The Genetic Code

Is protein synthesis high energy-demanding or low energy-demanding

High energy- it is tightly regulated and uses about 90% of the cell’s cehmical energy

Is there an excess or lack of protein copies produced in order to meet cellular needs

No, there is an even balance between the two, with synthesis balanced by degradation

Do proteins have target destinations

Yes, they are targeted to specific cellular locations

How does degradation affect cellular homeostasis

It maintains cellular homeostasis

Over how many biomolecules does protein synthesis involved in eukaryotes

Over 300 biomolecules

What and how many biomolecules are involved with eukaryotic protein synthesis

• Over 70 ribosomal proteins

• Approximately 20 amino acid activation enzymes

• About 20 protein factors for initiation, elongation, and termination

• Roughly 100 enzymes for post-translational processing

• Around 40 types of tRNAs and rRNAs

Who discovered the identification of ribosomes as the site of protein synthesis and when

Paul Zamanick’s group in 1995

Who discovered that RNA is similar to DNA (later understood as mRNA) and when

Volkin and Astrachan in 1956

Who discovered that amino acids are found attached to tRNA, indicating activation for synthesis, and when

Zamenick and Hoagland in 1958

Who discovered that messenger RNA (mRNA) is the DNA-like RNA carrying genetic information, and when

Sydney Brenner, Crick, and Francois Jacob in 1960

How many amino acids do one nucleotide triplet (codon) code for

1

How many amino acids are there

20

Can a group of two (doublet) suffice to encode all amino acids

No, it will only encode 16

Is the genetic code overlapping or non-overlapping and how are codons read

Non-overlapping: Codons are read one at a time

What does it mean for a code to be unpunctuated

There are no gaps or punctuation between codons

In what direction is the mRNA read

in the 5’ —> 3’ directions

How many codons are possibly to encode all the amino acids

64

How many termination (stop) codons exist

3: UAA, UGA, UAG

What is the start codon and what amino acid is associated with in

AUG —> Methionine (Met)

Are most amino acids encoded by one or more codons

More than one codon

Which amino acids have only one codon

Methionine (Met) and Tryptophan (Trp)

Which base of the codon is the least critical in codon-anticodon recognition

The third base

How does the anticodon on tRNA pair in relation to the mRNA codon

It pairs antiparallel and complementary

What does the antiparallel and complementary pairing to the mRNA allow for

Flexibility in the third base position

Wobble base pairing

A flexible bonding between the 5’ base of a tRNA anticodon and the 3’ base (third position) of an mRNA codon containing weaker H-bonds than the others

What nucleotide do some tRNAs contain and what can it pair with during wobble base pairing

Inosinate (I), which can pair with U, C, or A

How does wobble pairing affect translation

It increases the efficiency and accuracy or translation without requiring a tRNA for every codon

Is the genetic code universal across all prokaryotes and eukaryotes

Yes

Does mitochondrial DNA (mtDNA) use the same or a different genetic code

It uses a slightly different genetic code

What codon codes for tryptophan (Trp) instead of STOP in Mitochondrial DNA

UGA

What two codons code for STOP instead of arginine (Arg) in Mitochondrial DNA (mtDNA)

AGA and AGG

How many tRNAs do Mitochondria have

22

Silent Mutation

Change in DNA that does not alter the amino acid sequence due to code degeneracy

How do silent mutations affect proteins

It has no effect

Missense mutation

Codon change resulting in a different amino acid

How do missense mutations affect proteins

It can cause conservative or nonconservative changes

Nonsense mutation

Codon change resulting in a premature stop codon

How do Nonsense mutation affect proteins

It truncates the protein

Run-on mutation

It stops the codon mutated to code for an amino acid

How does run-on mutations affect proteins

It makes the protein longer than normal

How does the genetic code’s degeneracy affect mutations

It provides resistance to mutations, minimizing harmful effects

Where does protein synthesis occur

In the ribosomes, which are complexes of rRNA and proteins

Where are ribosomes attached to in the endoplasmic reticulum (ER)

It is attached to the cytosolic face of the ER

Explain how tRNA acts as an adapter

It carries specific amino acids and matches mRNA codons through its anticodon

What guides protein targeting to specific cellular locations

N-terminal sequence

Are post-translational modifications necessary for protein function

Yes

Do mRNA’s undergo editing before translation

Yes, it involves the addition, deletion, or alteration of nucleotides

What facilitates the RNA editing process

guide RNAs (gRNAs)

What do guide RNAs (gRNAs) do

They hybridize with mRNA and serve as templates

What do deamination reactions do

They convert adenosine or cytidine residues enzymatically to alter mRNA sequences

Aminoacyl-tRNA synthetases

Enzymes that charge tRNAs with amino acids

Protein factors

Initiation, elongation, and termination proteins