Nonenzymatic Protein Function And Protein Analysis

Question 1

structural proteins

Answer 1

compose the cytoskeleton, anchoring proteins, and much of the extracellular matrix
most common: collagen, elastin, keratin, actin, tubulin
generally fibrous in nature

Question 2

motor proteins

Answer 2

have one or more heads capable of force generation through a conformational change
have catalytic activity, acting as Atlases to power movement
muscle contraction, vesicle movement within cells, and cell motility are most common applications
common ex: myosin, kinesin, dynein

Question 3

binding proteins

Answer 3

bind a specific substrate, either to sequester it in the body or hold its concentration at a steady rate

Question 4

cell adhesion molecules (CAMs)

Answer 4

allow cells to bind to other cells or surfaces

cadherins, integrins, selectins

Question 5

cadherins

Answer 5

calcium-dependent glycoproteins that hold similar cells together

Question 6

integrins

Answer 6

have two membrane-spanning chains and permit cells to adhere to proteins in the extracellular matrix
some also have signaling abilities

Question 7

selectins

Answer 7

allow cells to adhere to carbohydrates on the surfaces of other cells and are most commonly used in the immune system

Question 8

antibodies (immunoglobulins, Ig)

Answer 8

used by the immune system to target a specific antigen
contain a constant region and variable region; the variable region is responsible for antigen binding
two identical heavy chains and two identical light chains form a single antibody; they are held together by disulfide linkages and noncovalent interactions

Question 9

antigen

Answer 9

may be a protein on the surface of a pathogen (invading organism) or toxin

Question 10

ion channels

Answer 10

can be used for regulating ion flow into or out of a cell

three main types: ungated, voltage-gated, ligand-gated

Question 11

ungated channels

Answer 11

ion channels that are always open

Question 12

voltage-gated channels

Answer 12

ion channels that are open within a range of membrane potentials

Question 13

ligand-gated channels

Answer 13

ion channels that open in the presence of a specific binding substance, usually a hormone or neurotransmitter

Question 14

enzyme-linked receptors

Answer 14

participate in cell signaling through extracellular ligand binding and initiation of second messenger cascades

Question 15

G-protein coupled receptors

Answer 15

have a membrane-bound protein associated with a trimeric G protein
also initiate second messenger systems
1. ligand binding engages the G protein
2. GDP is replaced with GTP; the α subunit dissociates from ß and γ subunits
3. the activated α subunit alters the activity of adenylate cyclase or phospholipase C
4. GTP is dephosphorylated to GDP; the α subunit rebinds to the ß and γ subunits

Question 16

electrophoresis

Answer 16

uses a gel matrix to observe the migration of proteins in response to an electric field

Question 17

native PAGE

Answer 17

maintains the protein’s shape, but results are difficult to compare because the mass-to-charge ratio differs for each protein

Question 18

SDS-PAGE

Answer 18

denatures the proteins and masks the native charge so that comparison of size is more accurate, but the functional protein cannot be recaptured from the gel

Question 19

isoelectric focusing

Answer 19

separates proteins by their pI; the protein migrates toward an electrode until it reaches a region of the gel where pH=pI of the protein

Question 20

chromatography

Answer 20

separates protein mixtures on the basis of their affinity for a stationary phase or mobile phase

Question 21

column chromatography

Answer 21

uses beads of a polar compound, like silica or alumina (stationary phase), with a non polar solvent (mobile phase)

Question 22

ion-exchange chromatography

Answer 22

uses a charged column and a variably saline fluent

Question 23

size-exclusion chromatography

Answer 23

relies on porous beads

larger molecules elute first because they are not trapped in the small pores

Question 24

affinity chromatography

Answer 24

uses a bound receptor or ligand and an fluent with free ligand or a receptor for the protein of interest

Question 25

X-ray crystallography

Answer 25

method of determining protein structure after protein is isolated
NMR can also be used

Question 26

Edman degradation

Answer 26

determines amino acid sequencing through sequential degradation

Question 27

Bradford protein assay

Answer 27

determine protein concentration
uses a color change from brown-green to blue to test for protein
most common