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Comparing Proteins
Protien and RNA Working Together
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Primary Structure
Secondary Structure
Sickle Cell Anemia
Biotechnology
Tertiary Structure
Introduction
Tertiary structures refer to the further folding of the polypeptide molecule.
These compact structures are often referred to as globular proteins. They are
responsible for the synthesizing, transportive, and metabolizing functions
which cells perform.
I Characteristics of Globular Proteins
Tertiary structures are the direct product of secondary structures
( a- helix, b-sheet) folding in on themselves. Many globular proteins contain
prosthetic group, which are small noncovalently or covalently molecules bonded
to the protein which enables that protein to perform some function.
II Various Forms of Globular Protein Structures
It may seem that an infinite number of folding possibilities may occur which
is theoretically true however, upon closer observation of known regularly
occurring tertiary structures there are a number of similarities which may be
found from one globular protein to the next. One of these similarities is
known as the domain. A domain is a compact, locally folded region of tertiary
structure. Domains are connected to each other via the polypeptide strand that
runs through the entire molecule. There are two major patterns of domains,
those that are built about a-helices and those that are based on the framework
of b-sheet structures. There are several observations which have been made
which seem to run throughout the various forms of globular proteins that may
exist:
Various Forms of Proteins
. globular proteins have a defined inside and outside region
. b- sheets are usually twisted or wrapped into barrel structures
. polypeptide chain can turn curves in a number of ways in order to go from b
segments to a-helices and back.
. not all parts can be so easily classified as helix B sheets or turns
III Role of Environment
The role of the environment in which a protein is located may have adverse
effects on it depending on whether or not that protein is able to function or
adapt to those conditions. If the temperature is increased or the pH becomes
to acidic or basic it may result in the protein unfolding. This process is
know as denaturation. If this occurs the protein is no longer a compact
structure but a random coil unable to perform is designated function. The
folding of proteins is clearly based on thermodynamic processes.
IV. Mechanism of Protein Folding
1. Nucleation = internal formation of some a-helix and b-sheet segments
2. Structural consolidation; tertiary folding
3. Final Rearrangements
Stages of Protein folding
Us - unfolded turn; no enzymatic activity
ll - partially folded; some amide protons protected form exchange; some
secondary structure present, bun no enzymatic activity
ln - almost completely folded; enzymatic activity but some incorrect alignments
retained
N- Native Protein
Globular Proteins in E -Coli
V Chaperonins
Chaperonins are a, family of proteins which help in the proper assembly of
protein structure. They primarily serve preventing polypeptide chains form
folding or combining with other chains prematurely. They are know as heated
shock proteins because they accumulate after cells have been subject to sudden
increase in temperature or other stress.
Quaternary Structures
Quaternary structures are the last level of protein organization. They are
analogous to cells which group into tissues to perform a certain function in
that they usually consist of two or more folded polypeptides chains. This
leads to the development of multisubunit proteins.
I Structure
The overall composition of polypeptide chains consist of asymmetric units the
overall structure may exhibit a variety of symmetries. In globular or
quaternary structures the group lie in totally different regions. This is
called a heterologous interaction. Most protein subunits are not based
primarily on helical symmetry but on what is called point-goup symmetry. This
involves a exact number of subunits arranged about one or more axes of symmetry. Isologous interactions are also possible in which the two subunits are related to each other. Many of the heterologous interactions that occur are a direct result of noncovalen forces at complementary protein surfaces.
