Engineering Proteins
EP2 Protein Synthesis
Amino Acids
Some of the 20 Naturally Occurring Amino Acids
Amino Acids - Summary
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Zwitterions
Acid / Base Chemistry (Buffers)
Optical Isomerism – chiral centre, CORN
Peptide – Secondary Amides
Naming dipeptides – NH2 on left
Hydrolysis of peptides
Condensation to form polypeptides and
proteins
Dipeptides
Condensation
Protein Structure
4 levels of structure:o Primary Structure – Sequence of Amino Acids;
o Secondary Structure – Spatial arrangement of sections
of primary Structure (e.g. helices);
o Tertiary Structure – Overall 3D Shape of protein;
o Quaternary Structure – Protein “Monomers”
coordinated into tetramers (haemoglobin), or hexamers (insulin).
Primary Structure
Secondary Structure
 - Helix
 - Sheet
Tertiary Structure – gyrase
Quaternary Structure – Insulin Hexamer
Insulin Hexamer
Building Proteins
Cells build proteins directly from L-Amino Acids.
To synthesise a protein, a Chemist would need:-
1)
2)
3)
Instructions / knowledge of the primary structure;
Supplies of pure amino acids;
A method of forming peptide links.
Cells adopt a similar approach – Protein Synthesis.
Protein synthesis – The role of RNA
1) Messenger RNA - Temporary set of instructions
for one protein molecule;
2) Transfer RNA – collects amino acids;
3) Ribosomal RNA – present in ribosomes, which
catalyse the formation of peptide links between
amino acids.
1) Messenger RNA (mRNA)
2) Transfer RNA (tRNA)
3) Ribosomal RNA (rRNA)
What is RNA? – ribonucleic acid
Nucleic Acids
mRNA triplet base codes (ppt)
RNA Base Pairs
A Permanent set of Instructions
DNA
DNA – deoxyribonucleic acid
1) Codes for many mRNA molecules.
2) The section of DNA coding for a
particular protein is called a gene.
3) Full set of genes = genome
(humans 3.5 x 109 bases)
Differences between RNA and DNA
DNA Base Pairs
DNA
DNA
How Cells Make Proteins
DNA
Transcription
mRNA
Transcription
Transcription – in the nucleus
1) DNA double helix unwinds;
2) hydrogen bonds break;
3) free nucleotides hydrogen bond to the complementary
exposed bases;
4) Enzyme (RNA polymerase) links the hydrogen bonded
nucleotides to form a strand of mRNA;
5) mRNA is released and the DNA double helix is reformed.
How Cells Make Proteins
DNA
Transcription
mRNA
Translation
a.a. activation
Protein
Chain
Amino Acid Activation
Amino Acid Activation
1.
tRNA molecule forms an ester link with a
specific amino acid;
2. tRNA – amino acid complex moves to the
Ribosome.
Translation (ppt)
Translation - in the cytoplasm
1)
2)
3)
4)
5)
6)
mRNA attaches to ribosome;
Hydrogen bonding between complementary bases
binds the correct tRNA anticodon to the 1st codon
(set of 3 bases on mRNA);
A 2nd tRNA – amino acid complex binds to the
adjacent mRNA codon in the ribosome;
Ribosome catalyses the formation of the peptide
bond between amino acids;
The tRNA is released once the amino acid is
delivered;
Ribosome moves along the mRNA chain to the end.
How Cells Make Proteins
DNA
Transcription
mRNA
Translation
a.a. activation
Protein
Chain
3D
Protein
Folding
Protein Synthesis
How Cells Make Proteins
DNA
Transcription
mRNA
Translation
a.a. activation
Protein
Chain
3D
Protein
Folding