Eukaryotic Cell Structure and Membrane Components

This page delves into the intricate structure of eukaryotic cells, with a focus on animal and plant cells, as well as the detailed composition of the plasma membrane.

Eukaryotic cells are characterized by their complex internal organization, including membrane-bound organelles. The page illustrates the key components of both animal and plant cells:

1. Animal Cell Components: Nucleus $containing nucleolus$ Ribosomes Rough and Smooth Endoplasmic Reticulum Golgi Body Mitochondria Lysosomes Centrioles Cytoplasm Plasma Membrane
2. Plant Cell Components $additional to animal cell structures$: Cell Wall Chloroplasts Large Central Vacuole

The plasma membrane, a crucial component of all cells, is described in detail:

• Bilayer structure composed of phospholipids
• Integral and peripheral proteins embedded in the membrane
• Carbohydrate side chains attached to the outer surface

The functions of various membrane components are explained:

• Peripheral and integral proteins assist in the passage of larger molecules through the cell membrane
• Adhesion proteins form junctions with adjacent cells
• Receptor proteins act as "docking sites" for specific molecules

The page also provides information on key cellular organelles:

• Nucleus: Houses DNA stored in chromosomes
• Nucleolus: Site of RNA production and ribosome assembly
• Ribosomes: Responsible for protein synthesis
• Endoplasmic Reticulum: Provides mechanical support and aids in intracellular transport
• Smooth ER: Involved in breaking down toxic chemicals and producing hormones and steroids

Vocabulary: Integral proteins - Proteins that span the entire phospholipid bilayer of the cell membrane.

Example: The rough endoplasmic reticulum is studded with ribosomes, giving it a "rough" appearance under an electron microscope.

Definition: The plasma membrane is a selectively permeable barrier that regulates the passage of substances in and out of the cell.

Highlight: The presence of a cell wall and chloroplasts are key features that distinguish plant cells from animal cells.

Quote: "Ribosomes make proteins required by the cell."

Cellular Organelles and Transport Mechanisms

This page continues the exploration of eukaryotic cell organelles and introduces various cellular transport mechanisms, which are crucial concepts in AP Biology Unit 2: cell structure and function.

The page begins by detailing the structure and function of several important organelles:

1. Golgi Complex: Modifies, processes, and sorts proteins and lipids. It also produces vesicles that carry products out of the cell.
2. Mitochondria: Often referred to as the "powerhouse" of the cell, these organelles convert energy into organic molecules. The inner membrane of mitochondria forms cristae, which increase the surface area to volume ratio, enhancing the efficiency of ATP production.
3. Lysosomes: Contain digestive enzymes that break down cellular waste, worn-out organelles, and engulfed particles. They also play a role in apoptosis $programmed cell death$.
4. Centrioles: Produce microtubules during cell division.
5. Vacuoles: Fluid-filled sacs that store food and other substances.
6. Peroxisomes: Detoxify substances and produce hydrogen peroxide as a byproduct. They are particularly common in liver and kidney cells.
7. Cell Wall: Present in plant cells, made of cellulose or chitin.
8. Chloroplasts: Contain chlorophyll and are responsible for photosynthesis in plant cells.
9. Central Vacuole: A large, fluid-filled organelle in plant cells, regulated by turgor pressure.

The page then transitions to discussing cellular transport mechanisms:

• The ability of molecules to move across the cell membrane depends on their size and charge.
• Facilitated transport: Required for hydrophobic molecules to pass through the lipid bilayer. This process uses specialized channels, such as aquaporins for water transport.
• Passive transport: Does not require metabolic input and occurs when substances move down their concentration gradient.
• Osmosis: The movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Vocabulary: Cristae - The folded inner membrane of mitochondria that increases surface area for ATP production.

Example: Aquaporins are specialized protein channels that facilitate the rapid movement of water molecules across cell membranes.

Definition: Passive transport is the movement of substances across a cell membrane without the expenditure of cellular energy, always occurring down the concentration gradient.

Highlight: The Golgi complex plays a crucial role in modifying, sorting, and packaging proteins and lipids for secretion or use within the cell.

Quote: "Mitochondria: The 'power house' that converts energy into organic molecules."

Tonicity, Water Potential, and Active Transport

This page delves into the concepts of tonicity, water potential, and active transport, which are crucial for understanding cellular processes and homeostasis in AP Biology Unit 2: cell structure and function.

Tonicity is introduced as a way to describe the osmotic gradient between solutions:

1. Isotonic: A state of equilibrium where the concentration of solutes is equal on both sides of a semipermeable membrane.
2. Hypertonic: A solution that has a higher concentration of solutes compared to the cell, causing the cell to shrivel due to water loss.
3. Hypotonic: A solution that has a lower concentration of solutes compared to the cell, causing the cell to swell as water enters.

The concept of water potential is explained as the tendency of water to flow from an area of higher water concentration to an area of lower water concentration. The relationship between water potential and concentration is expressed mathematically, with the constant R given as 0.0831.

Active transport is described as the movement of substances against their natural flow $typically from an area of lower concentration to an area of higher concentration$. This process requires energy in the form of ATP. The sodium-potassium pump is presented as an example of active transport, where three sodium ions are moved out of the cell while two potassium ions are brought in.

Vocabulary: Tonicity - The ability of a solution to cause a cell to gain or lose water through osmosis.

Example: When a plant cell is placed in a hypotonic solution, it becomes turgid as water enters the cell, pressing the cell membrane against the cell wall.

Definition: Water potential is a measure of the potential energy of water per unit volume relative to pure water in reference conditions.

Highlight: The sodium-potassium pump is a crucial example of active transport, maintaining the electrochemical gradient necessary for nerve impulse transmission and other cellular functions.

Quote: "Active Transport: movement against natural flow & to ↑ Concentration"

Cellular Structure and Basic Processes

This page introduces fundamental concepts in cell biology, focusing on cellular structure and basic processes essential for life.

The importance of surface area to volume ratio in cellular efficiency is highlighted. Smaller organisms have a larger surface area to volume ratio, allowing for more efficient exchange of materials with the environment. This concept is crucial for understanding cellular adaptations and limitations.

The endosymbiosis theory is introduced, explaining the origin of chloroplasts and mitochondria in eukaryotic cells. This theory is a cornerstone in understanding the evolution of complex cellular structures.

Various cellular transport mechanisms are described:

1. Endocytosis: The process by which cells engulf external substances. Pinocytosis: "Cell drinking" for taking in liquids Phagocytosis: "Cell eating" for ingesting solid particles Receptor-mediated endocytosis: Selective uptake of specific molecules
2. Bulk flow: The one-way movement of fluid driven by pressure, exemplified by blood flow in the circulatory system.
3. Dialysis: The diffusion of solutes across a selectively permeable membrane, a process crucial in kidney function.
4. Exocytosis: The mechanism by which cells expel waste materials.

The page also provides an overview of prokaryotic cell structure, including:

• Capsule: The outermost protective layer
• Cell wall: Composed of peptidoglycans
• Plasma membrane: The lipid bilayer enclosing the cell
• Nucleoid: The region containing the cell's genetic material
• Ribosomes: Smaller than those found in eukaryotes
• Cytoplasm: The jelly-like substance filling the cell

Vocabulary: Endosymbiosis - A theory proposing that certain organelles, such as mitochondria and chloroplasts, originated as independent prokaryotic cells that were engulfed by larger cells.

Example: Pinocytosis can be observed when amoebae take in water droplets from their environment.

Definition: Bulk flow refers to the movement of fluids in one direction due to pressure differences, such as blood flowing through blood vessels.

Highlight: The surface area to volume ratio is a critical factor in determining a cell's efficiency in exchanging materials with its environment. This concept explains why smaller cells are generally more efficient than larger ones.