biolmol2

Question 1

List all factors affecting enzyme activity.

Answer 1

Temperature, pH, [enzyme], [substrate], competitive and non-competitive inhibition.

Question 2

How does temperature affect enzyme activity?

Answer 2

1. Increased T = molecules have a higher KE.
2. More successful collisions between enzymes and substrate per unit time - more E-S complexes formed per unit time.
3. However, excessive vibration from high temperatures (usually 60+ degrees) can break bonds holding the enzyme’s tertiary structure together - denatured.

Question 3

How does pH affect enzyme activity?

Answer 3

1. Change in pH alters the charges on the amino acids that make up the enzyme’s active site - no E-S complexes can be formed as substrate can’t attach.
2. Could cause the bonds maintaining the tertiary structure to break - i.e. interferes with the ionic bonds etc. in tertiary structure. This alters the shape of the active site and therefore prevents E-S complexes from forming.

Question 4

How does [enzyme] affect enzyme activity?

Answer 4

1. Increase in [enzyme] = increase in rate as more E-S complexes formed per unit time - more likely collisions between enzymes and their substrate per unit time.
2. But if [substrate] is limited, there are enough active sites to accommodate all the available substrate molecules - no further increase in rate.

Question 5

How does [substrate] affect enzyme activity?

Answer 5

Assuming a fixed [enzyme]:

1. [Substrate] is steadily increased, the rate increased in proportion initially - limited number of substrate molecules for enzymes.
2. More substrate added until Vmax (max rate) is reached - all active sites are full so adding more makes no difference.
3. [Substrate] decreases with time, so rate also decreases with time - therefore the initial rate is the highest rate during a reaction.
4. Rate levels off if substrate in excess.

NB = On a volume of x produced by y enzyme/time graph, if line tails off, it is likely because all substrate used up.

Question 6

Describe competitive enzyme inhibition.

Answer 6

1. Inhibitor has similiar structure to the substrate complementary to the enzyme.
2. Occupies the enzyme’s active site, competing with the substrate molecules.
3. This prevents E-S complexes from being formed.

NB = the relative [substrate]/[inhibitor] determines how much inhibition

i. e. high [inhibitor] = little substrate reaches enzyme active site.
i. e. high [substrate] = will increase chances of substrate reaching enzyme active site and increases rate of inhibited reaction, up to a certain point.

Question 7

Describe non-competitive inhibition.

Answer 7

1. Inhibitors bind elsewhere on the enzyme away from the active site.
2. Enzyme shape and therefore active site shape changes.
3. Prevents E-S complexes from forming as substrate cannot bind.
4. Increase in [substrate] won’t make any significant difference.

Question 8

How can we see if an enzyme-controlled reaction is being inhibited by competitive or non-competitive inhibition?

Answer 8

Increase the [substrate] and observe rate.

If rate increases, competitive inhibition.
If rate stays virtually constant, non-competitive inhibition.

Question 9

Describe end-product enzyme inhibition (+).

Answer 9

Enzymes at the start of a metabolic pathway are inhibited more or less by the product of the pathway.

Basically a system of negative feedback - high product concentration - less needed so enzyme A at start of pathway inhibited so less produced and works vice versa.

Usually non-competitive inhibition.

=> Ensures an almost constant [product].

Question 10

Functions of DNA and RNA - generally.

Answer 10

DNA - holds genetic information, coding for proteins. Long polynucleotide chain.

RNA - transfers genetic information from DNA to the ribosomes. Relatively short polynucleotide chain.

Question 11

DNA nucleotide structure.

RNA nucleotide structure.

Answer 11

Deoxyribose 5C sugar, bonded to an organic nitrogenous base on C1 and to a phosphate group on C4.

Ribose 5C sugar, bonded to an organic nitrogenous base (T replaced by U) on C1 and to a phosphate group on C4.

Question 12

Importance of condensation reactions in forming DNA.

Answer 12

Bonds holding nucleotide together are formed by condensation reactions.

Phosphodiester bonds (bonds between individual nucleotides - C3 on sugar and phosphate) formed by condensation reactions.

Question 13

Complementary base pairing occurs between which nitrogenous bases? How many H-bonds?

Answer 13

Adenine – Thymine. 2 x H-bonds.

Cytosine —Guanine. 3 x H-bonds

Question 14

DNA is in what form? Why is it a stable molecule?

Answer 14

Long polynucleotide chain coiled into a double helix due to hydrogen bonding between the bases. Antiparallel polynucleotide strands run in opposite directions.

Stable because:

1. Phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
2. MANY hydrogen bonds link the organic base pairs, adding more stability. More C—G pairing leads to a more stable DNA molecule, as more H-bonds.

Question 15

DNA’s structure-function relationship.

Answer 15

1. Stable, hereditary structure which rarely mutates.
2. 2 separate DNA strands joined by H-bonds so can be separated in DNA replication and protein synthesis.
3. Extremely large molecule - holds lots of genetic information.
4. Base pairs within the helical cylinder - largely protected by external chemical and physical forces.
5. Base pairing leads to DNA being able to replicate and to transfer information as mRNA.

Question 16

Comment on DNA’s simplicity.

Answer 16

The relative simplicity of DNA led many scientists to doubt that it carried the genetic code.

Question 17

Comment on 5’ to 3’ direction.

Answer 17

Two strands are antiparallel as one runs in the 5’ (C5) to 3’ (C3) direction.

DNA polymerase can only add new nucleotides to 3’ C3 (has an -OH group - condensation reactions).

Therefore, new nucleotides can only be added in the 5’ to 3’ direction as it needs to attach onto 3’ carbon, so if in 3’ to 5’ direction, wouldn’t work as would need to add to 5’ C.

Question 18

Why is DNA replication described as being semi-conservative?

Answer 18

Each of the new DNA molecules contains one of the original DNA strands - half of the original DNA molecule is present in each new DNA molecule.

Question 19

Describe the process of semi-conservative DNA replication.

Answer 19

1. DNA helicase enzyme breaks the H-bonds linking the base pairs of DNA.
2. Double helix separates into two strands and unwinds.
3. Each exposed polynucleotide strand then acts as a template to which complementary free nucleotides bind by specific, complementary base pairing.
4. DNA polymerase joins together polynucleotide strand, as each of the original DNA polynucleotide strands
5. Each of the new DNA molecules contains one of the original DNA strands.

NB - a source of chemical energy is required to drive the process.

Question 20

Suggest evidence for the Watson-Crick model of semi-conservative replication.

Answer 20

1. Bacteria with 15N placed in 14N medium so no new 15N available.
2. After one generation, one 15N/14N mixed strand. (1 double strand).
3. After two generations, one 15N/14N mixed strand and one 14N molecule. (2 double strands).
4. After three generations, one 15N/14N mixed strand and three 14N molecules (4 double strands).

Question 21

What is ATP? Uses and reasons?

Answer 21

• Adenosine Triphosphate.
• Phosphorylated macromolecule - nucleotide derivative.
• Used as an immediate energy source to carry out processes in cells.
• Can store energy because of the unstable bonds between the phosphate groups. These bonds release a considerable amount of energy while being relatively easy to break and having a low activation energy.
• NOT a good long term energy store as very unstable.

Question 22

ATP synthesis/hydrolysis reactions?

Answer 22

ATP hydrolysed to ADP + Pi by ATP hydrolase enzyme.

ATP synthesised from ADP + Pi by ATP synthase in a condensation reaction.

Question 23

In which processes is ATP synthesised?

Answer 23

• Photophosphorylation in plants during in photosynthesis.
• Oxidative phosphorylation in animals and plants during respiration.
• Substrate-level phosphorylation in plant and animal cells - donor molecules donate Pi to ADP. Occurs during Krebs Cycle?

Question 24

Roles of ATP?

Answer 24

1. Immediate source of energy for a cell; better immediate source of energy than glucose because:
   - energy is in more manageable quantities as energy from 1 ATP molecule is less than energy from 1 Glucose molecule.
   - hydrolysis of ATP -> ADP + Pi is a single reaction whereas glycolysis takes longer as it is a series of reactions.
2. ATP hydrolysis coupled to other energy-requiring processes/reactions in cells.
3. ATP provides energy needed to build up macromolecules from their basic units, such as polypeptides from amino acids.
4. Muscle contraction - energy provided for muscle fibres to slide past one another and to therefore shorten length of muscle fibre.
5. Active transport - ATP provides energy to change shape of carrier proteins in plasma membranes so molecules/ions can be moved against a concentration gradient.
6. Secretion - ATP needed to form the lysosomes necessary for the secretion of cell products, such as insulin from pancreas/plant auxins.
7. ATP is also used to phosphorylate other compounds - which lowers the Ea of enzyme-catalysed reactions -> phosphorylation of glucose molecules at the start of glycolysis.

Question 25

Small intestine epithelial cells and muscle fibre cells may contain many ____? Why?

Answer 25

MANY large mitochondria - produce a lot of ATP for movement/active transport => very metabolically active cells.

Question 26

Where do inorganic ions occur? In what concentrations?

Answer 26

• Occur in cell cytoplasm and body fluids of organisms.

- In varying concentrations, from very high to very low.

Question 27

List the relevant inorganic ions and their roles.

Answer 27

H+ => determines the pH of solutions and therefore the functioning of enzymes.

Fe 2+ => Component of haemoglobin; plays a role in the transport of O2.

Na+ => important in the co-transport of glucose and amino acids across plasma membranes.

PO4 3- => structural role in DNA molecules and a role in storing energy in ATP molecules.

Question 28

Explain water’s role as a metabolite.

Answer 28

• Used to break down complex molecules in hydrolysis reactions.
• Produced in condensation reactions.
• Chemical reactions take place in an aqueous medium.
• Major raw material in photosynthesis.

Question 29

Explain water’s role as a solvent.

Answer 29

• Water readily dissolves other substances due to its polarity, such as:
  1. Gases like O2 and CO2.
  2. Wastes like urea and NH3.
  3. Inorganic ions and small hydrophilic molecules (ATP, amino acid and monosaccharides).
  4. Enzymes, whose reactions take place in solution.

Question 30

Explain the biological importance of water’s high specific heat capacity.

Answer 30

• Hydrogen bonding between water molecules allows it to buffer sudden temperature changes - aquatic environments are temperature stable.
• Organisms are mostly water - we are also buffered against sudden temperature changes.

Question 31

Explain the biological importance of water’s large latent heat of vaporisation.

Answer 31

• Hydrogen bonding between water molecules means that a lot of energy to evaporate 1g of water.
• Therefore, sweating is an effective way of cooling as body heat used to evaporate the water. Little water lost and can control body temperature.

Question 32

Explain the biological importance of water’s strong cohesion.

Answer 32

• Water molecules stick together because of hydrogen bonding between them.
• Cohesive forces allow water to be pulled up through a tube such as a xylem vessel.

Question 33

Explain the biological importance of water’s surface tension.

Answer 33

• When water molecules meet air, they’re pulled back into the body of water rather than escaping from it.
• Therefore, water surface acts like a skin and is strong enough to support small organisms such as pond skaters.

Question 34

Other important features of water and their biological importance?

Answer 34

1. It is transparent - aquatic plants can photosynthesise and light can reach the retina.
2. Not easily compressed - provides support - hydrostatic skeleton of earthworms and turgor pressure in herbaceous plants.