Vitamin C

Question 1

T/F most vertebrates have a requirement for vitamin C

Answer 1

False, most vertebrates can make it themself

Question 2

Why can’t humans create vitamin C

Answer 2

We are lacking one enzyme involved in its synthesis

Question 3

Which enzyme do humans and primates lack for vitamin C synthesis

Answer 3

gulonolactone oxidase due to mutations in the gene

Question 4

what is the precursor for vitamin C

Answer 4

UDP-glucose

Question 5

Describe the absorption of vitamin C

Answer 5

dependent on intake
90% of intake is absorbed
Unabsorbed vitamin C is metabolized by intestinal bacteria

Question 6

T/F there is a difference between synthetic and natural sources of vitamin C

Answer 6

false

Question 7

What are vitamers

Answer 7

Different forms of a vitamin but both have activity

Question 8

What is dehydroascorbic acid

Answer 8

The oxidized form of vitamin C that also has activity

It is readily reduces back to vitamin C in the ER

Question 9

How is ascorbate and DHA taken up into tissues

Answer 9

Ascorbate- sodium-dependent transports
DHA- GLUT transporter

Question 10

Ratio of ascorbate to DHA

Answer 10

8:1 AA to DHA

Question 11

Is there a specific storage organ for vitamin C

Answer 11

No
adrenal and pituitary gland show the highest concentration

Question 12

Describe the excretion of ascorbate

Answer 12

Major fate of ascorbate is excretion in urine as ascorbate or DHA
both can be filtered by kidney and reabsorbed

Question 13

Does vitamin C have many metabolic actions

Answer 13

yes

Question 14

What are the biochemical functions of ascorbate

Answer 14

Most characterized role is as a coenzyme in hydroxylation reactions

also plays an antioxidant role and evidence that it plays a role in regulating genes

Question 15

What is collagen stabilized by

Answer 15

Stabilized by hydroxylations

Hydroxyproline helps stabilize the triple helix structure

Question 16

what are the two AAs that are hydroxylated using ascorbate

Answer 16

lysine and proline

Question 17

What is the enzyme used to hydroxylate proline

Answer 17

Proline hydroxylase

Question 18

How does ascorbate help in hydroxylations

Answer 18

It donates electrons to hydroxylate the shit

Question 19

How does ascorbic acid affect dopamine

Answer 19

Hydroxylates it to norepinephrine

Question 20

what are the two general reactions where vitamin C acts as an oxidant

Answer 20

It can react with a superoxide and a proton to generate hydrogen peroxide which can be degraded by catalase

It can interact with a hydroxy radical (OH-) to produce water

Question 21

How does vitamin C effect the skin

Answer 21

Skin is the primary barrier to pathogens and the epidermis synthesizes and secretes much collagen which contains vitamin C. Vitamin C stimulates collagen gene expression

Question 22

How does vitamin C affect leukocyte function

Answer 22

Neutrophils and monocytes accumulate vitamin C and they protect against oxidative damage by scavenging and maintaining levels of other antioxidants, it promotes thiol-dependent signaling and gene expression pathways

Question 23

What are the four ways vitamin C affects the immune system

Answer 23

Through the skin, leukocyte function, lymphocyte function, and inflammation

Question 24

How does vitamin C affect lymphocyte function and inflammation

Answer 24

Lymphocyte: both B and T lymphocytes accumulate vitamin C to provide antioxidant protection and promote proliferation

Inflammation: Modules cytokines which are important to inflammation

Question 25

How does vitamin C affect gene expression

Answer 25

Vitamin C stimulates procollagen gene transcription

Lowers expression of myelin protein gene PMP22

downregulated 31 genes

Question 26

What are the three mechanisms whereby vitamin C has effects on gene expression

Answer 26

1. Redox-dependent transcription regulation
2. Increase in DNA 5-hydroxymethylcytosine content: catalyzed by proline hydroxylase, can lead to decrease or increase in gene activity
3. Decreases some DNA methylation by induction of a miRNA for Dnmt3a

Question 27

Vitamin C deficiency

Answer 27

Scurvy
takes 4-6 motnhs to appear
results from collagen synthesis deficiency

Question 28

Vitamin C requirements

Answer 28

Vary depending on circumstances
but RDA is 50-90 mg/day

Optimum wound haling requires 20 mg/day