Cell Structure, Function, and Tissue Types: Comprehensive Biology Notes

Cell Theory

The foundational principle of biology. Core Ideas: (1) The cell is the smallest unit of life. (2) All organisms are made of one or more cells. (3) New cells arise from pre-existing cells.

Basic Cell Structure

All cells share 4 main components: Plasma Membrane (regulates entry/exit), DNA region (genetic instructions), Cytoplasm (jelly-like fluid where organelles are suspended), Biochemical molecules & pathways (proteins, enzymes, metabolic reactions).

Plasma Membrane

Fluid Mosaic Model: phospholipid bilayer with proteins "floating." Key components: phospholipids, cholesterol, proteins, glycoproteins/glycolipids. Selective permeability depends on solubility, size, polarity, charge. Specialized features: microvilli, junctions (tight, desmosomes, gap).

Transport Across Membranes

Passive transport (diffusion, osmosis, facilitated diffusion, filtration). Active transport (Na⁺/K⁺ pump, H⁺ pump). Secondary active transport (symport, antiport). Bulk transport (endocytosis, exocytosis).

Membrane Proteins

Ion channels: mechanically gated, voltage gated, ligand gated. Porins (large, less specific). Aquaporins (water transport).

Nucleus

Contains DNA, controls cell activities, nuclear envelope with pores, nucleolus forms ribosomes.

Endoplasmic Reticulum

Rough ER: protein synthesis (ribosomes). Smooth ER: lipid synthesis, detoxification.

Ribosomes

Sites of protein synthesis, either free in cytoplasm or bound to ER.

Mitochondria

"Powerhouse of the cell," site of aerobic respiration, produces ATP.

Golgi Complex

Modifies, sorts, packages proteins and lipids.

Lysosomes

Contain digestive enzymes. Functions: digestion, autophagy, autolysis.

Peroxisomes

Break down toxic substances, contain oxidative enzymes (common in liver).

Cytoskeleton

Provides shape/support, intracellular transport. Includes cilia/flagella (movement) and amoeboid motion.

Mitosis

Cell division for growth, repair, replacement, and asexual reproduction. Phases: prophase, metaphase, anaphase, telophase. Cytokinesis = division of cytoplasm.

DNA Replication

Occurs in S phase. Enzymes: primase, DNA polymerase, exonuclease, ligase. Base pairing ensures accuracy (A-T, G-C).

Protein Synthesis

Transcription (DNA → mRNA) in nucleus, splicing to form mature mRNA. Translation (mRNA → protein) in ribosome using tRNA. Start codon AUG = methionine.

Cancer

Uncontrolled cell growth due to mutations in proto-oncogenes (→ oncogenes) or tumor suppressor genes. Caused by carcinogens (chemical, biological, physical), lifestyle factors, or inherited risks. Stages: mutation → promotion → progression → metastasis.

Stem Cells

Unspecialized cells with self-renewal and differentiation capacity. Types: embryonic, fetal, adult, umbilical cord, placental, induced pluripotent. Functions: plasticity, homing, engraftment. Applications: tissue repair, cancer treatment, autoimmune therapy, drug testing.

Tissues

Group of cells with common function. Four types: epithelial, connective, muscle, nervous. Origin: ectoderm, mesoderm, endoderm.

Epithelial Tissue

Functions: protection, absorption, secretion, sensation. Types: simple squamous, cuboidal, columnar; stratified squamous; pseudostratified columnar; transitional. Glands: exocrine (merocrine, holocrine, apocrine), endocrine.

Connective Tissue

Functions: binding/support, protection, insulation, transport. Types: loose (areolar, adipose, reticular), dense (regular/irregular), cartilage (hyaline, elastic, fibrocartilage), bone, blood.

Muscle Tissue

Skeletal (striated, voluntary), cardiac (striated, involuntary, intercalated discs), smooth (non-striated, involuntary).

Nervous Tissue

Neurons (impulse transmission) + neuroglia (support, protect, insulate).

Integumentary System

Skin functions: protection, excretion, thermoregulation, vitamin D synthesis, sensation. Layers: epidermis (5 strata), dermis (papillary/reticular), hypodermis. Appendages: hair, nails, glands. Disorders: cancers (BCC, SCC, melanoma), burns (1st-3rd degree).

Still learning (1)

You've started learning these terms. Keep it up!