Cell Biology Flashcards
All translation begins in the ____
cytosol
*note that not all protein translation ends in the cytosol, but all of it does begin inthe cytosol
Which proteins finish translation in the RER
secreted proteins, transmembrane proteins, lysosomal proteins
How are proteins modified so that they can be sent to the RER to finish translation?
a “signal sequence” (made up of AA) is added to the protein so the cell knows to send that protein to the RER to finish translation
Where is the signal sequence found on secreted proteins? When is this signal sequence removed?
It is found within the first few tranlsated AA of that protein (which means its on the N terminus of that protein)
This sequence is removed at the end of translation
What signal sequence can be found in a membrane-bound protein? When is this signal removed?
A signal sequence can be found anywhere within the AA sequence, and may appear several times
This signal is not removed, and will actually remain as a transmembrane element
what is oxidative stress?
when the level of reactive oxygen species production (H2O2 or free oxygen) results in the formation of radicals in a cell, and this level becomes so high that the cell no longer has the ability to detoxify them
how do immune cells use reactive oxygen species to kill pathogens?
activated phagocytes may produce nitric oxide (NO) or superoxide (O2-)
what is regenerative capacity?
the ability to restore damaged tissues, which depends on how stem cells are maintained in the body of an organism
what is senescence?
biological aging, both on the cellular and organismal level
For eukaryotes, the length of telomeres are a measure of cellular age
what are caspases?
proteases that carry out apoptosis
have a cysteine residue on their active site and they cleave their target proteins at specific aspartic acid sites, hence their name “c-asp”-ases
they are produced in their inactive form procaspases
Distinguish between initiator caspases and effector caspases
initiator: respond to intracellular or extracellular death signals (which cause the cell to shrink and the initiators to become clustered together); when clustered together, the initiators become activated, which then activate the effectors
effector: responsible for cleaving a variety or cellular proteins to trigger apoptosis (responsible for eating the cell inside out)
What are microtubules made out of and what major components of the eukaryotic cell do they make?
made out of alpha-tubulin and beta-tubulin (which are 2 globular proteins that noncovalently bind together to create dimers)
centrioles, eukaryotic cilia and flagella, and intracellular transport are comprised of microtubules
What are microfilaments made out of and what major components of the eukaryotic cell do they make?
made out of actin (globular proteins that form long chains, 2 chains are wrapped around each other to form the actin filament)
used in muscle contraction, cytokinesis (the actin belt cinches), and pseudopod formation/amoeboid movement (help in gross cellular movement of the cell)
What are intermediate filaments made out of and what major components in eukaryotic cells do they make?
are heterogenous, as they are made of a wide variety of polypeptides
differentiate between tight junctions, gap junctions, and desmosomes
tight junctions: form a (complete) seal between the membranes of adjacent cells that block the flow of molecules across the entire cell layer
gap junctions: pore-like connections between adjacent cells, allowing the 2 cells’ cytoplasms to mix, exchanging solutes like ions, AA, and carbohydrates (but not big enough to allow transfer of polypeptides or organelles)
desmosomes: do not for a seal, but just help hold the cells together at concise points (not bands all the way around a cell like tight junctions); made up of intermediate filaments called keratin
distinguish between apical surface and basolateral surface
apical surface is the “outer” surface i.e. the lumen of the intestine
basolateral surface is the “inner” surface i.e. the underlying tissues lying against the intestinal cell wall.
What does the G-protein phospholipase C pathway initiate?
activated GTP alpha subunit on G-protein will trigger phospholipase C to cleave phosphoinositol bisphosphate into IP3 and DAG
IP3 increases intracellular Ca++ levels
DAG activates kinases, which change enzyme activity
What is signal amplification?
in regards to the second messenger system, it refers to the signal of one molecule (first messenger i.e. neurotransmitter) creating multiple secondary messenger signals (i.e.cAMP, IP3, or DAG), which then each create more signals
d/t signal amplification, secondary messenger systems are fast acting
What is the effect of the G-protein, Adenylyl cyclase system?
epinephrine activates the alpha subunit of the G protein, which will drop its GDP for GTP and also disengage from the G protein altogether, will float around until it becomes bound to adenylyl cyclase. Adenylyl cyclase then uses ATP to produce multiple cyclic AMPs, which then activate cAMP-dependent protein kinases, which cause enzyme phosphorylation and a change in enzyme activity
what type of cell messenger system do G-proteins participate in?
secondary messenger systems
what is cAMP?
the secondary messenger signal known as the “universal hunger signal” because it is the second messenger of epinephrine and glucagon, which causes energy mobilization (glycogen and fat breakdown)
The molecule that serves as the key for a given cell-receptor is termed the _____
ligand
What type of signals do cell-surface receptors receive?
extracellular signals from a ligand (generally a hormone or neurotransmitter).
once bound to a ligand, this initiates a response within the cell, a process termed signal transduction
differentiate between passive and active transport
passive (inc. simple and facilitated diffusion): allows passage of molecules down their concentration gradient and therefore doesn’t require energy
active: moves molecules against their concentration gradient, which requires energy
what is coupling transport (or cotransport)
refers to transport of different molecules cotransporting (or hitching a ride so-to-speak) with the flow of Na+ ions down a concentration gradient
i.e. glucose cotransports with Na+ in the intestinal lining. glucose must cotransport because it is not moving down its concentration gradient (but rather against), but Na+ is.
differentiate between ion channels and carrier proteins
both are types of facilitated diffusion
ion channels are simply a tunnel through the cell membrane that allows the passage of small molecules
carrier proteins are not tunnels, and must bind to their specific carrier molecule, which causes a conformational change in the protein, which then allows passage of the molecule into/out of the cell. there are uniports, symports, and antiports
Differentiate between diffusion and osmosis
diffusion is transfer of molecules down their concentration gradient, which means going from higher to lower concentration of molecules (in other words, it travels from a hypertonic solution to a hypotonic solution)
osmosis is transfer of water down its concentration gradient, as it is moving from a concentration high in water to a concentration that is low in water (in other words, it travels from a hypotonic to hypertonic solution)
how does concentration of solutes affect the following 4 colligative properites: vapor-pressure, freezing point, boiling point, and osmotic pressure
an increase in concentration of solutes will decrease the vapor pressure (by increasing IMF) and decrease the FP
an increase in concentration of solutes will increase the BP and increase the osmotic pressure
functinon of lysosomes
degradation of biological molecules via hydrolysis
responsible for autophagy (eating damaged cell parts), phagocytosis (cell eating by consuming phagocytic vesicles), and crinography (digestion of unneeded or excess secretory products)
what are the enzymes in lysosomes that are responsible for degradation?
acid hydrolases (these enzymes will only hydrolyze substrates when they are in an acidic environment, which is why the inside of a lysosome has a pH ~5 compared to the rest of the cell of pH 7.4)
function of peroxisomes
perform a wide variety of metabolic tasks: is essential for lipid breakdown; essential for assisting in detoxification of drugs and chemicals in the liver
contains enzymes that produce H2O2 as a byproduct, but also contains catalase to convert this into H2O and O2 before it leaves the peroxisome.
function of SER
detoxification and glycogen breakdown in liver
steroid synthesis in gonads
