Bio163:Ch 3 Notes

Overview of the Cell Structure

  • The cell consists of three main parts: the cell membrane, the cytoplasm, and the nucleus.

Cell Membrane

  • Visual Description

    • The cell membrane is represented by a brown structure that holds the contents of the cell.

    • Functions to keep certain materials in and others out.

  • Definition: The cell membrane, or plasma membrane, surrounds the cell.

  • Key Characteristics

    • Selective Permeability: Regulates what enters and exits the cell.

    • Composed mainly of phospholipids, cholesterol, and proteins.

Cytoplasm

  • Visual Description

    • Encompasses everything between the cell membrane and the nucleus.

  • Definition: The cytoplasm includes the area between the cell membrane and the nucleus.

  • Composition

    • Divided into two main parts: cytoskeleton and organelles.

Cytoskeleton

  • Definition: The cytoskeleton provides structural support to the cell and facilitates movement within the cell.

  • Composition

    • Made up of protein fibers.

  • Functions

    • Gives the cell its shape and allows for movement of the cell and movement of materials within the cell.

  • Types of Protein Fibers in Cytoskeleton

    • Microtubules

    • Description: Hollow tubes composed of tubulin protein.

    • Functions: Provide structure, aid in movement, and influence where organelles are placed within the cell.

    • Microfilaments

    • Description: Solid, thin protein fibers, smaller in diameter than microtubules.

    • Analogy: Similar to the filament in traditional Edison light bulbs.

    • Functions: Aid in cell movement and shape.

Structures Composed of Microtubules

  1. Centrioles

    • Description: Cylindrical structures made of microtubules, observed under a microscope.

    • Function: Assist in cell division.

  2. Cilia

    • Description: Numerous short, hair-like structures made of microtubules.

    • Function: Help move fluids and particles across surfaces of cells.

  3. Flagella

    • Description: Long, tail-like structures, also made of microtubules.

    • Function: In humans, sperm cells are the only cells with flagella, which aid in cell movement.

Organelles

  • Definition: Organelles are the "little organs" within the cell that perform specific functions.

  • Key Organelles of the Cell

  1. Ribosomes

    • Description: Small structures seen as specks in the cytoplasm; can be free-floating or attached to the endoplasmic reticulum (ER).

    • Function: Responsible for protein synthesis by assembling amino acids.

  2. Endoplasmic Reticulum (ER)

    • Rough ER

      • Description: Has ribosomes attached, appears rough.

      • Function: Synthesizes proteins and helps in protein-folding.

    • Smooth ER

      • Description: Lacks ribosomes, appears smooth.

      • Functions: Synthesizes lipids and participates in detoxifying enzymes.

  3. Golgi Apparatus

    • Description: Located next to the ER; often called the Golgi body.

    • Function: Modifies, sorts, and packages proteins and lipids for distribution or secretion.

  4. Mitochondria

    • Nickname: Often referred to as the "powerhouse" of the cell.

    • Function: Site of ATP production through aerobic respiration.

  5. Vesicles

    • Description: Small membrane-bound sacs that transport substances within the cell.

    • Types:

      • Transport Vesicles: Carry molecules from one part of the cell to another.

      • Lysosomes: Vesicles containing digestive enzymes for breaking down waste.

Nucleus

  • Definition: The nucleus is often referred to as the "control center" of the cell, similar to the nucleus of an atom.

  • Description

    • Usually large and centrally located, surrounded by a nuclear envelope.

  • Key Components

    • Nuclear Envelope: Membrane enclosing the nucleus; contains nuclear pores that control what enters and exits.

    • Nucleolus: Inside the nucleus; a site for RNA synthesis and ribosome assembly.

    • Chromatin: The DNA, RNA, and proteins within the nucleus; appears as a tangle of fibers that condense into chromosomes during cell division.

Membrane Physiology

  • Cell Membrane Functions: Encloses the cell, maintaining a stable internal environment by being selectively permeable.

  • Components: Comprised mainly of phospholipids forming a bilayer, along with cholesterol and proteins.

  • Passive Transport Mechanisms

    • Diffusion:

      • Definition: The movement of molecules from an area of high concentration to low concentration.

      • Affected by temperature, size of molecules, and concentration gradient.

    • Facilitated Diffusion:

    • Definition: A process that helps specific molecules cross the membrane with the assistance of carrier proteins.

    • Example: Movement of ions or large molecules down their concentration gradient without energy usage.

    • Osmosis:

    • Definition: A specific type of diffusion involving the movement of water across a selectively permeable membrane.

    • Concepts of Tonicity:

      • Isotonic Solution: Equal concentration inside and outside, no net movement of water.

      • Hypertonic Solution: Higher concentration of solutes outside, causing the cell to lose water (crenation).

      • Hypotonic Solution: Lower concentration of solutes outside, causing the cell to gain water (lysis).

Summary

  • The cell is structured into three primary parts: the membrane, cytoplasm, and nucleus.

  • Each component has distinct roles in maintaining cellular structure and performing essential functions such as transport, energy production, and protein synthesis.