L13 B-Vitamins and One-Carbon Metabolism

Question 1

What is B1?

Answer 1

Thiamin

Question 2

What is B2?

Answer 2

Riboflavin

Question 3

What is B3?

Answer 3

Niacin

Question 4

What is B5?

Answer 4

Pantothenic Acid

Question 5

What is B6?

Answer 5

Pyridoxine

Question 6

What is B7?

Answer 6

Biotin

Question 7

What is B9?

Answer 7

Folate

Question 8

What is B12?

Answer 8

Cobalamin

Question 9

What is the natural form of folate also known as?

Answer 9

Polyglutamate

Question 10

What is the synthetic form of folate?

Answer 10

Folic acid/monoglutamate

Question 11

What form is folate in to be absorbed in the intestine?

Answer 11

Polyglutamate is hydrolysed to monoglutamate

Question 12

How much folate is stored in the body and where is most of it?

Answer 12

11-28mg with 50% in the liver

Question 13

What are two active forms of Cobalamin called?

Answer 13

Methylcobalamin and Adensylcobalamin

Question 14

How much B12 is stored in the body and where is most of it?

Answer 14

2-4mg with 50% in the liver and 50% in other tissues

Question 15

How is folate absorbed and activated?

Answer 15

• Folate is eaten and broken into di- then monoglutamate
• Methyl group is added to make 5-methyltetrahydrofolate, then it can be absorbed
• Folate is trapped in an inactive form
• B12 removes the methyl group, making both folate and B12 active. Active folate is tetrahydrofolate (THF)

Question 16

What is an important function of THF?

Answer 16

Acts as a coenzyme in the transfer of one-carbon compounds such as methyl groups

Question 17

How is B12 digested and absorbed?

Answer 17

• Pepsin and HCL get B12 from food
• B12 binds to salivary (R) protein
• Carried to the small intestine where B12 is released from R protein and bound to intrinsic factor (IF)
• IF complex binds to receptors in the ileum where IF breaks down and B12 is bound to a transporter protein in the blood stream - Transcobalamin

Question 18

What is a main complication from folate deficiency?

Answer 18

Neural tube defects
- Anencephaly - brain doesn’t form properly
- Spina bifida - incomplete development of the spine

Question 19

What folate mandate did FSANZ implement in 2009?

Answer 19

Mandatory folate fortification of bread flour

Question 20

What is a complication of folate and/or B12 deficiency? And what are its symptoms?

Answer 20

Megoblastic Macrocytic Anaemia - production of abnormally large blood cells and less RBCs in circulation
Symptoms include fatigue, weakness, headaches, palpitations

Question 21

What are some causes of B12 deficiency? (3)

Answer 21

• Malabsorption
• Poor dietary intake
• Surgical/post op

Question 22

What are some causes of folate deficiency? (4)

Answer 22

• Poor dietary intake
• Increased demand (e.g. pregnancy)
• Malabsorption
• Anti-folate drugs

Question 23

What is epigenetics?

Answer 23

The study of how your behaviors and environment can cause changes that affect the way your genes work

Question 24

What is the methyl-folate trap? What does this cause?

Answer 24

Without B12, 5-methyl THF cannot donate its methyl group to B12 which is how it becomes active
This causes a build up of homocysteine

Question 25

What are some adverse effects of hyperhomocysteinaemia? (5)

Answer 25

- Damages blood vessels and degrades proteins - Risk factor for CVD and thrombosis - Role in Alzheimer's disease - Pregnancy complications - Oxidative stress

Question 26

What one-carbon nutrients are involved in pregnancy? (5)

Answer 26

- Folate (main) - B12 (main) - Methionine - Choline - B6

Question 27

Why are one-carbon nutrients important in pregnancy? (3)

Answer 27

- Vital for epigenetic regulation of placenta and foetus - Enabling DNA synthesis - Required for optimal tissue growth and development

Question 28

What is homocysteine (Hcy)?

Answer 28

A thiol containing amino acid

Question 29

What are the two potential fates of homocysteine?

Answer 29

- Recycled into methionine - Converted into cysteine

Question 30

What are some factors that may cause hyperhomocysteinaemia? (8)

Answer 30

- Age - Male gender - Menopause - Smoking - High coffee consumption - Low consumption of fruits and vegetables - Diabetes - Some drugs