Biology Unit 3 Questions Megathread

[Russ]

RE: reducing environments, I'm thinking it's either the amount of water in the cytosol or the fact that physiological pH is ~7.4

Either way, you don't need to know it.

[WhoTookMyUsername]

Thanks for the help Even i'm not sure what i want to know exactly :S


1) I think i am confused about what dissolve actually entails.

Correct me if i'm wrong (i think i am)
For ionic compounds, dissolve means that it dissociates into its non - metal and metal parts, while for
Organic compounds (with covalent bonds) it entails splitting into individual monomers / molecules, not individual atoms (e.g. dissolving of glucose doesn't mean splitting into Carbon atoms).
OR (/and)
Does it mean:
E.g. glucose molecules being surrounded by water and hydrogen bonds but not breaking the covalent bonds?

So for instance: Why is the glycerol and/or phosphate on a lipid *water soluble* does it dissolve further? or just has an affinity to be surrounded by water molecules.


*original question* Does water soluble refer to the complete breakdown of the molecular compound / molecule structure (e.g. NaCl -> Na + Cl) and/or the tendency for substances to seperate into individual, unconnected parts in water (e.g. full glucose molecule). Does it depend on Ionic / Covalent bonds?


2)

Does a monosaccharide (in monomer form) have any functions other than immediate energy supply?

3)
I'm also still confused about cell membranes. Is a plasma membrane by definition any phospholipid bilayer?

(e.g. if there was a picture of a cell with an arrow pointing to outer membrane, do i say plasma  membrane or cell membrane?)


4)
The elements of Proteins are defined as
(CHON(S,P)) Which (any?) amino acids contain phosphorus? (if not, why is P in proteins sometimes?)


5)
Are there any amino acids which are non - polar and are form peptide hormones?
If they are do they transfer signals like lipid based hormones?

6) How are thyroid hormones different to Steroid hormones?

[Russ]

I'm not going to give a chemical definition of dissolve but if you put something in water and the water molecules can bind it (ie it's polar) then it is capable of dissolving. Whether or not it does dissolve depends upon how many bonds form/size of the molecule etc.

2. Anabolic pathways

3. A phospholipid bilayer is a plasma membrane but not all plasma membranes are phospholipid bilayers. (I would write cell membrane but either is OK)

4. Huh, I never thought about that. From memory none of the standard amino acids have P in them but there may be others that do, or it may be acquired from lipids/ATP/chaperone proteins that are intimately associated with the protein whilst it forms

5. Individual amino acids are generally polar (NH+/COO-) but the side chain may be non polar. I can't think of any examples of an amino acid acting as a hormone though. Hypothetically, something like Glycine might be able to get across the cell membrane because it's not particularly large and find a cytosolic receptor but that's really not relevant/I'm not sure how correct it is. Opinions from anyone else?

6. Thyroid hormones are just hormones from the thyroid gland, steroid hormones are hormones with a steroid ring structure

[shinny]

5. Individual amino acids aren't hormones, but there are many amino acid derivatives which are. The most obvious example would be noradrenaline which is made from tyrosine, but there's some others such as serotonin and such too. That's not particularly relevant anyhow. Point is, they act similar to peptides in that they do not cross the cell membrane and act on extracellular receptors, and do not require assistance to travel in the bloodstream. As for amino acids being hormones, that wouldn't make any sense. If they could, then these receptors would be constitutively active within any cell given that these amino acids are pretty much floating around everywhere. Hence, that's why these amino acids are changed a little to give some derivatives which are a bit more specific.

[WhoTookMyUsername]

How are amino acids active in anabolic  pathways?

[shinny]

How are amino acids active in anabolic  pathways?

You mean monosaccharides? AAs is pretty self-explanatory o.O

[shinny]

Not too sure what Russ meant by it, but they can be used in anabolic pathways either through providing energy for them (i.e. same as the first answer we had), or through actually being a building block of them. For example, cellulose and chitin are both polymers made from monomers of glucose or derivatives of it. Overall I wouldn't worry too much about this question. All that's important is the main function.

[WhoTookMyUsername]

Can the act as NADH or carrier molecules or something?

Also: Does Chitin dissolve in water>/.

[HERculina]

Also: Does Chitin dissolve in water>/.

hm i think they dont, cause usually complex CHOs are insoluble in water

btw, do both polar and non-polar molecules have no overall charge?

[WhoTookMyUsername]

Neither have an overall charge  - polar simply has ends that are slightly charged

Are all non - polar substances have a pH of 7?

and

What feature makes the protein of spider webs so elastic (how is this due to beta plating) and strong?


and

Is a promoter sequence just a Methionine?

[Russ]

Polar molecules might have an overall charge, although I guess it depends how you define polar.

Are all non - polar substances have a pH of 7?

This doesn't make sense..?

Is a promoter sequence just a Methionine?

No, a promoter sequence controls expression of the gene. The first amino acid in the protein chain is Met.

[WhoTookMyUsername]

Polar molecules might have an overall charge, although I guess it depends how you define polar.

Are all non - polar substances have a pH of 7?

This doesn't make sense..?

I mean, e.g.

a polar molecule must be charged.

Acidic or Basic substances must have an excess of H or OH as charge?

So does that mean all acidic or basic substances are charged?

[HERculina]

Polar molecules might have an overall charge, although I guess it depends how you define polar.

Hm, polar molecules have no overall charge cause theyre made from covalent bonds? :/
... not made of charged ions? :O

What feature makes the protein of spider webs so elastic (how is this due to beta plating) and strong?

I think its the fact that beta pleated sheets are stronger structures than alpha helices. plus spider webs are fibrous proteins thus theyd be very tough and insoluble in water? (i got most of this from biozone ^^ )

[WhoTookMyUsername]

Well if you think about it, a web does still bend quite a bit, so i guess that's elasticity

But why does Beta plating lead to bending? (or is it just less relative to alpha?)

[HERculina]

Well if you think about it, a web does still bend quite a bit, so i guess that's elasticity

But why does Beta plating lead to bending? (or is it just less relative to alpha?)

wait...i read about something a bit like this in NOB...

o here it is:

The major protein of wool is alpha-keratin, a spiral molecule. If the fi bre is
stretched and the hydrogen bonds are broken the fi bre becomes extended. If
the fi bre is then ‘let go’, the hydrogen bonds reform and the fi bre returns to its
original length.
• The major protein of silk is fi broin that is fully extended and lacks the coiling
found in the structure of wool. The silk molecules form a beta-pleated sheet
(see fi gure 1.18b). The polypeptide chains of silk are already extended and
cannot be extended further.