Studied by 26 peoplecell wall
structure: external outer covering made of cellulose
function: provides support and mechanical strength, prevents excess water uptake
types of cells: bacterium and plant
not considered organelle
centrosome
structure: microtube organizing center
function: microtubes form spindle fibers and contribute to cell division (mitosis/meiosis)
types of cells: animals
chloroplast
structure: double membrane structure with internal stacks of membranous discs
function: site of photosynthesis, manufactured organic molecules are stored in various plastids
types of cells: plants
contains three membranes (outer, inner and thylakoid) that creates three distinct compartmentalized areas (intermembrane space, stroma and thylakoid space)
cytoskeleton
structure: filamentous scaffolding within the cytoplasm
function: provides internal structure and mediates intracellular transport
types of cells: bacterium, plants, animals
not considered organelle
cytosol
structure: mostly water, but full of enzymes and other molecules
function: hold organelles in place and catalyses reactions (like glycosis)
types of cells: bacterium, plants, animals
endoplasmic reticulum (rough), aka RER
structure: folded membrane studded with bound ribosomes, forms series of flattened sacs and tubes
function: protein synthesis and modification for export
types of cells: plants and animals
endoplasmic reticulum (smooth)
structure: folded membrane continuous with the nuclear envelope
function: production of lipids and metabolism of toxins
types of cells: plants and animals
golgi apparatus
structure: an assembly of vesicles and folded membranes located near the cell membrane
function: involved in the sorting, storing, modification, and export of secretory products, exocytosis
types of cells: plants and animals
organized into cis, medial and trans compartments
lysosome
structure: membranous sacs filled with hydrolytic enzymes
function: breakdown / hydrolysis of macromolecules and waste
types of cells: animals
requires enzymes
mitochondrion
structure: double membrane structure, inner membrane highly folded into internal cristae, outer membrane is permeable to many small molecules and ions
function: site of aerobic respiration, produce ATP through the breakdown of molecules (glucose)
types of cells: plants and animals
contains transport proteins that assist in moving larger molecules to mitochondria
nuclear envelope
structure: double membrane that surrounds nucleus
function: control movement in and out of nucleus
types of cells: plants and animals
nucleoid region
structure: area in prokaryotes where the bacterial DNA is concentrated
function: holding place for DNA
types of cells: bacterium
nucleolus
structure: dense, darker region in the nucleus
function: site of ribosome synthesis
types of cells: plants and animals
nucleus
structure: double membrane structure with pores (outer membrane is part of RER)
function: stores genetic material (DNA) and chromatin, protects DNA from damage, double membrane regulates gene expression
types of cells: plants and animals
peroxisome
structure: membranous sac containing a variety of catabolic enzymes
function: catalyzes breakdown of toxic substances (eg H2O2) and other metabolites
types of cells: plants and animals
similar to lysosomes but have a different set of enzymes that are involved in detoxification of harmful compounds and lipid metabolism
plasma membrane
structure: phospholipid bilayer embedded with proteins
function: semi-permeable and selective barrier surrounding the cell
types of cells: bacterium, plants, and animals
ribosome
structure: two subunits made of RNA and protein, larger in eukaryotes (80S) than prokaryotes (70S)
function: site of polypeptide synthesis (called translation)
types of cells: bacterium, plants, and animals
vacuole
structure: fluid-filled internal cavity surrounded by a membrane (tonoplast)
function: maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)
types of cells: plants and sometimes animals
organelle
subunits of cells that perform specific functions
both prokaryotic and eukaryotic cells, but membrane-bound organelles only found in eukaryotic
compartmentalization
organization or different functions and processes within specific areas or structures within the cell that are separated by plasma membranes
allows for the development of specialized cell structures (chloroplasts and mitochondria)
allows specific reactions to occur in specific places
can delay a cell’s ability to respond to the environment
cytoplasm
matrix that surrounds organelles and other structures in the cell
not a discrete structure with specific function, so not an organelle
responsible for metabolic processes (including translation of mRNA to protein on the ribosomes)
ribosomes
structures that make proteins out of mRNA from nucleus
not membrane-bound but are considered organelles because they have a specific function
can be bound or free (have same structure and function either way)
post-transcriptional modification
eukaryotic cells
mRNA produced in the nucleus needs to be changed by removing pieces of it, which makes a working protein
cristae (mitochondria)
allow more of the enzymes needed for ATP production to be present on membranes in mitochondria by increasing surface area
increases efficiency and speed of cell respiration by increasing number of enzymes available for various reactions
matrix (mitochondria)
space between inner membranes in mitochondria
contains a lot of enzymes and other molecules in high concentration needed for the Krebs cycle
a key pathway in cell respiration
intermembrane space (mitochondria)
small space between outer and inner membranes of mitochondria
allows high concentrations of molecules to accumulate
creates concentration gradient across inner membrane that is used to generate ATP
thylakoid membrane (chloroplast)
form thylakoids (look like stacked pancakes), where the light dependent reactions of photosynthesis take place
absorbs light energy and uses it to generate ATP to power photosynthesis
separate the stroma from the thylakoid space (small space, allows chloroplast to quickly generate a high concentration gradient)
granum (chloroplast)
many thylakoids together in a stack
maximize the amount of sunlight absorbed by chloroplast
connected to thylakoid membranes called lamellae
stroma (chloroplast)
space between inner and thylakoid membranes
contains all enzymes/substrates required for remaining steps of photosynthesis (Calvin cycle) that will make glucose molecules
gene expression
process by which the information in DNA is translated into proteins
entry and exit of signaling molecules and transcription factors are critical components in regulation of it
nuclear pores
allow entry and exit of molecules into nucleus
integral proteins
serve as channel proteins that also regulate mRNA leaving nucleus for RER or free ribosomes
bound ribosomes
ribosome bound to cytosolic side of RER
proteins it produces ends up inside RER and will be exported outside of cell
tend to be more numerous
free ribosomes
located in cytoplasm
tend to be less numerous
endoplasmic reticulum lumen
inside of flattened sacs in the RER system
cis compartment (golgi)
receives newly modified proteins from RER
vesicle fuses with it and releases protein inside golgi
medial compartment (golgi)
contains proteins destined for use within the cell (lysosomes)
proteins undergo further modifications before final destination
trans compartment (golgi)
contains proteins destined for export outside of cell
packages proteins into vesicles for secretion
vesicles
small membrane-bound cell structures
play a key role in transport and storage of protein and other products , act as delivery trucks
transport and release proteins, lipids, and RNA from one part of cell to another
types of cells: plants and animals
transport vesicles
transport materials from one part of a cell to another
intracellular
secretory vesicles
store and transport molecules (hormones, neurotransmitters, digestive enzymes) to be secreted outside the cell
clathrin
protein that plays important role in formation of vesicles
brings together the cytoskeleton and other proteins necessary for budding/scission of vesicles from membranes
involved in endocytosis, phagocytosis, transport of cargo from golgi to plasma membrane, and formation of lysosomes
forms cage-like structure, protects vesicle
phospholipid
amphipathic (both hydrophilic and hydrophobic)
form bilayer (heads on outside, tails on inside)
major structural component of almost all membranes
hydrophobic tails make bilayer selectively permeable
protein
amino acid side chains determine properties
3D structure determines function
conjugated proteins (glycoproteins) contain non-protein parts
selective permeability
only certain substances can cross bilayer without assistance
polarity/size/charge of substance determines permeability
permeable molecules
small non-polar molecules
“lipid soluble” molecules
ex: O2, CO2, N2, steriods
mostly permeable molecules
small uncharged polar molecules
ex: H2O and glycerol
mostly impermeable molecules
large uncharged polar molecules
ex: glucose, sucrose, other mono/disaccharides
impermeable molecules
ions and anything with a charge
ex: Na+, K+, Cl-, H+, Ca2+
integral proteins
membrane protein
embedded in bilayer
amphipathic (part inside bilayer = hydrophobic, part outside bilayer = hydrophilic)
mostly transmembrane
difficult to isolate
transmembrane
spans across entire membrane
parts outside cell, inside bilayer, and inside cell
peripheral proteins
membrane protein
located on surface of bilayer (either side)
hydrophilic
easier to isolate
functions of membrane proteins
transport
ID tags, cell-cell recognition
receive chemical signals (when bonded to receptor proteins)
enzymes (can be embedded in/associated with bilayer)
adhesion (cells with same tissue are joined by membrane proteins)
transport proteins
membrane protein
transmembrane
transport materials across bilayer
ex: channels, carriers, pumps
glycoproteins
conjugated proteins
carb chain (oligosaccharide) covalently bonded to protein
on extracellular side of bilayer
glycolipids
carb chain (oligosaccharide) covalently bonded to lipid
on extracellular side of bilayer
amphipathic
carb groups are polar and extend into extracellular environment
lipid groups are nonpolar and embedded in bilayer
contribute to membrane stability and form hydrogen bonds to water molecules surrounding cell
functions of glycoproteins and glycolipids
cell recognition (carb chains = ID tags)
cell adhesion (carb chains bind to chains on other cells)
cell signaling (receptor for chemical messengers)
cell protection (carb creates glycocalyx)
glycocalyx
carb groups create sticky layer on extracellular surface of cell
forms protective layer
glycoproteins and glycolipids
cholesterol
steriod
found in animal cell membranes
amphipathic
prevents fatty acid chains from sticking together and freezing at low temperatures, increases fluidity
stabilizes membrane and decreases fluidity at high temperatures
fluid mosaic model
proposed by singer and nicolson (1972)
“fluid” - bilayer = viscous, move around and flow past each other
“mosaic” - embedded with proteins, mosaic of components
membrane fluidity trends
temperature increases, fluidity increases
at low temps - cholesterol increases fluidity
shorter fatty acid tails increase fluidity
unsaturated fatty acid tails increase fluidity (kinks)
saturated fatty acid tails decrease fluidity (straight)
ecothermic
cold blooded animals
increase proportions of unsaturated fatty acids in membranes at low temperatures
hibernating mammals
as body temp decreases, proportion of unsaturated fatty acids in membranes increases
simple diffusion
movement of molecules of a substance down a concentration gradient (from region where concentration is higher to region where its lower)
spontaneous
movement of molecules eventually results in equal concentration among both regions
passive transport (doesn't need energy)
osmosis
net movement of water into cell
water moves from lower solute concentration to higher solute concentration
type of diffusion, passive transport
aquaporins
type of channel/integral protein
specific to H2O
bidirectional
permit rapid movement of water in and out of cells
facilitated diffusion
movement of molecules down the concentration gradient
assisted by transport proteins
passive transport
requires help from transmembrane integral protein (channel or carrier protein)
channel proteins
transmembrane proteins
assemble to form channels for the passage of polar molecules
selectively permeable because of hydrophilic/phobic side chains inside channel
can be opened or closed (gated)
many only allow one type of ion/molecule through
ex: ion channels
carrier proteins
transmembrane proteins
play important role in facilitated diffusion, bind to solute molecules
undergoes a conformational change when molecule binds to it
transfers molecules to other side of membrane
ex: glucose transporter
active transport
comes into play when molecules need to be transported from lower concentration to higher concentration
uphill energy required, exergonic reaction
helps to take up essential nutrients, remove waste, maintain right concentrations of ions in cells
uses carrier proteins
direct active transport
where energy released by exergonic reaction is used to transport molecules across cell membrane
indirect active transport (cotransport)
movement of one solute down its concentration gradient drives movement of second solute against its concentration gradient
plays an important role in glucose absorption by the intestinal epithelial cells
membrane fluidity
depends on the fatty acid composition of the phospholipids
saturated fatty acids provide stability (because of higher melting points)
lower temperatures = lower fluidity
depends on cholesterol in animal cells (at high temperatures, reduces fluidity)
endocytosis
bulk transport mechanism by which particles are moved into the cell
cell membrane progressively invaginates and engulfs particles, pinches off to form vesicle
phagocytosis
ingestion of large solid particles
bulk transport
cellular eating
ex: white blood cells
pinocytosis
ingestion of liquids
bulk transport
smaller vesicles than phagocytosis
exocytosis
reverse of endocytosis
bulk transport of material to be secreted/excreted out of cell
via vesicles
vesicles fuse with cell membrane & contents are discharged to extracellular space
ex: secretion of glycolipids/neurotransmitters, excretion of waste
cell-adhesion molecules (CAMs)
crucial role in cell adhesion
glycoproteins
mediate the binding of cells with other cells/extracellular matrix
play a vital role in the formation of tissues
cell junctions (anchoring junctions)
connect cells to each other
allow intracellular transport and communication
important for cell proliferation and migration
prevent unregulated movement of materials between cells
adhesive junctions
present in epithelial & cardiac cells
facilitate cell adhesion
ensure stability
tight junctions
present in epithelial cells
form tight seal between neighboring cells
act as occluding junctions
barrier prevents unregulated movement of molecules across barrier
gap junctions (communicating junctions)
present in several cell types
intracellular channels connect neighboring cells for movement of molecules
help in cell-cell transfer of small molecules
desmosomes
adhesive junctions that help to anchor cells
water
universal solvent
two hydrogens covalently bonded to one oxygen atom
dipolar molecule because of differences in electronegativity
high specific heat capacity
ions
atoms that have lost/gained electrons
dissolution
separation of solute particles because of hydration shells (water molecules surrounding ions)
diffusion
general process of particle movement from an area of high concentration to an area of low concentration
passive transport
ex: air freshener
hypertonic solution
more solute concentration in this solution than other solution
water flows in
other solution is hypotonic to this solution
opposite of hypotonic
hypotonic solution
lower solute concentration in this solution than another solution
water flows out
other solution is hypertonic to this solution
opposite of hypertonic
lysis
disintegration of a cell by rupture of the cell membrane
plasmolysis
water leaving plant by osmosis
in hypertonic solution
cell membrane shrinks away from cell wall
loses turgor (internal) pressure
ectothermic
cold-blooded
higher proportioon of unsaturated fatty acids in membrane at lower temperatures
concentration gradient
difference in concentration
can be visualized as a hill
“down” = high concentration to low concentration
passive transport
does not require additional input of energy (ATP)
simple diffusion
facilitated diffusion
osmosis
active transport
does require additional input of energy (ATP)
pump proteins
bulk transport - exocytosis & endocytosis (pinocytosis and phagocytosis)
dynamic equilibrium
no net movement
equal concentration on both sides
constant movement back and forth
permeable & some mostly permeable molecules
factors that impact diffusion rate
concentration gradient (“steeper”→faster diffusion)
distance (shorter→more efficient diffusion)
temperature (higher temps, more movement→faster diffusion)
size (smaller → faster diffusion)
polarity (more polar→slower diffusion)
solvent
does the dissolving
almost always H2O
solute
what is being dissolved
ex: salt, sugar, etc
solution
solute + solvent
tonicity
ability of a solution to make water move into/out of a cell by osmosis
Note
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