1A Polysaccharides Flashcards
What are the three key polysaccharides?
Starch, Glycogen & Cellulose
What polysaccharide stores glucose in plant cells?
Starch
Describe the structure of starch.
> TWO polysaccharides of ALPHA GLUCOSE (amylose & amylopectin)
Linked by 1,4 GLYCOSIDIC BONDS
Branching occures every 30 UNITS
What are the properties of starch?
> Large (so can’t leave the cell)
> INSOLUBLE so doesn’t affect the WATER POTENTIAL
What polysaccharide stores glucose in animal cells?
Glycogen
Describe the structure of glycogen.
> Polysaccharide of ALPHA GLUCOSE
> It is HIGHLY branched - every 10 UNITS
What are the properties of glycogen?
> Highly branched so is EASILY HYDROLYSED to release glucose
Describe the structure of cellulose.
> Made up of BETA GLUCOSE
In a STRAIGHT layout - every other unit is FLIPPED 180 DEGREES to allow this
The chains are linked with MANY HYDROGEN BONDS to form STRONG MYOFIBRILS
Give an example of where the polysaccharide cellulose is used.
Plant cell walls
Describe the Benedict’s test for reducing sugars and state what a negative result would look like.
> Add BENEDICT’S REAGENT to the sample & HEAT it in a BOILING water bath
If a reducing sugar is present, the solution will turn a BRICK-RED colour
In a negative result, the solution will stay BLUE
How would you find out the reducing sugar CONTENT of a sample?
> Carry out the Benedict’s test
> FILTER out the solution & WEIGH the precipitate
Describe the Benedict’s test for non-reducing sugars.
> Add DILUTE HYDROCHLORIC ACID to a sample & HEAT in a BOILING water bath - This will break the sugars down into monosaccharides
NEUTRALISE the solution by adding SODIUM HYDROCARBONATE & carry out the Benedict’s test like normal
Describe the test for starch and state what a negative result would look like.
> Add IODINE DISSOLVED IN POTASSIUM IODIDE SOLUTION to the sample
If starch is present, the sample will turn a BLUE-BLACK colour
In a negative result, the solution will remain a BROWNY-ORANGE
