carbohydrates and carbohydrate metabolism

Question 1

glycosidic linkage

Answer 1

bond between two sugar molecules

Question 2

function of glycogen

Answer 2

serves as an energy storage carbohydrate in plants, starch serves the same function in plants

Question 3

maltase

Answer 3

catalyzes hydrolysis of maltose into two glucose macromolecules, which is thermodynamically favorable.

Question 4

function of NAD+ and FAD

Answer 4

reduced to NADH and FADH2 when glucose is oxidized, then oxidized when delivering electrons to electron transport chain, generating the proton gradient used to generate ATP

Question 5

glycolysis

Answer 5

glucose is partially oxidized to form two identical pyruvic acid molecules.
Small amount of ATP and NADH produced, occurs in cytoplasm, doesn’t require oxygen.

produces 4 ATP and 2 NADH per glucose

Question 6

pyruvate dehydrogenase complex

Answer 6

pyruvate from glycolysis is decarboxylated to form an acetyl group, which is attached to coenzyme A.

small amount of NADH is produced (2 per glucose)

occurs in matrix, the innermost compartment of the mitochondria

Question 7

Krebs cycle or tricarboxylic acid cycle or citric acid cycle

Answer 7

citric acid formed from acetyl group in PDC, which is then decarboxylated and isomerized to regenerate the original oxaloacetate

2 carbon acetyl unit from acetyl CoA is combined with oxaloacetate to release two CO2 molecules

modest amount of ATP, 6 NADH, 2 FADH2, and 2 GTP per glucose are produced

Question 8

electron transport/oxidative phosphorylation

Answer 8

high energy electrons carried by NADH and FADH2 are oxidized by electron transport chain, dumping their electrons at beginning of chain

Protons pumped out of innermost compartment of mitochondria, providing energy for ATP flow

goals of this process are to reoxidize all the electron carriers reduced in glycolysis, PDC, and Krebs cycle and store energy in form of ATP in the process

Question 9

hexokinase

Answer 9

catalyzes first step of glycolysis, phosphorylation of glucose to glucose-6-phosphate

Question 10

why is phosphofructokinase responsible for the committed step of glycolysis

Answer 10

catalyzes transfer of phosphate group from ATP to fructose-6-phosphate to form fructose 1,6 biphosphate, which is a very favorable reaction (practically irreversible)

Question 11

fermentation function

Answer 11

regenerates NAD+ in anaerobic conditions, allowing glycolysis to continue in the absence of oxygen.

Question 12

oxidative decarboxylation

Answer 12

conversion of pyruvate to activated acetyl unit, attached to coenzyme A.

Question 13

cofactors

Answer 13

non protein compounds required by enzymes for biological activity

Question 14

two membranes of mitochondria

Answer 14

outer and inner membrane, each composed of a lipid bilayer

enzymes of electron transport chain and ATP synthesis involved in oxidative phosphorylation are bound to inner mitochondrial membrane

Question 15

prokaryotic aerobic respiration

Answer 15

don’t have to use energy to shuttle electrons into a mitochondrial matrix, so prokaryotes get two more high energy phosphate bonds from aerobic respiration than eukaryotes do

Question 16

electron transport chain

Answer 16

group of five electron carriers, each one reducing next member down the line.

first carrier is NADH dehydrogenase, which receives electrons from NADH. Final carrier is cytochrome C oxidase, which passes its reducing power to O2

Question 17

ATP synthase

Answer 17

large protein complex which contains a proton channel that spans the inner membrane.

passage of protons from intermembrane space through ATP synthase channel causes it to synthesize ATP from ADP + Pi

Question 18

What is the cost of ATP synthesis?

Answer 18

Four protons per molecule of ATP,

NADH is responsible for the pumping of 10 protons, so each NADH provides energy to produce approximately 2.5 ATP molecules

Question 19

glycerol phosphate shuttle

Answer 19

transports electrons from NADH generated in glycolysis to mitchondria

Question 20

gluconeogenesis

Answer 20

“glycolysis in reverse”

occurs when dietary sources of glucose are unavailable and when the liver has depleted its stores of glycogen and glucose

produces glucose and uses similar enzymes as glycolysis

produces glucose from non carbohydrate sources

lactate, oxaloacetate, and α-ketoglutarate are used as starting materials

Question 21

pyruvate carboxylase

Answer 21

responsible for first step of gluconeogenesis

Question 22

PEP carboxykinase

Answer 22

responsible for second step of gluconeogenesis, where oxaloacetate is phosphorylated to form phophoenolpyruvate (PEP)

Question 23

functions of fructose 1,6 biphosphatase and glucose-6-phosphatase

Answer 23

responsible for reversing the irreversible phosphorylation reactions of glycolysis and removing the phosphate groups from the intermediates

Question 24

reciprocal control function in glycolysis and gluconeogenesis

Answer 24

same molecule regulates two enzymes in opposite ways,

enzymes that catalyze irreversible reactions are heavily regulated by glycolytic intermediates that activate one enzyme and inhibit the other

Question 25

fructose-2,6 biphosphate

Answer 25

exerts reciprocal control on PFK and F-1,6-BPase, concentration of this intermediate is controlled by insulin and glucagon

high levels of insulin stimulates formation of F-2,6, BP, stimulating PFK and activating glycolytic pathway, fructose 1,6-biphosphatase is inhibited, turning off gluconeogenesis

when blood glucose is low, glucagon triggers breakdown of F-2,6-BP, stopping the stimulation of PFK and inhibiting glycolysis. Inhibition of fructose-1,6-biphosphatase is stopped, stimulating gluconeogenesis.

Question 26

when is cellular respiration stimulated and inhibited?

Answer 26

stimulated by energy defecits (high ADP:ATP or NAD+:NADH ratios) and inhibited by energy surpluses (high ATP:ADP ratios and high NADH:NAD+ ratios).

Question 27

glycogen

Answer 27

main form of carbohydrate storage in animals, formed by glycogenesis

Question 28

glycogenolysis

Answer 28

forms glucose from the dephosphorylation of glucose-6-P

glycogen breakdown

Glycogen phosphorylase is the enzyme that catalyzes the rate-limiting step in glycogen breakdown

Question 29

glycogenesis vs glycogenolysis

Answer 29

both occur in the liver and in skeletal muscle, opposing processes

insulin stimulates glycogenesis in order to store glucose

glycogenolysis occurs in response to glucagon when blood sugar levels are low, causing glucose to be released from the liver into the blood

Question 30

pentose phosphate pathway

Answer 30

diverts glucose 6 phosphate from glycolysis to form NADPH, ribose-5-phosphate, and glycolytic intermediates.

NADPH serves as an important reducing agent in many anabolic processes such as fatty acid synthesis, also neutralizes reactive oxygen species.

Question 31

glucose 6 phosphate dehydrogenase

Answer 31

first enzyme in PPP, inhibited by NADPH in negative feedback

Question 32

Krebs Cycle Steps

Answer 32

1. pyruvate dehydrogenase complex turns pyruvate into acetyl COA, releasing CO2 and NADH
2. Acetyl COA combines with oxaloacetate to form citrate, catalyzed by citrate synthase
3. Citrate turned to isocitrate by aconitase
4. Isocitrate dehydrogenase turns isocitrate to alpha ketoglutarate, one co2 is released and NADH is formed
5. Alphaketoglutarate dehydrogenase catalyzes formation of succinyl COA from Alpha ketoglutarate, releasing CO2 and NADH
6. Succinyl COA converted to Succinate by Succinyl COA synthase, releasing GTP
7. Succinate dehydrogenase catalyzes formation of Fumarate from Succinate, FADH2 generated
8. Fumarate converted to malate by Fumarase
9. Malate converted to Oxaloacetate by malate dehydrogenase, forming NADH.