Lecture 1 - bioenergetics - energy and ATP Flashcards
what is ATP?
a ubiquitous, ancient energy currency
What is ATP used for?
In a cell the energy released from an exergonic reaction can be used for many different types of work. Apart from building complex molecules, the energy can for example be used to build up a concentration gradient across a membrane by pumping substances through the membrane. Or the energy can be used for movement, for example to move actin along myosin in the muscle. Some organisms even produce light.
what are specific examples of ATP?
-Synthesis of RNA or DNA by Nucleoside monophosphate activation
-Protein synthesis by Amino acid activation
-Post-translational de-/activation of proteins
-Active transport, e.g. Ca2+ pump. Ca2+ pumps in the plasma membrane, ER and tonoplast maintain a low cytoplasmic Ca2+ concentration, which is a prerequisite for fast, transient Ca2+ signals.
-Myosin Motion Along Actin Filament
how much ATP is required for the human body?
ATP content: 100 – 250 g (0.1 moles)
ATP requirement/day: 50 - 75 kg!
ATP recycled from ADP: > 500 x per day
how do you regulate energy in metabolism?
High concentrations of ATP inhibit the relative rates of a typical ATP-generating (catabolic) pathway and stimulate the typical ATP-utilizing (anabolic) pathway
how is ATP synthesised?
there are two basic mechanisms. The first is called substrate phosphorylation. Here an energy-rich phosphate group is directly transferred from a substrate onto ADP. The substrate looses its energy-rich phosphate group, it is de-phosphorylated, and ADP is phosphorylated to ATP. The two events are directly linked usually by physical interaction of the substrate and the ADP molecule with an enzyme. The second mechanism how ATP is formed is completely different. Here a gradient of protons across a membrane is used to drive an enzyme called ATP synthase that produces ATP. x Now, remember, yesterday we looked at pumps that consumed ATP to create a proton gradient across the membrane. These were called ATPases. Here, we have the opposite mechanism where an existing proton gradient is used to make ATP, and the protein complex involved is called ATP synthase.
what is the structure of the ATP synthase?
Rotor: spins clockwise when H+ ions flow past it
Stator: holds rotor and knob in position
Rod: turns with the rotor and activates the knob
Knob: catalytic sites join Pi to ADP making ATP
what is the localisation of mitochondria?
Mitochondria are often particularly numerous in ATP-consuming tissues and are closely associated with ATP-consuming organelles to maximize the speed of ATP transfer
is ATP synthase reversible?
If [ATP] is low the energy of the electrochemical proton gradient is converted into chemical-bond energy (ADP + Pi -> ATP).
If [ATP] is high the energy of the phosphate bond is converted into an electrochemical proton gradient (ATP -> ADP + Pi, proton pumping).
what is ADP/ATP and Pi transport?
The ADP-ATP exchanger maintains low [ATP]
in the matrix of the mitochondria.
The Pi/H+ co-transporter imports Pi into the matrix
what is the difference between endergonic and exergonic?
Exergonic: Amount of free energy released G < 0
Endergonic: Amount of free energy required
G > 0
In metabolic pathways exergonic and endergonic reactions are often linked
in time and space to minimise energy loss.
However, in many cases production and usage of energy are separated in time and/or
space.
We therefore need an ‘energy currency’.
