Biology Chapter 5: Enzymes and Energy

Energy and ATP Cycle

• Exergonic reactions release energy, where reactants have more energy in bonds than in products, an example being cellular respiration.
• Endergonic reactions input and store energy, where reactants with low potential energy absorb energy from surroundings, an example being photosynthesis.
• Energy released from exergonic reactions is transferred to endergonic reactions through energy coupling.
• ATP cycle: energy from exergonic reactions adds a phosphate group to ADP (phosphorylation) to produce ATP, and when the cell needs energy, hydrolysis breaks the bond and releases the stored energy, returning back to ADP.

Enzymes

• Enzymes are proteins that speed up chemical reactions by lowering the activation energy and energy barrier.
• The energy barrier is the minimum amount of energy required for a chemical reaction to initiate and occur.
• An enzyme's shape determines the substrate, or reactant it acts on.
• The substrate fits in the active site, a pocket on the surface of the enzyme.
• Enzyme induced fit: the enzyme changes shape or contorts bonds to strain them for proper reaction.
• Enzyme releases the products after the reaction.

Enzyme Inhibitors

• Competitive Inhibitor: blocks substrate molecules from entering the active site, but can be overcome by increasing substrate concentration.
• Noncompetitive Inhibitor: binds to an allosteric site, preventing the enzyme from changing shape or allowing substrate to fit in the active site.

Enzyme Characteristics

• Enzymes prefer pH 6-8, temperatures of 95-104 degrees Fahrenheit, and medium salt concentration.
• If conditions are not met, the enzyme might denature and become dysfunctional.
• Saturation point: enzyme activity increases until this point, as there are only so many enzyme active sites.

Cellular Reproduction

• Cell cycle: Interphase (90%), Mitosis (10%), and Gap 0 (cell stops dividing and continues normal functions).
• Interphase: Gap 1 (G1), Synthesis (S), and Gap 2 (G2).
• Mitosis: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

Chromosomes

• Chromatin: long, loose state of DNA before mitosis.
• Chromosome: condensed version of DNA, containing several genes and locus at each gene.
• Centromere: the region where sister chromatids connect.
• Chromatid: ½ of the chromosome.
• Tetrad: two homologous chromosomes joined at a chiasma during Prophase 1 of Meiosis.
• Homologous chromosomes: chromosomes are identical in length, structure, and gene sequence.

Understand the role of enzymes in chemical reactions, including exergonic and endergonic reactions, and how they relate to cellular respiration and photosynthesis.