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Chapter 4: From Cells to Organ Systems & Chapter 17.1-17.3: Cell Reproduction

Chapter 4: From Cells to Organ Systems & Chapter 17.1-17.3: Cell Reproduction

Introduction to Unicellular and Multicellular Life

  • Unicellular organisms
    • Consist of just one cell.
    • Depend on their immediate external environment, which can vary extensively.
  • Multicellular organisms
    • Consist of many cells.
    • Greater size.
    • Able to seek out or maintain a favorable external environment.
    • Cells specialize and contribute to the well-being of other cells.

Tissues: Groups of Cells with a Common Function

  • Tissues: Groups of specialized cells that are similar in structure and perform a common function.
  • Several types of tissue can be grouped to form an organ.
  • Four primary tissues:
    1. Epithelial tissues
    2. Connective tissues
    3. Muscle tissues
    4. Nervous tissues

Epithelial Tissue

  • Organization:
    • Organized as sheets of cells, one or more layers thick.
    • Cells are attached to a basement membrane.
    • Avascular (lacks blood vessels).
    • Covers exterior body surfaces and lines internal cavities and organs.
    • When surface cells die, they are replaced by cells below them.
  • Functions of Epithelium:
    • Physical protection and maintenance of integrity.
    • Regulation of nutrient absorption and ion transport.
    • Provide sensation.
    • Produce specialized secretions (via endocrine and exocrine glands).
  • Glands:
    • Epithelial cells adapted to form glands.
    • Glands are epithelial tissues specialized to synthesize and secrete a specific product.
  • Classification Based on Number of Layers:
    • Simple: Single-layer.
      • Adapted for diffusion across cell barriers.
      • Line glands, and the respiratory, digestive, and reproductive systems.
    • Stratified: Multiple-layers.
      • Provide protection, as seen on the skin surface.
  • Classification According to Shape:
    1. Squamous:
      • Flattened cells.
      • Forms the outer surface of the skin.
      • Lines blood vessels, lungs, mouth, throat, and vagina.
    2. Cuboidal:
      • Cube-shaped cells.
      • Form the lining of kidney tubules and glandular tissue.
    3. Columnar:
      • Column-shaped (tall, rectangular) cells.
      • Line the digestive tract, certain reproductive organs, and the larynx.
      • May include goblet cells that secrete mucus.
  • The Basement Membrane:
    • Noncellular layer directly beneath epithelial tissue.
    • Composed of proteins secreted by epithelial cells and connective tissue.
    • Provides structural support to overlying cells.
    • Attaches the epithelial layer to underlying connective tissue.
  • Cell Junctions—Hold Adjacent Cells Together:
    • Tight junctions:
      • Seal plasma membranes tightly together.
      • Found in the digestive tract lining and bladder lining, preventing leakage.
    • Adhesion junctions (spot desmosomes):
      • Permit some movement between cells.
      • Allow tissues to stretch and bend, as in the skin.
    • Gap junctions:
      • Protein channels that enable movement of materials between adjacent cells.
      • Found in the liver and heart, allowing rapid communication.

Connective Tissue: Supports and Connects Body Parts

  • General Functions:
    • Support softer organs of the body.
    • Connect parts of the body.
    • Store fat.
    • Produce blood cells.
  • Structure:
    • Contains cells embedded in a nonliving matrix.
    • The matrix provides the strength.
  • Two General Types:
    • Fibrous
    • Specialized

Fibrous Connective Tissue

  • Provides strength and elasticity.
  • Contains fibers and cells embedded in a gel-like ground substance (matrix).
  • Ground substance:
    • Intercellular material that gives the connective tissue its characteristics.
  • Cells:
    • Fibroblasts (produce and secrete proteins that form fibers like collagen and elastin).
    • Macrophages
    • Lymphocytes
    • Neutrophils
    • Fat cells
    • Mast cells
  • Fibers:
    • Collagen fibers:
      • Most abundant, very strong but flexible.
      • Found in straight bundles, very important in ligaments, tendons, and bones.
    • Reticular fibers:
      • Interwoven immature collagen fibers.
      • Support nerves, blood, and lymphatic vessels.
    • Elastic fibers:
      • Branched and wavy, capable of stretching and recoiling.
      • Found in respiratory, vascular, urinary, and skin systems.
  • Four General Types of Fibrous Connective Tissue (varying in density and fiber type):
    1. Loose (Areolar) Connective Tissue:
      • Surrounds internal organs, muscles, and blood vessels.
      • Few collagen and elastic fibers, with no specific pattern.
    2. Dense Connective Tissue:
      • Forms tendons, ligaments, and deeper layers of skin.
      • Many collagen fibers in a parallel arrangement.
    3. Elastic Connective Tissue:
      • Surrounds hollow organs (e.g., stomach and bladder) that regularly change shape or size.
      • Characterized by many elastic fibers.
    4. Reticular Connective Tissue:
      • Makes up the internal framework of soft organs (e.g., liver) and the lymphatic system.

Specialized Connective Tissues

  • Serve special functions.
    1. Cartilage:
      • Transitional tissue from which bone develops.
      • Maintains the shape of the nose and ears.
      • Protects and cushions joints and vertebrae.
      • Structure:
        • Dense connective tissue of collagen fibers.
        • Ground substance produced by chondroblasts.
        • Slow to heal when injured due to lack of blood vessels (avascular).
    2. Bone:
      • Forms the skeleton.
      • Contains relatively few living cells.
      • Matrix (ground substance) composed of calcium phosphate.
      • Contains numerous blood vessels.
    3. Blood:
      • Fluid matrix of plasma.
      • Cells derived from stem cells in bone marrow.
      • Transports materials throughout the body.
      • Cell types:
        • Red blood cells: Transport oxygen, carry away wastes.
        • White blood cells: Defend the body (immune defenses).
        • Platelets: Function in blood clotting.
    4. Adipose Tissue:
      • Fat storage tissue.
      • Few fibers, very little ground substance.
      • Adipocytes (fat cells): Store fat in vacuoles.
      • Location: Under the skin and around internal organs.
      • Functions: Insulate, protect, and energy storage.
      • Weight loss reduces the size of individual adipocytes but does not necessarily reduce their number.

Muscle Tissue: Contracts to Produce Movement

  • Muscle cells shorten (contract), producing movement.
  • Muscle cells are also called muscle fibers; they are long, thin, and arranged parallel to each other.
  • Three types of muscle tissue:
    1. Skeletal muscle
    2. Cardiac muscle
    3. Smooth muscle

Types of Muscle Tissue

  • Skeletal Muscles:
    • Move body parts.
    • Connect to tendons which attach to bone.
    • Composed of thousands of individual muscle fibers (cells) arranged in parallel.
    • Fibers have multiple nuclei.
    • Voluntary: Under conscious control.
    • Activated only by nerves.
  • Cardiac Muscle:
    • Cells activate each other.
    • Located only in the heart.
    • Shorter cells, blunt-ended, with one nucleus per cell.
    • Gap junctions: Allow direct electrical connections between adjoining cells, enabling coordinated contraction of the entire heart.
    • Involuntary: Heart contracts rhythmically entirely on its own.
  • Smooth Muscle:
    • Surrounds hollow structures and tubes (e.g., blood vessels, digestive tract, uterus, bladder).
    • Slim cells tapered at the ends.
    • One nucleus per cell.
    • Involuntary.

Nervous Tissues: Transmit Impulses

  • Rapid communication network including the brain, spinal cord, and nerves throughout the body.
  • Neuron:
    • Specialized nervous system cell.
    • Function: Generate and transmit electrical impulses.
  • Glial cells:
    • Functions:
      • Surround and protect neurons.
      • Provide nutrients to neurons.

Organs: Integration of Tissues

  • Structures composed of two or more tissue types joined together; perform specific functions.
  • Example: Heart
    • One essential function: Pump blood.
    • Made up of:
      • Cardiac muscle
      • Smooth muscle in cardiac blood vessels
      • Nervous tissue
      • Connective tissue (valves)
      • Epithelial tissue (lining chambers)
  • Some organs have more than one function.

The Human Body Is Organized by Organ Systems

  • Organ Systems: Groups of organs that serve a broad function important to the survival of an individual or the species.
  • 11 organ systems make up the human body.

Organ Systems are Housed in Body Cavities

  • Anterior cavity:
    • Divided by the diaphragm into:
      • Thoracic cavity:
        • Two pleural cavities (each contains a lung).
        • Pericardial cavity (encloses the heart).
      • Abdominal cavity.
      • Pelvic cavity: The lower part of the abdominal cavity.
  • Posterior cavity:
    • Cranial cavity.
    • Spinal cavity.
  • Tissue membranes (serous membranes) line body cavities.

Tissue Membranes Line Body Cavities

  • Composed of connective tissue plus a layer of epithelial cells.
  • 4 types of tissue membranes:
    1. Serous membranes:
      • Line and lubricate internal body cavities.
      • Reduce friction between organs (e.g., around the heart, lungs, and abdominal organs).
    2. Mucous membranes:
      • Line airways, digestive tract, and reproductive tract.
      • Lubricate surfaces and capture debris.
    3. Synovial membranes:
      • Line spaces in movable joints.
    4. Cutaneous membrane:
      • Forms the outer covering (skin).

Body Planes Are Used to View Neighboring Organs

  • Sagittal: Divides the body into right and left halves.
    • Midsagittal: Divides the body into equal right and left parts.
  • Frontal (coronal): Divides the body into anterior (front) and posterior (back) halves.
  • Transverse: Divides the body into superior (upper) and inferior (lower) parts.
  • Oblique: Less standardized cut; at an angle.

Directional Terms Are Used to Describe Relationships

  • (No specific terms detailed in transcript, but acknowledged as a concept for describing relationships).

Cell Reproduction (Chapter 17.1-17.3)

  • Cells Reproduce by Dividing into Two:
    • In multicellular organisms, cell division enables growth from a fertilized egg to a multicellular individual.
    • For humans, 1 fertilized egg yields ext{approx. } 10 ext{ trillion} cells.
    • Cell division is followed by differentiation, where cells become different from each other and from the parent cell and more specialized.

The Cell Cycle Creates New Cells

  • Cell Cycle: Includes two major phases:
    • Interphase (period between cell divisions).
    • Mitotic phase (cell division).
  • Interphase:
    • Long growth period between cell divisions.
    • G1 (Gap 1): Primary growth phase, very active growth.
    • S (Synthesis): Synthesis of DNA for the next cell division.
    • G2 (Gap 2): Final growth phase before cell division.
  • Mitotic phase (Cell Division Phase):
    • Mitosis: Nuclear division; duplicated DNA is distributed between two daughter nuclei.
    • Cytokinesis: Cytoplasm divides, and two new daughter cells are formed.
  • Timing:
    • A complete cell cycle takes 18 ext{–} 24 hours.
    • Mitosis and cytokinesis take less than one hour of the complete cell cycle.
  • Many cells enter a nondividing state, G0.

DNA Structure and Function: An Overview

  • Human DNA is organized into 46 separate chromosomes containing 3 ext{ billion} base pairs of DNA.
  • Chromosomes: Consist of DNA and histones (proteins).
  • Chromatin: Throughout most of the cell cycle, DNA is loose and diffuse.
  • Compacted Chromosomes (during Mitosis):
    • DNA is compacted into chromosomes that are visible under the microscope.
    • Each chromosome consists of two sister chromatids joined at the centromere.
  • Gene: A short segment of DNA that contains the code, or recipe, for a protein.
  • There are 20,000 ext{–} 21,000 genes on the 46 chromosomes.
  • Three processes essential to DNA function:
    1. Replication: Process of copying the cell’s DNA prior to cell division.
    2. Transcription: Process of creating a coded message (working copy) of a single gene in RNA that can be carried out of the nucleus (messenger RNA, mRNA).
    3. Translation: Process of using the coded message (mRNA) to assemble amino acids into proteins useful to the cell.

Replication: Copying DNA Before Cell Division

  • DNA Replication: The process of copying DNA prior to cell division.
  • Makes exact copies of all 46 chromosomes.
  • Steps:
    1. DNA uncoils and “unzips,” pulling apart the two strands.
    2. A new complementary strand of DNA is built upon each template strand, using appropriate base-pairing rules (adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C)).
    • DNA polymerase: The major replicating enzyme.

Mutations Are Alterations in DNA

  • Mutation: An alteration in the nucleotide sequence of DNA.
  • Somatic cell mutations (in non-gametes):
    • May affect the function of tissues or cause cancer.
    • Not passed on to descendants.
  • Gamete mutation:
    • Passed on to future generations.

Mechanism of DNA Repair

  • Enzymes recognize errors in the DNA sequence.
  • Errors are cut out with enzymes.
  • The damaged section is replaced.
  • The DNA backbone is reconnected.
  • Numerous different DNA repair enzymes exist.
  • Repair enzymes are most active between the time of DNA replication and the beginning of mitosis.

Basics of Transcription & Translation

  • Transcription:
    • The synthesis of RNA under the direction of DNA.
    • RNA is the bridge between genes and the proteins for which they code.
    • Transcription produces messenger RNA (mRNA).
  • Translation:
    • The synthesis of a polypeptide (protein), using information in the mRNA.
    • Ribosomes are the sites of translation.

Transcription: Converting a Gene’s Code into mRNA

  • Process:
    1. The DNA of a gene unwinds.
    2. RNA polymerase assists in copying the DNA nucleotide sequence into a polymer of RNA nucleotides.
    3. A primary transcript (RNA) is made.

RNA Processing (Checking for Errors Before Moving On)

  • Enzymes modify pre-mRNA (RNA processing) before the genetic messages are passed to the cytoplasm.
  • Introns: Non-coding regions that are edited out by catalytic RNAs called ribozymes.
  • Exons: Carry genetic information and are spliced appropriately.
  • The result is a functional messenger RNA (mRNA) strand.

The Genetic Code

  • The code is read as a triplet code (codon).
  • A codon is a sequence of 3 mRNA bases that codes for a specific amino acid.
  • All 64 codons were deciphered by the mid-$1960 ext{s}$.
  • Of the 64 triplets:
    • 61 code for the 20 amino acids.
    • 3 triplets are “stop” signals to end translation.
  • Start codon: AUG
    • Codes for the amino acid methionine, which begins all genes.
    • Translation starts at AUG.

Translation: Making a Protein from RNA

  • Components:
    • Messenger RNA (mRNA): A copy of the “recipe” that specifies the order of amino acids in a protein.
    • Transfer RNAs (tRNA): RNA molecules that escort amino acids to the ribosome.
      • tRNA has anticodons that will pair with complementary codons in mRNA.
    • Ribosomes: Made of ribosomal RNA (rRNA) and protein.
      • Contain sites for mRNA and incoming amino acid-tRNA.
  • (The transcript mentions