Cell Types and Structure, Biological Membranes and Membrane Transport, Cell Cycle and Mitosis

Cell Types and Structure

  • Size Range of Cells:

    • Prokaryotic cells typically range from 0.1 to 5.0 micrometers in diameter.

    • Eukaryotic cells are generally larger, ranging from 10 to 100 micrometers in diameter.

  • Endosymbiont Theory:

    • This theory proposes that eukaryotic cells evolved from symbiotic relationships between prokaryotic cells.

    • The main reasoning behind this theory includes:

    • Presence of double membranes surrounding mitochondria and chloroplasts.

    • Mitochondria and chloroplasts contain their own circular DNA, similar to prokaryotic DNA.

    • These organelles reproduce independently within the cell, akin to prokaryotic binary fission.

  • Comparison of Cell Types:

    • Prokaryotic Cells:

    • Lack a nucleus and membrane-bound organelles.

    • Typically smaller and simpler in structure.

    • Example: Bacteria.

    • Animal Cells:

    • Have a defined nucleus and various organelles (e.g., lysosomes and centrioles).

    • Lack cell walls, leading to flexible structures.

    • Plant Cells:

    • Contain a nucleus and organelles, including chloroplasts and a rigid cell wall.

    • Do not have lysosomes or centrioles.

  • Cell Structures and Functions:

    • Eukaryotic Cells:

    • Nucleus: Contains genetic material and regulates gene expression.

    • Mitochondria: ATP production through cellular respiration.

    • Chloroplasts in plants: Photosynthesis.

    • Prokaryotic Cells:

    • Nucleoid: Region containing loose DNA, where genetic material is found.

    • Ribosomes: Protein synthesis.

    • Plasma membrane: Regulates entry and exit of substances.

Biological Membranes and Membrane Transport

  • Major Components of the Cell Membrane:

    • Phospholipid bilayer: Forms the fundamental structure.

    • Membrane proteins: Integral and peripheral proteins that facilitate transport and communication.

    • Carbohydrates: Attached to proteins and lipids for cell recognition.

  • Selectively Permeable Membrane:

    • A membrane that allows certain molecules to pass while blocking others, regulating the internal environment of the cell.

  • Molecules and Simple Diffusion:

    • Classification of molecules based on ease of movement across a membrane:

    • Small, nonpolar molecules (e.g., oxygen, carbon dioxide) diffuse easily.

    • Polar molecules (e.g., water) can also cross, but with more difficulty via specialized channels.

    • Large, charged molecules (e.g., ions, glucose) require transport proteins for movement.

  • Predicting Chemical and Physical Properties:

    • Given data or an observation:

    • A. Assess chemical structure to infer polarity or charge.

    • B. Determine potential interactions with the plasma membrane based on hydrophobic or hydrophilic characteristics.

  • Transport Proteins:

    • Types:

    • Channels: Proteins that provide passageways for particular substances, often ions.

    • Carriers: Proteins that change shape to transport substances across the membrane.

    • Pumps: Proteins that use energy to move substances against their concentration gradient.

  • Determining Transport Type:

    • For a given process, one should analyze the properties of the molecule and the required energy input to determine:

    • The kind of transport protein being utilized.

    • Whether active or passive transport is necessary.

  • Active vs. Passive Transport:

    • Active Transport:

    • Movement of molecules against their concentration gradient, requiring energy (e.g., ATP).

    • Passive Transport:

    • Movement of molecules along their concentration gradient without energy investment.

  • Types of Passive Transport:

    • Simple Diffusion:

    • Direct movement of molecules through the membrane (e.g., O2).

    • Facilitated Diffusion:

    • Movement through channels or carriers without energy (e.g., glucose via transporters).

    • Osmosis:

    • The diffusion of water across a membrane.

  • Primary vs. Secondary Active Transport:

    • Primary:

    • Direct use of ATP to transport molecules (e.g., Na+/K+ pump).

    • Secondary:

    • Utilizes the gradient created by primary active transport indirectly to move another substance (e.g., co-transport of glucose and Na+).

  • Prediction of Molecule Movement:

    • Given data observations:

    • A. Evaluate concentration gradients to discuss direction and movement across the membrane.

    • B. Identify whether passive or active transport is occurring, including the specific type involved.

Lecture 10: Cell Cycle and Mitosis

  • Stages of Interphase:

    • G1 Phase:

    • Cell growth and preparation for DNA replication.

    • Involved in protein synthesis and organelle duplication.

    • S Phase:

    • DNA replication occurs, resulting in two sister chromatids per chromosome.

    • G2 Phase:

    • Continued cell growth and preparation for mitosis, including error checking of replicated DNA.

  • Stages of Mitosis:

    • Prophase:

    • Chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down.

    • Metaphase:

    • Chromosomes align at the cell’s equatorial plate.

    • Anaphase:

    • Sister chromatids are pulled apart towards opposite poles of the cell.

    • Telophase:

    • Nuclear envelopes reform around two sets of chromosomes, which begin to decondense.

  • Behavior of Chromosomes During Mitosis:

    • Chromosomes undergo condensation to become visible and then segregate into daughter cells to ensure each daughter cell receives an identical set of chromosomes.

  • Internal Checkpoints of the Cell Cycle:

    • G1 Checkpoint:

    • Assess DNA damage, cell size, and the presence of growth signals.

    • G2 Checkpoint:

    • Checks for DNA replication errors and proper cell size before mitosis.

    • M Checkpoint (Metaphase Checkpoint):

    • Ensures all chromosomes are properly aligned for an equal distribution during cell division.

  • Regulation of the Cell Cycle:

    • Positive Regulators:

    • Proteins that promote progression through the cell cycle; examples include cyclins and cyclin-dependent kinases (CDKs).

    • Negative Regulators:

    • Proteins that inhibit cell cycle progression; examples include p53, which halts cell division if DNA is damaged.

  • Cancer and Unregulated Cell Growth:

    • Cancer is a result of uncontrolled cell division leading to tumor formation. Mutations in regulatory genes can lead to this unregulated growth.

  • Genes Related to Cancer:

    • Proto-oncogenes:

    • Normal genes that, when mutated, become oncogenes which contribute to cancer.

    • Oncogenes:

    • Mutated genes that drive the uncontrolled growth of cells.

    • Tumor Suppressor Genes:

    • Genes that prevent cell division and tumor formation; mutations can lead to loss of growth control.