B3 - Biological molecules Flashcards
Why is water a polar molecule?
- Oxygen is more electronegative, so has stronger attraction to the electrons in the covalent bond.
- Oxygen is partially negative, Hydrogen is partially positive (due to its weaker electronegativity compared to the oxygen)
- Uneven share of electrons created a dipole (positive and negative region)
Water has strong hydrogen bonding between hydrogens and oxygens of adjacent molecules, which gives water its properties. What are these properties of water? (6)
High specific heat capacity:
- Lots of thermal energy required to raise temp of 1kg of a substance by 1d.c
- Large energy to break H-bonds.
-Temperature doesn’t fluctuate drastically
- Provides suitable habitats
- Maintains temp in body and cells.
High specific latent heat of vaporisation:
- Large energy required to change state liquid to gas(due to many H-bonds).
- acts as a coolant for organisms as only a little water needs to evaporate for organism to lose a lot of heat.
Solvent:
- water = polar, so can dissolve ions
- Act as medium for chemical reactions
- Help transport dissolved compounds in & out cell.
High boiling point:
-large energy to break H-bonds & inc H2O temp
Ice:
- Ice less dense than liquid state, as H-bonds produce a solid lattice structure with polar molecules more spread out in a fixed position.
- Same volume but more area covered.
- Ice floats above water and can insulate aquatic organisms living underneath.
Cohesion & adhesion:
- H-Bonds allow strong cohesion between water molecules (stick together)
- creates surface tension where water body meets air, forming a film for insects to walk on
- adhesion to other molecules e.g. cellulose to move up xylem.
Name 3 monosaccharides (one simple sugar)
- glucose
- galactose
- ribose
- fructose
Lactose and sucrose are both disaccharides (double sugars). What monosaccharides are they made from?
Lactose:
glucose + galactose
Sucrose:
glucose + fructose
What is the difference between alpha and beta glucose?
Alpha:
OH group is on the bottom of carbon 1/ below the ring
Beta:
OH group is o the top of carbon 1/ above the ring.
Glucose is highly soluble and can be dissolved in the cytosol of the cell. How is glucose so soluble?
- Due to it’s polarity It can H-bond to water
- H-Bond forms between hydroxyl group and water
What is the bonding called between monosaccharides?
glycosidic bonding
What is a condensation reaction in carbohydrates?
when the hydroxyl groups of two monosaccharides join to form a disaccharide.
‘condensation’ because water is also released.
What are the 2 polysaccharides in starch? Explain their bonding.
Amylose:
- alpha glucose joined by 1-4 glycosidic bonds
- bonding angle causes chain to twist & form helix shape, which is stabilised by H-bonding.
- more compact, less soluble.
Amylopectin:
- has 1-4 AND 1-6 glycosidic bonds
- gives it a branching shape
What are the differences between starch and glycogen?
glycogen:
- Stores as small granules.
- Animals store carbohydrates as glycogen (eat starch but store as glycogen)
- less dense, more soluble than starch so can be broken down more rapidly due to higher metabolic requirements in animals.
Starch:
- Plants store glucose as starch
- stored as starch grains in plastids
- plastids have green chloroplasts and colourless amyloplasts
What is a hydrolysis reaction?
- Reverse of condensation
- Addition of water to break bonds
e.g. starch & glycogen undergo hydrolysis reactions to release glucose.
Describe the properties of cellulose.
- fibrous
- very strong & prevents cell bursting
- structural role
- beta 1-4 glycosidic bonds (has to flip to react)
- Hard to break down due to straight chain molecule
What test is used for carbohydrates?
Benedict’s - Copper (II) sulfate (alkaline solution)
Describe the set up for benedict’s test of a reducing sugar. (3)
- monosaccharides = reducing sugars (donate electrons to reduce another molecule)
1) Place sample in boiling tube. If not liquid form, grind or blend in water
2) Add equal volume of benedict’s solution
3) Heat mixture gently in boiling water ~5 mins.
Describe and explain the colour changes in a Benedict’s test for a reducing sugar.
Reducing sugars add electrons to blue Cu2+ ions, making a brick-red precipitate, indicating a positive result.
Traffic light colour change
green: low conc
yellow: medium conc
red: high conc
Describe the benedict’s test for a non-reducing sugar.
- nonreducing won’t react with solution
- stays blue = negative result
- if sucrose (non-reducing) boiled with HCl to hydrolyse into glucose + fructose, then warmed with benedict’s, then the test will be positive.
What is the test for starch?
- Iodine test
- Iodine drops dissolved in potassium iodide solution and mixed with sample.
- If turns purple/black starch is present = positive result.
Lipids are stored in adipose tissue. What are the three main roles of adipose tissue? (3)
Heat insulation:
- under skin, reduces heat loss in mammals
Protection:
- Around delicate organs, cushioning them against impacts
Hormonal communication:
- lipids are the basis or many hormonal molecules.
What are the two types of lipids? Explain them in detail.
Triglycerides:
- Main components of fats & oils
- non polar & hydrophobic
- consists of glycerol (alcohol) and fatty acids (carboxylic acids, which can be saturated, mono-unsaturated, or poly-unsaturated)
Phospholipids:
- modified triglycerides (contain phosphorus)
- 2 fatty acids and 1 phosphate ion bonded to 1 glycerol
- Amphipathic (hydrophilic/polar phosphate & hydrophobic/non-polar fatty acids)
Phospholipids can form bilayers and monolayers. How are they formed?
hydrophobic tails point to centre of sheet, protected from water by hydrophilic heads.
Phospholipids can form bilayers and monolayers. How are they formed?
hydrophobic tails point to centre of sheet, protected from water by hydrophilic heads.
Triglycerides are formed by esterification. How is an ester bond formed?
hydroxyl (OH) group of glycerol bonds with the carboxyl group (COOH) of fatty acids.
