Genetics Block 2 Flashcards
codons ? how many are there?
64 - 61 plus 3 STOP UAG (never a C, starts with U, only A can repeat
can an amino acid have more than one codon coding for it?
Yes, proline: CCU, CCC, etc
all life uses same code, except for 10 exceptions found so far
does one codon always code for same AA?
Yes - proline - CCU
So we say - genetic code is unambiguous, degerate (redundant), universal (almost), nonoverlapping and comma-less
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
Stages of translation
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
Preparation (Charging) - Amino Acid Activation:
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
Requirements for translation:
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
aminoacyl-tRNA synthetases - 2 high energy bonds from ATP required for charging step to create t-RNA amino acid complex
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
1st step of charging
two step process, uses 2 bonds from ATP - end up with AMP
three steps of translation
initiation
elongation
termination
Initiation
two ribosomal subunits (large and small)
mRNA to be translated
tRNA specified by first codon
GTP (for energy)
Initiation factors
ribosomes - if associated w/ RER proteins are destined for
Large:
proK - 70 sedimentatino coefficient
euk 80
exported from cell,
integrated into plasma, ER, or Golfi
incorporated into lysosome
what holds two subunits together?
proK - 50s, 30s
euk - 60S/ 40 S
magnesium, Mg++
ribosomes - have a P site and an A site
polysomes or polyribosome is a beaded chain of 5 - 8 ribosomes
mRNA very long, allow several ribosomes to work at translation at same time
prok - mRNA guides to start by Shine Dalgarno sequence
GTP required fro small ribosomal subunit binding to mRNA
upstream of AUG - 6 - 10 based upstream,
located start codon - - AUG, codes fMET
A site - P site - E site
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
EuKaryotes - NO Shine Delgarno
5” cap
3’- Poly (A) tail also help figure out where to bind
uses GTP to bind
40S (small) binds to 5’cap, moves down until find UAG (methione codon)
Elongation
requires elongation factors
codons match up with anti codons
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
wobble hypothesis - there don’t have to be 61 tRNAs to recognize 61 codons
tRNA can recognize more than one codon at 3 position
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
shuts down euk protein synthesis - via the elongation factor eEF2
termination - UAG, UAA, UGA -
brings in release factors - requires GTP
Energy required for protein synthesis
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
Inhibitors of protein synthesis?
Drugs
Tetracycline, Doxycicline, Tigecycline - 30S
Chloramphenical - 50S
Erythromycin (other mycins) 50S
Spectinomycin - 30S
binding to ribosomal subunit - Looks like competitive binding to me?
Gray Baby syndrome - chlorampheniol
esp newborns
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
post transational modifications
trimming - endoproteases - proteolysis
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
