Carbohydrates 2

Question 1

Carbohydrates in diet

Answer 1

Starch
Glycogen
sucrose, maltose, fructose
cellulose and hemicellulose
Oligosaccharides => 1-6 glucose, roughage 
Glucose, fructose

Question 2

Digestion in mouth

Answer 2

Salivary amylase breakdown alpha 1-4 of starch

Question 3

Digestion in stomach

Answer 3

Nothing

Question 4

Digestion in duodenum (small intestine)

Answer 4

Pancreatic amylase enters through duct

Question 5

Digestion in jejenum

Answer 5

Enzymes in mucus break 1-6
Glucoamylase remove glucose from non reducing end
Sucrase hydrolyse sucrose and lactase hydrolyse lactose

Question 6

Main products of carbohydrate digestion

Answer 6

Glucose, galactose and fructose (monosaccharide)

Question 7

Absorption of glucose

Answer 7

High sodium forces glucose in cell together
Low cellular sodium maintained by pump
Glucose move cell==> blood

Question 8

Absorption of galactose

Answer 8

Similar to glucose

Question 9

Absorption of fructose

Answer 9

Binds to GLUT5 channel and moves down gradient - not ATP dependent

Question 10

What do cellulose and hemicellulose do?

Answer 10

Increase faecal bulk

Decrease transit time

Question 11

What are cellulose polymers broken down by and to?

Answer 11

Bacteria

Methane and hydrogen

Question 12

Deficiencies in disaccharides

Answer 12

• severe intestinal infection or removal
• inflammation of gut
• drugs injuring gut wall

Question 13

What are disaccharide deficiencies categorised by?

Answer 13

Abdominal pain and cramps

Question 14

Lactose intolerance

Answer 14

Most common disaccharide deficiency
Loss of lactase activity
Undigested lactose ==> methane
Lactose drains water from gut => lumen

Question 15

What is glucose immediately phosphorylated to?

Answer 15

Glucose-6-phosphate by hepatocytes in liver

Question 16

Why phosphorylate glucose?

Answer 16

• trapped In cell

- Glycolysis

Question 17

Glucokinase

Answer 17

In liver
High km and vmax
Only pick up glucose for liver in high conc

Question 18

Hexokinase

Answer 18

Low km and k max

Found in other tissues which are easily satisfied

Question 19

What enzyme G6P => Glucose

Answer 19

Glucose - 6 - phosphatase

Question 20

Is Synthesis of glycogen directly from glucose monomers?

Answer 20

No

Question 21

What does glycogenin do?

Answer 21

Covalently bind glucose from UDP to form chains of 8 glucose residues

Question 22

Step 2 of glycogen synthesis

Answer 22

Glycogen synthase extends the chain
Chains broken by glucose branching enzyme
Reattached via alpha 1-6 for branch points

Question 23

Degradation of glycogen

Answer 23

• Glucose removed one at a time from non reducing ends as G1P by glycogen phosphorylase
• De branching enzyme removes glucose near branch
• transferase release glucose and reattach at non reducing end
• Glucosidase removes final glucose by breaking alpha 1-6
• unbranched chain further degraded

Question 24

G6P -> with glucose 6 phosphatase

Answer 24

Glucose -> blood

Question 25

G6P with substrate level phosphorylation

Answer 25

Lactate

Question 26

Von Gierke’s disease

Answer 26

G6P deficient

little and often carb eating

Question 27

McArdles disease

Answer 27

Skeletal muscle phosphorylase deficiency

Avoid strenuous activity