Cell Biology Overview

Cell Theory

• The cell is the basic structural and functional unit of living organisms.
• The activity of an organism depends on the collective activities of its cells.
• The continuity of life from one generation to another has a cellular basis.

Cell Structure

• Cells are organized into three main regions:
  • Nucleus
  • Cytoplasm
  • Plasma membrane

Nucleus

• The nucleus is the control center of the cell.
• It contains genetic material (DNA).
• It has three regions:
  • Nuclear membrane
  • Nucleolus
  • Chromatin

Nuclear Membrane

• The nuclear membrane is a barrier for the nucleus.
• It consists of a double phospholipid membrane.
• It contains nuclear pores that allow for the exchange of material with the rest of the cell.

Nucleoli

• The nucleus contains one or more nucleoli.
• Nucleoli are the sites of ribosome production.
• Ribosomes migrate to the cytoplasm through nuclear pores.

Chromatin

• Chromatin is composed of DNA and protein.
• It's scattered throughout the nucleus.
• Chromatin condenses to form chromosomes when the cell divides.

Plasma Membrane

• The plasma membrane is a barrier for cell contents.
• It's a double phospholipid layer with hydrophilic heads and hydrophobic tails.
• The plasma membrane also consists of proteins, cholesterol, and glycoproteins.

Functions of a Cell

• Reproduction by cell division.
• Utilization of enzymes and other proteins coded by DNA genes and made via messenger RNA intermediates and ribosomes.
• Metabolism.
• Response to external and internal stimuli, such as change in temperature, pH, or levels of nutrients.
• Cell contents are contained within a cell surface membrane made of a phospholipid bilayer with embedded proteins.

DNA Replication

• Genetic material gets duplicated.
• This readies a cell for division into two cells.
• It occurs toward the end of interphase.
• DNA uncoils and each side serves as a template.

Cell Division

• Cell division is the process by which a cell replicates itself.
• Has two main stages:
  • Mitosis (division of the nucleus).
  • Cytokinesis (division of the cytoplasm).

Stages of Mitosis

• Interphase: No cell division occurs, the cell carries out normal metabolic activity and growth.
• Prophase: The first part of cell division, centromeres migrate to the poles.
• Metaphase: The spindle fibers from the centromeres are attached to chromosomes aligned in the center of the cell.
• Anaphase: Daughter chromosomes get pulled toward the poles, and the cell begins to elongate.
• Telophase: Daughter nuclei begin forming, and a cleavage furrow begins to form for cell division.

Protein Synthesis

• Proteins are essential for all aspects of cell life.
• The DNA blueprints, known as genes, are essential for protein synthesis.
• The process of protein synthesis is known as translation.
• RNA is essential for protein synthesis, acting as a messenger between DNA and ribosomes.
• Proteins have many functions:
  • Building material for cells (fibrous or structural proteins).
  • Biological catalysts (enzymes), which speed up chemical reactions that occur in cells.

Connective Tissue Types

• Connective tissue is a type of tissue that supports and binds other tissues.
• Types of connective tissue:
  • Cartilage: Supports and protects tissues, found in the nose, ears, and joints.
    • Hyaline cartilage (smooth, glassy, found in joints).
    • Elastic cartilage (provides elasticity, found in external ear).
    • Fibrocartilage (highly compressible, forms cushions between vertebrae).
  • Dense connective tissue: Main matrix element is collagen fibers, cells are fibroblasts. Examples include tendons and ligaments.
  • Areolar connective tissue: Most widely distributed connective tissue, soft, pliable, contains all fiber types, can soak up excess fluid.
  • Adipose tissue: Matrix is an areolar tissue where fat globules predominate. Many cells contain large lipid deposits. Functions include insulation, protection, and fat storage.
  • Reticular connective tissue: Forms a delicate network of interwoven fibers, forms the stroma (internal supporting network) of organs like lymph nodes, spleen, and bone marrow.
  • Blood: Blood cells surrounded by a fluid matrix, fibers are visible during clotting. It serves as a transport vehicle for materials.

Muscle Tissues

• Muscle tissue is the only tissue that can produce movement.
• Types of muscle tissue:
  • Skeletal muscle: Controlled voluntarily, cells attach to connective tissue, striated, cells have more than one nucleus.
  • Cardiac muscle: Found only in the heart, functions to pump blood involuntarily, cells attached to other cardiac muscle cells at intercalated disks, striated, one nucleus per cell.
  • Smooth muscle: Found in walls of hollow organs like the stomach and intestines, involuntary, lacks striations, one nucleus per cell.

Developmental Aspects of Tissues

• Liver cells stop dividing but retain the ability to divide if damaged for repair.
• Heart muscle and nervous tissue become amitotic (lose the ability to divide) when fully mature.
• Amitotic tissues cannot regenerate when damaged.
• The aging process begins after maturity.
• Certain events are part of the aging process:
  • Epithelial membranes thin and are more easily damaged.
  • Skin loses elasticity and begins to sag.
  • Exocrine glands become less active, leading to dryness.
  • Endocrine glands produce fewer hormones, slowing body processes.
  • Connective tissue structures change with age:
    • Bones become weak.
    • Tissue repair is slower.
    • Muscles start to waste away.
• Decreased efficiency of the circulatory system, affecting nutrient and oxygen delivery to body tissues, is a contributing factor to age-related changes.
• Abnormal cell growth can lead to a neoplasm (new growth), which can be benign or malignant.