MCAT CHAPTER1

Cell theory: the 4 tenets

(1) All living things are composed of cells. (2) The cell is the basic functional unit of life. (3) Cells arise only from preexisting cells. (4) Cells carry genetic information as DNA, passed from parent to daughter cell.

Why are viruses NOT considered living (cell theory)?

Acellular; cannot reproduce without a host cell (violates tenet 3); may use RNA as genetic material (violates tenet 4).

Eukaryotic cell

Cell with a true membrane-enclosed nucleus and membrane-bound organelles; may be unicellular or multicellular.

Prokaryotic cell

Cell with NO nucleus and NO membrane-bound organelles; single circular DNA in the nucleoid region. Includes all bacteria (and Archaea).

Cell membrane (eukaryotic)

Phospholipid bilayer: hydrophilic surfaces (face aqueous environments), hydrophobic core; highly selective barrier.

Cytosol

Semifluid medium in which organelles are suspended; allows diffusion of molecules throughout the cell.

Nucleus

Control center of the cell; contains all genetic material (DNA organized into chromosomes); site of transcription. Most heavily tested organelle.

Nuclear membrane (nuclear envelope)

Double membrane separating the nucleus from the cytoplasm; allows compartmentalization of transcription (nucleus) from translation (cytoplasm).

Nuclear pores

Openings in the nuclear envelope that allow selective two-way exchange of material between nucleus and cytoplasm.

Gene

Coding region of DNA.

Histones

Organizing proteins that linear eukaryotic DNA is wound around. (Also found in Archaea; NOT in bacteria.)

Chromosome

Linear strand of DNA wound around histones and further coiled (eukaryotes).

Nucleolus

Subsection of the nucleus (about 25% of its volume; dark spot) where ribosomal RNA (rRNA) is synthesized.

Mitochondria

'Power plants' of the cell; electron transport chain and oxidative phosphorylation make ATP; can trigger apoptosis by releasing ETC enzymes.

Outer mitochondrial membrane

Barrier between the cytosol and the inner environment of the mitochondrion.

Inner mitochondrial membrane

Folded into cristae; contains the molecules and enzymes of the electron transport chain.

Cristae

Infoldings of the inner mitochondrial membrane that increase surface area for ETC enzymes.

Intermembrane space

Space between the inner and outer mitochondrial membranes; protons are pumped here to create the proton-motive force.

Mitochondrial matrix

Space inside the inner mitochondrial membrane.

Serial endosymbiosis theory

Organelles (mitochondria, chloroplasts, organelles of motility) arose when one prokaryote engulfed another and a symbiotic relationship formed.

Semiautonomous (mitochondria)

Mitochondria contain some of their own genes (circular, double-stranded DNA) and replicate independently of the nucleus by binary fission.

Apoptosis

Programmed cell death; can be triggered by release of mitochondrial ETC enzymes or lysosomal enzymes.

Lysosome

Membrane-bound (single membrane) organelle containing hydrolytic enzymes that break down endocytosed material and cellular waste.

Autolysis

Release of lysosomal hydrolytic enzymes into the cell, degrading cellular components and causing apoptosis.

Endoplasmic reticulum (ER)

Interconnected membranes (single membrane, central lumen) contiguous with the nuclear envelope; two types: rough and smooth.

Rough ER (RER)

ER studded with ribosomes; translates proteins destined for secretion directly into its lumen.

Smooth ER (SER)

ER lacking ribosomes; lipid synthesis, detoxification of drugs/poisons, and transport of proteins from the RER to the Golgi.

Golgi apparatus

Stacked membrane-bound sacs; modifies (carbohydrates, phosphates, sulfates), sorts, and repackages ER products into vesicles.

Signal sequences

Tags added in the Golgi that direct a product to a specific cellular location.

Exocytosis

Secretory vesicle fuses with the cell membrane and releases its contents outside the cell.

Peroxisome

Contains hydrogen peroxide; breaks down very long chain fatty acids by beta-oxidation; helps synthesize phospholipids; contains some pentose phosphate pathway enzymes.

Beta-oxidation

Breakdown of fatty acids; peroxisomes handle very long chain fatty acids.

Cytoskeleton

Provides cell structure/shape and transport pathways. Three parts: microfilaments, microtubules, intermediate filaments.

Microfilaments are

composed of actin, they resist compression/fracture; interact with myosin for muscle contraction and also form the cleavage furrow.

Actin

Protein that makes up microfilaments.

Myosin

Motor protein that uses ATP to interact with actin filaments (e.g., muscle contraction).

Cytokinesis

Division of materials between daughter cells; an actin ring contracts and pinches the cells apart.

Cleavage furrow

Contractile ring of microfilaments (actin) at the division site between two daughter cells during mitosis.

Microtubules

Hollow polymers of tubulin; main tracks for kinesin/dynein vesicle transport; form cilia, flagella, centrioles, and the spindle.

Tubulin

Protein that makes up microtubules.

Kinesin and dynein

Nonenzymatic motor proteins that carry vesicles along microtubules.

Cilia

Microtubule-based projections that move materials along the cell surface (e.g., mucus in the respiratory tract). 9 + 2 structure.

Flagella (eukaryotic)

Microtubule-based structures that move the cell itself (e.g., sperm). 9 + 2 structure; different from bacterial flagella.

9 + 2 structure

Ring of 9 microtubule DOUBLETS around 2 central microtubules; seen ONLY in eukaryotic cilia and flagella.

Centriole

Nine TRIPLETS of microtubules with a hollow center; organizes microtubules and the mitotic spindle; migrates to opposite poles in mitosis.

Centrosome

Region of the cell where centrioles are found; microtubule-organizing center.

Mitotic spindle

Microtubule structure organized by centrioles that separates sister chromatids.

Kinetochores

Protein complexes on chromosomes where spindle microtubules attach to pull sister chromatids apart.

Intermediate filaments

Diverse filamentous proteins (keratin, desmin); withstand tension; cell-cell adhesion; anchor organelles including the nucleus; cell/tissue-specific.

Keratin

Example of an intermediate filament protein.

Example of an intermediate filament protein.

desmin and keratin

4 tissue types

Epithelial, connective, muscle, and nervous tissue.

Epithelial tissue

Covers the body and lines cavities; protects against pathogens and desiccation; absorption, secretion, sensation. Forms the parenchyma of most organs.

Basement membrane

Layer of connective tissue underlying epithelial cells that they are tightly joined to.

Parenchyma

Functional parts of an organ; made of epithelial cells (e.g., nephrons, hepatocytes).

Polarized (epithelial cells)

One side faces a lumen or the outside world; the other side interacts with blood vessels and structural cells.

Lumen

Hollow inside of an organ or tube.

Simple epithelium

One layer of cells.

Stratified epithelium

Multiple layers of cells.

Pseudostratified epithelium

Appears to be multiple layers because cell heights differ, but is really ONE layer.

Cuboidal cells

Cube-shaped epithelial cells.

Columnar cells

Long and thin epithelial cells.

Squamous cells

Flat, scalelike epithelial cells.

Connective tissue

Supports the body and provides a framework for epithelium; forms the stroma. Includes bone, cartilage, tendons, ligaments, adipose, and blood. (Muscle is NOT connective tissue.)

Stroma

Support structure of an organ; formed by connective tissue.

the Extracellular matrix is created with what materials and where are these materials secreted from

Material (e.g., collagen and elastin) secreted by connective tissue cells such as fibroblasts

Collagen and elastin

Proteins secreted by connective tissue cells to form the extracellular matrix.

Nucleoid region

Area of a prokaryotic cell where the single circular DNA molecule is concentrated; no nuclear envelope.

3 domains of life

Archaea, Bacteria, Eukarya (Archaea and Bacteria are prokaryotes).

Monera

Old kingdom that grouped Archaea and Bacteria together; abandoned because their evolutionary paths differ as much as either differs from Eukarya.

Archaea

Single-celled prokaryotes with genes/pathways more like eukaryotes; often extremophiles; resistant to many antibiotics.

Extremophile

Organism living in harsh environments (high temperature, high salinity, no light); classically Archaea.

Chemosynthetic

Generating energy from inorganic compounds (sulfur, ammonia); common in Archaea.

Archaea similar to eukaryotes

Start translation with methionine, similar RNA polymerases, DNA associated with histones.

Archaea similar to bacteria

Single circular chromosome, divide by binary fission or budding, no nucleus/membrane-bound organelles, similar overall structure.

Bacteria

Prokaryotes with a cell membrane and cytoplasm; some have flagella or fimbriae; can be symbiotes or pathogens.

Fimbriae

Bacterial projections similar to cilia (used for attachment).

Symbiote

Organism in a relationship where both host and microbe benefit (e.g., gut bacteria making vitamin K and biotin).

Pathogen

Organism that benefits at the host's expense by causing disease; may be intracellular (Chlamydia trachomatis) or extracellular (Clostridium tetani).

Cocci

Spherical bacteria (e.g., Streptococcus pyogenes, Staphylococcus aureus).

Bacilli

Rod-shaped bacteria (e.g., E. coli).

Spirilli

Spiral-shaped bacteria (Treponema pallidum, Borrelia burgdorferi, Leptospira interrogans).

Treponema pallidum

Spiral bacterium that causes syphilis; still penicillin-sensitive.

Borrelia burgdorferi

Spiral bacterium that causes Lyme disease.

Leptospira interrogans

Spiral bacterium that causes Weil's syndrome.

Obligate aerobe

REQUIRES oxygen for metabolism; cannot survive without it.

Anaerobe

Bacterium that does not require oxygen for metabolism (e.g., uses fermentation).

Obligate anaerobe

Cannot survive in oxygen; O2 produces reactive oxygen radicals leading to cell death. Treated with hyperbaric oxygen.

Facultative anaerobe

Uses oxygen for aerobic metabolism if present; switches to anaerobic metabolism if absent. Survives either way.

Aerotolerant anaerobe

Cannot use oxygen for metabolism but is not harmed by its presence.

Cell wall (bacterial)

Outer barrier that provides structure and controls solute movement; type (gram + or -) determined by Gram stain.

the Envelope (bacterial) is composed of?

Cell wall + cell membrane together.

Gram-positive

Absorbs crystal violet and stains deep PURPLE; thick peptidoglycan wall plus lipoteichoic acid; NO outer membrane.

Gram-negative

Does not hold crystal violet; takes up safranin counterstain and stains PINK-RED; thin peptidoglycan plus an outer membrane with phospholipids and lipopolysaccharides.

Peptidoglycan

Polymer of amino acids and sugars forming the bacterial cell wall; cross-linking is blocked by penicillin, causing osmotic lysis.

Lipoteichoic acid

Gram-positive cell wall component; can activate the human immune system (weaker response than LPS).

Lipopolysaccharide (LPS)

Gram-negative outer membrane component that triggers a strong human inflammatory response.

Chemotaxis

Detecting chemical stimuli and moving toward (food) or away from (toxins, immune cells) them.

Bacterial flagellum: 3 parts

Filament (hollow helix of flagellin), basal body (anchor + rotary motor, up to 300 Hz), hook (connects filament and basal body, transmits torque).

Flagellin

Protein making up the bacterial flagellar filament (vs. tubulin in eukaryotic flagella).