Structure of Common Macromolecules
Macromolecules are any molecules that have a relatively large molecular weight. They include proteins and nucleic acids (DNA and RNA), which are essential for the growth of living organisms. Other polymers are carbohydrates and lipids.
Macromolecules play a vital role in the survival of living things because they make up structures such as tissues and organs. Macromolecules also function to produce the energy needed by cells for growth or reproduction.
In this post, we will be discussing the structure of common biological macromolecules. There are four major macromolecules: carbohydrates, proteins, nucleic acids, lipids, and fats. They are made up of a specific type of monomer molecule, then bonded together to form polymers.
Monomers consist of carbon and hydrogen atoms that bond together differently depending on their chemist creators’ chemical formula. The most commonly known monomer is water with two hydrogens and one oxygen atom for its chemical formula (H2O). However, should you chose to skip this blog, our professional writers for hire are ready to cover you by acing that assignment for you.
Proteins are the most complex of the four main macromolecules. Their chemical structure and formula are crucial to the understanding of how cells work.
Proteins are made up of amino acids, with a long chain structure with different amino acids creating variations. These polymers differ in structure and function.
The chemical formula is the order in which these amino acids are arranged and for proteins. These biological macromolecules differ in shape depending on which amino acids are being used.
The order and sequence of these different amino acids can be seen in the protein sequence, and proteins are made up of many sequences.
These different chains create a large variety of shapes that give the protein a function. For instance, some proteins can build up cells while others can break them down.
Examples of proteins that build up cells are actin and myosin. While those that break down cells are hemoglobin, peroxidase, and cytochrome C.
There are four levels of the protein structure:
The first level is the primary structure, which means how many amino acids there are in a sequence and their order. This is the level that interacts with other macromolecules, such as DNA. For example, hemoglobin has a primary structure of 141 amino acids.
The secondary structure is the shape that forms as a consequence of hydrogen bonding. Hydrophobic interactions and not covalent bonds form this structure.
The two types of secondary structures are alpha-helix and beta-sheet, with the former being thinner than the latter. These shapes give proteins their shape, function, and stability.
In the Alpha-helix, the backbone is a helix, and in beta-sheets, they are sheets. These two types of secondary structures can be found together as well and are called pleated sheets.
Examples of proteins with alpha-helix are the hemoglobin protein, while those with beta-sheets include keratin and collagen.
The third level is the tertiary structure which defines a protein’s three-dimensional shape.
Here, covalent bonds come into play and form the protein’s shape. These bonds are formed by hydrogen bonding, ionic interactions, or disulphide bridges
The last level is the quaternary structure. At this level, two or more polymers of amino acids bond together to form a single protein.
You can also check the extracellular matrix function, which is made of proteins and polysaccharides!
These are the simplest of the four biological macromolecules. They are made up of a single sugar molecule, such as glucose (C12H22O11), fructose (C14H22O11), or lactose (C12H22O11). They are made up of a chemical formula that is the order in which these sugars are arranged.
Carbohydrates can be monosaccharides (one sugar molecule) or disaccharides (two sugars). A simple sugar has a different structure and function from a complex sugar.
Monosaccharides are the simplest carbohydrate units. They have a chemical formula of CnH(x)O. Examples of monosaccharides include glucose, fructose, and galactose.
Disaccharides are made of two simple sugars. They are formed when monosaccharides are bonded together and have a chemical formula of CnH(x)O.
- Glucose + galactose = lactose
- Galactose + glucose = maltose
- Glucose + fructose = sucrose
Sucrose is the most common disaccharide and is made up of one glucose molecule bonded with one fructose.
Disaccharides have the chemical formula of CmnH(x)O. Some examples are sucrose (C12H22O11), lactose (C12H24O11), and maltose (C12H22O11).
Polysaccharides are long polymers made up of monosaccharides and disaccharides. Their chemical formulas are made up of monosaccharide units.
They are formed when monosaccharides and disaccharides are bonded together in different proportions.
Different structures of polysaccharides can be achieved by changing the monosaccharide and disaccharide proportions. Each structure of these complex sugars has a different chemical formula.
Examples of polysaccharides are:
- Glycogen (C12H22O11)
- Amylopectin (Cm(x)H(x)O)
- Amylose (C12H22O11(HO))
- Starch (Cx(y)O and cellulose.
These biological macromolecules contain the information for making proteins. Nucleic acids are made of nucleotides called monomers. The two main nucleic acids are DNA and RNA.
DNA is made up of four mononucleotide units which are monomers. Three of them are called nucleobases, while the fourth is a sugar and phosphate molecule that forms the backbone.
The mononucleotide units in nucleic acids are as follows:
- DNA – adenine, thymine, guanine, and cytosine (A, T, G, and C).
- RNA – adenine, uracil (U), guanine, and cytosine (A, U, G, and C).
- ATP – adenine, uracil (U), cytosine, and guanine.
The nucleotides that make the DNA are connected by hydrogen bonds between the base pairs (adenine-thymine, guanine-cytosine). Therefore DNA has polarity. The double helix structure of DNA makes it very compact.
If the cell contains eukaryotic cells, DNA is in the nucleus and, if the cell has prokaryotic cells, DNA can be found in a region of bacteria called a nucleoid.
Nucleotides combine to form units called nucleosides. The mononucleotide unit has a base and a sugar molecule in its structure. A nucleotide is made of three parts:
- A pentose sugar
- A nitrogenous base
- A phosphate group.
The pentose sugar is ribose, deoxyribose, or any monosaccharide. The nitrogenous base is either adenine (A), thymine (T), guanine (G), or cytosine (C), while the phosphate group is found in ATP.
In every nucleotide, the nitrogenous base is attached to the sugar molecule and the phosphate group.
In case you need to visualize these structures better, you can check out our guide on the fluid mosaic model!
The Double-helix DNA Structure
The double-helix structure of the DNA is the most well-known of all three structures.
The two strands are made up of mononucleotide units called nucleotides and form a helix shape. This shape forms when the mononucleotide units are in pairs and form hydrogen bonds (A-T, C-G).
The sugar and the phosphate group alternate outside each strand to form the DNA backbone. The two strands of DNA strand are twisted together around the backbone to form a double-helix.
Pairs of nitrogenous bases are on the inside of the strands forming staircase shapes. Hydrogen bonds link the pairs together. Nucleotide A pairs with T while C pairs with G.
Types of RNA
There are three types of RNA, two that are monomers called ribosomal and transfer. The third type is a monomer called a messenger.
Ribosomal RNA (rRNA) monomers are ribosomal A, S, and L. The rRNA monomers are found in ribosomes, where they help to translate mRNA monomers into proteins.
Transfer RNA (tRNA) monomers are called Uracil (U), thymidine (T), and tryptophan. The tRNA monomer binds with the corresponding mRNA monomer in the ribosome to form an aminoacyl-tRNA complex.
Messenger RNA (mRNA) monomers are adenine, uracil (U), cytosine, and guanine. These units form the template for making proteins and are called nucleobases.
Lipids and Fats
Lipids and fats are macromolecules that are made up of monomers. The monomer of lipids is glycerol (Cx(y) HxO), while the monomer of fat is a fatty acid (CxH (z)OO).
Lipids are non-soluble in polar solvents, while fats are soluble in both polar and non-polar solvents. The non-polar carbon-carbon bonds in lipids and fats are what make them insoluble.
Fatty acids are chains of monomers with a carboxylic acid (-COOH) at one end. They are monomers that are found in lipids and fats.
Lipids are building blocks of some hormones, and they form part of the plasma membrane. These macromolecules include oils, fats, waxes, steroids, and phospholipids.
Oils are non-polar organic compounds with monomers that are glycerol and fatty acids.
Some oils include olive, fish oil, soybean, corn oil, and peanut oil. These monomers come from food sources, and the cooking process forms them into an edible product for human consumption.
Fats are monomers that make up the monomer glycerol and fatty acids. Saturated fats have high levels of monomers, while unsaturated fats have low levels.
Saturated fats have a maximized number of hydrogens attached to the carbon atom. In unsaturated fats, the hydrocarbon chain has a double bond.
Phospholipids monomers are glycerol and fatty acids. These monomeric chains make up the phosphodiester backbone that is found in cell membranes.
The head of these monomers is negatively charged, while the tail has a phosphate group with two oxygen atoms attached to it.
A phospholipid has two regions: hydrophobic (fatty acids) and hydrophilic (phosphate group). The monomeric chains are arranged to make the hydrophobic region buried inside and the hydrophilic region on the outside.
In a cell membrane, the fatty acids face inside to avoid the water, while the phosphate can face either direction.
Steroid monomers are cholesterol and a variety of monosaccharides. The monomeric chains in steroids have four attached hydrogens – two at the end of each chain.
The steroid monomers can be modified with carboxylic acid groups found on hormones to make them active or inactive.
They have a ring-like structure and are monomers that form hormones, fat storage, and vitamin D.
Examples of steroid monomers are cholesterol monomer, aldosterone monomer (steroid hormone), and vitamin D monomer.
Waxes on plants are monomeric chains with a hydrocarbon chain and esters, alcohols (-OH), or acid salts as monomers. Beeswax monomers include palmitic acid (C16:0) and stearyl alcohol (C18:0).
Interesting Structural Differences between Proteins and Nucleic Acids
Proteins, DNA and RNA, are all closely related macromolecules, but they exhibit some structural differences.
The building blocks for proteins are amino acids, the building blocks for DNA are nucleobases, and the building blocks for RNA are nucleotides. Also, DNA and RNA have an additional sugar group compared to proteins.
Proteins have a very complex three-dimensional shape to provide active sites for specific biochemical reactions. DNA is linear and only has two strands, while RNA is single-stranded.
Also, proteins are made up of a backbone, mainly peptide bonds (the same bonds present in DNA). On the other hand, nucleic acids have phosphodiester bonds and a backbone made out of sugars.
The DNA has a double-stranded structure, while proteins and RNA only have a single-stranded structure. However, RNA can sometimes be double-stranded.
Proteins have many conformations in water and living cells, while DNA has only one conformation (the so-called B-form) found both in the cell and an isolated molecule.
Density and hydration
DNA has a much higher density than proteins or RNA, as well as a lower percentage of water molecules bound to its backbone (DNA: 32%, RNA: 30%, Proteins: 50%).
The DNA has a repair system that fixes damage to its backbone or bases. However, the repair system of cells only works for proteins under specific conditions. The RNA doesn’t have a repair system.
The DNA has a highly conserved sequence among all species (with some variation). At the same time, there are quite significant variations in protein and RNA sequences and their structure among different organisms.
DNA has a very large genome size, as most of the DNA in cells is not protein-coding. RNA has an intermediate genome size within the range of proteins, and it can code for proteins or be involved as functional molecules.
Both proteins and DNA can be synthesized from their building blocks, while there is no mechanism to synthesize RNA from its building blocks. Instead, RNA is made by DNA-dependent RNA polymerase. Unlike proteins, biological machinery can be used for the replication of both DNA and RNA.
Before You Go
Macromolecules are large molecules that make up the structures and compositions of body cells. They perform various functions in us, such as storing energy or helping to transport oxygen throughout the body.
There is a wide range of macromolecules which include carbohydrates, proteins, lipids, and nucleic acids. You can learn more about these biological building blocks by reading some posts on this blog focused on macromolecular topics. Also, in case you are not sure how to start your biology assignment, our professional writers for hire are ready to help.