Comprehensive Cell Structure and Function Notes

Cell Structures and Functions

Nucleus

• Area of Cell Structure: Located in the center of the cytoplasm.
• Function: Contains DNA and controls all cell activities.
• Description: The nucleus is a sphere-shaped organelle encased by a double membrane called the nuclear envelope. This membrane has pores that regulate the movement of substances in and out of the nucleus. Inside the nucleus is the nucleolus.
• Sketch: Circle with double membrane and pores; contains a smaller nucleolus inside.

Nucleolus

• Area of Cell Structure: Found inside the nucleus.
• Function: Makes ribosomes.
• Description: A small, dark-staining spherical body within the nucleus, composed of proteins and RNA. It is the site of ribosome synthesis.
• Sketch: Small dark circle inside the nucleus.

Cytoplasm

• Area of Cell Structure: Fills the cell.
• Function: Holds organelles in place and is the site of many biochemical reactions.
• Description: The cytoplasm is a gel-like substance consisting of water, salts, and organic molecules. It suspends the organelles and allows for the transport of substances throughout the cell.
• Sketch: Fluid filling the cell with organelles floating in it.

Cell Membrane

• Area of Cell Structure: Surrounds the cell.
• Function: Acts as a semi-permeable barrier that controls what enters and exits the cell.
• Description: A thin, flexible barrier composed of a phospholipid bilayer with embedded proteins. It regulates the passage of ions, water, and other molecules into and out of the cell, maintaining cell homeostasis.
• Sketch: Thin line around the entire cell with a flexible, wavy edge.

Mitochondria

• Area of Cell Structure: Found throughout the cytoplasm.
• Function: Produces energy in the form of ATP through cellular respiration (the "powerhouse of the cell"). The equation for cellular respiration is:
  C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + ATP
• Description: Bean-shaped organelles with a double membrane. The inner membrane is highly folded into cristae, which increases the surface area for ATP production.
• Sketch: Bean-shaped with a squiggly inner membrane.

Ribosomes

• Area of Cell Structure: Found floating in the cytoplasm or attached to the rough endoplasmic reticulum (ER).
• Function: Makes proteins through protein synthesis.
• Description: Small structures made of ribosomal RNA (rRNA) and proteins. They translate genetic code from messenger RNA (mRNA) into an amino acid sequence to build proteins.
• Sketch: Tiny dots, either free-floating or on the ER.

Endoplasmic Reticulum (ER)

• Area of Cell Structure: Network of membranes throughout the cytoplasm.
• Function: Helps make and transport proteins and lipids.
• Description: An extensive network of interconnected tubules and flattened sacs called cisternae. The ER is continuous with the nuclear envelope and exists in two forms: rough ER and smooth ER.
• Sketch: Folded membrane channels connected to the nucleus.

Rough ER

• Area of Cell Structure: Part of the endoplasmic reticulum.
• Function: Synthesizes and transports proteins due to the presence of ribosomes on its surface.
• Description: The rough ER is studded with ribosomes, giving it a rough appearance. It plays a crucial role in the synthesis, folding, and modification of proteins that are destined for secretion or insertion into membranes.
• Sketch: Same as ER but with dots (ribosomes) on it.

Smooth ER

• Area of Cell Structure: Part of the endoplasmic reticulum.
• Function: Synthesizes lipids, phospholipids, and steroids. It also detoxifies toxins.
• Description: The smooth ER lacks ribosomes and is involved in lipid metabolism, detoxification, and calcium storage.
• Sketch: Smooth folded membranes without dots.

Lysosomes

• Area of Cell Structure: Found in animal cytoplasm.
• Function: Breaks down waste, food, and old cell parts (the "clean-up crew").
• Description: Small, spherical sacs containing digestive enzymes (hydrolases). They break down cellular waste, debris, and ingested substances, recycling the components back into the cell.
• Sketch: Small circular sac with digestive enzymes.

Cytoskeleton

• Function: Provides structure, support, and facilitates cell movement and intracellular transport.

Microfilaments

• Description: Thin protein filaments made of actin.
• Function: Provides structure and help with cell movement.
• Sketch: Thin lines or threads crossing the cytoplasm.

Microtubules

• Description: Hollow tubes made of tubulin proteins.
• Function: Give shape to the cell and track the movement of organelles.
• Sketch: Thicker tubes running through the cytoplasm.

Chloroplasts

• Area of Cell Structure: Found in plant cytoplasm.
• Function: Site of photosynthesis; contains chlorophyll to make food from sunlight. The equation of photosynthesis is:
  6CO2 + 6H2O + Light \rightarrow C6H{12}O6 + 6O2
• Description: Oval-shaped organelles with a double membrane. Inside, there are stacks of thylakoids called grana, which contain chlorophyll.
• Sketch: Oval with stacks of thylakoids inside (grana).

Vacuoles

• Area of Cell Structure: Present in both plant and animal cells.
• Function: Store nutrients, waste, and water.
• Description: Membrane-bound sacs that store water, ions, nutrients, and waste. In plants, there is usually one large central vacuole that maintains cell turgor pressure. In animals, there are typically several small vacuoles.
• Sketch: In plants: one large sac. In animals: several small bubbles.

Centrioles

• Area of Cell Structure: Found in animal cells near the nucleus.
• Function: Help with cell division.
• Description: Paired, cylindrical structures composed of microtubules. They are involved in the organization of the spindle fibers during cell division.
• Sketch: Two cylinder-shaped structures at right angles near the nucleus.

Golgi Bodies (Golgi Apparatus)

• Area of Cell Structure: Located in the cytoplasm.
• Function: Modifies, sorts, and packages proteins for delivery (the "post office" of the cell).
• Description: A stack of flattened, membrane-bound sacs (cisternae). It processes and packages proteins and lipids synthesized in the ER, directing them to their final destinations within or outside the cell.
• Sketch: Stack of flattened pancakes or sacs.

Cell Wall

• Area of Cell Structure: Rigid outer layer in plant cells.
• Function: Provides support and protection.
• Description: A rigid layer composed of cellulose in plant cells. It provides structural support and protection to the cell. It is located outside the cell membrane.
• Sketch: Thick outermost layer outside the cell membrane in plant cells.