Biological molecules

Define monomers.

the smaller units from which larger molecules are made

Define polymers.

molecules made from a large number of monomers joined together

Give 3 examples of monomers

Monosaccharides, amino acids and nucleotides

Define condensation reaction

A reaction that releases a molecule of water when it links molecules together

Define hydrolysis reaction

A chemical reaction in which water is used to break a chemical bond

What are carbohydrates?

Organic compounds made up of carbon, hydrogen, and oxygen

What are monosaccharides?

the monomers from which larger carbohydrates are made

Give examples of monosaccharides

glucose, fructose, galactose

What does a condensation reaction between two monosaccharides form?

A glycosidic bond

What are disaccharides formed by?

condensation of two monosaccharides

Give examples of disaccharides

sucrose, maltose, lactose

What is sucrose made of?

glucose and fructose

What is maltose made of?

glucose and glucose

What is lactose made of?

glucose and galactose

What are the two isomers of glucose?

alpha glucose and beta glucose

What are isomers?

compounds with the same formula but different arrangement of atoms

What is the difference between alpha and beta glucose?

Their hydroxyl groups are reversed

What are polysaccharides formed by?

Condensation of many glucose units

What are glycogen and starch formed by?

condensation of alpha glucose

What is cellulose formed by?

condensation of beta glucose

What is glycogen?

the main energy storage molecule in animals

How is glycogen structured?

many alpha-glucose monomers joined by 1-4 and 1-6 glycosidic bonds to form highly branched chains

Give some properties of glycogen

- Compact

- Insoluble

- Highly branched - Releases energy quickly

What is starch used for?

energy storage in plants

What polysaccharides make up starch?

amylose and amylopectin

What is amylose?

unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds

What is amylopectin?

A long, branched chain of alpha glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds

What are some properties of starch?

- Insoluble in water (no osmotic effect)

- Large molecule - Can't diffuse out of the cell

- Branched - Compact

What is cellulose?

polysaccharide of beta glucose

What is the function of cellulose?

structural component of plant cell walls

What is the structure of cellulose?

long, unbranched chains of β glucose linked by hydrogen bonds to form microfibrils. Every other beta glucose molecule is inverted to form 1,4 glycosidic bonds.

What are microfibrils?

strong fibres made of many cellulose chains held together by hydrogen bonds

How does cellulose prevent the cell from bursting?

exerts inward pressure that stops the influx of water, keeping cells turgid and rigid

How do you test for starch?

Add a drop of dilute iodine solution to the subject. If starch is present it will turn a 'blue-black' colour.

What is a reducing sugar?

A sugar that can donate electrons to another chemical

Give examples of reducing sugars

All monosaccharides and some disaccharides — maltose and lactose

Describe the test for reducing sugars

Add benedicts and heat in water bath for 5 minutes.

if sample contains reducing sugars = turn brick red

Give examples of non reducing sugars

Some disaccharides e.g. sucrose and all polysaccharides

Describe the test for non reducing sugars

1. Do Benedict's test with negative result

2. Heat in water bath with dilute HCl (to hydrolyse into reducing sugars)

3. Neutralise with sodium hydrogencarbonate

4. Re-test using Benedict's reagent

5. Positive result = colour change

What are the two types of lipids?

triglycerides and phospholipids

What are triglycerides composed of?

1 glycerol and 3 fatty acids

How are triglycerides formed?

condensation of glycerol and 3 fatty acids forming ester bonds and 3 water molecules

What are the 2 types of fatty acids?

Unsaturated and saturated

Describe the difference between unsaturated and saturated fatty acids

Unsaturated fatty acids have at least one double bond between carbon atoms while saturated fatty acids don't have any

What are the properties of triglycerides?

-the long hydrocarbon chains contain lots of energy

-insoluble in water so no osmotic effect (fatty acid tails are hydrophobic)

-low mass to energy ratio making them good storage molecules

What are phospholipids composed of?

glycerol, 2 fatty acids, and a phosphate group

What are phospholipids made of?

hydrophilic head and hydrophobic tail

What does the hydrophilic head contain?

glycerol and phosphate

What does the hydrophobic tail contain?

fatty acids

What do phospholipids make up?

Hydrophobic bilayer of cell membranes

What can carbohydrates combine with phospholipids in the cell surface membrane to create?

Glycolipids - Important in cell recognition

Are phospholipids polar and how does this relate to it's function?

Yes - so can form a bilayer

Are triglycerides polar and how does this relate to it's function?

No - makes them hydrophobic - useful for storage

List 4 roles of lipids

- Source of energy

- Waterproofing (insoluble)

- Provides insulation

- Protects organs

Describe how to test for lipids in a sample

1. Dissolve solid samples in ethanol.

2. Add an equal volume of water and shake.

3. Positive result: milky white emulsion forms

The scientist used quantitative Benedict's tests to produce a calibration curve of colorimeter reading against concentration of maltose.

Describe how the scientist would have produced the calibration curve and used it to obtain the results in the graph.

- Make maltose solutions of different concentrations (and carry out Benedict's test on each);

- Use colorimeter to measure colorimeter value of each solution and plot calibration curve

- Find concentration of sample from calibration curve

What test did the scientist use to produce a calibration curve for maltose concentration?

Quantitative Benedict's tests

What is the first step the scientist took to produce the calibration curve?

Make maltose solutions of different concentrations and carry out Benedict's test on each.

How did the scientist measure the colorimeter value of each solution?

Using a colorimeter.

What did the scientist do after measuring the colorimeter values?

Plot the calibration curve.

How does the scientist find the concentration of a sample?

By using the calibration curve.