Cell Structure and Function Quiz

Cell Structure and Function

• Cells are fundamental units of life, with three primary components: plasma membrane, cytoplasm, and nucleus.
• The plasma membrane acts as a barrier between the cell's internal environment and its surroundings.
• The cytoplasm is the cellular material outside the nucleus; it includes the cytosol (intracellular fluid), organelles, and inclusions.
• The nucleus houses the cell's genetic material (DNA).

Cytoplasm

• Cytoplasm is the area between the plasma membrane and the nucleus.
• It's composed of cytosol, organelles, and inclusions.
• Cytosol is the fluid portion of the cytoplasm, composed largely of water with dissolved solutes (e.g., salts, sugars, proteins)
• Organelles are specialized structures with specific functions inside the cell (e.g., mitochondria, ribosomes).
• Inclusions are varied chemical substances, often stored, depending on the cell type (e.g., glycogen, lipid droplets, crystals).

Plasma Membrane

• The plasma membrane is a phospholipid bilayer that encloses the cell contents and controls what enters and exits.
• Lipids (phospholipids and cholesterol) contribute to membrane fluidity and stability.
• Proteins embedded in the membrane have diverse functions, including transport, signaling, and structural support.
• Glycolipids and glycoproteins are attached carbohydrate-based molecules that project from the exterior surface of the cell; these are involved in cell-to-cell recognition and interaction.
• The membrane is selectively permeable, meaning it controls which substances can pass through.

Membrane Fluidity

• Membrane fluidity is influenced by temperature and fatty acid composition (saturated vs. unsaturated).
• Cholesterol strengthens and stabilizes the membrane.

Membrane Proteins

• Membrane proteins perform a diverse range of tasks, including transport, cell signaling, and structural support.
• Integral proteins are embedded in the lipid bilayer; peripheral proteins are loosely attached.

Diffusion

• Diffusion is the tendency of molecules to spread from areas of high concentration to areas of low concentration.
• Factors influencing diffusion rate include concentration gradient, temperature, molecule size, and membrane permeability.
• Diffusion across the membrane can be passive (no energy required) or facilitated (aided by membrane proteins).

Active Transport

• Active transport moves molecules against their concentration gradient, requiring energy (often ATP).
• Primary active transport directly uses ATP for transport.
• Secondary active transport uses the electrochemical gradient established by primary active transport to drive the movement of another substance.
• Types of active transport include pumps and cotransport systems.

Vesicular Transport

• Vesicular transport involves the movement of substances across the membrane within vesicles.
• Exocytosis is the process where materials are expelled from the cell using vesicles.
• Endocytosis is the process where materials are taken into the cell using vesicles (e.g., phagocytosis, pinocytosis, receptor-mediated endocytosis).

Tonicity and Osmosis

• Tonicity describes the ability of a solution to cause a cell to gain or lose water.
• Isotonic solutions have equal solute concentrations inside and outside the cell, resulting in no net water movement.
• Hypotonic solutions have a lower solute concentration than inside the cell, causing water to move into the cell, potentially causing swelling or lysis.
• Hypertonic solutions have a higher solute concentration than inside the cell, causing water to move out of the cell, potentially causing shrinking or crenation.

Membrane Permeability

• Selectively permeable means the cell membrane allows some substances to pass through but not others. Molecules have varying degrees of permeability across the membrane (polar/non-polar, small/large).
• The membrane is semi-permeable, letting select molecules pass through.
• Gases, hydrophobic molecules, small polar molecules, and water can easily pass through the lipid bilayer. Larger polar molecules and ions require assistance.

Specialised transport proteins (gated channels)

• Channel proteins form hydrophilic channels in the membrane allowing specific molecules/ions to move through.
• Ligand-gated channels only open when a specific signaling molecule (ligand) binds.
• Voltage-gated channels have sensitivity to changes in membrane potential.

Osmotic pressure

• The opposing pressure needed to completely stop net movement of water by osmosis.
• Hydrostatic pressure refers to pressure exerted by water against a membrane.

Cytoskeleton

• A network of protein filaments that supports the cell shape and facilitates movement.