Carbohydrates Flashcards
Why are carbohydrates needed?
For energy
What are carbohydrates made of?
Hydrogen, oxygen and carbon
What type of compounds are carbohydrates?
Organic compounds
What is the single carbohydrate monomer?
Monosaccharide
What is a pair of monosaccharides called?
Disaccharide
What is the name for lots of monosaccharides bonded together?
Polysaccharide
What are three types of monosaccharides?
Glucose, fructose and galactose
What type of monosaccharide is glucose?
A hexose monosaccharide
Can monosaccharide dissolve in water?
Yes
What are the two isomers of glucose?
Alpha glucose and beta glucose
What are pentose monosaccharides?
5 carbon monosaccharides
What are two examples of pentose monosaccharides?
Ribose and deoxyribose
Where is deoxyribose found?
DNA
Where is ribose found?
RNA
What bond forms between two monosaccharides?
A glycosidic bond
What is the test for reducing sugars?
Benedict’s test
What is a reducing sugar?
A sugar that can donate electrons to and reduce another chemical
What is Benedict’s reagent?
An alkaline solution if copper(II) sulfate
What happens when Benedict’s reagent is heated with a reducing sugar?
It forms an insoluble red precipitate of copper (I) oxide
How is Benedict’s test carried out?
- Add 2cm^3 of the food sample to be tested to a test tube in liquid form
- Add an equal volume of Benedict’s reagent
- Heat the mixture in a gently boiling water bath for five minutes
What is Benedict’s test?
Semi-quantitative
What is the colour change for a high concentration of reducing sugar?
Brick red
What is the colour change for a medium concentration of reducing sugar?
Yellowish brown
What is the colour change for a low concentration of reducing sugar?
Yellowish green
What is the colour change for a very low concentration of reducing sugar?
Green
What is the colour change for no reducing sugars?
No change, will remain blue
What reaction occurs when a monosaccharide forms a disaccharide?
A condensation reaction
How do condensation reactions work?
Formation of water from the H2O that is lost
How does a disaccharide go back to a monosaccharide?
Hydrolysis
What happens during hydrolysis?
Water is added
What disaccharide is formed when alpha glucose joins to alpha glucose?
Maltose
What disaccharide is formed when glucose joins to fructose?
Sucrose
What disaccharide is formed when glucose joins to galactose?
Lactose
How is alpha glucose different to beta glucose?
In alpha glucose the H is above the OH on carbon 1, in beta glucose the OH is above the H on carbon 1
How do you test for a non-reducing sugar?
Hydrolyse the disaccharide or polysaccharide into a monosaccharide and then carry out Benedict’s test
How do you confirm that a reducing sugar isn’t present?
- Get the sample into its liquid form
- Add 2cm^3 of Benedict’s reagent to 2cm^3 of the food sample
- Place in a water bath, if no colour change, then a reducing sugar is not present
How do you test for a non-reducing sugar?
- Add 2cm^3 of food sample to an equal amount of dilute HCL in a test tube and gently boil for 5 minutes. The dilute HCL will hydrolyse disaccharides into their monosaccharides
- Slowly add sodium hydrocarbonate to neutralise the HCL (Benedict’s wont work in acidic conditions) test with pH paper to check for alkaline
- Retest with Benedict’s
What polysaccharide is a polymer of glucose?
Starch
Where is starch found?
Chloroplast stroma
What polysaccharide is a polymer of alpha-glucose?
Glycogen
Where is glycogen found?
Muscle cells
What polysaccharide is a polymer of beta-glucose?
Cellulose
Where is cellulose found?
Plant cell walls
What polysaccharide is a polymer of glucosamine?
Chitin
What is glucosamine?
Glucose with an amino acid attached
Where is chitin found?
The exoskeleton of Arthropods
What is a three carbon sugar?
A triose sugar
In the test for a reducing sugar, why would you not boil the test solution?
It would split a disaccharide into a monosaccharide
How can you accurately measure the colour change for a positive result of a reducing sugar?
Use a colorimeter
What are the functions of carbohydrates?
- immediate respiratory substrates
- energy stores
- structural components
- metabolites
- cell-to-cell attachment molecules
- transport
Give an example of a carb acting as a respiratory substrate
Glucose
Give an example of carbs being used as energy stores
- glycogen in mammals
- starch in mammals
Give examples of carbs being used as structural components
- cellulose in plant cell walls
- chitin in arthropod exoskeletons
- pentose sugars (ribose and deoxyribose are components of RNA and DNA respectively)
Give an example of carbs being used as metabolites
Intermediates in biochemical pathways
Give an example of carbs being used as cell-to-cell attachment molecules
Glycoproteins and glycolipids on the plasma membranes
Give an example of carbs being used for transport
Sucrose in plant phloem tissue
