Biochem chapter 9 MCAT

glut 2

found in the liver (for glucose storage) and pancreatic b-islet cells(as part of the glucose sensor) it has a high km

glut 4

found in adipose tissues and muscles and is stimulated by insulin, has a low km

glycolysis

occurs in the cytoplasm of call cells and does not require oxygen. Yield 2 ATP from 1 molecule of glucose

glucokinase

the first step of glycolysis, converts glucose into glucose 6 phosphate. It is present in b islet cells as part of a glucose sensor, and is responsive to insulin

hexokinase

converts glucose into glucose 6 phosphate in peripheral tissues

phosphofructokinase-1(PFK-1)

phosphorylates fructose 6 phosphate into fructose 1,6 bisphosphate in the rate limiting step of glycolysis. Activated by AMP and fructose 2,6 bisphosphate and it is inhibited by atp and citrate

ATP and citrate

inhibits PFk-1

AMP and fructose 2,6 bisphosphate (F2,6-BP_

activates pfk-1

phosphofructokinase 2 (PFK-2)

produced fructose 2,6 biphosphate that activates pfk-1. activated by insulin and inhibited by glucagon

glucagon

inhibits phosphofructokinase 2 (PFK-2)

insulin

activates phosphofructokinase 2 (PFK-2)

glyceraldehyde 3 phosphate dehydrogenase

produces NADH which can feed the electron transport chain

pyruvate kinase

the enzyme that catalyzes the irreversible conversion of phosphoenolpyruvate (PEP) to pyruvate, generating ATP in the final step of glycolysis.

3- phosphoglycerate kinase

an enzyme that catalyzes the reversible transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP, producing 3-phosphoglycerate and ATP.

glucokinase/hexokinase, pfk-1, and pyruvate kinase

the enzymes that catalyze the irreversible reactions in glycolysis

mitochondrial electron transport chain

the NADH from glycolysis is oxidized by —— when oxygen is present

cytoplasmic lactate dehydrogenase

the NADH from glycolysis is oxidized by —— when oxygen or mitochondria are not present

lactate dehydrogenase

an enzyme that catalyzes the reversible conversion of pyruvate to lactate, and also converts NADH to NAD+.

galactose

comes from lactose in milk. It is trapped in the cell by galactokinase and is converted into glucose 1 phosphate by galactose-1-phosphate uridyltransferase and epimerase

fructose

comes from honey, fruit, and sucrose(table sugar). it is trapped in the cell by fructokinase, and then cleaved by aldolase b to form glyceraldehyde and DHAP

pyruvate dehydrogenase

a complex of enzyme s that convert pyruvate into acetyl coa. Stimulated by insulin and inhibited by acetyl coa

glycogenesis

(glycogen synthesis) production of glycogen using 2 main enzymes

glycogen synthase

creates the a 1,4 glycosidic links between glucose molecules. It is activated by insulin in liver and muscle

branching enzyme

moves a block of oligoglucose from one chain and adds it to the growing glycogen as a new branch using an a 1,6 glycosidic link

glycogenolysis

breakdown of glycogen

glycogen phosphorylase

removes a single glucose 1- phosphate molecule by breaking an a 1,4 glycosidic link. IN the liver this is activated by glucagon to prevent low blood sugar; in skeletal muscle this is activated by epinephrine and amp to provide glucose for the muscle itself

debranching enzyme

moves a block of oligoglucose from one branch and connects it to a chain using an a 1,4 glycosidic link. It also removes the branchpoint, which is connected via an a 1,6 glycosidic link- releasing a free glucose molecule

gluconeogenesis

creating glucose from a novel source. Occurs in the cytoplasm and the mitochondria, but mostly in the liver. There is a small contribution from the kidneys. This process is basically reverse glycolysis

pyruvate carboxylase

converts pyruvate to oxaloacetate which is converted to phosphoenolpyruvate (PEP) bu phosphoenolpyruvate carboxykinase

pyruvate carboxylates and phosphoenolpyruvate carboxykinase

these two enzymes bypass pyruvate kinase (first step in gluconeogenesis)

phosphoenolpyruvate carboxykinase/ pep carboxykinase

converts oxaloacetate into PEP

Fructose 1,6 diphosphatase

converts f 1,6- bp into fructose 6 phosphate bypassing pfk-1. This is the rate limiting step of gluconeogenesis. This step is activated by ATP directly and glucagon indirectly. It is inhibited by AMP directly and insulin indirectly

glucose 6 phosphatase

converts glucose 6 phosphate into free glucose, bypassing glucokinase. Found only in the ER of the liver

pentose phosphate pathway (PPP)

occurs in the cytoplasm of most cells, generates NADPH and sugars for biosynthesis

glucose 6 phosphate dehydrogenase

rate limiting step of ppp, activated by NADP+ and insulin, inhibited by NADPH

NADPH

a crucial reducing agent, particularly important for anabolic reactions and antioxidant defense.

NADH

energy carrier