2.2 - Biological Molecules Flashcards
Draw a water molecule and label the charges on the atoms
Delta positive charge on H
Delta negative charge on O
What bonds are formed between the hydrogen and oxygen of different water molecules?
Hydrogen bonds
What does it mean for a molecule to be polar?
It means the molecule has an unequal spread of electrons so has partial charges within the molecule
How are the electrons shared within a water molecule? Why?
Unequally, electrons spend more time around oxygen because:
- Oxygen is highly electronegative element, more electronegative than hydrogen
- Therefore the oxygen atom attracts electrons towards it
How is a hydrogen bond drawn?
A dotted line
Between which atoms does a Hydrogen bond form?
Hydrogen and Oxygen of different water molecules
What is the difference between adhesion and cohesion?
Adhesion is when water ‘sticks’ to another surface whereas cohesion is when water is attracted to other water molecules.
What is meant by a high specific heat capacity of water?
A lot of energy is require to increase the temperature of water
Why does water have a high specific heat capacity?
- the hydrogen bonds between the molecules must be overcome to increase the temperature of water
- this requires energy
Why does ice float on liquid water?
- When water freezes a crystal lattice structure is formed so the molecules are held further apart
- this decreases density
Explain what is meant by the phrase ‘like dissolves like’
- polar substances dissolve other polar substances
- non-polar substances dissolve non-polar substances
Name 6 physical properties of water
- High specific heat capacity
- High latent heat of evaporation
- Ice floats on liquid water
- Surface tension
- Can act as a solvent for polar molecules
- Good transport medium
How does a high latent heat of evaporation of water help organisms to survive?
A lot of energy is required to change water from liquid to gas therefore it is very effective in cooling surfaces by evaporation. This helps animals in hot environments (E.g dogs panting)
How does the ability of ice to float on liquid water enable organisms to survive? (3 ways)
1-Provides LAND animals a means of sheltering and catching food even in freezing temperatures
2-Floating ice insulates water floating underneath, assisting aquatic animals survival in low temperatures as they do not freeze
3-Ice insulates water so water remains liquid and organisms can still swim and catch prey
How does water as a liquid assist the survival of organisms? (5 ways)
- Water is polar so is a good solvent for polar molecules
- As good solvent water can transport vital substances around organisms (e.g. glucose in the blood)
- Can dilute toxic substances within an organism
- Cohesion gives water surface tension which provides invertebrates with a habitat
- High specific heat capacity means water provides aquatic organisms with a thermostable habitat, ensuring enzymes work optimally
Suggest how water acting as a solvent for ions (such as nitrates) can contribute to a stable environment for aquatic organisms
- Plants are able to absorb the dissolved nitrates and grow well
- Plants provide food source for other organisms
- Plants photosynthesise and produce oxygen which is needed by other organisms for survival
- Nitrates are used to build amino acids in plants
Define Hydrophilic
Readily attracted to water
Define Hydrophobic
Repelled by water
Why do hydrogen bonds form between hydrogen and oxygen atoms of different water molecules?
Hydrogen has a partial positive charge and Oxygen has a partial negative charge (due to the electronegativity of oxygen) so they attract and form a hydrogen bond.
What is the function of carbohydrates?
To provide energy. This can be immediately (e.g. glucose) or as stored energy (e.g. glycogen in animals and starch in plants).
What are the 3 broad groups carbohydrates can be split into?
Monosaccharides, disaccharides, and polysaccharides
What is the general formula for monosaccharides?
Cn(H2O)n
What properties must a substance have to be classed as a sugar?
- Must dissolve in water
- Must be crystalline
- Must be sweet to taste
Are all monosaccharides classed as sugars?
Yes
What is the general name for monosaccharides containing:
a) 3 carbons
b) 5 carbons
c) 6 carbons
a) triose
b) pentose
c) hexose
Give an example of a 3 carbon sugar
G3P
How is sucrose formed?
A condensation reaction between alpha glucose and fructose
What hydrolyses sucrose?
Sucrase
Give 3 examples of disaccharides
Maltose, sucrose, and lactose
What kind of bond forms between sugars in a condensation reaction?
A glycosidic bond
How is maltose formed?
From a condensation reaction between two alpha glucose molecules
What hydrolyses maltose?
Maltase
How do two alpha glucose molecules bond to form maltose?
There is a reaction between the hydroxyl group of Carbon 1 of one molecule and Carbon 4 of the other molecule (be careful to specify C1 of one molecule and C4 of another)
Is the bond formed in the condensation reaction of alpha glucose above or below the plane of the ring?
Below
Give the two functions of polysaccharides
1) Energy storage
2) Structure in the form of cellulose in plant cell walls or chitin in insect wings and fungi walls
In what form is energy stored in:
i) plant cells
ii) animal cells
i) Starch
ii) Glycogen
Why are polysaccharides not classed as sugars? (3 reasons)
- They do not taste sweet
- They are not crystalline
- They do not dissolve in water
What are the three physical properties of both starch and glycogen that make them excellent storage molecules?
- They are insoluble in water
- They form very compact molecules
- They can be easily hydrolysed to release a glucose
(i) How does Starch and glycogen’s insolubility in water make them good storage molecules?
(ii) What would happen if they were soluble in water?
(i) They do not dissolve and therefore do not affect the water potential of cells
(ii) They would dissolve and change the water potential of the cell, causing water to move into the cell by osmosis and cause cell damage
Why is the ability to form compact molecules favourable for a storage molecule?
A lot of the molecules can fit into a small space, meaning more efficient storage
Why is it beneficial that starch and glucose can be easily hydrolysed?
Easy hydrolysis means that both starch and glycogen can provide a readily available source of glucose for respiration and so provide quick release energy.
What reacts to form glycogen?
Alpha glucose
What type of bonding occurs in glycogen? Why?
1,4 and 1,6 glycosidic bonding
- This allows for branching so each molecule has many ends where glucose can be added
- This means glycogen is a more compact molecule
- This means more terminal glucose molecules that can be simultaneously hydrolysed
What are the two components of starch?
Amylose and Amylopectin
i) What happens to the shape of amylose once it has been formed?
ii) What shape does this give it?
iii) What causes this change in shape to occur?
i) It coils
ii) Giving a helical shape
iii) Hydrogen bonds form within the coil
i) Which molecules make up amylose?
ii) What kind of bonding links these together?
iii) Therefore what kind of molecules is produced?
i) Alpha-glucose
ii) 1,4 glycosidic bonds
iii) Linear
i) What molecules make up amylopectin?
ii) What kind of bonding is present in amylopectin?
iii) Therefore which molecule is amylopectin similar to?
i) Alpha-glucose
ii) 1,4 and 1,6 glycosidic bonds
iii) Glycogen
i) How can the presence of starch be tested for?
ii) What is observed if starch is present?
iii) Why does this occur?
i) Potassium iodide solution is added
ii) The solution will go from being orange/brown to black/blue
iii) The iodine sits in the coils of the amylose component of starch, this complex appears blue/black
Where is cellulose found?
In plant cell walls
What is the monomeric unit of cellulose?
Beta glucose
What is the structure of a glycerol molecule?
Draw a simplified version of a phospholipid
Draw a phospholipid bilayer
What is the structure of a glycerol molecule?
Draw a phospholipid bilayer
Draw a simplified version of a phospholipid
