Genetic Code

Question 1

Protein synthesis takes up what percent of energy used by cell?

Answer 1

90%

Question 2

How many amino acids? How many base combos?

Answer 2

20, 4^3

Question 3

Codon proof

Answer 3

Insertion/ deletion screws reading frame

Question 4

Nirenburg and Matthaei experiment

Answer 4

PolyU mRNA and E. coli and gtp and atp and 20 amino acids

Each tube had a different base isolated

Only tube with phenylaline created peptide

Same for polyA and polyC

Question 5

Khorana

Answer 5

Repeating bases to find codon patterns

AC little n

Question 6

Initiation codon

Answer 6

AUG

Met

Question 7

Stop codon

Answer 7

UAA
UAG
UGA

Question 8

Stop codon

Answer 8

UAA
UAG
UGA

Question 9

Typical protein ORF

Answer 9

500+ codons

Question 10

Genetic code different for mitochodrion

Answer 10

Unusual wobble rules
Different number of tRNAs

Question 11

“I”

Answer 11

Nucleotide inosinate

Present in anti codons
Binds with a, u, c but to a weaker extent

Wobble base
3rd position in codon

Aligns with 1st base of mRNA read 5-3

Question 12

What would anticodon ICG pair with ?

Answer 12

CGA
CGU
CGC

Had to flip and then align

Question 13

Wobble hypothesis

Answer 13

1. First two bases on codon pair strongly with anticodon
   = majority of specificity
2. 1st base of anticodon determines number of codons that can be recognized

C or A = only one codon

U = 2 codons (a or g)

I = 3 codons (a, u, or c)

3. Given rules above, sometimes same Amino acid needs multiple tRNAs depending on codon
4. 32 tRNAs is min number for 61 codons (excludes go and stop)
   But most cells have more

Helps with efficiency because wobble base dissociates more quickly

Question 14

Most common mutation

Answer 14

Transition Mutation
1st codon mutates and ends up coding for similar amino acid

Question 15

Gag pol overlap

Answer 15

Hiccup near gag stop codon

Allows for stop codon to be skipped and also read pol gene = gag pol gene

= rous sarcoma virus —> becomes mature reverse transcriptase
= occurs 5% of time

Question 16

Sometimes mRNA edited before translation

Examples

Answer 16

Guide RNAs inserting U residues

Nucleotide alteration = enzymatic deamination of adenosine and cytidine

Question 17

Deamination of adenosine

Answer 17

Performed by ADARs

Becomes inosine

Question 18

Deamination of cytidine

Answer 18

Performed by APOBECs

Becomes uridine

Question 19

ADAR enzymes

Answer 19

A to I deamination

Duplex regions of mRNA (double stranded)

Alu makes duplex more probable

Big issues health wise if not present

Question 20

APOBEC proteins

Answer 20

C to U deamination

2 classes:
- 1-5 and AID

1 and 3: mRNA editing: Can convert CAA mRNA codon to UAA = stop codon

2,4,5 act on DNA

Over expression = tumor