AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Monosaccharides, amino acids and nucleotides are examples of monomers.
Full specification wording
Monomers and polymers: Monosaccharides, amino acids and nucleotides are examples of monomers.
Three monomers cover nearly every polymer in the specification.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 4 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Three monomers cover nearly every polymer in the specification. Monosaccharides such as glucose join by glycosidic bonds to make disaccharides and polysaccharides. Amino acids join by peptide bonds to make dipeptides and polypeptides. Nucleotides join by phosphodiester bonds to make the polynucleotides DNA and RNA. Be precise about a nucleotide: it is three components joined together - a pentose sugar, which is deoxyribose in DNA and ribose in RNA, a phosphate group, and a nitrogen-containing organic base - not simply the base. Each monomer has a general structure you may have to recognise or draw: a hexose monosaccharide has the formula C₆H₁₂O₆; an amino acid carries an amine group, a carboxyl group, a hydrogen atom and an R group on the same central carbon. All three are joined by condensation, releasing one water molecule per bond, and all three are released again by hydrolysis.
What earns the marks
- Award credit for naming monosaccharides, amino acids and nucleotides as monomers.
- Award credit for stating that DNA is a polymer of nucleotides, accepting polynucleotide.
- Award credit for describing a nucleotide as deoxyribose, a phosphate group and an organic or nitrogen-containing base.
- Award credit for naming the bond each monomer forms: glycosidic, peptide or phosphodiester.
- Award credit for naming the polymer each monomer builds.
Common mistakes and how to put them right
Describing a nucleotide as a base only, leaving out the pentose sugar and phosphate group.
Put it right: A nucleotide has three parts - pentose sugar, phosphate group and organic base.
Writing that DNA is a polymer of bases rather than of nucleotides.
Put it right: DNA is a polynucleotide, a polymer of nucleotides.
Giving ribose as the sugar in a DNA nucleotide.
Put it right: DNA contains deoxyribose, RNA contains ribose.
Naming glycerol and fatty acids as the monomers of lipids.
Put it right: Glycerol and fatty acids are components of triglycerides, which are not polymers.
Writing 'sugar' without specifying deoxyribose or ribose when the question names DNA or RNA.
Put it right: State the specific pentose sugar.
Exam tips
- Learn the three parts of a nucleotide as a set phrase - pentose sugar, phosphate group, organic base - because the mark is usually for all three.
- Match monomer to polymer to bond in a three-column table when revising; questions test the links, not the lists.
- If a question asks for examples of monomers, give the three named in the specification rather than a specific molecule such as glucose alone.
Try the lesson
The start of the Monomers and polymers: Monosaccharides, amino acids and nucleotides are examples of monomers. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is an example of a monomer?
Listen
Three monomers cover nearly every polymer in the specification. Monosaccharides such as glucose join by glycosidic bonds to make disaccharides and polysaccharides. Amino acids join by peptide bonds to make dipeptides and polypeptides. Nucleotides join by phosphodiester bonds to make the polynucleotides DNA and RNA. Be precise about a nucleotide: it is three components joined together - a pentose sugar, which is deoxyribose in DNA and ribose in RNA, a phosphate group, and a nitrogen-containing organic base - not simply the base. Each monomer has a general structure you may have to recognise or draw: a hexose monosaccharide has the formula C₆H₁₂O₆; an amino acid carries an amine group, a carboxyl group, a hydrogen atom and an R group on the same central carbon. All three are joined by condensation, releasing one water molecule per bond, and all three are released again by hydrolysis. A strong answer earns marks for these points. Award credit for naming monosaccharides, amino acids and nucleotides as monomers. Award credit for stating that DNA is a polymer of nucleotides, accepting polynucleotide. Award credit for describing a nucleotide as deoxyribose, a phosphate group and an organic or nitrogen-containing base. Award credit for naming the bond each monomer forms: glycosidic, peptide or phosphodiester. A common slip: describing a nucleotide as a base only, leaving out the pentose sugar and phosphate group. Instead, a nucleotide has three parts - pentose sugar, phosphate group and organic base. Exam tip: Learn the three parts of a nucleotide as a set phrase - pentose sugar, phosphate group, organic base - because the mark is usually for all three.
Key words
Say what each word means before you turn the card.
monosaccharides
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amino acids
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nucleotides
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nucleotide components
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See every definition
- monosaccharides
- Examples of monomers, such as glucose, which join by glycosidic bonds to make disaccharides and polysaccharides.
- amino acids
- Examples of monomers which join by peptide bonds to make dipeptides and polypeptides.
- nucleotides
- Examples of monomers which join by phosphodiester bonds to make the polynucleotides DNA and RNA.
- nucleotide components
- Three components joined together: a pentose sugar, which is deoxyribose in DNA and ribose in RNA, a phosphate group, and a nitrogen-containing organic base.
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