Chapter 6: Cell structure

Essential Parts of Any Cell

• Cytosol – The semifluid substance inside the cell.

• Chromosomes – Contain DNA, carrying genetic information.

• Ribosomes – Synthesize proteins.

• Plasma Membrane – Selective barrier controlling passage of materials.

Eukaryotes vs. Prokaryotes

Differences

Similarities

• Both have: DNA, ribosomes, cytoplasm, and plasma membranes.

Cell Structures & Functions

Ribosomes (Protein Factories)

• Function: Synthesize proteins.

• Location:

  • Free ribosomes in cytosol.

  • Bound ribosomes on rough ER and nuclear envelope.

  • Also found inside mitochondria and chloroplasts.

Nucleus (Genetic Control Center)

• Function: Stores genetic material (DNA).

• Key Components:

  • Nuclear Envelope – Double membrane with nuclear pores.

  • Nucleolus – Site of rRNA synthesis and ribosome assembly.

  • Chromatin – DNA wrapped around histones.

Endoplasmic Reticulum (ER) (Biosynthetic Factory)

• Rough ER:

  • Studded with ribosomes.

  • Synthesizes proteins (e.g., glycoproteins).

  • Transports proteins to the Golgi apparatus.

• Smooth ER:

  • Lacks ribosomes.

  • Synthesizes lipids.

  • Detoxifies drugs.

  • Stores calcium ions.

Golgi Apparatus (Shipping & Receiving Center)

• Structure: Stacks of flattened sacs (cisternae).

• Function:

  • Modifies, sorts, and packages proteins/lipids from ER.

  • Sends materials via vesicles.

Lysosomes (Digestive Compartments)

• Function:

  • Contains hydrolytic enzymes that digest macromolecules.

  • Breaks down damaged organelles (autophagy).

  • Involved in phagocytosis (engulfing & digesting food particles).

Vacuoles (Storage & Maintenance Compartments)

• Three Types:

  1. Food Vacuoles – Formed by phagocytosis.

  2. Contractile Vacuoles – Pump excess water out (found in protists).

  3. Central Vacuole – Stores water & nutrients in plant cells.

Mitochondria & Chloroplasts (Energy Converters)

• Why They Are Special:

  • Both have their own DNA & ribosomes (supporting the Endosymbiont Theory).

  • Mitochondria:

    • Perform cellular respiration (convert glucose into ATP).

    • Found in almost all eukaryotic cells.

  • Chloroplasts:

    • Perform photosynthesis (convert light into chemical energy).

    • Contain chlorophyll (green pigment).

Cytoskeleton (Cell Structure & Movement)

• Network of protein fibers that provide support and movement.

• Three Components:

  1. Microtubules – Provide shape, serve as "tracks" for organelle movement.

  2. Microfilaments – Involved in muscle contraction & cell shape changes.

• 3. Intermediate Filaments – Provide structural support.