Carbohydrates Flashcards
Monomers, the polymers they form and the bonds within them
Alpha glucose- starch (amylose) and glycogen joined with (glycosidic C1-C4, + glycosidic C1-C4 chain and C1-C6 branches.) bonds.
Beta glucose- cellulose joined by glycosidic C1-C4 bonds.
Amino acids- polypeptides joined by peptide bonds.
Nucleotides- DNA, RNA joined by phosphodiester bonds.
What’s the empirical formula for carbohydrates?
Carbon: hydrogen: oxygen ratio CH2O(n) where n= the number of carbon atoms.
The role of carbohydrates
Monosaccharides: single unit sugars e.g. glucose, fructose, galactose.
- source of energy/ aerobic respiration/ generates ATP
- make up polysaccharides
- building DNA and RNA nucleotides
- chemical intermediates
Polysaccharides: large, insoluble polymers e.g.starch (amylose), glycogen, cellulose.
- starch acts as energy stores in plants/ animals
- cellulose makes plant cell walls and has a structural role.
Alpha and beta glucose
What’s an isomer?
a-glucose: the H on the right and left point above the plane of the ring.
b- glucose: the H on the right points below the plane of the ring while the H on the left points above.
Glucose is an isomer: both alpha and beta forms are the same molecule but different arrangement.
The food test for reducing sugars
Add 2cm3 Benedict’s solution to the sample.
Heat in water bath, 90 degrees for 5 minutes.
Colour change from light blue to red (copper II sulphate) if reducing sugars is present.
Scale. Blue, green, orange, red.
Name 3 common disaccharides and the monosaccharides that make them.
Maltose- 2 alpha glucose. A reducing sugar.
Sucrose- glucose and fructose. A non-reducing sugar.
Lactose- glucose and galactose. A reducing sugar.
Food test for non-reducing sugars
If the solution stays blue in the Benedict’s test, it’s a non-reducing sugar.
Boil with hydrochloric acid then neutralise with alkali.
Repeat Benedict’s test by heating at 90 degrees for 5 minutes.
Colour change from light blue to red.
Formation of starch
Condensation reaction between many alpha glucose monomers.
Water released.
Forms C1-C4 glycosidic bonds.
Tightly coiled/ compact, insoluble polysaccharide.
The role of starch in plants
Starch consists mainly of polysaccharide amylose.
It is a storage polysaccharide for energy.
Amylose is compact, so a plant cell can store a lot of energy in a small space.
Amylose is coiled by hydrogen bonding within the chain.
It is insoluble so cell water potential/ enzymes are not affected and it cannot diffuse out of cells.
Hydrolysis of starch releases glucose for use in respiration to make ATP.
What are the similarities and differences between starch (amylose) and glycogen (containing amylose and amylopectin)?
Similarities: Both polymers made from alpha glucose. Compact. Insoluble. Store of energy for respiration/ ATP. Condensation reaction between monomers forming glycosidic bonds.
Differences:
Amylose has C1-C4 glycosidic bonds only whereas glycogen has C1-C4 chains and C1-C6 branches.
Amylose is in plants while glycogen is in animals.
Amylose is an unbranched, coiled chain while glycogen is heavily branched so has more ‘terminal ends’ which allows for rapid hydrolysis/ release of glucose for respiration.
Food test for starch
Add 2cm3 of iodine/ potassium iodide solution.
Colour change from orange to blue/black.
The formation of cellulose
Polymer of beta glucose (monomer).
Condensation reaction between monomers forming C1-C4 glycosidic bonds.
Every 2nd beta glucose rotates 180 degrees.
Forms a straight cellulose strand.
Multiple parallel strands, bonded by extensive hydrogen bonding.
Forming microfibrils.
Many microfibrils combine to form macro fibres.
Macro fibres combine to form cellulose.
Relate the structure of cellulose to its function with plant cells.
Fibrous polysaccharide.
Tensile.
Withstand osmotic forces when cells absorb water by osmosis and become turgid.
Spaces between cellulose strands allow material to pass through freely to cell surface membrane.