Lecture 4: Cellular Processes

BIOL 5 BIOLOGY FOR HEALTH Lecture 4: Cellular Processes

Instructor: Jeff Harold E. Romeroso
Contributors: PEHernando, JNBaldomero, AJLagera, HIRotairo
Department: Department of Biological Sciences College of Arts & Sciences Cavite State University

Objectives

  • Describe the major phases of the cell cycle and the events that occur in each phase.

  • Compare & contrast mitosis & meiosis.

  • Identify the general parts of all cells.

  • Differentiate passive transport from active transport.

  • Explain the mechanisms of direct & indirect active transport.

  • Define the different tonicity and explain how they affect cells.

Topic Outline

  • Cellular Division

  • Cell Transport

  • Cellular Respiration

Cellular Division

Chromosomes

  • Definition: Carries genes.

  • Parts:

    • Centromere/Primary Constriction:

    • The constricted region where the kinetochore attaches.

    • Kinetochore:

    • Site where spindle fibers attach during cell division.

Homologous Chromosomes

  • Definition: Chromosomes that have important genetic similarities; they contain identical gene sites along their lengths, known as loci (plural of locus).

  • Parental Contribution: In sexually reproducing organisms, one chromosome of each pair is derived from the maternal parent (via the ovum) and the other from the paternal parent (via the sperm).

  • Compensation Mechanism: If one chromosome is damaged, the other can compensate genetically.

Interphase

  • Description: The stage where the cell spends most of its time.

  • Functions:

    • The cell grows.

    • Chromosomes are replicated.

    • The cell prepares for division.

  • Phases of Interphase:

    • GAP 1 (G1) Phase:

    • Cell increases in volume and doubles its mass.

    • Synthesis (S) Phase:

    • Active synthesis and replication of DNA.

    • GAP 2 (G2) Phase:

    • Synthesis of RNA and proteins for chromosome synthesis.

Cell Division (M-phase)

  • Description: The stage where the cell divides.

  • Types of Division:

    • Mitosis: For somatic cells.

    • Meiosis: For sex cells.

Cell Division: Mitosis

  • Definition: A process of cell division that occurs in somatic/body cells.

  • Outcome: Results in two genetically identical daughter cells.

  • Importance: Essential for body growth, development, and repair.

  • Phases of Mitosis:

    • Prophase:

    • Chromosomes thicken and coil.

    • The nucleolus shrinks and disappears.

    • Metaphase:

    • Chromosomes align in the middle of the cell (metaphase plate).

    • Anaphase:

    • Each chromatid pair separates into two identical chromosomes, pulled to opposite ends by spindle fibers.

    • Telophase:

    • Chromosomes begin to decondense, spindle breaks down, and nuclear membranes and nucleoli re-form.

  • Cytokinesis:

    • Nuclear envelope surrounds chromosomes, and a cleavage furrow forms.

    • Results in two daughter cells.

Cell Division: Meiosis

  • Definition: A type of cell division that occurs in sex cells/gametes.

  • Outcome: Results in four unique haploid daughter cells.

  • Importance: Essential for sexual reproduction.

  • Meiosis I: (Reductional Division)

    • Stages:

    • Prophase I:

      • Nuclear envelope breaks down, and chromatin condenses into chromosomes.

      • Homologous chromosomes pair to form tetrads/bivalents.

      • Crossing over occurs, introducing genetic variation.

    • Metaphase I:

      • Bivalents align at the equatorial plane (metaphase plate).

    • Anaphase I:

      • Homologous chromosomes separate from each other.

    • Telophase I:

      • Nuclear membrane and nucleolus reappear, forming two haploid nuclei.

      • Cytokinesis may follow; in some cases, cytokinesis does not occur after meiosis I.

  • Meiosis II: (Equational Division)

    • Similar to mitotic prophase but has half the chromosome number.

    • Stages:

    • Prophase II: Nuclear membrane disintegrates.

    • Metaphase II: Condensed chromosomes align along the metaphase plate.

    • Anaphase II: Chromosomes are pulled to the poles, separating centromeres.

    • Telophase II: Spindles disappear, nuclei form, and cytokinesis takes place.

    • Results in four haploid daughter cells.

Cell Transport

Plasma Membrane

  • Definition: Separates the cell's interior from the external environment.

  • Structure: Consists of a lipid bilayer that is semi-permeable.

  • Function: Controls the movement of substances in and out of the cell.

Passive Transport

  • Definition: Substances cross the plasma membrane without any energy input from the cell.

  • Mechanism:

    • Movement occurs from areas of higher concentration to areas of lower concentration.

  • Key Components:

    • Solution: Composed of solvent (water) and solute (dissolved substance).

    • Concentration: Refers to the number of solute particles present.

Types of Passive Transport

  • Simple Diffusion:

    • Net movement of particles due to the concentration gradient (unequal distribution).

    • Dynamic equilibrium exists when equal concentrations are reached.

  • Osmosis:

    • The movement of water from a region of high water concentration to a region of low water concentration through a semi-permeable membrane.

    • Tonicity Solutions:

    • Hypertonic Solution: Higher solute concentration outside the cell, leading to water moving out of the cell.

    • Isotonic Solution: Equal solute concentration inside and outside the cell, water movement is balanced.

    • Hypotonic Solution: Lower solute concentration outside the cell, leading to water moving into the cell.

  • Facilitated Diffusion:

    • Movement facilitated by transport proteins when diffusion of large or charged molecules (e.g., glucose) occurs.

    • Types of Transport Proteins:

    • Channel Proteins:

      • Allow water molecules and small ions to pass through without contact with lipid tails.

    • Carrier Proteins:

      • Bind with specific ions/molecules and change shape to carry them across the membrane.

Active Transport

  • Definition: The pumping of molecules or ions through a membrane against their concentration gradient, requiring energy.

  • Energy Source: ATP (adenosine triphosphate).

  • Types of Active Transport:

    • Direct Active Transport:

    • Specific transmembrane proteins or pumps bind ATP directly to drive the transport process.

    • Indirect Active Transport:

    • Uses potential energy stored in the gradient of directly pumped ions to drive the transport of other molecules against their gradient.

  • Key Concepts:

    • Primary transport builds potential energy by generating a concentration difference across the membrane.

    • Secondary transport utilizes this established concentration gradient to transport other substances.

Cellular Respiration

Overview

  • Definition: The process by which cells break down food molecules, like glucose, to release energy.

  • Energy Storage: Cells store extracted energy in the form of ATP (adenosine triphosphate).

    • A single cell uses approximately 10 million ATP molecules per second.

  • Key Components of ATP:

    • Nitrogenous base (Adenine), three phosphates, and a 5-carbon sugar.

Stages of Cellular Respiration

  1. Glycolysis:

    • Splitting glucose into two pyruvate molecules.

    • Requires two ATPs to split glucose but generates four ATPs, resulting in a net gain of two ATP molecules.

  2. Transformation of Pyruvate:

    • Occurs in mitochondria, converting pyruvate into Acetyl-CoA (a two-carbon acetyl group linked to coenzyme A).

    • Resulting compound is termed Acetyl CoA.

  3. Krebs Cycle (Citric Acid Cycle):

    • Takes place in the matrix of mitochondria.

    • Each pyruvate yields 1 ATP.

    • Involves electron carriers:

      • NADH (Nicotinamide adenine dinucleotide)

      • FADH₂ (Flavin adenine dinucleotide)

  4. Oxidative Phosphorylation:

    • Also known as Electron Transport Chain (ETC).

    • Found in the inner membrane of mitochondria, transferring electrons across the inner membrane into the intermembrane space.

    • Produces 30-32 ATP.

Summary of ATP Production:

  • Glycolysis: 2 ATP

  • Krebs Cycle: 2 ATP

  • ETC: 30-32 ATP

  • Total: Up to 34-36 ATP molecules can be generated from one glucose molecule during cellular respiration.

End of Lecture

Copyright

  • Jeff Harold E. Romeroso © PEHernando, JNBaldomero, AJLagera, & HIRotairo Department of Biological Sciences College of Arts & Sciences Cavite State University