Chapter 1
Sponsored Links
This presentation is the property of its rightful owner.
1 / 41

Chapter 1 PowerPoint PPT Presentation

  • Uploaded on
  • Presentation posted in: General

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?.

Download Presentation

Chapter 1

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Chapter 1



  • 1.Chemical components

  • 2.Molecular structures

  • 3.Structure-function relationship

  • 4.Physical and chemical properties

  • 5.Exploration of proteins

What are proteins?

Proteins are macromolecules composed of amino acids linked together through peptide bonds.

Section 1 Chemical Componentsof Proteins

Element components of


  • majorelements

    C, H, O, N, S.

  • traceelements

    P, Fe, Cu, Zn, I, …

  • The average nitrogen content in proteins isabout 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

A Classification of Amino Acids

  • Amino acids are grouped as

    (1) non-polar, hydrophobic;

    (2) polar, neutral;

    (3) acidic;

    (4) basic.

Special amino acids

  • Gly

  • Pro

  • Cys

optically inactive

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.

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 activepeptides

Glutathione (GSH)

As a reductant to protect nucleic acids and proteins

Peptide hormones

Neuropeptides responsible for signal transduction

Section 2Molecular Structures of Proteins

Primary Structure


Tertiary Structure

Spatial structure

Quaternary Structure

Primary Structure

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.

Secondary 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.

Four common types of secondary structure

  • α-helix

  • β-pleated sheet

  • β-turn

  • random coil


When several local peptides of defined secondary structures are close enough in space, they are able to form a particular structure---Motif.

Zinc finger

HLH (helix-loop-helix)

HTH (helix-turn-helix)

Tertiary Structure

  • The tertiary structure is defined as the three-dimensional arrangement of all atoms of a protein.

Five types of interactions stabilize the protein tertiary structure.

  • •hydrophobic interaction

  • •ionic interaction

  • •hydrogen bond

  • •van der Waals interaction

  • •disulfide bond


Large polypeptides may be organized into structurally close but functionally independent units---Domain


Chaperones are large, multisubunit proteins that promote protein foldings

Quaternary Structure

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

Protein classification

  • Constituents

    simple protein

    conjugated protein = protein +

    prosthetic groups

Overall shape

Globular protein long/short < 10

Fibrous proteinlong/short > 10

Section 3 Structure-Function Relationshipof Proteins

  • Relationship between primary structure and function

    Primary structure is the fundamental to the spatial structures and biological functions of proteins.


  • Proteins having similar amino acid sequences demonstrate the functional similarity.

  • The alternation of key AAs in a protein will cause the lose of its biological functions.

Relationship between spatial structure and function

  • A particular spatial structure of a protein is strongly correlated with its specific biological functions.


1.The denatured protein remains its primary structure, but no biological function.

2. Allosteric change of hemoglobin by O2

Section 4 Physical andChemical Properties of Proteins


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 denaturationrenaturation, precipitation and coagulation

  • The process in which a protein loses its native conformation under the treatment of denaturants is referred to as protein denaturation.


sterilization, lyophilization

4UV absorption

  • Trp, Tyr, and Phe have aromatic groups of resonance double bonds.

  • Proteins have a strong absorption at 280nm


  • Biuret reaction

  • Ninhydrinreaction

Section 5 Explorationof Protein

  • Isolationandpurification

    • Centrifugation





Protein Sequence Determination

  • Edman degradation

  • Deduction fromDNA sequence


  • Circular dichroism spectroscopy

  • X-ray crystallography

  • Nuclear magnetic resonance spectroscopy

  • Computer simulation

  • Login