Psyxwar's Biology 3/4 Question Thread

[pi]

Hydrogen bonds are only N/O/F, not Cl-

Wow, how could I forget this? :S

You also forgot that NaCl isn't a molecule and hence hydrogen bonding isn't even relevant

[psyxwar]

^Thanks.

When say, a polar molecule like NaCl is dissolved in water, is the attraction between the H and the Cl a hydrogen bond? If it is, aren't they weaker than ionic bonds? How does it manage to "rip apart" the salt compound? Is this because they are surrounded by them/ there is more than one hydrogen around each chlorine? Or am I completely off?

Also do hydrophilic and polar necessarily mean the same thing? My dictionary seems to suggest only molecules can be polar. So would salt be just hydrophilic? (wording in the NOB textbook is a little confusing)

1) When NaCl dissolves, ion-dipole bonds are formed. And btw, NaCl is an ionic substance, it is not a polar molecule

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2) For the sake of VCE bio, just assume hydrophilic and polar are the same for molecules However, ionic substances (salts, etc.) can also be hydrophilic, so hydrophilic is more of a broader term imo. Keep that distinction in mind

edit: wrote 1) and 1) -_- woops

Oh yeah LOL. Damn I probably should read up on a bit of chemistry for the sake of clarity. What's the term for the type of attraction present in this case then?

Thanks for the answers guys. So I guess I don't need to know this much depth about these things in Biology? I guess that's a (temporary) relief.

[pi]

Oh yeah LOL. Damn I probably should read up on a bit of chemistry for the sake of clarity. What's the term for the type of attraction present in this case then?

Thanks for the answers guys. So I guess I don't need to know this much depth about these things in Biology? I guess that's a (temporary) relief.

Between the Na+ and the Oxygen (for example)? Ion-dipole interactions. Of course, dispersion forces are also present. Both of which are really topics for Chem rather than for Bio though as Chem goes into that depth

[psyxwar]

"Starch is insoluble in water and so its presence in a cell has little or no effect on osmotic action of the cell"

Why is this the case? Wouldn't the presence of starch affect the concentration of water, regardless of whether or not it is water-soluble? Or does the concentration of water only refer to say, a solvent:solute ratio?

[Stick]

Yep, concentration is a ratio of solute to solvent.

[psyxwar]

Yep, concentration is a ratio of solute to solvent.

Ah I see, that makes sense. Thanks!

[Stick]

A lot of Chapter 1 makes sense with Chemistry, so don't stress.

[psyxwar]

A lot of Chapter 1 makes sense with Chemistry, so don't stress.

Haha thanks. It would've been convenient to have done 1/2 chem prior...

"Explain how the chemistry of amino acids enables them to act as buffers in biological tissues:"

I know this question might not be completely relevant to the biology course, but I'm curious anyway. I know the carboxyl group of the amino acid gives the molecule acidic properties and that the R group can also affect the alkaline/acidic nature of the molecule, but how does this enable them to act as a buffer in biological tissue? Apparently they remove excess H+ and OH- ions, but how exactly does this work?

[pi]

"Explain how the chemistry of amino acids enables them to act as buffers in biological tissues:"

I know this question might not be completely relevant to the biology course, but I'm curious anyway. I know the carboxyl group of the amino acid gives the molecule acidic properties and that the R group can also affect the alkaline/acidic nature of the molecule, but how does this enable them to act as a buffer in biological tissue? Apparently they remove excess H+ and OH- ions, but how exactly does this work?

You're on the right track

Firstly, it's important to understand the nature of an amino acid in a neutral pH (say a pH of 7 at 25deg). Amino acids are essentially "zwitterions", which means that they can have charges on both the amino & carboxylic groups, and yet have no net charge ata neutral pH. Hence, there is a neg charge on the carboxylic acid and a positive charge on the amine.

If amino acids are added to an acidic solution (excess H+ ions), the carboxylic acid group (which has a neg charge normally) can "pick up" extra H+ ions (protons) to buffer the solution closer to neutral. Likewise, if added to a basic solution, the amine groups (positive charge normally) can donate a H+ ion to again buffer the solution to closer to neutral.

[ilovecats101]

have a look in biozone !

[Stick]

Very interesting, indeed. Thanks, Rohit! Again, this is probably more relevant to Chemistry than Biology but I guess it's good to know anyway.

[psyxwar]

You're on the right track

Firstly, it's important to understand the nature of an amino acid in a neutral pH (say a pH of 7 at 25deg). Amino acids are essentially "zwitterions", which means that they can have charges on both the amino & carboxylic groups, and yet have no net charge ata neutral pH. Hence, there is a neg charge on the carboxylic acid and a positive charge on the amine.

If amino acids are added to an acidic solution (excess H+ ions), the carboxylic acid group (which has a neg charge normally) can "pick up" extra H+ ions (protons) to buffer the solution closer to neutral. Likewise, if added to a basic solution, the amine groups (positive charge normally) can donate a H+ ion to again buffer the solution to closer to neutral.

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Thanks! That was an interesting and informative read. So at an intermediate pH, the carboxyl group is COO- instead of COOH because the functional group is a weak acid and therefore dissociates into the ions H+ and COO- in such a solution? Is it a similar case with NH2 and NH3+?

[pi]

I'm not 100% on the chemical explanation (forgot all my chem lol), but that's more than enough for bio COOH denotes a weak acid group and NH2 is a beak base group (for lack of better terms).

[curry_bro]

psyxwar, u do NOT need to know that much detail for it. its good ur reading all this stuff (im sure ull do really well) but just read the basics and start learning the things listed on the study design first before u start detailed biochemical studies of content a tad distant from whats required

[Shenz0r]

That zwitterion concept is mostly explored in Chemistry 3/4. As curry_bro says, won't need to go into those specifics for Bio 3/4.

For Biology, it's also important to know that protein structure can be affected by pH, because some of the amino acids in the sequence will donate/accept protons with their R-Variable group.