Genetics Block 2

Question 1

codons ? how many are there?

Answer 1

64 - 61 plus 3 STOP UAG (never a C, starts with U, only A can repeat

Question 2

can an amino acid have more than one codon coding for it?

Answer 2

Yes, proline: CCU, CCC, etc

all life uses same code, except for 10 exceptions found so far

Question 3

does one codon always code for same AA?

Answer 3

Yes - proline - CCU

Question 4

So we say - genetic code is unambiguous, degerate (redundant), universal (almost), nonoverlapping and comma-less

Answer 4

Unambiguous (specific)
A specific codon always codes for the same amino acid
example: CCU = proline
Degenerate (redundant)
A given amino acids may have more than one codon coding for it
example: proline : CCU, CCC, CCA, CCG
Universal (Almost)
All organisms studied so far use the same genetic code
Fewer than 10 exceptions are known
Example: ln mammalian mitochondria, AUA codes for Met and UGA for Trp, and AGA and AGG serve as chain terminators
Nonoverlapping and comma-less
Code is read from a fixed starting point as a continuous sequence of bases, taken 3 at a time
Example: A B C D E F G H I
Read as: ABC DEF GHI
Not: ABC BCD CDE DEF EFG FGH GHI

Question 5

Stages of translation

Answer 5

A. Preparation - formation of aminoacyl-tRNA
B. Translation:
Initiation – recognition of a start point, assembly of a ribosome
Elongation – synthesis of a polypeptide
Termination – stop codon associated release of a protein from mRNA

Question 6

Preparation (Charging) - Amino Acid Activation:

Answer 6

In activation, the correct amino acid is joined to the correcttransfer RNA (tRNA).

There are 20 AA participating in formation of proteins
At least 1 tRNA for each amino acid (some amino acids have more than 1 specific tRNA)
Humans – with at least 50 species of tRNA
Bacteria – with 30-40 species of tRNA

Question 7

Requirements for translation:

Answer 7

mRNA – required as a template, that is read in 5’-3’ direction
rRNA and ribosomal proteins – components of a ribosome
Amino acids – monomers of a protein
tRNA – adaptor molecule that translate the codons into the amino acid sequence of a protein
Protein factors
Include initiation, elongation, and termination (release) factors
ATP and GTP – sources of energy

Question 8

aminoacyl-tRNA synthetases - 2 high energy bonds from ATP required for charging step to create t-RNA amino acid complex

Answer 8

Activation of amino acids is carried out by a 2-step process catalyzed by aminoacyl-tRNA synthetases ✮

Have a proofreading or editing activity✮
Remove mischarged amino acids from the tRNA molecule

Question 9

1st step of charging

Answer 9

two step process, uses 2 bonds from ATP - end up with AMP

Question 10

three steps of translation

Answer 10

initiation
elongation
termination

Question 11

Initiation

Answer 11

two ribosomal subunits (large and small)

mRNA to be translated
tRNA specified by first codon
GTP (for energy)
Initiation factors

Question 12

ribosomes - if associated w/ RER proteins are destined for

Large:
proK - 70 sedimentatino coefficient
euk 80

Answer 12

exported from cell,
integrated into plasma, ER, or Golfi
incorporated into lysosome

Question 13

what holds two subunits together?

proK - 50s, 30s
euk - 60S/ 40 S

Answer 13

magnesium, Mg++

Question 14

ribosomes - have a P site and an A site

polysomes or polyribosome is a beaded chain of 5 - 8 ribosomes

Answer 14

mRNA very long, allow several ribosomes to work at translation at same time

Question 15

prok - mRNA guides to start by Shine Dalgarno sequence

GTP required fro small ribosomal subunit binding to mRNA

Answer 15

upstream of AUG - 6 - 10 based upstream,

located start codon - - AUG, codes fMET

Question 16

A site - P site - E site

Answer 16

a - binds incoming tRNA - proofreading

P binds occuPied TRNA

E is empty, just exiting

large ribosome moves along

when STOP codon found, all stops, releasing factor comes in - releases - all moves on

Question 17

EuKaryotes - NO Shine Delgarno
5” cap
3’- Poly (A) tail also help figure out where to bind

uses GTP to bind

Answer 17

40S (small) binds to 5’cap, moves down until find UAG (methione codon)

Question 18

Elongation

Answer 18

requires elongation factors

Question 19

codons match up with anti codons

Answer 19

anti-codon written backwards when you read it - because you are reading it 5 - 3 - so…

mRNA is GCG ACG UCC 5 - 3

anticoden reads

CGC - CGU - GGA 5 - 3

Question 20

wobble hypothesis - there don’t have to be 61 tRNAs to recognize 61 codons

Answer 20

tRNA can recognize more than one codon at 3 position

Question 21

diptheria toxin - carried by Corynbacterium diptheria - Pseydomonas work same way - this is a type of infection - see in health care centers - spreads via water or soil - pneumonia, etc

Answer 21

shuts down euk protein synthesis - via the elongation factor eEF2

Question 22

termination - UAG, UAA, UGA -

Answer 22

brings in release factors - requires GTP

Question 23

Energy required for protein synthesis

Answer 23

2 ATP or 2 ATP phosphates for building tRNA complex

2 GTP - one for binding, one for translation

Gripping and Going

Additional ATP and GTP for initiation in EuK, and additional GTP in both proK and euK for termination

Question 24

Inhibitors of protein synthesis?

Drugs
Tetracycline, Doxycicline, Tigecycline - 30S

Chloramphenical - 50S

Erythromycin (other mycins) 50S

Spectinomycin - 30S

Answer 24

binding to ribosomal subunit - Looks like competitive binding to me?

Question 25

Gray Baby syndrome - chlorampheniol

esp newborns

Answer 25

if this given, baby may die - used to fight bacterial infections eg meningitis) - baby can’t excrete drug - builds up, leads to cyanosis, death, low BP

Question 26

post transational modifications

trimming - endoproteases - proteolysis

Answer 26

trimming - endoproteases - proteolysis

prenylation - allows protein to work with lipids (immunology) - anti inflammatory, statins - cholesterol

dydroxylation (vit C - proline, lysine - in ER

Y-carboxylation - produces CA2 binding sites

glycosolation - golgi and ER - adds olgosac as protein

phsophylation- adds phostphate by protein kinases GOLGI

Acetylation - histones