Biophysics Lecture 1: The Cell
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Questions and Answers

Which type of cell is characterized by having a nucleus bound by a membrane?

  • Eukaryotic cells (correct)
  • Bacterial cells
  • Monocellular organisms
  • Prokaryotic cells

    • What is the primary function of the plasma membrane in a cell?

  • To produce energy for the cell
  • To control cell division
  • To contain cell contents and regulate the entry and exit of substances (correct)
  • To store genetic information

    • What component of phospholipids interacts with water?

  • Nucleus
  • Hydrophilic head (correct)
  • Cytoplasm
  • Hydrophobic tail

    • Which of the following is NOT a type of eukaryotic cell?

    <p>Bacterial Cells</p> Signup and view all the answers

    What describes the overall structure of a plasma membrane?

    <p>A double layer of phospholipids</p> Signup and view all the answers

    Which of the following is a characteristic common to all cells?

    <p>Surrounding membrane</p> Signup and view all the answers

    What does protoplasm consist of within a cell?

    <p>Thick fluid that contains the cell</p> Signup and view all the answers

    Which statement is NOT true regarding the characteristics of all cells?

    <p>All cells can reproduce independently</p> Signup and view all the answers

    What is the function of the surrounding membrane of a cell?

    <p>To act as a barrier and control entry and exit</p> Signup and view all the answers

    Which of the following components is essential for the cell's structural integrity?

    <p>Protoplasm</p> Signup and view all the answers

    What is bulk transport primarily used for?

    <p>Transport of large molecules or large amounts of small particles</p> Signup and view all the answers

    Which statement accurately describes bulk transport?

    <p>It involves the movement of substances against their concentration gradient.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of bulk transport?

    <p>Limited to small solutes</p> Signup and view all the answers

    What type of transport is bulk transport classified as?

    <p>Active transport</p> Signup and view all the answers

    In which scenario would you expect bulk transport to occur?

    <p>An abundance of large particles not entering the cell</p> Signup and view all the answers

    Which of the following statements about bulk transport is correct?

    <p>It transports large quantities of substances simultaneously.</p> Signup and view all the answers

    What distinguishes bulk transport from other transport mechanisms?

    <p>It uses vesicles to transport materials.</p> Signup and view all the answers

    What is the primary function of the Rough Endoplasmic Reticulum?

    <p>Manufactures proteins</p> Signup and view all the answers

    Which statement is true regarding the Smooth Endoplasmic Reticulum?

    <p>It contains enzymes that help build carbohydrates and lipids.</p> Signup and view all the answers

    What role does the Golgi Apparatus play in the cell?

    <p>It serves as the packaging and shipping station of the cell.</p> Signup and view all the answers

    What is the primary function of lysosomes?

    <p>Contain digestive enzymes to break down waste materials.</p> Signup and view all the answers

    Which of the following structures lacks attached ribosomes?

    <p>Smooth Endoplasmic Reticulum</p> Signup and view all the answers

    How are vesicles related to the Golgi Apparatus?

    <p>They are made for endocytosis and exocytosis.</p> Signup and view all the answers

    Which of the following statements correctly describes the Rough Endoplasmic Reticulum?

    <p>Some ribosomes are attached to its surface.</p> Signup and view all the answers

    What distinguishes the Smooth Endoplasmic Reticulum from the Rough Endoplasmic Reticulum?

    <p>Involvement in carbohydrate and lipid synthesis.</p> Signup and view all the answers

    Study Notes

    Biophysics: Lecture 1 "The Cell"

    • All cells share common characteristics: a membrane, protoplasm (a thick fluid), organelles, and a control center with DNA.
    • Cell types include prokaryotic and eukaryotic.
    • Eukaryotic cells have a membrane-bound nucleus and many organelles. Examples include fungi, protists, plants, and animal cells.

    Plasma Membrane "Phospholipid Bilayer"

    • The plasma membrane is a phospholipid bilayer.
    • It contains cell contents.
    • It has a hydrophilic head and hydrophobic tails.
    • The phospholipids arrange with their hydrophilic heads facing outward, and hydrophobic tails facing inward.

    Membrane Proteins

    • Membrane proteins include channels/transporters (moving molecules in one direction), receptors (recognizing chemicals), glycoproteins (identifying cell types), and enzymes (catalyzing substance production).

    Cytoplasm

    • The cytoplasm is a viscous fluid containing organelles and interconnected filaments/fibers.
    • It's also called cytosol.

    Nuclear Envelope

    • Separates the nucleus from the rest of the cell.
    • It has pores (10-50nm apart).
    • The outer membrane is continuous with the Rough Endoplasmic Reticulum.

    DNA

    • Hereditary material.
    • Chromosomes are originated from DNA.
    • The nucleolus is involved in RNA synthesis, and forms ribosomes.

    Endoplasmic Reticulum

    • Helps move substances within cells.
    • A network of interconnected membranes.
    • Types:
      • Rough ER (RER): Has ribosomes attached, manufactures proteins.
      • Smooth ER (SER): No ribosomes, builds carbohydrates & lipids.

    Golgi Apparatus

    • Involved in plant cell wall synthesis.
    • A packaging and shipping station for the cell.
    • Responsible for vesicles used in endocytosis and exocytosis

    Lysosomes

    • Contain digestive enzymes.
    • Aid in cell renewal; break down old cell parts; digest invaders.

    Mitochondria

    • The "powerhouse of the cell".
    • Generates ATP (chemical energy source for the cell).
    • Has its own DNA.
    • Bound by a double membrane.
    • Used in signaling, cellular differentiation, control of cell cycle and growth.
    • Breaks down fuel molecules (glucose, fatty acids).

    Lecture 2: "Plasma Membrane, Membrane Proteins & Transport Across the Plasma Membrane"

    • Cell membranes are flexible, also known as the plasma membrane; a phospholipid bilayer that forms boundaries around the cells (provides a protective function).
    • Membranes are responsible for bioelectricity (ion movement).
    • Facilitates chemical communication (signaling) between cells.
    • Controls the trafficking of molecules in and out of the cell.

    Structure of Plasma Membrane

    • Phospholipid arrangement: hydrophilic heads & hydrophobic tails arranged as heads-tail-tail-heads.
    • Fluid Mosaic Model: A membrane is a mosaic of components (proteins, and other molecules). Most proteins and phospholipids are free to move within the membrane.

    Membrane Proteins

    • Integrins: Integrated within the phospholipid bilayer, strengthening the membrane.
    • Integral Proteins: Transfer substances in and out of the cell.
    • Glycoproteins: Carbohydrate chains on the surface, acting as recognition modules/fingerprints, and span the membrane transversely.

    Intercellular Junction proteins

    • Help cells stick together and communicate.
    • Intercellular junctions form channels.
    • Subunits are connexins, assembled to make connexons joining two cells.
    • Connexons form gap junctions to allow small molecules between adjacent cells.
    • Gap junctions have hemichannels, each has 12 units (each hemichannel with 6 units).

    Simple Diffusion

    • Movement of molecules from high to low concentration, without energy or carrier proteins.
    • Concentration gradient is the driving force.

    Facilitated diffusion

    • Transport of small polar molecules and ions through passive transport proteins (no energy needed).
    • Solute-specific proteins (e.g., glucose) facilitate diffusion into/out of cells.

    Osmosis

    • Diffusion of water across a selectively permeable membrane from high to low water concentration (higher water concentration to lower water concentration).
    • Integral membrane proteins for facilitated transport.

    Signal Transduction Proteins

    • Bind hormones and other substances outside the cell.
    • Binding triggers intracellular changes (signal transduction).
    • Example: insulin binding to receptors, leading to glucose transport protein insertion into the membrane.

    Transport Across the Membrane

    • Active transport proteins require energy (e.g., Sodium-Potassium pump) to move substances across the membrane.
    • Passive transport proteins do not require energy. Types: simple diffusion, facilitated diffusion, osmosis.

    Lecture 3: "Active Transport"

    • Bulk transport: a mode of active transport in which large molecules or small particles are transported across the plasma membrane using vesicles.
    • Vesicles are used to transport large particles across the plasma membrane.
    • Transport against concentration gradient (low to high concentration).
    • Requires energy e.g. ATP (adenosine triphosphate)
    • Protein Phosphorylation is when a molecule gains a phosphate, becoming phosphorylated; a molecule loses a phosphate, becoming de-phosphorylated.
    • Protein Conformation: Spatial arrangement of protein changes affect the protein function.
    • Types of Active Transport:
      • Exocytosis (outwards): materials are transported from inside to outside the cell within membrane-bound vesicles.
      • Endocytosis (inwards): particles are transferred into a cell by enclosing them within a vesicle made of plasma membrane. This includes Phagocytosis ("solid substances") and Pinocytosis ("liquid substances").
      • Receptor-mediated endocytosis; specific cellular uptake.

    Lecture 4: "Generation of membrane potential"

    • Cations are positively charged ions (e.g., K+, Na+, Ca2+). Anions are negatively charged ions (e.g., Cl-).
    • Electrical gradient: difference in electrical charge across a membrane.
    • Chemical gradient: difference in ion concentration across a membrane.
    • Movement of ions across the cell membrane: ions move from higher to lower concentration; ions attract opposite charges and repel like charges; cell membrane permeability to ions determines their movement.
    • Membrane potential/voltage results from unequal ion distribution across the membrane, creating a charge imbalance (inside more negative, outside more positive).
    • Important for the generation of cellular activity, e.g. muscle contractions, nerve impulses.

    Lecture 5 "Nernst Potential"

    Factors defining the movement of ions across a cell membrane:

    • Concentration Gradient: ions move from higher concentration to lower concentration
    • Electrical Gradient: ions move from areas of like charge to different charges
    • Ion Channel Number: permeability of the cell membrane to the ions define their movement across the membrane.
    • Equilibrium Potential (Nernst Potential): the voltage across the cell membrane that balances out the difference in concentrations, across the membrane (no net movement of the given ion).
    • Calculated using the Nernst equation (important information on factors which determine the Nernst value given is included in formula form in the notes).

    Lecture 6 "Action Potential"

    • Ion channels: transmembrane proteins that transport ions across cell membranes, grouped in gated and open channels.
    • Gated Channels: open/close in response to certain stimuli (include voltage and ligand-gated ion channels).
    • Ligand Channels: open when a specific ligand binds to it.
    • Voltage Channels: open when voltage difference changes.
    • Action Potential: a rapid rise and fall in membrane potential in a cell; action potentials must pass a threshold voltage in order for the action potential to happen, if it does not reach that threshold then it is known as failed initiation. Different states (amplitude); resting, depolarization, repolarization, hyperpolarization; characterized by differences in ion movement (ion flow) across the membrane.
    • Action potentials have refractory periods: the time immediately after stimulation that another stimulus will not have the same effect.

    Lecture 7 "Generation of Nerve Signal"

    • Neurons: nerve cells sending messages throughout the body.
    • Nerve Cell Structure:
      • Dendrites: receive information from other neurons and carry it to the cell body.
      • Cell body (soma): contains the cell nucleus.
      • Axon: transmits signals to other cells, can be myelinated or unmyelinated.
      • Nodes of Ranvier: areas of exposed axon in myelinated axons.
      • Schwann cells: form the myelin sheath surrounding axons in myelinated neurons, speeding up signal conduction in neurons.
    • Synapse: space between two neurons where signals are transmitted (neurotransmitters released).
    • Neurotransmitters: chemical substances that communicate between neurons.
    • Synaptic Transmission Process: Neurotransmitters released from vesicles to receptors on postsynaptic neurons; the process (in brief) and their impact on neuron activity.
    • Examples of neurotransmitters such as Acetylcholine, Serotonin, and Dopamine.

    Lecture 8 "The mechanism of muscle contraction"

    • Motor Unit: A group of muscle fibers controlled by one motor neuron. Different sizes/types of motor units.
    • Synapse Between Neurons and Muscle Fibers: space between the neuron terminal and the muscle fiber where neurotransmitters diffuse.
    • Muscle types: skeletal, smooth, and cardiac.
    • Muscle Terminology: Sarco-, Myo-; related to Greek origin
    • Sarcoplasmic reticulum, Sarcolema, Sarcoplasm, Myocyte

    Muscle Structure and Contraction

    • Myofibril structure describes parts of a muscle at a microscopic scale: Z discs, M lines, I Bands, and A Bands.
    • Sliding Mechanism of Muscle Contraction details how actin and myosin filaments interact and slide over each other when a muscle contracts.
    • Myosin head structure details (active binding sites).

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    Description

    This quiz covers the fundamental characteristics of cells, including structures like the plasma membrane and cytoplasm. You will explore the differences between prokaryotic and eukaryotic cells, as well as various membrane proteins and their functions. Test your understanding of these essential biophysical concepts.

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