Cell Membranes and Signalling

Question 1

state what it is meant by the key term - ligand

Answer 1

a ligand is any molecule, or ion, that is bound to a protein by electrical attractions or hydrophobic forces

Question 2

state, and explain, the two forces in which ligands can be bound to proteins

Answer 2

1. electrical attractions between oppositely charged ionic or polarised groups on the ligand and protein
2. weaker attraction due to hydrophobic forces between non polar forces on the two molecules

Question 3

state, and explain, what it is meant by the key term - binding site (4 points)

Answer 3

1. the point on the protein which the ligand binds to
2. not covalent + easily reversible
3. binding causes a conformational change in the shape of the protein
4. then proteins specific function is then activated/inactivated

Question 4

state what it is meant by the key term - chemical specificity

Answer 4

the ability of a protein binding site to bind specific ligands (in order to bind correctly, they must have a complementary shape)

Question 5

state 2 facts about binding sites

Answer 5

1. conformation determined by sequence of amino acids in the primary protein structure
2. some binding sites are only complementary in shape / specific to one ligand, and some to several

Question 6

state what it is meant by the key term - affinity

Answer 6

the strength of a ligand-protein binding - affinity determines how easily binding occurs and releases

Question 7

state the definitions for the three type of binding in relation to affinity

Answer 7

1. strong binding - site containing a positively charged amino acid side chain
2. less strong bonding - a site which has the same shape but not a positively charged amino acid side chain
3. weaker bonding - different shape and no positively charged amino acid side chain

Question 8

state what it is meant by the key term - saturation

Answer 8

the percentage total ligand binding sites that are occupied at one point in time

Question 9

state the two determinants of percentage saturation

Answer 9

1. concentration of unbound ligands in solution

2. ligand affinity to ligand binding site

Question 10

state the two ways to control protein activity

Answer 10

1. change the protein shape - alters ligand binding ability

2. regulating protein synthesis and degradation

Question 11

there are two mechanisms in cells which can selectively alter protein shape. name these two mechanisms

Answer 11

1. allosteric modulation

2. covalent modulation

Question 12

state what it is meant by the key term - allosteric modulation

Answer 12

occurs when a protein has two binding sites and the binding of a protein to one of the binding sites alters the shape of the other binding site

Question 13

state the names of the two binding sites on a protein (allosteric modulation)

Answer 13

1. functional/active site - carries out the proteins physiological functions
2. regulatory site

Question 14

state what it is meant by the key term - modulator molecules (allosteric modulation)

Answer 14

modulator molecules are ligands that bind to regulatory sites. it’s binding modulates the shape, and therefore activity, of the active site/functional unit of the protein

Question 15

state what it is meant by the key term - cooperativity

Answer 15

when a ligand binds to the first of several active/functional sites on a molecule and induces a change that increases the affinity of the other active/functional sites

Question 16

state what it is meant by the key term - covalent modulation

Answer 16

the covalent bonding of charged chemical groups to some of the protein side groups

Question 17

explain what kinase and phosphatase is (covalent modulation)

Answer 17

1. kinase - an enzyme that adds a phosphate group to another molecule
2. phosphatase - an enzyme that removes the phosphate group from another molecule

Question 18

metabolism consists of two aspects. state and explain these two aspects

Answer 18

1. anabolism - the synthesis of organic molecules

2. catabolism - the breakdown of organic molecules

Question 19

state what it is meant by the key term - 1 calorie

Answer 19

1 calorie = the amount of heat required to raise the temperature of 1 g of water by 1’c

Question 20

state what is is meant by the key term - 1 kcal

Answer 20

1 kcal = the amount of heat required to raise the temperature of 1000 g of water by 1’c

Question 21

state the 4 determinants of reaction rate

Answer 21

1. reactant concentration
2. activation energy
3. temperature
4. catalyst (present or not)

Question 22

state what it is meant by the key term - activation energy

Answer 22

the energy required to overcome the mutual repulsion from electrons surrounding the atoms that need to bump into each other

Question 23

state what it is meant by the key term - reaction rate

Answer 23

how many molecules of a product are formed per unit of time

Question 24

state what it is meant by the key term - ‘law of mass action’

Answer 24

the concentration of reactants, or produce, can determine the direction at which the net reaction proceeds (forward reaction, backward reaction, reversible reaction)

Question 25

state 3 facts about enzymes

Answer 25

1. they lower the activation energy 2. to function, an enzyme must come into contact with reactants 3. reactants bind to the active site of the enzyme

Question 26

state 3 facts about cofactors

Answer 26

1. most enzymes are inactive without cofactors 2. many cofactors are trace metals 3. binding of a metal to an enzyme alters it's conformation so that it can bind to the substrate (allosteric regulation)

Question 27

state 3 facts about coenzymes

Answer 27

1. the term coenzyme is used to describe an organic molecule 2. it directly participates as one of the substrates in the reaction 3. coenzymes are usually derived from vitamins

Question 28

give two examples of coenzymes

Answer 28

1. nicotinamide adenine dinucleotide (NAD) - derived from Niacin from green veg, meat, poultry, fish and eggs 2. flavine adenine dinucleotide (FAD) - derived from Riboflavin from milk, meat, eggs, nuts and green veg

Question 29

regulation of enzyme mediated reactions: (3 things)

Answer 29

1. substrate concentration 2. enzyme concentration 3. enzyme activity

Question 30

state what it is meant by the key term - maximal rate

Answer 30

maximal rate of reaction is reached when all the active sites are occupied by substrates

Question 31

state what it is meant by the key term - metabolic pathway

Answer 31

the sequence of enzyme mediated reactions leading to the formation of a particular product

Question 32

state what it is meant by the key term - 'the rate limiting reaction'

Answer 32

as all enzymes have different concentrations and activities, it is likely that one of the enzymes in the chain will be slower than the others - 'the rate limiting factor'

Question 33

state 2 facts about 'rate limiting enzymes'

Answer 33

1. often the site of allosteric of covalent modulation | 2. control of enzymes via modulation can be important in regulating the direction of reversible/irreversible reactions

Question 34

state the difference between agonists and antagonists when talking about receptors and cell signalling

Answer 34

1. antagonists - drugs that act as inhibitors | 2. agonists - drugs that mimic the messenger

Question 35

state what it is meant by the key term - receptor

Answer 35

a specific protein that a chemical messenger binds with, thereby invoking a biologically relevant response in that cell

Question 36

state what it is meant by the key term - specificity

Answer 36

the ability of a receptor to only bind to one, or a limited number, of structurally related types of chemical messengers

Question 37

state what it is meant by the key term - saturation

Answer 37

the degree to which receptors are saturated by messengers

Question 38

state what it is meant by the key term - affinity

Answer 38

the strength with which a chemical messenger binds with it's receptor

Question 39

state what it is meant by the key term - competition

Answer 39

the ability of different molecules to compete with a ligand for binding to it's receptor

Question 40

state what it is meant by the key term - antagonist

Answer 40

a molecule that competes with a ligand for binding to it's receptor but does not activate signalling normally associated with the natural ligand. therefore preventing the natural ligands actions

Question 41

state what it is meant by the key term - agonist

Answer 41

a chemical messenger that binds to the receptor and triggers a cell response

Question 42

state what it is meant by the key term - down-regulation

Answer 42

a decrease in the number of target cell receptors for a given messenger

Question 43

state what it is meant by the key term - up-regulation

Answer 43

an increase in the total number of target cell receptors for a given messenger

Question 44

state what it is meant by the key term - increased sensitivity

Answer 44

the increased responsiveness of a target cell to a given messenger

Question 45

state what it is meant by the key term - first messenger

Answer 45

the intercellular chemical messenger that reaches the cell and binds to it's receptor

Question 46

state what it is meant by the key term - second messenger

Answer 46

substances that enter, or are generated, in the cytoplasm as a result of receptor activation

Question 47

state what it is meant by the key term - protein kinases

Answer 47

transfer a phosphate from ATP to a protein and is often how a signal is transferred

Question 48

binding of a ligand to a receptor leads to 1 of 5 cell responses. state these 5 cell responses

Answer 48

1. the permeability, transport properties, or electrical state of the cell 2. metabolism 3. sensory activity 4. rate of proliferation and/or differentiation 5. contraction

Question 49

state 4 facts about water soluble messengers

Answer 49

1. broad range of receptors 2. receptors activate intracellular signalling cascades which effect cell function 3. receptors can activate downstream mediators which effect DNA transcription and other effects 4. faster response and less sustained that lipid soluble messengers