Unit 1 - Biological Molecules Flashcards
(27 cards)
1
Q
What is hydrolysis?
(2 marks)
A
- The breaking of a chemical bond between two molecules
- Via the insertion of a molecule of water
2
Q
What is a condensation reaction?
(2 marks)
A
- The forming of a chemical bond between two molecules
- Via the removal of a molecule of water
3
Q
Compare and contrast glycogen and cellulose.
(4 marks)
A
- Cellulose is a polymer of β-glucose monomers whereas glucose is a polymer of α-glucose
- Cellulose molecules are linear whereas glycogen is branched
- Cellulose molecules are linear whereas glycogen is coiled & compact
- Glycogen has 1,4- and 1,6- glycosidic bonds whereas cellulose has only 1,4- glycosidic bonds (think chemistry)
4
Q
How is the structure of glycogen related to it’s function?
(5 marks)
A
- Insoluble in water so doesn’t affect water potential (osmotically inactive)
- Coiled, compact structure to store a large amount of glucose in a small area
- Polymer of glucose so can provide glucose for respiration
- Branched structure to provide more ends for a fast hydrolysis of glucose
- Large molecule, so cannot cross the stell membrane (ergo it is stored)
5
Q
Describe the test for a reducing sugar.
(2 marks)
A
- Heat with Benedict’s reagent
- Colour change from blue to brick-red
6
Q
Describe the test for a non-reducing sugar.
(4 marks)
A
- Heat with Benedict’s reagent and no colour change
- Boil with HCl
- Neutralise with NaOH
- Re-heat with Benedict’s reagent and colour change from blue to brick red
7
Q
Describe the test for starch.
(2 marks)
A
- Add potassium iodide solution
- Colour change from brown to blue-black
8
Q
Describe how triglycerides are formed.
(3 marks)
A
- One glycerol and three fatty acids
- Condensation reactions occur, three molecules of water are removed
- Ester bonds are formed
9
Q
Compare and contrast triglycerides and phospholipids.
(8 marks)
A
- Both contain ester bonds
- Both contain glycerol
- Both contain fatty acids that may be saturated or unsaturated
- Both are insoluble in water
- Both contain C, H, O and phospholipids also contain P
- Triglycerides have three fatty acids whereas in phospholipids one fatty acid is replaced by a phosphate group
- Triglycerides are fully hydrophobic and non-polar whereas phospholipids have both hydrophilic and hydrophobic reigions
- Phospholipids can form a bilayer whereas triglycerides cannot
10
Q
Describe how an ester bond is formed in a phospholipid molecule.
(2 marks)
A
- Condensation reaction
- Between a molecule of glycerol and two fatty acids
11
Q
Describe the test for lipids.
(3 marks)
A
- Dissolve the sample in ethanol and shake gently
- Then add water
- A white milky emulsion forms
12
Q
Describe the structure of proteins.
(7 marks)
A
- Polymer of amino acids
- Joined by peptide bonds
- Formed by condensation reactions
- The primary structure is the unique sequence of amino acids that form the polypeptide chain
- The secondary structure is where the primary structure folds due to hydrogen bonding
- The tertiary structure is where the primary structure folds further into a unique 3D shape due to ionic bonds and disulphide bridges between R-groups
- The quarternary structure is when there is more than one polypeptide chain
13
Q
Describe the tests for proteins.
(2 marks)
A
- Add biuret’s reagent
- Colour change from blue to lilac
14
Q
Describe the induced fit model of enzymes.
(3 marks)
A
- Active site is not perfectly complementary to the substrate
- The shape of the active site changes as the substrate binds
- Bending bonds in the substrate (leading to a quicker reaction)
15
Q
Describe how higher temperatures increase the rate of enzyme activity.
(4 marks)
A
- Particles have more kinetic energy
- More movement of particles
- More frequent collisions between substrates and active sites
- More formation of enzyme-substrate complexes
16
Q
Describe how an enzyme becomes denatured due to high temperatures.
(5 marks)
A
- Heat above the optimum breaks hydrogen bonds in the enzyme structure
- This causes the tertiary structure of the enzyme to change shape
- So the active site changes shape
- The substrate is no longer complementary to the active site
- Fewer enzyme-substrate complexes can form
17
Q
Describe how an enzyme becomes denatured due to changes in pH.
(5 marks)
A
- Ionic bonds holding the tertiary structure together break
- This causes the tertiary structure of the enzyme to change shape
- So the active site changes shape
- The substrate is no longer complementary to the active site
- Fewer enzyme-substrate complexes can form
18
Q
Describe how increasing the substrate concentration affects the rate of reaction.
(2 marks)
A
- High initial rate of reaction as there is an excess of substrate
- Levels off eventually as the substrate is used up
19
Q
Describe and explain the temperature graph of enzyme reaction rate.
(5 marks)
A
- Initial rate of reaction is faster
- As molecules have a greater kinetic energy
- More enzyme-substrate complexes can form (due to more collisions)
- Graph levels off
- As the substrate is used up
20
Q
Compare and contrast competitive and non-competitive enzyme inhibition.
(3 marks)
A
- A competitive inhibitor binds to the active site of an enzyme whereas a non-competitive inhibitor binds to an allosteric site on the enzyme
- A competitive inhibitor does not cause a change in the shape of the active site whereas a non-competitive inhibitor does
- A competitive inhibitor can be overcome with higher substrate concentrations whereas a non-competitive inhibitor can not
21
Q
Describe DNA replication.
(6 marks)
A
- DNA helicase unwinds the double helix & breaks hydrogen bonds between complementary base pairs
- Both strands act as templates
- Free DNA nucleotides line up in complementary pairs (A-T, C-G)
- DNA polymerase joins adjacent nucleotides
- Via the formation of phosphodiester bonds
- Each new DNA molecule consists of one old and one new strand
22
Q
Describe the structure of DNA.
(5 marks)
A
- Polymer of nucleotides
- Each nucelotide is formed from deoxyribose, a phosphate group and a nitrogen-containing base
- Contains phosphodiester bonds between nucleotides
- Double helix held by hydrogen bonds between complementary bases
- Thymine pairs with adenine, guanine pairs with cytosine
23
Q
Describe and explain how the structure of DNA allows accurate replication.
(4 marks)
A
- Two strands, therefore semi-conservative replication can occur
- Hydrogen bonds between strands are weak, allowing strands to separate
- Bases can act as a template, due to complementary base pairing
- DNA contains one parent strand and one new strand
24
Q
Describe how a phosphodiester bond is formed between two nucleotides in a DNA molecule.
(3 marks)
A
- Condensation reaction occurs
- Between phosphate group and deoxyribose
- Catalysed by DNA polymerase
25
What are the uses and properties of ATP as an energy source?
(5 marks)
- Releases a relatively small amount of energy, so little energy is lost as heat
- Releases energy instantaneously
- Phosphorylates other compounds to make them more reactive
- Can be rapidly resynthesised
- Does not leave cells
26
Compare the structure of ATP with that of a DNA nucleotide.
(3 marks)
- ATP has ribose whereas DNA has deoxyribose
- ATP has three phosphate groups whereas DNA only has one
- The base in ATP is always adenine whereas in DNA it varies (A, C, G, T)
27
What are the properties that make water important for organisms.
(6 marks)
- It is a metabolite in important processes such as condensation, photosynthesis, respiration, etc
- A solvent so metabolic reactions can occur in solution
- High heat capacity buffers changes in temperature, maintaining aquatic habitats
- Large latent heat of vaporisation so it can provide a cooling effect through evaporation
- Cohesion between water molecules produces surface tension to support small organisms
