Lecture 5- eukaryotic cell structure Flashcards
origin of eukaryotes = the _____ hypothesis
endosymbiotic
good roommate
describe the ‘good roommate’ hypothesis
- heterotrophic bacteria are sensitive to increasing [O2]
- eukaryotes evolved O2 neutralizing enzymes
- bacteria ingested but not digested… these became organelles mitochondria and chloroplast
endomembrane system=
membrane-bound organelles that arose from infoldings of membrane and are connected via vesicles
vesicle=
membrane-bound compartment that contains cargo
list the 4 organelles in endomembrane system
- outer nuclear membrane
- ER
- golgi
- lysosome
nucleus/ nucleolus city analogy:
____ is the whole city, ____ is downtown
(they are not physically separate)
nucleus
nucleolus
the nucleus stores ___ and is the site of ___ _____
DNA
gene expression
the ___ is double-membrane bound with the outer membrane continuous with the ___
nucleus
ER
What does the NPC (nuclear pore complex) do?
transmembrane complexes that span both bilayers
- allows nonspecific transport
____ is the site of ribosomal subunit assembly
- subunits associate with their rRNAs at the ____
nucleolus
nucleolus
ribosomal subunits leave the nucleus as independent subunits and come together in the ____ during ____
cytoplasm
translation
the nuclear envelope includes both nuclear membranes
- function:
- structure:
fxn= protects DNA structure = 2 lipid bilayers plus nuclear lamina
chromatin=
DNA associated with protein
- within a chromosome
why package DNA?
organize it and protect it from damage
what are the 4 orders of DNA packaging?
- nucleosome
- solenoid/ 30nm fiber
- looped domains
- mitotic chromosome
describe the 1st order of packaging
nucleosome:
- DNA wrapped around a histone octamer
describe the 2nd order of packaging
solenoid/ 30nm fiber
- nucleosomes stack with the help of histone H1
describe the 3rd order of packaging
looped domains
- 30nm fiber loops off a non-histone protein scaffold
- found in all cell stages
describe the 4th order of packaging
mitotic chromosome
- fully condensed chromosome only appears during cell division
- so tightly wound that you can’t get any info/ gene expression off it
histone =
pos charged proteins
the rough ER is covered in ___ which are the enzymes of____
ribosomes
translation
The ____ ___ is associated with translation of proteins destined for within the endomembrane system. They’re called ___ ribosomes (___ribosomes are free floating in cytoplasm)
rough ER
bound
free
function of rough ER?
- site of protein quality control (lots of chaperones, folding)
- site of protein synthesis for proteins that fxn within the endomembrane system
Proteins destined for the cytoplasm or nucleoplasm are synthesized on ____ ribosomes
free
proteins destined for the plasma membrane or are exported/ secreted are synthesized on ___ ribosomes
bound
the smooth ER has no ___
ribosomes
List 4 examples of functions of the smooth ER
- ion storage (Ca2+)
- phospholipid synthesis
- steroid synthesis
- detoxification of drugs and alcohol
The _____ _____ receives cargo from the ER (everything the ER makes) and sorts cargo to 3 different destinations:
1.
2.
3.
Golgi apparatus
- lysosome
- plasma membrane
- back to ER
The golgi packages cargo into ___
it’s like the FedEx of the cell
vesicles
The structure of the golgi is a set of flattened membranous sacs called ____
cisternae
2 models of golgi trafficking
- Vesicle Trafficking:
- cargo from ER moves through CIS, medial, and trans (vesicle containing cargo comes out of the shipping side- trans) - Cisternal Maturation
- cargo from ER enters CIS and stays there; the CIS moves, not the cargo (escalator analogy)
- New CIS cisternae forms by fusion of vesicles from ER
- trans golgi turns into vesicles
Evidence for Vesicle trafficking model (Golgi)
- small vesicles are associated w/ golgi
- there are cisternal- specific enzymes
Evidence for Cisternal Maturation model (Golgi)
- molecules too big to fit in the golgi- associated vesicles can move through golgi
lysosomes can ___ anything
digest
____ contain many hydrolytic enzymes that fxn best @pH=5
lysosomes
How to lysosomes maintain low pH? Why is it important to maintain low ph?
- they actively pump in H+
- low pH protects the cells from accidental autophagy (eating itself)
example of lysosomal storage disorder?
Tay Sachs- lack an enzyme to digest a particular lipid
- therefore the lipid accumulated and causes neuronal death
Vacuoles have different fxns depending on cell type. List 3
- food vacuoles
- contractive vacuoles: pump excess water out of the cell
- cenrtal vacuole: specific organelle of plants - fxns in storage and part of plant endomembrane system
List 3 organelles not in the endomembrane system.
Why aren’t they in the endomembrane system?
- mitochondria and chloroplasts
- peroxisomes (involved in detox of alcohol, metabolism of fats- dangerous rxns happen here)
- cytoskeleton (fxn in support, motility and cell shape)
Because they have a different evolutionary origin
what are the 3 different fibers that make up the cytoskeleton?
- microtubules (MT)
- microfilaments
- intermediate filaments
Microtubules are composed of ___ ___
tubulin dimers
Function of microtubules:
compression resistance (rods prevent squish)
tubulin (the monomer of microtubules) is a diamer of ___;___ tubulin monomers
alpha; beta
motor protein=
protein that change shape with ATP hydrolysis that generates force
2 motor proteins associated with microtubules
- Kinesin: (+) end directed MT motor; uses monkeybar movement
- Dynein: (-) end directed MT motor
mechanism of dynein movement unclear
- note: (-) end is on the left of the MT, (+) on right
example of MT function
eukaryote flagellum
- movement is generated by dynein (kinesin moves vesicles)
microfilaments (MF) or “actin filaments” are composed of ____ monomers and is a double twisted chain of ____ ____
actin
actin subunits
fxn of microfilaments
tension resistance
- movement: cytokinesis and muscular contraction
what’s the ‘motor’ of microfilaments?
myosin
eg. in muscles, pulling of myosin shortens the muscle
Intermediate filaments function in ____ ___ (like MFs)
tension bearing
structure of intermediate filaments
many different subunit types that form rope-like filaments
do intermediate filaments have any associated motor proteins?
no
give 2 examples of intermediate filaments
- laminin (intermediate filament forming nuclear lamina)
provides support - keratin- in hair and nails
