BIOL 20A Midterm 2

Topic 6: Introduction to Cells/Biological Membranes

  1. Prokaryotic vs. Eukaryotic Cells:

    • Prokaryotic cells: Simple cells without a nucleus or membrane-bound organelles. They have a single circular DNA molecule, ribosomes, and a plasma membrane. Examples include bacteria and archaea.

    • Eukaryotic cells: More complex cells with a nucleus containing linear DNA, membrane-bound organelles (e.g., mitochondria, chloroplasts), and a cytoskeleton. Examples include plant and animal cells.

  2. Fluid-Mosaic Model:

    • This model describes the structure of biological membranes, where the lipid bilayer is fluid and proteins are embedded within it, floating like "mosaic" pieces. The lipid bilayer allows for membrane flexibility and movement, while proteins perform various functions like transport, signaling, and structural support.

  3. Semi-Permeable Barriers:

    • Biological membranes are semi-permeable, meaning they allow certain substances (e.g., gases, small nonpolar molecules) to pass freely, while others (e.g., large, charged molecules) require transport proteins to cross.

Key Terms:

  • Nucleus: The membrane-bound organelle that contains the cell’s genetic material.

  • Cytoplasm: The jelly-like substance inside the cell, excluding the nucleus.

  • Nucleoplasm: The substance within the nucleus that contains nucleotides and enzymes for DNA/RNA processes.

  • Organelle: Specialized structures within a cell that perform specific functions (e.g., mitochondria, Golgi apparatus).

  • Mitochondria: Organelles responsible for energy production through cellular respiration.

  • Chloroplast: Organelles in plant cells that perform photosynthesis.

  • Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis.

  • Golgi Apparatus: Organelles that modify, sort, and package proteins and lipids.

  • Cytoskeleton: A network of fibers that provide structural support and facilitate cell movement.

  • Plasma Membrane: The outer boundary of the cell that controls what enters and leaves.

  • Integral Membrane Protein: Proteins that are embedded within the lipid bilayer.

  • Peripheral Membrane Protein: Proteins that associate with the membrane’s surface but don’t embed within the lipid bilayer.

Topic 7: Transport across Biological Membranes

  1. Influence of Size, Polarity, and Charge on Diffusion:

    • Small, nonpolar molecules (e.g., oxygen, carbon dioxide) can diffuse easily across the lipid bilayer. Larger, polar, or charged molecules (e.g., glucose, ions) require transport proteins.

  2. Comparison of Diffusion Methods:

    • Passive Diffusion: Movement of molecules from high to low concentration without energy input.

    • Facilitated Diffusion: Passive movement aided by transport proteins like channels or carriers.

    • Active Transport: Movement against the concentration gradient, requiring energy (usually ATP) and a pump or co-transporter protein.

  3. Osmosis:

    • Water moves across membranes by osmosis, from areas of low solute concentration to areas of high solute concentration.

  4. Carrier Proteins vs. Channels:

    • Carrier Proteins: Bind and change shape to move molecules across the membrane.

    • Ion Channels: Form pores in the membrane for ions to pass through.

  5. Co-Transporters vs. Pumps:

    • Co-Transporters: Move two or more ions or molecules in the same or opposite direction using the gradient of one solute to power the transport of another.

    • Pumps: Actively transport ions or molecules against their gradient, often using ATP (e.g., sodium-potassium pump).

  6. Sodium-Potassium ATPase:

    • This pump maintains the cell’s resting membrane potential by moving sodium ions out of the cell and potassium ions into the cell, using ATP.

  7. Exocytosis & Endocytosis:

    • Exocytosis: Process by which cells expel materials in vesicles that fuse with the plasma membrane.

    • Endocytosis: Process by which cells intake materials by engulfing them in vesicles.

  8. Pinocytosis, Phagocytosis, and Receptor-Mediated Endocytosis:

    • Pinocytosis: "Cell drinking," where the cell engulfs extracellular fluid.

    • Phagocytosis: "Cell eating," where the cell engulfs large particles or pathogens.

    • Receptor-Mediated Endocytosis: Specific molecules are brought into the cell through receptor binding.

Key Terms:

  • Passive Diffusion: Movement from high to low concentration without energy.

  • Facilitated Diffusion: Transport aided by proteins.

  • Active Transport: Energy-driven movement of molecules against the concentration gradient.

  • Osmosis: Water movement across a membrane.

  • Hypotonic: Solution with lower solute concentration than the cell.

  • Isotonic: Solution with equal solute concentration as the cell.

  • Hypertonic: Solution with higher solute concentration than the cell.

  • Ion Channel: Protein channel that allows ions to pass.

  • Carrier Protein: Protein that changes shape to transport molecules.

  • Pump: Protein that uses energy to transport molecules against a gradient.

  • Co-transporter: Protein that moves multiple molecules together.

  • Sodium-Potassium ATPase: Pump that maintains ion gradients in cells.

  • Exocytosis: Expulsion of materials from the cell.

  • Endocytosis: Uptake of materials into the cell.

  • Phagocytosis: Engulfment of large particles by the cell.

  • Pinocytosis: Uptake of extracellular fluid by the cell.

  • Receptor-Mediated Endocytosis: Selective uptake via receptor binding.

Topic 8: DNA and the Genetic Code

  1. Experimental Evidence for DNA as the Genetic Material:

    • Key experiments like Griffith’s transformation experiment, Avery's DNA identification, and Hershey-Chase experiment provided evidence that DNA carries genetic information.

  2. DNA Replication:

    • The process involves DNA helicase unwinding the DNA, DNA polymerase adding complementary nucleotides, and DNA ligase sealing the new strands. It’s semi-conservative, meaning each new DNA molecule has one old and one new strand.

  3. DNA Encodes Proteins:

    • Messenger RNA (mRNA) is transcribed from DNA and is translated into protein sequences in the ribosome.

  4. Genetic Code:

    • DNA sequences are translated into amino acids via mRNA codons. Each codon corresponds to a specific amino acid or a start/stop signal.

  5. Key Properties of the Genetic Code:

    • Universal, Redundant, and Unambiguous. A codon always encodes one specific amino acid.

  6. mRNA Sequence:

    • mRNA is synthesized from the DNA template strand, with A pairing with U in RNA, and it codes for the amino acid sequence of a protein.

Key Terms:

  • Semi-Conservative: Replication where each new molecule has one old and one new strand.

  • DNA Helicase: Enzyme that unwinds DNA.

  • Replication Fork: Y-shaped structure where DNA replication occurs.

  • DNA Polymerase: Enzyme that adds nucleotides to the growing DNA strand.

  • Okazaki Fragments: Short DNA segments synthesized on the lagging strand.

  • DNA Ligase: Enzyme that joins DNA fragments.

  • RNA Polymerase: Enzyme that synthesizes RNA from DNA.

  • Codon: A three-nucleotide sequence on mRNA that specifies an amino acid.

  • Start Codon: The first codon in mRNA that signals the start of translation.

  • Stop Codon: The codon that signals the end of translation.