Lecture 2.2 - The Cell Membrane

Flashcards covering key vocabulary related to the structure and function of cell membranes as discussed in the Biological Systems Module 2 lecture.

Plasma Membrane

The membrane that surrounds all cells, separating internal components from the external environment and maintaining homeostasis.

Selectively Permeable

A property of biological membranes that allows some substances to cross more easily than others.

Fluid Mosaic Model

Describes the structure of the plasma membrane as a mosaic of various proteins that float in or on the fluid lipid bilayer.

Phospholipid Bilayer

A double layer of phospholipids that makes up the fundamental structure of cell membranes.

Passive Transport

The movement of substances across a cell membrane without the use of energy, following the concentration gradient.

Osmosis

The diffusion of free water across a semi-permeable membrane.

Aquaporins

Membrane proteins that facilitate the transport of water across the cell membrane.

Active Transport

The movement of molecules across a cell membrane against their concentration gradient, requiring energy input.

Endocytosis

The process by which cells internalize substances from their external environment by engulfing them in a vesicle.

Concentration Gradient

A difference in the concentration of a substance across a distance, which drives the movement of molecules during diffusion.

Turgor Pressure

The pressure exerted by the fluid (usually water) inside plant cells against the cell wall.

Hypertonic Solution

A solution that has a higher concentration of solutes than inside the cell, leading to water moving out and cell shrinkage.

Hypotonic Solution

A solution with a lower concentration of solutes than the cell, causing water to enter the cell and can lead to cell bursting.

Isotonic Solution

A solution with equal concentrations of solute inside and outside the cell, leading to no net movement of water.

What type of external environment can the biological membrane sense?

Protein and carbohydrates on surface detect external cues

Phospholipids are…

Amphipathic → spontaneously forms a bilayer

Amphipathic

Contains both hydrophilic and hydrophobic regions

Membrane serves as an…

Effective barrier for large, polar (hydrophilic) or charged molecules

What type of molecules can cross unaided across the membrane?

Small, nonpolar molecules (e.g. gases, hydrophobic molecules

Are the heads in the membrane hydrophilic or hydrophobic?

The heads in the membrane are hydrophilic, allowing them to interact with water

Are the tails in the membrane hydrophilic or hydrophobic?

The tails in the membrane are hydrophobic, repelling water and forming a barrier that prevents the passage of polar molecules.

What does the biological membrane contain? (not the head and tails)

• Proteins and carbohydrates

• Sterols

Proteins and carbohydrates in the membrane

Act as gates, sensors, ID cards, anchors

Sterols in the membrane

Maintain proper fluidity and stability

Membrane protein functions

• Transport across cell membrane (protein carriers and protein channels)

• Enzymatic activity

• Receptor proteins (signal transduction)

• Cell-cell recognition

• Intercellular joining

• Structure (connect with cytoskeleton in cell

Diffusion

The process by which molecules move from an area of higher concentration to an area of lower concentration, resulting in an even distribution.

Does spontaneous process need energy

No, it occurs naturally without energy input.

Why does passive transport occur?

The cell does not have to spend energy to make it happen - the concentration gradient drives it

Is the cell membrane permeable or semi-permeable

The cell membrane is semi-permeable, allowing certain substances to pass while blocking others.

What is the cell membrane permeable to?

Permeable to water molecules

What does the cell membrane do to gain water?

Open channels called aquaporins

What is the cell membrane impermeable to?

Charge ions (require channels or pumps)

What happens when a cell does not have enough water?

Cells shrivel and die

What happens when the cell has too much water?

Cells swell and burst

Osmoregulation

Animal cells and protists must live in isotonic environment, or actively control solute concentration

Turgor pressure

Cell wall pushes back against water pressure in hypotonic environment

Which of the following statements about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) speeds up the process of osmosis

Membrane transport

Movement across plasma membranes depends on size of the substance and its concentration gradient

Passive transport in small molecules

• With concentration gradient

• No energy required

• Diffusion and facilitated diffusion

Active transport in small cells

• Against concentration gradient

• Used energy (ATP)

Examples of facilitated diffusion

• Lipid bilayer normally blocks flow of polar molecules, such as water

  • Aquaporins are membrane channels (proteins) that allow water to cross the cell membrane

Example of active transport

Sodium-potassium pump (Na+/K+ pump)

Exocytosis

To export large macromolecules (tagged for export by the Golgi), the cell packages them into vesicles, which then merge with the membrane, releasing contents in extracellular space

One type of endocytosis

Phagocytosis

Based on the figure, which of these experimental treatments would increase the rate of sucrose transport into a plant cell

Decreasing extracellular pH