Lecture 2: Glucose transport, glucose and glycogen Flashcards
what is the Gibbs free energy value for ATP
-7.3
true or false: all derivatives of ATP and ADP and ADMp have negative free energy values
True
is glucose tranported into the cell through energy in most cells
no , down a concentration gradient by facilitated diffusion
is a protein carried needed for glucose transport? is the energy needed?
protein yes
energy no
what are the 2 most commonly studied glucose carriers and do they require insulin
glut (no insulin) and glut 4 (insulin dependent)
true or false: most post absorptive glucose uptake by cells does not require insulin
true
where is the glut 4 (insulin dependant) located
skeletal muscles, adipose and heart tissue)
do all glut receptors/carriers require insulin
no
are all glucose transporters membrane-bound?
no , glut 4 is in vessicles in the skeletal, adipose amd heart tissue
which glut receptors are membrane bound
glut 1
glut 2
glut 3
which receptor is in vesicles
glut 4
Where is glut 1 receptors located
most tissues (brain, RBS, placenta)
where are glut 2 receptors located
liver, kidneys, intestine, pancreatic b cells
where are glut 3 receptors located
low levels in most tissues but high expression in neurons
where are glut 4 transporters located
msucle, adipose and heart
affinity defintion
degree of attraction that glucose has to tranposter
km defintion and why
concentration of glucose at which uptake velocity is half maximal
this is the point the transporter is most active phase
features of Glut 1
LOW KM (1 mM) HIGH AFFINITY (NEAR CONSTANT UPTAKE) = glucose binds very easily to transporter
what glucose transporter has a near constant uptake
glut 1
features of glut 2
High Km (15-20 mM) respond only to high glucose concnetration
when is glut 2 very active
POST PRANDIAL BLOOD LEVELS
explain glut 1:
high concentration in the brain cells and rbc
They are constantly taking up glucose therefore there is a strong attraction and you do not need a high concentration of it to activate the transporter
explain glut 2 transporter
After eating, there is a high concentration of glucose in the cell.
The liver will take excess carbs of glucose and store it as glycogen to lower the glucose blood level
RESPONDS FAVORABLY TO HIGH CONCENTRATIONS OF GLUCOSE
will not activate at low levels of glucose or it will cause you to uptake too much glucose
which transporter responds favourably to high concentrations of glucose
glut 2
what is typical blood glucose concentration
4-8 MM
features of glut 3
low Km (less than 1), high affinity allows for preferential uptake of glucose during hypoglycemia
which transporter allows preferential uptake of glucose during hypoglycemia
glut 3
glut 4 features
medium km (2.5-5), insulin dependancy in recruitment of glut 4 from intracellular stores
true or false: all gluts are ACTIVE MEDIATED transporters
ie. transport glucose up concentration gradient only
false
PASSIVE
down concentration gradient
STUDY THE GRAPH OF GLUCOSE TRANSPORTERS AND KM
.
ranks these in increasing order of KM
glut 1,2,3,4
glute 1
glute 3
glute 4
g;ute 2
Tissues with low km and high affinity use which 2 glut transporters
glut 1 and glut 3
what is the function of tissues with low km and high affinity
protect from any negative affects of hypoglycemia (ex: syncope)
true or false: RBC have no mitochondria which is why they need near constant uptake of ATP
true
true or false and explain: RBC and neuron are not only fueled by glycolysis
false, RBC metabolism is solely on glyoclysis so there needs to be an intake of glucose in the cell (dont need alot of energy and responds to low concerntration)
explain how RBCs and Neurons protect themselves from hypoglycemia
SInce they have such a high afinity and low km, they do not need a lot of glucose to function correctly
Even during periods of low concentration (2.5 MM of glucose, they will still take up atp)
which glut transporter works best for periods of transcietn HYPERGLYCEMIA/post prandial
glut 2
which glut transporter works better in periods of hyperglycemia
glute 2
which glute receptor works best for periods of normal blood sugar
glute 4
which glut receptors work best with hypoglycemic conditions
glute 1 and glute 3
explain why tissues with high km and low affinity are good for hyperglycemia
Glut 2 (in liver, b cells) have an extremely high rate of transport but only at high concentrations of blood glucose therefore it will take up a lot of glucose as glycogen and secreting insulin to allow glycogen storage in muscles
what are the two pathways for glucose/sucrose etc
can be stored as glycogen
go to glycolysis
true or false: the skeletal muscles can only take up glucose?
false, it can take up glucose, fructose and galactose
fructose, galactose and glucose all need ATP
true
When ATP is broken down with galactose, what does galactose become
galactose 1 phosphate
when atp is broken down, what does the glucose become
glucose 6 phosphate
when atp is broken down, what does frcutose become
fructose 6 phsophate
true or false, all sugars need to go through phosphorylation for reactions within the cell
true
what is fructose made from
sucrose and glucose
what is galactose made from
glucose and lactose
what is the enzyme that converts galactose to galactose 1 phosphate
galactokinase
what is the enzyme that converts glucose to glucose 6 phosphate
glucokinase (liver)
hexokinase
what is the enzyme that converts fructose to fructose 6 phosphate or fructose 1 phosphate
fructokinanse (1)
hexokinase (6)
is glucokinase found anywhere in the body?
no , only found in the liver
is hexokinase found in the liver?
no
true or false: hexokinase can be used only for glucose
false, can also be used for fructose
true or false: glucose 6 phosphatase enzyme is only found in the liver
true
function of glucose 6 phosphatase
Allows stores carbohydrates in the liver to be reprocessed into glucose (phosphate from glucose 6 phosphate binds to the enzyme) and allows glucose to leave the liver cells and enter the blood circulation
convert monosacharrides (fructose and galactose) to glucose for export
What is the only way we can constantly maintain blood circulation levels of blood glucose
through glucose 6 phosphate being reprocessed to glucose by the enzyme and exiting the liver
is the process of glycogenesis reversible and if so what is it called
yes and glycogenolysis
what is glycogenesis
new formation of glycogen in tissues to be stored
explain glycogenesis in the liver
After eating, liver is going to take high levels of glucose.
It enters the cell and gets converted to glucose 6 phosphate by GLUCOKINASE=spontanously
Once converted to glucose 6 phosphate it can go up the pathway to become glycolysis, down the pathway to be glycolosis or it can go back out into the blood by phosphotase (glucose6phosphostase)
what is glycogenolysis
breakdown of glycogen for energy when needed
done by glucose 6 phosphotase
what is the last step needed to store the glucose as glycogen
need UTP instead of ATP
Explain glucose into glycogen
1) glucose into glucose6 phosphate by hexokinase everywhere in the body and glucokinase in the liver(ATP drives reaction)
2) Glucose 6 phosphate to glucose 1 phophshate
3) Glucose 1 phoshphate into UDP glucose (UTP drives reaction)
UTP is broken down, UDP binds to the glucose
4) UDP-glucose is stored AS GLYCOGEN by glycogen syntahse
what is UTP
high energy compound (purine with ribose and 3 phosphates)
what is the enzyme responsible for accelerating UDP glucose into glycogen
GLYCOGEN SYNTHASE
do all glut receptors/carriers require insulin
no
what hormone is going to stimulate glycogen synthase and why
insulin
and increased insulin stimulates uptake og glucose into the cell that will be stored as glyocgen
what is glycogenin
protein that acts as an achor that allows glucose to bind and start to form the glycogen tree
