M2C Unit 2 Lesson 1 and 2

Where is starch found?

Plants and fungi

Where is glycogen found?

animals

Starch is a mixture of what?

amylose (unbranched) and amylopectin (branched)

What is Maltose?

Glucose + Glucose

What is Amylose?

Unbranched glucose polymer

What is amylopectin?

Branched glucose polymer

What is glycogen?

highly branched glucose polymer

What is lactose?

Galactose + Glucose

What is cellobiose?

Unbranched glucose polymer (glucose + glucose)

What is the result of Deficiency of disaccharidases?

Passage of undigested carbohydrates into the large intestine

What are the two effects of disaccharidase deficiency?

• Osmotically active, brings water, causes bloating and diarrhea

• Bacterial fermentation leads to accumulation of CO2 and H2 Flatulence

How can abnormal degradation of disaccharides be diagnosed?

Measure H2 gas in the breath

A newborn shows symptoms of failure to thrive and develops osmotic diarrhea after being fed a standard infant formula. If a disorder in carbohydrate digestion is suspected, which of the following tests would most effectively identify the underlying issue?

A.

What does a Clinitest help with?

A urine test for Reducing Sugars. A positive result is indicative of an underlying pathology because sugars are not normally present in urine and can be followed up by more specific tests to identify the reducing sugar.

What is the role of GLUT1?

• Basal glucose uptake in erythrocytes and brain

• Provides constant glucose uptake even when blood glucose is low

• high affinity

What is the role of GLUT2?

• In the pancreas, it plays a role in the regulation of insulin.

• In the liver, it removes excess glucose from the blood. It transports glucose, galactose, and fructose

• Low affinity, high capacity

• Moves glucose in or out, depending on concentration, and helps pancreatic β-cells sense blood glucose

• active after a meal (fed state)

What is the role of GLUT3?

• Basal glucose uptake in neurons

• Very high affinity

• Ensures neurons receive glucose even during hypoglycemia (low glucose)

What is the role of GLUT4?

• The amount of muscle plasma membrane increases with endurance training

• Insulin-responsive transporter

• Insulin causes GLUT4 vesicles to move to the membrane

• Exercise also stimulates GLUT4 insertion independently of insulin

What is the role of GLUT5?

Primarily transports fructose

What is the role of SGLT1?

• sodium-glucose cotransporter that absorbs glucose and galactose together with sodium (Na⁺) using secondary active transport.

• Intestinal glucose/galactose absorption

What is the role of SGLT2?

• responsible for reabsorbing most filtered glucose in the kidney

• Renal glucose reabsorption in proximal tubule

What does Lactase breake lactose down into?

Glucose and Galactose

What does Sucrase break Sucrose into?

Fructose and Glucose

When is Glucagon released?

fasting state

What does glucagon do?

Maintains blood glucose levels by increasing blood glucose secretion by liver

Glycolysis of Net Reaction

Glucose + 2 ADP + 2 NAD+ + 2 Pi → 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

What steps contain the Four kinases in glycolysis?

Steps 1,3,7,10

Which isozyme of Hexokinase is active at higher glucose levels?

Hexokinase IV (Glucokinase)

What is the rate limiting step for glycolysis?

Phosphofructokinase-1 (PFK-1)

Fructose-6-phosphate → Fructose-1,6-bisphosphate

• Step 3

What are the three enzymes for the irreversible steps of glycolysis?

• Hexokinase

• Phosphofructokinase -1 (PFK-1)

• Pyruvate Kinase (PK)

How does Arsenate (AsO4 -3) poisoning occur?

Arsenate can replace Pi as a substrate for G3PDH

What is the fate of pyruvate in Aerobic conditions?

acetyl-CoA then TCA

What is the fate of pyruvate in Anaerobic conditions?

ethanol or lactate

What enzyme can reconvert lactate to pyruvate?

lactate dehydrogenase

Net reaction for glucose degradation to lactate?

Glucose + 2 Pi 2- + 2 ADP3- → 2 Lactate- + 2 ATP4- + 2 H2O

Glucose 6-phosphate serves as an inhiitor for what?

Hexokinase

Where is Hexokinase mainly found?

in all tissues

Where is Glucokinase mainly found?

In the liver (insulin induced)

Fructose 2,6-bisphosphate which is made by PFK2, is an allosteric activator for what?

PFK-1

Insulin _______PFK-2 via _______

activates; dephosphorylation

Glucagon _______ PFK-2 via ________

inhibits ; phosphorylation

Lactic acidosis can result from what?

insufficient oxygen (an increase in lactic acid and decrease in blood pH)

Lactate formed in skeletal muscles during exercise is transported where to do what?

to the liver to be reconverted to pyruvate

What enzyme reconverts lactate to pyruvate?

lactate dehydrogenase

What are the three regulatory enzymes in glycolysis?

1. Hexokinase/Glucokinase 2. Phosphofructokinase 3. Pyruvate kinase

Phosphofructokinase-1 (PFK-1) functions in the muscle when?

there is a need for ATP

2,3-biphosphoglycerate is an (inhibotor/activator) for Phosphofructokinase-1.

activator

Fructose 1,6- bisphosphate is an (activator/inhibitor) for pyruvate kinase.

activator

How do AMP and fructose 2,6-bisphosphate (F2,6BP) active PFK-1?

relieve the inhibition of PFK-1 by ATP

When ATP levels are sufficient, PFK-1 is?

inhibited by ATP and citrate

When there is excess glucose-6-phosphate, what is inhibited?

Hexokinase

What type of molecule is GLUT?

hexose transporters

Which GLUT transporter is stimulated by insulin?

GLUT4

Glucose 1-phosphate is used to convert Glycogen to what?

Glucose-6-phosphate

In the Pentose Phosphate pathway, Glucose 6-phosphate is converted to what?

Ribose 5-phosphate + NADPH

Glucose 6-phosphate is converted to what for export in blood?

Glucose

Glucose 6-phosphate is converted to Glucose for export in blood by what enzyme?

Glucose 6-phosphatase

Elevated levels of citrate (activate/inhibit) PFK-1.

inhibit

F2,6BP is formed from F6P by what enzyme?

phosphofructokinase-2 (PFK-2)

fructose 2,6-biphosphate

Fructose 6-phosphate

fructose 2,6-biphosphatase

PFK-2

PK is allosterically (activated/inhibited) by F1,6BP

activated

What stimulates protein kinase A which phosphorylates PK converting it to a less active form (liver and intestinal cells)?

Glucagon

Glucagon stimulates protein kinase A which phosphorylates what converting it to a less active form (liver and intestinal cells)?

Pyruvate Kinase (PK)

Under anaerobic conditions the conversion of glucose to pyruvate is much higher/lower than under aerobic conditions (yeast cells produce more ethanol and muscle cells accumulate lactate)?

higher

What is The Pasteur Effect?

the slowing of glycolysis in the presence of oxygen

More ATP is produced under (aerobic/anaerobic) conditions than under anaerobic conditions, therefore less glucose is consumed aerobically

aerobic

Other sugars can also be made into sugars (diff types)

Fructose → DHAP or G3P

What is mannose converted to in the fructose sugar pathway?

Fructose 6-phospjhate

Erythrocytes contain bisphosphoglycerate mutase, which forms what from what?

2,3BPG from 1,3BPG