Biological Molecules Flashcards
How do hydrogen bonds form between water molecules?
Water is polar: O is more electronegative than H so attracts electron density in covalent bond more strongly.
This creates a delta negative charge on the O and a delta positive charge on the H.
There are intermolecular forces between a lone pair on the delta negative O of one molecule and the delta positive H on an adjacent molecule.
State 7 biologically important properties of water.
- high latent heat of vaporisation (energy to change from liquid to gas) therefore evaporation of sweat is an effective cooling mechanism
- High specific heat capacity which makes it a thermally stable environment for aquatic organisms
- Hydrogen bonds make the ice form a lattice when it solidifies so it expands which provides a habitat for some animals and insulates the water underneath due to ice being less dense than water
- Effective solvent so allows plants to take up nitrates through their roots
- Cohesion (water molecules sticking together) helps transpiration stream
- Adhesion (water molecules sticking to other things) allows lignin to be attracted to xylem which helps the transpiration stream
- Surface tension as hydrogen bonds are strong enough to allow invertebrates to walk om water providing a good habitat
Water is transparent allowing plants underwater to photosynthesise
Why is the incompressible nature of water important for organisms?
- Provides turgidity to plant cells
Define monomer and polymer.
monomer = smaller units that join together to make larger molecules
polymer = molecules formed when many monomers join together
Give some examples of monomers.
monosaccharides (glucose, fructose, ribose, galactose)
amino acids
nucleotides
Give some examples of polymers.
Polysaccharides (starch, cellulose, glycogen)
proteins
DNA
What happens in condensation reactions?
Chemical bond forms between two molecules and water molecule is produced
What happens in a hydrolysis reaction?
A water molecule is used to break a chemical bond between two molecules
Give some examples of hydrolysis reactions.
Breakingof a chemical bond between two molecules:
- Peptide bonds in proteins
- Ester bonds between fatty acids
- Glycerol in lipids
Name the elements found in carbohydrates, lipids, proteins and nucleic acids.
- Carbohydrates and lipids: C, H, O
- Proteins: C, H, O, N, S
Nucleic acids: C, H, O, N, P
How do you draw alpha glucose?
hexose monosaccharides (6 carbons) OH goes below the H
How do you draw beta glucose?
hexose monosaccharides (6 carbons) OH goes above the H
Describe the properties of alpha glucose.
- Small and water soluble so easily transported in bloodstream
How do you draw the structure of ribose?
Pentose monosaccharide (5 carbons) OH is above the H
What types of bond forms when monosaccharides react?
1,4 or 1.6 glycosidic bond
If there are 2 monomers then only 1 bond will form and it will create a disaccharide
If there are many monomers then many bonds will form and it will create a polysaccharide.
Name 3 disaccharides and describe how they form.
Condensation reaction forms glycosidic bonds between two monomers:
maltose = glucose + glucose
sucrose = glucose + fructose
lactose = glucose + galactose
Describe the structure and function of starch.
Starch is a storage polymer of alpha glucose in plant cells as it is :
- insoluble so has no osmotic effect on cells
- large so doesnt diffuse out of cells
Starch is made from amylose and amylopectin.
What is the difference between amylose and amylopectin?
Amylose has:
- 1,4 glycosidic bonds
- Alpha glucose
- is coiled structure with intermolecular hydrogen bonds - is compact
Amylopectin has:
- 1,4 and 1,6 glycosidic bonds
- coiled structure
- alpha glucose
- is branched so has many terminal ends for hydrolysis into glucose
Describe the structure and function of glycogen.
Main storage polymer of alpha glucose in animal cells
Has 1,4 and 1,6 glycosidic bonds
Branched so has more terminal ends for hydrolysis into glucose
Insoluble so has no osmotic effect and does not diffuse out of cells
Compact
Describe the structure and function of cellulose.
Polymer of beta glucose which aids rigidity of plant cell walls
1,4 glycosidic bonds
Straight chain unbranched molecule
Alternate glucose molecules are rotated 180 degrees so the OH can bond with the H and make water (condensation reaction)
Hydrogen bond cross-links between parallel strands form microfibrils
Contrast saturated and unsaturated fatty acids.
Saturated:
- Contain only single bonds
- Straight chain molecules have many contact points
- highermelting points - solid at room temp
- found in animal fats
Unsaturated:
- Contains 1 or more carbon carbon double bonds
- “kinked molcules” have fewer contact points
- lower melting point = liquid at room temperature
- found in plant oils
How do triglycerides form?
Condensation reactions occur between one molecule of glycerol and 3 fatty acids which forms ester bonds
Relate the structure of triglycerides to their function.
- High energy: mass ratio = high calorific value from oxidation
- Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
- Slow conductor of heat = thermal insulation
- Less dense than water = buoyancy of aquatic animals
Describe the structure and function of phospholipids.
Amphipathic: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
- Forms phospholipid bilayer in water = component of membranes
- Tails can splay outwards = waterproofing e.g for skin
