Cellular Level of Organization - Flashcards

Cell Theory and Basic Cell Structure

Cell theory:
- Cells are the building blocks of all plants and animals.
- All new cells come from division of preexisting cells.
- Cells are the smallest unit that perform all vital physiological functions.
Extracellular fluid (ECF): watery medium surrounding cells; in many tissues called interstitial fluid.

Plasma membrane: selectively permeable barrier controlling entry of ions/nutrients, wastes, and secretions.
Components:
- Phospholipid bilayer with hydrophilic heads and hydrophobic tails.
- Cholesterol stabilizes membrane.
- Glycocalyx: glycolipids & glycoproteins on outer surface for cell recognition.
- Integral (transmembrane) proteins and peripheral proteins.
- Cytoskeleton connections to membrane.
Functions: physical isolation, regulation of exchange, sensitivity to environment, structural support.
Membrane transport: selectively permeable based on material and membrane properties.
Key terms to recall:
- Glycocalyx, glycoproteins, glycolipids, proteoglycans.
- Integral vs peripheral proteins.
Quick facts:
- Typical membrane thickness: about 6-10\ \text{nm}.

Components and sizes:
- Microfilaments: <6\ \text{nm}; mainly actin; periphery of cell; form microvilli and terminal web.
- Intermediate filaments: 7-11\ \text{nm}; durable structural support.
- Microtubules: 25\ \text{nm}; radiate from centrosome; organize organelles and form spindle during division.
Other structures:
- Centrioles: two per centrosome; 9 groups of triplets; organize DNA movement during division.
- Cilia: nine pairs of microtubules around a central pair; basal body anchors; move fluids/secretions.
Functions: provide shape, organization, intracellular transport, and movement.

Ribosomes: protein synthesis; two subunits (large and small).
- Free ribosomes synthesize proteins for cytosol.
- Rough ER has fixed ribosomes and synthesizes proteins to be packaged or exported.
Endoplasmic Reticulum (ER): network of membranes with cisternae.
- Smooth ER (SER): lacks ribosomes; synthesizes phospholipids/cholesterol, steroid hormones; stores glycogen/ glycerides.
- Rough ER (RER): has ribosomes; modifies proteins; ships to Golgi.
Golgi apparatus: modifies, sorts, and packages proteins for secretion or delivery; membrane renewal; lysosome enzyme packaging.
Lysosomes: contain digestive enzymes; autolysis possible; “suicide packets.”

Produce ATP via carbohydrate metabolism; double membrane with inner membrane folds (cristae).
Matrix contains enzymes for citric acid cycle; cristae increase surface area for energy production.
Not all cells have mitochondria (e.g., red blood cells lack them).

Nucleus: usually largest cellular structure; control center for gene expression.
Nuclear envelope: double membrane with nuclear pores for material exchange.
Nucleolus: site of ribosomal RNA synthesis and ribosome assembly.
Nucleoplasm: fluid inside nucleus; contains DNA, RNA, proteins, ions.
DNA organization:
- Chromatin in nondividing cells (loosely coiled).
- Chromosomes in dividing cells (tightly coiled).
- DNA packaging with histones into nucleosomes.
Genes: functional units of heredity; contain nucleotides needed to produce specific proteins/RNA.

DNA basics:
- Long chains of nucleotides with bases A, T, C, G.
- Triplet code specifies an amino acid.
Transcription (nucleus -> mRNA):
- Gene activation increases accessibility; RNA polymerase binds promoter.
- mRNA is formed complementary to DNA template strand; introns removed, exons spliced to mature mRNA.
- mRNA leaves via nuclear pores; contains codons (triplets).
Translation (cytoplasm):
- mRNA binds to small ribosomal subunit; tRNA with anticodons brings amino acids.
- Large and small ribosomal subunits assemble around mRNA; polypeptide elongation occurs.
- Stop codon terminates translation; ribosomal subunits disassemble.
Key terms:
- Codon (mRNA), Anticodon (tRNA), Triplet (DNA), Mature mRNA, Exons/Introns.
Translation yields a polypeptide chain which folds into a functional protein.

Diffusion: movement down a concentration gradient; can be through lipids or channels.
Osmosis: diffusion of water across a selectively permeable membrane.
Osmolarity vs Tonicity:
- Isotonic: no net water movement.
- Hypotonic: water moves into the cell; may cause swelling/hemolysis.
- Hypertonic: water moves out of the cell; may cause crenation.
Carrier-mediated transport:
- Facilitated diffusion: no ATP; carrier proteins may saturate.
- Active transport: uses ATP (e.g., Na+/K+ ATPase) and moves substances against gradients.
- Secondary active transport: uses gradient created by primary transport; does not itself expend ATP.
Sodium–potassium pump: 3\ \mathrm{Na}^+\text{ out},\; 2\ \mathrm{K}^+\text{ in} per ATP hydrolyzed.
Vesicular transport: endocytosis and exocytosis require ATP; receptor-mediated endocytosis, pinocytosis, phagocytosis, and vesicle fusion/exocytosis.

Receptor-mediated endocytosis: ligands bind receptors, cluster, endocytose into coated vesicles, fuse with lysosomes, receptors recycle.
Pinocytosis: nonspecific "cell drinking"; vesicles form from plasma membrane.
Phagocytosis: cells ingest solids; phagosomes fuse with lysosomes; digestion occurs.
Exocytosis: vesicles fuse with plasma membrane to release contents.

Cell life cycle: interphase and cell division.
Interphase: G0, G1, S, G2 phases.
- G0: cells performing normal functions; some cells remain here.
- G1: growth and organelle duplication.
- S: DNA replication.
- G2: final protein synthesis and centriole replication.
Mitosis: produces two identical daughter cells.
- Prophase: chromosomes condense; nuclear envelope breaks down; centrioles migrate; spindles form.
- Metaphase: chromosomes align at metaphase plate.
- Anaphase: sister chromatids separate; pulled to opposite poles.
- Telophase: chromosomes arrive at poles; nuclear membranes reform; cytokinesis begins.
- Cytokinesis: cytoplasm divides; cleavage furrow forms.
Meiosis (not detailed here): sex cells; 23 chromosomes each.

Cancer: mutations lead to abnormal cell division rates.
Neoplasm (tumor): a mass of abnormal cells.
Benign: remains within tissue of origin.
Malignant: invasive; can metastasize to secondary sites; often requires angiogenesis.