Carbohydrates - Biological Molecules Flashcards
What elements do carbohydrates contain?
Carbon, hydrogen and oxygen
What is the general formula of carbohydrates?
Cx(H2O)y
What are the types of carbohydrates?
- monosaccharides
- disaccharides
- polysaccharides
What are monosaccharides?
Simple sugars, they are the larger units from which larger carbohydrates can be made
Their general formula (CH2O)n where n is any number from 3-7
What is triose?
Has 3 carbon atoms
Formula: C3H6O3
What is pentose?
5 carbon atoms
Formula: C5H10O5
E.g. ribose, deoxyribose
What is hexose?
6 carbon atoms
Formula: C6H12O6
E.g. glucose, galactose, fructose
What is the structure of glucose?
Exist in straight chain or stable ring
The ring excises in alpha and beta forms
What is the structure of alpha glucose?
Carbon-1 has its hydroxyl group below the plain of the ring
What is the structure of beta glucose?
Carbon-1 has its hydroxyl group above the plane of the ring
Remember the difference between alpha and beta glucose
ABBA
alpha below
beta above
How to remember monomers?
Mavis fries greasy gammon
Monosaccharides
Fructose
Glucose
Galactose
What are all monosaccharides?
Reducing sugars
What are the functions of monosaccharides?
- Release energy during respiration
Hydrolysed and energy locked up in bonds is released and used to make ATP - Can join together to make larger carbohydrates
Which act as a store of energy and enter the composition of important cell structures
What are disaccharides?
Two monosaccharides are joined by a glycosidic bond
What reaction forms disaccharides?
A condensation reaction
2 -OH groups lose a water molecule between them
What is maltose made from?
A-glucose + a-glucose
What is sucrose made from?
A-glucose + fructose
What is lactose made from?
A-glucose + galactose
How to remember disaccharides?
Doris smells like mould
Disaccharide
Sucrose
Lactose
Maltose
What are polysaccharides?
Polymers formed by joining many monosaccharides with glycosidic bonds
Formed by condensation reactions
What are the properties of polysaccharides?
- very large and insoluble
- un-reactive
- usually folded into a compact shape
Where is starch found?
In plants in the form of grains
Mainly in leaves and seeds
How is starch formed?
Linking of many a-glucose molecules by glycosidic bonds in a series of condensation reactions
How to test for starch?
Add iodine, if blue-black, then positive and no colour change for negative (yellow-brown)
How is the shape of starch held in place?
Coiled to form a helix to form a compact molecule. Hydrogen bonds between the hydroxyl groups hold the shape in place.
How is structure of starch suited to its function?
- Large and insoluble - cannot diffuse out of the cell
- Insoluble doesn’t cause water to be drawn out of the cell by osmosis
- HELICAL which makes it compact and store more in small space
- Readily hydrolysed into alpha glucose for respiration
Where is glycogen found?
In animals (never plants)
In muscle and liver cells
Made of many alpha glucose molecules
What is the structure of glycogen?
More highly branched than starch and shorter
How is the structure of glycogen suited for its function?
- Insoluble - doesn’t affect osmotic potential of cell
- Insoluble - doesn’t diffuse out of cells
- Compact - large amounts can be stored in small space
- More highly branched than starch so more ends for enzymes to act upon - glucose is released more rapidly (easily hydrolysed for respiration)
What is the structure of cellulose (molecular)?
Made of BETA GLUCOSE
Due to the position of hydroxyl group on carbon-1 (above plane of ring) each molecule must be inverted to neighbour in order to form glycosidic bonds
What is the structure of cellulose?
- straight unbranched chains which run parallel to each other
- allows hydrogen bonds to form between molecules
- cross linkages are very strong
How are cellulose molecules grouped?
-grouped to form microfibrils
- arranged in parallel groups called fibrils
- cellulose is found in cell walls of plants and has strong role in providing rigidity
Where do hydrogen bonds form?
Between OH groups
Each monomer inverted so that OH groups occur on both sides of the molecule so that H bonds can form with other chains
What is the function of cellulose?
Provide strength and rigidity
So it can:
Resist turgor pressure
Resist actions by microorganisms/ enzymes and resist digestion
How is structure of cellulose adapted to its function?
- Made of B-glucose joined by glycosidic bonds (formed during condensation reactions) and so form long, straight, unbranched chains - run parallel to each other
- Each B-glucose is inverted to its neighbour - bonds form between hydroxyl groups of neighbouring parallel chains, increasing collective strength
- Chains arranged in groups to form microfibrils - arranged to form fibrils adding yet more strength
What is a glycosidic bond?
The bond formed between carbohydrate molecules
What is hydrolysis?
A reaction that breaks a chemical bond between molecules when water is added (chemically)
What is a macromolecule?
A giant molecule made from many repeated units
What is a reducing sugar?
A sugar that acts as a reducing agent by donating electrons
What is a non-reducing sugar?
A sugar that doesn’t act as a reducing sugar by donating electrons
What is semi-quantitative?
Tests that give a rough estimation of concentration
What is an isomer?
Molecules with the same molecular formula and different structural formula
What carbohydrates are reducing?
All monosaccharides and some disaccharides (maltose and lactose)
What are the results of Benedict’s test?
A high conc = brick red
A low conc = green
Negative = no colour change (blue)
How does the Benedict’s solution work?
Contains blue copper (II) sulphate ions
They are reduced to insoluble red-brown copper (I) oxide (containing copper (I) ions)
Copper (I) oxide seen as precipitate
Cu2+ + e- -> Cu+
(Electrón from reducing sugar)
What is the test for non-reducing sugars?
-first test solution - negative result obtained
- add dilute HCl and boil
- add NaHCO3 to neutralise
- check neutral
- add Benedict’s again - result will be positive
- prescene shown by negative then positive after boiling with acid
