Carbohydrates Flashcards
What is the general formula for carbohydrates?
CnH2nOn
So they contain carbon, hydrogen and oxygen
Describe carbohydrates
Group of organic compounds associated with energy, but also with structural applications in cell membranes and cell walls
Describe carbon
- present in all biological molecules except for water
- an form 4 bonds in a tetrahedral arrangement
- used as scaffolding for the molecules
Carbohydrate functions
- provide energy-rich nutrients to organisms
* used to built their body structures
Examples of carbohydrates
- sugars
- starch
- glycogen
- cellulose
Describe monosaccharides
- simplest -> ‘simple sugars’ 3-7 carbons
- white crystalline solids
- soluble in water -> dissolve to form sweet tasting solutions
Name the hexoses
- α-glucose
- β-glucose
- fructose
- galactose
Define isomers and give an example of a pair
Same molecular formula, but a different structural formula
E.g.: α-glucose and β-glucose
Name the pentoses:
- ribose
* deoxyribose
Name a triose
• glyceraldehyde
Describe reducing sugars
- all monosaccharides are reducing sugars (+ some disaccharides)
- have an aldéhyde functional group
- can donate electrons to reduce other chemicals
Test for reducing sugars
- add 2cm3 of a food sample in liquid form (pestle and mortar)
- add 2cm3 of Benedict’s reagent
- heat in water-bath for 5 mins
Describe the results of the reducing sugars test
- blue -> none
- green/yellow -> traces of reducing sugars
- orange/red -> moderate amount of reducing sugars
- brick red -> large amount of reducing sugars
Describe the differences between α-glucose and β-glucose
- positioning of hydrogen and hydroxyl groups on carbon atom 1
- α-glucose: OH group is below carbon atom 1
- β-glucose: OH group is above carbon atom 1
Describe the similarities between α-glucose and β-glucose
- ring structures
* CH2OH group is above the ring
What are the consequences of the differing structures of α-glucose and β-glucose
- α-glucose: combines to form starch
* β-glucose: combines to form cellulose
Describe how to make calibration curves:
1) create a dilution series of glucose using distilled water. Use six boiling tubes to make concentrations ranging from 0-10mol/dm3
2) place 2cm3 of each of the unknown samples in separate boiling tubes
3) add 2cm3 of Benedict’s solution to all boiling tubes
4) place boiling tubes in water bath at 90°C for 4 minutes
5) use tongs to take the boiling tubes out of the water bath. Leave to cool
6) zero the colorimeter using a cuvette with distilled water (reference cuvette). The colorimeter should be set to the red filter
7) place known samples into cuvettes and measure the absorbance of each, using the colourimeter
8) make a calibration curve, plotting the absorbance against the known glucose concentrations
What is the function of glucose?
- major source of energy for most animals
- 1g yields approximately 16kJ energy when fully broken down in respiration (a lot!)
- main form in which carbohydrates are transported around the body in animals
What are the common disaccharides
- sucrose
- lactose
- maltose