Dental Board Exam Review: Cell Biology

Cellular Structure

• Cell membrane: also known as plasma membrane or cytoplasmic membrane, semi-permeable, regulates passage of substances in and out of the cell
• Nucleus: covered by bilayered membrane (nuclear envelope), contains DNA and RNA
  • Chromosome: thread-like structure that carries genetic information, contains a single double-stranded DNA molecule
  • Chromatin: material that makes up chromosomes, complex of DNA and its associated protein (DNA + histones), "beads on string" appearance
  • Chromatid: chromosome copy
  • Sister chromatids: chromatids that are bound to each other by a centromere
  • Nucleolus: structure found within the nucleus responsible for ribosomal synthesis

Mitochondria

• Powerhouse of the cell
• Contains folds known as cristae
• Site of:
  • Kreb cycle/Citric acid cycle/Tricarboxylic acid cycle
  • Oxidative phosphorylation
  • Mechanisms for ATP production

Ribosomes

• Non-membrane bound organelle responsible for protein synthesis
• Composed of rRNA that are created in the nucleolus
• Types of RNA:
  • rRNA: Ribosomal RNA, forms ribosomes, translates mRNA
  • mRNA: Messenger RNA, carries genetic information of DNA, end product of transcription
  • tRNA: Transfer RNA, carries amino acids to the ribosomes during translation

Endoplasmic Reticulum

• Rough Endoplasmic Reticulum (RER):
  • Contains ribosomes, giving it a "rough" appearance
  • Site of protein synthesis
• Smooth Endoplasmic Reticulum (SER):
  • Does not contain ribosomes, giving it a "smooth" appearance
  • Site of:
    • Steroid synthesis
    • Lipogenesis
    • Detoxification of different substances

Lysosomes

• Packaged products of Golgi apparatus
• Contains hydrolytic "lysozymes" or enzymes
• Responsible for apoptosis or "programmed cell death"

Centrosome

• Holds the chromosomes during cellular division
• Contains pair of centrioles made of microtubules arranged in a "cartwheel pattern"

Cellular Accessories

• Microvilli:
  • Increases surface area of a cell, increasing its absorption property
  • Example of location: Epithelium of stomach to 2/3 anus (simple columnar with microvilli)
• Cilia:
  • "9+2 pattern" or "9+0 pattern" arrangement of microtubules
  • Example of location: Upper part of respiratory tract and fallopian tube
• Flagella:
  • Made up of axoneme
  • For motility of the cell, longer than cilia
  • Types of flagella:
    • Atrichous: absence of flagellum
    • Monotrichous: single flagellum
    • Amphitrichous: flagella are present at both ends of the microorganism
    • Lophotrichous: tufts of flagella at one end of the microorganism
    • Amphilophotrichous: tufts of flagella at both ends of the microorganism
    • Peritrichous: flagella are found around the microorganism

Cellular Division

• Interphase:
  • G1 phase: "first gap phase", cell grows and still functions as usual
  • S phase: "synthesis phase", DNA replication, RNA synthesis
  • G2 phase: "second gap phase", cells prepare for mitosis, organelles double in number
• Mitosis (PMAT): division of somatic cells, results in 2 genetically identical daughter cells (diploid cells)
  • Prophase: nuclear membrane and nucleolus disintegrate, chromatin coils and condenses
  • Metaphase: mitotic spindles from centrosomes attach to centromere, chromosomes align at the equator of the cell
  • Anaphase: chromosomes split, going towards opposite poles
  • Telophase: nuclear membrane reappears, cleavage furrow forms, cytokinesis occurs
• Meiosis: division of sex cells
  • Meiosis 1: same as mitosis, but homologous chromosomes move towards opposite poles
  • Meiosis 2: unique haploid daughter cells enter meiosis 2 (23 chr)

Cellular Physiology

• Body composition:
  • Body fluid (water): 60% of body weight
  • Proteins: 17%
  • Fats: 15%
  • Carbohydrates: 1%
  • Others: 7%
• Types of cellular transport:
  • Passive transport:
    • Simple diffusion
    • Facilitated diffusion
    • Osmosis
  • Active transport:
    • Uses ATP
    • Examples: Na-K pumps, proton pumps
    • Bulk transports: exocytosis, endocytosis

Electrolytes

• Ion: sodium (Na+), potassium (K+), chlorine (Cl-), bicarbonate (HCO3-), phosphate (PO4-)
• Extracellular fluid (ECF): sodium most numerous cation, chloride most numerous anion
• Intracellular fluid (ICF): potassium most numerous cation, phosphate most numerous anion

Body Tissues

• Types of body tissues:
  • Epithelial: lines and covers body surfaces and body cavities
  • Connective: protect, support, and bind body tissues together
  • Muscular: for movement
  • Nervous: receives stimuli and conducts impulses

Cellular Junctions

• Desmosomes: attaches same cells together, example of location: epidermis and cardiac muscle cells
• Hemidesmosomes: attaches different cells together, example of location: between epidermal cells and basement membrane
• Gap junctions: forms a bridge that allows ion diffusion between cells, example of location: nerve cells and cardiac muscle cells
• Tight junctions: "zona occludens", prevents leaking of substances
• Adherens junctions: "zona adherens", prevents separation of epithelial cells during intestinal contraction### Bone Structure
• There are two main types of bone: Primary bone and Secondary bone
• Primary bone (aka Woven bone or Immature bone) has randomly arranged cells and fibers, and is less calcified
• Secondary bone (aka Lamellar bone or Mature bone) has parallel bundles of collagen, is heavily calcified, and has two subtypes: Spongy bone and Compact bone

Types of Secondary Bone

• Spongy bone (aka Cancellous bone or Trabecular bone) is made up of trabeculae
• Compact bone is the strongest type of bone and has a functional unit known as the Haversian system or Osteon

Blood Components

• Plasma makes up 55% of blood and is mostly water (around 95%) and other substances
• Formed Elements (45%) consist of blood cells: Red Blood Cells (RBC), White Blood Cells (WBC), and Platelets
• White Blood Cells (WBC) are also known as Leukocytes
• There are two types of WBC: Granulocytes (Basophil, Eosinophil, and Neutrophil) and Agranulocytes (Monocyte and Lymphocyte)

Granulocytes

• Basophil: least numerous, releases Histamine and Heparin, dark blue/purple granules, bilobed or S-shaped nucleus, lives for several months
• Eosinophil: kills parasites and modulates inflammation, bilobed nucleus, red/dark pink granules, lives for 1 to 2 weeks
• Neutrophil: first line of defense of WBC, kills and phagocytose microorganisms, faint/light pink granules, 3-5 lobes nucleus, lives for 1 to 4 days

Agranulocytes

• Monocyte: precursor of macrophages and other mononuclear phagocytic cells, largest leukocyte, single nucleus (indented/C-shape/Kidney-shape), lives for hours to years
• Lymphocyte: smallest leukocyte with spherical nucleus, important for adaptive immunity, lives for hours to years
  • B-lymphocyte: matures in bone marrow
  • T-lymphocyte: matures in thymus
    • CD4: T helper
    • CD8: Cytotoxic
    • NK cells: special type of CD8

Red Blood Cells

• Most numerous cells in the body, with a lifespan of 120 days
• Females: 4-5 million cells/microliter of blood, Males: 5-6 million cells/microliter of blood
• Contains Hemoglobin that allows it to carry oxygen

Platelets

• Determines fragility of capillaries, with a lifespan of 10 days
• Normal value: 150,000 to 450,000 cells/microliter of blood

Lymphatic System

• Functions: absorbs fluids not absorbed by veins, filters the fluid in the circulatory system
• Lymphatic organs: Primary (Bone Marrow and Thymus), Secondary (Spleen, tonsils, and lymph nodes)
• Important structures: Lymphatic ducts (carry lymph at the junction of Internal Jugular Vein and Subclavian vein), Cisterna chyli (dilated sac at the lower end of thoracic duct that drains lymph from intestinal and lumbar area)

Integumentary System

• Largest system of the body, composed of two parts: Epidermis and Dermis
• Epidermis: Keratinized Stratified Squamous epithelium with four cell types:
  • Keratinocytes: most numerous cells in epidermis, produce keratin
  • Melanocytes: produce the pigment melanin, originated from embryonic cells known as neural crest cells
  • Langerhans cells: macrophage of epidermis
  • Merkel cells: least numerous, detect "Touch" sensations