Transcript Chapter 1
Chapter 1
Protein
Contents
1. Chemical components
2. Molecular structures
3. Structure-function relationship
4. Physical and chemical properties
5. Exploration of proteins
What are proteins?
Proteins are composed of macromolecules amino acids together through linked peptide bonds .
Section 1 Chemical Components of Proteins
Element components of proteins
major elements C, H, O, N, S.
trace elements P, Fe, Cu, Zn, I, …
The average nitrogen content in proteins is about
16%.
The protein quantity can be estimated.
protein in 100g sample = N per gram x 6.25 x 100
The basic building blocks of proteins
Amino Acids
only 20 types of amino acids are used for protein synthesis in biological systems.
L-α-Amino acid
L-α-Amino acid
H 2 N COOH C ¦Á H R ²à Á´ ¹² ͬ²¿ ·Ö
A Classification of Amino Acids
Amino acids are grouped as (1) non-polar, hydrophobic; (2) polar, neutral; (3) acidic; (4) basic.
Gly
Special amino acids
optically inactive
Pro Having a ring structure and imino group
Cys active thiol groups to form disulfide bond
Peptide
A peptide is a compound of amino acids linked together by peptide bonds .
peptide bond
A peptide bond is a covalent bond formed between the carboxyl group of one AA and the amino group of its next AA with the elimination of one H2O molecule.
Biologically active peptides
Glutathione (GSH) As a reductant to protect nucleic acids and proteins Peptide hormones Neuropeptides responsible for signal transduction
Section 2 Molecular Structures of Proteins Primary Structure Secondary Structure Tertiary Structure Quaternary Structure Spatial structure
Primary Structure
The primary structure bonds. of proteins is defined as a linear sequence of amino acids joined together by peptide Peptide bonds and disulfide bonds responsible for maintaining the primary structure.
are
Secondary Structure
The secondary structure defined as of a protein is a local spatial structure of a certain peptide segment, that is, the relative positions of backbone atoms of this peptide segment.
H-bonds are responsible for stabilizing the secondary structure.
Repeating units of Ca-C(=O)-N(-H) Ca constitute peptide chain.
the backbone of Six atoms, Ca-C(=O)-N(-H)-Ca , constitute a planer peptide unit.
Four common types of secondary structure
α-helix
β
-pleated sheet
β
-turn random coil
Motif
When several local peptides of defined secondary structures are close enough Motif .
in space, they are able to form a particular structure-- Zinc finger HLH (helix-loop-helix) HTH (helix-turn-helix)
Tertiary Structure
The tertiary structure the three-dimensional arrangement of all atoms is defined as of a protein.
Five types of interactions stabilize the protein tertiary structure.
• • • •
hydrophobic interaction ionic interaction hydrogen bond van der Waals interaction
•
disulfide bond
Domain
Large polypeptides may be organized into structurally close but functionally independent units-- Domain
Chaperon
Chaperones proteins foldings are large, multisubunit that promote protein
Quaternary Structure
The quaternary structure is defined as the s p a t i a l a r r a n g e m e n t o f multiple subunits of a protein.
These subunits are associated through H-bonds, ionic interactions , and hydrophobic interactions .
From primary to quaternary structure
Protein classification
Constituents simple protein conjugated protein = protein + prosthetic groups Overall shape Globular protein Fibrous protein long/short < 10 long/short > 10
Section 3 Structure-Function Relationship of Proteins
Relationship between primary structure and function Primary structure is the fundamental to the spatial structures and biological functions of proteins.
Example
1.
2.
Proteins having similar amino acid sequences demonstrate the functional similarity .
The alternation of key AAs protein will cause the lose of its biological functions .
in a
Relationship between spatial structure and function
A particular spatial structure protein is strongly correlated of a with its specific biological functions .
Example
1.The denatured protein remains its primary structure , but no biological function.
2.
Allosteric change of hemoglobin by O 2
Section 4 Physical and Chemical Properties of Proteins 1.
Amphoteric
isoelectric point (pI)
The pH at which the protein has zero net-charge is referred to as isoelectric point (pI)
2. Colloid property
Hydration shell and electric repulsion make proteins stable in solution.
3 Protein denaturation renaturation, precipitation and coagulation
The process in which a protein loses its native conformation referred to as under the t r e a t m e n t o f d e n a t u r a n t s i s protein denaturation .
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Applications sterilization, lyophilization
4 UV absorption
Trp, Tyr, and Phe have aromatic groups of resonance double bonds .
Proteins have a strong absorption at 280nm
5 Coloring reactions
Biuret reaction Ninhydrin reaction
Section 5 Exploration of Protein
• • • • •
Isolation and purification Centrifugation Dialysis Precipitation Chromatography Electrophoresis
Protein Sequence Determination
Edman degradation Deduction from DNA sequence
Structure Determination
Circular dichroism spectroscopy X-ray crystallography Nuclear magnetic resonance spectroscopy Computer simulation