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Biological Molecules

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Biological Molecules

Biological molecules (sometimes called biomolecules) are fundamental building blocks of cells in living organisms.

There are small and large biological molecules. Water, for example, is a small biological molecule composed of two types of atoms (oxygen and hydrogen).

The larger molecules are called biological macromolecules, of which there are four essential types in living organisms. DNA and RNA belong to this category of biological molecules.

In this article, as we focus primarily on the larger molecules, we will use the term biological macromolecules in certain parts.

What kind of molecules are biological molecules?

Biological molecules are organic molecules . This means that they contain carbon and hydrogen. They might contain other elements such as oxygen, nitrogen, phosphorus or sulfur.

You might find them referred to as organic compounds . This is because they contain carbon as their backbone.

Organic compound: a compound that, in general, contains carbon covalently bound to other atoms, especially carbon-carbon (CC) and carbon-hydrogen (CH).

Serving as the backbone, carbon is the most important element in biological molecules. You may have heard that carbon is the foundation of life, or that all life on Earth is based on carbon. This is due to carbon's function as an essential building block for organic compounds.

Take a look at Figure 1, which shows a molecule of glucose. Glucose is composed of carbon, oxygen and hydrogen atoms.

Notice that carbon is in the middle (more precisely five carbon atoms and one oxygen atom), forming the base of the molecule.

Biological Molecules, structure of glucose with carbon, oxygen and hydrogen atoms, StudySmarterGlucose is composed of carbon, oxygen,and hydrogen atoms. Carbon serves as the backbone of the molecule.Carbon atoms are omitted for simplicity

All biological molecules contain carbon except one: water.

Water contains hydrogen, but it does not contain carbon (remember its chemical formula ). This makes water an inorganic molecule.

Chemical bonds in biological molecules

There are three important chemical bonds in biological molecules: covalent bonds, hydrogen bonds, and ionic bonds.

Before explaining each of them, it is important to recall the structure of the atoms that are the building blocks of molecules.

Biological Molecules, Atomic structure of carbon, StudySmarterAtomic structure of carbon

Figure 2 shows the atomic structure of carbon. You can see the nucleus (a mass of neutrons and protons). Neutrons have no electrical charge, while protons have a positive charge. Therefore, overall a nucleus will have a positive charge.

Electrons (blue in this image) orbit the nucleus and have a negative charge.

Why is this important? It is helpful to know that electrons are negatively charged, and they orbit the nucleus, in order to understand how different molecules are bound on an atomic level.

Covalent bonds

The covalent bond is the bond most commonly found in biological molecules.

During covalent bonding, atoms share electrons with other atoms, forming single, double, or triple bonds. The type of bond depends on how many pairs of electrons are shared. For example, a single bond means a single pair of electrons is shared, etc.

Biological Molecules, Examples of single, double, and triple bonds, StudySmarterExamples of single, double, and triple bonds

The single bond is the weakest of the three, while the triple bond is the strongest.

Remember that covalent bonds are very stable, so even the single bond is much stronger than any other chemical bond in biological molecules.

When learning about biological macromolecules, you will come across polar and nonpolar molecules, which have polar and nonpolar covalent bonds respectively. In polar molecules, electrons are not distributed evenly, for example in a molecule of water. In non-polar molecules, electrons are evenly distributed.

Most organic molecules are non-polar. However, not all biological molecules are non-polar. Water and sugars (simple carbohydrates) are polar, as well as certain parts of other macromolecules, such as the backbone of DNA and RNA, which is composed of sugars deoxyribose or ribose.

Interested in the chemistry side of this? For more details on covalent bonds, explore the article on Covalent bonding in the chemistry hub.

The importance of carbon bonding

Carbon can form not only one, but four covalent bonds with atoms. This fantastic ability allows for the formation of large chains of carbon compounds, which are very stable as covalent bonds are the strongest. Branched structures can be formed as well, and some molecules form rings that can attach to each other.

This is highly significant since different functions of biological molecules depend on their structure.

Thanks to carbon, large molecules (macromolecules) that are stable (due to covalent bonds) are able to build cells, facilitate different processes and overall constitute all living matter.

Biological molecules, ring and change structures with carbon backbone, StudySmarterExamples of carbon bonding in molecules with ring and chain structures

Ionic bonds

Ionic bonds form when electrons are transferred between atoms. If you compare this to covalent bonding, electrons in covalent bonding are shared between the two bonded atoms, while in ionic bonding they are transferred from one atom to another.

You will come across ionic bonds while studying proteins since they are important in protein structure.

To read more about ionic bonds, check out the chemistry hub and this article: Ionic bonding.

Hydrogen bonds

Hydrogen bonds form between a positively charged part of one molecule and a negatively charged part of another.

Let's take water molecules as an example. After oxygen and hydrogen have shared their electrons and covalently bonded to form a water molecule, oxygen tends to “steal” more electrons (oxygen is more electronegative) which leaves hydrogen with a positive charge. This uneven distribution of electrons makes water a polar molecule. Hydrogen (+) is then attracted to negatively charged oxygen atoms of another water molecule (-).

Individual hydrogen bonds are weak, in fact, they are weaker than both covalent and ionic bonds, but strong in large quantities. You will find hydrogen bonds between nucleotide bases in DNA's double helix structure. So, hydrogen bonds are important in water molecules.

Biological Molecules, Hydrogen bonds between water molecules, StudySmarterHydrogen bonds between water molecules

Four types of biological macromolecules

The four types of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids ( DNA and RNA ).

All four types share similarities in structure and function, but have individual differences that are crucial for the normal functioning of living organisms.

One of the biggest similarities is that their structure affects their function. You will learn that lipids are able to form bilayers in cell membranes because of their polarity and that, due to the flexible helical structure, a very long chain of DNA can fit perfectly neatly into the tiny nucleus of a cell.

1. Carbohydrates

Carbohydrates are biological macromolecules that are used as an energy source. They are especially important for the normal functioning of the brain, and in cellular respiration.

There are three types of carbohydrates: monosaccharides, disaccharides, and polysaccharides.

  • Monosaccharides are composed of one molecule of sugar (mono- means 'one'), such as glucose.

  • Disaccharides are composed of two molecules of sugar (di- means 'two'), such as sucrose (fruit sugar), which is composed of glucose and fructose (fruit juice).

  • Polysaccharides (poly- means 'many') are composed of many smaller molecules (monomers) of glucose, ie individual monosaccharides. Three very important polysaccharides are starch, glycogen and cellulose.

Chemical bonds in carbohydrates are covalent bonds called glycosidic bonds , which form between monosaccharides. You will come across hydrogen bonds here as well, which are important in the structure of polysaccharides.

2. Lipids

Lipids are biological macromolecules that serve as energy storage, build cells, and provide insulation and protection.

There are two major types: triglycerides , and phospholipids .

  • Triglycerides are built of three fatty acids and alcohol, glycerol. Fatty acids in triglycerides can be saturated or unsaturated.

  • Phospholipids are composed of two fatty acids , one phosphate group and glycerol.

Chemical bonds in lipids are covalent bonds called ester bonds , which form between fatty acids and glycerol.

3. Proteins

Proteins are biological macromolecules with various roles. They are the building blocks of many cell structures, and act as enzymes, messengers and hormones, carrying out metabolic functions.

Monomers of proteins are amino acids . Proteins come in four different structures:

Primary chemical bonds in proteins are covalent bonds called peptide bonds , that form between amino acids. You will come across three other bonds as well: hydrogen bonds, ionic bonds and disulfide bridges. They are important in the tertiary protein structure.

4. Nucleic acids

Nucleic acids are biological macromolecules that carry the genetic information in all living things and viruses. They direct protein synthesis.

There are two types of nucleic acids: DNA and RNA .

  • DNA and RNA are made up of smaller units (monomers) called nucleotides . A nucleotide is made up of three parts: a sugar, a nitrogenous base, and a phosphate group.

  • DNA and RNA are neatly packed inside the nucleus of a cell.

Primary chemical bonds in nucleic acids are covalent bonds called phosphodiester bonds , that form between nucleotides. You will come across hydrogen bonds as well, which form between DNA strands.

Biological Molecules - Key takeaways

  • Biological molecules are fundamental building blocks of cells in living organisms.

  • There are three important chemical bonds in biological molecules: covalent bonds, hydrogen bonds, and ionic bonds.

  • Biological molecules can be polar or non-polar.

  • The four major biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.

  • Carbohydrates are composed of monosaccharides, lipids are built of fatty acids and glycerol, proteins are composed of amino acids, and nucleic acids of nucleotides.

  • Chemical bonds in carbohydrates are glycosidic and hydrogen bonds; in lipids, those are ester bonds; in proteins, we find peptide, hydrogen, and ionic bonds as well as disulfide bridges; while in nucleic acids there are phosphodiester and hydrogen bonds.

Frequently Asked Questions about Biological Molecules

Biological molecules are organic molecules, meaning they contain carbon and hydrogen. Most biological molecules are organic, except water, which is inorganic.

The four major biological molecules are carbohydrates, proteins, lipids, and nucleic acids.

Enzymes are proteins. They are biological molecules that carry out metabolic functions.

An example of a biological molecule would be carbohydrates and proteins.

Proteins are the most complex biological molecules due to their complex and dynamic structures. They consist of combinations of five different atoms, namely carbon, hydrogen, oxygen, nitrogen, and sulphur, and can come in four different structures: primary, secondary, tertiary, and quaternary.

Final Biological Molecules Quiz

Question

Both DNA and RNA are _____ acids.

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Answer

Nucleic.

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Question

Compare the functions of DNA and RNA.


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Answer

DNA stores genetic information while RNA transfers this genetic information for protein synthesis.

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Question

Where is DNA found in the cells of eukaryotes and prokaryotes?


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Answer

In eukaryotes, DNA is in the nucleus, mitochondria and chloroplast (in plants). 


In prokaryotes, DNA is in the nucleoid and plasmids.

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Question

Where is RNA found in the cells of eukaryotes and prokaryotes?


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Answer

In eukaryotes, RNA is in the nucleolus and ribosomes. 


In prokaryotes, RNA is in the nucleoid, plasmids and ribosomes.

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Question

Identify the three different types of RNA.


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Answer

Messenger RNA (mRNA), transfer RNA (tRNA) and ribosomes RNA (rRNA).

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Question

What nitrogenous bases can DNA nucleotides have?


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Answer

Adenine, thymine, cytosine or guanine.

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Question

What nitrogenous bases can RNA nucleotides have?


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Answer

Adenine, uracil, cytosine and guanine.

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Question

Identify the pyrimidine and purine bases. 


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Answer

The pyrimidine bases are cytosine, uracil and thymine. 


The purine bases are adenine and guanine.

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Question

DNA contains the _____ pentose sugar while RNA contains the _____ pentose sugar. 


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Answer

Deoxyribose. 

Ribose.

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Question

________ reactions form polynucleotides while _____ reactions break polynucleotides. 

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Answer

Condensation. 

Hydrolysis.

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Question

What are phosphodiester bonds and how are they formed?


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Answer

Phosphodiester bonds link nucleotides together. They are formed between the phosphate group of one nucleotide and the hydroxyl group at the 3 'pentose sugar of another nucleotide.

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Question

Compare the structure of a DNA and RNA molecule. 


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Answer

DNA is an anti-parallel double helix made of 2 polynucleotide strands while RNA is a single-stranded molecule made of 1 polynucleotide strand.

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Question

What is complementary base pairing? 


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Answer

Complementary base pairing is the joining of a pyrimidine base to a purine base via hydrogen bonds.

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Question

In complementary base pairing, how many hydrogen bonds are formed between the base pairs?


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Answer

Adenine forms 2 hydrogen bonds with thymine in DNA, or uracil in RNA. 


Cytosine forms three hydrogen bonds with guanine.

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Question

DNA and RNA are polynucleotides. The monomers that make up these polynucleotides are called _____.

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Answer

Nucleotides.

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Question

What is the definition of biological molecules?


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Answer

Biological molecules are fundamental building blocks of all living things.


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Question

What kind of molecules are biological molecules?

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Answer

Biological molecules are organic molecules, meaning they contain carbon and hydrogen. 


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Question

All biological molecules are organic. 

True or False.

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Answer

False. Water is an example of an inorganic biological molecule. 

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Question

What are the three chemical bonds in biological molecules?


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Answer

Covalent, hydrogen, and ionic bonds.


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Question

Which bond is the most commonly found in biological molecules?
Choose a correct answer.     

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Answer

Covalent

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Question

What kind of covalent bonds form when there is an uneven distribution of electrons?


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Answer

A polar covalent bond.


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Question

How many covalent bonds can a carbon atom form?


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Answer

​4

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Question

What are the four major biological macromolecules?


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Answer

The four major biological macromolecules are: 

  • carbohydrates
  • lipids
  • proteins 
  • nucleic acids: DNA and RNA.

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Question

What are the different types of carbohydrates?


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Answer

Monosaccharides, disaccharides, and polysaccharides.


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Question

What is the covalent bond between monosaccharides called?

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Answer

A glycosidic bond.

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Question

What are the building blocks of lipids?

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Answer

Fatty acids and glycerol

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Question

What are the two major types of lipids?

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Answer

Triglycerides and phospholipids.

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Question

What is the covalent bond in lipids called?

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Answer

An ester bond.

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Question

What are the four different protein structures?

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Answer

Primary, secondary, tertiary, and quaternary. 

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Question

The covalent bond between amino acids is called a phosphodiester bond. True or False

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Answer

False. It is called a peptide bond. 

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Question

What are monomers of nucleic acids called?

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Answer

Nucleotides. 

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Question

What are the two types of nucleic acids?

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Answer

DNA and RNA

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What is the covalent bond between nucleotides called?

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Answer

A phosphodiester bond. 

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Question

What is the definition of a monomer?

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Monomers are small molecules, single repeating units, in polymers. 

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What is the definition of a polymer?

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Polymers are very large molecules made of monomers that are joined together with chemical bonds.

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What is the relationship between monomers and polymers?

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Answer

Monomers are the building blocks of polymers. They are joined together with chemical bonds to form polymers. Polymers consist of monomers.

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What are the three categories of monomers? They are m_______, a_____ a_____, and n_______.

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Answer

monosaccharides, amino acids, and nucleotides.

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What are monosaccharides monomers of?

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Answer

Polysaccharides (carbohydrates). 

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What are amino acids monomers of?

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Answer

Polypeptides (proteins). 

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Question

What are nucleotides monomers of?

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Answer

Polynucleotides (nucleic acids).

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Question

What are the three categories of polymer?

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Answer

Polysaccharides, polypeptides, and polynucleotides.

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Question

What are the biologically most important polynucleotides?

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Answer

DNA and RNA

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Question

What is the process of monomers joining together to form polymers called?

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Answer

Polymerisation. 

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Question

What are the two different reactions in charge of making and breaking polymers?

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Answer

Condensation and hydrolysis reactions

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Question

What happens during condensation? Fill in the gaps: 

During condensation, c_______ form between m________, which then join together to form p__________. Water is r________.

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Answer

During condensation, covalent bonds form between monomers, which then join together to form polymers. Water is removed.


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Question

What are the different covalent bonds between monomers called?

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Answer

Glycosidic, peptide, and phosphodiester bonds.

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Question

What is the covalent bond in lipids called?

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Answer

Ester bond. 

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Question

Which monomers bond together with a peptide bond?

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Answer

Amino acids

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Question

What happens during hydrolysis? Fill in the gaps:

During hydrolysis, c_________ bonds between monomers b______, and a polymer is b_____ d_____ into m________. Water is a_______.

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Answer

During hydrolysis, covalent bonds between monomers break, and a polymer is broken down into monomers. Water is added.


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Question

It is said that hydrolysis is the opposite of condensation. Why is that?

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Answer

Hydrolysis is the opposite reaction to condensation because, during hydrolysis, polymers are broken down into monomers, while during condensation monomers are joined together to form polymers. Covalent bonds are broken during hydrolysis and created during condensation. 


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