2.1.2 - Biologial Molecules (set B - Carbohydrates) Flashcards
Explain what a carbohydrate is?
molecules that only contains the elements carbon,hydrogen and oxygen- they are known as saccharides or sugars
Give the general formula of carbohydrates, where n is the number of carbons in the molecule?
(CH ₂O) ₙ
Define a monosaccharide?
Single sugar unit, eg glucose, fructose and ribose
Define a disaccharide?
formed when two monosaccharides are joined together by a glycosidic bond, happens in a condensation reaction which involves the removal of a molecule of water, eg maltose or sucrose
Give three examples of monosaccharides?
- glucose
- fructose
- ribose
Give three examples of disaccharides?
- lactose
- maltose
- sucrose
Define a polysaccharide?
A long chain of monosaccharides which are linked together by glycosidic bonds, eg glycogen, cellulose and starch
- multiple monomers
Give three examples of polysaccharides?
- glycogen
- cellulose
- starch
What is glucose?give its formula and both its structural variations?
Glucose is a monosaccharide with the molecular formula of C ₆H ₁₂O ₆ it is important for providing energy to cells - excess glucose is stored as glycogen
- 2 structural variations of glucose molecules, alpha and beta - main difference is the hydroxyl groups are opposite
What are the two structural variations of glucose?
Alpha and beta glucose molecules
Why are glucose molecules soluble in water?significance?
The reason glucose dissolves readily in water is because it has lots of polar hydroxyl groups which can form hydrogen-bonds with water molecules
- important as it allows glucose to pass through the cell membrane of cells
Explain what a condensation reaction is?
a reaction in which two molecules combine to form a single molecule - a small molecule, often water is usually removed during the reaction
- involved in the formation of a disaccharide
Explain how a disaccharide is formed with reference to the bond formed?
Formed when two monosaccharides are joined together by a glycosidic bond in a condensation reaction which also involves the removal of a water molecule
Explain how the disaccharide maltose if formed?
During condensation reaction, bond is formed between carbon 1 of one alpha glucose molecule and carbon 4 of the other alpha glucose molecule (called 1-4 glycosidic bond) - water also formed as product
Explain 3 factors of the polysaccharide cellulose?
- polymer of long unbranched chains of beta glucose - orientated alternately upwards and downwards
- condensation reaction links carbon atom 1 to carbon atom 4 on the next beta glucose molecule
- cellulose molecule is a straight chain
Give the structure of cellulose?
- cellulose chains are linked together by hydrogen bonds which form cellulose microfibrils which join together to make macrofibrils which combine to produce fibres
- tensile strength of cellulose provides structural support for the cell
How is cellulose strong?why is it important?
Cellulose chains are linked together by hydrogen bonds which form cellulose microfibrils - gives it high tensile strength and allows it to support cells and prevents them from bursting
Explain 2 factors of the polysaccharide cellulose?
- Energy store for plants, where excess glucose is stored as starch, so it can be broken down to release energy when needed
- mixture of the two polysaccharides of alpha glucose (amylase and amylopectin)
Explain and describe the structure of amylose?
Long unbranched chain of alpha glucose - due to the angle of the glycosidic bond it has a coiled cylinder structure, allows for efficient storage
Explain and describe the structure of amylopectin?
Long branched chain with 1-4 glycosidic bonds between alpha glucose molecules (some glycosidic bonds between carbon 1 and carbon 6 on two glucose molecules) has side branches which allows enzymes to easily break down and access the glycosidic bond - so glucose can be released quickly
Explain 3 factors of the structure of the polysaccharide starch?
- condensation reaction links carbon atom 1 via a glycosidic bond to carbon atom 4 on the next alpha glucose molecule
- glucose molecules ordinated in the same way - as opposed to alternately up and down like cellulose
- starch molecule is curved and the size if not fixed
Explain 2 factors of the polysaccharide glycogen?
- main energy storage material in animals and fungi - excess glucose stored as glycogen in the liver and muscles of humans
- polymer of repeating alpha glucose sub-units, similar structure to amylopectin but has more side branches so more energy can be released
Explain 2 factors of the structure of the polysaccharide glycogen?
- glycogen is very compact - makes it a good energy store
- glycogen does not affect the osmosis balance of cells
Explain how cell walls are made,reference starch and fibres?
Cellulose molecules make hydrogen bonds with each other forming microfibrils which join together to form macro fibrils which then combine to produce fibres
- these fibres are strong and insoluble and are used to make the cell wall
Explain the significance of glycogen having more branches then amylopectin?
- more compact, so it requires less space to be stored - due to coiling of the polymer chain
- more free ends on the branches - so glucose molecules can be added or removed efficiently
What are the two monosaccharides which are condensed to form maltose?
Condensation of two alpha glucose molecules
What are the two monosaccharides which are condensed to form sucrose?
Condensation of a glucose molecule and fructose
What are the two monosaccharides which are condensed to form lactose?
Condensation of a glucose molecule and a galactose molecule
What is the difference between a hexose monosaccharide and a pentose monosaccharide?
Pentose is a five-carbon monosaccharide, whereas hexose contains six carbon atoms
Give an example of a hexose monosaccharides?
- glucose
Give an example of a pentose monosaccharide?
- ribose
Explain what a hydrolysis reaction is?
Reverse of condensation reaction, a larger molecule forms two smaller molecules with a water molecule being consumed in order to break a chemical bond between 2 molecules
- eg ester bonds between fatty acids and glycerol in lipids
Explain how glucose is released from starch or glucose, reference hydrolysis reactions?
To release glucose for respiration, starch or glycogen undergo hydrolysis reactions, and require the addition of water molecules
- reaction is catalysed by enzymes
Define what a monomer is and give some examples?
Smaller units that join together to form large molecules - for example monosaccharides (glucose,fructose and ribose) amino acids and nucleotides
Define what a polymer is and give some examples?
Molecules formed when many monomers join together - for example polysaccharides, proteins and DNA/RNA
Describe the properties of alpha glucose - give 3?
- small and water soluble - easily transported in bloodstream
- complementary shape to antiport for co-transport for absorption in gut
- complementary shape to enzymes for glycolysis - respiratory substrate
Name 3 disaccharides, describe how they form?
Condensation reaction forms glycosidic bond between 2 monosaccharides
- maltose : glucose + glucose
- sucrose : glucose + fructose
- lactose : glucose + galactose
Explain what type of bonds cellulose,glycogen and starch have?
- Starch - alpha 1-4 glycosidic bonds
- glycogen - alpha 1-4, 1-6 glycosidic bonds
- cellulose - beta 1-4 glycosidic bonds
