carbohydrate metabolism

metabolism of carbs stage 1

occurs extracellularly in GI tract

Complex molecules → building block molecules → absorbed from the GI tract into circulation via F.D by GLUT 1-5 transporters

C-N and C-O bond broken (no C-C broken)

No energy produced

What enzyme breaks down starch and glycogen and what does it break it down into?

Amylase

starch/ glycogen → dextrins → monosaccharides

What type of enzymes are released by the small intestine? Give examples

Disaccharidases

• lactase

• Sucrase

• Pancreatic amylase (break alpha-1,4 bonds)

• Isomaltase (breaks alpha-1,6 bonds)

metabolism of carbs stage 2

Occurs intercellularly (in cytosol/ mitochondria)

Building block molecules → simpler molecules

C-C bond broken → some energy (ATP) produced

Oxidative (required coenzymes eg.NAD+ which gets reduced)

What are the functions of glycolisis?

• yields NADH (used for reduction)

• 2 ATP Per mol glucose (exergonic reaction)

• Produces C6 and 2 C3 (Pyruvate) intermediates

• Lactate can be produced with low O2 from Pyruvate

Why is lactase production important and how is it removed?

Pyruvate is reduced to lactate

Regenerates NAD+ needed for glycolysis

Metabolised by liver and heart and disposed in the kidney

What are some important glycolysis intermediates?

Dihydroxyacetone phosphate (DHAP) → glycerol phosphate (lipid regulation ??)

1,3-BPG → 2,3-BPG (affects haemoglobin affinity)

What is the difference between hyperlactatemia and lactic acidosis?

Hyperlactatemia: conc of lactose 2-5mM (below renal threshold so no change in blood pH)

Lactic acidosis: >5mM of lactose (above renal threshold so blood pH decreases)

Function of Penrose phosphate pathway

Produce NADPH

(In RBC): maintaining free -SH (thiol) groups on cysteine residues (important in G6PDH deficiency)

Produces C5 ribsose sugar for synthesis of nucleotides

How can fructose and galactose be metabolised?

Fructose: converted to G-3-P and enters glycolisis pathway

Galactose: converted to G-1-P which is converted to G-6-P and enters glycolysis / can be converted to glycogen

What is classical galactosaemia and what are the symptoms?

Deficiency In GALT → accumulation of galacticol which depletes NADPH from tissues

Symptoms: cataracts, glaucoma, damage to liver, brain and kidney

Treatment: non lactose diet

what is non-classical galactosaemia and what are its symptoms?

Deficiency in galactokinase (GALK)

Milder symptoms of cataracts, liver disease and delayed growth development

How is acetyl CoA made?

Pyruvate → acetate + CoA → acetyl CoA

(Releases CO2)

Enzyme: Pyruvate dehydrogenase(allosteric regulator)

What is Pyruvate dehydrogenase (PDH) activated by?

• Pyruvate

• NAD+

• ADP

• Insulin

• Dephosphorylation

What is Pyruvate dehydrogenase (PDH) inhibited by?

• acetyl CoA

• NADH

• ATP

• phosphorylation

What is lactic acidemia Leigh’s disease?

Also know as Necrotising encephalopathy

Deficiency in PDH → high Pyruvate → high lactic acid → acidic blood

X-linked recessive

What does the TCA/ kerbs cycle produce?

• 1 ATP

• 3 NADH

• 1 FADH2

• 2 CO2

What are the intermediates of the TCA cycle used for?

C4-5: biosynthesis of non-Essential A.A eg. Succinate, fumerate

C4: Biosynthesis of human and glucose eg. Alpha-ketoglutaric acid

C6: Biosynthesis of fatty acids eg. Citric acid, isocitric acid

What regulated the TCA cycle?

ATP/ADP ratio (high ADP is a low energy signal → telling the body we need more energy)

NADH/NAD+ ratio (High NADH is a high energy signal → telling the body we don’t need more energy)

What is stage 4 and where does it happen?

Oxidative phosphorylation occurs on mitochondrial inner membrane Cristae)

Uses NADH + FADH2

What happens to the oxygen in oxidative phosphorylation?

O2 + 2H+ → 2H2O at the complex IV

How is ATP made in oxidative phosphorylation?

• NADH + FADH are oxidised releasing H+ + e-

• e- move down ETC releasing energy

• Energy is used to pump H+ across

• H+ move down conc gradient through ATP Synthase (complex V): ADP + H+ → ATP

how is mitochondrial deficiency bad?

• loss of efficiency in ETC → less ATP

• DNA mutations → abnormal components of respiratory chain

What types of poisons can stop oxidative phosphorylation?

Uncoupling agents (UCP 1-5) are important for heat production

Inhibitors of UCP 1-5: Inhibit transport of electrons so no ATP produced → no heat

How can cyanide poisoning affect the metabolism of carbs ?

?