competitive binding/ cell surface receptors

Question 1

what does the plasma membrane of eukaryotic cells consist of?

Answer 1

50% protein, 40% lipid, and 2-10% carbohydrate

Question 2

describe the structure of eukaryotic cell membranes

Answer 2

-lipids form a continuous double layer (bilayer)
-some proteins extend across the bilayer and are exposed to both external and internal surfaces of the membrane

Question 3

what does the lipid bilayer in the plasma membrane of eukaryotic cells do?

Answer 3

inhibits the flow of most water-soluble molecules

Question 4

what are the most common proteins in the plasma membrane? less common?

Answer 4

-transmembrane proteins exposed to the external and internal surfaces of the membrane
-proteins exposed to the aqueous environment on only one surface of the membrane

Question 5

describe membrane carbohydrates. what do they form?

Answer 5

-oligosaccharide chains that are bound to proteins on the cell surface
-form a layer of glycoproteins referred to as the cell coat

Question 6

how is the entire membrane a dynamic structure?

Answer 6

protein and lipid components can move about laterally in a semi-fluid medium

Question 7

what are cell-surface receptors?

Answer 7

a class of membrane proteins that are involved in chemical signaling between cells

Question 8

what do ion-channel-linked receptors do?

Answer 8

convert chemical signals into electrical ones

Question 9

where can ion-channel-linked receptors be found?

Answer 9

in the nervous system where signals move at “warp speed” across synapses

Question 10

how do ion-channel-linked receptors work in the nervous system?

Answer 10

-chemical signals in the form of neurotransmitters are converted by the receptors into an electrical signal in the form of a voltage difference across the plasma membrane
-when the neurotransmitter binds to the ion-channel-linked receptor, the receptor changes its conformation such that a channel opens or closes, and allows ions to cross the membrane
-while one side of the membrane has numerous ions, the other does not, and the channel provides an opening through which the ions will rush into or out of the cell
-this flow of ions will either stop or start a nerve impulse

Question 11

where is the channel for ion-channel-linked receptors?

Answer 11

either through or near the receptor

Question 12

what ions generally go through ion-channel-linked receptors?

Answer 12

Na+, K+, Cl-

Question 13

what is the most numerous type of cell-surface receptor?

Answer 13

G-protein-linked receptors

Question 14

describe the structure of a G-protein-linked receptor

Answer 14

a single polypeptide chain that threads back and forth across the lipid bilayer seven times

Question 15

how do G-protein-linked receptors work?

Answer 15

-when a signal binds to the receptor, it moves through the G-protein and turns it on the internal side of the membrane
-the activated protein instigates a process that will alter cellular behavior

Question 16

what are some examples of G-protein-linked receptors (2)?

Answer 16

-the light activated photoreceptors in the eye
-the olfactory receptors that interpret odors

Question 17

which cell surface receptor triggers the slowest response?

Answer 17

enzyme-linked receptors

Question 18

how do enzyme-linked receptors work?

Answer 18

-the internal side of the receptor acts as an enzyme, which is only activated when the appropriate ligand binds to the external portion of the receptor
-the enzyme triggers a chain of events inside the cell

Question 19

give an example of enzyme-linked receptors

Answer 19

-insulin receptors
-the largest class of receptors within this family act as tyrosine kinases in which the phosphorylated protein residues will go on to affect responses to the original signal

Question 20

how can human disease be caused by changes in cell surface receptors

Answer 20

-if the receptor that activates a signaling cascade that regulates cellular functions such as cell division or cell development is compromised

Question 21

where is insulin produced?

Answer 21

the pancreas

Question 22

what can a lack of insulin lead to?

Answer 22

diabetes mellitus

Question 23

what does insulin do?

Answer 23

-increase in glucose transport and protein synthesis

Question 24

what cells will respond to insulin?

Answer 24

cells containing insulin receptors on their plasma membrane

Question 25

describe how insulin receptors work

Answer 25

-an increase in blood glucose levels stimulates the pancreas to release insulin -the hormone travels through the circulation and is recognized by cells containing the insulin receptor -insulin binds to the hormone binding domain of the receptor which is localized on the surface of insulin responsive cells -the binding of insulin to the receptor is a specific interaction analogous to the binding of an enzyme to its substrate -as a result of the binding, the receptor is activated and undergoes a structural change which is transmitted through the membrane to the effector domain of the receptor located on the cytoplasmic side -the activated receptor then causes a cascade of events within the cell, ultimately leading to an increase in glucose transport and protein synthesis

Question 26

what is the effector domain of the insulin receptor?

Answer 26

an enzyme (a tyrosine kinase) that is catalytically active only in the presence of insulin

Question 27

describe the blood typing procedures of human red blood cells

Answer 27

-when red blood cells containing the A glycoprotein (type A blood) are mixed with antibodies against this glycoprotein, the cells agglutinate

Question 28

what are lectins?

Answer 28

proteins or glycoproteins of nonimmune origin that cause cells to stick or clump together

Question 29

describe the structure of lectin receptors

Answer 29

-glycoproteins on the cell surface are composed of proteins covalently bound to oligosaccharide chains

Question 30

describe the oligosaccharides on lectin receptors

Answer 30

-usually contain fewer than 15 sugar residues -composed of glucose, mannose, galactose, fucose, galactosamine, and sialic acid

Question 31

describe the receptors for lectins and briefly how they function

Answer 31

-cell-surface glycoproteins -lectins bind to different sugar residues and hence bind to different cell-surface glycoproteins

Question 32

what are lectins sued for in cell biology?

Answer 32

to localize, characterize, and isolate specific membrane glycoproteins

Question 33

what are some common ways to detect Con A through microscopy?

Answer 33

-couple the lectin to a fluorescent dye and visualize it after cell binding by fluorescence microscopy -couple Con A to horse radish peroxidase which catalyzes a color producing reaction at the site of the receptor and lectin binding

Question 34

what can be used to determine the carbohydrate to which a lectin has an affinity to?

Answer 34

competitive binding or competitive inhibition

Question 35

how does competitive binding work?

Answer 35

-all cells have an assortment of carbohydrates on their surface included in their array of cell surface receptors -when an epithelial cell or blood cell is exposed to a lectin, the lectin will bind to the cell, form bridges between cells, and cause agglutination -addition of specific extraneous carbohydrate to the environment that contains cells with receptors will inhibit the agglutination in that the lectin will bind with the carbohydrate rather than the cell surface receptor -the competition for the binding sites of the lectin will be proportional in that the more extraneous carbohydrate that is present, the less lectin will be bound to the cells, and the less agglutination will be visible

Question 36

what will happen if a carbohydrate without the proper affinity for the lectin is added to the reaction?

Answer 36

the carbohydrate will not affect or inhibit the binding of the lectin to the cell surface receptor and the reaction will be observed as if no extra carbohydrate is present

Question 37

what are the components of the plasma membrane (7)?

Answer 37

-phospholipids -integral transmembrane proteins -peripheral proteins -glycoproteins -glycolipids -GPI anchored proteins -cholesterol

Question 38

describe the composition of glycoproteins (6)

Answer 38

-N-acetylglucosamine -mannose -fucose -galactose -sialic acid -N-acetylgalactosamine

Question 38

describe the assembly and location of glycoproteins

Answer 38

-near N-term of the protein -attached to the ER -folded by calreticulin -modified in the golgi -face the outside of the cell in the plasma membrane -no sugar residues on the inside/ cytoplasmic side of the membrane

Question 39

what are the functions of glycoproteins (9)? what glycoproteins provide each function?

Answer 39

-structure- collagen -protection- mucin -transport- transferrin -immunologic- immunoglobins, antibodies -catalysis- proteases, nucleases -enzyme- alkaline phosphatase -call attachment- fibronectin, laminin -receptor- insulin receptor -miscellaneous- glycophorin (RBC), fibrinogen (clotting)

Question 40

what do lectins do?

Answer 40

-play roles in cell surface receptor interaction and signaling -binds specifically with short oligosaccharide chains made up of sugar residues such as galactose, glucose, mannose, fructose, N-acetylglucosamine, N-acetylgalactosamine, and sialic acid -have multiple sugar binding sites causing cells to clump together -include abrus precatorius from jequirity bean and concanavalin A from jack bean

Question 41

describe how agglutination and competitive binding work together in blood

Answer 41

-lectin induced hemagglutination due to lectin linkage to the carbohydrates on the surface of the RBC -hemagglutination inhibited when lectin is incubates with specific carbohydrate prior to adding RBC. excess carbohydrate specifically binds lectin and competitively inhibits binding and clumping of RBC