Topic 1.2/1.3/1.4 - Carbohydrates (mono, di and poly) Flashcards
What are carbohydrates made of?
Carbon, Hydrogen and Oxygen
Name 3 monosaccharides
Glucose, fructose and galactose
What isomers are there of glucose?
Alpha and Beta
Why do we need carbohydrates?
For energy
What are the 3 types of carbohydrates?
monosaccharides, disaccharides and polysaccharides
What are the 2 polymers of alpha glucose?
/ What are 2 types of starch?
amylose and amylopectin
What type of sugar is glucose?
A hexose monosaccharide/sugar
What are monosaccharides?
The simplest single sugars
How are disaccharides/polysaccharides formed?
Through condensation reactions, where water is removed and is a product,
What is the bond that is formed when monosaccharides join together?
Give an example
Glycosidic bond
Alpha glucose joins together to form the disaccharide maltose, it forms a 1-4 glycosidic bond as carbon 1 and carbon 4 bond together (water is then formed as a product)
What happens when monosaccharides react with water?
They dissolve to form sweet tasting solutions
What happens when polysaccharides/disaccharides break down?
They hydrolyse (water is added)
What makes up a disaccharide?
2 monosaccharides
What makes up a polysaccharide?
Many monosaccharides
What is the structure of amylose?
A chain of glucose molecules that form a helix structure by hydrogen bonding
What is the function of the structure of amylose?
The helix forms a compact shape which is good for packaging and therefore making it a good storage molecule
What is the structure of amylopectin?
Chains of glucose molecules, after every 25 glucose molecules adjacent chains are connected by alpha 1-6 glycosidic bonds, giving it a BRANCHED STRUCTURE
What is the function of the structure of amylopectin?
The branched ends can be hydrolysed rapidly, allowing the rapid release of alpha glucose for energy
What are three types of polysaccharide?
Starch, glycogen and cellulose
What is the test for reducing sugars (all monosaccharides and some disaccharides, like maltose)?
Benedict’s test
For the Benedict’s test, name the colours for the level of concentration of reducing sugars.
No reducing sugars = blue Very low concentration = green Low concentration = yellow Medium concentration = orange High concentration = red
What is starch used for?
It is the main storage polysaccharide in plants as small grains
Where is large amounts of starch found?
In seeds and storage organs
How is the structure of starch suited to its function?
Insoluble - does not affect water potential
Large - does not diffuse out of cells
Compact - lots stored in a small space (due to spiral shape)
Branched form has many ends - alpha glucose released rapidly (which is then easily transported and readily used)
What is the structure of starch?
Made up of alpha glucose monomers which are joined together through condensation reactions and forms glycosidic bonds.
What is glycogen used for?
It is a major storage polysaccharide of animal and fungi cells
Where is glycogen usually found?
Muscle and liver
What is the structure of glycogen?
Similar to starch, but more highly branched and has shorter chains
How is the structure of glycogen suited to its function?
Insoluble - does not draw water in and does not diffuse out of cells
Compact - lots can be stored in a small space
More highly branched - more enzymes can act on it at once and so rapidly hydrolysed
Why might glycogen need to be more highly branched than starch?
Glycogen is found in animal cells, where starch is found in plants. If it is more highly branched, then it can be hydrolysed quicker due to enzymes acting on ends simultaneously, which will support animals higher metabolic rate where it needs more glucose monomers for respiration.
What is cellulose used for?
- It is used in cell walls of plants
- For humans, cellulose is also a major source of needed fibre in our diet.
What is the structure of cellulose?
It is made up of beta glucose which forms straight and unbranched chains which run parallel to each other
What is the function of cellulose?
- Cellulose cell wall prevents cell from bursting (from osmosis) by exerting an inward pressure that prevents influx of water
How is the structure of cellulose suited to its function?
- Hydrogen bonds between beta glucose chains add to collective strength
- Cellulose groups together to form microfibrils, which in turn are grouped together to form fibrils (all of which provides more strength)
What bonds are the glucose chains in cellulose linked by?
Beta 1-4 glycosidic bonds
What are the three types of disaccharide?
Maltose, sucrose and lactose
What is maltose the product of?
Glucose + Glucose
What is sucrose the product of?
Fructose + Glucose
What is lactose the product of?
Galactose + Glucose
What is the test for starch?
The iodine test
How do you conduct a test for non-reducing sugars?
- Add 2cm cubed of food sample to 2cm cubed of hydrochloric acid
- Add sodium hydrogencarbonate solution to neutralise HCl
- Re-test solution by heating it with 2cm cubed of Benedict’s reagent
- If there is reducing sugar present, it will turn a certain degree of colour (usually orange/brown)
Why must sodium hydrogencarbonate neutralise the HCl in the non-reducing sugars test?
Benedict’s reagent does not work in acidic conditions
How would you conduct the Benedict’s test?
- Add 2cm cubed of food sample
- Add 2cm cubed of Benedict’s reagent
- Heat mixture in a water bath for 5 minutes
- If reducing sugars are present it should turn a different colour depending on the concentration of reducing sugars
How would you conduct a test for the presence of starch?
- Starch will turn iodine from yellow to blue/black
- Add a few drops of a food sample into a spotting tile
- Add a drop or two of iodine into each depression
- The presence of starch will be indicated when the solution turns black/blue
