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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: ATP and Cellular Energy
Every cell in your body needs energy to function - from your brain cells helping you read this page to your muscle cells allowing you to turn the page. But where does this energy come from and how is it stored and used? The answer lies in a remarkable molecule called ATP.
Key Definitions:
ATP (adenosine triphosphate) is often called the "energy currency" of cells. Just like you need money to buy things, cells need ATP to power almost everything they do. ATP stores energy in its chemical bonds and releases it when needed, making it perfect for transferring energy within cells.
Cells require energy for countless processes including muscle contraction, protein synthesis, active transport across membranes, cell division and maintaining body temperature. Without a constant supply of ATP, these vital functions would stop and cells would die.
Understanding the structure of ATP helps explain how it works as an energy carrier. ATP consists of three main parts:
A nitrogen-containing base (similar to those found in DNA).
A five-carbon sugar that forms part of the backbone.
Three phosphate groups attached in a chain - these store the energy!
The key to ATP's function is in the phosphate groups. The bonds between these phosphates are called "high-energy bonds" because they release a lot of energy when broken. When the end phosphate group is removed, energy is released that can power cellular processes.
ATP works through a continuous cycle of energy storage and release:
When a cell needs energy, ATP loses its end phosphate group, becoming ADP (adenosine diphosphate) and releasing energy:
ATP → ADP + Pi + Energy
This energy powers cellular activities like muscle contraction, protein synthesis and active transport.
During cellular respiration, energy from glucose is used to reattach a phosphate group to ADP, reforming ATP:
ADP + Pi + Energy → ATP
This recycling process happens thousands of times per day in each of your cells!
Your body uses and regenerates its own weight in ATP every day! A typical human might use about 50-75 kg of ATP daily, but you don't need to eat that much because ATP is constantly recycled. At any given moment, you only have about 250g of ATP in your body.
Cells produce ATP primarily through cellular respiration - breaking down glucose to release energy. There are two main types:
This is the main way your cells make ATP most of the time. It requires oxygen and produces a lot of energy.
The equation: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (38 ATP)
Aerobic respiration happens in three main stages:
Occurs in the cytoplasm. Glucose is split into two pyruvate molecules, producing a small amount of ATP and NADH.
Happens in the mitochondria. Pyruvate is broken down further, producing CO2, more NADH and a little ATP.
The final stage in the mitochondria. NADH donates electrons that ultimately help produce most of the ATP.
When oxygen is in short supply (like during intense exercise), your cells can still make some ATP without oxygen, but much less efficiently.
Glucose → Lactic acid + Energy (2 ATP)
This happens in your muscles during intense exercise when oxygen can't be delivered fast enough. The lactic acid buildup causes muscle fatigue and the "burn" feeling.
Glucose → Ethanol + Carbon dioxide + Energy (2 ATP)
This is how yeast makes bread rise and how alcoholic drinks are produced - it's anaerobic respiration in yeast cells!
When sprinters run a 100m race, they rely primarily on ATP already stored in their muscles and anaerobic respiration for the first 10-15 seconds. This is why sprinters can go so fast but only for short distances. In contrast, marathon runners rely on aerobic respiration, which provides a steady supply of ATP over a longer period but at a lower rate. This is why training for different sports focuses on developing different energy systems in the body.
ATP is involved in almost everything your cells do. Here are some key processes powered by ATP:
ATP powers the sliding of actin and myosin filaments in muscle cells, allowing movement.
ATP powers membrane pumps that move substances against their concentration gradient.
ATP provides energy for building proteins from amino acids according to DNA instructions.
ATP is the universal energy currency in all living cells. It stores energy in its phosphate bonds and releases it when needed to power cellular processes. Through the continuous ATP-ADP cycle, your cells maintain a constant energy supply. The energy for making ATP comes primarily from cellular respiration, where glucose is broken down either with oxygen (aerobic) or without (anaerobic).
Understanding ATP helps explain how your body powers everything from thinking to running and how different types of exercise rely on different energy systems. This remarkable molecule is what keeps every cell in your body alive and functioning!
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