BIO315H5 Lecture Notes - Lecture 1: Molten Globule, Protein Folding, Alternative Splicing
ProfessorCheng Hai- Ying( Mary)
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What we need -> produce regularly.
Level of regulation of transcription: promoters, alternative splicing, inhibitors and
We have further avenues of regulations besides from DNA to protein. The final protein
product is also affected by protein folding.
Regulation of transcription
Many different types of chemical reactions are required to produce a properly folded protein
from the information contained in a gene
Regulation of Protein Expression
Hydrophobic residues buried in its interior core
Large numbers of noncovalent interactions
Primary structure (AA sequence), secondary (alpha-helix and beta sheets), tertiary
(3D conformation) - these interactions including hydrophobic interactions allow
secondary structures to fold even more.
Quaternary structure - assembly of different polypeptides. Can have the same
gene and identical proteins coming together. Alternative splicing: 1 gene - 1
protein, spliced differently -> different proteins.
Sum of all energetically favorable arrangements -> final folding protein. Might need to
spend energy to change the folding.
Process of gene expression is not over when the sequence of amino acids is generated. To be
useful to the cell, this new polypeptide must fold up into its unique 3D conformation, at the
correct speed: (structure and function relationship is essential)
As each protein domain emerges from the ribosome starting from the N-terminus
Contains most final secondary features
Aligned in roughly the right conformation
Less highly ordered than final folded form
Usually dynamic and flexible state
Starting point for a relatively slow process in which many side-chain adjustments
occur that eventually form the correct tertiary structure
Within a few seconds it forms a molten globule
For some proteins, much of the folding process is complete by the time the ribosome
releases the C-terminal end of a protein, then…
Bind any small-molecule cofactors required for its activity
Certain modifications require certain environments e.g. in the cytosol, organelles,
pH level, etc.
Undergo covalent modification, e.g. protein glycosylation, phosphorylation (kinases), or
other - over 200 different types, then…
Assemble correctly with the other protein subunits with which it functions
For some proteins, this folding begins immediately. But It takes several minutes to synthesize
a protein of average size. Usually the N-terminus starts folding.
Not all available paths lead to correct/most stable fold.
Information needed for all the above steps is ultimately contained in the AA sequence which
have been selected through many millions of years of evolution - not only for conformation,
but also for an ability to fold rapidly.
September 5, 2017
Ch6 Page 1
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