Cellular level

Cellular Organization and Cell Theory

  • A cell is the structural and functional unit of life.

  • Over 200 distinct human cell types, differing in size, shape, and function.

Cell Structure

  • Generalized cell consists of three components:

    • Plasma membrane: flexible boundary.

    • Cytoplasm: intra-cellular fluid with organelles.

    • Nucleus: contains DNA, control center.

Plasma Membrane

  • Acts as a barrier between intracellular (ICF) and extracellular fluid (ECF).

  • Composed of a phospholipid bilayer, proteins, and carbohydrates (glycocalyx).

  • Functions include:

    • Mechanical barrier.

    • Selective permeability.

    • Communication and cell signaling.

Cell Junctions

  • Types:

    • Tight junctions, desmosomes, gap junctions.

Membrane Transport

  • Passive transport (no energy required):

    • Diffusion (simple, facilitated).

    • Osmosis.

  • Active transport (energy required):

    • Active transport, vesicular transport (endocytosis, exocytosis).

Cytoplasm

  • Composed of cytosol, inclusions, and organelles.

    • Membranous organelles: mitochondria, ER, Golgi apparatus, lysosomes.

    • Nonmembranous organelles: ribosomes, cytoskeleton, centrioles.

Mitochondria

  • Produce ATP via aerobic respiration.

  • Contain their own DNA.

Ribosomes

  • Sites of protein synthesis, either free or membrane-bound.

Endoplasmic Reticulum (ER)

  • Series of interconnected tubular structures; Rough ER (with ribosomes) and Smooth ER (no ribosomes).

Golgi Apparatus

  • Modifies and packages proteins and lipids received from ER.

    • Three pathways for vesicle transport: secretion, insertion into membranes, or lysosomes.

Cytoskeleton

  • Network of protein rods; includes microfilaments, intermediate filaments, and microtubules.

Nucleus

  • Largest organelle, contains genetic material.

  • Components: nuclear envelope, nucleolus, chromatin.

Cell Cycle

  • Two main phases: interphase (growth and metabolism) and mitotic phase (cell division).

  • Mitosis consists of prophase, metaphase, anaphase, and telophase.

Protein Synthesis

  • Occurs in two stages: transcription (DNA to mRNA) and translation (mRNA to protein).

  • RNA types: mRNA (messenger), rRNA (ribosomal), tRNA (transfer).