Biol 213 ch. 15, 16, 17, 18 Flashcards
what creates enclosed compartments that segregate different metabolic processes
internal membranes
what is the nucleus surrounded by?
a double membrane (nuclear envelope)
how does the nucleus communicate with the cytosol?
via nuclear pores that perforate the envelope
cytosol function
-contains metabolic pathways
-protein synthesis
-cytoskeleton
nucleus function
-contains main genome
-DNA and RNA synthesis
Smooth ER function
-lacks ribosomes
-site of steroid hormone synthesis in adrenal gland
-site where a variety of organic molecules (like alc) are detoxified in liver cells
Rough ER function
synthesis of most lipids
Golgi Apparatus function
-modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelles
lysosomes function
endosomes function
sorting of endocytosed material and recycle some back to membrane
mitochondria main function
ATP synthesis by oxidative phosphorylation
chloroplasts function
ATP synthesis and carbon fixation by photosynthesis
peroxisomes function
-packed with enzymes that digest toxins and synthesize certain phospholipids
-oxidative breakdown of toxic molecules
-produce H2O2
what do cytoskeletal filaments do?
-provide tracks for moving the organelles around
-direct traffic of vesicles between 1 organelle and another
how did mitochondria and chloroplasts evolve?
aerobic bacterium was engulfed by a larger anaerobic eukaryotic cell
what determines protein synthesis?
amino acid sequnce
what does signal sequence/ sorting signal do?
directs proteins to organelles where they are required
what happens to proteins without sorting signals?
remain in cytosol
how do molecules go from cytosol to nucleus?
nuclear pores
what are nuclear pores?
selective gates that actively transport specific macromolecules (but also allow free diffusion of smaller molecules)
how do molecules enter mitochondria/chloroplasts?
transported by protein translocators
-transported protein must unfold for translocator to guide it across hydrophobic interior
-signal sequence is removed after translocation is complete
how do molecules go from ER (EMS) go anywhere?
transport vesicles that pinch off membrane of 1 compartment and fuse with membrane of a second compartment
what is the nuclear lamina?
meshwork of protein filaments that lines the inner face of inner membrane and provides structural support for nuclear envelope
what does the nuclear envelope do?
encloses the nuclear DNA and defines the nuclear compartments
what are desmosomes
cell-cell junctions where the plasma membrane is connected to that of another cell
nuclear lamina
underlies and strengthens the nuclear envelope
what is in the inner nuclear membrane
-proteins thata act as binding sites for chromosoems
-proteins that provide anchorage for nuclear lamina
what drives nuclear transport?
energy supplied by GTP hydrolysis
what does Ran-GAP do?
turns GTP into GDP
-activates GTPase
what do chaperone proteins do?
help pull protein across membranes and fold once it is inside
what is the only organelle that serves as an entry point for proteins destined for other organelles
ER
where do proteins that are destined for Golgi Apparatus, endosomes, lysosomes, and those destined for cell surface first go?
ER. From then on they will be transported by vesicles
what kinds of proteins are transferred from cytosol to ER?
1) water-soluble- destined for secretion or lumen in an organelle in EMS
2) prospective transmembrane- destined to reside in membrane of EMS organelles or plasma membrane
what signal sequence directs protiens to ER?
8+ hydrophobic amino acid
what are the 2 types of ribosomes in the cytosol and what are their functions?
1) membrane-bound- make proteins destined for ER
2) free ribosomes- make proteins encoded by DNA
what are the 2 types of ribosomes in the cytosol and what are their functions?
1) membrane-bound- make proteins destined for ER
2) free ribosomes- make proteins encoded by DNA
what end of polypeptide chain must pass through translocator for protein to be released into ER lumen?
C terminus of growing polypeptide chain
how do proteins get to ER membrane?
SRP binds to exposed ER sequence
outward secretory pathway
proteins are transported form ER through Golgi apparatus to plasma membrane
how do components travel through the Golgi Apparatus>
via vesicles that shuttle between its individual cisternae
what are protein coat functions?
1) shape membrane into a bud
2) capture molecules for onward transport`
what do clathrin molecules do?
form basketlike cages that help shape membranes into vesicles
what do clathrin-coated vesicles do?
1)Golgi to lysosome (via endosome)
2) plasma membrane to endosomes
what do adaptins do?
secure clathrin coat to vesicle membrane and help some cargo molecules for transport
-bind cargo receptors in Golgi App.
-bond cargo receptors in plasma membrane
what do dynamin proteins do?
assemble around the neck of a budding vesicle, hydrolyze GTP, and pinch off vesicles
what provides initial recognition between vesicle and target membrane?
Rab and tehtering proteins
what are SNARE proteins?
transmembrane proteins that provide addiitional recognition in ensuring transport vesicles dock at appropriate target membranes
what serves as molecular markers for each membrane type?
Rab proteins
what do disulfide bonds do?
stabilize structure of proteins that will encounter degradative enzymes and changes in pH outside cell
why don’t disulfide bonds form in cytosol?
the environment in cytosol is reducing
what do oligosaccharides do?
- protect a protein from degradation
-hold protein in ER until it is properly folded
-form cell’s outer carb layer (glycocalyx)
what is the ER retention signal?
C-terminal sequence of 4 a.a.
what is the difference between cis and trans sides of Golgi App
cis: adjacent to ER
trans: points towards plasma membrane where proteins exit
what are endosomes?
where ingested materials go
-there, ingested materials are recycled to plasma membrane or sent to lysosomes for digestion
what do phagocytic cells do?
-ingest large particles
-defend against infection by ingesting invading microorganisms
-scavenge dead and damaged cells
what are macrophages?
-a type of phagocytic cell found in tissues and other WBC
how do macrophages engulf bacterium?
particles bind to surface receptors, which induces phagocytic cell to extend sheet-like projections of plasma membrane (pseudopods) that engulf bacterium and fuse their tips to form phagosome
what do phagosomes do?
fuse with lysosomes, where microbes are destroyed
what is pinocytosis?
cell ingestion of their plasma membrane
-cells SA and vol. dont change -> equal rates of endo and exocytosis
-carried out mainly by clathrin-coated vesicles
cholesterol
-extremely insoluble lipid in water
-transported in bloodstream in the form of low-density lipoproteins (LDL), which enters cell via
receptor- mediated endocytosis
where are early endosomes?
just beneath plasma membrane
-matura gradually into late endosomes as they fuse w each other
where are late endosomes?
located closed to nucleus
how does the endosome stay acidic?
by ATP-driven H+ pump in endosomal membrane that pumps h+ into endosome lumen from cytosol
how do proteins stay from getting digested by the lysosomal proteases?
sugars (glycosylated)
proteases, nucleases, proteases, lipases, phosphatases, sulfatases, phospholipases
what is the function of the cell cycle?
duplicate DNA in chromosomes and segregate DNA into genetically identical daughter cells
why doesn’t the cell grow in M phase?
cannot produce new proteines in that phase because it is in heterochromatin (super coiled)
-so it can’t be transcribed and therefore no mRNA synthesis
What are the checkpoints?
after G1: checks if environment is favorable (sufficient nutrients, specific signal molecules)
after G2: checks DNA is undamaged and fully replicated
after M: before chromosomes are pulled apart, checks duplicated chromosomes are properly attached and aligned on mitotic spindle
what do kinases do?
phosphorylate
what do phosphatases do?
perform dephosphorylation
what do cyclins do?
turn kinases on and off
what are Cdks?
cyclin-dependent protein kinases of the cell control system
-only activate once bound to cyclin
why is increase in cyclin concentration gradual?
because of continued transcription of cyclin genes and synthesis of cyclin proteins
what is fall in cyclin concentratation rapid?
full scale targeted destruction of the protein by APC/C
what drives the removal of M cyclin at the end of mitosis?
1) activation of APC/C
2) APC/C tags cyclin with ubiquitin
3) cyclin gets taken away to proteasomes
what does APC/C stand for?
anaphase promoting complex
what triggers the rapid activation of M-cdk?
phosphatase (cdc 25) removes inhibitory phosphates that inhibitory kinase put
what is p27?
an inhibitory protein that inactivates Cdks and cell can’t progress through G1 into S phase
what are the mechanisms in the cell-cycle that pause the cycle at specific points?
after G1: Cdk inhibitors block entry to S phase and replication of DNA
after G2: inhibition of activating phosphastase (Cdc25) supressess activation of M-Cdk
after M: inhibition of APC/C activation, preventing degradation of M cyclin
what happens in G1 phase?
DNA is made replication-ready by recruitment of proteins to origins of replication
-Cdks are inactivated
what do mitogens do and what happens if a cell is deprived of them?
mitogens are extracellular signals/stimuli that tell cells to grow
-if deprived, cell cycle arrests in G1
how does a cell escape cell-cycle arrest?
buildup of cyclins triggers G1/S- Cdk activity, which relieves the negative controls that otherwise block progression from G1 to S phase
What is the Rb protein?
Retinoblastoma
-inhibiti
What is the Rb protein?
Retinoblastoma
-inhibiti
What is the Rb protein?
Retinoblastoma
-inhibiti
