In this class we will treat these C-H bonds as effectively nonpolar covalent bonds. This means that methyl groups are unable to form hydrogen bonds and will not interact with polar compounds such as water.
The amino acid isoleucine on the left and cholesterol on the right. Each has a methyl group circled in red. Attribution: Created by Marc T. Facciotti Own work adapted from Erin Easlon. The methyl groups highlighted above are found in a variety of biologically relevant compounds.
In some cases, the compound can have a methyl group but still be a polar compound overall due to the presence of other functional groups with polar properties see Polar Functional Groups discussed below. As we learn more about other functional groups, we will add to the list of non-polar functional groups.
Stay alert! A hydroxyl alcohol group is an —OH group covalently bonded to a carbon atom. The oxygen atom is much more electronegative than either the hydrogen or the carbon, which will cause the electrons in the covalent bonds to spend more time around the oxygen than around the C or H. Therefore, the O-H and O-C bonds in the hydroxyl group will be polar covalent bonds.
The hydroxyl functional group shown here consists of an oxygen atom bound to a carbon atom and a hydrogen atom. These bonds are polar covalent, meaning the electron involved in forming the bonds are not shared equally between the C-O and O-H bonds. Attribution: Created Marc T.
Facciotti Own work. The hydroxyl functional groups can form hydrogen bonds, shown as a dotted line.
Dipoles shown in blue arrows. Facciotti original work. Hydroxyl groups are very common in biological molecules. Hydroxyl groups appear on carbohydrates A , on the R-groups of some amino acids B , and on nucleic acids C. Can you find any hydroxyl groups in the phospholipid in D? Hydroxyl groups appear on carbohydrates A glucose , on some amino acids B Serine , and on nucleotides C Adenosine triphosphate. D is a phospholipid. Carboxylic acid is a combination of a carbonyl group and a hydroxyl group attached to the same carbon, resulting in new characteristics.
This results in a delocalized negative charge on the remaining oxygen atoms. The carboxyl group is very versatile. In its protonated state, it can form hydrogen bonds with other polar compounds. In its deprotonated states, it can form ionic bonds with other positively charged compounds. This will have several biological consequences that will be explored more when we discuss enzymes.
Can you identify all the carboxyl groups on the macromolecules shown above? The amino group consists of a nitrogen atom attached by single bonds to hydrogen atoms. An organic compound that contains an amino group is called an amine. Like oxygen, nitrogen is also more electronegative than both carbon and hydrogen which results in the amino group displaying some polar character. Amino groups can also act as bases, which means that the nitrogen atom can bond to a third hydrogen atom as shown in the image below.
Once this occurs, the nitrogen atom gains a positive charge and can now participate in ionic bonds. The amine functional group can exist in a deprotonated or protonated state. When protonated the nitrogen atom is bound to three hydrogen atoms and has a positive charge. The deprotonated form of this group is neutral.
Attribution: Created Erin Easlon Own work. The oxygen atoms are more electronegative than the phosphorous atom resulting in polar covalent bonds. Phosphate groups also contain a negative charge and can participate in ionic bonds. Phosphate groups are common in nucleic acids and on phospholipids the term "phospho" referring to the phosphate group on the lipid.
Below are images of a nucleotide monophosphate A and a phosphoserine B. Water is a unique substance whose special properties are intimately tied to the processes of life. Water solvates or "wets" the cell and the molecules in it, plays a key role as reactant or product in innumerable number of biochemical reactions, and mediates the interactions between molecules in and out of the cell. Thus CO2 is not a polar molecule, even though it has polar bonds.
In Bis2a, the ubiquitous role of water in nearly all biological processes is easy to overlook by getting caught up in the details of specific processes, proteins, the roles of nucleic acids, and in your excitement for molecular machines it'll happen.
However water plays key roles in all of those processes and we will need to continuously stay aware of the role that water is playing if we are to develop a better functional understanding. Be on the lookout and also pay attention when your instructor points this out. In order to condense the structure and focus on the hydroxyl group the oxygen and hydrogen bound to the second carbon , everything besides the hydroxyl group would replaced with an R, as follows:. Molecules with other elements in their carbon backbone are substituted hydrocarbons.
Each of the four types of macromolecules—proteins, lipids, carbohydrates, and nucleic acids—has its own characteristic set of functional groups that contributes greatly to its differing chemical properties and its function in living organisms.
A functional group can participate in specific chemical reactions. Some of the important functional groups in biological molecules include: hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl groups. These groups play an important role in the formation of molecules like DNA, proteins, carbohydrates, and lipids.
Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity. An example of a hydrophobic group is the non-polar methane molecule. Among the hydrophilic functional groups is the carboxyl group found in amino acids, some amino acid side chains, and the fatty acid heads that form triglycerides and phospholipids. Other functional groups, such as the carbonyl group, have a partially negatively charged oxygen atom that may form hydrogen bonds with water molecules, again making the molecule more hydrophilic.
Simple structure Sulfhydryl Polar Characterized by presence of S. Characterized by central C bound to O and OH. Characterized by presence of N. What functional groups can be found in a fructose molecule?
Leucine is an amino acid that plays an important role in muscle development. What functional groups can be found in a leucine molecule? Hydrogen bonds between functional groups within the same molecule or between different molecules are important to the function of many macromolecules and help them to fold properly into and maintain the appropriate shape for functioning.
Hydrogen bonds are also involved in various recognition processes, such as DNA complementary base pairing and the binding of an enzyme to its substrate, as illustrated in Figure 1. Figure 1. Hydrogen bonds connect two strands of DNA together to create the double-helix structure.
The unique properties of carbon make it a central part of biological molecules.
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