CHAPTER 8

Question 1

chemical reaction

Answer 1

-occurs when atoms have enough energy to combine or change bonding partners
-reactants –> products
-chemical reactions in cells are organized in metabolic pathways that er interconnected

Question 2

metabolism

Answer 2

-sum total of all chemical reactions occurring in a biological system at a given time

Question 3

metabolic reactions

Answer 3

involve energy changes

Question 4

energy

Answer 4

-is the capacity to do work, or the capacity for change
-potential or kinetic energy
-energy can be converted from one form to another

Question 5

potential energy

Answer 5

energy stored as chemical bonds, concentration gradient, or change imbalance

Question 6

kinetic energy

Answer 6

the energy of movement

Question 7

anabolic reactions

Answer 7

complex molecules are made from simple molecules; energy is required

Question 8

catholic reactions

Answer 8

complex molecules are broken down to simpler ones; energy is released

Question 9

how are catabolic and anabolic reactions linked?

Answer 9

the energy released in catabolic reactions is used to drive anabolic reactions to do biological work; its an on going cycle

Question 10

laws of thermodynamics

Answer 10

-apply to all matter and all energy transformations in the universe
-energy is neither created nor destroyed
-when energy is converted from one form to another, some of that energy becomes unavailable to do work

Question 11

entropy

Answer 11

(S): a measure of the disorder in a system

Question 12

in biological systems:

Answer 12

-total energy is called enthalpy (H)
-free energy (G) is the usable energy that can do work
-unusable energy is represented by entropy (S) multiplied by the absolute temperature (T)
- H = G + TS

Question 13

change in energy can be measured in?

Answer 13

-calories or joules

Question 14

change in free energy (ΔG) of a chemical reaction

Answer 14

ΔG = ΔH -TΔS

Question 15

if ΔG is -

Answer 15

free energy is released

Question 16

if ΔG is +

Answer 16

free energy is required

Question 17

if free energy is not available

Answer 17

the reaction does not occur

Question 18

what does the second law of thermodynamics also state

Answer 18

-that disorder tends to increase because of energy transformations

Question 19

exergonic reactions

Answer 19

-release free energy (-ΔG)
-cell respiration
-catabolism

Question 20

catabolism

Answer 20

-breaks down an ordered reactant into smaller, more randomly distributed products –> complexity decreases (generates disorder)

Question 21

endergonic reactions

Answer 21

-consume free energy (+ΔG)
-active transport
-cell movements
-anabolism

Question 22

anabolism

Answer 22

-makes a single product (a highly ordered substance) out of many smaller reactants (less ordered) –>complexity (order) increases.

Question 23

chemical equilibrium

Answer 23

balance between forward and reverse reactions, a state of no net change
ΔG = 0

Question 24

ΔG is related to the equilibrium point

Answer 24

-the further towards completion the point of equilibrium is, the more free energy is released
-ΔG values near zero are characteristic of readily reversible reactions
-final equilibrium does not change, and ΔG does not change

Question 25

ATP

Answer 25

(adenosine triphosphate) -captures and transfers free energy -can be hydrolyzed to ADP and P, releasing a lot of energy for endergonic reactions -can also phosphorylate (donate a phosphate group to) other molecules, which gain some energy

Question 26

formation of ATP

Answer 26

-it is endergonic -ADP + P + free energy ---> ATP +H2O

Question 27

catalyst

Answer 27

increases rates of chemical reactions; they are no altered by the reactions

Question 28

most biological catalysts are?

Answer 28

-enzymes (proteins) that act as a framework in which reactions can take place -enzyme lower the energy barrier for reactions -enzymes can increase reaction rates by 1 million to 10^17 times

Question 29

activation energy (Ea)

Answer 29

-the amount of energy required to start a reactions -some reactions are slow because of an energy barrier -can come from heating the system -enzymes lower the energy barrier by bringing the reactants together

Question 30

transition state

Answer 30

activation energy puts the reactants in a reactive mode

Question 31

transition state intermediates

Answer 31

activation energy changes the reactants into unstable forms with higher free energy

Question 32

substrates

Answer 32

-another name for reactants -substrate molecules bind to the active site of the enzyme

Question 33

what determines an enzymes specificity

Answer 33

-the 3D shape determines it -changes in the shape changes the function -depends on precise interlocking of molecular shapes and interactions of chemical groups at the active site

Question 34

six categories of enzymes

Answer 34

-oxidoreductases -transferases -hydrolases -lyases -isomerases -ligases

Question 35

enzyme-substrate complex (ES)

Answer 35

-is held together by hydrogen bonds, electrical attraction, or covalent bonds - E + S --> ES --> E + P -enzyme may change while bound to the substrate but returns to its original form

Question 36

an enzyme may use on or more mechanisms to catalyze a reaction:

Answer 36

-orient substrates so they can react -induce strain by stretching the substrate-- makes bonds unstable and more reactive to other substrates -temporarily add chemical groups

Question 37

adding chemical groups:

Answer 37

-acid-base catalysis: side chains in the active site transfer H+ to or from the substrate, destabilizing covalent bonds (shift change) -covalent catalysis: a functional group in a side chain forms a temporary covalent bond with the substrate (break down over time) -metal ion catalysis: metal ions such as copper, iron, and manganese lose or gain electrons without detaching from the enzymes (important for oxidation-reduction reactions)

Question 38

induced fit

Answer 38

some enzymes change shape when it binds the substrate, which alters the shape of the active site

Question 39

ribozymes

Answer 39

-RNA molecules acting as biological catalysts -EX: RNA molecule catalyzes formation of peptide bonds between amino acids

Question 40

some enzymes require "partners"

Answer 40

-prosthetic groups: non-amino acid groups bound to enzymes -inorganic cofactors: ions permanently bound to enzymes -coenzymes: small carbon-containing molecules; not permanently bound

Question 41

what does the rate of catalyzed reactions depend on?

Answer 41

-depends on substrate concentration -concentration of an enzyme is usually much lower than the substrate -at saturation, all enzyme is bound to substrate; it is working at maximum rate

Question 42

maximum rate is used to calculate enzyme efficiency:

Answer 42

-molecules of substrate converted to product per unit time (turnover number) -range 1 to 40 milion molecules/second

Question 43

enzyme activity can be controlled in two ways:

Answer 43

-regulation of gene expression: how many enzyme molecules are made -regulation of enzyme activity: enzyme may change shape, or be blocked by regulators

Question 44

systems biology

Answer 44

-the complex pathways are modeled using computer algorithms -enzymes help organize and regulate metabolic pathways

Question 45

enzyme inhibitors

Answer 45

-molecules that bind to the enzyme and slow reactions rate -naturally occurring inhibitors regulate metabolism -artificial ones can be used to read disease, kill pests, or study how enzymes work

Question 46

irreversible inhibition

Answer 46

-inhibitor covalently bonds to side chains in the active site and permanently inactivates the enzyme

Question 47

reversible inhibition

Answer 47

-inhibitor bonds non-covalently to the active site and prevents substrate from binding

Question 48

competitive inhibitors

Answer 48

-compete with the natural substrate for binding sites -degree of inhibition depends on concentration of substrate and inhibitor -EX: cancer drug methotrexate

Question 49

uncompetitive inhibitors

Answer 49

-bind to the enzyme -- substrate compex, preventing release of products

Question 50

noncompetitive inhibitors

Answer 50

-bind to enzyme at a different site (not the active site) -the enzyme changes shape and alters the active sire (allostery)

Question 51

allosteric regulation

Answer 51

-a non-substrate molecule binds enzyme at a site different from the active site, which changes enzyme shape -active form: proper shape to bind substrate -inactive form: cannot bind substrate -non-substrate molecules may be an inhibitor or an activator

Question 52

allosteric enzymes

Answer 52

-reaction rate is very sensitive to substrate concentration -they are very sensitive to low concentrations of inhibitors -making them important in regulating metabolic pathways

Question 53

metabolic pathways

Answer 53

-first reaction is the commitment step -- other reactions then happen in sequence -feedback inhibition: the final product acts as a noncompetitive inhibitor of the first enzyme, which shuts down the pathway

Question 54

how are enzymes regulated? and activated or deactivated?

Answer 54

-many enzymes are regulated through reversible phosphorylation -can be activated when protein kinase adds a phosphate group, and activated by a protein phosphatase

Question 55

when are enzymes most active?

Answer 55

-most active at a particular pH, which influences ionization of functional group

Question 56

enzymes in relation to temperature

Answer 56

-every enzyme has an optimal temperature; high temps, non covalent bonds begin to break; warming up --> speeds up, but too much warming denatures it -some are adapted to warm temps and do not denature -ex: most human enzymes are more stable at high temps