METABOLISM SYLLABUS 1: Intro to Metabolism & to Metabolic Regulation by Insulin & Glucagon

Question 1

metabolism?

Answer 1

sequence of enzyme-catalyzed reactions that brings about the transformation of substrate to product

Question 2

major purposes of metabolism?

Answer 2

1) obtain & trap chemical energy from substrates
2) build precursors to macromolecules from substrates
3) assemble precursors into macromolecules like DNA, glycogen, fat
4) degrade macromolecules into simpler molecules (like glycogen to glucose)

Question 3

catabolism vs. anabolism?

Answer 3

catabolism: oxidative breakdown of large macromolecules into smaller, simpler compounds. accompanied by release of free energy, trapping it as ATP - e.g. glucose -> pyruvate

anabolism: enzymatic synthesis of large macromolecules from smaller, simpler precursors. requires energy input - e.g. pyruvate -> glucose

Question 4

what are amphibolic pathways?

Answer 4

pathways w/ both cataboilc and anabolic components - so can both breakdown and synthesize

e.g. TCA cycle

Question 5

what are the major differences in catabolism and anabolism? why?

Answer 5

1) ENZYMES

2) ENERGETICS: ATP made in catabolism, used in anabolism

3) COFACTORS: NAD⁺->NADH in catabolism and NADPH -> NADP⁺in anabolism

4) CELLULAR LOCALIZATION: fatty acid oxidation in th emito, fatty acid synthesis in the cyto

identical pathways would prevent regulation, lead to futile cycling and energy waste

Question 6

what regulates metabolism?

Answer 6

1) availability and concetration of substrates & cofactors
2) availability and need for energy/ATP
3) regulatory enzymes
4) enzyme characteristics
5) genetic control of amt of enzyme in cell
6) hormonal regulation

Question 7

what is end product feedback inhibition?

Answer 7

principle that anabolic reations are often inhibited by products of that very anabolic reaction

Question 8

constituitive vs. adaptive enzymes?

Answer 8

constituitive: enzymes that’re always present in constant or near-constant amount; are the more important enzymes

adaptive: enzymes that can increase or diecrease under certain metabolic conditions, in reaction to a substrate, toxin, or drug which changes their amount in response to a signal

Question 9

hormones?

Answer 9

chemical messenger produced in a tissue which will modify a specific metabolic reaction in aonther tissue

often acts on regulatory enzymes or activates or represses gene expression

Question 10

what methods can determine the rate limiting step in a biochemical pathway?

Answer 10

1) assays on relative activites
2) comparisons of the equilibrium constant to the mass action ratio

Question 11

which enzyme in a pathway is the rate limiting enzyme?

Answer 11

enzyme with the lowest relative activity and enzymes with big discrepancy between their Keq and mass action ratio

Question 12

what are the rate limiting enzymes of glycolysis?

Answer 12

hexokinase, phosphofructokinase, and pyruvate kinase

Question 13

what is the effect of an inhibitor on a rate-limiting vs. non-rate-limiting enzyme?

Answer 13

an inhibitor of a rate-limiting enzyme inhibits the overall pathway

an inhibitor of a non-rate-limiting enzyme inhibits the enzyme but likely not the overall pathway

Question 14

what enzymes are most likely to be regulated?

Answer 14

relatively low active enzymes and enzymes that fail to maintain equilibrium are likely to be regulated

Question 15

what is the RBC’s only form of energy?

Answer 15

glucose. they do not have mitochondria!

Question 16

what organi is the major controller of our metabolism?

Answer 16

liver

Question 17

what processes during glycolysis cause the release of ATP?

Answer 17

susbtrate level phosphorylation or oxidative phosphorylation

Question 18

what kind of energy does ATP hydrolysis yield?

Answer 18

ATP -> ADP + P_ihas a deltaG of 7-8 Kcal/mol

ATP is a high energy compound, and yields a middle-amount of energy compared to other compounds

Question 19

what happens when ATP is hydrolyzed to ADP?

what happens when ATP is hydrolyzed to AMP?

Answer 19

ATP -> ADP + P_idissipates 1 high energy bond

ATP -> AMP + P_iP_idissipates 2 high energy bonds

P_iP_i, pyrophosphate, is rapidly hydrolyzed to 2 molecules of P_iby pyrophosphatase

Question 20

what is the structure of NAD⁺ vs NADH

Answer 20

NAD+ is oxidized, NADH is reduced

Question 21

what is the difference between FAD and FADH₂?

Answer 21

FAD is oxidized, FADH₂ is reduced

Question 22

what hormones regulate glucose/fatty acid metabolism?

Answer 22

insuiln, glucagon, epinephrine (epi)

insulin + epi regulate glucose & fatty acid metabolism in mayn tissues

glucagon acts primarily on the liver & adipose tissue

Question 23

where is epi produced? when?

Answer 23

in adrenal glands

in response to stress

produced from phenylalanine + tysoine by catacholamine synthesis pathway

Question 24

where are insulin and glucagon produced? when?

Answer 24

beta (insulin) and alpha (glucagon) cells of the pancrease

in response to glucose levels:

INSULIN in response to HIGH glucose (high carb diet)

GLUCAGON in response to LOW glucose (starvation)

Question 25

primary function of insulin?

Answer 25

promote use of glucose

Question 26

primary function of glucagon?

Answer 26

promote production of glucose by the liver

Question 27

what causes type 1 diabetes?

Answer 27

destruction of the B cells of teh pacnreas largely via autoimmune attack on these cells leads to lack of insulin production

Question 28

what causes type 2 diabetes?

Answer 28

insulin is produced but its effectiveness in enhancing utilization of glucose is decreased, which means increased resistance to actions of insulin

Question 29

what do obesity + lack of exercise lead to

Answer 29

type 2 diabetes

Question 30

what metabolic problems does diabetes cause

Answer 30

build up of high levels of glucose, esp. in the blood, lead to: 1) impaired energy production from glucose 2) fat metabolism's elevated to provide energy, but much fat is oxidized to acidic ketone bodies -\> ketosis 3) high circulating glucose levesl react non-enzymatically w/ prteins/enzymes, glycosylate them, form modified proteins w/ altered funtions 4) glucose can be reduced by aldose reducatse to sorbitol which increaes osmotic pressure

Question 31

what is assay for measuring long-term blood glucose levels?

Answer 31

hemoglobin A1c level - measures that hemoglobin reacts w/ high glucose to form hemoglobin A1c, a glycosylated hemoglobin high levels of A1c (\> 7 mg%) indicate poor glucose control

Question 32

what are glucagons functions

Answer 32

1) promotes glucose production in the liver by gluconeogenesis and stimulation of glycogen breakdown 2) increases fatty acid release from triglycerides stored in adipose tissue

Question 33

glycogen is?

Answer 33

polymer made of many glucose residues functions as storage form of glucose

Question 34

how does glucagon exert its effects?

Answer 34

1) by stimulating the activites of critical enzymes involved in synthesis of glucose & breakdown of glycogen and fat 2) by transcriptionally activating the genes for these critical enzymes

Question 35

what are insulin's main actions?

Answer 35

promotes utilization of glucose by 1) stimulating glycolysis 2) stimulating glucose uptake in some tissues like muscle & adipose tissue 3) stimulating glycogen formation 4) stimulating fatty acids synthesis from glucose 5) stimulating protein synthesis

Question 36

how does insulin exert its effects?

Answer 36

1) by increasing critical enzyme activities 2) by increasing synthesis of these enzymes

Question 37

how do insulin/glucagon work in relation to each other? what pathways does each stimulate/inhibit?

Answer 37

they work in opposite actions - so glucagon does the opposite of everything here **insulin stimulates: **glucose-utilizing pathways: glycolysis, glycogen synthesis, fatty acid synthesis **insulin inhibits:** gluconeogenesis, glycogen breakdown, fat breakdown

Question 38

how does insulin exert its effects?

Answer 38

via the insulin receptor on the plasma membrane of all tissues insulin receptor has 2 alpha + 2 beta subunits. insulin binds alpha subunits, which span membrane, causing tyrosine kinase activity/dimerization of beta subunits, yielding phoshphotyrosine residues the phosphotyrosine residues of beta subunit phosphorylate proteins IRS-1 and IRS-2 phosphorylated IRS-1 and IRS-2 phosphoryate & activate PI# kinase, which activates AKT pAKT activates phosphatases, PKC, mTOR, which carry out insulin's actions ***take away: insulin binding stimulates activity of protein phosphatases which carry out downstream actions of insulin***

Question 39

what is the structure of glucagon and epi receptors?

Answer 39

glucagon's are in liver, fat tissues; epi's are widely present both are GPCRs with 7 TM spanning loops alpha subunit binds GDP in inactive state activated lgucagon or epi receptor catalyzes exchange of GDP with GTP; follwed by dissociation of beta-gamma subunits to form activate a-GTP G protein this activates adenylate cyclase to produce cyclic AMP cAMP activates PKA by binding to and dissociating regulatory subunits of PKA this frees activte catalytic subunits of PKA PKA promotes phoshporylation of many enzymes important in metabolism of glucose and fat - these phoshporylations may activate or inhbit the enzyme or txn factor

Question 40

what is the difference in phosphorylation btwn glucagon/epi and insulin?

Answer 40

glucagon and epi: promote phosphrylation of enzymes by activating cAMP-dependent PKA insulin: promotes dephosphorylation of enzymes by activating phosphatases eg protein phosphatase 2A

Question 41

how is the glucagon/epi signal turned off?

Answer 41

alpha-GTP subunit has a GTPase activity; with time, GTP is hydrolyzed to form alpha-GDP subunit this reassociates w/ the Beta-gamma subunits, reestablishes the inactive GDP-alpha-beta-gamma G protein eventually, glucagon and epi dissociate from the receptor also, cAMP is hydrolyzed by phosphodiesterase to AMP; so cAMP-PKA signal is turned off

Question 42

what does insulin do to phoshpodiesterase?

Answer 42

increases phosphodiesterase activity phosphodiesterase hydrolyzes cAMP to AMP, turning off the cAMP-PKA signal this is a way then that insulin counters the actions of glucagon and epi

Question 43

what is difference in glucagon/insulin re: - where each is made - what it activates - its target - when it is released

Answer 43

Question 44

why do glucose carriers exist?

Answer 44

glucose is highly polar structure - does not get into cells well, considering all of its OH groups thus need glucose transporters/carriers to carry glucose from our diet into our cells

Question 45

how would you prove glucose uptake occurs by a carrier?

Answer 45

1) **kinetics:** plot energy vs. velocity curve, see that will eventually saturate the carrier 2) **specificity: **apply inhibitors and show that carriers are specific re: what they uptake

Question 46

what are the functions of GLUT1 and GLUT3 carriers? where do they work? when are they saturated?

Answer 46

work in most all tissue - liver, RBC, brain, pancreas, most cells do passive carrier-mediate glucose transport have a **low Km/high affinity for glucose (1mM)** so **catalyze basal glucose uptake ** they thus are **almost always saturated at normal glucose levels **since normal glucose is **4-8 mM**

Question 47

what is GLUT2 carrier function? where is it present? what is its function?

Answer 47

**high kM, low affinity **for glucose (15-20 mM kM) present in **liver and pancreas** senses** high glucose **levels - for pancreas to produce insulin, and liver to utilize high glucose

Question 48

does insulin effect rate of glucose uptake by GLUT 1, 2, 3?

Answer 48

no

Question 49

where is GLUT4? function?

Answer 49

muscle, fat cells is the **insulin responsive glucose transporter** **insulin elevates number of GLUT4 carriers on plasma membrane of muscle and fat cells so glucose uptake is elevated** does this by **translocating GLUT4 from Golgi to PM** this is a way to **increase glucose uptake in muscle and fat cells** **fat** converts glucose -\> fat, triglycerides **muscle** converts glucose -\> glucose, stored as glycogen

Question 50

GLUT5 function, location?

Answer 50

GI tract and kidney catalyzes **active transport** of glucoses moves molecules against concentration gradient; linked w/ Na+ transport