Cell Structures, Transport, and Communication Practice
Study Guide Notes for Cell Biology Exam
Exam Overview
- The exam will consist of:
- Approximately 25 multiple choice questions.
- Approximately 5-10 short answer questions, which will likely have multiple parts.
Lesson 2.1: Cell Structures and Functions
Smallest Unit of Life:
- The smallest unit of life is the cell.
Definition of Organelle:
- An organelle is an interior structure within a cell that performs specific functions.
Differences Between Prokaryotes and Eukaryotes:
- Prokaryotes:
- Simple and less compartmentalized.
- Examples of structures:
- Nucleotide (not enclosed in a nucleus).
- Cytoplasm.
- Ribosome.
- Cell membrane.
- Cell wall.
- Flagella.
- Pili.
- Genetic information stored as a single circular DNA molecule (chromosome) that floats freely within the cytoplasm.
- Unicellular organisms, usually reproduce asexually.
- Eukaryotes:
- More complex but organized into compartments.
- Structures include additional membrane layers for protection.
- Can be unicellular or multicellular.
Unique Organelles in Prokaryotes:
- No nucleus or other membrane-bound organelles.
Shared Organelles:
- Both prokaryotes and eukaryotes have:
- Cytoplasm.
- Ribosome.
- Cell membrane.
Eukaryotic Organelles and Their Functions:
- Cytoplasm: The gel-like substance within the cell where organelles are suspended.
- Ribosome: Site of protein synthesis.
- Cell Membrane: Semi-permeable barrier that surrounds the cell.
- Mitochondria: Known as the powerhouse of the cell; generates ATP through cellular respiration.
- Nucleus: Contains genetic material (DNA) and regulates gene expression.
- Endoplasmic Reticulum (ER):
- Rough ER: Studded with ribosomes; involved in protein synthesis and processing.
- Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.
- Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or delivery to other organelles.
- Lysosome: Contains enzymes for digesting macromolecules and recycling cellular components.
Organelles Unique to Plants:
- Cell Wall: Provides structure and protection.
- Chloroplast: Site of photosynthesis.
- Vacuoles: Large storage sacs that also maintain turgor pressure.
Organelles Unique to Animals:
- Centrioles: Organize microtubules during cell division.
Organelles for Movement:
- Cilia: Hair-like structures that help move fluid across the surface of cells.
- Example: Lungs (clear mucus and debris).
- Flagella: Tail-like structures that propel the cell.
- Example: Sperm cells.
Lesson 2.2: Cell Transport
Distinctions:
- Intracellular: Processes occurring within the cell, specifically in the cytosol.
- Intercellular: Processes occurring between cells, across cell membranes.
Intracellular Transport:
- Mainly involves vesicles which are transport sacs carrying molecules within the cell.
Cell Membrane Structure:
- Comprised of a phospholipid bilayer:
- Phosphate Head: Polar, hydrophilic (water-loving).
- Fatty Acid Tails: Nonpolar, hydrophobic (water-repelling).
- Cholesterol: A lipid that helps maintain membrane structure and fluidity.
- Proteins: Serve roles in signaling and transport.
Concentration Gradient:
- Definition: A difference in concentration of substances across a space.
Passive Transport:
- No energy required; occurs freely due to random molecular motion:
- Diffusion: Random movement causes molecules to spread from an area of high concentration to an area of low concentration.
- Facilitated Diffusion: Molecules that are blocked by the membrane move down their concentration gradient via membrane proteins.
- Types of Membrane Proteins:
- Ion Channels: Allow ions to move freely.
- Carrier Proteins: Assist in transporting larger molecules.
Active Transport:
- Requires energy, often in the form of ATP, to move molecules against their concentration gradient.
Differences Between Diffusion and Facilitated Diffusion:
- Diffusion: Spontaneous movement based on concentration gradient.
- Facilitated Diffusion: Assisted movement when molecules are blocked by the membrane.
Osmosis:
- Movement of water toward areas of higher solute concentration.
- Principle: "Where salt goes, water follows."
- Hypertonic: Outside of the cell has a higher concentration of solute than inside; water flows out causing the cell to shrink.
- Hypotonic: Outside of the cell has a lower concentration of solute than inside; water flows in causing the cell to swell and possibly burst.
- Isotonic: The concentration of solute inside and outside the cell is balanced; water flow is equal.
Biological Consequences of Osmosis:
- Hypertonic Solutions: Water exits cell leading to cellular shrinkage.
- Hypotonic Solutions: Water enters cell leading to possible lysis (bursting).
Examples of Active Diffusion Proteins:
- Symporters: Both molecules move in the same direction (e.g., sodium-glucose linked transporter - SGLT).
- Antiporters: Molecules move in opposite directions (e.g., sodium-potassium pump - Na+-K+ pump).
Endocytosis vs. Exocytosis:
- Endocytosis: Cell takes in materials by forming a vesicle from the cell membrane.
- Phagocytosis: Engulfing solid materials.
- Pinocytosis: Engulfing liquids.
- Exocytosis: Cell expels materials by fusing vesicles with the cell membrane.
Lesson 2.3: Cell Communication
Definitions:
- Ligand: Signaling molecules used in cell communication.
- Receptor: Proteins that bind to ligands.
Interaction:
- Ligands and receptors fit together like puzzle pieces; specificity in binding is crucial.
Direct vs. Indirect Communication:
- Direct Communication: Cells communicate through direct contact (targeted and close interaction).
- Indirect Communication: Cells release signals to affect multiple nearby or distant cells (broad and distant).
Types of Cell Communication:
- Autocrine: Cell communicates with itself.
- Paracrine: Cell communicates with nearby cells.
- Endocrine: Long-distance communication involves hormones.
Direct Communication Mechanism:
- Gap Junctions: Protein structures called connexons connect the cytosol of two adjacent cells, allowing ions and small molecules to pass through, enabling rapid communication.
Importance of Paracrine Signaling:
- Common in the nervous system; allows for quick responses to immediate environmental changes.
Endocrine System Communication:
- Primarily involves hormones, which can affect cells throughout the body as they travel via the bloodstream.
Signal Transduction Steps:
- Receptor Activation: The signal molecule binds to the receptor protein.
- Signal Transduction: The signal is transmitted via intracellular pathways to the target area of the cell.
- Cell Response: The cell's intended response is activated.
Conformational Change:
- The binding of a ligand causes a shape change in the receptor, initiating the signaling cascade (signal transduction).
Receptor Locations:
- Receptors can be found both inside and outside the cell, indicating their roles in either intracellular or intercellular communication.
Types of Receptors:
- Enzyme-Linked Receptors: Involves catalytic activity when ligands bind.
- G Protein-Coupled Receptors (GPCRs): Involve a complex signaling mechanism; characterized by 7 transmembrane domains.
- Ligand-Gated Ion Channels: Convert chemical signals (e.g., neurotransmitters) into rapid electrical signals, crucial for neuron signaling.
Role of Secondary Messengers:
- Secondary messengers are crucial for amplifying and speeding up cellular messages.
- Most common secondary messenger: cyclic AMP (cAMP).
Location of Cell Response:
- Responses often occur at the genetic level, leading to changes in gene expression.
Apoptosis:
- Programmed cell death, which is biologically important for controlling cell population, preventing tissue damage, and eliminating worn-out or potentially cancerous cells.
- Apoptosis is initiated through communication signals indicating that a cell is to be terminated.