Metabolism

Question 1

metabolism:

Answer 1

all chemical processes going on continuously inside the body that allow life and normal functioning (homeostasis)

Question 2

catabolism:

Answer 2

breakdown of larger molecules

Question 3

anabolism:

Answer 3

synthesis of larger molecules

Question 4

what is the reaction of glucose (including metabolism)

Answer 4

C6H12O6 + 6O2 -> 6CO2 + 6H2O (metabolism occurs in the middle, at the arrow)

Question 5

what is ∆G

Answer 5

change in free energy during a reaction in vivo

Question 6

exergonic reaction:

Answer 6

free energy is released, ∆G is negative

Question 7

endergonic:

Answer 7

an input of free energy is needed to drive the reaction, ∆G is positive

Question 8

what happens when ∆G is 0

Answer 8

a system is at equilibrium and no net change can take place

Question 9

what is ∆G°’:

Answer 9

change in free energy during a reaction under standard conditions

Question 10

where does the free energy used in glycolysis come from

Answer 10

the hydrolysis of ATP

Question 11

the hydrolysis of ATP is

Answer 11

exergonic

Question 12

enzymes:

Answer 12

• catalysts that speed up chemical reactions
• are not permanently altered during the course of a reaction
• affect only the rates of reactions
• are present in small amounts
• are highly specific for their particular reactants (substrates)
• can be regulated to meet the needs of a cell

Question 13

enzymes may be conjugated with:

Answer 13

non-protein components (co-factors and co-enzymes)

Question 14

enzymes are mediators of:

Answer 14

metabolism, responsible for virtually every reaction that occurs in a cell. without enzymes, metabolic reactions would proceed so slowly as to be imperceptible

Question 15

the active site and the substrate have:

Answer 15

complimentary shapes that allow substrate specificity

Question 16

the active site:

Answer 16

• region of the enzyme that binds substrate (and cofactor/coenzymes)
• contains the residues that directly participate in the making and breaking of bonds (catalytic groups)

Question 17

catalyst:

Answer 17

a substance that increases the rate or velocity of a chemical reaction (without itself being changed in the overall process)

Question 18

how does a catalyst work?

Answer 18

• by lowering the activation energy thereby increasing the fraction of molecules that have enough energy to attain the transition state and makes the reaction go faster

Question 19

what happens to free energy with a catalyst

Answer 19

nothing, it stays the same. only the rate of the reaction changes

Question 20

Vmax:

Answer 20

the velocity at saturation (at saturation every enzyme is working at full capacity)

Question 21

Km:

Answer 21

the Michaelis constant, the substrate concentration at one-half of Vmax

Question 22

what is the relationship between Km and affinity

Answer 22

the higher the Km, the greater the substrate concentration that is required to reach one half Vmax and the lower the affinity of the enzyme for that substrate. The lower Km = higher affinity

Question 23

what are other factors that strongly influence enzyme kinetics

Answer 23

pH and temperature

Question 24

temperature effects of enzymes

Answer 24

enzymes have an optimal temperature where activity peaks. At temperatures lower, activity decreases and at temperatures higher, denaturation occurs

Question 25

pH effects of enzymes

Answer 25

reaction rates are highest at the optimal pH. enzymes are activated at different pH

Question 26

Km is the concentration of substrate at which:

Answer 26

half of the enzyme sites are filled and therefore provides a measure of the substrate concentration required for ‘significant’ catalysis to occur

Question 27

ethanol forms into toxic methanol and ethylene glycol. how do you prevent these toxic metabolic products to form?

Answer 27

alcohol dehydrogenase has a higher affinity for ethanol than it does for methanol or ethylene glycol (lower Km)

Question 28

an increase in glucose in the bloodstream following a rich carbohydrate meal stimulates the secretion of ____ by the pancreas. ____ binds to:

Answer 28

1. insulin, insulin
2. insulin receptor which results in a variety of signals transmitted to the cell. among these signals are the recruitment of glucose transport proteins (GLUT4) from the cytosol to the membrane in muscle cells and adipocytes

Question 29

glycated hemoglobin (GHB):

Answer 29

is used to measure ‘average’ blood glucose concentrations over time

Question 30

what would you expect to see if blood glucose concentrations are elevated over time?

Answer 30

AGEs

Question 31

AGEs:

Answer 31

advanced glycation end products. can covalently cross-link to proteins. the more of this that occurs, the higher the potential damage

Question 32

irreversible inhibitors:

Answer 32

bind tightly to the enzyme (often covalently)

Question 33

competitive inhibitors:

Answer 33

compete with the substrate for active sites and usually resemble the substrate in structure. a type of reversible inhibitor

Question 34

noncompetitive inhibitors:

Answer 34

bind to a site different than the substrate and change the conformation of the enzyme inhibiting substrate binding (allosteric inhibitors). a type of reversible inhibitor

Question 35

allosteric inhibition steps:

Answer 35

without allosteric inhibitor: high affinity form of enzyme. substrate binds to active site, product formation occurs.
with allosteric inhibitor: low affinity form of enzyme. allosteric inhibitor binds to site other than active site, changing conformation of active site. substrate can’t bind or can’t bind well, leading to little or no product formation.

Question 36

allosteric activation steps:

Answer 36

without allosteric activator: low affinity form of enzyme, allosteric site is empty, substrate does not bind to active site = little or no product formation
with allosteric activator: high affinity form of enzyme, allosteric activator binds to allosteric site, changing conformation of active site allowing substrate to bind, product formation occurs

Question 37

how is ATP made

Answer 37

one 6 carbon glucose is converted to two 3 carbon molecules of pyruvate at the end of the 10 steps of glycolysis. 2 ATP is used, 4 ATP are generated for a net gain of 2 ATP. 2 NADH are generated

Question 38

NADH

Answer 38

carries 2 electrons that will be passed onto the electron transport chain and will be transferred to molecular oxygen resulting in formation of ATP

Question 39

FADH2

Answer 39

carries 2 electrons that will be passed onto the electron transport chain and will be transferred to molecular oxygen resulting in formation of ATP

Question 40

NADH and pyruvate from glycolysis:

Answer 40

enters the mitochondrial mix

Question 41

pyruvate is converted to:

Answer 41

acetyl-CoA. these reactions occur on the pyruvate dehydrogenase complex

Question 42

where are the 3 carbons lost in glycolysis

Answer 42

2 carbons are lost through CO2 during the formation of 2 molecules of pyruvate, 2 molecules are lost during the citric acid cycle (TCA) - which runs twice (totalling 4)

Question 43

glycolysis also forms:

Answer 43

3 molecules of NADH, one molecule of FADH2, both of which go to the electron transport chain

Question 44

describe the electron transport chain

Answer 44

• complexes 1,3,4 are proton pumps: protons accumulate in the intermembrane space
• protons flow down through ATP synase
• this turns C subunit, gamma and changes conformation of alpha beta dimers
• leads to ATP synthesis as protons move down their gradient back to the matrix

Question 45

1. ___ protons per pair of electrons that enter complex ___ from ____
2. ___ protons per pair of electrons that enter complex ___ from ____

Answer 45

1. 10, 1, NADH
2. 6, 2, FADH2

Question 46

protons flow from the inner membrane:

Answer 46

through a channel in the a subunit, then enter the c subunit. this results in a rotation of the c subunit and the gamma subunit which is associated with the c subunit

Question 47

ATP synthesis occurs as a result of:

Answer 47

the conformational changes of the alpha-beta dimers

Question 48

there are ___ dimer conformations.

Answer 48

3, at any given time, each of the 3 dimers is in one of them.

Question 49

in order to synthesize ATP, each dimer goes through:

Answer 49

all 3 conformations

Question 50

what happens in the 3 conformations of the dimer

Answer 50

1. in the loose conformation, substrate enters/is trapped (ADP and inorganic phosphate (Pi)
2. in the tight formation, ATP is formed
3. in the open conformation, ATP is released

Question 51

what are the importance of coupled reactions

Answer 51

when a reaction is endergonic (requires energy), it is very unlikely that this reaction will occur. An exergonic reaction such as hydrolysis of ATP that releases a lot of energy can be ‘coupled’ to the endergonic reaction, therefore pushing the reaction along and getting rid of the positive delta G.