ATP, Water & Inorganic Ions

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The Structure of ATP

ATP stands for adenosine triphosphate and is known as the universal energy currency because it transfers energy in all energy-requiring processes in cells.
ATP is a phosphorylated nucleotide made from adenosine (adenine + pentose sugar) combined with three phosphate groups.
Adenosine monophosphate (AMP) has one phosphate group, adenosine diphosphate (ADP) has two, and ATP has three.
Adenine is a nitrogenous base, while adenosine is a nucleoside (adenine combined with a sugar).
Energy from respiration is used to make ATP, which then supplies energy for processes such as anabolic reactions, active transport, and movement of substances within cells.

Hydrolysis of ATP

Hydrolysis of ATP to ADP and an inorganic phosphate group (π) is catalysed by the enzyme ATP hydrolase (also called ATPase).
The hydrolysis of ATP releases a useful quantity of energy that can be used for cellular processes such as active transport, enzyme-controlled reactions, and muscle contraction.
The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
The inorganic phosphate released during hydrolysis can be used to phosphorylate other compounds, often making them more reactive.
ATP hydrolysis is quick and simple, allowing cells to respond to sudden energy demands.
ATP is stable at cellular pH and does not break down unless an enzyme is present, preventing energy wastage.
ATP is soluble, so it can be transported to different areas of the cell for energy release.

Synthesis of ATP

ATP synthesis occurs when ADP combines with an inorganic phosphate (π) group, catalysed by the enzyme ATP synthase.
ATP synthesis is a condensation reaction because water is released as a waste product.
ATP is made during respiration and photosynthesis; all of an animal's ATP comes from respiration.
Humans use more than 50 kg of ATP per day but only have about 200 g in the body at any one time, so ATP must be made continuously.
ATP is synthesised by substrate-linked phosphorylation (in glycolysis) and by chemiosmosis (in the electron transport chain).
Cells cannot store large amounts of ATP, and ATP rarely passes through the cell surface membrane, so it must be made as and when needed.

The Properties of Water

Water is a polar molecule because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges.
Hydrogen bonds form between the positively and negatively charged regions of adjacent water molecules.
Water is an excellent solvent, has a relatively high specific heat capacity, a relatively high latent heat of vaporisation, is less dense when solid, and has high surface tension and cohesion.
Water is a metabolite in many reactions, including condensation and hydrolysis reactions.
In condensation reactions, smaller molecules combine to form a larger molecule with the removal of a water molecule (e.g. formation of peptide, glycosidic, and ester bonds).
In hydrolysis reactions, water is added to break a bond within a larger molecule, splitting it into smaller units (e.g. breaking proteins into amino acids, starch into glucose, triglycerides into fatty acids and glycerol).

Water as a Solvent

The polarity of water molecules allows hydrogen bonds to form between adjacent water molecules.
Many ions (e.g. sodium chloride) and covalently bonded polar substances (e.g. glucose) dissolve in water.
Dissolved solutes are more chemically reactive because they are free to move about, allowing chemical reactions to occur within cells.
Metabolites can be transported efficiently in water, except non-polar molecules, which are hydrophobic.
Due to its polarity, water is considered a universal solvent.

High Specific Heat Capacity of Water

Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 °C.
Water has a high specific heat capacity of 4200 J/kg/°C, meaning a relatively large amount of energy is required to raise its temperature.
The high specific heat capacity is due to the many hydrogen bonds present in water; it takes a lot of thermal energy to break these bonds and a lot of energy to build them.
This means the temperature of water does not fluctuate greatly, providing stable habitats for aquatic organisms.
Water absorbs lots of heat with minimal temperature change, helping to maintain stable internal and external temperatures essential for enzyme function.
Water in blood plasma transfers heat around the body, aiding temperature regulation; as blood flows through warmer tissues, it absorbs heat without large temperature shifts.

Latent Heat of Vaporisation, Cohesion and Adhesion

Water has a relatively high latent heat of vaporisation: a large amount of thermal energy must be absorbed to break hydrogen bonds and evaporate water.
This is an advantage because only a little water needs to evaporate for an organism to lose a great amount of heat, providing a cooling effect (e.g. transpiration from leaves, sweating on skin).
Hydrogen bonds between water molecules allow for strong cohesion between water molecules.
Cohesion allows columns of water to move through the xylem of plants and the blood vessels in animals.
Cohesion also enables surface tension where a body of water meets the air, creating a film on the surface.
Water can also hydrogen bond to other molecules such as cellulose, which is known as adhesion; this helps water move up the xylem due to transpiration.

Inorganic Ions: General Principles

An ion is an atom (or group of atoms) that has an electrical charge.
A positively charged ion is a cation; a negatively charged ion is an anion.
An inorganic ion is an ion that does not contain carbon.
Inorganic ions occur in solution in the cytoplasm and body fluids of organisms.
The concentration of certain ions can fluctuate and can be used in cell signalling and neuronal transmission.

Roles of Specific Inorganic Ions

Hydrogen ions (H+) are protons; the concentration of H+ determines pH, with an inverse relationship (more H+ = lower pH).
The concentration of H+ is very important for enzyme-controlled reactions, which are all affected by pH; body fluids normally have a pH of approximately 7.4.
Iron ions exist as Fe2+ (ferrous) and Fe3+ (ferric); they are essential as they can bind oxygen.
Haemoglobin is made up of four polypeptide chains, each containing one Fe2+ that binds to oxygen.
Sodium ions (Na+) are required for the co-transport of glucose and amino acids across cell-surface membranes (e.g. in the small intestine) and for the transmission of nerve impulses.
Phosphate ions (PO43−) are an essential component of DNA, RNA, and ATP; in DNA and RNA, phosphate groups allow nucleotides to bond to form polynucleotides.
In ATP, the bonds between phosphate groups store energy; when broken, they release a large amount of energy for cellular processes.
Phosphates are also found in phospholipids, which are key components of the phospholipid bilayer of cell membranes.

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1.Which of the following best describes ATP?
Easy
- AA phosphorylated nucleotide
- BA protein made of four polypeptide chains
- CA non-polar lipid
- DA polysaccharide
2.Which enzyme catalyses the hydrolysis of ATP?
Easy
- AATP hydrolase
- BATP synthase
- CDNA polymerase
- DAmylase
3.Which of the following is a product of the hydrolysis of ATP?
Easy
- AADP and inorganic phosphate
- BAMP and two inorganic phosphates
- CAdenosine and three inorganic phosphates
- DADP and water
4.Which statement correctly describes the synthesis of ATP?
Easy
- AADP combines with inorganic phosphate in a condensation reaction.
- BADP combines with inorganic phosphate in a hydrolysis reaction.
- CATP is formed by the breakdown of glucose.
- DATP is synthesised by the addition of water to ADP.
5.Which of the following is NOT a property of water that makes it important for life?
Medium
- AIt is a non-polar molecule.
- BIt has a high specific heat capacity.
- CIt is an excellent solvent.
- DIt has a high latent heat of vaporisation.
6.Which type of bond forms between adjacent water molecules?
Medium
- AHydrogen bonds
- BCovalent bonds
- CIonic bonds
- DPeptide bonds
7.Which inorganic ion is a component of haemoglobin?
Medium
- AIron (Fe2+)
- BSodium (Na+)
- CPhosphate (PO43−)
- DHydrogen (H+)
8.Which inorganic ion is essential for the co-transport of glucose and amino acids across cell membranes?
Medium
- ASodium (Na+)
- BIron (Fe2+)
- CPhosphate (PO43−)
- DHydrogen (H+)

複習筆記

## ATP - **ATP = adenosine triphosphate** — a **phosphorylated nucleotide**: pentose sugar + adenine (nitrogenous base) + three phosphate groups. Adenosine = adenine + sugar (a nucleoside). - One phosphate = **AMP**, two = **ADP**, three = **ATP**. - ATP is the **universal energy currency**; energy from respiration is transferred to ATP for all energy-requiring processes. ### Hydrolysis - Catalysed by **ATP hydrolase (ATPase)**: ATP + H₂O → ADP + Pi. - Released energy is coupled to: **active transport** of ions against a concentration gradient, energy-requiring enzyme reactions, **muscle contraction**, DNA synthesis. - The **Pi released can phosphorylate other compounds**, often making them more reactive. - Advantages: quick and simple (one enzyme); small but sufficient energy (no waste, cell control); stable at cellular pH; soluble so it can be transported; recyclable. ### Synthesis - **ADP + Pi → ATP** by **ATP synthase** — energy-requiring **condensation** reaction (water released). - Made in **respiration** and **photosynthesis**; all animal ATP comes from respiration. - Two routes: **substrate-linked phosphorylation** (glycolysis) and **chemiosmosis** (electron transport chain). - Humans use >50 kg ATP/day but store only ~200 g — ATP is made as and when needed. ## Water - O + 2H joined by **covalent bonds**; water is **polar** (uneven charge distribution). - **Hydrogen bonds** form between the positive and negative regions of adjacent molecules (O of one to H of another). - Properties: excellent **solvent**; relatively **high specific heat capacity**; relatively **high latent heat of vaporisation**; less dense as a solid; high **surface tension and cohesion**; acts as a **reagent/metabolite**. - **Metabolite**: condensation (peptide, glycosidic, ester bonds) removes water; hydrolysis adds water (proteins→amino acids, starch→glucose, triglycerides→fatty acids + glycerol). - **Solvent**: polarity means ions (NaCl) and polar covalent substances (glucose) dissolve; solutes are more reactive when free to move; non-polar molecules are hydrophobic. - **Specific heat capacity** = energy to raise 1 kg of a substance by 1 °C. Water = **4200 J/kg/°C** — many hydrogen bonds must be broken/built, so temperature barely fluctuates: stable aquatic habitats, stable internal temperatures for enzyme function, blood plasma transfers heat around the body. - **Latent heat of vaporisation**: much thermal energy breaks hydrogen bonds to evaporate, so little water loss gives great cooling — transpiration, sweating. - **Cohesion/adhesion**: hydrogen bonds hold water in unbroken columns in xylem and blood vessels; surface tension at air–water surfaces; adhesion to cellulose helps water move up xylem. ## Inorganic ions - An **ion** is a charged atom/group; **cation** = positive, **anion** = negative; **inorganic** = no carbon. They occur in solution in cytoplasm and body fluids; concentrations can be used in **cell signalling and neuronal transmission**. - **H⁺**: protons; concentration determines **pH** (inverse relationship — more H⁺, lower pH). Body fluids ~pH 7.4; changes affect enzyme structure. - **Fe²⁺ (ferrous) / Fe³⁺ (ferric)**: bind oxygen; each of haemoglobin's four polypeptide chains contains one Fe²⁺. - **Na⁺**: **co-transport** of glucose and amino acids across cell-surface membranes (e.g. small intestine); nerve impulse transmission. - **PO₄³⁻**: phosphate groups in **DNA, RNA and ATP**; bond nucleotides into polynucleotides; bonds between phosphate groups store energy and release it when broken; also in phospholipids of membranes.

ATP (adenosine triphosphate): A phosphorylated nucleotide (pentose sugar + adenine + three phosphate groups) that transfers energy in all energy-requiring processes in cells; the universal energy currency.
ADP: Adenosine diphosphate — adenosine with two phosphate groups; formed when ATP is hydrolysed and used to resynthesise ATP.
AMP: Adenosine monophosphate — adenosine with one phosphate group.
ATP hydrolase (ATPase): The enzyme that catalyses the hydrolysis of ATP to ADP and an inorganic phosphate group (Pi), releasing free energy.
ATP synthase: The enzyme that catalyses the condensation of ADP and Pi to form ATP (an energy-requiring reaction that releases water).
Phosphorylated nucleotide: A nucleotide with one or more phosphate groups attached, e.g. AMP, ADP, ATP.
Substrate-linked phosphorylation: One of the two ways ATP is made; occurs in the glycolysis stage of respiration.
Chemiosmosis: One of the two ways ATP is made; occurs in the electron transport chain stage of respiration.
Polar molecule: A molecule with an uneven distribution of charge, such as water, allowing hydrogen bonds to form between adjacent molecules.
Hydrogen bond: A bond formed between the positively and negatively charged regions of adjacent water molecules (oxygen of one to hydrogen of another).
Specific heat capacity: A measure of the energy required to raise the temperature of 1 kg of a substance by 1 °C; water's is 4200 J/kg/°C.
Latent heat of vaporisation: The large amount of thermal energy water must absorb to break hydrogen bonds and change from liquid to gas, giving organisms a cooling effect.
Cohesion: Strong attraction between water molecules via hydrogen bonds, allowing columns of water to move through xylem and blood vessels.
Adhesion: Water's ability to hydrogen bond to other molecules, such as cellulose, helping water move up the xylem during transpiration.
Metabolite: A substance involved in metabolic reactions; water is a metabolite in condensation and hydrolysis reactions.
Inorganic ion: An ion that does not contain carbon; occurs in solution in the cytoplasm and body fluids of organisms.
Cation: An ion with a positive charge.
Anion: An ion with a negative charge.
Hydrogen ions (H⁺): Protons; their concentration determines pH (inverse relationship), which is vital for enzyme-controlled reactions.
Iron ions (Fe²⁺/Fe³⁺): Ferrous (Fe²⁺) and ferric (Fe³⁺) ions; essential as they bind oxygen, each haemoglobin polypeptide chain containing one Fe²⁺.
Sodium ions (Na⁺): Required for the co-transport of glucose and amino acids across cell-surface membranes and for the transmission of nerve impulses.
Phosphate ions (PO₄³⁻): Attach to other molecules to form phosphate groups; essential components of DNA, RNA and ATP, and found in phospholipids of cell membranes.

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