Biology Year 9

Enzymes are protein molecules that act as biological catalysts, meaning they speed up chemical reactions within living organisms without being used up in the process. They are highly specific, meaning each enzyme only works on one type of molecule called a substrate. Their active site is the region where the substrate binds to initiate the reaction, often explained by the "lock and key" model. 

Key points about enzymes:

• Definition: Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in living organisms. 

• Substrate: The specific molecule that an enzyme acts upon is called a substrate. 

• Active site: The part of the enzyme where the substrate binds and the reaction occurs. 

• Lock and key model: This model explains enzyme specificity, where the shape of the active site only fits with one specific substrate, like a key fitting into a lock. 

Important aspects of enzyme function:

• Temperature and pH:

  Enzymes have optimal temperature and pH ranges where they function best. Extreme changes in temperature or pH can denature (distort) the enzyme, making it inactive. 

• Factors affecting enzyme activity:

  • Substrate concentration: Increasing substrate concentration generally increases the reaction rate until the enzyme becomes saturated. 

  • Enzyme concentration: Increasing enzyme concentration increases the reaction rate. 

  • Inhibitors: Molecules that can block the active site of an enzyme, preventing the substrate from binding and slowing down the reaction to stop the enzyme from producing more product than needed

Examples of enzymes in the human body:

• Salivary amylase: Found in saliva, breaks down starch into smaller sugars. 

• Pepsin: Found in the stomach, it breaks down proteins into smaller peptides. 

• Lactase: Found in the small intestine, it breaks down lactose

• Lipase: Found in the small intestine and liver, it breaks down fats into fatty acids

Active transport is the movement of particles from a region of low concentration to a region of high concentration, requiring energy to go against the concentration gradient, while diffusion is the movement of particles from a high concentration to a low concentration, happening naturally without the need for energy; both processes occur across cell membranes to move substances in and out of cells.

Key points about diffusion:

• Movement:

  Particles move from an area of high concentration to an area of low concentration. 

• No energy needed:

  Diffusion is a passive process, meaning it does not require energy to occur. 

• Examples:

  Oxygen moving from the lungs into the blood, perfume scent spreading in a room. 

Key points about active transport:

• Movement:

  Particles move from an area of low concentration to an area of high concentration. 

• Requires energy:

  This process needs energy, usually in the form of ATP, to move particles against the concentration gradient. 

• Examples:

  Root hair cells absorbing mineral ions from soil (where the concentration is lower) into the plant cell (where the concentration is higher).