Cellular Structure and Function

• Completion of this unit enables students to explain and compare cellular structure and function, and analyze the cell cycle, cell growth, death, and differentiation.

Cellular Structure and Function

• Cells are the basic structural unit of life on Earth
• Distinctions exist between prokaryotic and eukaryotic cells
• Both plant and animal cells have organelles
• Plant and animal cell organelles have distinct functions, including chloroplasts and mitochondria
• The plasma membrane's structure and function is to control the passage of water, hydrophilic and hydrophobic substances via osmosis, facilitated diffusion, and active transport

Cell Membrane Diagram

• Key components of the cell membrane include: Cholesterol, Glycolipid, Glycoprotein, Phospholipid, Phospholipid bilayer, Channel and Carrier Protein
• Cell membranes are semi-permeable or selectively permeable
• Cholesterol maintains membrane fluidity, whereas glycolipids and glycoproteins are involved in cell recognition and signaling
• Transport proteins facilitate the movement of specific molecules across the membrane
• Two types of transport proteins exist: channel proteins and carrier proteins
• The fluid mosaic model describes the structure of the plasma membrane
• Plasma membranes have various functions, including regulating transport, cell signaling, and cell adhesion

Membrane Transport

• Active transport requires energy, whereas passive transport does not
• Types of passive transport: Osmosis, Diffusion, and Facilitated diffusion
• Processes like Diffusion, Osmosis, and Facilitated Diffusion enable molecules to move across the membrane
• Hypertonic solutions cause cells to shrink, hypotonic solutions cause cells to swell, and isotonic solutions have no effect on cell volume
• In hypertonic environments, animal cells shrink; in hypotonic environments, they may lyse
• In hypertonic environments, plant cells plasmolyze; in hypotonic environments, they become turgid
• Lysis is the bursting of a cell
• Turgid refers to a cell being swollen and rigid due to water uptake
• Plasmolysis is the contraction of the protoplast of a plant cell as a result of loss of water from the cell
• Animal cells undergo lysis in hypotonic environments due to water influx
• Active transport requires energy to move molecules against their concentration gradient
• Endocytosis is the process of cells engulfing substances.
• Exocytosis is the process of cells expelling substances.
• Facilitated diffusion uses transport proteins to aid movement down the concentration gradient, while active transport uses energy to move molecules against the concentration gradient

Transport Proteins

• Transport proteins are involved in facilitated diffusion
• Transport proteins are involved in active transport
• Glucose is transported via facilitated diffusion
• Carbon dioxide is transported via simple diffusion
• Amino acids are transported via active transport or facilitated diffusion
• Oxygen is transported via simple diffusion
• Lipophilic drugs are transported via simple diffusion
• Chloride ions are transported via facilitated diffusion
• Magnesium ions are transported via facilitated diffusion
• Ethanol is transported via simple diffusion
• Steroids are transported via simple diffusion
• Sodium ions are transported against the concentration gradient via active transport
• Water is transported via osmosis
• Potassium ions are transported via active transport
• Alcohol is transported via simple diffusion
• Chloroform is transported via simple diffusion
• Calcium ions are transported via active transport or facilitated diffusion

Key Words

• Plasma membrane: The outer boundary of a cell that regulates what enters and exits
• Intracellular: Inside the cell
• Extracellular: Outside the cell
• Phospholipid: A lipid containing a phosphate group in its molecule
• Selectively Permeable: Allows certain substances to pass through
• Semi-Permeable: Selectively permeable
• Phosphate head: The hydrophilic, polar portion of a phospholipid
• Fatty acid chain: The hydrophobic, nonpolar portion of a phospholipid
• Fluid Mosaic: A model of the cell membrane structure
• Cholesterol: A lipid that helps maintain membrane fluidity
• Glycolipid: A lipid with a carbohydrate attached
• Glycoprotein: A protein with a carbohydrate attached
• Phospholipid bilayer: A double layer of phospholipids that forms the cell membrane
• Polar: Having an uneven distribution of charge
• Nonpolar: Having an even distribution of charge
• Hydrophilic: Attracted to water
• Hydrophobic: Repelled by water
• Amphipathic: Having both hydrophilic and hydrophobic parts
• Transport Protein: A protein that helps move substances across the cell membrane
• Carrier Protein: A protein that binds to a specific substance and transports it across the cell membrane
• Channel Protein: A protein that forms a channel through which specific substances can pass
• Cell membrane: The outer boundary of a cell that regulates what enters and exits
• Active Transport: Movement of molecules across the cell membrane against their concentration gradient, requiring energy
• Passive Transport: Movement of molecules across the cell membrane down their concentration gradient, without requiring energy
• Concentration gradient: The difference in concentration of a substance across a space
• Diffusion: The movement of molecules from an area of high concentration to an area of low concentration
• Osmosis: The movement of water across a semi-permeable membrane from an area of high water concentration to an area of low water concentration
• Hypotonic: Having a lower solute concentration than another solution
• Isotonic: Having the same solute concentration as another solution
• Hypertonic: Having a higher solute concentration than another solution
• Facilitated Diffusion: The movement of molecules across the cell membrane with the help of transport proteins
• Lysis: The bursting of a cell
• Turgid: Swollen and rigid due to water uptake
• Plasmolysis: The contraction of the protoplast of a plant cell as a result of loss of water from the cell
• Solute: A substance that is dissolved in a solvent
• Solvent: A substance that dissolves a solute
• Solution: A mixture of a solute and a solvent
• Sodium-Potassium Pump: A transport protein that pumps sodium ions out of the cell and potassium ions into the cell
• Endocytosis: The process of cells engulfing substances from outside the cell
• Pinocytosis: A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes
• Exocytosis: The process of cells expelling substances to outside the cell
• Phagocytosis: A type of endocytosis in which the cell engulfs large particles or cells
• Bulk Transport: The movement of large amounts of substances across the cell membrane