What a functional group is. Some of the key types of functional groups found in biological molecules.
Hydrocarbons, made up entirely of carbon and hydrogen atoms, make wonderful combustion fuels (such fuels include propane, butane, and the bulk of commercial gasoline). But can you build a living organism out of only combustion fuels? Probably not. Most large biological molecules in fact contain many types of atoms beyond just carbon and hydrogen. These additional atoms allow for functionality not typically seen in hydrocarbons.
Large biological molecules are generally composed of a carbon skeleton (made up of carbon and hydrogen atoms) and some other atoms, including oxygen, nitrogen, or sulfur. Often, these additional atoms appear in the context of functional groups. Functional groups are chemical motifs, or patterns of atoms, that display consistent “function” (properties and reactivity) regardless of the exact molecule they are found in. Biological molecules can contain many different types and combinations of functional groups, and a biomolecule’s particular set of groups will affect many of its properties, including its structure, solubility, and reactivity.
A few of the most important functional groups in biological molecules are shown in the table below. Functional groups can be classified as hydrophobic or hydrophilic based on their charge and polarity characteristics. The only hydrophobic group below is the methyl (CH
) group, which is nonpolar. The remaining six functional groups in the table all have varying degrees of hydrophilic character.
One example of a strongly hydrophilic group is the carboxyl group (COOH), which can act as an acid and lose a proton to form a negatively-charged carboxylate ion (COO
). Carboxyl groups are commonly found in amino acids, fatty acids, and other biomolecules. An example of a less hydrophilic group is the carbonyl group (C=O), an uncharged but polar (contains partial positive and partial negative charges) functional group. Carbonyls are found in many different biological molecules, including proteins, peptides, and carbohydrates.
Common functional groups in biology
|Carboxyl||Charged (forms R-COO|
|Amino||Charged (forms R-NH|
|Phosphate||Charged (forms R-OPO|
Table modified from: OpenStax Biology.
In the table above, the letter R is used to represent the rest of the molecule that a functional group is attached to. For instance, R might be an ethyl (CH
CH ) group, in which case the first entry in the table would correspond to ethanol. But R could also represent the bulk of a much larger molecule, such as a protein. The letter R is used throughout biology and chemistry to simplify chemical structures and highlight the most important parts (often the functional groups!) of a molecule.
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- In the table, what is the difference between a functional group being polar and being charged?(11 votes)
- A charged group is either positive or negative (gains or loses an electron) and a polar group contains atoms that have a difference in electronegativity.(30 votes)
- There are many more functional groups,any tips for remembering there names?(16 votes)
- You could try active recall where you watch a video or read and then you close it and try and write down as many things as you can remeber. (This works because it is more difficult at first telling your brain that it needs to focus on it creating connections between your brains nerves)(3 votes)
- Can someone please elaborate on what makes a molecule or atom, polar/non-polar or acidic/basic?(6 votes)
- Sure thing! An atom is the smallest building block of life, it cannot be broken down further (like Carbon). A molecule is a group of atoms chemically bonded in a fixed proportion (like CO2), which can be further broken down. An atom is polar molecularly if it is asymmetrical (in terms of bonding, it is polar when its electronegativity difference is >0.6). An atom is nonpolar molecularly if it is symmetrical (in terms of bonding, it's EN difference is <0.6). An atom is acidic when there are more positively charged hydroniums than negatively charged hydroxyls (same vise-versa).(17 votes)
- Are aldehydes and ketones (carbonyls) significantly soluble in water like alcohols and carboxylic acids? If not, why not?(5 votes)
- The short molecules are soluble in polar substances like water because they are relatively polar. The longer the carbon chain is however, the greater the non-polar tail is, and the less soluble aldehydes and ketones become.(7 votes)
- is phosphate group polar or non-polar?(3 votes)
- The phosphate group is non-polar, it is made up of a polar head but three non-polar tails, making the overall charge, non-polar(6 votes)
- is it normal that in the video, it written. that an Amino group is N-H-H, while here its R-N-H-H(3 votes)
- Well first thing is that we don’t write condensed structural formulas like that. The formula is written in a specific order so we know what is bonded to what. So if you write N-H-H or R-N-H-H, it looks as if nitrogen is bonded to only one hydrogen and that there’s a bridging hydrogen joining the nitrogen to the other hydrogen. If we have multiple atoms bonds to the same central atom, we use subscripts.
If it’s an amine, we need that ‘R’ part of the formula to show that the nitrogen is bonded to a larger organic molecule. Otherwise it looks like a lone nitrogen molecule, like ammonia. So it’s properly written as R-NH2 (where the 2 is a subscript).
Another thing to point out that we can have slightly different types of amines depending on how many carbon atoms are bonded to it from the rest of the organic molecule. An amine is essentially an ammonia molecule where a hydrogen has been replaced by a carbon atom. But since ammonia has a formula of NH3, we have the possibility of replacing all three hydrogen atoms with carbon atoms.
An amine with only one carbon atom is called a primary amine (symbolized 1°) with a formula of R-NH2.
An amine with two carbon atoms is called a secondary amine (2°) with a formula of R2-NH.
An amine with three carbon atoms is called a tertiary amine (3°) with a formula of R3-N.
Hope that helps.(6 votes)
- how alkanes are less reactive. why?(3 votes)
- Alkanes are less reactive than alkenes.
This is because alkenes have double bonds (C=C).
It is easy to break just one of these bonds in the double bond and make a reaction happen, but breaking the C-C single bond in an alkane is difficult(5 votes)
- In what year in school do we learn this? I am home schooled and i want to learn 11th grade, but i am not sure if this is near grade 11 or is it for 9th graders or for collage. What grade do you learn this?(4 votes)
- this would be basic chemistry so you could learn this is 9th or 10th or even 11th grade if you take biology or chem(4 votes)
- Does anybody know whether there is a difference between O-H and OH?(2 votes)
- There is no difference. OH has an imaginary bond between them (seen in O-H). We assume it is there. It is a common group so we do not have to draw the bond every time.(8 votes)
- How can you tell if a functional group is acidic or basic just by looking at the functional group?(5 votes)