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Kaplan MCAT Biology Chapter 1 Notes

Kaplan Biology Chapter 1: The Cell (1D, 2A, 2B)
1.1 Cell Theory
 3 tenets of cell theory:
o All living things are composed of cells
o The cell is the basic functional unit of life
o Cells arise only from pre-existing cells
 Fourth tenet: cells carry genetic information in the form of deoxyribonucleic acid (DNA).
This genetic material is passed on from parent to daughter cell.
1.2 Eukaryotic Cells
 Eukaryotic cells contain a true nucleus enclosed in a membrane
 Membrane-bound organelles
 Nucleus
o Contains the genetic material necessary for cell replication
o Surrounded by nuclear membrane or envelope
o Nuclear pores allow selective two-way exchange of material between the
cytoplasm and the nucleus
o The nucleolus is where ribosomal RNA is synthesized
 Mitochondria
o Outer membrane serves as a barrier between the cytosol and inner environment
of the mitochondrion
o Inner membrane arranged in cristae contains the molecules and enzymes of the
electron transport chain
o Semi-autonomous; they contain some of their own genes and replicate
independently of the nucleus via binary fission
o Can initiate apotosis
 Lysosomes
o Membrane bound structures containing hydrolytic enzymes that are capable of
breaking down many different substrates
o Can also initiate apoptosis through release of hydrolytic enzymes
 Endoplasmic Reticulum
o A series of interconnected membranes that are actually contiguous with the
nuclear envelope
o Smooth ER: lacks ribosomes and is utilized primarily for lipid synthesis and detox
of certain drugs and poisons
o Rough ER: studded with ribosomes, which permit the translation of proteins
destined for secretion directly into the lumen
 Golgi apparatus
o Stacked membrane-bound sacs
o Modifies cellular products with carbs, phosphates, and sulfates
o Exocytosis: secretory vesicles merge with the cell membrane to release its
o Contain hydrogen peroxide to breakdown very long chian fatty acids via oxidation
o Provides structure to the clel and helps it to maintain its shape
o Made of three components:
 Microfilaments: made up of solid polymerized rods of actin
 Resistant to compression and fracture; can use ATP to generate
force for movement by interacting with myosin
 Cytokinesis: division of materials between daughter cells
 Cleavage furrow during mitosis is formed by microfilaments
 Microtubules:
 Hollow polymers of tubulin proteins
 Organized into a ring of 9 doublets and 2 central microtubules
 Provide primary pathways along which motor proteins like kinesin
and dynein carry vesicles
 Composes:
o Cilia: projections from a cell that are primarily involved in
the movement of materials along the surface of the cell
o Flagella: structures involved in the movement of the cell
 Intermediate filaments
 Involved in cell-cell adhesion or maintenance of the overall
integrity of the cytoskeleton
 Includes keratin, desmin, vimentin, and lamins
Tissue Formation
o Epithelial tissue: covers the body and cavity linings for protection, absorption,
secretion, and sensation
 Basement membrane
 Parenchyma: functional parts of the organ
 Types of epithelial cells:
 Simple: one layer of cells
 Stratified: multiple layers
 Pseudostratified epithelia: appear to have multiple layers due to
differences in cell height but are only one layer
 Cuboidal: cube shaped
 Columnar: long and thin shaped
 Squamous: flat and scale-like
o Connective tissue supports the body and provides a framework for epithelial cells
to carry out their functions
 Main contributor to the stroma or support structure
 Examples include: bone, cartilage, tendons, ligaments, adipose tissue,
1.3 Classification and Structure of Prokaryotic Cells
 Archaea: single-celled organisms that are visually similar to bacteria, but contain genes
and several metabolic pathways that are more similar to eukaryotes than to bacteria
o Extremophiles
o Both eukaryotes and archaea start translation with methionine, contain similar
RNA pols, and associate their DNA with histones
o Resistant to many antibiotics
 Bacteria contain a cell membrane and cytoplasm, and some have flagella or fimbriae
o Bacteria outnumber human cells 10:1
 Classification of bacteria by shape
o Cocci: spherical bacteria
o Baccilli: rod-shaped bacteria
o Spirilli: spiral-shaped bacteria
 Aerobes and Anaerobes
o Obligate aerobes
o Anaerobes
o Obligate anaerobes
o Facultative anaerobes
o Aerotolerant anaerobes
 Prokaryotic Cell Structure
o Cell Wall
 Forms the outer barrier of the cell followed by the cell membrane
 Cell wall + cell membrane = envelope
o Gram staining:
 Gram positive: If the envelops absorbs the crystal violet stain, it will
appear deep purple
 Consists of a thick layer of peptidoglycan and lipoteichoic acid
 Gram negative: If the envelope does not absorb the crystal violet stain,
but absorbs the safranin counterstain, the cell will appear pink-red
 Contains smaller amounts of peptidoglycan and
o Flagella
 Long, whip-like strcutres that can be used tor propulsion
 Chemotaxis: ability of a cell to detect chemical stimuli and move toward
or away from them
 Composed of a filament, a basal body, and a hook
 Prokaryotes carry out the electron transport chain using the cell membrane
 Prokaryotic ribosomes are smaller than eukaryotic ribosomes (30S and 50S rather than
40S and 60S)
1.4 Genetics and Growth of Prokaryotic Cells
 Bacteria reproduce via Binary Fission: form of asexual reproduction seen in prokaryotes
o Circular chromosome attaches to cell wall  replicates while cell grows 
invagination  2 daughter cells
Genetic recombination increases bacterial diversity
o Transformation: integration of foreign genetic material into the host genome
o Conjugation: transfer of genetic material from one bacterium to another across a
conjudation bridge; a plasmid can be transferred from F+ cells to F- cells, or a
portion of the genome can be transferred from an Hfr cell to a recipient
o Transduction: only genetic recombination process that requires a vector – a virus
that carries genetic material from one bacterium to another
o Bacteriophages can accidentally incorporate a segment of host DNA during
o Transposons: genetic elements capable of inserting and removing themselves
from the genome
o Also seen in eukaryotes
Bacterial growth curve is an example of a semilog plot
o Lag phase: bacteria adapt to new local conditions
o Exponential phase: growth increases
o Stationary phase: resources reduced, growth levels off
o Death phase: resources are depleted, bacteria die
1.5 Viruses and Subviral Particles
 Viral Structure
o Made of genetic material, protein coat (capsid), and sometimes an envelope of
o Can be circular, linearly, single or double stranded, and composed of RNA or DNA
o Enveloped viruses are easier to kill
o Viruses are obligate intracellular parasites
 Viral Genomes
o Positive sense: the genome may be directly translated to functional proteins by
the ribosomes of the host cell, just like mRNA
o Negative sense: negative sense strand acts as a template for synthesis of a
completementary strand, which can then be used as a template for protein
 Must carry an RNA replicase
o Retroviruses are enveloped, single-stranded RNA viruses
 Carries reverse transcriptase which synthesizes DNA from ss RNA
 Viral Life Cycle
o Infection: binding to specific receptors on the host cell
o Translation and progeny assembly
 Translocation of the genetic material to the correct location in the host
cell  DNA virus goes to nucleus for mRNA transcription  then to
cytoplasm for translation into proteins
 The viral genome must be returned to its original form before packaging
o Progeny release
May result in cell death  spilling of viral progeny
Host cell lyses due to too much virions inside
 Disadvantage to the virus due to loss of machinery
 Viral extrusion: virus leaves the cell by fusing with its plasma membrane
o Lytic and Lysogenic Cycles
 Lytic cycle: bacteriophage maximizes the use of the cell’s machinery with
little regard for host cell survival  causes cell lyses
 Viruses in this phase are termed virulent
 Lysogenic cyle: virus integrates into the host genome as a pro-virus or
prophage, which can then reproduce along with the cell. The proviruses
can remain in the genome indefinitely, or may leave the genome in
response to a stimulus and enter the lytic cycle
 Virus enters as a provirus or prophage
Prions: infectious proteins and are nonliving things
o Causes disease through misfolding of secondary proteins structures; forms
protein aggregates
o Causes mad vow disease, Creutzfeldt-Jakob disease, familial fatal insomnia
Viroids: small pathogens consisting of a very short circular single-stranded RNA that
infect plants
o Also infects humans with heptatis D virus (HDV) – alone is innocuous, but when
coinfected with HBV, HDV can silence human hepatocytes