2.1.2: Biological molecules Flashcards
(47 cards)
How do hydrogen bonds form between water
molecules?
Water is polar: O more electronegative than H, so attracts electron density in covalent bond more strongly.
Forms O πΏ- (slightly negative) & H πΏ+ (slightly positive).
There are intermolecular forces of attraction between a lone pair on O πΏ- of one molecule & H πΏ+ on an adjacent molecule.
State 7 biologically important properties of water.
β reaches maximum density at 4β β high surface tension β incompressible β metabolite/ solvent for chemical reactions in the body β high specific heat capacity β high latent heat of vaporisation β cohesion between molecules
Why is the incompressible nature of water important for organisms?
Provides turgidity to plant cells.
Provides hydrostatic skeleton for some small animals e.g. earthworms.
Explain why ice floats on water. Why is this important
for organisms?
Ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other.
Insulates water in arctic climates so aquatic organisms can survive. Water acts as a habitat.
Why is the high surface tension of water important
for organisms?
Slows water loss due to transpiration in plants.
Water rises unusually high in narrow tubes, lowering demand on root pressure.
Some insects can βskimβ across the surface of water.
Why is water an important solvent for organisms?
Polar universal solvent dissolves & transports charged particles involved in intra & extracellular reactions e.g. PO4 3- for DNA synthesis.
Why are the high specific heat capacity and latent of
vapourisation of water important for organisms?
Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity.
Cooling effect when water evaporates from skin surface as sweat/ from mouth when panting.
Define monomer and polymer. Give some examples.
monomer: smaller units that join together to form larger molecules
β monosaccharides (glucose, fructose, galactose, ribose)
β amino acids
β nucleotides
polymer: molecules formed when many monomers join together
β polysaccharides
β proteins
β DNA/ RNA
What happens in condensation and hydrolysis
reactions?
Condensation: chemical bond forms between 2 molecules & a molecule of water is produced.
Hydrolysis: a water molecule is used to break a chemical bond between 2 molecules e.g. peptide bonds in proteins, ester bonds between fatty acids & glycerol in lipids.
Name the elements found in carbohydrates, lipids,
proteins and nucleic acids.
carbohydrates & lipids: C, H, O
proteins: C, H, O, N, S
nucleic acids: C, H, O, N, P
Whatβs the difference between βΊ-glucose and π½-glucose?
If the -OH group attached to it is below the ring, the molecule is alpha glucose.
If the -OH group is above the ring, the molecule is beta glucose.
Describe the properties of πΌ glucose.
β Small & water soluble = easily transported in bloodstream.
β Complementary shape to antiport for co-transport for absorption in gut.
β Complementary shape to enzymes for glycolysis = respiratory substrate.
Difference between ribose and deoxyribose?
ribose is a pentose sugar, whereas deoxyribose is a hexose sugar.
deoxyribose is found in RNA, whereas ribose is found in DNA.
ribose binds a phosphate at the 3β² position, whereas deoxyribose binds a phosphate at the 2β² position. deoxyribose has one less oxygen molecule than ribose
What type of bond forms when monosaccharides react?
(1,4 or 1,6) glycosidic bond
β 2 monomers = 1 chemical bond = disaccharide.
β Multiple monomers = many chemical bonds = polysaccharide.
Name 3 disaccharides. Describe how they form.
Condensation reaction forms glycosidic bond between 2 monosaccharides. β maltose: glucose + glucose β sucrose: glucose + fructose β lactose: glucose + galactose all have molecular formula C12H22O11
Describe the structure and functions of starch.
Storage polymer of πΌ-glucose in plant cells:
β insoluble = no osmotic effect on cells
β large = does not diffuse out of cells
made from amylose:
β 1,4 glycosidic bonds
β helix with intermolecular
H-bonds = compact
and amylopectin:
β 1,4 & 1,6 glycosidic bonds
β branched = many terminal ends
for hydrolysis into glucose
Describe the structure and functions of glycogen.
Main storage polymer of πΌ-glucose in animal cells
(but also found in plant cells):
β 1,4 & 1,6 glycosidic bonds.
β Branched = many terminal ends for hydrolysis.
β Insoluble = no osmotic effect & does not diffuse out of cells.
β Compact.
Describe the structure and functions of cellulose.
Polymer of π½-glucose gives rigidity to plant cell walls
(prevents bursting under turgor pressure, holds stem up).
β 1,4 glycosidic bonds.
β Straight-chain, unbranched molecule.
β Alternate glucose molecules are rotated 180Β°.
β H-bond crosslinks between parallel strands form microfibrils = high tensile strength.
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol & 3 fatty acids which forms ester bonds.
Contrast saturated and unsaturated fatty acids.
Saturated:
β contain only single bonds
β straight-chain molecules have many contact points
β higher melting point = solid at room temperature
β found in animal fats
Unsaturated:
β contain C=C double bonds
β βkinkedβ molecules have fewer contact points
β lower melting point = liquid at room temperature
β found in plant oils
Relate the structure of triglycerides to their functions.
β High energy:mass ratio = high calorific value from oxidation (energy storage).
β Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.
β Slow conductor of heat = thermal insulation e.g. adipose tissue.
β 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 & 1 hydrophilic polar phosphate head.
β Forms phospholipid bilayer in water = component of membranes.
β Tails can splay outwards = waterproofing e.g. for skin.
Are phospholipids and triglycerides polymers?
No; they are not made from a small repeating unit. They are macromolecules.
Describe the structure and function of cholesterol.
Steroid structure of 4 hydrocarbon rings.
Hydrocarbon tail on one side, hydroxyl group (-OH) on the other side.
Adds stability to cell surface phospholipid bilayer by connecting molecules & reducing fluidity.
