TOPIC 1: biological molecules

What’s some evidence for evolution

What’s some evidence for evolution

All living things share the same biological molecules. All have a similar biochemical basis.

What’s a monomer?

Smaller unites which can create larger molecules (polymers) e.g. glucose, amino acid, nucleotide, monosaccharides

What’s a polymer?

Molecules made from larger numbers of monomers joined together e.g. starch, cellulose, glycogen, polypeptide (protein), DNA+RNA

Condensation def

Joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

Hydrolysis def

breaks a chemical bond between two molecules and involves the use of a water molecule

what are carbohydrates made of

carbon, hydrogen, oxygen

monomers of carbohydrates

carbohydrates are made up of monomers. The basic monomer unit is a sugar- saccharide. Thus, called a monosaccharide.

Pair= disaccharide

(much) larger numbers= polysaccharide

Monosaccharide general formula + examples

(CH₂O)_n (n= any number 1-7)

glucose, galactose, fructose

Alpha and beta glucose

glucose is a hexose (6 carbon sugar). It has 2 isomers: alpha and beta glucose.

Alpha Below Beta Above (whether OH is above or below)

How are disaccharides formed?

Two monosaccharides join through a condensation reaction. The bond formed is called a glycosidic bond. The breaking of a disaccharide is called a hydrolysis reaction.

what monosaccharides are maltose, sucrose and lactose made from

• maltose= glucose + glucose

• sucrose=glucose + fructose

• lactose= glucose + galactose

formula= C₁₂H₂₂O₁₁

disaccharide diagram

Polysaccharides

Formed by many monosaccharides by condensation reactions. Very large molecules → insoluble → suitable for storage.

Reducing sugars

All monosaccharides and some disaccharides (maltose) are reducing sugars.

Reducing sugar= a sugar that can donate electrons to (reduce) another chemical. E.g. benedicts reagent

What’s benedict’s reagent

alkaline solution of copper (II) sulfate. When a reducing sugar is heated the solution forms an insoluble red precipitate of copper(II) oxide.

Benedicts test

• Add 2cm³ of the sample to a test tube. Grind up in water if it’s not in liq form.

• Add an equal volume of benedicts reagent.

• Heat mixture in a gently boiling water bath for 5 minuets

  • reducing sugars present= orange-brown colour

Test for non-reducing sugars

(e.g. sucrose).

• Do a benedicts test, if it doesn’t change colour→ reducing sugars not present

• add another 2cm³ of the sample to 2cm³ of dilute hydrochloric acid in a test tube and place it in a gently boiling water bath for 5 minuets. It will hydrolyse any disaccharide present into its constituent monosaccharides

• Slowly add some sodium hydrogen carbonate solution to test tube→ to neutralise the acid (benedicts reagent doesn’t work on acidic solutions). Test with pH paper to check it’s alkaline

• Re-test the resulting solution and if non-reducing sugar was present it should turn orange-brown. Due to reducing sugars produced from the hydrolysis of the non-reducing sugar

Test for starch

Starch changes the colour of the iodine in potassium iodine solution from yellow to blue-black. Test at room temp.

• 2cm³ of the sample into a test tube. (or two drops of the sample into a depression on a spotting tile)

• 2 drops of iodine solution and shake/stir

• starch present= blue-black colour

where is starch found

plant cells in the form of small grains (e.g. inside chloroplasts). Cells get energy from glucose→ plants access glucose as starch (when needing energy → breaks down starch)

starch structure

polysaccharide formed from two polymers of alpha-glucose- amylose and amylopectin.

starch role and properties

main role: energy storage=

• insoluble= doesn’t affect water potential→ water not drawn into cells by osmosis.

• large and insoluble= doesn’t diffuse out of cells

• compact= a lot can be stored in a small space

• when hydrolysed it forms alpha-glucose, which is easily transported→ to be used in respiration

  • branched form has many ends→ each can be acted on by enzymes→ glucose monomers are released rapidly.

Amylose

Long, unbranched chain of alpha-glucose. Forms a 1-4 glycosidic bond through condensation reactions. Coiled structure= good storage, can fit more into a small space. Hydrogen bonds help hold it in its helical structure

Amylopectin

long, branched chain of alpha-glucose. 1-6 glycosidic bonds create a branch. Its side branches allow enzymes that break down the molecule to get at glycosidic bonds easily= glucose released quickly

Where is glycogen found

animal and bacteria cells. In animals it’s stored as small granules mainly in the muscles and the liver. Mass of carbohydrate stored in animals is relatively small because fat is the main storage molecule.

glycogen structure

apha-glucose. similar to starch- has 1,4 and 1,6 glycosidic bonds. However, it has shorter chains and is more highly branched

glycogen role and propeties

main role= energy storage:

• Insoluble: doesn’t draw water into the cells by osmosis and doesn’t diffuse out of cells

• Compact: a lot can be stored in a small space

  • More highly branched: more ends that can be acted on by enzymes. More rapidly broken down to form glucose monomers, used in respiration. Important for animals to have a higher metabolic rate + respiratory rate than plants bc they are more active.

where is cellulose found

plant cell walls

cellulose structure

Made of monomers of beta-glucose. Straight, unbranched chains that run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent chains- adds little to the strength, but overall number makes contribution. Cellulose molecules grouped together to form microfibrils- arranged in parallel groups called fibres.

Cellulose main role and properties

Main role= providing support + rigidity:

• made of beta-glucose= form long, straight, unbranched chains

• they run parallel to each other + crossed linked by hydrogen bonds → add to collective strength

• molecules grouped to form microfibrils → grouped to form fibres which provides more strength