Catabolic Metabolism I and II

Question 1

How do cells couple ATP hydrolysis to work?

Answer 1

mechanical work - protein changes conformation

transport work - transfer of phosphate changes conformation for transport of molecules across membranes

biochemical work - coupling favorable to unfavorable reactions, creation of activated intermediates

Question 2

cellular homeostasis

Answer 2

the property of a sytem that regulates its internal environment and tends to maintain a stable, constant condtion of properties

Question 3

Name the three homeostatic mechanisms.

Answer 3

1. receptor that senses a stimulus
2. control center (integrator) that determines the response to the stimulus
3. effector that carries out instructions from the control center using positive or negative feedback mechanisms

Question 4

Are most sugars in the body D or L sugars?

Answer 4

D sugars

Question 5

mutarotation

Answer 5

opening and closing of the carbohydrate ring that allows changes in the position of the hydroxyl attached to the anomeric carbon

Question 6

pyolol

Answer 6

formed by reduction of the aldehyde in an aldose sugar, all of the carbons contain hydroxyl groups

Question 7

Name the major dietary carbohydrates and their subcompnents.

Answer 7

Maltose - glucose 1-4 glucose

Lactose - galatose 1-4 glucose

Sucrose - glucose 1-2 fructose

Question 8

Name the three types of storage sources for glucose.

Answer 8

amylose, amylopectin, and glycogen

Question 9

glycogen

Answer 9

branched polymer of glucose linked by 1-4 glycosidic bonds except at branches which are 1-6 bonds, highly branched, degraded by glycogen phosphorylase and debranching enzyme

Question 10

How does glucose get transported into the cell?

Answer 10

Question 11

Recite glycolysis.

Answer 11

Question 12

What is the key regulatory step of glycolysis?

Answer 12

phosphorylation of Fructose-6-P to fructose-1,6-bisphosphate, catalyzed by phosphofructokinase-1, thermodynamically and kinetically irreversible

Question 13

fructose metabolism

Answer 13

transported into cells by GLUT5

mainly metabolized in the liver

Question 14

essential fructosuria

Answer 14

benign condition due to absence of fructokinase, fructose is excreted in the urine

Question 15

hereditary fructose intolerance

Answer 15

due to absence of aldolase B, leading to accumulation of fructose 1-phosphate

Question 16

galactose metabolism

Answer 16

also known as Leloir Pathway, converted to glucose to enter glycolysis

Question 17

classical and non-classical galactosemia

Answer 17

classical - GALT deficiency, build up of galactose-1-P, can lead to neurological damage

non-classical - GALE deficiency, galactose excreted in urine

Question 18

Describe the different regulatory mechanisms in glycolysis

Answer 18

regulation by ATP/ADP/AMP and cintrate levels

levels of product and substrate regulate PFK-1 and PFK-2

glucokinase in liver regulated byby nuclear mechanism GKRP

Question 19

anaerobic glycolysis

Answer 19

NADH is reoxidized in the cytosol by lactate dehydrogenase by the reduction of pyruvate to lactate

Question 20

hemolytic anemia

Answer 20

erythrocyte pyruvate kinase deficiency

Question 21

Warburg Effect

Answer 21

high rate of glycolysis in malignant tumor cells, need for ATP and ribose-5-phosphate, many times these cells experience anaerobic conditions in tumors

Question 22

metabolism of sugar alcohols

Answer 22

in hyperglycemic conditions, excess sorbitol can cause tissue damage due to osmotic effects

Question 23

fatty acid oxidation

Answer 23

major source of energy between meals and during increased demand

during fasting, provides ketone bodies as fuel for many tissues

higher energy yield per mole than glucose

occurs primarily in the mitochondrial matrix

Question 24

activation and transport of fatty acids

Answer 24

uses carnitine to transfer fatty acids into the mitochondrial matrix, several important transfer proteins are used such as carnitine palmitoyl transferase I (CPTI)

Question 25

Describe the beta-oxidation process of long chain fatty acids

Answer 25

shortened 2 carbons at a time by a series of 4 reactions

general process - oxidation, hydration, oxidation, cleavage

Question 26

regulation of beta oxidation

Answer 26

blocked at high levels of reduced factors

oxidation pathways turn off malonyl-CoA

oxygen and a functioning ETC is required

Question 27

oxidation of odd chain fatty acids

Answer 27

undergo beta-oxidation until a 3 carbon propionyl CoA, which is converted to succinyl CoA for the TCA cycle

Question 28

energy yield for beta-oxidation

Answer 28

1 mole of palmitate (C16) leads to 28 moles of ATP from the 7 FADH2 and 7NADH molecules generated, 2 moles were consumed for activation

Question 29

very long chian fatty acid oxidation

Answer 29

usually for more than 22 carbons, undergoes alpha and beta oxidation in the peroxisome

first step produces hydrogen peroxide

acetyl-CoA molecules and short acyl-CoAs are derivatized with carnitine and diffuse from peroxisomes to be taken up by mitochondria and fully oxidized

Question 30

omega-oxidation

Answer 30

carried out in the ER

omega methyl group is oxidized to an alcohol and then turned into a carboxylic acid

the resulting dicarboxylic acids are oxidzed by beta-oxidation to compounds that are 6-10 carbons long

released in the blood and then oxidized or excreted in urine (usually indicating failure of beta-oxidation pathways)

Question 31

oxidation fo ketone bodies

Answer 31

oxidation of beta-hydroxybutyrate and acetoacetate, the first is more reduced and provides more energy

done in mitochondrial matrix, often used in starvation conditions

Question 32

disorders of fatty acid oxidation

Answer 32

carnitine deficiency or defect in carnitine transferase or translocase

hyperketotic hypoglycemia - caused by medium chain fatty acyl CoA dehydrogenase deficiency

dicarboxylic aciduria - consequence of omega oxidation when beta oxidation is impaired

Zellweger syndrome - defect in peroxisome biogenesis, cannot oxidize very long chain fatty acids

Question 33

pyruvate dehydrogenase complex (PDC)

Answer 33

lniks glycolysis to TCA cycle by oxidizing pyruvate to acetyl CoA, mitochondiral large multi-subunit enzyme complex with three functional proteins

reaction uses oxidation to liberate CO2 from pyruvate - called oxidative decarboxylation

Question 34

Name the three subunits of PDC and their functions.

Answer 34

pyruvate dehydrogenase (E1) - uses thiamine pyrophosphate as a cofactor, catalyzes the decarboxylation step and transfers acetyl group to lipoate cofactor of E2

dihydrolipoyl transacetylase (E2) - uses lipoate and CoA to transfer acetate to CoA

dihydrolipoyl dehydrogenase (E3) - uses FAD and NAD to re-oxidize the lipoate cofactor of E2

Question 35

regulation of pyruvate dehydrogenase

Answer 35

ATP/ADP, NADH/HAD+, and acetyl-CoA/CoA ratios are the main regulators

phosphatase and kinase activate and deactivate the complex

during starvation there is high kinase, which prevents glycolysis from preceding, turning to fat and muscle oxidation

Question 36

Describe and recite the tricarboxylic acid cycle.

Answer 36

accounts for 2/3 of ATP production from fuel oxidation

utilizes acetyl CoA from glucose, fatty acids, amino acids, and keton bodies

occurs in the mitochondrial matrix

activity tightly cooridnated with rate of electron transport chain and oxidative phosphorylation by feedback regulation reflecting the demand for ATP

Question 37

What are the steps that are largely negative in the TCA cycle?

Answer 37

citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase

Question 38

What are the important positive free energy steps of the TCA cycle?

Answer 38

malate dehydrogenase and aconitase

Question 39

Deficienccies of what three enzymes in the TCA are more commonly found in diseases?

Answer 39

fumarase, succinate dehydrogenase, and alpha-ketoglutarate dehydrogenase

Question 40

alcohol metabolism

Answer 40

Question 41

disulfuram

Answer 41

a drug that inhibits acetaldehyde dehydrogenase, makes person sick after alcohol, negative stimulus for drinking