Carbohydrate Metabolism Flashcards
What are sources of ATP in the body? Describe
Creatinine phosphate - short term replacement, found in muscle
Anaerobic metabolism
Aerobic metabolism
What is the source of creatinine phosphate? When is it used?
Short term replenishment, found in muscle, used for intense exercise
List examples of polysaccharides in diet?
Starch
Cellulose
List examples of disaccharides in diet?
maltose
sucrose
lactose
List examples of monosaccharides in diet?
glucose
fructose
how does alphaD glucose differ from BetaD glucose?
AlphaD = -OH group is below C atom BetaD = -OH group is above C atom
Why are dense starches slowly digested?
They have a smaller surface area for enzymes to work on
What affect does a high glycemic index have on digestion time?
Food with a high glycemic index e.g. banana takes less time to digest (since mostly glucose)
Since beans have a low glycemic index, what effect does this have on its digestion time?
Low glycemic index = longer digestion time
Which body tissues/organs are dependant on a constant supply of glucose? Explain why
Brain: the blood brain barrier does not allow lipids to cross so must use carbohydrates to source their glucose. Brain can also only make neurotransmitters using glucose (so even if lipids could pass BBB, would still need glucose for NTs)
Erythrocytes: Don’t have mitochondria so no aerobic respiration. They need a constant glucose supply.
What is the storage form of carbohydrates in humans?
Glycogen
what is the normal range of plasma glucose concentration in fasting state?
4-5 mM
what is the normal range of plasma glucose concentration after a meal?
8-12 mM
What are the 2 main hormones involved in glucose homeostasis?
Insulin and glucagon
Where can glucose be synthesised DE NOVO?
In the liver and in kidneys (only in extreme starvation mode)
where in the body is glycogen stored and how do they differ?
In liver (stored during fasting state) In muscle (glucose stored here as glycogen can only be used by THAT muscle)
how does transportation using GLUT and SGLT1/2 transporters compare?
GLUT - involves passive diffusion
SGLT - involves active transport (cotransport of sodium)
Where are SGLT1/2 transporters found? What do they transport?
Kidney tubules and intestinal mucosa
Co transports glucose/galactose along with sodium ions (NOT FRUCTOSE)
Where are GLUT-1 transporters found? What do they transport?
Found in every tissue
Has a high affinity for glucose, transports glucose and galactose only.
Where are GLUT-2 transporters found? What do they transport?
Liver, pancreatic beta cell, small intestine, kidney
Transports glucose, galactose and fructose.
It is a low affinity, high capacity glucose transporter.
Where are GLUT-3 transporters found? What do they transport?
In brain, placenta, testes
transports glucose and galactose
Where are GLUT-4 transporters found? What do they transport?
Skeletal and cardiac muscle, adipocytes
Has high affinity for glucose
Where are GLUT-5 transporters found? What do they transport?
small intestine and sperm
transport ONLY FRUCTOSE
which glut transporter is insulin sensitive?
GLUT 4
how do GLUT4 transporters respond in the presence of insulin?
in presence of insulin, GLUT4 vesicles fuse with plasma membrane and GLUT4 allows glucose to move into cell.
what is gluconeogenesis? Where does it occur?
Making glucose from other sources e.g. lipids and proteins. It occurs in the liver.
what is the process of converting glucose to glycogen?
Glycogenesis
What does the pentose phosphate pathway involve?
Synthesis of sugars for RNA/DNA
What is the first step which all glucose pathways undergo in a cell? what effect does this have?
undergo phosphorylation to make glucose-6-phosphate. this traps it within the cell and kenos the glucose concentration low as it is immediately phosphorylated.
What catalyses the phosphorylation of glucose?
hexokinase I-IV
what is hexokinase IV also known as?
glucokinase
which tissues express glucokinase ? Describe it glucose affinity.
Expressed by beta cels of pancreas and liver
It has a low affinity for glucose
which tissues express hexokinase 1-3? Describe it glucose affinity.
expressed in all other tissues
It has a high affinity for glucose
describe the pathway of converting glucose to fructose-1,6-bisphopshate
Glucose to Glucose-6-phosphate (using Hexo/glucokinase)
Glucose 6-phosphate to fructose-6-phosphate
Fructose-6-phosphate to Fructose-1,6-bisphosphate (using phosphofructokinase-1)
How is phosphofructokinase regulated?
It is inhibited by ATP, citrate
which enzyme converts pyruvate into acetyl-coA? and where does it occur?
pyruvate dehydrogenase
in the mitochondria
What enzyme is involved in converting pyruvate to lactate?
Lactate dehydrogenase
Where does the TCA cycle occur?
In mitochondria