Eukaryotic Cells Flashcards
Organelles
Small structure within a cell that carries out specific cellular functions
Nucleus function and number of membranes surrounding
Contain & protects DNA, transcription and partial assembly of ribosomes
2
Mitochondria function and number of membranes surrounding
Produce ATP via the Kreb cycle and oxidative phosphorylation
2
Ribosomes function and number of membranes surrounding
Synthesize proteins
0
RER function and number of membranes surrounding
Location of synthesis/modification of secretory, membrane-bound and organelle proteins
1
SER function and number of membranes surrounding
Detoxification and glycogen breakdown in liver; steroid synthesis in gonads
1
Golgi apparatus function and number of membranes surrounding
Modification and sorting of proteins, some synthesis
1
Lysosomes function and number of membranes surrounding
Contain acid hydrolyses which digest various substances
1
Peroxisomes function and number of membranes surrounding
Metabolize lipids and toxins using peroxides (h2o2)
1
The nucleus contains the genome and is surrounded by the
Nuclear envelope
Nuclear envelope
separates the contents of the nucleus into a distinct compartment, isolated from other organelles and the cytoplasm
In eukaryotes, _____, ____ and ____ occur in the nucleus while ____ occurs in the cytoplasm
replication, transcription, and splicing occur in N
translation occurs in C
Genome is so large in humans that it is split into pieces, each a separate linear DNA molecule called
How many are there in humans
Chromosomes
23
Since humans and animals are diploid,
have 2 copies of each chromosome
Chromosomes have a _____ in the center to ensure that they are properly replicated during cell division… one copy to each daughter cell
Centromere
Each chromosome also has special structures at both ends termed ______ which have large numbers of repeats of specific DNA sequence and with the help of a special DNA poly termed _____ , __________ during DNA replication
Telomeres
Telomerase, which maintains the ends of linear chromosomes
Locus
Specific location on the chromosome where the gene resides allowing gene regulation
Heteochromatin
Densely packed chromatin within which genes are inaccessible and turned off
Euchromatin
More loosely packed into chromatin and allow genes to be activated
Nuclear matrix/nuclear scaffold
Attached to DNA chromosomes and modifies gene expression via access to promoters and enhancers to discrete chromosomal regions known as domains
Nuclear matrix is attached to DNA chromosomes and modifies gene expression via access to promoters and enhancers to discrete chromosomal regions known as ______
Domains
Nucleolus
Ribosome factory
There is ____ membrane separating the nucleolus from the rest of the nucleus
no
The nucleolus consists of
loops of DNA, RNA poly, rRNA and protein components of ribosome
The nucleolus is the site of transcription of ___ and ___
rRNA and RNA poly I
The ribosome is partially assembled in the nucleolus, the protein components are _____ .
After partial assembly the ribosome is exported from the nucleus, remaining ____ until ______ in the _____ .
This may serve to prevent
transported in from the cytoplasm
Inactive until assembly is completed in the cytoplasm
Translation of hnRNA
The nuclear membrane has two two lipid bilayer membranes. The inner nuclear membrane surface faces _____ and the outer surface faces ______
Surface of the envelope facing the nuclear interior
Surface faces cytoplasm
The membrane of the ____ is at points continuous with the outer nuclear membrane. This makes the interior of the ____ (____) contiguous with the space between the two nuclear membranes
Endoplasmic reticulum
ER (lumen on the ER)
The nuclear envelope has many ______ that allow passage of material into and out of the nucleus
What can pass?
Nuclear pores
Small molecules (less than 60kD) and proteins can freely diffuse, but larger proteins cannot pass freely through the pores and are excluded from the nucleus unless they are AA sequence
Nuclear localization sequence
AA sequence of a large protein trying to pass through nuclear pores
Translated on cytoplasmic ribosomes and then imported into the nucleus via specific transport mechanisms
In addition to nuclear localization sequences, ___ is transported out of the nucleus by a specific transport mechanism rather than _____
RNA
Freely diffusing
Mitochondria are the site of ______
Oxidative phosphorylation
Matrix of the mitochondria
Bounded by inner and outer membranes and contains pyruvate dehydrogenase and enzymes of the Krebs cycle
Inner membrane of the mitochondria
Impermeable to the free diffusion of polar substances, like proteins, and is folded into the matrix in projections called cristae
Inner membrane of the mitochondria is impermeable to the free diffusion of polar substances, like proteins, and is folded into the matrix in projections called
Cristae
The outer membrane of the mitochondria is
Smooth and contains large pores that allow free passage of small molecules
Space between inner and outer membranes of the mitochondria is called
Intermembrane space
ATP produced within mitochondria is
Transported out into the cytoplasm to drive a greater variety of cellular processes
Mitochondria process their own genome which is ___ and ____
Much smaller than the cellular genome and consists of a single circular DNA molecule that encodes rRNA, tRNA and proteins (of the Electron transport chain/ATP synthase complex)
To explain that mitochondria possess a second system of inheritance, researchers suggest they
Originated as an independent unicellular organism living within larger cells
Endosymbiotic theory of mitochondrial evolution
To explain that mitochondria possess a second system of inheritance, researchers suggest they originated as an independent unicellular organism living within larger cells
Mitochondria exhibit maternal inheritance meaning
The mitochondria are inherited only from the mother, since the egg cytoplasm becomes the zygote cytoplasm
The sperm contributes only genomic (nuclear) DNA
The ER is a large system of folded membrane that accounts for
over half of the cell membrane
Rough ER is rough due to
Large number of ribosomes bound to its surface
Rough ER is the site of
Protein synthesis for proteins targeted to enter the secretory pathway
Smooth ER contains
enzymes involved in steroid hormone biosynthesis (gonads) or degradation of environmental toxins (liver)
The rough ER plays a key role in
directing protein traffic to different parts of the cell
Proteins translated on the free cytoplasmic ribosomes are headed towards
Peroxisomes, mitochondria, nucleus or cytoplasm
Proteins translated on the rough ER are headed towards
extracellular environment, plasma membrane, or membrane/interior of Golgi, ER, or lysosomes
Proteins synthesized on the rough Er are transported in vesicles that bud from the ER to the ____, then to the ____ or _____
Golgi apparatus
plasma membrane or lysosome
How is it determined which location the protein is translated on?
All start in cytoplasm, some have an AA signal sequence at N-terminus that tells them to go to the RER
The AA signal sequence is recognized by
Signal recognitions particle (SRP) which binds to the ribosome
The RER has SRP receptors to dock the AA signal sequence bearing protein on the RER membrane. When the protein is translated,
the polypeptide is pushed into the ER lumen (signal peptide first)
After translation is complete, the signal peptide is ____ by a ____ in the ____
removed by a signal peptidase in the ER lumen
For secreted proteins, once the signal sequence is removed the protein is transported to the
Interior of vesicles through the Golgi apparatus to the plasma membrane where it is released by exocytosis into the extracellular environment
Integral membrane proteins have
Sections of transmembrane domains that are signal sequences found on interior of protein (not N-terminus)
Not removed after translation
Transmembrane domains
hydrophobic AA residues that pass through lipid bilayer membranes
Not removed after translation
Observed on interior of protein
During translation, transmembrane domains are
threaded through the ER membrane and the protein is transported in vesicles to the Golgi apparatus and plasma membrane in same manner as a secretory protein
Additional functions of the rough ER include the initial post-translational modification of proteins… some ____ occurs in the rough ER, though it is usually associated with the Golgi apparatus
Glycosylation (adding saccharides to proteins)
Also in the ER Lumen to modify proteins post translation, ___ occurs
Disulfide bond formation
Default target for proteins going through the secretory path is the
Plasma membrane
Targeting signals are needed if a
protein going through the secretory path to the plasma membrane needs to be going elsewhere (i.e. the Golgi, ER or lysosome)
Proteins made in the cytoplasm that need to be sent to an organelle that isn’t in the secretory path (nucleus, mitochondria or peroxisomes) require
localization signals
Protein final destination: Secretory
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
N
N
Protein final destination: Plasma membrane
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
Y
N
Protein final destination: Lysosome
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
N
Y
Protein final destination: Rough ER
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
N
Y
Protein final destination: Smooth ER
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
N
Y
Protein final destination: Golgi apparatus
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
Y
N
N
Y
Protein final destination: Cytoplasm
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
N
N
N
N
Protein final destination: Nucleus
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
N
Y
N
N
NProtein final destination: Mitochondria
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
N
Y
N
N
Protein final destination: Peroxisome
Signal Sequence?
Localization Sequence?
Transmembrane Domains?
Targeting Signal?
N
Y
N
N
Golgi apparatus functions (3)
- Modifies proteins made in RER (esp. oligosaccharides)
- Sorting and sending proteins to destinations
- Synthesizes macromolecules for secretion such as polysaccharides
Vesicle traffic to Golgi is ____
Unidirectional
The membrane bound or secreted proteins which are to be sorted/modified enter / exit the Golgi at
enter at one defined region and exit at another
Retrograde traffic
Opposite of unidirectional traffic occurs when protein escapes rough ER and must be put back by the golgi
Cis stack of golgi
Nearest rough ER
Proteins from the Cis stack are modified and transferred to the ___ where they are:
Medial stack where they are further modified
After the medial stack modifies the proteins they are sent to the
Trans stack where they leave in transport vesicles
The route taken by a protein is determined by its
signals within the protein that determine which vesicle a protein is stored into in the trans Golgi
Lysosome function
degradation of biological macromolecules by hydrolysis
Lysosome proteins are made in the ___, modified in the ____ and released in their final form in the ____
RER
Golgi
Golgi trans
Organelles that are no longer functional
can be degraded in the lysosome
Autophagy
Organelles that are no longer functional can be degraded in the lysosome.
Phagocytosis
Lysosomes degrade large particulate matter engulfed by the cell
Macrophages
In immune system engulfs bacteria and viruses
Phagocytic vesicle
Particles that are engulfed end up here and then are fused with a lysosome
After hydrolysis, the lysosome releases molecular
building blocks for reuse into the cytoplasm
Enzymes responsible for degradation in lysosomes are called
Acid hydrolyses
Acid hydrolases
Enzymes responsible for degradation in lysosomes only in ACIDIC environment
Acid hydrolyses are used as a safety mechanism. The pH of the lysosome is __ so the ___ because the pH of the cytoplasm is ___.
Therefore If the lysosome ruptures will the cell be damaged?
5
acid hydrolyses are in action
7.4
No because the acidic fluid will be diluted and the acid hydrolyses will be inactivated, however if many rupture at once the cell can be destroyed
Peroxisomes function
Variety of metabolic tasks
Peroxisomes contains enzymes that produce
hydrogen peroxide as byproducts
Peroxisomes are essential for ____
lipid breakdown
In the liver, peroxisomes assist with
detoxification of drugs and chemicals
H2O2 is a dangerous chemical so how does it exist as a byproduct in the peroxisome?
Peroxisomes contain an enzyme catalase which converts it to water and oxygen
Separation this activity into the peroxisomes prevents the cell from getting damaged by peroxides or oxygen radicals
Animals rely on ____ and a ____ to keep their structure and differentiate between the inside and outside of the cell
Cell membrane
Cytoskeleton
All membranes of the cell are composed of
Lipid bilayer membranes
Three most common lipids is eukaryotic membranes
(#1 Phospholipids), glycolipids and cholesterol
Phospholipids and glycolipids both have two portions that are distinctly
Hydrophilic and hydrophobic
In water, phospholipids arrange themselves spontaneously into ____ which is
lipid bilayer membrane
lowest energy state for the molecules so they can reseal and repair if a small portion is removed
The interior of the membrane is very ______, molecules such as ions, carbohydrates, and amino acids are ______ because they are ______ and molecules such as CO2, O2 and steroid hormones are _____ because they are ______
Water passes through the membrane via _____
Hydrophobic
I,C,AA: impermeable because they are polar
C,O,SH: permeable because non polar
Specialized protein channels
Hydrophobic component of the phospholipid plasma membrane is ____ and hydrophilic component is ____
Hydrophobic: tails
Hydrophilic: heads
Mitochondrial membrane is different in that it has
More proteins than lipids
Cell-surface receptors
Proteins that bind extracellular signaling molecules such as hormones and relay these signals into the cell
Channel proteins
Selectively allow ions or molecules to cross the membrane
Integral membrane proteins
Embedded into the membrane by hydrophobic interactions
Transmembrane domains
Membrane crossing regions
Peripheral membrane proteins
Not embedded in the membrane; Stuck into the integral membrane proteins, held by hydrogen bonding and electrostatic interactions
Fluid Mosaic Model
Lipids and portions making up the membrane are free to move back and forth fluidly, to diffuse laterally but not free to flip-flop
Move in 2D only
In the Fluid Mosaic Model, the membrane is not allowed to flip-flop meaning that
The membrane is polar because the inside and outside face remain different
One exception to the Fluid Mosaic Model
Some proteins are held in the cytoskeleton and therefore cannot move in any direction
Van der Waals interactions are a good determinant of membrane fluidity
The saturated fatty acids (lacking double bonds) have a very straight structure and are packed tightly in the membrane with: ___ VDW forces & fluidity ___
Unsaturated fatty acids, with one or more double bonds, have a kinked structure and are packed loosely: ____ VDW forces & fluidity ____
Saturated is strong and fluidity is low
Unsaturated is weak and fluidity is high
____ also plays a key role in maintaining optimal membrane fluidity
Cholesterol
Passive vs active transport
Passive requires no cellular energy and active does require cellular energy
Electrolytes
Free ions in a solution dissociated from their substance
Strong-electrolytes vs weak-electrolytes vs non-electrolytes
S: Dissociate completely into solution
W: Some dissociation
N: Covalent bonds that don’t dissociate at all
Van’t Hoff Ionizability factor
- C6H12O2
- NaCl
- HNO3
- CaCl2
How many ions a substance prod in solution
- i=1 because it is non-ionic
- i=2 because it is ionic
- i=2 because H and NO3
- i=3 because it is Ca and Cl, Cl
Colligative properties depend on
Number of solute particles, not the type or identity of particles
Vapor-Pressure
Pressure exerted by the gaseous phase of a liquid that evaporated
___ IMF, higher VP, ___ evaporation
weaker IMF, higher VP, more easy to evaporate
Volatile liquids
High VP, easy to evaporate, IMF easy to overcome
What happens to vapor pressure when a compound is dissolved in solution?
The VP goes down because there are more forces to be broken (compound is attracted to solution “anchors”)
Vapor pressure depression
Boiling point definition
Temp at which the VP is equal to the atmospheric pressure over the solution
Adding more solute to a solution ill ___ VP
Decrease
What happens to boiling point when a compound is dissolved in solution?
The BP goes up because more energy is required to break the additional bond to the anchor molecules
Boiling point elevation equation
Change in BP = k (solution bp elevation constant) x i (ionizability factor) x m (molar concentration)
k for water is 0.5
What happens when you add a solute to a liquid and freeze it?
Presence of solute will interfere with efficient arrangement of solvent molecules into solid lattice that maximizes IMF
As a result, liquid will be less able to achieve the solid state and will have a lower freezing point
FP GOES DOWN
Freezing Point Depression Equation
Change in BP = - k (solution bp elevation constant) x i (ionizability factor) x m (molar concentration)
Same as BP elevation but with a minus sign
Water k= 1.9
Diffusion
Tendency for liquids and gases to fully occupy the available volume
If all particles are concentrated in one section we have an orderly arrangement which is
Unfavorable acc to the law of entropy
A solution will always diffuse
Down its gradient from high to low concentration until evenly distributed throughout the available volume and non net movement will continue (back and forth does continue)
Osmosis
Solvent diffuses rather than a solute
Net movement of water from a region of low solute conc to high solute conc in an effort to dilute the higher conc
If sucrose and water are each in one half of a container and allowed to diffuse this process is called: ___ and this will happen:
If there is a semipermeable membrane that allows water but not sucrose then:
Membrane is semipermeable meaning
Osmosis
Sucrose and water will move until both sides has equal concentration of both
Diffusion of sucrose between the chambers cannot occur and osmosis draws water into the sucrose chamber to reduce the sucrose concentration as well as the volume in the water chamber (ignoring gravity water will flow in until the concentration of sucrose is even cross the membrane)
Water can cross via osmosis but not most polar molecules
Tonicity describes
Isotonic/isoosmotic:
Hypertonic/hyperosmotic:
Hypotonic/hypoosmotic:
Osmotic gradients
I: Solute concentration is the same inside and outside
Hyper: More total dissolved solutes than the cell
Hypo: Less total dissolved solute than the cell
Osmotic pressure
Pressure to stop osmosis from occurring
Osmotic pressure equation (van’t Hoff equation)
Osmotic pressure (atm) = M (molarity) x i (ioniziabilty factor) x 0.0821 x T (K)
Osmotic pressure are affected only by the ___ not the ___
Number of particles not the identity
Passive transport
Any thermodynamically favorable movement of electrons of solute across a membrane
Movement down a gradient no energy required
Simple diffusion
Without help from a protein solute moves through a membrane
Non-polar, hydrophobic compounds
Facilitated diffusion
Movement of solute across a membrane when the solute is initially impermeable through the membrane
Only down conc gradient
Channel and carrier proteins do which type of diffusion?
Channels and carriers give the membrane its primary function of:
Facilitated
Selective permeability to some things despite impermeability to most things
Ion channels only allow
One type of ion to flow
Highly selective
Gated ion channels
If the channel is open in response to certain environmental stimuli
Voltage-gated channel
Opens in response to changes in electrical potential across a membrane
Ligand-gated channel
Opens in response to binding of a specific molecule
Can ion channels move ions against an electrochemical gradient
No only facilitated diffusion
Carrier proteins: how do they transport molecules across the membrane
Bind the molecule and then undergo a conformational change to move it to the other side
Uniports
Transport only one molecule across the membrane at a time
Symports
Transport two substances across a membrane in the same direction
Antiports
Carry two substances in opposite directions
Pore
Tube through a membrane that is so large it is not selective for any particular molecule, but instead all molecules of a certain size can pass
Sensitive to size and charge
Pores are formed by _____
Polypeptides known as porins
Eukaryotes do not have pores because
Pores destroy the barrier function of the membrane, allowing solutes into the cytoplasm to freely diffuse out of the cell
Rate of simple diffusion is limited only by the ___ and ___
The rate of facilitated diffusion is limited by ____
Surface area of the membrane and the size of the driving force/gradient
Finite number of integral proteins (saturation kinetics)
Facilitative diffusion exhibits saturated kinetics meaning when the driving force for facilitated diffusion increases,
the rate of diffusion (flux) increases, but only until a certain point when all the transport proteins are saturated and no further increase in flux is possible
Active transport
Moving molecules across their gradient (conc or charge, etc.)
Requires energy input
Always involves a protein
Primary active transport
Molecule transport coupled to ATP hydrolysis
Secondary active transport
ATP is used to create a gradient and then the potential energy of the gradient drives the transport of some other molecule across the membrane which in turn powers secondary active transport
ATP is an indirect here
Uses another molecules diffusion across gradient to power its diffusion
Na+/K+ ATPase is a transmembrane protein in all cells of the human body
Activity is to pump: ___ and in the process to ___
3 Na+ out and two K+ in
Hydrolysis one ATP
Na+ pumped out ____ and K+ pumped in ____ due to ____
Na+ stays out (membrane is impermeable)
K+ some goes out some stays in (K+ leak channels)
Potassium leak channels
K+ flows down its gradient and out of the cell through these channels to help maintain osmotic balance and creates a net negative charge since + is leaving the cell (resting membrane potential)
Driving force between secondary active transport of many molecules including sugars and AA
Concentration gradient of high Na+ outside the cell established but he Na+/K+ ATPase
What would the RMP be in a cell with Na+/K+ ATPase but no K+ leak channels?
-10mV determined experimentally because the resting membrane potential is only determined by the electrogenecity of the NaK pump
Conc inside and outside the cell for
Na+:
K+:
Cl-:
Ca2+:
Na: MORE out
K: MORE in
Cl-: MORE out
Ca2+: MORE out
Exocytosis
Transporting material outside of the cell via a vesicle in the cytoplasm fuses with the membrane and the contents are expressed into the extracellular space
I.e. hormones, digestive enzymes
Endocytosis
Materials are taken into the cell by an invagination of a piece of the cell membrane to form a vesicle
Cytoplasm is not allowed to mix with extracellular environment
New vesicle is formed: endosome
Endosome
New vesicle formed via endocytosis
Phagocytosis
Cell eating
Nonspecific uptake of large particulate matter into a phagocytic vesicle which will merge with a lysosome
Phagocytosed material will be broken down
NOT INVAGINATION
i.e. macrophages
Pinocytosis
Cell drinking
Nonspecific uptake of small molecules and extracellular fluids via invagination
Receptor-mediated endocytosis
Specific
Site is marked by receptors (outside cell) and clathrin coating (inside cell)
Clathrin
Used to mark sites for receptor-mediated endocytosis
Does not bind to the molecules to undergo uptake but does interact with the cell-surface of receptors
Signal Transduction
Binding of ligand to receptor initiates a response within the cell
Ligand Gated Ion Channels
open ion channel after binding a specific NT
Catalytic Receptors
enzyme active site on cytoplasm side of the membrane
enzyme activity is initiated by a ligand binding to the extracellular receptor surface
G-protein Linked Receptor
Transmits signal through a second messenger which is a chemical signal that relays instructions from the cell surface to enzymes in the cytoplasm and creates a much larger effect than a receptor alone would
Most important second messenger
G-protein is a signaling molecule which binds
cAMP
GTP
Signal Transduction
continuing a signal across a membrane
Eukaryote equivalent of the cell wall
Cytoskeleton
Function of the cytoskeleton:
Movement, transport of substances in the cell and structural support
Microtubules, intermediate filaments and microfilaments which is thickest/thinnest? What are they all made of?
Microfilaments are thinnest
Microtubules are thickest
All made of non-covalently polymerized proteins (massive quaternary structure)
Microtubule is a hollow row composed of two globular proteins: alpha-tubulin and beta-tubulin
Once formed, the microtubule can elongate by:
Adding ab-tubulin dimers to one end, the other end cannot elongate because it is anchored to the microtubule organizing center (MTOC) near the nucleus
Dynamic and can get longer or shorter by adding tubular monomers to one end
Within the MTOC (place the microtubule cannot elongate) is a pair of
Centrioles
Mitotic Spindle
Microtubules radiate out of the centrioles during mitosis (aster)
polar fibers connecting the chromosomes to the aster
The centromere of each chromosome contains: A kinetochore
Attached to the spindle by tiny microtubules called kinetochore fibers
In mitosis the MTOC is essential but the centrioles are not.
What is the two major pieces of evidence for proving this?
Plants without centrioles undergo mitosis
Removing centrioles from animal cells and still undergo mitosis
In nerve cells, materials are transported from the cell body to the axon terminus on a
Microtubule railroad
Cilia
Small hairs on the cell surface which moves fluids past the cell surface
Mucociliary escalator
Sweep mucus toward the mouth
Flagellum
Large tail which moves the cell by wiggling
The only cell with a flagellum is the
Sperm
Cilia and flagellum have the same structure __ + __
Which is:
9+2
9 pairs of MT form a ring around two lone MT in the center
Each MT in the 9+2 arrangement is bound to its neighbor by a
contractile protein called dynein (movement of filament past one another)
The cilia or flagella (E only) is bound to the plasma membrane by a
basal body which has the same structure as a centriole (9 triplet ring)
Microfilaments
Rods formed in the cytoplasm from protein “actin”
Actin monomers form a chain, and then two chains wrap around each other to dorm a
filament
MF are dynamic and are responsible for
Gross movement of the entire cell such as pinching the cell in division and amoeboid movement
Amoeboid movement
Changes in the cytoplasmic structure which causes cytoplasm and the rest of the cell to move in one direction
Intermediate filament
Named for thickness, between MT and MF
Heterogeneous, wide range of polypeptides
Provide cell structure and are more permanent
Tight Junctions (aka Occluding Junctions)
Cells forming a tight seal preventing items from moving freely between the two cells
A band around the membrane not a spot on it
Desmosomes (aka Spot Desmosomes)
Held together tightly but do not form a seal
Points not a band
Gap junctions
Allow ions to flow back and forth between them
Apical vs. basolateral surface
?
Apical: facing outside
Basolateral surfac: facing inside contents
Inside each cell the desmosomes are anchored to the plasma membrane by the protein
keratin
Gap junctions are large enough to allow flow of:
But too small to allow:
Can pass AA, ions and carbs
Not pass organelles and polypeptides
Gap junctions in smooth and cardiac muscle allow the membrane to ______
depolarize AP to pass directly from one cell to another
Cells reproduce themselves by first _____ and then splitting in half
Doubling everything in the cytoplasm and genome
Synthesis (S) phase
When the cell activity replicates its genome
M phase
Mitosis and cytokinesis
Mitosis is
partitioning of cellular components into two halves
Cytokinesis
Physical process of cell division
Between M and S phases there are two gap phases:
G1 and G2
Interphase
G1, G2 and S phase
The cell spends most of its time in
Interphase
Metabolizing and synthesizing materials
Some cells become permanently stuck in
Interphase
More specialized a cell comes, the less likely it is to
Come out of interphase and replicate
During interphase, the genome is
Spread out and DNA is accessible to the enzymes of replication
By the end of the S phase the nucleus contains
Two copies of the genome (2x the normal amount of DNA)
Mitosis is divided into 4 phases:
Prophase, metaphase, anaphase and telophase
First sign of prophase
Genome into densely packed chromosomes instead of diffuse chromatin
Sister chromatids
When mitosis Is complete, each new daughter cell will have ___ chromosomes each consisting of a single chromatid, separated from its sister
23 homologous pairs of identical chromosomes (23 pairs of pairs)
Difference between homologous chromosomes and sister chromatids
HC: equal but not identical, not attached
SC: identical, connected at the centromere
During prophase what occurs
Genome packed into chromosomes, nucleolus disappears, spindle and kinetochore fibers appear and the centriole pairs begin to move to opposite ends of a cell
After prophase the cell has
2 MTOC’s called asters and the nuclear envelope converts itself into many tiny vesicles
Metaphase
Chromosomes line up at center of the cell forming the metaphase plate, each member of the chromatid pair is pulled toward the opposite pole of the cell
Anaphase
Spindle fibers shorten and centromeres of each sister chromatid pair are pulled apart
Cell elongates and cytokinesis beings with cleavage furrow (ring of actin filaments encircle and contract)
Cleavage Furrow
Ring of actin filament encloses and contracts
Telophase
Chromosomes de-condense and a nucleolus appears in each daughter cell
Each daughter cell has 2n chromosomes
Oncogenes
Cells needed for growth and regulation of the cell cycle that have become mutated & can cause cancers
Protooncogenes
Normal version of the genes that allow for regular growth patterns but can be converted into oncogenes due to mutation or exposure to a mutagen
Tumor supressor genes
Produce proteins that are the inherent defense system to prevent conversion of cells into cancer
2 primary means of cancer protection
- detect damage to the genome and halt cell growth and division until repair
2 trigger programmed cell death if the damage is too severe to be repaired
Common tumor suppressor gene: ___
Though normally at low levels in the cell, its production is
p53
Scaled up when genetic damage occurs or oncogene activity is detected
If repair is too far gone, the p53 will cause the cell to go into apoptosis
Apoptosis
Allows cell to shrink and die while simultaneously minimizing damage to nearby cells and limiting exposure of cytosolic contents
The death of a cell is triggered by
internal or external stressors
Process of apoptosis
Cell shrinks, cytoskeleton dissembles, nuclear envelope breaks down and genome is broken into pieces, phagocytes finish deconstructing and clearing the dead cell
Caspases
Carries out events of apoptosis
Cleave target proteins
Caspases are produced in their
Inactive form as procapases
Initiator caspases
Respond to extra or intra cellular death signals by clustering together to activate one another
Effector caspases
Are activated in an amplification cascade after the initiation caspases are activated
Responsible for cleaving cellular proteins to trigger apoptosis
Senescene
Biological aging occurring at both the cellular and organismal level
In E, ____ is a measure of cellular age
Length of telomeres
As cells age, they become prone to
apoptosis to remove cells due to age
Cumulative effects of senescene lead to aging of entire organism… functioning of the organism is effected to the point at which
The body stops working and death occurs
