Biological molecules 1 (Water and Carbohydrates) Flashcards
What percentage of water makes up a living cell?
80%
Roles of water
- biological solvent
- regulates temperature
- transport medium
- site of chemical reactions
- used in hydrolysis
- acts as a cooling mechanism (sweat evaporating)
- provides habitats
Properties of water
- polar molecule
- individual bonds provide stability
- high specific heat capacity
- hydrogen bonding
- ice is less dense than liquid water
- water is a good solvent (polar molecule)
Water is a polar molecule, what properties does this provide?
- makes it cohesive
2. a good solvent
Define Cohesive
the attraction between molecules of the same type of type meaning they sick together, this allows water to be a great transport mechanism
How does polarity allow water to be a good solvent?
The slightly positive end will be attracted to the negative ion and the slightly negative end will be attracted to the positive ion, allowing ions to dissolve as they become surrounded
Polar
A partial positive charge on one side and a partially negative charge on the other
Charge of oxygen molecule in water
slightly negative
Charge of hydrogen molecule in water
slightly positive
Define hydrogen bonding
primarily electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom
What properties does hydrogen bonding account for in water?
- High specific heat capacity
2. High latent heat of evaporation
Specific heat capacity
The energy needed to raise the temperature of 1g of substance by 1℃
Specific heat capacity of water
H bonds between molecules absorb at lot of energy therefore water takes a lot of energy to heat it up.
High latent heat of evaporation
It takes a lot of heat energy to break the H bonds in water, this is useful for organisms as it allows water to be a good cooling mechanism (e.g sweating)
Water is less dense when it freezes, describe the structure
Molecules are held further apart in ice because each molecule forms 4 H bonds to other molecules making a lattice structure. Less dense than L water allowing it to float
Elements in carbohydrates
Carbon, hydrogen and oxygen
In what three sugars do carbohydrates exist in?
Modnosaccarides, disaccaride and polysaccharides
How many carbon atoms in a polysaccharide?
8 or more
Glucose
An abundant monosaccharide, containing six carbon atoms (hexose sugar) and is highly soluble
Two structural isomers of glucose
Alpha and beta
Alpha glucose
Hydrogen above the OH on C1
Beta glucose
Hydrogen below the OH on C1
Condensation reaction
A reaction between two monosaccharides to from a disaccharide, a hydrogen atom on one monosaccharide bonds to an OH group releasing a molecule of water
Opposite of condensation reaction
Hydrolisis
What bond is formed in alpha glucose following a condensation reaction?
1-4 glycosidic bond
How does b-glucose join during a condensation reaction?
Every other one gets turn upside down in order to join chains
Pentose sugars
Pentose monosaccharides contain 5 carbon atoms and are long enough to form a ring (e.g maltose, sucrose and lactose)
Maltose
Formed from two glucose alpha 1-4 glycosidic bonds
Sucrose
Formed from glucose + fructose and forms alpha 1-2 glycosidic bonds
Lactose
Formed from galactose and glucose joined by a 1-4 glycosidic bond
Define polysaccharide
Polymers containing many monosaccharides linked via glycosidic bonds and are formed via condensation reactions
Examples of polysaccharides
Starch, cellulose and glycogen
Glycosidic bond
A type of covalent bond that joins and carbohydrate to another molecule
Starch
- Used for medium term storage in plants (NEVER ANIMALS)
- can be broken down to a-glucose
- found in seeds and tubers
- insoluble
- compact
Molecular structure of starch
Made of both amylose and amylopectin
Amylose
Made of condensations between alpha glucose, the are linked 1-4 , NO branches
Amylopectin
Long chains of a-glucose, straight chains linked 1-4 and branches linked 1-6
Glycogen
- Medium term storage for animals
- similar to starch, shorter chains and more branches
- more readily hydrolysed
- contains chains and branches
- insoluble
- does not diffuse out of cells (too big)
- a-glucose
Why does glycogen have short chains and many branches?
Easier for enzymes to access ‘free ends’ on the branches
Cellulose
- NOT storage provides structural purposes only
- made of b-glucose
- to form a straight chain each monomer rotates 180
- straight unbraced chains
- the H bonds alone are very weak but together create a stronger structure
- difficult to hydrolyse
What does Benedict’s test for?
Reducing sugars
Benedict’s test method
- Place sample in boiling tube
- add equal volume of Benedict’s reagent
- heat mixture gently in water bath for 5 minutes
Benedict’s test result
Positive = Brick red precipitate, Negative = Blue copper ions remain
Reducing sugar
any sugar that is capable of acting as a reducing agent all monosaccharides (glucose) and some disaccharides (maltose and lactose)
Non-reducing sugar
For example sucrose
Reagent test stops for non-reducing sugar
- add HCl (to hydrolyse the bond and break down to monosaccharides of sucrose) and heat in a water bath
- neutralise the solution with sodium hydrogen carbonate
- then carry out Benedict’s procedure and record observations
Test strips for glucose
The test strips are coated in a reagent. They are dipped into a test solution and compared to a colour chart
Iodine to test for stach
Add iodine dissolved in potassium iodide solution, if starch is present it will change form browny-orange to blue-black
