Lecture 30

Question 1

The molecular machine that performs translation? What are these structure mades up of?

Answer 1

the ribosome!!

-made up of RNA strands (rRNA), and dotted with protein chains

Question 2

When synthesizing a new protein…the large and small subunit come together with what in between? The ribosome then walks down the mRNA ______ nucleotides at a time, building a new protein.

Answer 2

mRNA trapped in the space between

3 nucleotides at a time

Question 3

Transcription produces a bunch of different RNAs, but only which one gets translated?

Answer 3

mRNA gets translated

Question 4

At the transcript level, the mRNA has a ____________ and the information in the
middle (the protein coding sequence) is what actual gets translated into protein. The leader
and trailer sections are not translated.

Answer 4

leader section @ 5’ and a trailer section @ 3’

Question 5

RNA triplet of three bases is called what? Which encodes what?

Answer 5

a codon, which encodes each specific amino acid

Question 6

AUG codes for…which is always the first amino acid in bacterial proteins. Although AUG at the beginning of a coding region encodes
N-forymylmethionine, AUG within the coding region encodes what?

Answer 6

N-formylmethionine (or F-Met)

encodes methionine

Question 7

the language of mRNA is in the form of what? Each codon “codes” for a particular amino acid. This is the _______ code.

Answer 7

codons, groups of three nucleotides

genetic code

Question 8

There are ______ possible codons, but only ______ amino acids. This means that most amino acids are signaled by several
alternative codons, a situation referred to as the _______ of the code. What does this allow for?

Answer 8

64, but only 20 amino acids

degeneracy – This allows for a certain amount of
change, or mutation, in the DNA without affecting the protein produced.

Question 9

Of the 64 codons, 61 are _______ codons which code for an amino acid, and 3 are ________
codons (also called stop codons) which do not code for an amino acid. They signal the end
of the protein molecule’s synthesis.

Answer 9

• sense

- 3 are nonsense

Question 10

A codon is recognized by specific base pairing with a complementary sequence of three
bases called the _________, a sequence found on ________.

Answer 10

anticodon found on tRNA

Question 11

what does tRNA also do?

Answer 11

Each tRNA can also carry on its other end the amino acid

encoded by the codon that the tRNA recognizes.

Question 12

what is a wobble position?

Answer 12

base pairing is more flexible for 3rd base of codon than first two

Question 13

Prokaryotic ribosome parts – describe the large and small subunits? Big picture here

Answer 13

small subunit 30s, large subunit 50s – the complete ribosome is 70s

Question 14

What is the 50s subunit made of?

Answer 14

31 proteins, and 2 rRNA molecules the 5s rRNA and the 23S rRNA

Question 15

what is the 50s large subunit involved in? In addition ______ binding proteins can interact with the subunit to aid in what?

Answer 15

involved in peptide bond formation through peptidyl transferase activity.

-GTP binding proteins aid in translational processes such as initiation, elongation, and termination

Question 16

The 5s rRNA molecule appears to act as what?

Answer 16

a seventh domain in the large ribosomal subunit in conferring stability to the entire 3-D structure

Question 17

The 23s rRNA is involved in? The most important feature of the 23S rRNA is the __________ center. What happens here?

Answer 17

translocation and peptide bond formation

-peptidyl transferase center, the site where peptide bonds are formed.

Question 18

The 30S or small subunit is

composed?

Answer 18

of 16S rRNA and 21 ribosomal proteins

Question 19

The 16s rRNA of the small subunit makes up the bulk of the subunit. It is important for what?

Answer 19

subunit association and translational accuracy

-on the 30S, the anticodon of an aminoacyl-tRNA is matched by base-paired
interactions to a codon on the mRNA. A key function of the small subunit is to
discriminate against aminoacyl-tRNAs that do not match the codon on the message.

Question 20

There are three important stages to protein synthesis:

Answer 20

Initiation, elongation and

termination

Question 21

In bacteria, initiation of protein synthesis always begins with what?

Answer 21

a free 30s ribosomal subunit

An initiation complex forms consisting of the 30S, plus mRNA, and formylmethioninetRNA
(F-Met tRNA), and several initiator proteins (IF1, 2, 3) and energy is required.

Question 22

See slide for order of initiation

Answer 22

??

Question 23

Just preceding the start codon on the mRNA is a sequence of three to nine nucleotides called the what? What does it help with, and where is this located?

Answer 23

Shine-Dalgarno sequence (aka ribosome binding site or leader sequence) that helps bind the mRNA to the ribosome. Ribosome binding site is at the 5’ end of the mRNA and is complementary to the base sequence in the 3’ end of the 16s rRNA (this complementary base pairing aids in holding down the ribosome to the correct reading frame on the mRNA)

Question 24

The mRNA threads through the ribosome primarily bonds to ______ subunit?

Answer 24

30s subunit

Question 25

The 50s ribosome has 3 important sites what are they?

Answer 25

A site, P site, E site

Question 26

A site

Answer 26

the acceptor site, where on the ribosome the new charged tRNA ( a charged tRNA has its cognate amino acid) first attaches

Question 27

The charged initiator tRNA carrying _________ (f-Met) recognizes the codon ______ on the mRNA and binds in a complementary fashion at the part of the _______ site on the 30s subunit.

Answer 27

N-formylmethionine
AUG
P-site

Question 28

Note: the F-Met-tRNA is only tRNA that can bind to the part of the P-site on 30S subunit to initiate protein synthesis.

Answer 28

Usually at the P-site, the growing polypeptide is held by a tRNA

Question 29

The second codon of the mRNA pairs with a tRNA carrying the second amino acid at the ______ site. The first amino acid joins to the second by a ______ bond. This attaches the polypeptide to the tRNA in the P site. The ribosome moves along the mRNA until the second tRNA is in the _____. The next codon to be translated is brought into the _______ site. The first tRNA now occupies the E site.

Answer 29

A site, by a peptide bond

• P site
• A site
• E site

Question 30

Initiation requires what proteins?

Answer 30

IF-1,2 and 3

Question 31

The ribosome moves along the mRNA in the _______ direction.

Answer 31

5’ to 3’ direction

Question 32

Translation: Elongation

what protein is used to catalyze the formation of a new peptide bond

Answer 32

see slide

peptidyl transferase

Question 33

aminoacyl tRNA

Answer 33

tRNA to which its cognated amino acid is chemically bonded (charged)

Question 34

ribosome must advance 3 nucleotides down mRNA during ________

Answer 34

translocation

see slide

Question 35

The last step is ______,the ribosome reaches a _______ codon (stop codon like UGA). No _____ binds here. Instead, _______ proteins bind in the vacant _______ site and cleave the attached polypeptide from the final tRNA, releasing the finished polypeptide.

Answer 35

• termination
• nonsense
• tRNA
• Release factor proteins (RF)
• A site

Question 36

In Bacteria, the process of transcription and translation are

Answer 36

simultaneous.

Question 37

Several ribosomes can simultaneously translate a single mRNA molecule, forming a complex called? What does this do?

Answer 37

polyribosome

Polyribosomes increase the speed and efficiency of translation, and because
the activity of each ribosome is independent of that of its neighbors, each ribosome in a
polyribosome complex makes a complete polypeptide.

Question 38

Advantages to coupling transcription and translation

Answer 38

One advantage involves the energy required for
transcription and translation; specifically, the energy needed to drive the process of
transcription could be provided by the large-scale expenditure of unstable nucleotide
triphosphates during the process of translation. Another advantage to coupled transcription
and translation is that it provides a novel mechanism for gene regulation.