Biology: Metabolism and Enzymes Quiz

Why We Need to Eat

• We need to eat food to get energy to survive
• Energy from food is stored in food's chemical bonds
• Food provides energy for building macromolecules like proteins and nucleic acids
• Energy from food is required for life-sustaining processes like active transport

Metabolism

• Metabolism is the sum of all chemical reactions in cells that keep us alive
• Metabolic reactions can be classified as either:
  • Catabolic: Reactions that break down molecules and release energy
  • Anabolic: Reactions that build up molecules and require energy
• Metabolic reactions can also be classified as either:
  • Exergonic: Reactions that release energy, meaning the products have less energy than the reactants
  • Endergonic: Reactions that require energy, meaning the products have more energy than the reactants

Enzymes

• Enzymes speed up chemical reactions
• Without enzymes, reactions would occur too slowly for organisms to function
• Enzymes help both anabolic and catabolic reactions
• Enzymes work on substrates to produce products

ATP and ADP

• ATP (adenosine triphosphate) and ADP (adenosine diphosphate) are the main forms of chemical energy in a cell
• Energy is stored in the bonds between phosphate groups in ATP and ADP
• ATP has 3 phosphate groups, high energy, and is made when the cell has extra energy
• ADP has 2 phosphate groups, some energy, and is made when the cell uses energy from ATP by removing a phosphate group

Cellular Respiration

• Cellular respiration is a series of reactions in which glucose is broken down to generate energy
• Energy from glucose is transferred to the bonds of ATP
• ATP is then used by cells as a source of energy by breaking its high-energy phosphate bonds

Glycolysis

• First step of cellular respiration
• Breaks down glucose (C6H12O6) into two pyruvate molecules (C3H4O3)
• Occurs in the cytoplasm
• Requires 2 ATP to start, but produces 4 ATP (net gain of 2 ATP)
• Also produces 2 NADH, which is an electron carrier molecule
• Does not require oxygen

Pyruvate Oxidation

• Second step of cellular respiration
• Occurs in the mitochondrial matrix
• Pyruvate is transported into the mitochondria
• Each pyruvate is converted into an acetyl CoA molecule
• Produces 2 CO2 and 2 NADH

The Citric Acid Cycle (Krebs Cycle)

• Third step of cellular respiration
• Occurs in the mitochondrial matrix
• Acetyl CoA is broken down, releasing more energy
• Produces 4 CO2, 2 ATP, 6 NADH, and 2 FADH2

Electron Transport Chain (ETC)

• Fourth and final step of cellular respiration
• Occurs in the inner mitochondrial membrane
• Electrons are transferred from NADH and FADH2 to proteins in the ETC
• These electrons lose energy along the chain, powering the movement of protons (H+) across the inner membrane
• Oxygen is the final electron acceptor

Chemiosmosis

• The movement of protons (H+) across the inner mitochondrial membrane creates a proton gradient
• This gradient powers ATP synthase to produce ATP
• Called oxidative phosphorylation

Fermentation

• Occurs in the absence of oxygen
• Allows for the production of ATP without oxygen
• Two main types:
  • Alcoholic fermentation: Pyruvate is converted to ethanol and CO2
  • Lactic acid fermentation: Pyruvate is converted to lactic acid

Feedback Inhibition

• Controls the rate of cellular respiration
• Prevents the overproduction of ATP
• When ATP is abundant, it inhibits enzymes involved in earlier steps of cellular respiration