Low Mr Antioxidants

Question 1

What is a chain breaking antioxidant?

Answer 1

Act by reacting with peroxyl radicals.
Either donors = tocopherol, ascorbate, UA
OR = sacrificial = NO

Question 2

What are the characteristics of a good chain breaking antioxidant?

Answer 2

Both antiox and its radical should be unreactive
Radical decays to harmless product
Doesn’t add O2 to make a peroxyl radical
Recycled
If an H atom donor, should be in middle of pecking order.

Question 3

Why can ascorbate recycle alpha tocopherol?

Answer 3

Lower redox potential (+282 compared to +480).

Question 4

How does alpha tocopherol position itself in the membrane?

Answer 4

Hydrophobic phytol chain positions the chromanol ring (with radical scavenging phenolic OH group) where it needs to be.

Question 5

Why is urate a good donor antioxidant?

Answer 5

Free radical formed has a single negative charged delocalised over the purine ring –> resonance stabilisation.

Question 6

What is the role of carotenoids in plants?

Answer 6

Quench singlet oxygen and prevent formation during photosynthesis.

Question 7

How may lycopene benefit human health?

Answer 7

Most strongly reducing carotenoid. Tomato consumption may lower prostate cancer risk (lycopene accumulates in testis and prostate).

Question 8

Outline the basic chemistry of carotenoids.

Answer 8

Long chains with alternating double and single bonds –> electron delocalisation.
Trans isomers preferentially absorbed in gut.
Hypho (in blood bound by lipoproteins / tissues in fat stores, hypho interiors of membranes, hypho domains of proteins).

Question 9

How can GSH become depleted in cells?

Answer 9

GST conjugates it to certain compounds

Peroxidase reactions

Export via MRP in some cells / CFTR in tracheobronchial cells.