Translation of mRNA questions

Flashcards covering the key concepts of protein translation, including the roles of mRNA, tRNA, ribosomes, and various factors involved in the process.

What did Archibald Garrod propose in 1902 regarding alkaptonuria?

Alkaptonuria is inherited via a recessive allele and patients lack a particular enzyme.

What is alkaptonuria?

An inborn error of metabolism due to a missing enzyme, namely homogentisic acid oxidase.

What did Beadle and Tatum use to damage DNA in their experiments?

X-rays

What hypothesis did Beadle and Tatum develop regarding genes and enzymes?

One-gene/one-enzyme hypothesis (later modified to one-gene/one-polypeptide hypothesis).

What did Beadle and Tatum analyze in their experiments?

Enzyme pathways for synthesis of vitamins and amino acids.

What is the modern modification of the one gene-one enzyme hypothesis?

One-gene/one-polypeptide hypothesis

What is translation in genetics?

The process where the nucleotide language of mRNA is translated into the amino acid language of proteins.

In mRNA, what are the groups of three nucleotides known as?

Codons

What is the function of the start codon AUG?

Defines the reading frame for all following codons and specifies methionine.

What are the stop codons?

UAA, UAG, and UGA

What does it mean that the genetic code possesses degeneracy?

More than one codon can specify the same amino acid.

What are synonymous codons?

Codons that specify the same amino acid

What are selenocysteine (Sec) and pyrrolysine (Pyl)?

Sometimes called the 21st and 22nd amino acids, coded by UGA and UAG codons, respectively.

What is the importance of the reading frame?

The reading frame is a series of codons beginning with the start codon, and determines the amino acid sequence.

What is the directionality of polypeptide synthesis?

Parallels the 5’ to 3’ orientation of mRNA, with an N-terminus and C-terminus.

How many standard amino acids are commonly found within polypeptides?

20

What determines the structure and function of proteins?

The amino acid sequences of polypeptides.

What are the four levels of structure in proteins?

Primary, secondary, tertiary, and quaternary

What stabilizes secondary structures in proteins?

Hydrogen bonds between atoms located in the polypeptide backbone.

What determines the tertiary structure of a protein?

Hydrophobic and ionic interactions as well as hydrogen bonds and van der Waals interactions.

What is a key category of proteins that accelerate chemical reactions within a cell?

Enzymes

Who were the two heads of research groups that deciphered the genetic code?

Marshall Nirenberg and H. Gobind Khorana

What enzyme was used to catalyze the covalent linkage of ribonucleotides into RNA and what is unique about it?

Polynucleotide phosphorylase; it does not use a template, so the order of nucleotides is random.

What does a cell-free translation system contain?

Ribosomes, tRNAs, and other factors required for translation, including enzymes that attach amino acids to tRNA molecules.

What did Nirenberg and Leder discover in 1964?

A 3 nucleotide RNA could cause a ribosome to bind a tRNA

What are the two functions of tRNA as proposed by Francis Crick?

Recognizing a 3-base codon in mRNA and carrying an amino acid that is specific for that codon.

How does the anticodon in tRNA bind to a codon in mRNA, and what rule does this binding follow?

Through complementary base pairing, following the AU/GC rule; the binding is anti-parallel.

What is the secondary structure of tRNAs

It exhibits a cloverleaf pattern with 3 stem-loop structures and an acceptor stem with a 3’ single strand region.

What enzyme attaches amino acids to tRNAs?

Aminoacyl-tRNA synthetases

What does it mean that selection of the correct amino acid must be highly accurate?

Or the polypeptides may be nonfunctional; error rate is less than one in every 10,000

What hypothesis did Francis Crick propose in 1966 to explain the degeneracy of the genetic code?

The wobble hypothesis which proposed that in the codon-anticodon recognition process, the first two positions pair strictly according to the AU ∕ GC rule, while the third position can “wobble” or move a bit, thus tolerating certain types of mismatches.

What does isoacceptor tRNA refer to?

tRNAs that are able to recognize the same codon

What is a ribosome composed of?

A large and small subunit, each assembled from proteins and rRNA.

What are on the surface of the 30S subunit during bacterial translation?

mRNA

What are the three discrete sites in ribosomes?

Peptidyl site (P site), Aminoacyl site (A site), and Exit site (E site)

What are the three stages of translation?

Initiation, Elongation, and Termination

What is the role of initiator tRNA in translation, and what is it designated as in bacteria?

Recognizes the start codon in mRNA; in bacteria, it is designated as fMet-tRNA

What is the Shine-Dalgarno sequence?

A ribosomal-binding site on mRNA that facilitates its binding to the 30S subunit.

How is translation initiation different in eukaryotes compared to bacteria?

Eukaryotes require additional factors, and the 7-methylguanosine cap on the mRNA is recognized by an eIF, causing the mRNA to bind to the ribosome; no Shine Dalgarno sequence.

What are Kozak’s rules?

Rules for optimal translation initiation in eukaryotes, including that the start codon must be AUG, there must be a guanine at the +4 position, and a purine (preferably an adenine) at the -3 position.

What is the approximate rate of amino acid addition in bacteria and eukaryotes during the elongation stage of translation?

In bacteria, 15 to 20 amino acids per second; in eukaryotes, 2 to 6 amino acids per second.

What is peptidyl transferase and what is it made of?

The enzyme involved in transferring a polypeptide from the tRNA in the P site to the amino acid at the A site; it is made of 23S rRNA, a component of the large subunit.

What happens during translocation?

Ribosome moves to the next codon in the mRNA, moving the tRNAs at the P and A sites to the E and P sites, respectively.

What recognizes stop codons during the termination stage of translation?

Release factors

What is coupling?

The phenomenon where translation begins before transcription ends, occurring in bacteria.

What do antibiotics do?

Inhibit the growth of microorganisms

What is the function of iron regulatory protein (IRP)?

When iron levels are low, the binding of iron regulatory protein (IRP) to an iron response element (IRE) found in the 5′-UTR of ferritin mRNA inhibits translation.

What are the main differences between translation in bacteria, archaea, and eukaryotes?

Differences in ribosome composition, initiation factors, mRNA binding, start codon selection, elongation rate, termination, translation location, and coupling to transcription.