BSCI330 cellular energetics

Question 1

what are catabolic reactions

Answer 1

taking big molecules and breaking them down into small molecules (anabolic is reverse)

Question 2

how is glucose catabolyzed

Answer 2

via glycolysis in cytosol and citric acid cycle in mitochondria

Question 3

what is cellular metabolism

Answer 3

process by which cells transfer energy from one source to another to do work

Question 4

where does cellular metabolism energy come from

Answer 4

chemical breakdown (catabolism) of nutrients

Question 5

what does it mean when something is oxidized

Answer 5

electrons are removed

Question 6

what is reduction

Answer 6

opposite of oxidation - addition of electrons

Question 7

why do enzymes reduce activation energy

Answer 7

to avoid the release of large quantities of heat

Question 8

how do enzymes allow energetically unfavorable reactions to occur

Answer 8

by coupling them with energetically favorable reactions

Question 9

what are the two types of coupling reactions

Answer 9

catabolism - energetically favorable
anabolism - energetically unfavorable

both reactions are coupled for ATP

Question 10

what happens in glycolysis

Answer 10

in cytosol - 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 11

what are the three phases of glycolysis

Answer 11

investment: 2 ATP are spent to activate glucose
cleavage: glucose is split into 2 3-carbon sugars

energy generation: 4 ATP molecules are generated

Question 12

what does glycolysis yield

Answer 12

2 ATP molecules/glucose molecule. further metabolism of pyruvate will generate more

also yields 2 NADH molecules. in the presence of O2, they can be oxidized back to NAD+, regenerating the cofactor required for glycolysis

Question 13

why must cells use fermentation

Answer 13

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 14

what are the two modes of fermentation

Answer 14

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

Question 15

what are the two oxidation steps of pyruvate that can occur with oxygen

Answer 15

citric acid cycle (aka Krebs): matrix

electron transport chain: inner mitochondrial membrane

Question 16

what does the Citric Acid Cycle begin with

Answer 16

the transport of pyruvate into the mitochondrial matrix, where it’s oxidized to form Acetyl CoA plus carbon dioxide

Question 17

how is citrate formed in the citric acid cycle

Answer 17

the 2-carbon acetyl group is added to oxaloacetate

Question 18

how is CO2 generated in the citric acid cycle

Answer 18

a series of steps rearrange the bonds and oxidize citrate to generate CO2, reducing power (NADH/FADH2) and GTP

Question 19

what is the net result of the citric acid cycle

Answer 19

one turn of the cycle produces 3 NADH, 1 GTP, 1 FADH2, and releases 2 CO2 molecules

the citric acid cycle generates 6 NADH and 2 FADH2 per glucose molecule (add that to the 2 NADH from glycolysis)

Question 20

what do proton pumps do

Answer 20

create a proton gradient across the inner mitochondrial membrane

Question 21

what does the krebs cycle generate

Answer 21

4 ATP

Question 22

what are the steps of the krebs cycle to generate ATP

Answer 22

stage 1: electron transport drives pump that pumps protons across membrane

stage 2: protein gradient is harnessed by ATP synthase to make ATP

the energy of the proton gradient is used by the F-type proton pump (aka ATP synthase) to convert ADP to ATP

Question 23

what does photosynthesis do

Answer 23

uses light energy to generate chemical energy (ATP) and reducing power (NADPH) to allow carbon dioxide to be fixed into organic molecules

Question 24

what is photosynthesis

Answer 24

synthesis of simple sugars from CO2 and H2O

Question 25

what are the two stages of photosynthesis

Answer 25

light reactions and dark reactions

Question 26

what are light reactions

Answer 26

(happen in light) harness light energy to generate ATP and NADPH: thylakoid membranes

Question 27

what are dark reactions

Answer 27

(don’t need light) use ATP and NADPH to fix carbon dioxide into 3-carbon sugars: stroma

Question 28

what are the three chloroplast sets of membranes

Answer 28

outer, inner, thylakoid

Question 29

explain light reactions

Answer 29

the energy of light is captured by chlorophyll in the form of excited electrons which is used to generate high energy electrons from an electron donor and transfer them to special chlorophyll molecules in the reaction center

in photosystem II
uses light energy to split 2 water molecules into 4 H+ and O2 and excite 4 electrons, which pass thru ETC to generate a proton gradient (generates ATP) and protons are pumped into thylakoid space

the final electron acceptor is Photosystem I, which excites the electrons and passes them to NADP+ to generate NADPH

Question 30

explain dark reactions

Answer 30

CO2, NADPH, and ATP are used to generate the 3-carbon sugar glyceraldehyde 3-phosphate

the reaction occurs in the calvin cycle, analogous to Krebs cycle, starts with addition of 3 CO2 to 3 molecules of ribulose 1,5-bisphosphate

some energy is lost as heat instead of being turned into ATP - this accounts for why dark reactions don’t net the same amount of ATP as oxidation of glucose does