2.2.22 · Biological Molecules
Covalent Bonds in Polymers — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
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Lesson summary
2.2.2 Covalent Bonds in Polymers — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe covalent bonding, condensation and hydrolysis, and the bonds in the four types of organic molecule.Definition — a covalent bond is the sharing of electrons between two atoms.Po…
- Multiple bonds
- Macromolecule
- Glycosidic bond
- Peptide bond
- Ester bond
- Triglyceride
Section 1 of 7Covalent bonds
Definition
- Definition a covalent bond is the sharing of electrons between two atoms.
Polarity
- Polarity equal sharing gives a non-polar bond, and unequal sharing gives a polar bond.
- (a more electronegative atom)
Valency
- Valency each atom forms a set number of bonds, e.g. H forms 1 and C forms 4.
Stability
- Stability covalent bonds need a lot of energy to break.
Multiple bonds
- Multiple bonds pairs of electrons can be shared to give double bonds, e.g. C=C in unsaturated fats.
Section 2 of 7Condensation reactions
Definition
- Definition monomers combine by covalent bonds and water is removed.
Outcome
- Outcome polymers form by polymerisation, and lipids form as macromolecules.
Mechanism
- Mechanism when monomers are close, their outer orbitals overlap and electrons are shared.
Section 3 of 7Hydrolysis reactions
Meaning
- Meaning hydro means with water and lyse means to break.
Outcome
- Outcome water is added and the covalent bond between monomers is broken.
Enzymes
- Enzymes different enzymes catalyse hydrolysis and condensation.
Section 4 of 7Bonds in each biological molecule
| Organic molecule | Covalent bond |
|---|---|
| Carbohydrates | Glycosidic |
| Proteins | Peptide |
| Lipids | Ester |
| Nucleic acids | Phosphodiester |
Section 5 of 7More from the specification
1Reducing sugars and non-reducing sugars
- Reducing sugars and non-reducing sugars heating test samples with Benedict's reagent identifies reducing sugars,
- whereas non-reducing sugars require acid hydrolysis first.
2Sucrose
- The sugar mainly transported in phloem.
3Non-reducing sugar
- A sugar that cannot reduce Benedict's reagent until hydrolysed.
4Condensation reaction
- A reaction joining molecules with the release of water.
5Glucose
- A simple sugar; the unit that starch, glycogen and cellulose are built from.
6Cellulose
- A structural polysaccharide of β-glucose.
7Starch
- An insoluble polysaccharide of glucose used by plants for energy storage.
8Triglyceride
- A lipid made of glycerol and three fatty acids.
9Phospholipid
- Glycerol, two fatty acids and a phosphate group, which is amphipathic.
10Monosaccharide
- A single sugar unit such as glucose, fructose or galactose.
11Hydrophobic
- Water-hating; non-polar and unable to dissolve in water.
12Carbon
- Element with four valence electrons that forms the backbone of organic molecules.
13Monomer
- Monomer a small molecule that can join to many others by covalent bonds to form a polymer.
14Macromolecule
- Macromolecule a very large molecule, such as a polysaccharide, protein or nucleic acid, built from many atoms.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Covalent bond | A bond formed by sharing electrons between atoms. |
| Condensation | A reaction joining two molecules with the loss of water. |
| Hydrolysis | A reaction splitting a bond by the addition of water. |
| Glycosidic bond | The bond between sugar units. |
| Peptide bond | The bond between amino acids. |
| Ester bond | The bond between glycerol and fatty acids. |
| Phosphodiester bond | The bond between nucleotides. |
Section 7 of 7Exam technique
1
Saying hydrolysis removes water — it adds water.
2
Saying condensation adds water — it releases water.
3
Naming the wrong bond for a molecule — carbohydrates glycosidic, proteins peptide, lipids ester, nucleic acids phosphodiester.
4
Saying covalent bonds are weak — they are strong and need high energy to break.
Marked practiceQuizzes for this lesson
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