Cellular Work
• The Cell does 3 kinds of work :
- Chemical
- Pushing endergonic reactions that wouldn’t happen on their own
- Ex: making polymers from monomers
- Transport
- Pumping substances across membranes
- Mechanical
- Muscle contraction, movement of chromosomes during cellular reproduction
• Often work is performed using energy coupling – The use of an exergonic process to drive an endergonic one I.e. Uses a process that releases energy to power a process that requires energy • In most cases, ATP is the source of energy that powers cellular work
• ATP (Adenosine triphosphate) – Ribose – Nitrogenous base (adenine) – Triphosphate (a chain of 3 phosphate groups) • Used for energy, and to make RNA
• Bonds between phosphate groups can be broken by hydrolysis • Terminal phosphate bond is broken – Molecule of Pi leaves – ATP becomes ADP (adenosine diphosphate) • Reaction is exergonic
• ATP is useful, because it releases more energy than most other molecules • Why? – All 3 phosphate groups are negatively charged – They repel each other – Triphosphate tail is like a compressed spring
• ATP hydrolyzed in a test tube – Energy released produces heat • In cells, Proteins harness energy released to do cellular work
• Mechanical work – ATP binds to motor protein – ATP hydrolyzed to ADP + Pi – Another ATP binds – Each time, motor protein shape changes, and it walks along
• ATP is constantly used – Can be regenerated by adding Pi to ADP • Energy required for this comes from catabolism in cell • Process is called ATP cycle – Couples exergonic processes to endergonic ones
• ATP cycle is fast – Working muscle cell recycles all its ATP in less than a minute – 10 million ATP molecules used and regenerated per second per cell ADP + Pi → ATP + water – Requires energy • Catabolic pathways used – Cellular respiration • Plants use light energy to make ATP