Biological Molecules (CARBOHYDRATES) Flashcards
Define a monomer
monomers are smaller, repeating units which can create larger molecules
Give some examples of monomers
amino acids, glucose, nucleotides, monosaccharides
Define a polymer
molecules from a large number of monomers joined together
Give some examples of polymers
proteins, cellulose, starch, glycogen
Define a condensation reaction
A reaction which joins 2 molecules (monomers) together with the formation of a chemical bond and the elimination of a water molecule
What is the opposite of a condensation reaction
A hydrolysis reaction - breaks a chemical bond between 2 molecules and involves the use of a water molecule
What are monosaccharides
Monosaccharides are the monomers from which larger carbohydrates are made (monomers specific to carbohydrates)
Give 3 monosaccharides
Glucose
Fructose
Galactose
How are disaccharides formed
By the condensation of 2 monosaccharides which forms a glycosidic bond
Give the 3 disaccharides
Maltose
Sucrose
Lactose
How is maltose formed
Glucose + glucose
How is sucrose formed
Glucose + fructose
How is lactose formed
Glucose + galactose
What are the 2 isomers of glucose
alpha (α) & beta (β) glucose
What is the difference in structure between alpha glucose and beta glucose
In alpha glucose, carbon 1 has the H at the top and OH at the bottom whereas the H is at the bottom and OH is at the top in beta glucose
REMEMBER TO ADD THE OXYGEN FOR BOTH
What glycosidic bond does maltose form
A 1 -4 glycosidic bond
How are polysaccharides formed
Polysaccharides are formed by the condensation of many glucose monomers
Give three polysaccharides
starch
glycogen
cellulose
what monomer is starch formed from
alpha glucose - amylose and amylopectin
Compare structure of amylose and amylopectin
amylose is an unbranched chain of alpha glucose that only has 1-4 glycosidic bonds which gives it a tight, coiled helix structure. This is due to the hydrogen bonding within amylose. Whereas amylopectin has 1-4 and 1-6 glycosidic bonds which gives it a branched structure
Where is starch found
Only in plant cells (eg: in chloroplasts)
what is the function of starch
It is an insoluble store of glucose
What are the properties of starch that make it suited to its function
It is insoluble - doesn’t affect water potential of cell so it doesn’t cause water to enter cell by osmosis which would make the cell turgid.
Helical structure = coiled structure → makes it compact = can fit more into a small space (= good for storage)
The branched structure increases surface area (ends) for rapid hydrolysis back to alpha glucose so glucose is easily released for respiration
what monomer is glycogen formed from
alpha glucose
( Glycogen is a polymer of alpha glucose)
where is glycogen found
in muscle and liver cells
what is the function of glycogen
stores excess glucose in muscle and liver cells
How is glycogen’s structure related to its function
Glycogen has a similar structure to amylopectin, except it has a lot more branches due to more 1 - 6 glycosidic bonds, Loads of branches means glucose can be quickly and easily released in respiration → important for energy releases in animals
It is insoluble and so doesn’t draw water in by osmosis. or affect water potential
It is compact, making it good for storage
Despite both starch and glycogen being branched molecules, why is glycogen more branched
Glycogen is found in animals and humans - they are more metabolically active than plants - branched structure means glycogen can hydrolysed to alpha glucose and be used in respiration
What monomer is cellulose formed from
Beta glucose
where is cellulose found
In cell wall of plant cells
What is the function of cellulose
Cellulose provides structural strength and support to plant cells
Describe the structure of cellulose
only contains 1-4 glycosidic bonds which creates long straight chains. These long straight chains lie parallel to each other and are held together by many hydrogen bonds.
What do chains of cellulose molecules form
Microfibrils which eventually form fibres
How is cellulose’s structure related to its function
Every other beta glucose molecule is flipped 180 degrees (inverted) so hydrogen bonds can form between cellulose chains. Individual hydrogen bonds are weak but due to the large number of them, collectively they provide strength
What is a reducing sugar
Sugars that can donate electrons to another chemical e.g. Benedict’s reagent
Describe the test for reducing sugars
1) Mix equal volumes of test sample and benedicts reagent
2) Heat in water bath at 80 degrees celsius
Positive test result shows solution turn from blue to brick red (brick red means a stronger concentration of reducing sugar present)
Describe the test for non reducing sugars
1) Do the reducing sugar test. If negative and benidicts remains blue:
2) Add hydrochloric acid
3) Boil in water bath for 2 mins (short period of time)
4) Add sodium hydroxide (an alkali) for neutralisation
5) Add benedicts reagent
6) Heat in water bath
Positive test result shows solution change to a brick red colour
What’s a more accurate way of comparing the amount of reducing sugar in different solutions than colour change
Filter solution, dry precipitate and weigh it
Why is hydrochloric acid added in the test for non reducing sugar
To provide hydrolysis and break the non-reducing sugar (disaccharide) into monosaccharides
Give the name of a non reducing sugar
Sucrose
Describe the test for starch
1) Mix iodine/potassium iodide with test solution
2) Positive test result shows solution goes from browny orange to a blue/black colour
