide bond formation) and 1 small (binds mRNA and tRNA)

Question 21

Ribosomes

In ribosome subunits, what does the S mean?

Answer 21

S is the unit of sedimentation coefficients that helps show the proteins MW and shape.

Question 22

RIbosomal Subunits

What does the large subunit do?

Answer 22

catalyzes the formation of the peptide bond

Question 23

RIbosomal Subunits

What does the small subunit do?

Answer 23

matches the tRNA to mRNA based on codon/anticodon

Question 24

RIbosomal Subunits

What do the ribosomal subunits do as a system?

Answer 24

move along mRNA adding AA to grow the protein chain

Question 25

RIbosomal Subunits

What are the 4 binding sites of ribosomal subunits?

Answer 25

mRNA binding site: on the small ribosome subunit

Peptidyl-tRNA binding site (P-site): holds tRNA attached to growing end of the protein

Aminoacyl-tRNA binding site (A-Site): holds incoming AA (charged tRNA)

Exit site (E-site)

Question 26

Initiation Process

Where/how do eukaryotic and bacterial translation differ?

Answer 26

At the initiation step (eukaryotic use Met while bacteria use fMet)

Question 27

Initiation in Prokaryotes

What is the initiation guided by in the mRNA?

Answer 27

Shine-Dalgarno (S-D) sequence

ribosomal binding site located around 8 bases upstream of start codon

Question 28

Initiation in Prokaryotes

What does the S-D sequence help with?

Answer 28

recruiting the ribosome to the mRNA for initiating protein synthesis (aligning them as well, small subunits first then large)

Question 29

Initiation in Eukaryotes

Why do initiation factors (eIFs) and other proteins bind to the 5’ cap and 3’ polyAtail of mRNA?

Answer 29

To make sure that both ends are intact before starting

Question 30

Eukaryoitc vs Prokaryotic

What is the difference between eukaryotic and prokaryotic protein synthesis?

Answer 30

Prokaryotic: have to 5’cap which tells where to begin (uses S-D instead). Is Polycistronic (forms multiple proteins from same mRNA)

Eukaryotic: monocistronic (forms one polypeptide per mRNA)

Question 31

Protein Release

When is the protein released?

Answer 31

When a stop codon is encountered

Question 32

Protein Release

How are the proteins released?

Answer 32

The cytoplasmic release factors recognize and bind to the stop codon, when the ribosome gets to the codon it adds H2O instead of AA which ‘breaks’ the ribosome

Question 33

Polyribosome

What is a polyribosome?

Answer 33

Where, as the ribosome moves down the mRNA, it allows for the addition of more ribosomes which start new protein chains. Every mRNA have multiple ribosomes attached which is called polyribosome