Mark Scheme Answers Flashcards
How does the formation of enzyme substrate complexes increase the rate of reaction? (2)
• Reduces the activation energy
• Due to the bending of bonds
How does a sugar called Lyxose increase the rate of reaction by binding to an enzyme (3)
• Binding alters the tertiary structure of the enzyme
• Active site changes shape
• Lyxose makes faster enzyme-substrate complexes to be formed
How does a change in hydrogen and ionic bonds of an enzyme affect its structure (1)
Changes the shape of the active site/ tertiary structure changes
What is the function of DNA helicase (1)
Breaks hydrogen bonds
Describe the role of enzymes in the digestion of proteins in a mammal
(Application, outline specific words) (4)
• Hydrolysis of peptide bonds
• Endopeptidase act in the middle of protein/polypeptide
• Exopeptidase act at the end of protein/polypeptide
• Dipeptidase acts on dipeptide/between two amino acids
What is role of single stranded fragments
(Apply your knowledge of single strands) (2)
• Used as a template
• Determines the order of nucleotide or bases
Describe the roles of iron ions, sodium ions and phosphate ions in cells (6)
Iron ions
* Haemoglobin binds/associates with oxygen/ haemoglobin transports/loads oxygen
Sodium ions
* Co-transport of glucose/amino acids (into cells)
* Because sodium is moved out by active transport
* Creates a sodium concentration/diffusion gradient
* Affects osmosis or water potential
Phosphate ions
* Affects osmosis/water potential
* Joins nucleotides/in phosphodiester bonds/in backbone of DNA/RNA in nucleotides
* Used in/to produce ATP
* Phosphorylates other compounds making them more reactive
* Hydrophilic/water soluble part of phospholipid bilayer/membrane
Explain how the active site of an enzyme causes a high rate of reaction (3)
• Lowers the activation energy
• Induced fit causes the active site to change shape
• Enzyme-substrate complexes can be formed cause bonds break/form
Suggest why (NO3-) are needed to make DNA (1)
- Nitrate ions contain nitrogen/N which forms part of the organic base in DNA
Kangaroos have been observed licking saliva onto their forearms in hot weather.
Using your knowledge of the properties of water, explain why this behavior helps the kangaroos to keep cool (3)
- Because water has a high latent heat of vaporization
- A lot of energy is removed from the Kangaroo’s body when the water in saliva evaporates from its forearms
- This reduces the kangaroos body temperature
Koalas have been observed to hug trees in hot weather.
This is thought to be because the trunks of trees are usually cooler than the surrounding air.
Tree trunks contain a lot of water.
Explain how this could contribute to the tree being cooler than the surrounding air (2)
• Water has a high specific heat capacity
• Which means it doesn’t heat up as quickly as the air
Describe the induced-fit model and how an enzyme acts as a catalyst (4)
- Reduces the activation energy
- Substrate binds to active site/enzyme
- Enzyme substrate complexes are formed
- Active site changes its shape slightly so it is COMPLIMENTARY to the substrate
Suggest and explain ways in which an enzyme-rate of reaction can be stopped at intervals (3)
- Add a strong acid/alkali to denature the enzyme
- Put in ice/fridge/freezer to lower the kinetic energy so that enzyme substrate complexes do not form
- Add a high concentration of an inhibitor so enzyme-substrate complexes do not form
Describe how the structures of starch and cellulose molecules are related to their functions (4)
Starch
• Helical/spiral shape so compact
• Large molecule/insoluble so osmotically inactive
• Branched so glucose is easily released for respiration
• Large molecule so cannot leave cell/cross cell-surface membrane
Cellulose
• Long, straight/unbranched chains of beta glucose
• Joined by hydrogen bonding
• To form micro/macro fibrils
• Provides rigidity/strength
Titin is a fibrous protein. Pepsin is a globular protein.
Compare the properties and functions of fibrous proteins in the human body. (4)
FIBROUS PROTEINS
Properties
• Insoluble
• Elongated/long/stands
• Strong/tough
• Flexible
Functions
• For structure
• Collagen in bone/ cartilage/ connective tissue/ tendons/ ligaments/skin/blood vessels
• For protection: Keratin in skin/hair/nails
• To give elasticity/ elastic properties
• For contraction/ mechanical movement
• Actin/myosin, in muscle
• Mictotubules in cilia/ flagella/spindle/cytoskeleton