Biology Chapter 6 (A Tour of the Cell) Flashcards
definition of Prokaryotic cells and its components
-defined by absence of membrane bound nucleus
components:
-nucleoid (houses circular DNA)
-ribosome (synthesizes proteins)
-plasma membrane (encloses cytoplasm)
-flagella (locomotion)
-cell wall (rigid structure outside membrane)
-cystosol (jelly-like fluid)
3 key differences between Prokaryotic and Eukaryotic
1) Eukaryotic is bigger
2) Prokarayotic chromosomes have loosely defined nucleoid; Eukaryotic chromosomes are enclosed in nucleus
3) cytoplasm of Eukarytoic cells is compartmentalized into distinct organelles rather than everything found in cytoplasm
Advantages of compartmentalization
1) chemical reactions are organized and can be partitioned
2) reactions are more efficient because reactants can be isolated and maintained at higher concentrations
3) enzymes can be grouped together in close proximity for efficiency
Nucleolus (Eukaryotic-Nucleus)
Where Ribosomal RNA is synthesized and where the subunits of ribosomes are assembled
Nuclear Envelope (Eukaryotic-Nucleus)
double membrane (double phospholipid bilayer)
Pore Complexes (Eukaryotic-Nucleus)
regulate entry and exit of proteins and RNA
Ribosomes
-no membranes (so they are not considered organelles by classical definition)
-either bound or free
-two subunits associated non-covalently for easier association and disassociation
-consists of nucleic acids (ribosomal RNA) and proteins
Parts of the endomembrane system
-Outer nuclear envelope
-Endoplasmic Reticulum
-Golgi Apparatus
-Lysosomes
-Vacuoles
-Plasma Membrane
Components are either continuous (connected by membranes) or interact via movement of membrane bound vesicles
Endoplasmic Reticulum and components (Endo-membrane system)
Smooth ER:
-system of membrane bound sacs and tubules
-[lacks ribosomes]
-contains enzymes involves in lipid based reactions. Site of phospholipid production for cell membranes and lipid detoxification/breakdown
-can store intracellular calcium. Keeping surrounding region low in calcium ions. Difference in concentration can be used for signaling
Rough ER:
-system of membrane bound sacs and tubules
-[ribosomes] generate proteins that function in ER, endomembrane system or that get secreted to cell exterior
Lumen:
-gaps in ER where protein folding and modification happens
-For ER synthesized proteins
modifications to proteins can happen in ER (ex. glycosylation)
Ratio of Smooth ER/Rough ER depends on cell and its function (ex. testes produce hormones which are made of lipids so they have a lot of smooth ER).
Golgi Apparatus (Endo-membrane system)
site of protein processing, folding and shipping
movement from cis(side close to ER) to trans (furthest from ER)
this process could involve membrane bound transport vesicles that assist with movement of proteins through the golgi
Lysosome (Endo-membrane system)
membranous sac of enzymes that perform hydrolysis (collectively called acidic hydrolases that function most optimally in acidic environments)
-proton pumps are required to maintain acidic conditions
-can also be referred to as a recycling component because smaller subunits from lysosomal degradation are exported out by transport proteins in the membrane of the lysosome to build other molecules
-Endoplasmic reticulum synthesizes the enzymes and membrane
-produced proteins processed by the golgi are shipped to the lysosome so this is why they are considered part of endomembrane system
phagocytosis (Endomembrane system)
a process where cells engulf other cells or food particles forming a vesicle (food vacuole/phagosome) that then binds to a lysosome resulting in degradation of components
autophagy (Endomembrane system)
a process used to recycle large structures and organelles.
-portions of the cytoplasm are enclosed within internal membrane to form a phagosome(vesicle) which merges with a lysosome to degrade the components
-the broken down contents can be recycled and ultimately get released to the cytosol
Vacuoles
can be found in plant cells
vacuoles replace lysosomes in plant cells. Some have hydrolases but many are used for storage (pigments, proteins for seeds, toxins depending on organism)
Mitochondria
significant ATP generator
Has two membranes (inner and outer):
-outer defines the structure
-inner has folding of sac like structures called cristae
cellular respiration: series of events that takes place along membrane and within matrix (contents within folding) of mitochondria
christae increase surface area
the mitochondria does contain linear chromosomes (mitochondrial DNA) that are independent of nuclear chromosomes.
only a fraction of genes in mitochondrial DNA is responsible for the function of the mitochondira
Some of the DNA encodes for RNA for mitochondrial ribosomes which produce some of the proteins found in mito, but most proteins in mito are produced by free ribosomes in cystosol
chloroplasts
Contains the green pigment chlorophyll and enzymes and molecules for photosynthesis
Has two membranes inner and outer. Inner has no christae
Has a third membrane found within the chloroplast called the thylakoids that are arranged in a stack called granum (plural grana)
peroxisomes
Site of reduction and oxidation reactions (transfer of electrons between atoms and molecules
An example of a reaction that takes place within the peroxisome is ethanol oxidation which produces hydrogen peroxide.
Hydrogen peroxide is reactive and harmful if it escaped the membrane bound organelle (compartmentalization partitions the reaction)
So there is an enzyme in the peroxisome whose role is to detoxify hydrogen peroxide into water and oxygen
Cytoskeleton network and its components
the cytoskeleton organizes structures and activities and anchors organelles
cytoskeleton is dynamic
-moves and changes to accommodate alterations to the cell shape
-can be involved with the movement of the cell itself
consists of 3 types of molecular structures
1) microtubules
2)microfilaments
3)intermediate filaments
microtubules (cytoskeleton)
largest cytoskeleton components with respect to diameter
has polypeptide subunits (alpha and beta tubulin) which associate non-covalently to polymerize. The subunits form the tubulin dimer
has polarity (a negative and a positive end)
-this is relevant because the rate of polymerization is not equal on either end
microtubules provide structural framework for organelles and separate genetic material during cell division. Also supports movement of cargo by allowing motor proteins to use the tubulin as a track
centrosome (a pair of centrioles)
centrioles (9 triplets of microtubules arranged in a ring)
in animal cells, microtubules originate from the centrosome
the ends are where polarity applies for a microtubule:
- positive end is area that grows faster
- the origin is the negative end
- positive end points away
- rate of polymerization/depolymerization is higher on the positive end
kinesin
motor protein that binds to the tubulin subunits to move towards the positive end of the microtubule
uses atp hydrolysis (atp to atp +pi) to take each step
made of two polypeptide subunits and has three regions on the protein (head, stalk and the tail)
head region binds to the tubulin and the tail region transports the vesicle
stalk connects head and tail
dynein
motor protein that moves towards the negative end of the microtubule (towards the origin)
microfilaments/actin filaments (cytoskeleton)
smallest component of cytoskeleton
composed of actin subunits associated non-covalently in a twisted chain
has polarity (positive end grows faster than negative end)
found under the plasma membrane and helps define the shape of the cell. Microfilaments are also involved in movement (amoeba move with actin protrusions and myosin can ratchet onto actin filaments and create muscle contractions)
myosin
motor protein that binds to actin for muscle contractions
-ATP hydrolysis involved (changes orientation of myosin)
-Change in state allows myosin to ratchet onto the actin filaments and create contractions
-Also needs calcium ion from endoplasmic reticulum
cytoplasmic streaming in plant cells
directional flow of cytosol and organelles along periphery of cell wall
movement occurs along actin filaments powered by myosin
intermediate filaments (cytoskeleton)
bigger than microfilaments
role is exclusively structural in nature
no polarity/sidedness
found inside nuclear envelope (inner side) and defines the shape of the nucleus and stabilizes the envelope
An example of intermediate filaments are keratins coiled together. This is for mechanical strength and is one of the last components to degrade in decomposing body.
Extracellular Matrix and components
the matrix found outside of cells that cells interact with
different tissue types will have different compositions of extracellular material
components:
-collagen (structural protein that imparts strength and flexibility)
-proteoglycan complex (protein-polysaccharide complex that provides the matrix that structural proteins are embedded in)
-fibronectin (adhesive glycoproteins that bind to proteoglycans and collagen molecules. Allows cells to attach to extracellular matrix. Composed of large polypeptides crosslinked by disulfide bridges)
-integrins (cell surface receptors that bind to ECM components. Composed of alpha and beta subunits associated non-covalently)
-glycoproteins()
-glycolipids()
cell walls of plants (extracellular material)
confer rigidity, barrier to substance movement and protects cell from physical damage
the components of the extracellular matrix is different compared to animal cells because plant cell walls contain cellulose microfibrils
cell walls secreted and synthesized in different stages
primary cell wall (composed of cellulose microfibrils and defines shape of the plant)
secondary cell wall (some plants don’t have this but it is possible for secretion of additional layer between plasma membrane and primary cell wall after maturation)
middle lamela (strucutre holds adjacent cells together)
tight junctions (animal cell junctions)
cell-cell attachment due to proteins in the plasma membrane of each adjacent animal cell
forms a tight seal that prevents things from passing through (good for stomach and intestines to prevent contents from leaking)
level of restriction of movement at tight junctions depends on the region of the body (different regions can have different tightness. Ex. bladder tighter than intestines bc intestines might want some level of absorption of nutrients and bladder deals with waste)
tight junctions can also change by stretching (ex. food moving through digestive track)
desmosome (animal cell junctions)
proteins found in membrane that forms bridges between anchoring proteins in adjacent cells that provide strong adhesion sites between cells
allows cells to work as a unit and resist mechanical stress
desmosomes are abundant anywhere where mechanical stress is present (heart, uterus, skin, etc.)
loss of desmosomes can lead to heart failure or skin defects
intermediate filaments reinforce desmosomes by attaching to anchoring proteins
gap junctions (animal cell junctions)
mechanism of cell communication
creates channels within membranes of adjacent cells which allow for movement of ions and small molecules
allows nearby cells to respond rapidly through fluctuations in concentration of ions and molecules (ex. heart has gap junctions to coordinate muscle contractions)
plasmodesmata (plant cell junction)
plant cell specific occuring at regions where there are holes in the cell wall
provides opportunity for plasma membrane of adjacent cells to come into contact with each other
allows for sharing cytoplasm which is similar to animal gap junctions but not identical
unlike gap junctions, plasmodesmota is lined w/ plasma membrane and has a central tubule connecting the endoplasmic reticulum of the two cells
bound ribosome products
free ribosome product
