ATP Powers Active Transport Across Membranes
Definition
Active transport
Active transport is the movement of molecules or ions across a membrane against their concentration gradient (from low to high concentration), which requires energy.
- Cells often need to move substances against their concentration gradient, from areas of low concentration to high concentration.
- This process of active transport, requires energy.
- Don’t confuse active transport with passive transport.
- Passive transport doesn’t require energy because it moves substances down their concentration gradient.
- The sodium-potassium pump is a classic example.
- It uses ATP to move sodium ions out of the cell and potassium ions into the cell, maintaining essential ion gradients for nerve impulses and muscle contractions.
ATP Powers The Synthesis of Macromolecules (Anabolism)
- Cells constantly build complex molecules like proteins, DNA, and polysaccharides.
- These anabolic reactions require energy because they are endothermic (energy-absorbing).
- Each monomer added to a growing polymer, such as a nucleotide in DNA or an amino acid in a protein, requires ATP.
Definition
Anabolic Reactions
Anabolic reactions are metabolic processes in which smaller molecules are built into larger, more complex molecules using energy.
Examples of Anabolic Processes
- DNA Replication: ATP provides energy to link nucleotides into long DNA strands.
- Protein Synthesis: During translation, ATP powers the formation of peptide bonds between amino acids.
- Polysaccharide Formation: ATP is used to assemble glucose molecules into glycogen or starch for energy storage.
Remember that anabolism builds molecules (think "A" for "assemble"), while catabolism breaks them down.
Common Mistake- Students often confuse catabolism (breaking down molecules) with anabolism (building molecules).
- Remember, anabolism consumes ATP, whereas catabolism generates it.
ATP Powers the Movement of Cells and Cell Components
Movement is essential for many cellular processes, from dividing cells to immune responses.
Types of Movement Powered by ATP
- Intracellular Movement: ATP drives the movement of organelles and vesicles along cytoskeletal tracks.
- Chromosome Movement: During mitosis, ATP powers the spindle fibers that separate chromosomes.
- Cell Locomotion: Cells like phagocytes use ATP to change shape and move toward infection sites.
During cytokinesis, ATP is used to pinch the cell membrane inward, dividing the cell into two daughter cells.
ATP Powers Muscle Contraction
- ATP is essential for muscle contraction, which involves the sliding of actin and myosin filaments in muscle fibers.
- ATP binds to the myosin head (a motor protein), allowing it to detach from actin, move, and reattach to another site on the actin filament.
More on this in B3.3.2 Sliding filament model of muscle contraction (HL only)
Theory of Knowledge- When we call ATP the “energy currency” of the cell, we’re using a metaphor from economics to explain a biological process.
- How do metaphors shape the way we understand scientific concepts?
- Can they also limit our understanding by making us think of living systems too much like human systems?
