Module 1 - Carbohydrates Flashcards
What is a carbohydrate
A carbohydrate is an organic molecule made of hydrogen, oxygen and carbon
What is a monosaccharide
A monosaccharide is an organic monomer that cannot be hydrolysed to a simpler sugar
What is a polysaccharide. Give 3 examples
A polysaccharide is a large chain of monosaccharides chemically bonded together joined by glyosidic bonds.
Cellulose, starch and glycogen
Give examples of hexose monosaccharides
Glucose, fructose and galactose
Give 4 ways in which glucose is important
For respiration, building larger carbohydrates, it is small so easily transported through cells and soluble so easily transported around organisms.
What are the 2 isomers of glucose
Alpha and beta glucose
What is a ribose and define the structure
Ribose is a pentose sugar made of 5 carbons and is founds in RNA and ATP which provides energy.
What is a disaccharide
A disaccharide is 2 monosaccharides chemically joined together in a condensation reaction in the presence of water
Give 3 disaccharides and how they are formed.
Alpha glucose + alpha glucose = Maltose
Alpha glucose + fructose = sucrose
Alpha glucose + galactose = Lactose
What is a glyosidic bond
A covalent bond formed between 2 monosaccharides by a condensation reaction.
How does alpha - glucose differ from beta - glucose
Alpha - glucose has a H (top) and OH (bottom) atom branching from carbon 1. In Beta - glucose, the H and OH atoms are switched at carbon 1.
What 4 properties do polysaccharides of alpha-glucose have.
They are compact so can be stored in a small space. They are insoluble so do not affect the water potential of a cell. Easily hydrolysed (readily accessible energy) and they are a large molecule so cannot diffuse out of a cell.
Where is starch found
Starch is found in photosynthesising cells in leaves and storage cells.
What are the 2 different polysaccharides starch contains
Amylose and amylopectin
Define the structure of both polysaccharides in starch
Amylose - a long chain of alpha-glucose molecules joined by 1,4 glycosidic bonds which coils up into a helix shape making them compact.
Amylopectin - a chain of alpha-glucose with 1,4 and occasional 1,6 glycosidic bonds.
Between Amylose and Amylopectin, which is quicker to break down? why?
Amylopectin because it has more than 2 accessible ends for enzymes to attach to and break down. This means that it is quicker for hydrolysis to occur.
Describe the structure of glycogen and where it is found
Glycogen has a similar structure to the polysaccharide Amylopectin however the 1,6 glycosidic bonds are more frequent. They are found in animal cells with high metabolic rate
How and where is glycogen stored
Glycogen is stored as small granules in the liver and muscle
Describe an important property that glycogen has
Glycogen is less dense and more soluble than starch. This allows it to break down more rapidly thus indicating the high metabolic requirements needed in animals compared to plants.
What is cellulose and how is it different from the other 2 polysaccharides
Cellulose is another polysaccharide useful for the overall structure of a plant. This is different from starch and glycogen as they are more important for being energy stores. Also consists of beta-glucose molecules.
What does turgidity means and how is this significant in plants
Turgidity means when enough strength is being provide to each cell in order for the structure of the plant to remain upright. In cells walls there is cellulose which supports cells with helping plants maintain their shape.
What is cellulose made from
Cellulose is made form thousands of beta-glucose molecules held together by 1,4 glycosidic bonds. To be able to form these 1,4 glycosidic bonds, each molecule must be inverted 180 degress from the previous molecule
How does each beta-glucose molecule being inverted 180 degrees from the previous molecule support the structure of cellulose.
It allows the chains of beta-glucose molecules to be straight and not coil up. This therefore allows chains to be parallel meaning hydroxyl groups will be in close proximity forming hydrogen bonds.
What is the significance of hydroxyl groups forming hydrogen bonds between each cellulose chain?
It allows cellulose to be very strong.
What do many cellulose chains form and what do these do to make plants very strong?
Many cellulose chains come together forming Microfibrils and then these wrap around plant cells in multiple layers at different angles making it strong
Why can animals not digest Cellulose
Animals do not contain the cellulose enzyme - cellulase - in order to hydrolyse the very strong cellulose.
Describe the reducing sugars benedict’s test. Say the possible results that could be concluded.
Reducing sugars are monosaccharides and some disaccharides.
First add a food solution to a test tube and add the same volume of benedict’s solution to the test tube. Then place it on a warm bath for 5 minutes and record results. Blue is negative, Green is very low concentration, yellow is low, orange is high and brick-red is very high.
Benedict’s solution is chemically known as copper (ii) sulphate solution. What happens to the copper ions that creates an orange-red precipitate.
The copper 2+ ions reduce to form copper+ ions.
Describe the non-reducing sugar test
If the reducing sugar test was negative, then a blue precipitate will form. So we add a clean food solution sample to a clean test tube and add hydrochloric acid to hydrolyse the disaccharide then place on a warm bath for 3 - 5 minutes. Then add some sodium hydrogen carbonate to neutralise the solution and place in hot bath for 5 minutes again. Repeat benedict’s test and if colour changes then a non-reducing sugar is present.
What are reducing sugars and give examples:
Reducing sugars can donate electrons. Examples include glucose, fructose and maltose.
What are non-reducing sugars and give examples:
Cannot donate electrons therefore cannot be oxidised
Examples include: sucrose.
