39 - The Genetic Code

What are the rules of the genetic code?

• 3 nucleotides = one amino acid

• Nonoverlapping

• No punctuation

• Directional

• Degenerative

• Nearly universal

Would the insertion or deletion of 3 consecutive bases in a DNA sequence have drastic or marginal effects?

Only a small effect, since it would not create a frameshift mutation like insertion/deletion of one or two bases

What was the Nirenberg experiment?

Discovered one of the first codons - that UUU makes phenylalanine by putting E.coli in a medium with radioactive bases

The start codon is _____, which makes the amino acid ________

AUG, methionine

Which RNA polymerase makes tRNA?

Rna pol III

Label the CCA terminus and anticodon loop

pink = CCA terminus

blue = anticodon loop

True or False: tRNAs always recognize ONLY one codon

False, they can “wobble” and recognize more than one

What is the structure of tRNA?

It has an acceptor stem, where it takes amino acids, and 4 arms

Does wobble base pairing occur at the 3’ or 5’ end of a codon?

3’ end

Wobble base pairing: C can bind to ______

Only G

Wobble base pairing: A can bind to _______

ONLY U

Wobble base pairing: U can bind to _______

A or G

Wobble base pairing: G can bind to ________

U or C

Wobble base pairing: I can bind to ______

U, C, or A (NOT G)

What is aminoacyl-tRNA, and what enzyme makes it?

tRNA conjugated to its amino acid, made by aminoacyl-tRNA synthase

The amino acid is connected to the _______ (5’ or 3’) end of the tRNA

3’

How are amino acids activated and transferred to RNA?

They are adenylated and then transferred via the formation of an ester bond

How does aminoacyl-tRNA synthetase work?

It binds ATP and the amino acid based on its properties, and then selectively binds tRNA based on its structure

What can synthetase recognize when binding the correct tRNA?

The anticodon and acceptor stem

How much ATP is consumed in order to synthesize aminoacyl-tRNA?

2 ATP molecules

Can aminoacyl-tRNA synthetases proofread?

Yes

What proportion of the ribosome is RNA?

2/3 of it

Aminoacyl tRNA synthase, DNA ligase, DNA polymerase, and RNA polymerase all produce a common byproduct, which is _________

AMP