The Structure of ATP, The ATP-ADP Cycle and the Important Properties of ATP
In This A-Level Biology Lesson “A Level Biology: The Structure of ATP, The ATP-ADP Cycle and the Important Properties of ATP” following the learning outcomes, you learned that living organisms need energy in order to carry out biological functions - of which you should now be able to list.
Following that brief introduction the ADP-ATP cycle was covered in enough detail for your a-level biology - naming the enzymes (ATP hydrolase and ATP synthase - which you must know).
Key terms are now being used in lessons, (such as hydrolysis and condensation, so make sure you have worked through the making and breaking polymers lesson above since this is a fundamental biochemistry lesson that will underpin much of your a-level biology - especially early on when discussing the formation of biomolecules, such as carbohydrates, proteins, lipids etc. and later, when biochemical pathways are covered in detail - such as photosynthesis and cellular respiration.
It was emphasised in this lesson that ATP is NOT energy! a fact often confused or misinterpreted by a-level biology students - so make sure you really understand this - and take care not to use the two synonymously (i.e. don’t say ATP is “energy” or vice versa, since this will lose you marks in an exam or assignment!)
Remember ATP is the energy storage molecule (the energy currency of living organisms).
Next the structure of ATP was illustrated and the term nucleotide derivative explained - specifically that ATP is a nucleotide composed of the pentose sugar (ribose) a nitrogenous base (Adenine) and a phosphate group, just one phosphate group make the nucleotide AMP (Adenosine Mono-phosphate), 2 phosphate make the nucleotide ADP (Adenosine Di-phosphate) and finally 3 phosphates make the nucleotide ATP (Adenosine Tri-phosphate).
From here the lesson went on to show that when energy is needed ATP is hydrolysed into ADP and Pi (inorganic phosphate). An important reiteration of the key enzyme needed for ATP hydrolysis (ATP hydrolase) is stated, followed by an explanation of why ATP contains energy in its high energy phosphate bonds - again a key point you must fully understand.
Diffusion of ATP within the cell is a fundamental property, and examples are provided of some cellular events that require ATP - once more, it is essential that you know these.
ADP and Pi are readily re-synthesised back into ATP - and the enzyme you need to know: ATP synthase. At this point you are introduced to anther ket term - Phosphorylation (the biological term used when a Phosphate is added onto a molecule). In this case Pi is added back onto ADP phosphorylating it to form ATP.
The lesson finished with a summary of the important properties of ATP - all of which you must know.
ATP key points:
ATP (adenosine triphosphate) can be hydrolysed (broken down) into ADP (adenosine diphosphate) and a ‘free’ inorganic phosphate (Pi).
ATP is a nucleotide (made up of a pentose sugar (ribose) a nitrogenous base (adenosine) and three phosphates.
Hydrolysis of ATP into ADP + Pi provides instant energy in small, usable amounts for the wide variety of energy-demanding processes.
ATP is the immediate energy source (universal energy currency) within cells and carries energy from the site of respiration (mainly mitochondria) - to where energy is needed.
ATP is a relatively small molecule that can diffuse quickly.
In cellular respiration, the “energy” contained in organic compounds is released in a series of steps. This “energy” is used to make ATP from ADP and inorganic phosphate (Pi). Thus, cellular respiration is essentially a process that maintains ATP supplies, ensuring ATP is made as quickly as it is used up.
ATP has many uses (as outlined in the video), However, as far as the examiners are concerned the top 2 uses are: -
Active transport.
Muscular contraction.
Be super careful when talking about ATP and “energy”. They are NOT the same things!
ATP is a molecule (often called the universal energy “currency” molecule). ATP releases “energy” when hydrolysed into ADP + Pi