CHO Metabolism, Insulin, Glycogen Flashcards
(30 cards)
What is ATP replenished by (as it only lasts for a few seconds)
Creatine phosphate (muscle - short term)
Anaerobic metabolism of CHO to lactate
Aerobic metabolism of CHO, fat and/or protein - most tissues use fatty acids
Name polysaccharides
Starch
Cellulose
Name disaccharides
Maltose (glucose and glucose)
Sucrose (glucose and fructose)
Lactose (glucose and galactose)
Name monosaccharides
Glucose
Fructose
Galactose
Monosaccharide structure
All have same chemical formula but just arranged in different way which affects the way they’re recognised by transporters
Disaccharide structure
Can be linked in different ways and so broken down in different ways
Briefly describe CHO digestion
Starch is broken down to glucose, maltose and dextrins (short chains of glucose) by salivary alpha-amylase
Pancreatic alpha amylase (from the pancreas) works in the small intestine and breaks the dextrins down into maltose which is broken down by maltase into glucose
The disaccharides are broken down by brush border enzymes i.e. lactose into glucose and galactose (lactase) and sucrose into glucose and fructose (sucrase)
Why are some starches slowly digested?
Trapped in intact starch granules/plant cell wall structure e.g. raw cereals, vegetables
Resistant to amylase as 3D structure too tightly packed (some processed foods, raw/cold potato)
Associated with dietary fibre (slows digestion/absorption as gut contents become viscous e.g. beans/legumes)
CHO containing high levels of fat may have delayed gastric emptying
What is the equation for glycaemic index
area under curve over 2 hours for food containing 50g carbohydrate
OVER
area under curve for 50g glucose
x 100
What happens with high GI foods
absorb glucose very rapidly - blood sugar increases very quickly after eating
List some high GI foods and low GI foods
Low GI lentils - 29 kidney beans - 29 haricot beans - 31 soya beans - 15
High GI
cornflakes - 80
wholemeal bread - 72
banana - 62
Relevance of cellulose in humans??
No cellulose really, we do not have the enzymes to cleave the beta links in cellulose and so don’t really get any nutritional benefit
What is the TRANSPORT form of carbohydrates
glucose
What is the STORAGE form of carbohydrates (and where is it stored)
Glycogen
- liver and muscle
Muscle = principle glycogen store
List some tissues dependent on constant supply of glucose?
RBCs (erythrocytes) - have no mitochondria - cannot oxidise their own glucose
Brain cells: cannot get lipids from the blood due to blood brain barrier; needs glucose for energy
Standard plasma glucose concentrations??
fasted and after meal
4-5 mmol/L (fasted)
8-12 mmol/L (fed)
people have different glucose tolerances though
How do GLUT transporters work??
Glucose transported down concentration gradient
From pores in plasma membrane
GLUT transporters let glucose into the cell if the glucose concentration in the cell is lower than out = influx of glucose
If cell concentration of glucose is higher than out the cell then glucose can transport out of the cell
How do SGLT transporters work?
Glucose is transported against a concentration gradient using energy provided by the contransport of sodium
Required in the intestine to absorb glucose from the gut lumen (to get all calories from food)
Also required in the kidneys to reabsorb glucose from filtrate
Uses ATP - Na/K/ATPase pump
SGLT-1
Found in mucosa of small intestine and second part of PCT in kidney (10% renal glucose reabsorption)
Co-transport one molecule of glucose/galactose along with sodium ion
Does not transport fructose
Uses Na/K/ATPase pump
SLGT-2
Found in first part of PCT in kidney (90% renal glucose reabsorption)
Co-transport one molecule of glucose or galactose along with sodium ion
Does not transport fructose
Uses Na/K/ATPase pump
GLUT-1
Found everywhere, in all cells.
Transports glucose (high affinity) and galactose
Does not transport fructose
GLUT-2
Found in liver, pancreatic beta cells, small intestine and kidney
Transports glucose, galactose and fructose
Low affinity but high capacity glucose transporter
Acts as glucose sensor
GLUT-3
Found in brain, placenta and testes
Transports glucose (high affinity) and galactose
Does not transport fructose
Is the primary transporter for neurons
GLUT-4
Found in skeletal and cardiac muscle and adipocytes
Insulin-responsive glucose transporter
High affinity for glucose
More activity when glucose is high e.g. after a meal
- more transporters are translocated to cell surfaces
and so more glucose transported in
Muscle: GLUT-4 also translocates in response to physical activity/exercise (independent of insulin)
