Carbohydrates

Question 1

What can be metabolised to Acetyl CoA?

Answer 1

Alcohol
Fatty acids
Glucose —> pyruvate
Amino acids —> keto-acids

Question 2

What can be metabolised to urea?

Answer 2

Amino acids —> urea

Question 3

What is the purpose of stage 1 of catabolism?

Answer 3

To convert nutrients into a form that can be taken up into cells

Extracellular (GI tract), no energy produced

Question 4

What happens to the nutrients that have been converted in stage 1?

Answer 4

The C-N and C-O bonds are broken and the building block molecules are absorbed from the GI tract into circulation

No energy produced

Question 5

What is the purpose of stage 2 of catabolism?

Answer 5

Degradation of building blocks to a small number of organic precursors (eg. Pyruvate, urea, a-keto acids)

Many pathways- not in all tissues

C-C bonds broken, oxidative, intracellular

Some energy produced as ATP

Question 6

Describe stage 3 of catabolism

Answer 6

Mitochondrial

Tricarboxylic acid cycle (Krebs cycle)

Oxidative, some energy produced as ATP

Acetyl (CH3CO-) converted to 2CO2

Also produces precursors for biosynthesis

Question 7

Describe stage 4 of catabolism

Answer 7

Mitochondrial

Electron transport & ATP synthesis (most energy produced)

O2 required (reduced to H2O)

NADH & FAD2H re-oxidised

Question 8

What are carbohydrates?

Answer 8

Come on dipshit u know what a carbohydrate is

Question 9

How many units are in a monosaccharide, disaccharide, oligosaccharide and polysaccharide?

Answer 9

Mono- 1 duh
Di- 2 cmon now
Oligo- Mkay fairs between 9 and 12 (eg. Dextrins)
Poly- 10-100

Question 10

What is the glucose concentration in blood?

Answer 10

About 5mM

Question 11

Which cells have an absolute glucose requirement?
What is the value?

Answer 11

RBCs, neutrophils, innermost cells of kidney medulla, lens of eye

Approx 40g/24 hours

Question 12

Which carbohydrases are found attached to the brush border membrane?

Answer 12

Lactase
sucrase
pancreatic amylase (1-4 bonds)
isomaltase (1-6 bonds)

Question 13

Describe primary lactase deficiency

Answer 13

Absence of lactase persistence allele
Only occurs in adults
Highest prevalence in north-west Europe

Question 14

Describe secondary lactase deficiency

Answer 14

Caused by injury to the small intestine
eg, gastroenteritis, coeliac disease, Crohn’s disease, ulcerative colitis
Occurs in both infants & adults
Generally reversible

Question 15

Descibe congenital lactase deficiency

Answer 15

Extremely rare
Autosomal recessive defect in lactase gene
Cannot digest breast milk

Question 16

Describe how monosaccharides are absorbed

Answer 16

Active transport into intestinal epithelial cells by SGLT1
Passive transport via GLUT2 into blood supply
Transport via blood to target tissues
Glucose uptake into cells by facilitated diffusion using GLUT1-GLUT5)

Question 17

Describe the features of glycolysis

Answer 17

Central pathway of CHO catabolism
Occurs in all tissues (cytosolic)
Exergonic, oxidative, irreversible
Only enzyme that can operate anaerobically (with LDH)

Question 18

Describe the functions of glycolysis

Answer 18

Oxidation of glucose
NADH production (2 per glucose)
Synthesis of ATP
Provide biosynthetic precursors for FA, amino acids and nucleotides

Question 19

What does hexokinase (glucokinase in liver) do?

Answer 19

Converts glucose to glucose-6-phosphate

Question 20

What does phosphofructokinase 1 do?

Answer 20

Catalyses step 3 of glycolysis