Chapter 3 fundamentals of protein biochemistry

Nucleic acid sequence must be translated into an amino acid sequence... Protein Translation—Termination  Termination of the amino acid chain is signaled by one of three nonsense, or t

Protein Synthesis and Function:

Chapter 3

Central Dogma

of the transfer of biological information.

Nucleic acid sequence must

be translated into an amino acid sequence.

Central Dogma

PROTEIN SYNTHESIS

D stem

D loop

CCA terminus

tRNA

aminoacyl-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

Ribosomal Subunits

Solving the Genetic

Code

 Four nucleotides must code for 20 amino acids.

 41 = 4, 42 = 16, 43 = 64, 44 = 256

Solving the Genetic Code

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

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 Structures

Isoelectric Point (pI)

 Amino acids are

neutral at a pH,

which is their

isoelectric point (pI)

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 due to ribosomes

 Proteins are synthesized and shunted into the ER

for packaging and transport

 First step in secretory pathway

Rough Endoplasmic Reticulum (RER)

OVERVIEW OF SYNTHESIS

POLYRIBOSOMES

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.

Cell membrane

Intracellular domains (hydrophilic)

Extracellular domains

(charged, glycosylated)

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

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

 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