Chapter 13_Translation Of mRNA

Question 1

One Gene One Enzyme Hypothesis

Answer 1

A single gene controls the synthesis of a single enzyme.

Question 2

Polypeptide

Answer 2

A linear sequence of amino acids.

Question 3

Protein

Answer 3

Composed of polypeptides.

Question 4

Translation

Answer 4

Involves the translation of a nucleotide sequence (mRNA) into an amino acid sequence (polypeptide).

Question 5

Sense Codon

Answer 5

The sequence of three bases in most codons specifies a particular amino acid.

Question 6

Start and Stop Codons

Answer 6

• Start: AUG (Methionine)

- Stop: UAA, UAG, and UGA

Question 7

Anticodons

Answer 7

3 nucleotide sequence that is complementary to codons in mRNA.

Question 8

The genetic code is degenerate, which means…

Answer 8

…more than one codon can specify the same amino acid.

Question 9

Reading Frame

Answer 9

A sequence of codons determined by reading bases in groups of three, beginning with the start codon.

Question 10

Peptide Bond

Answer 10

Formed between the carboxyl group in the last amino acid of the polypeptide chain and the amino group in the amino acid being added.

Question 11

N-Terminus

Answer 11

(Amino Terminal End) The first amino acid is located here. The 5’ end.

Question 12

C-Terminus

Answer 12

(Carboxyl Terminal End) The last amino acid is located here. The 3’ end.

Question 13

Side Chain

Answer 13

(R group) Each amino acid contains a unique side chain.

Question 14

Nonpolar, Aliphatic Amino Acids

Answer 14

Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, Cysteine, Methionine

Question 15

Aromatic Amino Acids

Answer 15

Phenylalanine, Tyrosine, Tryptophan

Question 16

Polar Neutral Amino Acids

Answer 16

Serine, Threonine, Asparagine, Glutamine

Question 17

Polar Acidic Amino Acids

Answer 17

Aspartic Acid, Glutamic Acid

Question 18

Polar Basic Amino Acids

Answer 18

Histidine, Lysine, Arginine

Question 19

Nonstandard Amino Acids

Answer 19

• Selenocysteine
• Pyrrolysine
• Occasionally incorporated into polypeptides by the use of stop codons.

Question 20

When does the folding process begin?

Answer 20

While the polypeptide is still being translated.

Question 21

The progression from the primary structure of a polypeptide the the 3D structure of a protein is dictated by…

Answer 21

…the amino acid sequence within the polypeptide. In particular, the chemical properties of the amino acid side chains play a central role in determining the folding pattern of a protein.

Question 22

Chaperones

Answer 22

Proteins that bind to polypeptides and facilitate their proper folding.

Question 23

Secondary Structure

Answer 23

• The first stage of folding involves the formation of a regular, repeating shape (the secondary structure)
• Comes in the form alpha helix and the beta sheet.
• A single polypeptide may have some regions that fold into an alpha helix and other regions that fold into a beta sheet.

Question 24

Tertiary Structure

Answer 24

Short regions of secondary structure within a polypeptide are folded relative to each other. This is a thermodynamically favorable process.

Question 25

Quaternary Structure

Answer 25

Proteins composed of two or more polypeptides that associate with each other to make a functional protein.

Question 26

Adaptor Hypthesis

Answer 26

The position of an amino acid within a polypeptide chain is determined by the binding between the mRNA and an adaptor molecule carrying a specific amino acid.

Question 27

Aminoacyl-tRNA Synthetases

Answer 27

Catalyze the attachment of amino acids to tRNA molecules. Cells produce 20 different of these, 1 for each of the 20 distinct amino acids.

Question 28

Charged tRNA

Answer 28

(Aminoacyl-tRNA) The amino acid is attached to the 3' end of the tRNA by a covalent bond.

Question 29

Catalytic function of aminoacyl-tRNA synthetase

Answer 29

- An amino acid and ATP bind to the enzyme. AMP is covalently bound to the amino acid, and pyrophosphate is released. - The correct tRNA binds to the enzyme. The amino acid becomes covalently attached to the 3' end of the tRNA. AMP is released - The "charged" tRNA is released.

Question 30

Isoacceptor tRNA

Answer 30

When two or more tRNAs that differ at the wobble base are able to recognize the same codon.

Question 31

Ribosome

Answer 31

The macromolecular arena where translation takes place.

Question 32

Bacterial and Eukaryotic Ribosomes are assembled from...

Answer 32

...rRNA and proteins

Question 33

Small and Large Subunits

Answer 33

- Bacteria: 30s (Small) + 50s (Large) = 70s | - Eukaryoitc: 40s (Small) + 60s (Large) = 80s

Question 34

Nucleolus

Answer 34

Where the assembly of the rRNAs and ribosomal proteins to make the 40s and 60s subunits.

Question 35

Ribosomes contain discrete sites where tRNAs bind and the polypeptide is synthesized.

Answer 35

- The two sites for tRNA binding to the robosome are peptidyl and aminoacyl site. - A third site is called the exit site.

Question 36

Stages of Translation

Answer 36

- Initiation: The ribosomal subunits, mRNA, and the first tRNA assemble to form a complex. - Elongation: The ribosome slides along the mRNA in the 5' to 3' direction, moving over the codons. - Termination: A stop codon is reached. Disassembly occurs, and the newly made polypeptide is released.

Question 37

Initiator tRNA

Answer 37

Recognizes the start codon in the mRNA.

Question 38

Describe initiation

Answer 38

- IF1 and IF3 bind to the 30S subunit. - IF2, which uses GTP, promotes the binding of the initiator tRNA to the start codon in the P site. - IF1 and IF3 are released. - IF2 hydrolyzes its GTP and is released. - The 50S subunit associates.

Question 39

Shine-Dalgarno Sequence

Answer 39

A nine nucleotide sequence within BACTERIAL mRNA. Facilitates the binding of mRNA to the ribosome.

Question 40

Describe Elongation

Answer 40

- A charged tRNA binds to the A site. EF-Tu facilitates tRNA binding and hydrolyzes GTP. - Peptidyltransferase, which is a component of the 50S subunit, catalyzes peptide bond formation between the polypeptide chain and the amino acid in the A site. The polypeptide is transferred to the A site. - The ribosome translocates 1 codon to the right. This translocation is promoted by EF-G, which hydrolyzes GTP. - An uncharged tRNA is released from the E site. - This process is repeated, again and again, until a stop codon is reached.

Question 41

Decoding function

Answer 41

16S rRNA can detect when an incorrect tRNA is bound at the A site and will prevent elongation until the mispaired tRNA is released from the A site. It is important in maintaining high fidelity of mRNA translation.

Question 42

Peptidyl transfer

Answer 42

The polypeptide is removed from teh tRNA in the P site and transferred to the amino acid at the A site.

Question 43

Release Factors

Answer 43

Molecular mimics that resemble the structure of tRNAs.

Question 44

Describe Termination

Answer 44

- tRNA in P site carries completed polypeptide. - A release factor (RF) binds to the A site. - The polypeptide is cleaved from the tRNA in the P site. The tRNA is then released. - The ribosomal subunits mRNA, and release factor dissociate.