Textbook 1.1 Flashcards
pg. 48-60, 71-72, 373-377, 726-728
in neutral aqueous solution…
the alpha carboxyl group loses its proton and exists as COO- and alpha amino group accepts a proton
Amino acids exist as
stereoisomers except glycine
How long is the average polypeptide chain?
450 amino acids
Can proteins contain components other than amino acids?
Yes, after polypeptide has been synthesized other things like carbohydrates (to form glycoproteins), metal- containing groups (to form metalloproteins), and organic groups (to form flavoproteins).
Polar charged amino acids
In physiologic pH, side chains of these amino acids are able to form ionic bonds with other charged species in the cell.
ex. aspartic acid
Polar uncharged amino acids
side chains can have partial pos. or neg. thus can form H bonds with other molecules (including water)
ex. tyrosine
Non polar amino acids
hydrophobic side chains, usually lack oxygen and nitrogen. Interactions are restricted to hydrophobic interactions and Van der Waals forces.
ex. Alanine
Other amino acids
Glycine - only has one stereoisomer (side chain is just H)
Proline - doesn’t really fit into any secondary structures and its alpha amino group is part of a ring (produces kinks and folds)
Cysteine - forms disulfide bridges
Post-translational modifications (PTMs)
proteins with different amino acids that arise from alteration of side chain of one of normal 20 amino acids AFTER its incorporation into a polypeptide chain
How can a single polypeptide chain exist as a number of distinct biological molecules?
Post-translational modifications can alter its biological activity
Examples of post-translational modifications
- reversible addition of phosphate group to a serine, threonine, or tyrosine residue
- lysine acetylation affects thousands of proteins in a mammalian cell
Where are polar residues usually found?
Situated near the surface of molecule where they can associate with nearby water molecules and contribute to solubility.
Primary Protein Structure
specific linear sequence of amino acids that constitute the chain
Secondary Protein Structure
describes conformation (spatial arrangement) of portions of the polypeptide chain
What did Linus Pauling and Robert Corey propose?
That polypeptide chains exist in preferred conformations that provide maximum number of possible H-bonds between neighbouring amino acids.
Alpha helix and beta sheet.
Alpha helix
backbone lies on inside of helix, side chains project out. In water soluble proteins, the outer surface of the alpha helix often contains polar residues in contact with the solvent (inward facing contains non-polar side chains).
Beta sheet
Consists of several segments of a polypeptide lying side by side. Backbone assumes folded or pleated conformation. Beta sheet also has hydrogen bonds but they are oriented perpendicular to the long axis of polypeptide chain and project across from one part of the chain to another.
Silk has a lot of…
beta sheets which make it resistant to pulling
Tertiary Structure
describes conformation of entire polypeptide. This kind of structure is virtually unlimited—many possible conformations.
Tertiary structures are stabilized by…?
Non covalent bonds between side chains of protein.
How is tertiary structure usually determined?
X-ray crystallography: crystal of protein is bombarded by thin beam of x-ray radiation that is scattered by electrons of the proteins which then strike radiation sensitive detector in an array of spots. Computer program is then used to convert the spatial arrangement of dots into protein structure.
Fibrous proteins
elongated shape
globular proteins
compact structure
Where are fibrous and globular proteins found?
Fibrous proteins are usually the structural material outside the living cell (collagens and elastins of connective tissues, keratins of hair, skin, and silk). They resist pulling or shearing forces. Most proteins within the cell are globular proteins.
