MCAT BIOLOGY
Chapter 1 - The Cell
Describe negative sense viruses.
!" Negative sense RNA cannot be directly translated
!" Complimentary strand must be synthesized in the host cell and can then
be translated to produce viral proteins
!" To ensure the complimentary RNA strand is synthesized, negative sense
viruses carry an enzyme called RNA replicase (RNA-dependent RNA
polymerase) - which synthesizes the complimentary strand described
previously
Describe positive sense viruses.
!" Viral genome can be directly translated by the ribosomes of the host cell,
just like mRNA
Describe the cell wall in Gram-positive cells.
!" Consist of a thick layer of peptidoglycan and lipoteichoic acid
Describe the cell walls in Gram-negative bacteria.
!" Consist of a thin layer of peptidoglycan
!" Also have an outer membrane beyond the peptidoglycan which is studded
with lipopolysaccharides
#" Note periplasmic space in diagram
Do eukaryotic cell walls have peptidoglycan?
!" No, peptidoglycan is only present in bacterial cell walls
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Do prokaryotes contain a cytoskeleton?
!" Yes, a primitive simple one
Do prokaryotic cells have organelles?
!" Yes, just not membrane-bound organelles
!" Have ribosomes
How are viral progeny released?
!" Through cell death, lysis, or extrusion
How do bacteria carryout the electron transport chain without mitochondria?
!" Use their own cell membrane to house the ETC enzymes
How do bacteria get so much genetic variability?
!" Transformation, transduction, and conjugation
!" Note: Not binary fission
How do prokaryotic ribosomes contrast with eukaryotic ribosomes?
!" Prokaryotic ribosomes are made of a 30S and a 50S subunit
!" Eukaryotic ribosomes are made of a 40S and a 60S subunit
How do the concentration of organelles in different cell types vary?
!" Concentration of organelles is different from cell type to cell type
!" Differences are functional
!" Ex. cells that need a lot of energy have a lot of mitochondria, cells that
secrete a lot have high RER and golgi apparatus
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How do viruses infect cells?
!" Attach specific receptors
!" Enter the cell by:
#" Fusing with the plasma membrane
#" Being brought in by endocytosis
#" Injecting their genome into the cell
How does a lysosome digest material?
!" Lysosomes must interact with a membrane-bound carrier of some sort
(usually something ending in -some) & fuse with vesicles to exert their
effects!
!" Fuses its membrane with the carrier
!" Injects its hydrolytic enzymes into the new macrostructure
!" Digests material inside carrier
How does a prion commonly function?
!" Causes conversion of α-helix to β-sheet in other proteins
!" Decreases the solubility of the protein and increases the cell's ability to
degrade the protein
!" Leads to aggregates that kill you
How does the environment in the nucleus compare to the environment of the rest
of the cell?
!" Environment in the nucleus is separate and distinct from the environment
in the rest of the cell
!" Because the nuclear membrane is selectively permeable
How is the DNA of prokaryotic cells stored?
!" Prokaryotic DNA exists as a single, circular molecule - which floats in a
region of space known as the nucleoid region
!" Prokaryotes do not have a nucleus (membrane-bound organelle)
In what 3 ways are Archaea similar to Eukarya?
1. Start translation with methionine like Eukarya
2. Contain similar RNA polymerases to Eukarya
3. Associate their DNA with histones like Eukarya
In what 3 ways are Archaea similar to bacteria?
!" Have a singular circular chromosome
!" Divide by binary fission or budding
!" Share a similar overall prokaryotic structure to bacteria
Infection with one strain of phage generally makes bacteria less susceptible to
superinfection.
The nuclear envelope permits the separation of these two steps of the central
dogma of biology:
!" Transcription and Translation
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What are cristae?
!" Infoldings of the inner mitochondrial membrane
!" Foldings increase the surface area available for electron transport chain
enzymes
What are high frequency of recombination (Hfr) cells?
!" Sex factor plasmid that has integrated into host chromosomal DNA through
process like transformation
!" When sex factor plasmid gets incorporated into bacterial genome, it will
attempt to replicate and transfer entire genome during conjugation, but
bridge usually breaks before it can
What are lysosomes?
!" Membrane-bound structures containing hydrolytic enzymes
!" Found floating in the cell's cytoplasm
What are nuclear pores?
!" Allow selective two-way exchange of material between the cytoplasm and
the nucleus
!" Doors into and out of the nucleus
What are plasmids?
!" Small pieces of circular DNA, usually acquired from the environment
!" Don't carry critical genetic information, but can sometimes carry genes that
provide the bacterium an evolutionary advantage
#" Ex. antibiotic resistance
What are some examples of connective tissues?
!" Bone
!" Cartilage
!" Tendons
!" Ligaments
!" Fat tissue
!" Blood
What are tail fibers?
!" Extensions of a bacteriophage that allow it to recognize and connect to
target cells
What are the 2 microtubule organizing centers of the cell?
!" Centrosome
!" Basal body of flagellum or cilia
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What are the 2 types of bacterial cell wall?
1. Gram Positive
2. Gram Negative
What are the 2 types of single-stranded RNA viruses?
1. Positive Sense
2. Negative Sense
What are the 3 components of bacterial flagella?
1. Filament
2. Basal Body (Apparatus)
3. The Hook
What are the 3 domains of life?
1. Archaea
2. Bacteria
3. Eukarya
What are the 3 forms of genetic recombination seen in bacteria?
1. Transformation
2. Conjugation
3. Transduction
What are the 3 functions of the peroxisome?
1. Important in the breakdown of long chain fatty acids (β-Oxidation), because
of their hydrogen peroxide
2. Participate in the synthesis of phospholipids
3. Contain some enzymes for the Pentose Phosphate Pathway
What are the 3 shapes of bacteria?
1. Cocci
2. Bacilli
3. Spirilli
What are the 3 shapes of epithelium?
1. Squamous
2. Cuboidal
3. Columnar
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What are the 3 structural components of the cytoskeleton?
1. Microfilaments
2. Microtubules
3. Intermediate Filaments
What are the 3 types of anaerobes?
1. Obligate anearobe
2. Facultative anaerobe
3. Aerotolerant anaerobe
What are the 3 types of layering found in epithelial cells?
1. Simple
2. Stratified
3. Pseudostratified
What are the 4 stages of bacterial growth?
1.
2.
3.
4.
Lag Phase
Log Phase
Stationary Phase
Death Phase
What are the 4 steps of a Gram stain?
!" Stain the bacterium with crystal violet
!" Add iodide, which binds the crystal violet and traps it in the cell
!" Add ethanol to disrupt the membrane and wash the crystal violet out
#" In Gram-positive cells, the thick layer of peptidoglycan will
withstand the ethanol and keep the violet in
#" In Gram-negative cells, the thin layer of peptidoglycan will be
washed away (along with the violet color)
!" Bacterium is counterstained with Safranin (pink)
What are the 4 tissue types?
1.
2.
3.
4.
Epithelial Tissue
Connective Tissue
Muscle Tissue
Nervous Tissue
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What are the 9 key differences between eukaryotes and prokaryotes?
Prokaryotes
1
Eukaryotes
DNA bound to
protein (histones)
2
Circular DNA
Linear DNA
3
~ No Introns
~ Has Introns
4
ø Nucleus
Has Nucleus
5
ø MembraneBound
Membrane-Bound
6
30S, 50S
Ribosomes
40S, 60 S
Ribosomes
7
Binary Fission
Mitosis, Meiosis
8
Single
Chromosome
(Haploid)
Paired
Chromosomes
(Diploid/etc.)
9
Smaller (~1-5 µm)
Larger (~10-100
µm)
What are the characteristics and 3 roles of intermediate filaments?
!" Intermediate filaments - diverse group of filament proteins
#" Ex. keratin, desmin, vimentin, and lamin
1. Able to withstand a lot of tension, which makes the cell structure more rigid
and is important in the overal maintenance of the cytoskeleton
2. Anchor organelles to certain locations in the cell
3. Important in cell-cell adhesion.
What are the characteristics and 3 roles of microfilaments?
!" Microfilaments - solid polymerized rods of actin
1. When organized into bundles and networks, actin filaments provide
resistance to compression and fracture for the cell
2. Actin filaments can also generate force for movement by interacting with
myosin
3. Actin Filaments are important for the formation of the cleavage furrow in
mitosis/meiosis (cytokinesis)
#" Accomplished by an actin ring which forms at the site of division
between cells
#" Ring contracts
#" Cell gets pinched into two
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What are the characteristics and 3 roles of microtubules?
!" Microtubules - hollow polymers of tubulin proteins
1. Radiate throughout the cell, providing pathways along which vesicles can
travel
#" Accomplished by motor proteins like kinesin and dynein, which travel
along the microtubules and drag vesicles with them
2. Important in the structures of cilia and flagella
3. Centrioles are composed of microtubules and use them to exert their
effects during mitosis
What are the characteristics of Archaea?
!" Single-celled organisms that look like bacteria, but have genes and
metabolic pathways that are more similar to eukaryotes
!" Historically considered extremophiles (high temperature, high salinity, no
light)
!" Notable for their ability to employ chemosynthesis, an ability to generate
energy from inorganic compounds like sulfur and nitrogen
What are the components of viruses?
!" Genetic material
!" Protein coat, also known as capsid
!" ~ Lipid-containing envelope
What are the four tenets of cell theory?
1.
2.
3.
4.
All Living things are composed of cells.
The cell is the basic functional unit of life.
Cells arise only from preexisting cells.
Cells carry genetic information in the form of DNA. This genetic material is
passed on from parent to daughter cell.
What are the functions of the centriole?
!" Organizing center for the microtubules within a cell
!" Play an important role in the separation of chromosomes during mitosis
#" Responsible for the correct division of DNA
#" In prophase, centrioles migrate to opposide poles of the cell and
begin to form spindle fibers
What are the functions of the epithelial tissues?
!" Cover the body and line its cavities
!" Being exterior tissues, provide protection against infection and dessication
(drying out)
!" In some tissues, epithelial cells are also involved in absorption, secretion,
and sensation
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What are the three places an endosome can transport material to?
1. To-from plasma membrane
2. To lysosomes
3. To trans-golgi
What are the two functions of the mitochondria?
1. Produce chemical energy in the form of ATP through the Citric Acid Cycle
and the Electron Transport Chain
2. Can induce apoptosis by releasing Electron Transport Chain enzymes into
cytoplasm
What are the two types of endoplasmic reticulum?
!" Rough ER and Smooth ER
What are virions?
!" Viral progeny after replication
What are viroids? How do they function?
!" Contain a very short, circular single-stranded RNA that usually infects
plants
!" Bind to RNA sequences or the genes themselves to silence genes
#" Result in metabolic and structural changes or cell death
!" Hepatitis D virus (HDV) is an example of a human viroid that needs the
hepatitis B virus (HBV) to exert its silencing effect
What color do Gram-positive and Gram-negative bacterium appear after Gram
staining?
!" Positive - Purple
!" Negative - Pink
What does it mean for a bacterium to be bacilli?
!" Bacilli bacteria are shaped like rods
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What does it mean for a bacterium to be cocci?
!" Cocci bacteria are shaped like small spheres
What does it mean for a bacterium to be spirilli?
!" Spirilli bacteria are shaped like long spirals
What does it mean that mitochondrion are semi-autonomous?
!" Semi-Autonomous - can do a couple of functions on their own,
independent from the cell
!" Mitochondria:
1. contain some of their own genes (in the form of circular DNA strands)
and have their own ribosomes (similar in size to prokaryotic
ribosomes)
2. can divide independently of the cell as a whole (by performing binary
fission)
What does it mean to be a male/donor bacterium?
!" F+ cell
!" Possess F (fertility) factor/sex factor (plasmid)
!" Can construct a conjugation bridge and share genetic information
What does it mean to be an female/recipient bacterium?
!" F- cell
!" Does not possess F (fertility) factor/sex factor (plasmid)
!" Can accept genetic information from donor cell via a conjugation bridge
What does it mean to be columnar epithelium?
!" Composed of long, thin, column shaped cells
What does it mean to be cuboidal epithelium?
!" Composed of cube shaped cells
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What does it mean to be pseudostratified epithelium?
!" Cells appear to be stratified, but are actually all attached to a basement
membrane like simple epithelium cells
What does it mean to be simple epithelium?
!" Consists of a single layer
What does it mean to be squamous epithelium?
!" Flat, scale like epithelial cells
What does it mean to be stratified epithelium?
!" Consists of multiple layers
What does it mean when we say epithelial cells are polarized?
!" One side of an epithelial cell will be attached to underlying structural cells
and the other side will be exposed to the lumen of an organ or the outside
world, because epithelial cells cover the body and line its organs
!" Two sides of the epithelial cell are different, because of these dramatically
different environments
#" Call this phenomenon polarization
!" Transport across a cell is possible because the membrane has transport
systems on one side that are different from the other side
#" Means that epithelial cells are polarized
What happens if a lysosome releases its enzymes?
!" Enzymes will begin to break the cell down from the inside out in a process
known as autolysis
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What is a bacteriophage?
!" Viruses that specifically target bacteria
What is a capsid?
!" Protein coat in a virus
What is a centriole?
!" Hollow structure composed of nine triplets of microtubules
!" Involved in microtubule organization in the mitotic spindle
What is a centrosome?
!" Region of the cell where the centrioles are found
What is a chromosome?
!" DNA molecule with some or all of the genetic information of a cell
What is a cilia?
!" Projections from a cell that are involved in movement of materials along
the cell's surface
!" Ex. cilia in the respiratory tract will undulate in order to move mucus.
What is a eukaryotic cell?
!" Cells that have nuclei and membrane-bound organelles
What is a facultative anaerobe?
!" Bacteria that can switch between anaerobic and aerobic metabolism
depending on the environment
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What is a flagella?
!" Structures involved in the movement of the cell itself
!" Achieve this by spinning and flailing, generating force for movement
What is a histone?
!" Protein in the nucleus around which eukaryotic DNA winds
!" Helps organize the DNA
What is a lumen?
!" Inside space of any hollow tubular structure
What is a mitochondrion?
!" Double-membraned organelle
!" Contains inner and outer membrane
!" Inner membrane - contains molecules enzymes for the e- transport chain
used for ATP generation
!" Outer membrane - serves as a selective barrier between the cytosol and
the inner environment of the mitochondrion
What is a peroxisome?
!" Single membrane bound organelle containing hydrogen peroxide
!" Hydrogen peroxide is generated with the help of a crystalline core
What is a prokaryotic cell?
!" Cells that have no nuclei
What is a provirus or prophage?
!" Latent piece of viral genome that has been integrated into the host's
genome
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What is a retrovirus?
!" Enveloped single-stranded RNA viruses that carry an enzyme called
reverse transcriptase
#" Reverse transcriptase enzyme synthesizes DNA from RNA, which
gets integrated into the host genome
#" DNA can then be integrated into genome
!" HIV is the most famous retrovirus.
What is a sex factor?
!" Plasmid that allows bacterium to form sex pili with which they can
conjugate to other bacteria
What is a sex pilus?
!" Appendages that F+ bacterium use to form conjugation bridge
What is a tail sheath?
!" Long, thin part of a bacteriophage
!" Can act like a syringe, injecting the genetic info into the bacterium
What is a transposon?
!" Genetic elements that are capable of inserting and removing themselves
from the host genome
What is a vesicle?
!" Umbrella term for small membrane bound sacs
!" Lysosomes, endosomes, exosomes, etc. are all examples of vesicles
What is a virulence factor?
!" Plasmid that specifically makes the bacterium more pathogenic
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What is an aerotolerant anaerobe?
!" Bacteria that cannot use oxygen in metabolism, but are not harmed by the
presence oxygen in the environment
What is an anaerobe?
!" Any bacterium that doesn't need oxygen to survive
What is an endosome?
!" Endocytic vesicle that pinches off from the membrane during endocytosis
What is an episome?
!" Plasmid that can integrate itself into the host bacterium's genome
What is an obligate aerobe?
!" Bacterium that requires oxygen to survive
What is an obligate anaerobe?
!" Bacterium that dies in the presence of oxygen and therefore needs a nonoxygen environment to survive
What is an organelle?
!" Any specific sub unit within the cell that has a specialized function
!" Functions range from generating energy, protecting the cell, digesting
things, transporting material, etc.
What is apoptosis?
!" Intentional/programmed cell death
!" Cell dies because it was told to die and it listened, not because it was
randomly killed
!" May occur via apoptotic signals or preprogramming
What is bacterial conjugation?
!" Bacterium forms a conjugation bridge with another bacterium and shares
genetic information (including the sex factor)
!" Sex factor is shared either through a plasmid (from F+ cell) or a portion of
the donor's genome (from Hfr cell)
!" With sex factor, recipient can then form a bridge with other bacteria
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What is bacterial transduction?
!" Virus accidentally traps the genetic information of one bacterium in itself
and then incorporates that genetic information into the genome of another
bacterium
What is bacterial transformation?
!" Bacterium picks up foreign genetic material and integrates it into its own
genome
What is binary fission?
!" Simple form of asexual reproduction seen in prokaryotes
!" Prokaryote copies its genetic information and then splits into two
What is chemotaxis?
!" Ability of a cell to detect and move towards (chemoattract) or away
(chemorepellent) from chemical stimuli
What is cytoplasmic/extranucleur inheritence?
!" Transmission of genetic material independent of the nucleus
#" Mitochondria
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What is exocytosis?
!" Material is packaged into a secretory vesicle
!" Secretory vesicle fuses with the plasma membrane
!" Contents of the secretory vesicle are released outside of the cell
What is parenchyma and of which tissue type is it usually comprised?
!" Functional parts of an organ
#" Ex. nephrons in the kidney or acid producing cells in the stomach
!" Usually made up of epithelial cells
What is rough ER? What is its function?
!" Rough ER - ER studded with ribosomes
!" Ribosomes take in ingredients from the cytosol, but secrete their proteins
directly into the lumen of the rough ER
!" Ability to make proteins that are protected from the cytosol is useful
!" Rough ER proteins - usually sent to smooth ER, where they are
packaged and sent to the Golgi apparatus
What is smooth ER? What are its 3 functions?
!" ER that takes on a tubular form
!" Has no ribosomes in its membrane
1. Where lipids are synthesized (ex. the phospholipids in bilayers and
steroids)
2. Detoxifies certain drugs and poisons
3. Proteins that were synthesized into the rough ER travel to the smooth ER
so they can be packaged and transported to the Golgi apparatus
What is superinfection?
!" Simultaneous infections
What is the Golgi apparatus' function?
!" To receive materials from the ER and modify these materials by adding
various functional groups
!" Functional groups serve to both modify the function of the materials and to
direct them to certain locations in the cell
!" Once the material has been modified and has a location-determining
functional group, the material will leave the golgi apparatus in an
appropriate vesicle and travel to its intended location
!" Intended location can be inside the cell, outside the cell, or back to the ER
What is the Golgi apparatus?
!" Series of stacked membrane bound sacs inside of the cell
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What is the bacterial flagellum filament?
!" Long hollow, helical structure composed of flagellin
What is the basal body?
!" Complex structure that anchors the flagellum to the membrane and
provides the motor force necessary to activate the flagellum
What is the basement membrane?
!" Underlying layer of connective tissue to which groups of epithelial cells will
be attached
!" This is so the epithelial cells stay close together and can remain a
cohesive unit
What is the cell envelope?
!" Name for all of the layers of the cell from the membrane and extending
outward
!" Ex.
#" In bacteria with a cell wall and a capsule, the envelope would be the
membrane, the cell wall, and the capsule
#" In bacteria without a capsule, the envelope refers just to the
membrane and the cell wall.
What is the cell wall? What organisms have them?
!" Rigid structure that forms the outer barrier of the cell
!" Found in almost all prokaryotes and in certain eukaryotes (plants, algae,
fungi)
What is the cytoskeleton?
!" Large network of 3 structural components that provides shape and
structure to the cell
!" Structural components also serve as paths by which things can be
transported to various locations in the cell
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What is the death phase?
!" Bacteria have completely consumed nearby resources and begin to quickly
die out due to starvation
What is the endoplasmic reticulum (ER)?
!" Series of interconnected membranes that are contiguous with the nuclear
envelope.
What is the extracellular matrix?
!" Vast collection of extracellular molecules secreted by cells that provide
structural and biochemical support to the individual cells within a tissue
!" Allows cells to associate and communicate with one another without being
directly attached
What is the function of connective tissue?
!" Support the body and provide a framework for the epithelial cells to carry
out their function
!" Secrete the various molecules that make up the extracellular matrix, such
as collagen and elastin
What is the function of lysosomes?
!" To digest both foreign material (ingested by endocytosis) that has been
brought into the cell and damaged/uneeded organelles
!" Also degrades misfolded proteins
What is the function of the cytosol?
!" Suspends the organelles
!" Allows diffusion of molecules throughout the cell
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What is the hook?
!" Connects the filament and the basal body in order to facilitate the motion in
the filament, which propels the bacterium forward
What is the intermembrane space?
!" Space between the outer and inner membrane of the mitochondrion
What is the lag phase?
!" Bacteria are adapting to the environmental conditions
What is the log phase?
!" Bacteria have adapted to the environment and start to grow exponentially
What is the lysogenic cycle?
!" 1 of 2 possible life cycles of a bacteriophage (way it can spread)
!" In the lysogenic cycle, the bacteriophage incorporates itself into the host
genome as a provirus or prophage
#" Virus will be replicated as bacterium reproduces
$" Each daughter cell will carry the information to make viruses
#" Provirus can:
$" Remain in genome indefinitely or
$" Leave the genome in response to a stimulus and enter the lytic
cycle
What is the lytic cycle?
!" 1 of 2 possible life cycles of a bacteriophage (way it can spread)
!" In the lytic cycle, the cell's machinery is hijacked to produce new viruses
#" Viruses accumulate
#" Once host cell is swollen, cell lyses
#" Other bacteria can be infected
!" Viruses in this cycle are said to be virulent
What is the mitochondrial matrix?
!" Space inside the mitochondrion's inner membrane
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What is the nuclear membrane? What does it contain?
!" Double membrane the surrounds the nucleus
!" Contains nuclear pores
!" Also called the nuclear envelope
What is the nucleolus?
!" Structure in the nucleus that synthesizes ribosomal RNA (rRNA)
!" Appears as a large dark spot in the nucleus
What is the nucleus?
!" Control center of the cell
!" Surrounded by a double-membrane envelope
!" Houses all of our genetic information and machinery
What is the order of taxonomy from most general to most specific?
!" Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species
#" Mnemonic: Kids Play Cod On Fuzzy Green Sofas)
What is the restriction on bacterial conjugation?
!" F+ Bacteria can only conjugate to F- Bacteria
!" F+ Bacteria cannot conjugate with other F+ Bacteria
What is the shared structure of flagella and cilia in eukaryotic cells?
!" 9 + 2 structure - 9 doublets of microtubules surrounding a central doublet.
What is the stationary phase in bacterial growth?
!" Bacteria have reduced resources to the point where they are starting to run
out and can no longer grow as quickly
What is the stroma and of which tissue type is it usually composed?
!" Support structure of an organ upon which the parenchyma depends
!" Made of connective tissue
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What is viral extrusion?
!" Virus leaves a cell by exocytosis, instead of just killing the cell
!" Keeps the host cell alive and allows for the continued use of the host cell
by the virus
#" Virus in this state are said to be in the productive cycle
What is viral lysis?
!" Virus kills the host cell
!" Host cell spills out its contents, including the virus, which goes off to infect
new cells
!" Disadvantagous because cell can't make any more virions
What kind of genetic information can viruses carry?
!" Basically any kind
!" Genetic info in viruses can be linear or circular, DNA or RNA, and singlestranded or double-stranded
What kinds of proteins are usually found in the rough ER?
!" Proteins that are destined for secretion
!" Proteins that are destined for integration into a membrane
Which bacterial recombination process is the only one that requires a vector?
!" Transduction