BIOC Lecture 3: Carbohydrate Flashcards
What is the fed state?
the digestive system is actively breaking down fats, AA’s and sugars
What is happening to blood glucose and insulin during the fed state?
Release of insulin from pancreatic beta cells, interaction of insulin with receptors
What are insulin dependent tissues?
Only break down glucose when insulin is present
What are examples of insulin dependent tissues?
Skeletal muscle, adipose tissue, cardiac muscle
What are insulin independent tissues?
Break down glucose whether or not insulin is present
What are examples of insulin independent tissues?
Brain and liver
What is the fate of glucose in the fed state?
Glycogenesis and storage or glycolysis and utilisation
What happens after the direct effects of a meal have diminished?
Decline in liver glycogen and blood glucose maintained
What is the key hormone of the fasted state?
Glucagon
What does glucagon do during the fasted state?
Synthesised and released from pancreatic islet alpha cells
What is gluconeogenesis?
the process of making glucose, AA’s play a role
Once we have exhausted our stores of glucose, how do we maintain our levels?
Primary precursors are amino acids, lactate is also an important precursor
What is the gut lumen?
Where the food, many bacteria and digestive enzymes are
How does the gut lumen have a high surface area?
Due to the folding of villi and microvilli
What is absorption mostly through?
Through cells (transcellular)
What is transcellular absorption?
substances move through the cells of the intestinal epithelium to be absorbed into the bloodstream
Where does most of the blood from the gut go?
to the liver
Where do fats go?
To the lymphatic system
What does digesting food cost?
Energy
What are the three main sources of energy?
proteins, CHO, fats
Why are amino acids required in our diet?
We rely on other organisms to make some AA’s and also to get bioavailable nitrogen
What can you use pyruvate to make?
AA’s and glucose
What can fat be used to make?
fatty acids, pyruvate and acetyl CoA but not glucose
What can all three PRO, CHO and FAT be converted into?
Acetyl CoA
What are common pathways for most ATP generation?
Glycolysis, CAC and oxidative phosphorylation
What is resting metabolism mostly fueled by?
fatty acids
What is the primary driver of glycolysis (and glycogenesis)?
An increase in glucose concentration
What is glycogen synthase?
Formation of glycogen
What is glycogen phosphorylase?
breakdown
Why can’t RBC do oxidative metabolism?
They don’t have mitochondria
Even at rest, how will you still have some lactate in your blood?
From RBC’s
How is glycogen synthesised in the liver?
Glucose is converted into Glucose-6-phosphate (G6P), then G6P is converted into Glut-1-Phosphate then glycogen
How is UDP-glucose involved in liver glycogen synthesis?
it serves as the immediate donor of glucose residues for glycogen chain elongation
Muscle vs Liver Glycogen synthesis
Similar, in muscle G6P is not present and therefore glucose cannot be released directly to blood
What is glycogenin?
A ‘kernel’ molecule made from protein and carbohydrate
What are the two stages of glycogen synthesis?
Chain extension and branching
What do branches increase the rate of?
The rate at which glucose can be added and removed - when we are well fed there will be a large and highly branched molecule
What are the two stages of glycogen synthesis?
Chain shortening and debranching
What is gluconeogenesis closely linked with?
Glycolysis
What does gluconeogenesis start with?
Pyruvate
What is the first stage of gluconeogenesis?
Pyruvate to PEP
What is PEP converted into?
F1,6BP
What is F1,6BP converted into?
F6P
What is F6P converted into?
G6P
What is G6P converted into?
Glucose
What are the substrates for the gluconeogenesis pathway?
Amino and keto acids
What does the use of AA’s require the disposal of?
Amino groups (NH3)
What is the primary site of the synthesis of glucose from gluconeogenesis?
The liver
