the smallest cells (some bacteria) are similar in size to large viruses (0.1um)
(juicy pieces of a citrus fruit are separate gigantic cells
Electro microscopy:
reached sun Angstrom (A) resolution in year 2000 by resolving the 0.89A spacing between carbon atoms of diamond (1A=10^-10m)
Composition of a prokaryotic cell
the content (cytoplasm) is not separated into compartments
DNA and ribosomes are freely floating in the cytoplasm
Structure of a prokaryotic cell:
cell envelope
plasma membrane
cell wall
glycocalyx
capsule
cell envelope includes:
plasma membrane
cell wall
glycocalyx (layer of polysaccharide outside cell wall)
plasma membrane:
a phospholipids bilayer much like the plasma membrane of eukaryotic cells
important role in regulating the entrance and the exit of substances into the cytoplasm
cell wall:
composed of a complex molecule peptidoglycan (amino disaccharide and peptide fragments)
maintains the overall shape of a bacteria cell (coccus, bacillus and spiral)
mycoplasma are bacteria that have no cell wall and therefore have no definite shape
Glycocalyx:
layer of polysaccharide laying outside the cell wall
glycocalyx aids against drying out by trapping water and help bacteria to resists a host's immune system
it allows that bacterium to attach itself to inert surface (like teeth and rocks), eukaryotes (streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony)
is found not only in bacterial cells but also in eukaryotic cells
fuzzy gel like, sticky lay made up mainly of proteins and sugars
it surrounds the outermost cellular membrane of cells
capsule:
organized layer of polysaccharide
protects the bacteria cell and is often associated with pathogenic bacteria
serves as a barrier against phagocytosis by white blood cells
Structure of prokaryotic cells: (Appendages)
Bacteria may have the following appendages
flagella
fimbriae
sex pili
flagella:
responsible for most types of bacterial motility
flagella are long appendages which rotate by means of a "motor" located just under the plasma membrane
bacteria may have 1, a few, or many flagella in different positions on the cell
fimbriae:
small fibers that sprout from the cell surface
not involved in motility
help bacteria attach to surfaces
Sex pili:
rigid tubular structure used by bacteria to pass DNA from a cell to cell
bacteria reproduce asexually by binary fission, but they can exchange DNA through the sex pili
Bacteria Flagella rotation:
it is one of the examples of a wheel principle in nature
Endoplasmic reticulum:
smooth ER
synthesis of lipids
metabolism of carbohydrates
detoxification of drugs and poisons
storage of Ca^2+ ions
endoplasmic reticulum:
rough ER
synthesis of glycoproteins (carbohydrates + proteins)
production of secretory vesicles
membrane factory (phospholipids)
Ribosomes
protein synthesis in 3 locations:
cytosol (free ribosomes)
roughER
nuclear envelope
Sedimentation
svedberg (S):
measure of sedimentation speed
Sedimentation
movement towards the bottom of the centrifuge tube
Ribosome 30S subunits sediment with speed of 30 um/s under the force of 10^6g
sedimentation speed depends on
weight
shape
temp
medium
(SVEDBERG UNITS ARE NOT ADDITIVE)
Prokaryotic ribosomes: 30S and 50S subunits together have speed of 70S (not 80S)
Eukaryotic ribosomes: 40S and 60S
The golgi apparatus:
shipping
receiving
manufacturing center
Golgi apparatus functions:
modification of polysaccharides, glycoproteins, phospholipids
synthesis of many secretory products
sorting and shipping to various locations
Lysosomes:
Digestive organelles
membrane bounded vesicles produced by the golgi apparatus
have a very low pH and contain a powerful hydrolytic digestive enzymes (acid hydrolases) to break down proteins, carbohydrates, nucleic acids and lipids
digest food particles, and engulfed viruses or bacteria through endocytosis
digest excess or worn out organelles through endoxytosis "autophagy"
the membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell
peroxisomes:
contain enzymes that remove hydrogen atoms and transfer them to O2 (hydrogen peroxyde H2O2 is a by product -> name "peroxysome")
reaction: (RH2 + O2 -> R + H2O2)
conversion of fatty acids to smaller molecules for use as fuel in mitochondria
detoxification of alcohol and other poisons in the liver cells
thought to have endosymbiotic origin
peroxisome (pt2)
relatively small organelles found in all eukaryotic cells
general function to catalyze certain chemical reactions, typically those that break down molecules by removing hydrogen or adding oxygen
hydrogen peroxide is immediately broken down to water and oxygen by another peroxysomal enzyme called catalase
Enzyme in peroxisome are cellspecific
in liver, peroxisomes produce bilesalts from cholesterol and other break down fats
types of vacuoles:
central vacuole (plants)
food vacuoles
contractile Vacuoles (protista)
vacuoles
functions varied and differ among cell types and environmental conditions
central vacuoles in plants for storage and support
contractile vacuoles in protists for expelling excess water
phagocytic vacuoles in protists and white blood cells for degradation
Endomembrane system
network of membranes enclosing the
nucleus
endoplasmic reticulum
golgi apparatus
lysosomes
vacuoles
plasma membrane
may be directly connected to each other or pass materials via vesicles
restrict enzymatic reactions to specific compartments within cell
mitochondria & chloroplasts
The endosymbiont theory
mitochondria and chloroplasts derive from ancient prokaryotes captured by a eukaryotic cell
proof
have their own DNA
divide independently
have ribosomes of bacterialtype (70S)
Mitochondria
mitochondrial matric and inner membrane contain enzymes involved in respiration and production of ATP (energy)
1 to 1000s mitochondria per cell, depending on metabolic activity of the cell
can change their shape
in metabolically active cells, mitochondria form a network of tubes
chloroplasts
contain enzymes involved in photosynthesis
can change their shape
fatty acid biosynthesis
amino acid biosynthesis
plant immune response
Cytoskeleton
is a network of fibers that organize structures and activities in the cell
3 types
microtubules (tubulin polymers)
microfilaments (actin filaments)
intermediatefilaments
Microtubules (tubulin polymers)
main functions
maintenance of cell shape (compression resisting "girders")
cell motility (cilia or flagella)
chromosome movements in cell division
organelle movements
column of tubulin dimers, 25nm width, space in the middle on the tube
microfilaments (active filaments)
main functions
maintenance of cell shape (tension-bearing elements)
changes in cell shape
muscle contraction
cytoplasmic streaming
cell motility (pseudopodia)
cell division (cleavage furrow formation)
actin subunits twisted together in a rope form, 7nm width
intermediate filaments
main functions
maintenance of cell shape (tension-bearing elements)
anchorage of nucleus and certain other organelles
formation of nuclear lamina
fibrous subunit, keratin coiled together, cord like form, 8-12nm
Cytoskeleton:
serves as internal skeleton that maintains cell shape (construction and organization) and assists in movement of its parts
contains 3 types of elements
microtubules
intermediate filaments
actin filaments (also knows as microfilaments)
microtubules
long cylindrical structure composed of polymers of alpha and beta tubulin
they have polar structure with a plus end and minus end
a single microtubule can oscillate between growing and shortening phases: dynamic instability
key roles
intercellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria and vesicle)
the axoneme of cilia and flagella
mitotic spindle
synthesis of the cell wall in plants
intermediate filaments
more stable than microtubules and actin filaments, readily polymerize and depolymerize
function in the maintenance of cell shape and rigidity by bearing tension
actin filaments
composed of 2 intertwined actinchains
actin filaments support the plasma membrane and provide strength and shape to the cell
participate in come cell to cell or cell to matricjunction
motor proteins
category of cellular proteins that use ATP as a source of energy to promote movement
motor proteins
cellular proteins that use ATP as a source of energy to promote movement
consist of 2 domains
head
hinge
tail
walking analogy
ground is a cytoskeletalfilament, your leg is the head of the motor protein, and your hip is the hinge
3 different movements for motor proteins
moves the cargo from one location to another
can remain in place and cause the filament to move
attempting to walk (both the motor protein and filament restricted in their movement) exerts a force that causes the filament to bend
convert chemical energy into mechanical energy by hydrolysis of ATP