Topic 1.who knows - Carbohydrates Flashcards
What elements are carbohydrates made up of?
Carbon, hydrogen and oxygen
What are the three main types of carbohydrates?
Monosaccharides, disaccharides and polysaccharides
What are monosaccharides?
Carbohydrates with relatively small molecules
What are characteristics of monosaccharides?
Soluble and sweet
Give examples of monosaccharides
Ribose
Glucose
Galactose
Fructose
What type of sugar is glucose and why?
A hexose bc C6H12O6 (also a reducing sugar)
What are isomers?
Same molecular formula but different structural formula
What are two isomers of glucose?
Alpha glucose and beta glucose
What is the difference between alpha and beta glucose?
The OH attached to C1 is on the bottom in alpha glucose and in beta glucose its on the top
What is a reducing sugar?
A substance which when heated with copper sulfate solution the carboxyl group of the sugar reduces copper sulfate to copper oxide and forms a brick red precipitate
What test do we use to test for reducing sugars?
Benedict’s test
Explain the method of the Benedict’s test
5cm3 of copper sulfate to 10cm3 of test solution. Test tubes placed in boiling bath for 5 mins. Colours compared
How does the amount of precipitate formed and the colour relate to the amount of reducing sugar there is?
The greater the concentration of sugar, the greater the colour change and the greater the amount of precipitate formed
What is a disaccharide?
Two monosaccharides linked by a glycosidic bond in a condensation reaction
Explain the test for non-reducing sugars.
Boil test sample with HCl and then neutralise with sodium hydrogen carbonate until fizzing stops then carry out Benedict’s test. If positive then there are non-reducing sugars
How can disaccharides be broken down into their monosaccharides?
Hydrolysis by adding water
What is maltose made up of?
Glucose and glucose
What is lactose made up of?
Glucose and galactose
What is sucrose made up of?
Glucose and fructose
Name some reducing sugars
Maltose and lactose
Name a non-reducing sugar
Sucrose
What are polysaccharides?
Many monosaccharides joined together by glycosidic bonds
What are some of the functions of polysaccharides?
Fuel stores and structure
What is starch made of?
Amylose and amylopectin
What are the similarities between amylose and amylopectin?
They’re both isomers of a-glucose
What are the differences between amylose and amylopectin?
Amylose forms straight unbranched chains but amylopectin forms branched chains
What bonds are in amylose?
1,4 glycosidic bonds
What bonds are in amylopectin?
1,4 and 1,6 glycosidic bonds
How is a starch molecule stabilised?
Glycosidic bonds keep the helix together and hydrogen bonds stabilise the starch molecules
What is the main storage carbohydrate of most plants?
Starch
Give some of the useful properties of starch
Insoluble
Branched
Highly branched so easily hydrolysed
What is the test for the presence of starch?
Adding potassium iodide and if it goes from yellow/brown to blue/black then starch is present
What is glycogen?
A polymer of a-glucose
Where is glycogen found?
Liver and muscle fibres but seen throughout the body apart from the brain
When does the body start to metabolise stored fat?
When the glycogen reserves are exhausted
What is cellulose?
A polymer of b-glucose held together by B 1,4 glycosidic bonds
How does cellulose form fibres?
Chains of b-glucose pack tightly into fibrils which are held together by hydrogen bonds
What is cellulose used for?
Plant cell walls
Where does the strength of the plant cell walls come from?
From the combined effect of the hydrogen bonds between the chains of b-glucose, the bonds within the chains and the way in which the fibres are arranged in different directions.
What are the uses of carbohydrates?
Respiration substrate Energy store Structure Transport Cell recognition
Why can too many carbohydrates lead to obesity?
Carbs are a source of energy
More energy in than out means its stored
Excess carbohydrates are stored as fats
