Carbohydrates Flashcards
What is a monosaccharide?
monomers from which larger carbohydrates are made
Give three examples of monosaccharides.
glucose, fructose and galactose
What is a disaccharide?
Two monosaccharides joined by a glycosidic bond through a condensation reaction
Give three examples of disaccharides
maltose, lactose and sucrose
What is maltose formed from?
two glucose monosaccharides
What is lactose formed from?
glucose and galactose
What is sucrose formed from?
glucose and fructose
What is a polysaccharide?
a large molecule formed from the condensation reaction of many glucose units joined by glycosidic bonds
What are the two isomers of glucose?
a glucose and b glucose
How does a and b glucose differ?
a glucose has two hydroxide groups facing downward whereas b glucose has one hydroxide facing upward and one facing downward
What are the three polysaccharides?
Starch, glycogen and cellulose
What is the structure of starch?
- starch is formed of amylose and amylopectin
What is the structure of amylose?
- amylose is an unbranched chain of glucose molecules joined by 1.4 glycosidic bonds.
- This means it is unbranched and coiled, compact
What is the structure of amylopectin?
- branched and made up of 1,4 and 1,6 glycosidic bonds
- contains many side chains which can be acted upon by enzymes
What are the properties of starch?
- it is insoluble so it does not affect the osmotic potential of cells
- it is large and insoluble so it doesn’t diffuse out of cells
- compact, can be stored
- it has branched ends which enzymes can act on so it can be easily broken down
What is the structure of glycogen?
- a main storage molecule for animals
- joined of many a - glucose monosaccharides joined by 1,4 and 1,6 glycosidic bonds
- a large number of branches
What are the properties of glycogen?
- insoluble, doesn’t affect osmotic potentials
- compact
- highly branched so can be easily acted upon by enzymes and used as an energy source In animals
What is the structure of cellulose?
- it is made of b - b-glucose monomers
- straight unbranched chains
- Chains of cellulose have each b glucose monomer inverted by 180 degrees
- the chains run parallel to one another which forms hydrogen cross-links between adjacent chains
What are the properties of cellulose?
- a main component of cell walls
- chains of cellulose form microfibrils which then group to form fibres
- This increases the strength of cell walls, reducing the chance of the cell wall bursting from osmotic pressure
- cellulose also exerts inward pressure, stopping the influx of water and helping cells remain turgid
How does cellulose help plants?
By exerting inward pressure, cells remain turgid and this helps to maximise the surface area of plants for photosynthesis
What is the test for reducing sugars?
- All monosaccharides are reducing sugars and some disaccharides are ( maltose)
- Add benedicts reagent to the sample
- heat
- The colour change if negative will remain blue
- If there is a reducing sugar the colour change is green, yellow, orange to brick red
What is the test for non-reducing sugars?
- Add your sample and an equal volume of benedicts reagent and warm in a water bath
- if the colour change isn’t from blue to brick red, there is no reducing sugar present
- add 2cm of dilute HCL and the same volume of your sample and place the test tube in another water bath
- The HCL will hydrolyse the disaccharides and polysaccharides into monosaccharides
- add sodium hydro carbonate to neutralise the test tube
- repeat the benedicts test and there should be a colour change from blue to brick red
What is the test for starch?
- Add 2cm of your sample to a test tube
- add 2 drops of iodine to the test tube
- a positive test is orange to blue - black
