Lecture 2

Question 1

how do the GLUT transport glucose

Answer 1

by facilitated diffusion, down a concentration gradient (carrier is needed but not E)

Question 2

describe GLUT 1 (tissue distribution and important features)

Answer 2

most tissues (brain, RBCs and placenta esp.)
low km (1mM); high affinity allows near constant uptake

Question 3

describe GLUT 2 (tissue distribution and important features)

Answer 3

liver, kidneys, intestine and pancreatic beta cells
high km (15-20mM), responds only to high [glucose] like post prandial blood levels

Question 4

describe GLUT 3 (tissue distribution and important features)

Answer 4

low levels in most tissues (high expressions in neurons)
low km (<1mM), allows preferential uptake during hypoglycemia

Question 5

describe GLUT 4 (tissue distribution and important features)

Answer 5

muscle, adipose tissue
medium km (2.5-5mM), insulin dependency in recruitment of GLUT 4 from intracellular stores

Question 6

what is km and affinity

Answer 6

km is the concentration of glucose at which uptake velocity is half maximal

affinity is the degree of attraction that glucose has to the transporter

Question 7

what happens to the GLUT transporters when blood glucose levels are high

Answer 7

glut 2 is activated and so insulin is secreted, Glut 4 will then be able to take glucose out of the circ and into the cell to bring the circ blood glucose levels down

Question 8

what will the slope look like for a GLUT that has high affinity in a graph that shows transport rate and [blood glucose]

Answer 8

very steap rise; at low [ ] it will reach 50% max very fast and very soon

Question 9

why is it needed for GLUT 1 to have a high affinity

Answer 9

since RBC deliver O2 to tissues and takes away CO2, it needs cte energy and so it needs to be delivering glucose constantly even at severe hypoglycemia

Question 10

what would happen if GLUT 2 had a km of 1mM instead of 15-20

Answer 10

insulin would be released constantly at low blood glucose levels and would bind to skeletal m. so in 10 min, your blood glucose would go from 5 to 2.5 (intense hypoglycemia)

Question 11

what is the normal range of blood glucose at rest

Answer 11

4-8 mM

Question 12

what relies 100% on glucose for ATP production and metabolism and can only manufacture ATP thru glycolysis

Answer 12

red blood cells

Question 13

why is it so important that rbc gets their ATP from glucose and glucose transporters

Answer 13

since the rbc don’t have a mitochondria, that produces a significant amount of ATP, it needs to rely on glucose metabolism instead

Question 14

why do neurons have a high rate of metabolism

Answer 14

because every A.P that fires needs ATP quickly so they rely on glycolysis and they need to function 100% of the time

Question 15

GLUT w high km and low affinity are most efficient during what conditions

Answer 15

transient periods of hyperglycemia

Question 16

how does the liver bring circ blood glucose back to normal levels after hyperglycemia

Answer 16

it takes its up glucose from circ at 10-15mM and stores it as glycogen

Question 17

when do the beta cells start producing insulin and where will the insulin go

Answer 17

when the blood glucose is at high levels
and insulin will go to bind to skeletal m. and adipose tissue

Question 18

what GLUT is found in higher concentration in the pancreas GLUT 2 or 1

Answer 18

GLUT 2

Question 19

what is lactose broken into and what is it broken by

Answer 19

its broken into galactose and glucose by lactase

Question 20

what is sucrose broken into and what is it broken by

Answer 20

glucose and fructose and by sucrase enzyme

Question 21

what sugar monomer can’t go thru glycolysis

Answer 21

galactose (it can only be stored as glycogen)

Question 22

what monomer is already in the circ and what monomer is taken up by the villa in the small intestines

Answer 22

glucose

fructose

Question 23

t/f sugar monomers all have their diff and specific transporters

Answer 23

true

Question 24

what do all the sugar monomers encounter as soon as they enter the cell

Answer 24

ATP hydrolysis rx

Question 25

what will determine if the substances go down to glycogenesis or glycolysis and when would each happen

Answer 25

if the cell has ATP needs (exercise) or not (excess carbs after a big meal will need to be stored)

Question 26

what is the diff btw glucokinase and hexokinase

Answer 26

glucose kinase is only found in the liver and hexokinase is found in skeletal m and they both speed up the phosphorylation of glucose to g-6-p

Question 27

what is the common hub of galactose, glucose and fructose

Answer 27

G-6-P

Question 28

what is the enzyme for phosphorylation of fructose and galactose

Answer 28

fructokinase galactokinase

Question 29

what is the fate of glucose in the liver

Answer 29

can either be stored as glycogen or go back into circulation

Question 30

what does glucose-6-phosphorylase do and where is it found solely

Answer 30

it will catalyze the G-6-P back into glucose so it can go back out into circ it is only found in the liver (it can also do the same for fructose and galactose)

Question 31

what are the steps of glycogenesis

Answer 31

1) blood glucose levels are high activating the Liver GLUT sys allowing glucose to enter liver 2) glucose encounters 1st enzyme (glucokinase) and becomes G-6-P and ATP becomes ADP 3) G-6-P encounters enzyme that moves P from 6th C to 1st C 4) G-1-P encounters enzyme and becomes uridine diphosphate glucose and UTP lets go of 2 P to add to G-1-P 5) UDP glucose w enzyme glycogen synthase gets stored as glycogen

Question 32

what is the UTP's purpose in glycogenesis

Answer 32

it prepares glucose to bind to the glycogen unit that's in skeletal m. and it needs E to push the rx forward

Question 33

what enzyme pushes the rx from G-1-P to UDP-glucose

Answer 33

UDT-glucose pyrophosphorylase

Question 34

what is the role of glycogenin

Answer 34

it acts as the anchor and the backbone of the glycogen tree so that it attaches to something that won't be metabolized

Question 35

what is the difference btw an alpha-1,4 and alpha-1,6 bond and what enzyme help the formation of each

Answer 35

1,4 is the bond found in btw each glucose monomer forming the main linear branch with the glycogen synthase and the 1,6 is when the branch branches off the main linear twig with a branching enzyme

Question 36

what is a non reducing end and what enzyme is it sensitive to

Answer 36

first one that will be broken off when glucose is needed for energy glycogen phosphorylase

Question 37

why can't the reducing end broken off

Answer 37

because it attaches to glycogenin and so it would be free in the cell if the bond was broken off

Question 38

what enzyme is activated when you need glucose to be broken off glycogen and form G-1-P

Answer 38

glycogen phosphorylase

Question 39

t/f the glycogen mol is reduced one residue at a time

Answer 39

true

Question 40

what enzymes break down and attach the 1,6 bond

Answer 40

branching enzyme will help build the 1,6 bond when you need to store more glucose as glycogen by helping the branching from the main linear branch debranching enzyme will break down one branch 1,6 and then activate the phosphorylase enzyme which will start breaking off the non reducing end off

Question 41

what hormone activates the glycogen synthase and branching enzyme and by doing what

Answer 41

insulin, by allowing glucose to enter the cell and to promote storage of glucose as glycogen during rest or after major meal

Question 42

what enzymes are stimulators of glycogenolysis

Answer 42

de branching and glycogen phosphorylase

Question 43

what 2 hormones stimulate the de branching and glycogen phosphorylase enzymes and where do they each come from

Answer 43

epinephrine (medulla of adrenal gland) and glucagon (alpha cells of pancreas)

Question 44

when there are high levels of AMP in the m. what does that mean

Answer 44

it means there are low levels of ATP and the m. needs a substrate to get ATP so it will start breaking down the stored glycogen (it happens at high needs of E)

Question 45

what does glycogen phosphorylase a and b do

Answer 45

a: will stimulate glycogenolysis when P is bound to it b: will inhibit glycogenolysis when P is not bound to it

Question 46

what does the glycogen synthase do when its phosphorylated

Answer 46

it will inhibit glycogenesis

Question 47

what do the hormones epi and glucagon activate in glycogenolysis and how do they do it

Answer 47

the activate the cAMO dependent protein kinase that will activate phosphorylase enzyme by adding a P and will inhibit glycogen synthase by adding a P as well

Question 48

when is the cAMP activated

Answer 48

it is activated during high I exercise to start breaking down glycogen

Question 49

with low I exercise what happens concerning glucose utilization

Answer 49

no need for glycogen to be broken down bc it has enough w only uptake of glucose and breakdown of fats (no need for ATP and no need to activate epi and glucagon)

Question 50

with moderate I exercise what happens concerning glucose utilization

Answer 50

gradual drop in glycogen content in liver and skeletal m., need additional substrate for more ATP (glucose or glycogen) and phosphorylase a is activated by epi and glucagon so starts breaking down non reducing ends

Question 51

with high I exercise what happens concerning glucose utilization

Answer 51

huge amounts of epi and glucagon binding to the m. and liver cells with even more phosphorylase enzymes activated immediate demand for this type of carb as a source of energy at 25% of glycogen, fatigue levels are really high

Question 52

t/f at this point, only carbs are used for E during exercise

Answer 52

false, fat metabolism is coming in and helping to manufacture ATP for E usage to help carbs not be the only ones