Carbohydrates Flashcards
Give the major monosaccharides in the diet
- glucose
- galactose
- fructose
Give the major disaccharides in the diet
- maltose
- sucrose
- lactose
Glucokinase and hexokinase are
isoenzymes
Isoenzymes
catalyse the same reaction, however their Km’s and Vmax’s differ
Glucokinase is found in the
liver
Glucokinase has a _
high Vmax and high Km
Glucokinase will only pick up glucose when
the concentration is high e.g. after a meal
The high Vmax of glucokinase allows it to
pick up glucose quickly so as much glucose as possible is trapped in the liver
Hexokinase has a _
low Vmax and low Km
Hexokinase can bind to glucose even at low concentrations
True or false?
True
Low Vmax means that the tissues that hexokinase is found in
are quickly satisfied
Glycogen is a polymer of
glucose (alpha-1 –> 4) linked subunits with (alpha 1 –> 6) branches every 8 to 12 residues
Glycogen does not form directly from
glucose subunits
Glycogen starts by
covalently binding glucose from UDP-glucose to form chains of approx 8 subunits
Glycogen synthase takes over and
extends the chains until they are broken by glycogen branching enzyme to for 1-6 branching points
During degradation, glucose subunits are
removed one at a time from the non-reducing end of the branches as G-1-P by phosphorylase
Glycolysis is
a metabolic pathway that serves to save some of the potential energy from glucose as ATP via substrate level phosphorylation
For every molecule of glucose broken apart, there is a net gain of
2 ATP molecules
2 NADH molecules
2 pyruvate molecules
Describe the functions of the lactate dehydrogenase
Used in converting lactate into pyruvate using NAD+ during gluconeogenesis
Describe the functions of pyruvate dehydrogenase
Converts pyruvate to acetyl coenzyme A
Describe the fate of blood lactate
Lactate is produced via substrate level phosphorylation during exercise when there is not enough O2
Lactate is then made back into glucose in the liver
What is the name given to the process of converting lactate back into glucose in the liver?
Gluconeogenesis
What is the name given to the cycle between glycolysis in the tissues and gluconeogenesis in the liver?
The Cori cycle
How many of the glycolytic reactions are reversible?
7 out of 10
Galactose joins the glycolysis cycle through conversion to
glucose-1-phosphate by UDP
Fructose joins the glycolysis cycle using ATP to form ___ and then ___ and finally ___
fructose-1-phosphate
glyceraldehyde
glyceraldehyde-3-phosphate (using another molecule of ATP)
The glycolysis cycle produces ___ and also metabolises ___
NADPH and pentose sugars needed for nucleic acid synthesis
the small amount of pentose sugars in the diet
What are the two phases of the glycolysis cycle?
- oxidative, irreversible part
- reversible, non-oxidative part
What happens in the oxidative phase of the glycolysis cycle?
- NADPH generated
- G-6-P converted into a pentose phosphate
What happens in the non-oxidative phase of the glycolysis cycle?
- G-6-P and pentose phosphate are interconverted to form lots of 3, 4, 5, 6 and 7 carbon sugars
