For a research project I need to know how the antioxidants Vitamin C
and Trolox (the watersoluble version of Vit E) work in the HaCat cell,
when the Hacat cell recieves  either 1.UVA or 2.UVB damage:

1. I need to know how long the antioxidants are stable in solution.
2. How long is the diffusion time into that cell?
3. What do the antioxidants do in the Hacat cell? How exactly do they work? 
   Do they interfere in the cell cycle (possibly by prolonging it)?
4. Do they prevent the damage from occuring or can they repair damage?
5. I also need good general background information about these antioxidants
   for an oral exam.
6. What other options are there for protecting cells in general from
UV-light damage?(e.g. Zink) And very briefly: how do they work?

HI I can not really help you with points 1-3 but I may be able to add
a few comments to the other items. Vit C and Vit E are just 2 of the
many antioxidant products available on the market. I am not cell
biologist so I can not really comment on the cell part of the question
but I am a polymer scientist so I can comment on antioxidants. One of
the biggest areas of consumption for antioxidants is plastic and
rubber stabilisation. The degradation processes that happens in
plastics and rubbers is the same as those in cells / biochemistry.
First you need to understand the principles of autoxidation.
Non Inhibited Autoxidation. The reaction of organic compounds with
molecular oxygen is called autoxidation because such reactions are
taking place automatically whenever organic materials are exposed to
the atmosphere. Typically autoxidation is characterised by two factors
1. Autocatalysis and 2. Inhibition (normally by additives).
The reaction mechanisms have been studied by many people and continue
to be studied and I would probably say that they remain not fully
understood. However the general mechanisms of degradation can be
summarised below where R is Alkyl group or chain.
Initiation 
RH  -> R'  where R' is a free radical state
Propagation
R' + O2 -> ROO'
ROO' + RH -> ROOH + R'
Chain Branching 
ROOH ->RO' + 'OH
2ROOH ->RO' + ROO' + H2O
Termination
2ROO' -> Inactive products + O2
R' + ROO' -> ROOR
2R' -> R-R

So the above reaction occur in all polymeric materials and as far as I
know the same reactions occur in human cells (which are just
biopolymers). This means that there is generally some starting
reaction ( free radical generation), propagation reactions followed by
some termination reactions. If you look at the sequence it is the free
radicals and the peroxy radical products that are the main culprits in
propagation and hence autocatalysis. The overally affect on a polymer
of the above reactions can be cross linking or chain splitting.
Typically is it the latter and hence you get degradation of the
product, cracking etc. In biochemistry you end up with cell damage.
Now on to antioxidants. This subject if far too big to discuss here
but in general antioxidants work by influencing the above outlined
processes in different ways depending on their structure. Two main
groups of AO are recognised. Chain terminating or primary antioxidants
and hydroperoxide decomposers or secondary antioxidants. The majority
of primary antioxidants are sterically hindered phenols or secondary
aromatic amines. They are capable of undergoing fast reactions with
the peroxy radicals and therefore are frequently called radical
scavengers. They transfer the radical product to a far more stable or
less reactive radical product. Seondary antioxidants are essentially
sulfur based compounds and have the ability to react with
hydroperoxides to give non radical products. Vitamin E or Alpha
Tocopherol is essentially a version of the hindered phenol
antioxidants and prevents the lipid peroxidation in a similar fashion
to that described above. I thin the same is true of Vitamin C. In fact
both products are being commerically marketed in the polymer industry
as suitable antioxidants.
So in summary antioxidants essentially prevent the propagation
reactions that occur. They dont necessarily stop the initially damage
and they can not repair the initial damage.
UV light is hazardous to polymers and cells because the energy in the
UV spectra coincides with the energy necessary to break chemical bonds
commonly found in polymers and biopolymers and cells. Hence UV light
breaks chemical bonds and creates free radicals which then goes on to
produce the autocatalysis reaction described above. The best way to
prevent cell damage or initiation is to prevent exposure. Zinc creams
work by absorbing the UV light and preventing exposure. Carbon black
does the same thing. In fact many pigements are capable of absorbing
UV light. You can also get chemicals called UV absorbers which are
specific additives that absorb UV light without producing free radical
by products. Like antioxidants you can also get something called UV
quenchers with inhibit the chain reaction in a similar way to that of
antioxidants.
Well hope that helps.