Energy Production-carbs

Question 1

What is Acetylco-enzyme A?

Answer 1

A carrier that feeds into the KRebb cycle

Question 2

Describe the first stage of catabolism

Answer 2

Conversion of nutrients to a form that can be taken up by cells
It’s extracellular (in the GI tract)
It turns complex molecules into building blocks
These blocks are absorbed into the blood stream
No energy release at this stage

Question 3

Describe the second step of catabolism.

Answer 3

Intracellular (cytoplasm and mitochondria)
The many building block molecules form few simple molecules
It’s oxidative and requires reducible coenzymes NAD
Some ATP energy is produced

Question 4

Describe the 3rd stage of catabolism

Answer 4

Takes place in mitochondria 
Krebbs (tricarboxylic acid) Cucle
Oxidative (needs NAD and FAD)
Some ATP energy directly produced
Acetyl turns to 2 CO2’s

It also produces precursors to biosynthesis

Question 5

Describe the 4th stage of catabolism

Answer 5

Takes place in mitochondria
Electron transport and ATP synth 
NADH and FAD2H re-oxidised
O2 needed (turns to H2O)
Large amounts of ATP produced

Question 6

What is the general formula of a carbohydrates

Answer 6

(CH2O)n

Can contain aldehyde or keto groups

Question 7

List the min 3 dietary monosaccharides

Answer 7

Glucose
Fructose
Galactose

Question 8

What cells have an absolute tissue requirement and why?

Answer 8

Red blood cells
Neutrophils
Innermost cell of kidneys medulla
Lens of the eye

No mitochondria so cant metabolise glucose
Their uptake depends directly on blood glucose

Question 9

Describe the metabolism pathway of carbohydrates from when they enter the body

Answer 9

Saliva-amylase
Stomach acid-kills enzymes +churning
Pancreas-amylase
Small intestine-disaccharidases attached to brush border membrane

Question 10

Why isn’t cellulose broken down by humans?

Answer 10

The beta glycosidic linkages are different to the alpha bands of starch so cant be digested

Question 11

Describe the criteria for primary lactase deficiency

Answer 11

An absence of lactase persistence allele
High prevalence in northwest Europe
Adults only

Question 12

Describe the criteria for secondary lactase deficiency

Answer 12

Caused by injury to small intestine (gastroenteritis, coeliacs, Chron’s, ulcerative colitis)
Occurs in adults and infants
Generally reversible as once underlying cause treated lactase production begins again

Question 13

Describe the criteria for congenital lactase deficiency

Answer 13

Extremely rare
Autosomal recessive defect in lactase gene
Cannot digest breast milk
Must be given alternatives

Question 14

List some symptoms of any lactose intolerance

Answer 14

Bloating
Cramps
Flatulence
Diarrhoea 
Vomiting
Loud rumbling stomach

Question 15

Hw are sugars absorbed into the blood from the SI

Answer 15

Active transport (sodium potassium pump)
Passive transport (via GLUT2)
Blood transport to tissues
Facilitated diffusion ( transport proteins into target cells)

Question 16

What are the functions of glycolysis?

Answer 16

Oxidise glucose
Produce NADH
Synthesise ATP from ADP
Produce C6 and C3 intermediates (Pyrvate)

Question 17

What are the features of glycolysis?

Answer 17

Central pathway of CHO catabolism
Occurs in all tissues (cytoplasm)
Exergonic and reductive 
C6 goes to 2C3 (no CO2 loss)
Only pathway that can work anaerobicly (when LDH added)
Irreversible

Question 18

Name the 3 enzymes in glycolysis that can have control exerted over them.

Answer 18

Hexokinase (glucokinase in liver)

Phosphofructokinase-1

Pyruvate kinase

Question 19

Why does glycolysis have so many steps?

Answer 19

Chemistry is easier in smaller stages
More efficient energy conversions
Gives versatility (interconnections with other pathways, intermediate products, parts are reversible)
Allows for finer control

Question 20

What steps in glycolysis are irreversible and why?

Answer 20

Step one and three due to their large negative change in energy. It’s an investment in ATP so is a waste if reversible.

Step 3 is the committing step its the first step that commits glucose to metabolism via glycolysis

Question 21

How can glycolysis be used in clinical situations?

Answer 21

Cancer cells have up to 200 times greater glycolysis rate
If give patient radioactive hexokinase substrate its taken up by metabolising cells and gets stuck in the tissues due to its negative charge. The radioactivity can be seen on imaging so shows in cells with sig higher rate