P1: bio-molecules: poly, mono and carbs

Paper 1 Topic 2 biological molecules. If it’s helpful feel free to save or check the other sets :)

Define monomer

Smaller units that join together to form larger molecules

Eg. monosaccharides (fructose, glucose and galactose)

Amino acids

nucleotides

Define Polymer

molecules formed when many monosaccharides join together

eg. Polysaccharides

proteins

DNA/RNA

What happens in a condensation reaction?

A chemical bond forms between 2 molecules and 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 and galactose

All have molecular formula C6H12O6

Name the type of bond formed when monosaccharides react

(1,4 or 1,6) Glycosidic bond

2 monomers→ 1 chemical bond=disaccharide

Multiple monomers→ many chemical bonds=polysaccharide

Name 3 disaccharides. Describe how they form

Condensation reaction forms glycosidic bond between 2 monosaccharides

maltose: glucose+glucose

sucrose: glucose+fructose

lactose: glucose+galactose

All have molecular formula C12H22O11

Draw the structure of B-glucose

OH on carbon 1 is above the ring

Describe the structure and functions of starch

Storage polymer of a-glucose in plant cells

• insoluble=no osmotic effect on cells

• large=does not diffuse out of cells

Made from amylose:

• 1,4 glycosidic bonds

• Helix w intermolecular H-bonds=compact

Made from Amylopectin:

• 1,4 and 1,6 glycosidic bonds

• Branched=many terminal ends for hydrolysis into glucose

Describe the structure and functions of glycogen

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

• 1,4 and 1,6 glycosidic bonds

• Branched=many terminal ends for hydrolysis

• Insoluble=no osmotic effect & does not diffuse out of cells

• compact

Describe the structure and function of cellulose

Polymer of B-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)

• 1,4 glycosidic bonds

• Straight chain, unbranched molecule

• alternate glucose molecules are rotated 180 degrees

• H-bonds cross links between parallel strands on oxygen molecules 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 an electric water bath at 100 degrees C for 5 mins

3. Positive result: colour change from blue to orange & brick-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 eg. Sucrose into their monomers by adding 1cm³ of dilute acid e.g HCL. Heat in a boiling water bath for 5 mins

3. Neutralise the mixture using an alkali

4. Proceed with the Benedict’s test as usual

Describe the test for starch

1. Add the iodine solution

2. Positive result: colour change from orange to blue-black

Outline how colorimetry could be used to give quantitative 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) concentration (x-axis)

3. Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration

Exam Q: Cellulose is a polysaccharide of B-glucose molecules. Describe how two B-glucose molecules are able to join together

• OH group on carbon 1 is above the ring but OH group on carbon 4 of adjacent B-glucose molecule is below the ring (1)

• only hydrogen available to form water with OH so no oxygen available to form glycosidic bond (1)

• Every other B-glucose ‘flips’ through 180 degrees to place two OH groups adjacent to each other (1)

• 1,4 glycosidic bonds are formed to created unbranched chains

draw the shorthand structural formula of alpha-glucose

note that the5 corners of the corners of the hexagon are C atoms while one is O. each of the C atoms is designated by a number, increasing by 1 starting at the O atom.

differences between beta and alpha glucose?

carbon 1 hydroxyl (OH) group lies below the ring

What is the general formula of monosaccharides?

(CH2O)n

name the 3 key polysaccharides:

glycogen, starch and cellulose.