Sugars Flashcards
What is sugar a general term for?
- Monosaccharides
* Disaccharides
What are monosaccharides?
The simplest sugars, and the building blocks of carbohydrates.
What elements do all carbohydrates contain?
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
Are monosaccharides monomers or polymers?
Monomers.
What type of monomers are carbohydrates made from?
Monosaccharides.
What are some examples of monosaccharides which can form carbohydrates?
- Glucose
- Fructose
- Galactose
What type of sugar is glucose?
A hexose sugar.
What is a hexose sugar?
A monosaccharide with six carbon atoms in each molecule
What are the two types of glucose?
- Alpha (α-glucose)
* Beta (β-glucose)
What are α-glucose and β-glucose both?
Isomers.
What are isomers?
Molecules with the same molecular formula as each other, but with the atoms connected in a different way.
What does α-glucose look like?
Image
What does β-glucose look like?
Image
How is a disaccharide formed?
When two monosaccharides chemically bond together.
How are monosaccharides bonded together?
Through condensation reactions.
What type of bond forms when two monosaccharides are bonded together?
A glycosidic bond.
How is a glycosidic bond created through a condensation reaction between two monosaccharides?
Two hydroxy groups react with each other, causing a molecule of water to be released, leaving a glycosidic bond.
What is a glycosidic bond?
A covalent bond using oxygen.
What does a glycosidic bond look like?
Image
What does the bonding of two monosaccharides look like (two α-glucose’s)?
Image
What are some examples of disaccharides?
- Maltose
- Sucrose
- Lactose
How is maltose formed?
When two α-glucose molecules bond together.
How is sucrose formed?
When a glucose molecule and a fructose molecule bond together.
How is lactose formed?
When a glucose molecule and a galactose molecule bond together.
What can all sugar be classified as?
- Reducing sugars
* Non-reducing sugars
What is the test for the presence of sugars?
The Benedict’s test.
What do reducing sugars include?
- All monosaccharides
* Some disaccharides (e.g. maltose and lactose)
What is the method of the Benedict’s test for reducing sugars?
- Add the Benedict’s reagent (blue) to a sample.
- Then heat the sample in the water bath (boiled).
- Then check for a positive or a negative result.
What will a positive result from the Benedict’s test for reducing sugars look like?
The sample will form a coloured precipitate, with solid particles suspended in the solution.
What are the colours of the precipitates if the Benedict’s test for reducing sugars is positive?
- Green
- Yellow
- Orange
- Brick red
Image
What will a negative result from the Benedict’s test for reducing sugars look like?
The sample will stay blue.
What does the higher the concentration of reducing sugars present in the Benedict’s test mean?
The further the colour change goes.
What can you use the colour change from the Benedict’s test for reducing sugars to do?
Compare the amount of reducing sugars in different solutions.
What are more accurate ways of comparing the amount of reducing sugars from the Benedict’s test?
- Filter the solution and weigh the precipitate.
* Remove the precipitate and use a colorimeter to measure the absorbance of the remaining Benedict’s reagent.
What could there be if the result of the Benedict’s test for reducing sugars is negative?
Non-reducing sugars present.
What is the test for non-reducing sugars?
By breaking them down into monosaccharides.
What is the method for breaking down non-reducing sugars into monosaccharides?
- Get a new sample of the test solution.
- Then add dilute hydrochloric acid and heat the sample in a water bath (boiled).
- Then neutralise the sample by adding sodium hydrogencarbonate.
What is the test for non-reducing sugars, once they are broken down into monosaccharides?
The Benedict’s test (the same method as the test for reducing sugars).
What will the results of the Benedict’s test for non-reducing sugars look like?
- If the sample stays blue, no non-reducing sugar is present.
- If a coloured precipitate is formed, non-reducing sugars are present.
