Chapter 3 fundamentals of protein biochemistry

Protein Synthesis
and Function:
Chapter 3


Central Dogma
Central Dogma
of the transfer of biological information.

DNA

RNA

protein

Nucleic acid sequence must
be translated into an amino
acid sequence.


PROTEIN SYNTHESIS


Protein Translation
tRNA

 mRNA: template
 Ribosomes: peptidyl
transferase
 tRNA: adaptors

Acceptor
end
CCA
terminus

T loop

T stem
D stem
Anticodon
stem

D loop
Variable loop
Anticodon
loop


Protein Translation
 Amino-acyl tRNA
synthetases
specifically attach
amino acids to
tRNAs.
 amino acid + ATP
aminoacyl-AMP + PPi
 aminoacyl-AMP +
tRNA aminoacyltRNA + AMP

Protein Translation


Protein Translation


Protein Translation—
Ter m ination
 Termination of the amino acid chain is signaled
by one of three nonsense, or termination
codons, UAA, UAG, or UGA which are not
charged with an amino acid.
 Termination or release factors trigger hydrolysis
of the finished polypeptide from the final tRNA.


Initiation of
Translation (Protein
Synthesis)


Attachment of
Preinitiation Complex


Scanning mRNA for
AUG


rRNA and Proteins of

Ribosomes
 Ribosomes are
composed of both
proteins and rRNA
 Confer some of
the specificity of
these complex
interactions


Ribosomal Subunits


Solving the Genetic
Code
 Four nucleotides must code for 20 amino acids.
 41 = 4, 42 = 16, 43 = 64, 44 = 256
 George Gamow


Solving the Genetic
Code
 Synthetic RNAs





UUUUUUUUU = phe-phe-phe
GGGGGGGGG = gly-gly-gly

CCCCCCCCC = pro-pro-pro
AAAAAAAAA = lys-lys-lys
 Marshall Nirenberg and Johann Matthaei


Solving the Genetic Code
 Synthetic RNAs of defined sequence
 UCUCUC = ser-leu-ser-leu

Gobind Khorana
 Three nucleotides = 1 codon = 1 amino acid


The Genetic
Redundancy
Wobble

Code:
And



Str ucture of an Amino
Acid


Amino Acids
Nonpolar
Alanine, Ala, A
Isoleucine, Ile, I

Leucine, Leu, L
Methionine, Met, M
Phenylalanine, Phe, F
Tryptophan,Trp, W
Valine, Val, V

Negatively Charged (Acidic)
Aspartic acid, Asp, D
Glutamic acid, Glu, E

Polar
Asparagine, Asn, N
Cysteine, Cys, C
Glutamine, Gln, Q
Glycine, Gly, G
Proline, Pro, P
Serine, Ser, S
Threonine, Thr, T
Tyrosine, Tyr, Y

Positively Charged (Basic)
Arginine, Arg, R
Histidine, His, H
Lysine, Lys, K


Amino Acid Stru ctures


Isoelectric Point (pI)

 Amino acids are
neutral at a pH,
which is their
isoelectric point (pI).


Peptide Bonds
 Amino acids are
joined together by
-C-C-N- linkages or
peptide bonds to
make proteins.


Amino
terminus
Carboxy
terminus


INITIATION OF
PROTEIN SYNTHESIS