Download Introduction to Proteins

PROTEINS
An Introduction to Structure and
Functions of Proteins
MALDI-TOF MS LAB
• Question?
– WHAT PROTEIN IS IT?
• Strategy
– Determine Molecular Weight (molar mass)
using MALDI-TOF MS
– Break it down (digest) with trypsin
– Identify fragment by MALDI-TOF
– Use data base to match fragments with data
base fragments of protein digest
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Proteins play key roles in living
systems
• Examples of protein functions
Alcohol
dehydrogenase
oxidizes alcohols
to aldehydes or
ketones
– Catalysis:
Almost all chemical reactions in a
living cell are catalyzed by protein
enzymes.
– Transport:
Some proteins transports various
substances, such as oxygen, ions,
and so on.
Haemoglobin
carries oxygen
– Information transfer:
For example, hormones.
– Control of genetic expression:
Insulin controls
the amount of
sugar in the
blood stream
Transcription factors
Amino Acid: Basic Unit of
Protein
R
H3N+ C
Amino group
H
Different side chains*,
determine the
COO- R,
properties of 20
Carboxylic
acid group amino acids.
An amino acid
Main Chain (backbone) Atoms(Cα,C=0,N)
2
Primary Structure
Biosynthesis proceeds for the N-terminal to the C
terminal of the protein.
Stabilize tertiary and quaternary structure of proteins
Create an organic solvent-like environment in the interior
3
Acid-base chemistry
Salt bridges builders
Lewis bases (ligands for metal ions)
Hydrogen bonds
Other dipole-dipole interactions
Lewis bases (Coordination Chemistry)
Redox chemistry (cysteine)
4
Hierarchical nature of Protein
Structure
Primary structure
(Amino acid sequence)
↓
Secondary structure
（α-helix, β-sheet）
↓
Tertiary structure
（Three-dimensional
structure formed by
assembly of secondary
structures）
↓
Quaternary structure
（Structure formed by
more than one
polypeptide chains）
Basic 3D structural units of
proteins: Secondary structure
α-helix
β-sheet
Secondary structures, α-helix
and β-sheet, have regular
hydrogen-bonding patterns.
Antiparallel
5
Antiparallel Beta Sheet (arrows)
Three-dimensional structure of
proteins
Tertiary
structure
Quaternary structure
6
Acid-Base Chemistry
Effect of primary structure: important for short side chains
Effect of tertiary structure
7