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Endocrinology > CHO Metabolism, Insulin, Glycogen > Flashcards

CHO Metabolism, Insulin, Glycogen Flashcards

1
Q

What is ATP replenished by (as it only lasts for a few seconds)

A

Creatine phosphate (muscle - short term)
Anaerobic metabolism of CHO to lactate
Aerobic metabolism of CHO, fat and/or protein - most tissues use fatty acids

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2
Q

Name polysaccharides

A

Starch

Cellulose

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3
Q

Name disaccharides

A

Maltose (glucose and glucose)
Sucrose (glucose and fructose)
Lactose (glucose and galactose)

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4
Q

Name monosaccharides

A

Glucose
Fructose
Galactose

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5
Q

Monosaccharide structure

A

All have same chemical formula but just arranged in different way which affects the way they’re recognised by transporters

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6
Q

Disaccharide structure

A

Can be linked in different ways and so broken down in different ways

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7
Q

Briefly describe CHO digestion

A

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)

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8
Q

Why are some starches slowly digested?

A

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

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9
Q

What is the equation for glycaemic index

A

area under curve over 2 hours for food containing 50g carbohydrate
OVER
area under curve for 50g glucose
x 100

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10
Q

What happens with high GI foods

A

absorb glucose very rapidly - blood sugar increases very quickly after eating

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11
Q

List some high GI foods and low GI foods

A 
Low GI
lentils - 29
kidney beans - 29
haricot beans - 31
soya beans - 15

High GI
cornflakes - 80
wholemeal bread - 72
banana - 62

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12
Q

Relevance of cellulose in humans??

A

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

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13
Q

What is the TRANSPORT form of carbohydrates

A

glucose

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14
Q

What is the STORAGE form of carbohydrates (and where is it stored)

A

Glycogen
- liver and muscle
Muscle = principle glycogen store

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15
Q

List some tissues dependent on constant supply of glucose?

A

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

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16
Q

Standard plasma glucose concentrations??

fasted and after meal

A

4-5 mmol/L (fasted)
8-12 mmol/L (fed)
people have different glucose tolerances though

17
Q

How do GLUT transporters work??

A

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

18
Q

How do SGLT transporters work?

A

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

19
Q

SGLT-1

A

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

20
Q

SLGT-2

A

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

21
Q

GLUT-1

A

Found everywhere, in all cells.
Transports glucose (high affinity) and galactose
Does not transport fructose

22
Q

GLUT-2

A

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

23
Q

GLUT-3

A

Found in brain, placenta and testes
Transports glucose (high affinity) and galactose
Does not transport fructose
Is the primary transporter for neurons

24
Q

GLUT-4

A

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)

25
Q

GLUT-5

A

Found in the small intestine and sperm

Transports fructose, but not glucose or galactose

26
Q

What happens to glucose when it first enters a cell?

A

It is phosphorylated to glucose-6-phosphate
Traps glucose in cell
Catalysed by hexokinase 1-4

27
Q

Glucokinase

A

Hexokinase 4
Expressed by beta cells of pancreas and liver
Has high Km
Low substrate affinity
Specific for glucose only
Regulated by enzyme synthesis
Permits accumulation of intracellular glucose for conversion to glycogen or triacylglycerols

28
Q

Hexokinase 1-3

A

Expressed in all other tissues/cells
Has low Km
High substrate affinity
Inhibited by G6P (its own product)
Specific for glucose, fructose and galactose
Provides cells with basal level of G6P needed for energy production

29
Q

Phosphofructokinase (PFK)

A

Inhibited by ATP, citrate (downstream products)
Its activity determines whether G6P from hexo/glucokinase is used for glycolysis or other purposes
Fructose-6-phosphate to fructose-1,6-bisphosphate
Committed step of glycolysis

30
Q

Glycolysis summary

A

2 molecules pyruvate formed at end
2 important enzymes: hexo/glucokinase and phosphofructokinase
Pyruvate kinase = last step of glycolysis
Used 2 ATP and made 4 ATP and 2 NADH = net gain of 2 ATP and 2 NADH

Endocrinology (3 decks)

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