1.1 - Monomers and polymers + 1.2 - Carbohydrates

What is a monomer?

smaller units that join together to form larger molecules

3 examples of monomers.

monosaccharides, amino acids, nucleotides

What is a polymer?

molecules formed when many monomers join together

3 examples of polymers.

polysaccharides, proteins, DNA

Describe a condensation reaction.

a chemical bond forms between 2 molecules & a molecule of water is produced.

What happens in a hydrolysis reaction?

a water molecule is used to break a chemical bond between 2 molecules.

Name 3 hexose monosaccharides

glucose, fructose, galactose

What type of bond forms when monosaccharides react?

(1-4 or 1-6) glycosidic bond

Name 3 disaccharides, and the monosaccharides which make them up

maltose: glucose + glucose
sucrose: glucose + fructose
lactose: glucose + galactose

Draw the structure of a - glucose

Draw the structure of b - glucose

Describe the function and properties of starch

storage of a - glucose in plant cells
- insoluble so does not affect the water potential of the cell
- large does not diffuse out of cells

Describe the structure of amylose

1-4 glycosidic bonds
helix with intermolecular H-bonds = compact

Describe the structure of amylopectin

1-4 & 1-6 glycosidic bonds
branched - many terminal ends for hydrolysis into glucose

Describe the function of glycogen

main storage polymer of a - glucose in animal cells (but also in plant cells)

describe the structure of glycogen

- 1-4 & 1-6 glycosidic bonds
- branched = many terminal ends for hydrolysis
- insoluble = doesn't affect the water potential & does not diffuse out of the cell
- compact

Function of cellulose

gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)

Structure of cellulose

- 1,4 glycosidic bonds
- straight chain, unbranched molecule
- alternate glucose molecules are rotated 180 degrees
- H-bond crosslinks between parallel strands form microfibrils = high tensile strength

Describe the Benedict's test for reducing sugars

1. add an equal volume of Benedict's reagent to a sample
2. heat the mixture in a water bath containing boiling water for 5 minutes
3. Positive result: colour change from blue to orange/red precipitate forms

Describe the Benedict's test for non-reducing sugars

1. Negative result: Benedict's reagent remains blue
2. Hydrolyse non-reducing sugars e.g. sucrose into their monomers by adding 1cm cubed of HCL. heat in a boiling water bath for 5 minutes.
3. Neutralise the mixture using sodium carbonate solution.
4. Then carry out the Benedict's test as usual.

Describe the test for Starch

1. Add iodine solution
2. Positive result: colour change from orange to blue-black

Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

1. make standard solutions with known concentrations. Record absorbance or % transmission values.
2. Plot calibration curve: absorbance or % transmission (y-axis) against concentration (x-axis)
3. Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration.

What elements make up Carbohydrates?

Carbon, oxygen, hydrogen