3.1.2 (carbohydrates) Flashcards
Describe the chemical formula of carbohydrates.
Organic compounds comprising of only carbon, hydrogen and oxygen
Hydrogen and oxygen present in a 2:1 ratio
What are monosaccharides? Name three.
Single sugar units - the monomers from which larger carbohydrates are made
Eg glucose,galactose,fructose
What is an isomer?
Chemicals with the same formula but different arrangements
What are the isomers of glucose? Draw them.
Alpha glucose
H |_ O H
X X
HO — OH
Beta glucose
H |_ O OH
X X
HO — H
What are disaccharides? How are they formed? Name 3 and what they are made from.
Double sugar units formed by the condensation of two monosaccharides
Sucrose=glucose+fructose
Maltose=glucose+glucose
Lactose=glucose+galactose
Describe polysaccharides
Large polymers of monosaccharides
Insoluble, unlike monosaccharides and disaccharides
How is a glycosidic bond formed?
A condensation reaction between two monosaccharides
What are carbohydrates used for?
Sources of energy in all organisms
Structural material within cells
Why is glucose not stored as glucose in plants and animals?
Glucose is soluble so would change the water potential
Describe what starch is and what it is made of.
Storage compound in plants
Made from amylose (long unbranched chain of glucose units) and amylopectin (highly branched polymer of glucose units)
Describe the structure of amylose.
Alpha glucose molecules joined by alpha 1,4 glycosidic bonds
CH2OH side chains stick out on same side causing chain to coil into a helix
How is amylose adapted for its function?
Compact - can store lots of energy in a small space
Can be hydrolysed to release many glucose molecules for respiration
Large - can’t diffuse out of cell
Insoluble - doesn’t affect water potential
Describe the structure of amylopectin.
Branched chain of alpha glucose
Straight chain bonded by alpha 1,4 glycosidic bonds
Branching caused by alpha 1,6 glycosidic bonds
How is amylopectin adapted for its function?
Compact - lots of energy stored in a small space
Can be quickly broken down to release many glucose molecules (branched ends means higher surface area)
Insoluble - doesn’t affect water potential
Large - won’t diffuse out of cell Insoluble
Describe the structure of glycogen.
Storage compound in animals
Branched polymer of alpha glucose
Stored in liver and muscles
More highly branched by amylopectin - more alpha 1,6 glycosidic bonds
Each branch shorter - only 8-12 residues per chain
Whole molecule coils
How is glycogen adapted for its function?
Compact - lots of energy stored in a small space
Can be very quickly hydrolysed to release many glucose molecules due to many branched ends
Insoluble - doesn’t affect water potential
Large - can’t diffuse out of cell
Describe the structure of cellulose.
Structural polysaccharide- major component of plant cell walls
Straight chain polymer of beta glucose
Side chains of CH2OH stick out on alternate sides making the molecules very straight
Long straight chains parallel to each other linked by hydrogen bonds
Describe the arrangement of beta glucose in cellulose.
Every alternate beta glucose is flipped to form a straight chain molecule.
How is cellulose arranged?
Small bundles of cellulose chains make thin fibres called microfibrils - extremely strong
Cross linking prevents hydrolysis by water - isn’t a good dietary carbohydrate in animals
Describe the biochemical test for reducing sugars.
Add Benedict’s solution and heat in a water bath at a minimum of 60’C
Positive result will go from blue to brick red
Describe the test for non reducing sugars.
Boil sample in hydrochloric acid (to break glycosidic bonds by acid hydrolysis releasing reducing sugars)
Neutralise sample by adding an alkali eg sodium hydrogen carbonate
Add Benedict’s solution and heat in a water bath at a minimum of 60’C
Positive result goes from blue to brick red
Describe the test for starch.
Add iodine solution to the sample
Positive result goes from brown to blue black
