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
Titin is a fibrous protein. Pepsin is a globular protein.
Compare the properties and functions of globular proteins in the human body (6)
Properties
• Soluble
• Spehrical/ball-shaped
• have, 3D/tertiary shape/structure
• Specific/complementary
• Conjugated/ contain a prosthetic group
• temperature/ pH, sensitive
• Hydrophilic on outside
Functions
• Enzymes/ metabolic rate/ to catalyse reactions to lower the activation energy
• Hormones/ receptors for cell signalling
• Antibody/ for immunity/ defence against infection
• to transport substances across cell membranes
• Carrier/ channel/pump
• To transport substances in blood
• Haemoglobin
• To package/ organise DNA
Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction (3)
- Attaches to the enzyme at a site other than the active site
- Changes the shape of the active site/ changes the tertiary structure of the enzyme
- The active site and substrate are no longer complementary so less/ no substrate can fit/bind
No large lipid droplets are visible with the optical microscope in the samples from suspension A( lipid and bile salts).
Explain why? (2)
• Emulsification
• Optical microscopes have a low resolution
How do bases bind (1)
Thymine/ BrdU is to adenine on template strand
Describe the biochemical tests you would use to confirm the presence of a non-reducing sugar and amylase in a sample (4)
NON-REDUCING SUGAR
• Do Benedict’s test and stays blue/negative
• Boil with acid then neutralise with alkali
• Heat with Benedict’s and becomes red/orange precipitate
AMYLASE
• Add biuret (reagent) and becomes purple/violet/mauve/lilac
• Add starch (leave for a time) test for reducing sugar/ absence of starch
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalysed only this reaction (4)
• Active site of enzyme has a specific shape/ tertiary structure
• ACTIVE SITE is complimentary to substrate
• Only maltose can bind
• To form enzyme substrate complexes
Suggest three reasons why it is more efficient to attach lactase to beads (3)
• Lactase can be reused/not washed away
• Allows a continuous process
• The enzyme is more stable
Monosaccharides and disaccharides are sweet. The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cows milk containing lactose explain why? (Application) (2)
- Lactose is hydrolysed to form galactose and glucose
- So more sugar molecules
Describe and explain how centrifuging a culture allows scientists to obtain a cell-free liquid (Knowledge) (3)
• Large/dense/heavy cells
• Form pellet/ move to bottom of the tube when centrifuged
• Liquid/supernatant can be removed
Give one function of lysosomes (1)
Break down cells
H.pylori cells produce an enzyme that neutralises acid.
Suggest one advantage to the H.pylori of producing this enzyme (2)
• To stop them from being destroyed/ killed
• By stomach acid
A principle of homeopaths is is the maintenance of a constant internal environment. An increase in the concentration of carbon dioxide would change the internal environment and blood pH.
Explain the importance of maintaining a constant blood pH (3)
• Named protein/enzyme in blood is sensitive to/affected by change in pH (Haemoglobin)
• Resultant change of tertiary structure
• Described effect on the named protein or enzyme (less oxygen binds to haemoglobin, less transport across membranes, fewer substances can fit the active site, fewer enzyme-substrate complexes)
The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different (2)
• Phosphate
• Instead of one of the fatty acids/ and two fatty acids
How is a non functional protein formed? (3)
• Change in the base sequence leading to a change in amino acid sequence
• Change in hydrogen/ionic/disulphide bonds
• Substrate not complementary/no enzyme substrate complexes formed
Give a general reason why different species are found in different depths (1)
• Other abiotic/biotic factors e.g oxygen concentration
What variables are controlled in an enzyme-controlled reaction (2 for 1 mark) Knowledge
- pH
- Concentration of the enzyme
- Volume of substrate concentration
What happens after an enzyme is denatures, application
- The substrate is still available
- But not converted to a product
The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how (1)
• Between NH and C=O group
Two proteins have the same number and type of amino acids but different tertiary structures explain why? (2)
• Different sequence of amino acids
• Position of hydrogen, ionic a bind is different
The new antibiotic is safe to use in humans because it does not inhibit the ATP
synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase is
inhibited (1)
Human ATP synthase has a different tertiary
structure to bacterial ATP synthase
OR
Human ATP synthase has a different shape
active site to bacterial ATP synthase
OR
Antibiotic cannot enter human cells/mitochondria
OR
Antibiotic not complementary (to human ATP
synthase);
Describe how an enzyme can be phosphorylated. (2)
- Attachment/association of (inorganic) phosphate
(to the enzyme); - (Released from) hydrolysis of ATP
OR
(Released from) ATP to ADP + Pi;
