Bio 1113 - Ch 7. (Cont) Cell Systems

nuclear transport

- import/export regulated by the nuclear pore complex (NPC), which are holes/channels in the nuclear envelope
- proteins to be imported into the nucleus contain a nuclear localization sequence (NLS)

nuclear localization sequence

- part of the primary structure of a protein
- located at the C-terminus of proteins that will be imported into the nucleus
- nucleus "zip code"
- has to be recognition tag on molecule recognized by NPC to let it into nucleus

endomembrane system

- protein sorting, packaging, shipping, and recycling
- rough ER --> golgi apparatus --> vesicles --> destination (organelles or plasma membrane)
- different tag/receptor pairs ensure proteins are packaged and shipped to correct locations

secretory pathway

1) protein enters ER
2) protein exits ER
3) protein enters cis face of golgi apparatus
4) protein exits trans face of golgi apparatus
5) protein secreted from cell

signal hypothesis

- hypothesis on how proteins are targeted to the rough ER
- protein produced in cytoplasm on free ribosome
- if ER signal sequence found, entire ribosome is directed to rough ER

free ribosomes

all protein production starts on _________________

n-terminus

ER signal sequence is located at the ______________

chaperones

- protein folding is assisted by chaperones
- proteins that help other proteins fold
- very prevalent in the ER

protein tagging

- proteins undergo glyosylation to become glycoproteins
- addition of carbohydrate groups to a protein
- tag determines the ultimate destination of the protein

golgi apparatus

folded and tagged proteins are then sent to the _________________

golgi process

1) proteins bound for different destinations carry distinct tags
2) proteins are sorted
3) transport vesicles bud
4) cytosolic and membrane proteins cause transport vesicles to attach and fuse at destinations
5) vesicles deliver contents

mannose-6-phosphate

- carbohydrate tag that is attached to acid hydrolases

tags

different receptors on trans side of golgi apparatus bind to different ________ on proteins

receptor-mediated endocytosis

- used to be called pinocytosis
- some tag-receptor pairing, bringing something into the cell; nutrients, food, pieces of protein; small molecules bind to cell, turned into lysosome

phagocytosis

- "cell eating"
- ex] WBCs engulfing large particles/molecules
- phagosome eventually turns into lysosome

autophagy

- "self-eating"
- surrounded by a membrane, lysosomal enzymes come and convert it to a lysosome
- autophagosome eventually turns into lysosome

enzymes

lysosomes don't just hang around in cytoplasm, send ____________ to convert things into lysosomes

actin

the subunit of microfilaments are ____________, where the molecules combine to form two coiled strands

function of microfilaments

*how muscles move*
-maintain cell shape by resisting tension (pull)
- move cells via muscle contraction or cell crawling
- divide animal cells in two
- move organelles and cytoplasm in plants, fungi, animals

thicker cables

the subunits of intermediate filaments - keratins, lamins, or others - are wound together to form ________________

function of intermediate filaments

*only find these involving structure*
- maintain cell shape by resisting tension (pull)
- anchor nucleus and some other organelles

tubulin dimers

the subunits of microtubules - alpha and beta -_______________ - come together to form a hollow tube

function of microtubules

*let things move throughout cell*
- maintain cell shape by resisting compression (push)
- move cells via flagella or cilia
- move chromosomes during cell division
- assist formation of cell plate during plant cell division
- provide tracks for intracellular transport

myosin

- motor protein that converts chemical energy (ATP) to kinetic/mechanical energy
- has a "head" that attaches to actin and moves, sliding the actin filament
- involved in muscle contraction

kinesin

- motor protein involved in intracellular transport
- protein that looks like it is "walking"

microtubule-organizing center

- plants: have many of these throughout the cell
- animals: centrosome (two centrioles)
- produce microtubules = assembly of tubulins to produce long strands