1: BIOLOGICAL MOLECULES - MONOSACCHARIDES AND POLYSACCHARIDES Flashcards
What are monosaccharides?
monomers that form polysaccharides (carbohydrates) (eg: glucose)
What are the 2 types of glucose?
- alpha glucose
- beta glucose
What are isomers?
molecules with the same molecular formula but with the atoms connected in different ways
What is the difference between alpha glucose and beta glucose?
- they are isomers
- the 2 types of glucose have the last groups reversed
How are disaccharides formed?
a disaccharide is formed when 2 monosaccharides are joined together by a condensation reaction
What type of bond is formed between monosaccharides as H2O is released in a condensation reaction?
a glycosidic bond
What is maltose?
a disaccharide formed from a condensation reaction between 2 alpha glucose molecules
What is sucrose?
a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule
What is lactose?
a disaccharide formed from a condensation reaction between a glucose molecule and a galactose molecule
What do reducing sugars include?
all monosaccharides and some disaccharides (eg: maltose and lactose)
How do you test for reducing sugars?
- add benedict’s reagent to a sample and heat in a water bath
- if the test is +ve it will form a coloured precipitate (green/yellow/orange/brick red depending on the conc. of sugar)
How do you test for non-reducing sugars (eg: sucrose)?
- add dilute HCL and gently heat to break the sample down into monosaccharides
- neutralise the solution by adding sodium hydrogencarbonate
- add benedict’s reagent and heat in a water bath
- if the test is +ve it will form a coloured precipitate (green/yellow/orange/brick red depending on the conc. of sugar)
What are polysaccharides?
carbohydrates
How are polysaccharides formed?
polysaccharides are formed when 3+ monosaccharides are joined together by condensation reactions
What are 3 examples of polysaccharides?
- starch
- glycogen
- cellulose
What is starch used for?
- plants store excess glucose as starch
- when a plant needs more glucose for energy, it breaks down starch to release the glucose
What is starch made up of?
- 2 polysaccharides of alpha glucose:
- amylose
- amylopectin
What is the structure of amylose and how does it relate to its function?
- long, unbranched chain of alpha glucose
- angles of glycosidic bonds give it a coiled structure which makes it more compact for storage
What is the structure of amylopectin and how does it relate to its function?
- long, branched chain of alpha glucose
- side branches allow enzymes that break down the starch to reach the glycosidic bonds easily so the glucose can be released easily
Is starch soluble/insoluble and how does that relate to its function?
- starch is insoluble and has no effect on water potential
- therefore it doesn’t cause water to enter the cell which would make the cell swell
- this makes it good for storage
What is glycogen used for?
- animals store excess glucose as glycogen
- when more glucose is required for energy, glycogen is broken down to release the glucose
What is the structure of glycogen and how does it relate to its function?
- long, branched chain of alpha glucose
- many side branches allow enzymes that break down the starch to reach the glycosidic bonds easily so the glucose can be released easily
- compact which makes it good for storage
What is the structure of cellulose and how does it relate to its function?
- long, unbranched chain of beta glucose
- cellulose chains linked together by hydrogen bonds to form microfibrils (strong fibres) which allow cellulose to provide structural support (eg: in cell walls)
How do you test for starch?
-add iodine dissolved in potassium iodide
-if the test is +ve the colour of the solution would change from orange/brown to blue black
