Biological Molecules Flashcards
Can you describe how hydrogen bonding occurs between water molecules?
A water molecule is H2O
O-H bond is a polar bond as
O is slightly negative
H is slightly positive
So it’s a polar molecule
So there is an attraction between water molecules
This force of attraction are called hydrogen bonds
Can you relate hydrogen bonding, and other properties of water, to the roles of water in living organisms?
Properties of water
7 and their explanations
Very high specific heat capacity
- a lot of energy required to change its temperature
- as a lot of energy is used to weaken/break hydrogen bonds
- rather than increase kinetic energy
Very high latent heat of vaporisation
- lots of thermal energy required to evaporate water
- which allows for cooling of organisms without losing lots of water
Bodies of water (eg ponds) contain dissolved oxygen
- which allows for aquatic animals to carry out aerobic respiration
Water in metabolic reactions
- used in hydrolysis and photosynthesis
- produced in condensation and aerobic respiration
Water is a good solvent
- used in transportation of substances eg blood plasma eg xylem
Cohesion of water molecules caused by hydrogen bonds
- eg transpiration stream in xylem
- eg surface tension for water as habitat for organisms
Ice is less dense than water
- so acts as insulator for water beneath
- and allows for water underneath to be lovable habitat
Explain six properties that make water important for organisms (6 marks)
- A metabolite in condensation/hydrolysis/photosynthesis/respiration
- A solvent so (metabolic) reactions can occur
- High heat capacity so buffers changes in temperature
- Large latent heat of vaporisation so provides a cooling effect (through evaporation)
- Cohesion (between water molecules) so supports columns of water (in plants)
- Cohesion (between water molecules) so produces surface tensions supporting (small) organisms
- Ice is less dense than water so insulates water beneath for survival of animals
Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to illustrate your answer (5 marks)
A condensation reaction joins two monomers together and forms a bond between monomers and releases water.
- For example , 2 alpha glucose (monomers) join to form a 1,4 glycosidic bond, water and maltose (starch)
A hydrolysis reaction breaks the bonds between the monomers by using water
- For example, By adding water to maltose (starch) , the 1,4 glycosidic bond is broken and alpha glucose molecules is produced
Suitable example is alpha glucose to starch/glucagon
Describe how the structures of starch and cellulose molecules are related to their functions. (5 marks)
Max 3 of each
Starch
1 large molecules so can not leave cell through cell membrane
2 molecule is insoluble in water so do not move into cell by osmosis ( osmotically inactive)
3 helical shape so compact structure
4 branched so glucose is easily accessible for enzymes to break down for respiration
Cellulose
1 long straight unbranched chains of beta glucose
2 provide rigidity as they withstand outwards force off cell contents
3 joined together by hydrogen bonds form macro fibrils
Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function
1 made from β-glucose;
2 and 3. joined by condensation to form 1,4 glycosidic bond
4. “flipping over” of alternate molecules;
- every 2nd beta glucose molecule is flipped
5. hydrogen bonds linking long straight chains;
6. cellulose makes cell walls strong;
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar, amylase in a sample (marks)
Lipid
1 Add equal amounts alcohol then water and shake
2 milky white emulsion forms, lipid is present, if not lipid is not present
Non- reducing sugar
- Do Benedict’s Test and stays blue/negative
- Boil with acid then neutralises with alkali
- Heat with Benedict’s and becomes red/orange (precipitate)
Amylase
- Add biuret (reagent) and becomes purple/vioelt/mauve/lilac
- Add starch, (leave for time), test for reducing sugar/absence of starch
There functions of triglycerides in living organisms
5 total
Production of phospholipids Energy source for respiration Energy storage Thermal insulation Electrical insulation
Explain how fatty acids in phospholipids allow for the formation of membranes
Fatty acids are hydrophobic
They form a phospholipid bilayer
Tails point inwards together
Similarities in molecular structure of cholesterol and glucose
Both have hydroxyl group
Both have oxygen
Both have carbon and hydrogen
Example formation of chitin molecule
Be careful chitin is made of beta molecules
Monomers are joined by condensation reaction
where water is removed
Every alternate glucose is flipped
As the OH group on C1 is in the wrong position
Forming straight chain
Structure of glucagon and how this allows it to perform its structure
7 marks
9 points
Contains alpha glucose used in respiration
Glucagon can be broken down by enzymes
A polysaccharide
It’s insoluble so does not effect water potential
Has 1,6 glycosidic bonds
Branched structure
So greater surface area for enzyme activity
As animals require rapid energy release
As they have a high metabolic rate
