Biochem 1: Proteins Flashcards
proteins are
polymers of 20 different amino acids (monomers) linked by peptide bonds
polypeptide chain is a
single unbranched polymer of amino acids
proteins consist of
one or more polypeptide chains folded into specific 3-D shapes
what defines the shape of the protein
the sequence of amino acids
polymers are formed by _____ reactions
condensation
monomers are joined by covalent bonds, energy must be added, and water is removed, this is also called a ______ reaction
dehydration
polymers are broken down into monomers in
hydrolysis reactions
hydrolysis releases energy
protein primary structure
is a polypeptide chain
protein secondary structure
occurs when the amino acid chain folds and coils in a helix or pleated sheet
protein tertiary structure
occurs when the helix or sheet fold irregularly, forming disulfide bridges, hydrogen bonds, hydrophobic interaction, and ionic bonds between amino acids in the chain
what 2 categories of proteins are there- divided into two large classes based on their three-dimensional structure
- fibrous proteins
- globular proteins
protein quaternary structure
consists of two or more polypeptides
proteins can undergo denaturation which is
occurs when proteins encounter hostile environments such as temperature and pH, and therefore lose their shapes and functions
what structure does hydrolysis destroy?
what structure does denaturation destroy?
- hydrolysis destroys primary structure
- denaturation destroys all other levels of structure (but not primary) - because primary has covalent bonds
globular proteins are proteins which are
folded to a more or less spherical shape
globular protein properties and example
-they tend to be soluble in water and salt solutions
example is hemoglobin
polar/nonpolar groups of globular proteins
- most of their polar side chains are on the outside and interact with the aqueous environment by hydrogen bonding and ion-dipole interactions
- most of their non polar side chains are buried inside
fibrous proteins contain
polypeptide chains organized approximately parallel along a single axis
properties of fibrous proteins
- consist of long fibers or large sheets
- tend to be mechanically strong
- are insoluble in water and dilute salt solutions
- play important structural roles in nature
examples of fibrous proteins
- keratin of hair and wool
- collagen of connective tissues of animals including cartilage, bones, teeth, skin, and blood vessels
collagen consists of
three polypeptide chains wrapped around each other in a replica twist to form a triple helix
collagen structure specifics
- 30% of amino acids in each chain are Pro and hydroxyproline
- every third position is Gly
- each polypeptide chain is a helix
- the three strands are held together by hydrogen bonding
collagen fibers with age
with age, collagen helices become crossed linked by covalent bonds formed between Lys and His residues
where are crystallins found
in the epithelial and fiber cells of the ocular lens
what are crystallins and what do they maintain
crystallins are structural, water soluble proteins
-maintain the elongated shape of lens fiber cells and lens structure and affect refraction of light
crystalline proteins in the lens contain significant amounts of
Cys and Met
what do molecular chaperons maintain
maintain normal conformation of other crystallins to prevent aggregation
80-90% of the bulk of the eye contains
collagen
collagen in the eye helps to
forms and maintains tissue structure, scaffolding and adhesion
-makes up the semiliquid gel of the vitreous humor
in the corneal storm, collagen fibers form
lamellae sheets that impose cross-sectional strength
collagen is also in ____, ___…. of the eye
in the sclera, ocular basement membranes called descemet’s membrane, lens capsule and blood vessels
anchoring collagen fibrils attach:
basal epithelial cells of cornea and outermost lamellae of corneal stroma
how senile cataracts form
- if oxidized, protein shape is altered through exposing more Cys sulfhydryl groups
- disulfide bonds form within and between crystallin protein
- high molecular weight aggregates are formed, which reduce the integrity and clarity of the lens itself
hemoglobin basic structure
tetramer of two alpha chains and two beta chains, a2b2
-each chain has 1 heme group
hemoglobin can bind up to __ molecules of ___
4 molecules of O2
what is O2 positive cooperativity in hemoglobin
when one O2 is bound, it becomes easier for the next O2 to bind
function of hemoglobin to
transport oxygen
what affects the ability of Hb to bind and transport oxygen
H+, Co2, Cl-, and 2,3-biphosphoglycerate (BPG)
the Bohr affect in binding affinity of O2 for Hb
H+ and CO2 bind to Hb and affect the binding affinity of Hb for O2
Bohr affect in lungs
when hemoglobin binds to O2
actively metabolizing muscle: Hb releases O2
Bohr affect in lungs
when hemoglobin releases H+
actively metabolizing muscle: Hb binds H+
what are antibodies
are Y-shaped molecules consisting of two identical heavy chains and two identical light chains held together by disulfide bonds
antibodies are classified as
glycoproteins
what is the variable region of an antibody
the variable region is found at the prongs of the Y and is the part of the antibody that binds to the antigen
the binding sites for the antibody on the antigen are called
epitopes
the importance of correct folding
proteins that do not fold correctly may interact with other proteins in an undesired manner and aggregates may results
