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?.
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Proteins are macromolecules composed of amino acids linked together through peptide bonds.
Section 1 Chemical Componentsof Proteins
Element components of
C, H, O, N, S.
P, Fe, Cu, Zn, I, …
The protein quantity can be estimated.
protein in 100g sample = N per gram x 6.25 x 100
The basic building blocks of proteins
only 20 types of amino acids are used for protein synthesis in biological systems.
(1) non-polar, hydrophobic;
(2) polar, neutral;
Having a ring structure and imino group
active thiol groups to form disulfide bond
A peptide isa compound of amino acids linked together by peptide bonds.
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.
As a reductant to protect nucleic acids and proteins
Neuropeptides responsible for signal transduction
The primary structure of proteins is defined as a linear sequence of amino acidsjoined together by peptide bonds.
Peptide bonds and disulfide bonds are responsible for maintaining the primary structure.
The secondary structure of a protein is defined as 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 the backbone of peptide chain.
Six atoms, Ca-C(=O)-N(-H)-Ca, constitute a planer peptide unit.
When several local peptides of defined secondary structures are close enough in space, they are able to form a particular structure---Motif.
Large polypeptides may be organized into structurally close but functionally independent units---Domain
Chaperones are large, multisubunit proteins that promote protein foldings
The quaternary structure is defined as thespatial arrangement of multiple subunits of a protein.
These subunits are associated through H-bonds, ionic interactions, and hydrophobic interactions.
From primary to quaternary structure
conjugated protein = protein +
Globular protein long/short < 10
Fibrous proteinlong/short > 10
Primary structure is the fundamental to the spatial structures and biological functions of proteins.
1.The denatured protein remains its primary structure, but no biological function.
2. Allosteric change of hemoglobin by O2
Hydration shell and electric repulsion make proteins stable in solution.