final cellular energetics

Question 1

why does cellular metabolism occur in a series of small enzyme-catalyzed steps

Answer 1

it allows energy to be stored/extracted in useful ways

Question 2

how do catabolic reactions extract energy

Answer 2

through the breakdown of larger molecules into smaller ones

Question 3

how is glucose catabolized

Answer 3

by glycolysis and the citric acid cycle

Question 4

what glycolysis

Answer 4

metabolism of glucose; happens in cytosol

Question 5

what does the citric acid cycle do

Answer 5

allows for further oxidation of glucose using respiration; happens in mitochondria

Question 6

what are the electrons from glycolysis and the citric acid cycle used for

Answer 6

to generate ATP vis the electron transport chain and oxidative phosphorylation

Question 7

what is catabolism

Answer 7

chemical breakdown

Question 8

where does energy for cellular processes come from

Answer 8

catabolism of nutrients

Question 9

how is energy harvested in useful quantities

Answer 9

sugar/other nutrients are oxidized in small, enzyme-catayzed steps

Question 10

what happens with oxidation

Answer 10

electrons are removed

Question 11

how do enzymes allow energetically favorable reactions to occur

Answer 11

by coupling them with energetically unfavorable reactions

Question 12

what are the two phases of coupling of reactions by enzymes

Answer 12

metabolism of food molecule releases some energy and enzymes will couple this with formation of activated carrier molecule, then carrier will interact with other reactions

Question 13

what is glycolysis at its core

Answer 13

take one molecule of glucose and convert it to two molecules of pyruvate with the net production of 2 ATP molecules and 2 NADH molecules

Question 14

why is NADH referred to as a reducing power

Answer 14

because it has electrons available to reduce something else

Question 15

what is the first phase of glycolysis

Answer 15

investment (2 ATP are spent to overcome activation energy barriers and activate glucose)

Question 16

what is the second phase of glycolysis

Answer 16

cleavage (glucose is split into 2 3-carbon sugars)

Question 17

what is the third phase of glycolysis

Answer 17

energy generation (4 ATP molecules are generated from final oxidation of the 3-carbon sugars)

Question 18

what is reduction

Answer 18

addition of electrons - opposite of oxidation

Question 19

what are the two types of coupling reactions

Answer 19

catabolism - energetically favorable
anabolism - energetically unfavorable

both reactions are coupled for ATP

Question 20

what happens in glycolysis

Answer 20

one molecule of glucose is converted to two molecules of pyruvate with the net production of 2 ATP and 2 NADH molecules (“reducing power”)

energetically unfavorable

Question 21

why must cells use fermentation

Answer 21

in the absence of O2, cells must use fermentation to oxidize NADH or they will run out of NAD+ and be unable to do glycolysis

Question 22

what are the details of glycolysis

Answer 22

• enzyme makes a covalent linkage with substrate
  a high energy bond is then replaced with a phosphate, which is transferred to ADP to make ATP
• the energy released by hydrolyzing this bond drives the reaction

Question 23

what is substrate-level phosphorylation

Answer 23

organic molecule (substrate) phosphorylates ADP to ATP

Question 24

what is oxidative phosphorylation

Answer 24

free phosphate is directly attached to ADP without organic compound intermediate

Question 25

what are the two modes of fermentation

Answer 25

first leads to excretion of alcohol and CO2, second leads to excretion of lactate

Question 26

how much ATP does glycolysis yield per glucose molecule

Answer 26

2 ATP. further pyruvate metabolism will generate more

Question 27

what does glycolysis yield in addition to ATP

Answer 27

2 NADH molecules. in the presence of O2, they can be oxidized back to NAD+, which can cycle back to be used for more glycolysis

Question 28

what is NAD+

Answer 28

electron acceptor and electron cofactor

Question 29

what happens in the absence of O2

Answer 29

cells use fermentation to oxidize NADH, or they'll run out of NAD+

Question 30

what is fermentation

Answer 30

the mechanism cells use to regenerate NAD+ (two types)

Question 31

what is alcoholic fermentation

Answer 31

microbes use it to oxidize NADH back to NAD+ so they can continue glycolysis

Question 32

how does alcoholic fermentation occur

Answer 32

- glucose goes through glycolysis to make pyruvate and 2 NADH - convert NADH to NAD+ by donating electrons back to pyruvate - pyruvate is decarboxylated (2 protons are added are CO2 is given off) - regenerate NAD by reducing aldehyde and taking electrons from NADH - generates ethanol

Question 33

what is lactic acid fermentation

Answer 33

generate pyruvate and 2 NADH and have to regenerate NAD+

Question 34

how does lactic acid fermentation occur

Answer 34

- take electrons and put them directly back on pyruvate at carbonyl group to convert it into hydroxyl group - pyruvate is converted to lactate - lactate can be oxidized back to pyruvate, which can be reduced back to glucose by liver

Question 35

what is the purpose of lactic acid fermentation

Answer 35

allows maintenance of high level of glucose for muscles when only have enough oxygen to do glycolysis

Question 36

what are the two steps that aerobic organisms use to further oxidize pyruvate to CO2 and water

Answer 36

citric acid cycle (occurs in matrix) and electron transport chain (occurs in inner mitochondrial membrane)

Question 37

what happens in the citric acid cycle

Answer 37

- 4-carbon molecule + 2-carbon molecule to get 6-carbon molecule - then oxidize this and release CO2 to get a 4-carbon molecule again - use energy from oxidation to generate NADH/FADH2 molecules and a GTP molecule

Question 38

what does glycolysis need for rearranging

Answer 38

glucose and enzymes

Question 39

what are the advantages of biochemical cycles

Answer 39

- greater possibilities for regulation bc there are many steps - provides entry pointes for other molecules (in glycolysis, entry points only allow for things related to glucose) - lots of molecules are generated that are difficult to make from scratch

Question 40

what are the disadvantages of biochemical cycles (i.e. krebs cycle)

Answer 40

you need oxaloacetate for krebs cycle

Question 41

what does the citric acid cycle generate

Answer 41

6 NADH and 2 FADH2 per glucose molecule (add that to the 2 NADH from glycolysis + 2 NADH from pyruvate -> Acetyl CoA) = 10 NADH, 2 FADH2

Question 42

how can the energy used to reduce NAD+/FAD be used

Answer 42

it can be extracted to generate ATP, done by a proton pump that uses the energy of NADH/FADH2 oxidation to create a proton gradient across the inner mitochondrial matrix

Question 43

what reduction helps drive the formation of the proton gradient

Answer 43

the reduction of O2 to H2O provides another energetically favorable reaction

Question 44

what pumps protons out of the mitochondrial matrix

Answer 44

NADH and FADH2

Question 45

what is oxidative phosphorylation

Answer 45

ADP -> ATP generation by ETC in mitochondria

Question 46

putting it all together with catabolic metabolism

Answer 46

- generate pyruvate in cytosol via glycolysis - pyruvate enters mitochondria and is converted to acetyl CoA, which passes thru citric acid cycle - generate CO2, NADH - electrons from NADH and FADH pass through electron transport chain - use oxygen to generate water - proton gradient makes ATP