Biological Molecules: Water, ATP And Inorganic Ions Flashcards
(17 cards)
What is ATP and why is it needed?
Plant and animal cells release energy from glucose — this process is called respiration. A cell can’t get its energy directly from glucose. So, in respiration, the energy released from glucose is used to make ATP (adenosine triphosphate).
ATP is made from the nucleotide base adenine, combined with a ribose sugar and three phosphate groups. It’s what’s known as a nucleotide derivative because it’s a modified form of a nucleotide.
Once made, where does ATP go?
Once made, ATP diffuses to the part of the cell that needs energy.The energy in ATP is stored in high energy bonds between the phosphate groups. It’s released via hydrolysis reactions.
How is ATP used?
When energy is needed by a cell, ATP is broken down into ADP (adenosine diphosphate) and Pi (inorganic phosphate). This is a hydrolysis reaction.A phosphate bond is broken and energy is released. The reaction is catalysed by the enzyme ATP hydrolase.
What are some additional uses of the ATP hydrolysis reaction?
- ATP hydrolysis can be ‘coupled’ to other energy-requiring reactions in the cell — this means the energy released can be used directly to make the coupled reaction happen, rather than being lost as heat.
- The released inorganic phosphate can also be put to use — it can be added to another compound (this is known as phosphorylation), which often makes the compound more reactive.
How can ATP be re-synthesised?
ATP can be resynthesised in a condensation reaction between ADP and Pi. This happens during both respiration and photosynthesis, and is catalysed by the enzyme ATP synthase
What % of the cell does water make up?
Water is vital to living organisms. It makes up about 80% of a cell’s contents and has loads of important functions, inside and outside cells:
What are the 4 key properties of water?
• Water is a metabolite in loads of important metabolic reactions, including condensation and hydrolysis reactions.
• Water is a solvent, which means some substances dissolve in it. Most metabolic reactions take place in solution (e.g. in the cytoplasm of eukaryotic and prokaryotic cells) so water’s pretty essential.
• Water helps with temperature control because it has a high latent heat of vaporisation and a high specific heat capacity.
• Water molecules are very cohesive (they stick together), which helps water transport in plants as well as transport in other organisms.
How is water a polar molecule?
A molecule of water (H2O) is one atom of oxygen (O) joined to two atoms of hydrogen (H2) by shared electrons: because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge (delta +). The unshared negative electrons on the oxygen atom give it a slight negative charge (delta -). This makes water a polar molecule - it has a slight (partial) negative charge on one side and a slight (partial) positive charge on the other
How do hydrogen bonds hold water molecules together?
Hydrogen bonds are weak bonds. Hydrogen bond between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule. Hydrogen bonds form between water molecules because the slightly negatively charged oxygen atoms of water attract the slightly positively charged hydrogen atoms of other water molecules. This hydrogen bonding gives water some of its useful properties.
How is water used as a metabolite?
- Many metabolic reactions involve a condensation or hydrolysis reaction.
- A hydrolysis reaction requires a molecule of water to break a bond. A condensation reaction releases a molecule of water as a new bond is formed.
- For example, amino acids are joined together to make polypeptides (proteins) by condensation reactions. Energy from ATP is released through a hydrolysis reaction.
How is water used as a solvent?
- A lot of important substances in biological reactions are ionic (like salt, for example). This means they’re made from one positively charged atom or molecule and one negatively charged atom or molecule (e.g. salt is made from a positive sodium ion and a negative chloride ion).
- Because water is polar, the slightly positively charged end of a water molecule will be attracted to the negative ion, and the slightly negatively charged end of a water molecule will be attracted to the positive ion.
- This means the ions will get totally surrounded by water molecules — in other words, they’ll dissolve. So water’s polarity makes it useful as a solvent (a substance capable of dissolving another substance).
- This means living organisms can take up useful substances (e.g. mineral ions) dissolved in water and these dissolved substances can be transported around the organism’s body.
How does the high latent heat of vaporisation of water make it useful?
- Water evaporates (vaporises) when the hydrogen bonds holding water molecules together are broken. This allows the water molecules on the surface of the water to escape into the air as a gas. It takes a lot of energy (heat) to break the hydrogen bonds between water molecules, so a lot of energy is used up when water evaporates. This means water has a high latent heat of vaporisation - lots of heat is used to change it from a liquid to a gas.
- This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water.
- When water evaporates it carries away heat energy from a surface, which cools the surface and helps to lower the temperature (e.g. when humans sweat to cool down).
How does water’s resistance to temperature change (buffer ability) make it useful?
- Hydrogen bonds give water a high specific heat capacity — this is the energy needed to raise the temperature of 1 gram of a substance by 1 °C.
- When water is heated, a lot of the heat energy is used to break the hydrogen bonds between the water molecules. This means there is less heat energy available to actually increase the temperature of the water. So water has a high specific heat capacity - it takes a lot of energy to heat it up.
- This is useful for living organisms because it means that water doesn’t
experience rapid temperature changes. This makes water a good habitat because the temperature under water is likely to be more stable than on land. - The water inside organisms also remains at a fairly stable temperature - helping them to maintain a constant internal body temperature.
How is the cohesive nature of water useful?
- Cohesion is the attraction between molecules of the same type (e.g. two water molecules).
- Water molecules are very cohesive (they tend to stick together) because they’re polar. Strong cohesion helps water to flow, making it great for transporting substances. For example, it’s how water travels in columns up the xylem (tube-like transport cells) in plants.
- Strong cohesion also means that water has a high surface tension when it comes into contact with air. This is the reason why sweat forms droplets, which evaporate from the skin to cool an organism down. It’s also the reason that pond skaters, and some other insects, can ‘walk’ on the surface of a pond.
What are ions?
An ion is an atom (or group of atoms) that has an electric charge. An ion with a positive charge is called a cation.
What is an inorganic ion?
An inorganic ion is one which doesn’t contain carbon (although there are a few exceptions to this rule). There are inorganic ions, in solution, in the cytoplasm of cells and in the body fluids of organisms. Each ion has a specific role, depending on its properties. An ion’s role determines whether it is found in high or low concentrations.
What are 4 examples of inorganic ions?
- Iron ions in haemoglobin
- Hydrogen ions
- Sodium ions
- Phosphate ions
