MCAT Bio Flashcards
Number of cells in the human body
37 trillion
Bacteria:eukaryotic cells in body
10:1
Cell Theory
1) all living things composed of cells
2) cell is basic functional unit of life
3) cells arise only from pre-existing cells
4) cells carry genetic information in from form of DNA. This genetic material is passed on from parent to daughter cell
Cell Theory Virus Dilemma
acellular, lack organelles and a nucleus
viruses contain genetic material, but unable to reproduce on their own (violates 3rd and 4th tenets of cell theory because contain RNA and can only reproduce by invading other organisms).
Therefore, viruses not considered living
eukaryotic cells
contain true nucleus enclosed in a membrane
can be unicellular or multicellular
prokaryotic cells
do not contain nucleus
organelles are suspended in
cytosol
most organelles in eukaryotes
membrane bound, allowing for compartmentalization of function
cytosol allows for
diffusion of materials throughout the cell
genetic material is encoded in
DNA
contains coding regions, genes
DNA is organized into
chromosomes
eukaryotic cells reproduce my
mitosis
nucleus
contains all the genetic information necessary for replication
surrounded by nuclear membrane
nuclear membrane/envelope
double membrane that maintains a nuclear environment separate and distinct from the cytoplasm
allows for compartmentalization of transcription and translation
nuclear pores
(in membrane)
allow for selective two-way exchange of material between cytoplasm and nucleus
linear DNA is wound around
histones (organizing proteins), then further wound into linear strands–chromosomes
nucleolus
where rRNA is synthesized
takes up 25% of volume of entire nucleus, can be identified as darker spot
mitochondria
contains two layers: outer and inner membranes
outer mitochondrial membrane
barrier between cytosol and inner environment of mitochondria
inner membrane
folded into cristae
contains molecules and enzymes necessary for ETC
intermembrane space
space in between mitochondrial membranes
mitochondrial matrix
space inside inner membrane
What establishes the proton motive force?
pumping protons from mitochondrial matrix to intermembrane space
during oxidative phosphorylation, protons ultimately flow through
ATP synthase to generate ATP
semiautonomous
mitochondira
replicate independently of nucleus via binary fission
thought to have evolved from anaerobic prokaryote and establishment of symbiotic relationship
cytoplasmic/extranuclear inheritance
transmission of genetic material independent of nucleus
kick starts apoptosis
enzymes of ETC released by mitochondria
lysosomes
membrane bound structures containing hydrolytic enzymes
lysosome enzymes
capable of breaking down many substrates, including substances ingested by endocytosis and cellular waste products
sequestered by membrane to prevent damage to rest of cell
autolysis
release of lysosome enzymes, results in apoptosis
released enzymes lead to degradation of cellular components
endoplasmic reticulum
series of interconnected membranes, contiguous with nuclear envelope
double membrane folded into complex structures with central lumen
smooth ER
lacks ribosomes, utilized primarily for lipid synthesis (i.e. phospholipids in cell membrane) and detoxification of certain drugs/poisons
transports proteins from RER to Golgi in vesicles
Rough ER
studded with ribosomes, which permits translation of proteins destined for secretion directly into lumen
Golgi Apparatus
consists of stacked membrane-bound sacs
modifies cellular products of ER by addition of various functional groups (carbs, phosphates, sulfates, etc.)
modifies cellular products by introducing signal sequences to direct delivery to specific cellular location
After modification in Golgi
cellular products repackaged in vesicles and transported to proper location
can be secreted by exocytosis
peroxisomes
contain hydrogen peroxide
breakdown of long fatty acid chains by beta-oxidation
participate in synthesis of phospholipids, contain some enzymes of pentose phosphate pathway
cytoskeleton
provides structure to cell and helps maintain its shape
provides conduit for transport of materials around the cell
3 components of cytoskeleton
microfilaments, microtubules, intermediate filaments
microfilaments
made of solid polymerized rods of actin
organized into bundles and networks–resistant to compression and fracture, protect the cell
myosin and actin
actin filaments can use ATP to generate force for movement by interacting with myosin–> muscle movement
microfilaments in cytokineses
division of material between daughter cells
microfilament forms cleavage furrow, organize a ring at site of division between new daughter cells
actin filaments contract, ring becomes smaller an eventually pinches off connection
mictotubules
hollow polymers of tubulin proteins
radiate throughout the cell, provide primary pathways for kinesin and dyenin to carry vesicles
cilia
composed of microtubules
projections form a cell that are primarily involved in movement of materials along cell surface
i.e. line respiratory tract for movement of mucus
kinesin and dyenin
motor proteins
examples of nonenzymatic protein function
flagella
composed of microtubules
structures involved in movement of cell itself, i.e. of sperm cell through reproductive tract
9+2 strucutre
cilia and flagella
9 pairs of MT form outer ring, 2 in center
seen only in eukaryotic organelles of motility
centrioles
found in centrosome
organizing centers for MTs
centriole structure
nine triplets of MTs with hollow center
Centrioles during mitosis
migrate to opposite poles of cell, organize mitotic spindle
MTs emanating from centrioles attach to chromosomes via kinetochores, can exert force on sister chromatids and pull them apart
kinetochores
complexes that attach centrioles to chromosomes
intermediate filaments
diverse group of filamentous proteins, including keratin, desmin, ,vimentin, lamins
many involved in cell-cell adhesion or maintenance of cytoskeleton integrity
able to withstand tremendous tension, make cell structure more rigid
help anchor other organelles i.e. nucleus
epithelial tissue
covers body and lines cavities, provide means for protection against pathogen invasion and desiccation
involved in absorption, secretion, and sensation
basement membrane
layer of connective tissue that underlies and tightly joins epithelial cells–> remain cohesive unit
parenchyma
functional part of the organ
epithelial cells in most organs i.e. nephrons (kidney), hepatocytes (liver), acid-producing (stomach)
epithelial structures
polarized: one side faces lumen/outside world, other interacts with underlying blood vessels/structural cells
lumen
hollow inside of organ or tube
simple epithelia
one layer of cells
stratified epithelia
multiple layers of cells
psuedostratified
appear to have multiple layers because of height differences, but in reality one layer
epithelial shapes
cuboidal
columnar
squamous (flat, scalelike)
connective tissue
supports the body, provides framework for epithelial cells to carry out functions
main contributors to stroma
i.e. bone, cartilage, tendons, ligaments, adipose tissue, blood
stroma
support structure for epithelial cells
extracellular matrix formed by
materials such as collagen and elastin, secreted by connective tissue cells
prokaryotes
simplest of all organelles, include all bacteria
do not contain any membrane bound organelles, do not have a nucleus
single celled organisms but can live in colonies with other cells that can signal and share information about environment
genetic material of prokaryotes
organized into single circular molecule concentrated in nucleoid region
not coiled around histones
can also have plasmids
domains that contain prokaryotes
archaea and bacteria
archaea
single celled organisms, contain genes and several metabolic pathways that are more similar to eukaryotes than bacteria
notable for ability to use alternative sources of energy-photosynthetic, chemosynthetic (inorganic compounds i.e. S or N based compounds)
archaea environments
historically considered extremophiles (extremely high temperatures, salinity, or not light) but more recent research has demonstrated greater variety of habitats
archaea and eukaryotic origin
hypothesized that shared
both start translation with Methionine, contain similar RNA polymerases, associate DNA with histones
Unique archaea characteristics
contain single circular chromosome
divide by binary fission or budding
overall share similar structure to bacteria
resistant to many antibiotics
All bacateria contain
cell membrane and cytoplasm, some have flagella or fimbriae
fimbriae
similar to cilia
Why is it difficult to target just bacteria with drugs?
Share very similar structure with archaea
however, even similarly structures have enough biochem differences to allow targeting of one organism
i.e. bacterial flagella and eukaryotic flagella distinct enough to be targeted
many antibiotics target bacterial ribosome–much smaller than eukaryotic ribosome
number of bacteria on earth
5E30
outnumber all plants and animals combined
mutualistic symbiotes
both humans and bacteria benefit from relationship
i.e. bacteria in human gut produce vitamin K and biotin (Vitamin B7), also prevents overgrowth of harmful bacteria
pathogens
also known as parasites
provide no advantage or benefit to host, cause disease
may live intracellularly or extracellularly
vitamin K
required for production of plasma proteins necessary for blood clotting
newborns are not yet colonized by bacteria, cannot product clotting factors–> at risk for hemorrhage
newborns given injection of Vitamin K to aid in production of clotting factors until colonization
bacteria shapes
cocci (spherical) i.e. streptococcus pyogenes
bacilli (rod shaped) i.e. E Coli
spirilli (spiral) i.e. causes syphilis
obligate aerobes
bacteria that require oxygen for metabolism
anaerobes
bacteria that use some other form of cellular metabolism that does not require oxygen i.e. fermentation
obligate anearobes
bacteria that cannot survive in oxygen-containing environment
presence of oxygen leads to production of reactive oxygen-containing radicals–> cell death
facultative anearobes
bacteria that can toggle between metabolic processes (aerobic or anaerobic)
aerotolerant anaerobrs
unable to use oxygen for metabolism, but are not harmed by its presence in the environment
cell wall
forms outer barrier of cell
provides structure and controls movement of solutes into and out of bacterium
envelope
cell wall + cell membrane
cell membrane of prokaryotes
plasma membrane, composed of phospholipids (similar to eukaryotes)
Gram staining
staining process with crystal violet stain, followed by cointerstain with safranin
crystal stain absorbed by peptidoglycan
gram positive
envelope absorbs crystal violet stain, appears deep purple
cell wall consists of thick layer of peptidoglycan, contains lipoteichoic acid
Gram negative
very thin cell wall, also contains peptidoglycan but in much lower amount
cell walls directly abut cell membrane
also have outer membranes
peptidoglycan
polymeric substance made from amino acids and sugars
structural/barrier functions
may also aid pathogen by providing protection from host organism’s immune system
lipoteichoic acid
unknown function for bacteria, but may activate human immune system
outer membrane
contains phospholipids and lipopolysaccharides
lipopolysaccharides
part of gram negative bacteria that triggers human immune response
much stronger inflammatory response than to lipo acid
human immune system can respond to
components of bacterial cell wall
bacterial flagella
long, whip like structures made of flagellin that can be used for propulsion
can have 1 or many
used to move towards food or away from toxins, immune cells
chemotaxis
ability of cell to detect chemical stimuli and move towards or away from it
flagella composition
filament, basal body, hook
*similar in gram positive and gram negative, slight differences due to different physical structures and chemical compositions of envelope
filament
hollow, helical structure composed of flagellin
basal body
complex structure that anchors flagellum to cytoplasmic membrane and is the motor (rotates at rate up to 300 Hz)
hook
connects filament and basal body so that as basal body rotates, exerts torque on filament which can then spin and propel bacteria forward
plasmids
circular structures that carry DNA acquired from external sources
carry DNA that are not necessary for prokaryotic survival (not considered part of genome) but may confer advantages such as antibiotic resistance
prokaryotic generation of ATP
lack mitochondria
use cell membrane for ETC and generation of ATP
prokaryotic cytoskeleton
contain a primitive one, but not nearly as complex as eukaryotes
prokaryotic ribosomes
smaller
30S and 50S subunits (eukaryotic contain 40S and 60S)
binary fission
simple form of asexual reproduction seen in prokaryotes
circular chromosome attaches to cell wall and replicates while cell continues to grow in size
eventually, plasma membrane and wall grow inwards along midline of cell to produce two identical daughter cells
speed of binary fission relative to mitosis
requires fewer events, proceeds more rapidly
beyond circular chromosome, many bacteria also contain
plasmids: extrachromosomal material
often carry genes that impart some benefit to bacterium i.e. antibiotic resistance
may also contain virulence factor
virulence factor
traits that increase how pathogenic a bacterium is, i.e. toxin production
toxin production
projections that allow the bacterium to attach to certain kinds of cells or evasions of host’s immune system
episomes
subset of plasmids capable of integrating into genome of bacterium
bacterial genetic recombination helps increase
bacterial diversity
permits evolution of bacterial species over time
transformation
results from integration of foreign genetic material into host genome
foreign material frequently comes from other bacteria that spill contents upon lysing
many gram negative rods are able to carry out this process
conjugation
bacterial form of mating
two cells form conjugation bridge
transfer is unidirectional
increases genetic variability
conjugation bridge
allows transfer of genetic material between bacterium
made from appendages called sex pili
unidirectional transfer
from donor male (+) to recipient female (-)
sex pili
found on donor male
sex factors
plasmids that contain necessary genes to form pilus
Fertility (F) Factor
in E. coli
bacteria that possess it termed F+, those that don’t F-
F Factor conjugation
F+ cell replicates its F factor, donates copy to recipient–> converts it to F+ cell
enable cell obtaining new plasmid to transfer copies to other cells
allows for rapid acquisition of antibiotic resistance, virulence factors throughout colony because other plasmids can also be passed through conjugation bridge
sex factor is a plasmid but through processes such as transformation . . .
can be integrated into host genome
in this case, when conjugation occurs, entire genome replicates because now contains sex factor
donor cell will then attempt to transfer entire copy of genome into recipient, but bridge usually breaks before full DNA sequence can be moved
Hfr
high frequency recombination
entire copy of genome can be transferred to recipient before bridge breaks
transduction
only genetic recombination process that requires a vector
when fragments of bacterial chromosome accidentally become packaged into viral progeny produced during viral infection, can subsequently be introduced into another bacterium by viral vector
increases genetic variability
vector
virus that corries genetic material from one bacterium to another
obligate intracellular pathogens
virusus
cannot reproduce outside of host cell
bacteriophage transduction
viruses that infect bacteria
can accidentally trap a segment of host DNA during assembly
when bacteriophage infects another bacterium, can release trapped DNA into new host cell
transferred DNA can integrate into genome, giving new host additional genes
tranposons
genetic elements capable of inserting and removing themselves from the genome
not limited to prokaryotes, also seen in eukaryotes
if transposon is inserted in coding region of gene
that gene may be disputed
bacteria grow in series of phases
lag
exponential
stationary
death
lag phase
in new environment, bacteria first adapt to new local conditions
exponential phase
as bacteria adapt, growth increases–> exponential increase in number of bacteria in the colony
aka log phase
stationary phase
as number of bacteria in colony grows, resources often reduced
reduction of resources slows reproduction
death phase
after bacteria have exceeded ability of environment to support number of bacteria, death occurs as resources have been depleted
viral structure
genetic material, protein coat, sometimes envelope containing lipids
viral genetic information
can be circular or linear, single or double stranded, DNA or RNA
capsid
protein coat of virus
viral envelope
surrounds capsid, composed of phospholipids and virus specific proteins
sensitive to heat, detergents, and desiccation–> easier to kill
*viruses without envelopes more resistant to sterilization, likely to persist on surfaces for extended period of time
viral reproduction
obligate intracellular parasites
must express and replicate genetic information within host cell
replicate and produce virions, which can be released to infect additional cells
viruses cannot reproduce independently because
lack ribosomes
virions
viral progeny released to infect other cells
bacteriophages
viruses that specifically target bacteria
do not actually enter bacteria–use tail to anchor to membrane and inject genetic material, leaving remaining structures outside infected cell
bacteriophage structure
capsid, tail sheath, tail fibers
tail sheath
can act like syrings, inject genetic material into bacterium
tail fibers
help bacteriophage to recognize and connect to correct host cell
some tail fibers have enzymatic activity, allowing penetration of cell wall and formation of pores in cell membrane
viral genomes
variety of shapes and sizes, any number of genes, single stranded DNA or RNA
single stranded RNA viruses may be
positive sense or negative sense
positive sense
genome may be directly translated to functional proteins by ribosomes of host cells, just like mRNA
negative sense
single stranded RNA viruses
require synthesis of RNA strand complementary to the negative sense RNA strand, which can then be used as template for protein synthesis
must carry RNA replicase in virion
RNA replicase
ensures that complementary strand of negative sense RNA virsus is synthesized
retroviruses
enveloped, single stranded RNA viruses in family Retroviridae
usually, virion contains two identical RNA molecules
carry reverse transcriptase
reverse transcriptase
synthesizes DNA from single stranded RNA
often makes errors that generates diversity into virus copies
retrovirus reproduction
Virsus fuses with cell, empties contents into cytoplasm
Reverse transcriptase
Integrase then inserts copy into host DNA, where replicated and transcribed as if host cell’s DNA–> cell infected indefinitely, only way to cure infection is kill infected cell itself i.e. HIV
cell machinery transcribes viral genes back into RNA, travels to cytoplasm, where ribosomes produce encoded proteins
viral RNA and proteins move towards cell membrane, father into budding virus particle
HIV life cycle
virus binds to CD4 and CCR5 proteins on cell surface
fuses, releases contents into cytoplasm
reverse transcriptase, integrase
viral genes back to RNA, then move to membrane and gather into budding particle
in new immature virus copy, HIV protease enzymes modifies viral protein chains, enabling virions to mature into form that can infect new cell
CCR5
receptor on white blood cells that HIV binds to
people who lack CCR5 receptor–> HIV immune
Infection
in order to infect cell, virus has to bind to specific receptors on host cell (without proper receptors, cell is essentially invisible to virus)
enveloped virus fuse with plasma membrane, allowing entry of virion into host cell
*sometimes host cell will accidentally bring virus into cell via endocytosis (mistakes it for useful molecule)
viral translation
translation must occur in order to reproduce
requires translocation of genetic material to correct location in cell
DNA viruses go to nucleus to be transcribed into mRNA
mRNA then goes to cytoplasm, where translated to proteins
positive sense: stays in cytoplasm, where directly translated to protein by host cell ribosomes
negative sense: require synthesis of complementary RNA strand via RNA replicase, which is then translated to form proteins
*DNA formed through reverse transcription in retroviruses also travels to nucleus, where integrated into host genome
progeny assembly
using host cell ribosomes, tRNA, AAs, and enzymes, viral RNA–>proteins
many proteins are structural capsid proteins, allow for creation of new virions in host cell cytoplasm
once viral genome replicated, can be packaged within capsid (*must be returned to original form before packaging)
methods of progeny release
viral invasion may initiate cell death–> spilling of viral progeny
host cell lyses because filled with extremely large number of virions
extrusion-allows for survival of host cell and continued use of host cell by virus (productive cycle)
extrusion
virus can leave cell by fusing with its plasma membrane
lytic cycle
bacteriophage makes maximal use of cell’s machinery with little regard for survival of host cell
once host swollen with new virions, cell lyses and other bacteria infected
virulent
bacteria in lytic phase
lysogenic cycle
if bacteria does not lyse bacterium, may integrate into host genome as provirus/prophage
virus will be replicated as bacterium reproduces because now part of host’s genome–may remain integrated into genome indefinitely, environmental factors (radiation, light, chemicals)–> provirus leaves genome and reverts to lytic cycle
trapping of segments in bacterial genome can occur when provirus leaves genome
allows transduction of genes from one bacterium to another
superinfection
simultaneous infection
infection with one strain of phage generally makes bacteria less susceptible to this
bacteriophages can kill host bacterium but . . .
may be benefit to having them integrated into lysogenic cycle
provirus is relatively innocuous, some be may evolutionary advantage to this association
prions
infectious proteins–> non-living things
cause disease by triggering misfolding of other proteins (usually alpha to beta)
drastically reduces solubility as well as ability of cell to degrade misfolded protein–> aggregates form, cell function reduced
ex: mad cow disease, creutzfeldt-jakob, familial fatal insomnia
viroids
small pathogens consisting of very short circular single-stranded RNA that infect plants
can bind to large number of RNA sequences, silence plant genome–> prevents synthesis of necessary proteins, can subsequently cause metabolic and structural derangements in plant cell
human viroid
HDV (Hepatitis D)
alone innocuous but when paired with Hep B, can exert silencing function on human hepatocytes
hepatocyte
human liver cell
main function of nucleolus
synthesis of ribosomal RNA
processes that increase genetic variability of bacteria
conjugation
transduction
shared mammalian characteristics
milk producing mammary glands three bones in middle ear, one in lower jaw fur/hair heterodont dentition sebaceous and sudoriferous glands
heterodont dentition
different kinds of teeth
