ATP, Water + Inorganic Ions

Question 1

What does ATP stand for?

Answer 1

• adenosine triphosphate

Question 2

What is ATP?

Answer 2

• a nucleotide derivative providing an immediate source of energy for biological processes such as metabolic reactions in cells that require a constant, steady supply of ATP

Question 3

What is a single molecule of ATP formed from?

Answer 3

• adenine (nitrogenous base)
• ribose (a pentose sugar)
• 3 inorganic (non-carbon containing) phosphate groups

Question 4

Draw the structure of a single ATP molecule.

Answer 4

• pentagon (ribose - a pentose sugar)
• rectangle connected to 2nd point (adenine - nitrogenous base)
• 3 circles connected in line to 5th point (phosphate groups)

Question 5

Why is the use of ATP beneficial as an energy store?

Answer 5

• it is quickly + easily hydrolysed, by enzyme ATP hydrolase, where energy is required within a cell
• a useful quantity of energy is released from hydrolysis of 1 ATP molecule dec energy waste + giving cell control over processes occurring
• it is relatively stable at cellular pH lvls

Question 6

Describe how an ATP molecule is formed.

Answer 6

• ATP is made during respiration from the addition of an inorganic phosphate to ADP (adenosine diphosphate) via a condensation reaction using enzyme ATP synthase

Question 7

Describe the hydrolysis of ATP.

Answer 7

• ATP is hydrolysed into ADP + Pi, catalysed by enzyme ATP hydrolase which breaks 1 bond between inorganic phosphate groups in a hydrolysis reaction
• this causes a small amount of energy to be released to surroundings, which can be used in energy requiring reactions in cells
• the Pi released from hydrolysis of ADP can phosphorylate other compounds to make them more reactive

Question 8

Describe how ATP is resynthesised.

Answer 8

• ATP is resynthesised from the addition of a Pi molecule to ADP (adenosine diphosphate) via a condensation reaction using enzyme ATP synthase, during respiration or photosynthesis

Question 9

What are the properties of ATP that make it a suitable immediate source of energy?

Answer 9

• releases energy in small, manageable amounts, so energy isn’t wasted
• is small + soluble for easy transport around cytoplasm to provide energy for chemical reactions within cell
• hydrolysis of only 1 bond is required to release energy, so is immediate
• it can phosphorylate another molecule, by transferring a Pi group, to make it more reactive
• ATP can’t pass out of cell, so cell has a constant, immediate supply of energy

Question 10

Why is glucose a less suitable immediate source of energy than ATP?

Answer 10

• large amounts of energy are release, resulting in wasted energy
• several bonds would need to be broken to release all its energy
• it can’t transfer energy to/phosphorylate another molecule bc it doesn’t contain a phosphate group
• glucose can pass out of cell, so cell can runout

Question 11

Why is water a major component of cells?

Answer 11

• bc it’s the medium in which all metabolic reactions take place in cells

Question 12

What is the structure of water molecules?

Answer 12

• dipolar molecules that have an unevenly distributed charge bc O atom is slightly negative + H atoms are slightly positive
• causes hydrogen bonds to form between the oxygen + a hydrogen atom in diff water molecules, resulting in 5 key properties of water

Question 13

What are the 5 key properties of water?

Answer 13

• it’s a metabolite (e.g. in condensation/hydrolysis reactions)
• it’s an important solvent in reactions
• has a high specific heat capacity
• has a large latent heat of vaporisation
• has strong cohesion between water molecules

Question 14

Why is water a good metabolite?

Answer 14

• bc water is involved in many metabolic reactions such as photosynthesis, condensation + hydrolysis reactions
• which is why cytoplasm of cells largely consists of water

Question 15

Explain why water is an important solvent in reactions.

Answer 15

• bc water is a dipolar molecule, many polar or charged molecules dissolve readily in water
• this is bc the slight pos. charge on H atoms attract neg. ions + slight neg. charge on O atoms attract pos. ions
• this enables them to be easily transported around animals + plants, either in blood or xylem, to cells they’re needed in within organism

Question 16

Explain why water has a relatively high specific heat capacity.

Answer 16

• bc lots of energy is required to inc T°C of water bc it contains many H bonds that need to be broken
• it buffers T°C, so water remains relatively stable, meaning internal T°C of plants + animals remain relatively constant, despite surrounding T°C fluctuations, bc have a large proportion of water
• important so enzymes don’t denature or dec in activity w T°C fluctuations + also provides a stable envi. for aquatic organisms

Question 17

Explain why water has a relatively large latent heat of vaporisation.

Answer 17

• lots of energy is required to convert water from liquid to gas bc many H bonds between water molecules need to be broken
• this provides a sig. cooling effect, which is advantageous to organisms, bc heat energy is transferred from skin to water, evaporating it + so removes lots of heat + cools organism

Question 18

Explain why water has strong cohesion between molecules.

Answer 18

• H bonds cause strong cohesion between water molecules allowing them to stick together
• this means water moving up xylem in plants, due to transpiration, occurs as a continuous column, making it easier to draw up water
• it also produces a surface tension where water meets air, so small invertebrates can move + live on surface, away from predators in water

Question 19

Where do inorganic ions occur?

Answer 19

• in solution in cytoplasm + body fluids of organisms + can occur in high or very low concentrations