Some Biochemistry Questions.

Factual Questions
1

Hi,

I was look under a thread about soft drinks v.s fruit juices. This was interesting, but it got me thinking back to my Organic Chemistry classes. (I swear, after two semesters of Orgo, you never look at the world the same again)

Here is the question.

What is easiest for your body to break down? Sucrose or Fructrose?

Additionally, what is the specific organic chemical mechanism in which sugar is broken down into glucose? Is Sucrose and Fructrose the same? Or is one inherently healthier?

Here is something else that just baffles me:

If the body completely self-working and self-regulating, how exactly can you inject venom into your bloodstream, and it specifically causes your body to release certain enzymes. Ok, that sounded odd, let me try again. Why does the body listen to other chemicals to tell it what to do? If that makes sense.

Also, why is it that people can build resistances to things like toxins. Do these resistances get passed on to children or no?

Finally, in our class, we did a problem which included an HIV anti-viral agent. Apparently, this drug (which escapes me for the moment) latches on to the sugar molecules on a DNA helix preventing it from dividing. (I believe I have the function wrong, but those who know the drug will know what I am talking about)

This seems such a roundabout way to combat HIV. (I am no doctor of course, just a bio major) Wouldn’t it be feasible to have the body ignore the HIV and let it go on its merry way? After all, it isn’t the HIV that kills, it’s the fact that it drags the immune system in a cat-and-mouse chase that it can’t win.

Whew! Ok, more thing. The Epstein Barr virus causes Mono in some patients. If Mono floods the body with white-blood cells, why can’t you infect HIV patients with this virus?
I know these are very stupid questions, but enlighten me!

Thanks

Brian

2

I would guess fructose would be easier to break down than sucrose, since sucrose is a disaccharide (made of 2 sugars, one of which is fructose the other glucose) and fructose is a monosaccharide (one sugar)

er… been too long since organic for me, I’ll leave this part for someone else ;D

Short answer: antibodies. When you first get infected with a virus, for example, your body has no clue what the invader is. Therefore, you get fairly ill, but your body starts to build antibodies that are specific to this invader. Next time you get the same illness, USUALLY your body is much better equipped because of having built up antibodies. The same idea works with vaccines, except you dont’ get sick the first time.

Well the HIV is what causes the immune system to be depressed… it’s the root of the problem, and therefore, the “easiest” or at least most logical thing to attack. It’s like… if you have a dam break and flood a residential area, are you going to stand downstream with buckets trying to bail yourself out, or are you going to fix the dam?

In my understanding, mononucleosis causes production of atypical white blood cells, which are fairly useless in helping the body’s immune system. Besides, I think the last thing an AIDS patient needs is one more infection. As you somewhat correctly noted, it’s not usually the HIV that kills you, it’s the fact that your depressed immune system can’t fight off all the other bugs that come along. Therefore, something simple like the common cold could actually kill you.

I’m just a chemist, but this answer is based on what I remember from bio courses…

3

Meant to add, no, resistance usually cannot be passed on to children. However, a mother’s breast milk contains some antibodies that can help her child.

4

Discover magazine recently published an informative article on venom (June 2003 Issue, so going by magazine time it probably came out three months ago). A local library probably has a copy and it will answer all your questions about why your body “listens” to venom.

5

Just one nit pick…antibodies do not protect your body against toxins, but they do work rather well against pathogens…:wink:

Oh, and i’m really not sure on what’s easier to convert to glucose. It would seem that a simple hyrdolysis reaction can cleave the glucose molecule from fructose in sucrose and there are enzymes capable of converting fructose to glucose. But what’s “easier” is a pretty vague query. I’m not really clear on the energetics of the hydrolysis of a sucrose molecule versus the conversion of a fructose to a glucose.

6

You figure out how to do that, and get back to us, and I’ll notify the Nobel comittee. Seriously, though, what would it do to have the body ignore the virus?? The problem is that the virus is invading the body’s cells, and killing them. If the body ignored it, that would just kill you all the faster. If you’re asking how to prevent the body’s cells from letting the virus in, well, see the above Nobel comment.

7

Sucrose hydrolizes instantaneously once it comes into contact with stomach acid. Its component parts, glucose and fructose, are then transported to the mitochondria of cells. There is no energy expenditure in the hydrolysis of the sucrose.

I believe you are thinking of the biochemical mechanism known as glycolysis, which takes place in the mitochondria. Sucrose and fructose are not the same, as one is a disaccharyde and the other a monosaccharyde. Since sucrose is hydrolyzed to glucose and fructose, both sugars enter the mitochondria pretty much as equals.

However, fructose is easier to breakdown than glucose, as one less enzymatic step is required. Since that step is one that uses ATP to isomerize glucose to fructose, there is some energy savings involved.

Well, it would make more sense if you were more precise on what you mean by toxins. Do you mean alcohol? Hot spices? Arsenic? Carbon monoxide? Bug spray? Spider bites? Do you have some specific reaction in mind? If so, please clarify.

Not everyone can build a resistance to each and every “toxin” they encounter. An example of this would be the widely varying responses to alcohol. Some people can drink quite heavily before becoming drunk, others can barely handle a glass of wine, still others don’t care to have more than a beer or two a month.

Yes and no. If resistance to a specific “toxin” is (1) heritable, and (2) not selected against, then it will be passed on. That is, the resistance must be something that is passed through the germ line (i.e., eggs and sperm cells) and it must not be something that decreases the chances of survival and/or reproduction.

Ummm… that’s been tried already. Review the 1980s for how well that particular method worked. cf especially Ronald Reagan and the Christian Right.

This is like saying that it isn’t carbon monoxide that kills you, it’s the fact that it irreversibly binds to hemoglobin that kills you.

Because (1) not all white cells are created equal. What works for one pathogen may be useless against another; (2) the vast majority of infections flood the body with white blood cells as part of the nonspecific and specific immune response so this is not unique to mono; and (3) secondary infection by another pathogen can be quite deadly for those infected by HIV.

8

HIV specifically infects CD4+ T cells, also known as helper T cells. As the name implies, their main role is to help other components of the immune system in fighting infection, generally by sending signals to those cells that activate them. This is somewhat oversimplified, but the whole story is much too complicated to get into here. (I’ve spent the past 2.5 years working on my Master’s degree in Immunology, and I’ve barely scratched the surface.)

So, long story short, HIV kills the helper T cells that it has infected, which means that the other immune cells don’t receive any help in fighting pathogens that have infected the body and the patient can’t mount an effective immune response. This means that if an HIV-infected individual were to get infected with EBV, not only would their immune system be unable to respond properly, the virus would be able to proliferate unchecked and cause massive problems for them.

The other problem with the scenario of using EBV to cause white blood cells to expand and thus combat HIV is that each T cell expresses a unique, specific receptor. A T cell that recognizes EBV (or any other pathogen you can think of) recognizes only that pathogen, and does not respond to anything else. It’s all very tightly regulated, and once again much too complicated to get into fully here.

Hope this helps, and that I haven’t just confused you.

9

What is easiest for your body to break down? Sucrose or Fructrose?

Fructose. It does not need to break down, but it needs to have phosphate groups added (use of ATP).

Additionally, what is the specific organic chemical mechanism in which sugar is broken down into glucose? Is Sucrose and Fructrose the same? Or is one inherently healthier?

Different enzymes break down different sugars. All they do is break a glycosidic bond (or more, depending on sugar). Sucrase breaks down sucrose, but in the small intestine, not stomach.

Both are good sugars, but fructose would probably be taken up before sucrose. Cells only absorb the monosaccharides glucose, galactose, and fructose. Anything else has to be broken down or converted into one of the three before it enters the cell.

10

The body is just a bloody big pile of chemical reactions. Why would you expect it to ignore some substances but not others?
The release of enzymes is part of the self-regulation process. Self-regulation is carried out by the network of chemical reactions that the body is made up of. The venom will react with substances in the body. Cells in the body have receptors on them that will latch onto the venom and trigger a cascade of enzymes.

A chemical reaction doesn’t distinguish between substances that are “supposed” to be part of the reaction and other substances that could also take part in the reaction. Imagine you are burning a candle. The candle wax is burning. It’s “self working” if you like. Then you put a balloon full of methane over the candle flame. Would you expect the candle flame to ignore the methane?

11

Ok, if you haven’t noticed, I am trying to figure out which is healthier.

Let me get this straight.

Sucrose is a disacchiride and requires more energy to break down.

Fructrose is a monosacchiride and requires less energy.

Sucrose is comprised of Fructrose and glucose. Which means th at once sucrose is broken down into its smaller consitutents, that the body must go a head and break fructrose (from the sucrose molecule) down. Do I have all of this correct?

Carbohydrates requires a lot of energy for the body to break down. Thusly, if sucrose requires more energy than fructrose to break down, wouldn’t be healther to eat table sugar and carbohydrates than to eat fruit sugar? (i.e more energy expenditure)
Thanks

12

I’m not sure sucrose needs more energy to use. IIRC, just breaking down glycosydic bonds does not require ATP input (hence no energy loss). Of course, you have to create the enzyme to break it down, and that can be regulated by the amounts of simpler sugars (in this case fructose) that you have. Another thing is that fructose is readily absorbed, while sucrose has to be broken down outside the cell in order to absorb glucose and fructose.

So:

In the presence of both fructose and sucrose, the cell will use fructose. The concentration of fructose probably regulates the formation of the enzyme required to break down sucrose, specially if the enzyme is not present already.

Fructose is not broken down into any other sugar, it just goes directly to glycolysis (like glucose would do).

You got the final part wrong.

Sucrose takes more time to break down, but it yields far more energy when it is finally converted to pyruvate.

Brief recap of cellular respiration (numbers not exactly correct):

For each glucose broken down, approximately 40 ATPs are formed… about 4 used… net yield is about 36 ATPs per glucose.

A sucrose molecule would take more time to break down and obtain the ATPs from its breakdown, but the total yield would be double that of fructose (which would act like glucose, energy producing-wise).

I repeat: Carbohydrates don’t take that much energy for the body to break down. They produce far more energy than they cost (thus it is favorable to break them down).

Carbohydrates not used are either stored as glycogen (similar to starch) or fats. Eating lots of fructose would give you less molecules to store than eating sucrose, so less glycogen/fat is accumulated. :slight_smile:

13

Correct me if I’m wrong, but KGs final statement should not mean that you revert to an all-fructose diet. Much of the ATP you create and use is used directly by the cell in order to do it’s basic functions and keep you alive, and so the cell needs a lot of it. That’s why mitochondria exist - they are specialised energy power plants for your cells. All-fructose would mean a LARGE decrease in available ATP, and you would have to consume some much more frequently in order to maintain your basic cell activity. It is really only excess carbohydrates that get converted to glycogen and fat, and these are what your body begins to break down when you’re hungry or otherwise use up a lot of the glucose/starch ATP. Once these are consumed, your body will begin to destry its own cells in order to gain energy - destruction of muscles, and starvation.

That said, fruits are still good for you, and a high-fruit-low-glucose diet can be effective if properly managed, such as in a diabetic diet.

14

Ahem… :wink:

Full article is
here. Used to work for a company that produced antivenin, and they used a similar process. Essentially, the concept is the same… the reason bacteria bother us so is the “toxins” they produce.

15

mnemosyne, you’re right… what I wanted to say is that eating a high sucrose diet is not necessarily better than a high fructose diet. More sucrose in diet, more excess energy to store. Sure, they consume more energy to break down, but they provide much more than they cost.

16

Well, in order to even get inside the T-cells, surface proteins on the HIV bind to surface proteins. In particular, it binds to the CD4 molecule, which is involved in the immune response and is found on cells like T-cells and macrophages. But that just gets the HIV bound to the cell. A co-receptor, which is normally used to bind to cytokines (a huge class of molecules in your body, and if I recall correctly, are produced during injury) is required in order to allow the membrane of the HIV particle to fuse with the membrane of the cell (which allows the viral genome to get inside the cell). To be specific, the co-receptor on macrophages is the CCR5 chemokine receptor, and the co-receptor on T-cells is the CXCR4 chemokine receptor.

Now, you were proposing it would be best for the body to just “ignore” the HIV. In order to do that, you would have to eliminate those receptors that allow HIV to bind. You can’t eliminate the CD4 molecule, because it has a huge function in the immune response. However, you weren’t too far off base in your idea, because some research has been done to see if you can prevent HIV from binding to the coreceptor (sure, you’d have HIV particles stuck to the outside, but their contents can’t get in. And those particles would be a target for your immune system to eliminate, because they’re just stuck on the outside of the cell and not doing anything).

Now, there are several ways to do this. If there are a lot of chemokines in the bloodstream, those would compete with HIV for spaces on the chemokine receptors. Which means there would be fewer available for HIV to bind to. In fact, individuals with elevated chemokine levels are HIV resistant. Also, people who have mutant chemokine receptors are also HIV resistant.

There are some people who do not express CCR5. They do not have that receptor, so HIV can’t get inside their cells. Now, this is what I thought was really nifty (all of this info was from my “Topics in Medical Biochemistry” class)–this mutation has a relatively high frequency in people in Europe. And why is that? That same receptor is involved in the bubonic plague. Having a mutated gene for CCR5 helped people survive the plague. Thus, a greater percentage of the population of post-plague survivors had this mutation than pre-plague. That’s why it’s still in high levels in Europe today.

For that last bit, my lecture notes included a map showing the frequency of the allele from the Sept. 1997 issue of Scientific American. The authors were O’Brien and Dean.

17

Absolutely fascinating.

So people who express this gene are immune to HIV? In other words, they can’t develop AIDS? Was the expression of this gene gradual? Or was it a defect before and these were the people who survived?

People in Africa are dealing with “plague” of HIV. Do you think decades from now, their offspring will be immune to HIV?

Also, in Orgo, we looked at the the molecule for Cellulose. I am NOT understanding why the body can’t break this molecule down. It looks like sucrose.

Also, with hemoglobin, what makes an OXYGEN bind to FE? That baffles me.

Thanks again.

I know these are stupid questions, but please sate my curiousity! :slight_smile:

Brian

18

It’s actually people who lack expression of CCR5 who are resistant to HIV. The virus can’t enter their cells, so no, they can’t get infected with the virus and thus can’t get AIDS. All of the chemokines and chemokine receptors are redundant, so people who lack a given receptor don’t have any obvious ill effects. So it’s likely that a small percentage of the population already lacked the gene before the bubonic plague (I hadn’t heard this theory before BTW, but it makes sense), but if the mutation gave them an advantage in surviving the plague, the mutation would be enriched in the general population. The lack of CCR5 can be detected in all populations in the world, it’s just that it’s more prevalent among people of western European ancestry.

There are other similar instances of a mutation giving people an advantage in surviving diseases. For example, sickle cell anemia. If someone has one copy of the sickle cell anemia gene, they have a greater resistance to malaria, which is why the mutation has persisted, despite the problems that arise when someone has two copies of the gene. There are other examples as well, but I’m feeling too lazy to go look them up right now.

So yes, I think it is likely that eventually a population will arise in sub-Saharan Africa that is resistant to HIV in some way. Whether this will be through the loss of expression of CCR5 or some other mutation, as well as how long this takes, remains to be seen though.

And I’m going to leave the biochem questions to people who actually did well in that subject. :slight_smile:

19

First, sucrose is a disacharide of glucose + fructose.

Maltose is a disacharide of glucose + glucose.

For the cellulose bit–this goes way back to high school biology, so it’s a bit hazy. Now, you know that glucose has a shape, and it has atoms “above” and “below” the “plane” of the glucose molecule (it’s more chair shaped than planar, but nevermind). Sometimes when glucose polymerizes, the two molecules look like people holding hands. Here’s a bad ASCII picture:

----------/----------

But in other polymers, it’s more of a diagonal type arrangement. Like this:



            /-----------
----------/

As you can imagine, those are vastly different shapes. I don’t remember which arrangement is characteristic of cellulose, but our enzymes for digesting polysaccharides can’t fit in between the molecules for cellulose, but CAN for things like glycogen and starch.

This website can let you see some of the molecules I’ve been talking about. Starch looks like maltose repeated over and over again, but you can see that cellulose looks different.

I don’t have time to get into the hemoglobin bit, but it’s all about the interactions of the electrons between oxygen and iron.