1.2 carbohydrates

what is the monomer from which larger carbohydrates are made and what are three examples?

A monosaccharide: glucose, galactose and fructose

what forms when there is a condensation reaction between two monosaccharides?

A glycosidic bond

how are disaccharides formed

Through a condensation reaction between 2 monosaccharides, with one mol of water being removed

monomers of maltose

alpha glucose + alpha glucose

monomers of sucrose

glucose and fructose

monomers of lactose

glucose and galactose

two isomers of glucose and what differentiates them

alpha glucose and beta glucose - alpha glucose has a hydroxyl above the ring where as beta glucose has the hydroxyl group below the ring

how are poly saccharides formed

Through the condensation of many glucose units

what is formed by the condensation of alpha glucose

glycogen or starch

what is formed when beta glucose condenses

Cellulose

structure and function of starch

Structure:

- insoluble: therefore doesn't affect the cells water potential

- Large (and insoluble): doesn't diffuse out of cells

- Coiled: compact/ a lot can be stored in a small space

- Hydrolysed to form alpha glucose which can be easily transported and readily used in respiration

- Branched (sometimes) which has many ends which can be hydrolysed simultaneously

Function:

- Energy storage molecule in plants

structure and function of glycogen

Structure:

- short(er) highly branched chains

- insoluble (doesn't affect water potential or diffuse out)

-coiled: compact / easily stored in a small place

- highly branched: rapidly broken down into glucose monomers

Function:

- a storage of energy for animals and bacteria (more metabolically active then plants)

structure and function of cellulose

structure:

- made from monomers of b-glucose linked via condensation reactions

- straight unbranched chains which run parallel to one another using hydrogen bonds to form cross linkages

- cellulose molecules are grouped together to form microfibrils which are arranged in parallel groups called fibres

Function:

- provides rigidity to cell walls of plants

- prevents cell from bursting as water enters by osmosis

test for reducing sugars, process and results

Benedict's test:

- add 2cm^3 of the sample and an equal volume of benedict's reagent to a test tube

- Heat the mixture in a gently boiling water bath for 5 minutes

Positive test = brick red

low concentrations = green to orange

negative test = blue

Test for non-reducing sugars

test as you would for reducing sugars (heat with benedict's solution) if no result:

- add dilute HCL to break down into monosaccharides

- add sodium hydrogen carbonate to neutralise the solution

- heat and observe colour change (blue to brick red)

test for starch

add aqueous iodine solution to a sample (orange) is starch is present, the solution will go blue / black

How to quantitively measure the data from qualitative tests

Use a colorimeter: the more concentrated a solution, the less light will be able to travel through.

you can make a calibration curve with five solutions of known concentration to compare the results with