Exam 2 Slides - Cell Bio

CH6 Slides

Enzymes: A Special Class of Protein

• Definition: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur.

• Structure: They are globular proteins with specialized three-dimensional shapes, allowing them to bind specific substrates.

• Naming: Typically recognized by the suffix -ase, indicating their function (e.g., Dehydrogenase facilitates dehydrogenation, Kinase transfers phosphate groups, and Phosphatase removes phosphate groups).

How do enzymes do it?

• Alignment of Reactants: Enzymes align the reactants in a way that decreases the activation entropy, positioning them optimally for reaction.

• Reactivity Alteration: They can change the reactivity of the substrate through interactions at the active site, enhancing the probability of the desired reaction taking place.

• Strain on Substrate: Enzymes may induce strain or alter the conformation of the substrate, making it more susceptible to breaking bonds or forming new ones.

Enzymes and Cofactors

• Requirement for Cofactors: While enzymes can function independently, many require metal ions or coenzymes (such as vitamins) to act as electron donors or acceptors.

• Holoenzyme Definition: The complete and active form of an enzyme that includes its cofactor is called a holoenzyme, essential for optimal enzymatic function.

Metabolism - An Example of Enzymatic Function

• Anabolism vs. Catabolism: Metabolism can be categorized into two main processes:

  • Anabolism: The synthesis of complex macromolecules from simpler building blocks, requiring energy input.

  • Catabolism: The breakdown of macromolecules into smaller units, releasing energy that can be captured in the form of ATP (Adenosine Triphosphate).

• ATP Hydrolysis: The conversion of ATP to ADP (Adenosine Diphosphate) and inorganic phosphate (Pi) describes a vital energy transfer that facilitates numerous biochemical reactions.

Glycolysis Overview

• Overall Reaction: The glycolytic pathway converts one molecule of glucose into two molecules of pyruvate, yielding a net gain of 2 ATP and 2 NADH, along with 2 water molecules and 2 protons.

• Pathway Stages: Glycolysis comprises an energy investment phase (where ATP is consumed) and an energy payoff phase (where ATP and NADH are produced).

Key Regulation of Glycolysis

• Phosphofructokinase Role: As a major regulatory enzyme, Phosphofructokinase (PFK) serves as a 'valve' controlling the flow of metabolites through glycolysis based on energy demands and substrate availability.

CH17 Slides

Aerobic Energy Production

Overview

Aerobic energy production is a biological process that requires the presence of oxygen for the conversion of glucose (or other substrates) into energy. This process primarily occurs in mitochondria, where oxygen is utilized to produce ATP (adenosine triphosphate), the energy currency of the cell.

Electron Transport Chain (ETC)

The electron transport chain is a series of protein complexes and other molecules located in the inner mitochondrial membrane. It plays a critical role in aerobic respiration by facilitating the transfer of electrons from NADH and FADH2 (generated from the Krebs cycle) to oxygen, resulting in the formation of water. As electrons move through the chain, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient that drives the synthesis of ATP through oxidative phosphorylation via ATP synthase.

Mitochondrial Membrane

The mitochondrial membrane is a key organelle structure composed of a double membrane system consisting of an outer membrane and a highly convoluted inner membrane. The inner membrane's folds, known as cristae, increase the surface area for chemical reactions involved in energy production. The mitochondrial membrane's integrity and functionality are crucial for efficient ATP production and overall cellular metabolism.

The Plasma Membrane

Function of the Membrane

The plasma membrane is a semipermeable barrier that defines the cell's boundaries, protecting it from the external environment. It mediates communication with other cells and regulates the transport of substances in and out of the cell, playing an essential role in maintaining homeostasis.

Experiments Leading to the Fluid Mosaic Model

The fluid mosaic model, which describes the structure of the plasma membrane, arose from historical experiments that included studies of membrane permeability and the observation of lipid and protein interactions in membranes. Notable experiments included the use of fluorescence recovery after photobleaching (FRAP), which provided insight into the mobility of membrane components.

Structure

The plasma membrane comprises a phospholipid bilayer interspersed with embedded proteins. The lipid bilayer primarily consists of phospholipids, which have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails, orienting themselves to create a barrier.

Lipids

Phospholipids are the main component of the membrane, organized into bilayers that form the fundamental structure. Other lipid types, such as cholesterol, also play critical roles in membrane fluidity and stability.

Proteins

The membrane contains integral proteins, which span the lipid bilayer, and peripheral proteins, which are attached to the membrane's surface. These proteins facilitate various functions such as transport, signal transduction, and acting as receptors.

Carbohydrates

Carbohydrate chains are located on the outer surface of the plasma membrane, contributing to cell recognition and communication through glycoproteins and glycolipids.

Membrane Functions

The plasma membrane serves several vital functions in the cell:

• Compartmentalization: It enables distinct environments for various cellular processes.

• Scaffolding: It provides structural support for maintaining cellular shape and integrity.

• Selectively Permeable Barrier: The membrane controls the entry and exit of ions and molecules, permitting selectivity based on size, charge, and solubility.

• Cell-Cell Communication: It facilitates signals between cells, vital for tissue function and immune responses.

• Energy Transduction: It is involved in ATP production and energy transformation processes crucial for maintaining cellular functions.

Additional Insights on Membranes

Membranes are not static; they exhibit fluidity, allowing lateral movement of proteins and lipids, a principle crucial for functions such as endocytosis and exocytosis. Moreover, asymmetry in the membrane composition contributes significantly to its functions, with different lipid and protein distributions in the outer and inner leaflets influencing signaling and cellular responses. Understanding these intricate details of membranes is fundamental to grasping their roles in biology and medicine.