Download Protein Synthesis and Function: Chapter 3

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—
Termination
 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 Code:
Redundancy And Wobble
Structure 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
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
Negatively Charged (Acidic)
Aspartic acid, Asp, D
Glutamic acid, Glu, E
Positively Charged (Basic)
Arginine, Arg, R
Histidine, His, H
Lysine, Lys, K
Amino Acid Structures
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
TRANSFER OF GROWING
CHAIN
Transfer Of Growing Chain
Termination Of Chain
Location Of Translation
Machinery
ENDOPLASMIC
RETICULUM
 Microscopic series of tunnels
 Involved in transport and storage
 Two types of ER:
 Rough ER (RER)
 Smooth ER (SER)
ENDOPLASMIC
RETICULUM
Rough endoplasmic
reticulum (RER)
 Originates from the outer membrane of
the nuclear envelop
 Extends in a continuous network through
cytoplasm
 Rough due to ribosomes
 Proteins are synthesized and shunted into
the ER for packaging and transport
 First step in secretory pathway
Smooth Endoplasmic
Reticulum (SER)
 Closed tubular network without
ribosomes
 Functions in
 nutrient processing
 synthesis and storage of lipids, etc.
Rough Endoplasmic
Reticulum (RER)
OVERVIEW OF SYNTHESIS
POLYRIBOSOMES
Protein Structure
 Primary: amino acid
sequence
 Secondary: Intrachain folding
 beta-pleated sheets
 alpha helices
Protein Structure
 Four levels of
structure
 Primary
 Secondary
 Alpha helix, beta
pleated sheet, random
coil
 Tertiary
 Quatanary
Primary Structure: Amino
Acid Sequence
Secondary Structure: Alpha
Helix, Beta-pleated Sheet, or
Random Coil
Amino Acid Content
Determines Protein
Structure and Function.
Extracellular domains
(charged, glycosylated)
Cell membrane
Intracellular domains
(hydrophilic)
Transmembrane
domains
(hydrophobic)
Protein Structure
 Tertiary: further folding, loss of which
denatures protein
 Quaternary: protein–protein interaction
for function. Monomers
form
multimers.
 Dimer
 Trimer
 Tetramer
Protein Function







Enzymes
Transport
Storage
Motility
Structural
Defense
Regulatory
Conjugated Proteins
 Lipoproteins–lipid
 Glycoproteins–carbohydrate
 Metalloproteins–metal atoms
Non-amino acid portion–nonprotein
prosthetic group
MODIFICATION OF
PROTEINS
MODIFICATION OF
PROTEINS
MODIFICATION OF
PROTEINS
POST TRANSLATIONAL
MODIFICATION OF PROTEINS
PROCESSING OF INSULIN
Golgi Apparatus
 Consists of a stack of flattened sacs called
cisternae
 Closely associated with ER
 Transitional vesicles from the ER containing
proteins go to the Golgi apparatus for
modification and maturation
 Condensing vesicles transport proteins to
organelles or secretory proteins to the outside
Golgi Apparatus
Golgi Apparatus
Transport Process
MULTIPLE CONTROL
POINTS
Summary
 Proteins are made of combinations of 20 amino
acids.
 Protein structure and function depends on the
amino acid content and organization.
 A gene is defined, in part, by an open reading
frame that contains the genetic code.
 In the genetic code, three nucleotides code for
each amino acid.
 Proteins are translated from mRNA by peptidyl
transferase activity in the ribosome, using tRNA
as adaptors.