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63 terms

MC3

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noncovalent interactions are
weak but collectively strong enough to define the folded structure of a protein
in a folded polypeptide, nonpolar side chains
tend to cluster at the core of the protein and away from the aqueous surrounding, leaving the polar and charged side chains at the surface
nonpolar amino acids form the
transmembrane domains of membrane proteins
polar and charged amino acids tend to be at the
regions of proteins that are exposed to the aqueous surrounding
hydrophobic core regions of polypeptides contain
nonpolar side chains
hydrogen bonds in polypeptides
can be formed to the polar side chains on the outside of the molecule
secondary structures are
alpha helixes and beta sheets
proteisn are synthesized as
polypeptides
maturation of proteins involves
correct folding, proteolytic cleavage, chemical modifications, formation of quaternary structures, association with co-factors
each step in protein synthesis and maturation can be a target for
control (gene expression)
protein degradation is
under tight control
chaperones bind to
nascent polypeptides andmaintina a stable unfolded state
when synthesis is complete
the chaperons release the polypeptides and allow them to fold correctly
chaperones stabilize the
newly synthesized polypeptide
chaperones
transport polypeptides
chaperons on the other side maintain
the unfolded state until translocation is complete
polypepties are allowed to fold when
they reach their final destination
what kind of bonds form between adjacent cysteine residues?
disulfide
disulfide bonds can link what?
two domains of the same polypeptide or different polypeptide chains
elastin fibers
a rubberlike elastic meshwork present in the extracellular matrix of some cell types
elastin fibers allow tissues such as skin, arteries and lungs to
stretch and recoil without tearings
examples of denaturants
urea or heat
denaturants can
unfold a polypeptide by breaking non-covalent interactions between amino acids
reducing agents ex.
2-mercaptoethanol
reducing agents are necessary to
break disulfide bonds
urea is produced in
the liver of mammals
urea helps
excrete ammonia (a toxic metabolic waste product)
urea can break
noncovalent interactions between amino acids
fibrillar collagens are
the major structural proteins of connective tissues
fribrillar collagens are built of
triple helices of procollagen polypeptides
TSEs
transmissible spongiform encephalopatheies
TSEs are a family of
fatal brain diseases characterized by lesions that appear as small cavities (spongy appearance)
Ex. of TSEs
scrapie (sheep), mad-cow disease (cattle), and Creutzfeldt-Jakod disease (CJD), or kuru ("to tremble with fear") (humans)
infectious agent in TSEs
prions (proteinaceous infectious particle)
TSEs protein only hypothesis
diseases are caused by incorrectly folded versions of the prion protein
prions (PrP^sc) are variations of
normal brain protein (PrP^c)
a PrP^sc can direct a PrP^sc
to unfold and re-fold into an identical PrP^sc prion
new prions can
continue propagation of PrP^sc
several strains of prions exist
variations of the prion protein tertiary structure that are also infectious
insulin protein
pancreatic hormone that regulates blood glucose levels
insulin protein is two chains linked by
disulfide bonds (between closely places cysteines)
the insulin protein is originally synthesized as a
single polypeptide preproinsulin
insulin protein: connecting polypeptide is removed after
disulfide bonds are made, result = mature insulin
regulation of protein activity may occur
at two levels
two levels of protein regulation:
regulation of gene expression (determines the amount of protein produced by the cell by limiting transcription and or translation), control of protein function (the protein is synthesized by its activity is restricted according to the needs of the cell
the folding of a polypeptide may create a specific ligand...
binding site
PKA
promotes glycogen metabolism
inactive PKA is a
tetramer: two regulatory subunits bound to two catalytic subunites
what activates PKA by binding to the regulatory subunits, causing the release of the catalytic subunits?
cAMP
the kinase activity of the released catalytic subunits (in PKA) do what?
phosphorylate multiple effector proteins
feedback inhibition: allosteric regulation:
a change in the conformation of a protein that affects its activity due to the binding of regulatory molecule
feedback inhibition: the end product of a biosynthetic pathway does what?
inhibits the enzyme that catalyzes the first step of its synthesis, causing the entire pathway to shut down
ex. of GTP regulated enzyme activity
the activation of Ran
phosphorylation is necessary for what?
the activation or inactivation of many proteins
protein kinase enzymes:
transfer a phosphate group from ATP to proteins
two types of kinases (depending on target amino acids_
serine/threonine, tyrosine
phosphatases
enzymes that remove phosphate groups from phosphorylated proteins
ubiquitin
a small protein that is attached to a target protein and is a label for regulation or destruction
the central cylinder of the proteasome contains
the active protease domain
ubiquitylation and proteasomal degradation: a ubiquitin ligase enzyme attaches several
ubiquitins to the target protein
ubiquitylation and proteasomal degradation: a cap domain of the proteasome (a protease complex)
recognizes the polyubiquitylated target protein
ubiquitylation and proteasomal degradation: the ubiquitins are
removed and recycled
ubiquitylation and proteasomal degradation: the proteasome degrades the target protein by
sequential ATP-dependent steps