Cell structure COPY Flashcards
prokaryotes
Unicellular
Include bacteria and archaea
Lack a nucleus and membrane bound organelles
One circular chromosome, made of double stranded DNA
May have plasmids = small circular DNA molecules, often confer antibiotic resistance
Transcription and translation occur in the cytoplasm
Peptidoglycan cell wall = target of antibiotics
Ribosomal subunits: 30S + 50S = 70S
Ribosomes are smaller than eukaryotic ribosomes = target of antibiotics
Can replicate asexually (fission) each 20 min
Roughly 1/10 size of eukaryotic cells, 10× bigger than virus
Bacterial shapes: bacillus (rod), coccus (sphere), spirilla/spirochete (spiral)
eukaryotes
Include animal cells, fungi, and protozoa
Nucleus and membrane bound organelles
Larger ribosomal subunits: 40S + 60S = 80S
for ribosome size think: Eukaryote = Even
nucleus
Nuclear envelope is a double lipid bilayer (inner & outer)
Nuclear pores allow passage of small molecules/proteins; active exit/entry of big proteins
DNA is in the nucleus packaged as histone-bound chromatin
Site of transcription and replication
Nucleolus is electron-dense area = site of rRNA transcription, partial ribosome assembly
RNA exits nucleus for translation in cytoplasm
ER
Rough and smooth types
Rough ER contiguous with nuclear envelope
Part of endomembrane system
Site of synthesis for secreted proteins, transmembrane proteins, lysosomal proteins
Rough ER abundant in secreting cells (e.g., plasma cells, pancreatic cells)
Studs on rough ER = bound ribosomes
Proteins with signal sequence are translated on bound ribosomes
These proteins move from rough ER → Golgi → secretion/membrane or lysosome
Signal sequence is at amino end of newly-formed polypeptide chain
BEGIN being translated on free ribosome then move to ER
free ribosomes
Proteins destined for cytoplasm, nucleus or mitochondria synthesized by free ribosomes
These proteins lack signal sequence, may have other marker to send them to a particular organelle (i.e.,“nuclear localization sequence” if destined for nucleus)
smooth ER
Smooth ER is for lipid & fatty acid synthesis and detoxification (abundant in liver)
ER plays key role in membrane synthesis
In muscle cells, a special type of smooth ER called the sarcoplasmic reticulum is responsible for storage of calcium ions which are needed to trigger the coordinated contractions of muscle fibers.
golgi
Network of flattened sacs, part of endomembrane system
Vesicles move from cis → medial → trans Golgi
Glycosylation in Golgi/ER, may target vesicles (e.g., mannose-6-phosphate sends protein to lysosomes)
Golgi is the source of lysosomes
lysosomes
Are the site of digestion and breakdown in the cell
Part of endomembrane system
pH 5 and filled with digestive enzymes for DNA, protein, lipid, sugars
Lysosomal storage disease = missing or mutated digestive enzyme
Substrate accumulates and is toxic (e.g., lipid in Tay-Sachs disease)
peroxisomes
Break down hydrogen peroxide in the cell via catalase enzyme: peroxide → water
Detoxifies alcohol in human liver
catalase enzyme is what breaks down peroxide*** into water*
mitochondria
Site of aerobic respiration to make ATP
Abundant in energy-intensive tissues (e.g., liver and muscle)
Inner and outer membranes
Cristae are folds on inner membrane that increase surface area
Outer membrane is like sieve, allows entry small proteins and molecules
Inner membrane is less permeable, site of ATP synthesis
Matrix is enzyme-rich and is enclosed by inner membrane
Endosymbiont theory: mitochondria came from ingested ancient bacteria
Mitochondria are self-replicating via fission
Mitochondria have their own circular DNA molecules
Mitochondria have their own ribosomes (similar size to prokaryotic ribosomes)
proteasome
Complex within cell that breaks down proteins by hydrolysis (using proteases)
Proteins tagged with ubiquitin → degraded by proteasome
death chamber of cell*
neurons
In adult, neurons are generally post-mitotic (do not replicate)
RBC
Called erythrocytes
RBC has no nucleus or organelles
Nucleus and organelles are lost during RBC differentiation
RBCs circulate in blood for approx. 120 days
microtubules
(part of cytoskeleton)
25 nm hollow tubes made of tubulin subunits
Dynamic assembly and disassembly
Plus and minus end; plus end elongates more rapidly
Key for cell division (mitosis) and cell movement
Microtubules form the mitotic spindle
Microtubules are in cilia (e.g., respiratory epithelia) and flagella (e.g., sperm)
Cilia & flagella have 9 + 2 microtubules: 9 pairs with dynein bridges, 2 central unpaired
Microtubule associated proteins include cap proteins and motor proteins
Motor proteins use microtubules as tracks for moving cargo (e.g., vesicles)
Motor proteins use ATP to move: kinesin → plus end, dynein → minus end
centrosomes*
Microtubules form the mitotic spindle
Centrosomes give rise to the mitotic spindle in animal cells
Centrosomes = microtubule organizing centers (not only for mitosis)
Each centrosome has 2 perpendicular centrioles
microfilaments
7 nm, solid, helical actin fibers
Involved in muscle contraction and cell movement
Rapid assembly and disassembly
Can extend/retract a membrane (e.g., intestinal microvilli)
Can interact with myosin and ATP to generate force
intermediate filaments
Composed of various proteins
Stabilizes cell shape
Nuclear lamina
membranes
Universal feature of all cells, basis of life
Biological membranes are selectively permeable
Amphipathic lipid structure: hydrophilic polar head, fatty hydrophobic tail
Integral (transmembrane or tightly associated) or peripheral (loosely associated) proteins
Fluid mosaic model: lipids and proteins move within the plane of the membrane
Some proteins anchored to cytoskeleton and move less than others
Cholesterol present in animal cell membranes
Cholesterol found in membrane in “lipid rafts”
Cholesterol buffers membrane fluidity: prevents melting at hi temp, freezing at low temp
membrane proteins
Transmembrane proteins pass through the membrane
Include receptors, channels, transporters, and adhesion molecules
Receptors receive signals or matter from outside
Channels/transporters permit matter to pass membrane (e.g., ions and other molecules)
Adhesion molecules allow cells and tissues to stick together
Transmembrane proteins inserted with a fixed polarity during their creation
Transmembrane proteins give unique properties to inside/outside of cell
Glycosylation on extracellular portions
receptors
Receptors are transmembrane proteins
Receptors bind/receive ligands
Ligand can be diffusible or attached to another cell
Receptors trigger signaling cascade inside of cell
Information flows from exterior to interior
Can internalize matter via receptor mediated endocytosis (e.g., cholesterol, bacteria)
diffusion
Molecule flows down a gradient- movement of particles from high concentration area to a low concentration area (like when working down mitochondria move down gradient back to matrix and make atp)
BIG RULE OF LIFE- things always want to go from high conc. to low concentraiton area- important for nervous system and muscles*
No energy input is required
With passage of time, random motion causes equalization in distribution
Water, gases (e.g., CO2 and O2), and small polar molecules (e.g., glycerol) can diffuse across a membrane
anything non polar can get through, and small can get through*** glucsoe too big and is polar*
Large hydrophobic molecules (e.g., steroid hormones) can also diffuse across membrane
osmosis
Water follows solute, movement of water
water moves from ITS high concentration area to ITS low concentration area***
- diffusion takes place high conc. to low conc. toward where there is less of X % for ex 10% of NaCl side A and 20% NaCl side B, will move toward side A
- can see in ex water goes down ITS concentration gradient
tonicity- Remember=
- these comparitive!
- these only relate to solute, not telling you how much water you have always referencing particles in your solution
ex, hypertonic solution= means more particles in that particular solution than whatever you are comparing it to
hypotonic= meanas fewer particles than whatever it is you are comparing it to
isotonic= same number of particles of….. (whatever comparign it to)
Passive transport/facilitated diffusion/carrier mediated transport
Molecule flows down a gradient with the aid of a transport protein- concentration gradient provides the driving force for movement
Requires no energy, but needs carrier protein
simple diffusion
-works well for small hydrophobic molecules, nonpolar! just movign down concentration gradient depending if more or less of it either going in or exiting the cell! ex. Co2 or O2, look at capillary beds just a very very thin cell, usually composed of some sort of epithelial cell allow it for simple diffusion to take place, steroids, lipids, most steroids not super small but hydrophobic enough to slip right through**
big narly bulky lipid will have to transport it in as seen in lecture 2, but small ones will get across because hydrophobic enough
facilitated diffusion
Larger polar molecules such as sugars, amino acids- needs helper protein of hydrophilic molecules! ex. ions, glucose, amino acids
small hydrophilic molecules, still moving down concentration gradient
Can alter a molecule once it is inside, to keep it there (e.g., phosphorylate glucose)
active transport
Molecule moves up a gradient with the aid of a transport protein (pump)
Needs ATP/energy to drive conformational change of pump
Creates electrochemical gradient: different charge and/or concentration across membrane
Can use electrochemical gradient to do work (e.g., ATP synthesis in mitochondria)
Na+/K+ pump
- Transmembrane pump moves 3 Na+ out, 2 K+ in
- ATP hydrolysis drives conformational change (active transport)
secondary active transport
Uses energy of electrochemical gradient for work (ATP only used indirectly)
Example: Na+/glucose co-transporter
Na+ goes down gradient into cell (favorable)
Coupled to glucose moving up gradient (unfavorable)
Symport = molecules go in same direction
Antiport = molecules go in opposite direction
endocytosis
Endocytosis: membrane can pinch off and engulf things
Internalization of small or big things (e.g., macrophage eats bacteria)
**significant becuase liek with exocytosis, nothing is crossing a membrane; budding process that goes on, whatever that thing is that is being brough into vesicle never had ot go through membrane* its being brought into teh cell without crossing a membrane*
exocytosis
Exocytosis: vesicles fuse with the plasma membrane and release contents extracellularly
The inside of a vesicle/organelle = lumen
Topologically, ER lumen = Golgi lumen = outside of cell
important becuase stuff doesnt have to thread itself through the membrane on its own
anchoring junctions
Structural anchoring of cells to each other, but molecules can still pass between cells; do not do much but keeps cells together grouped there!
Like plastic rings that hold together a six-pack
Desmosome: like a spot rivet, connected to cytoskeleton
Adherens junctions: zipper of adhesion proteins, connected to cytoskeleton
receptor mediated endocytosis
Receptor mediated endocytosis involves a transmembrane receptor; so whatever it is we want to be endocytosed it has to first be attached to a receptor* so then you get internalize it on receptor, has to bind to receptor and bring that into cell; depends on having right receptors on surface of cell, would not be possible if the receptor was not there; after this happens eventually receptor has to be recycled, receptor has to go back to plasma membrane in order to keep bringing in more substrate*
ex. from mcat, one example of this is LDL
Example is cholesterol uptake
Cholesterol packaged into low-density lipoprotein (LDL) that circulates in blood
LDL receptor binds LDL outside, brings it into cell via vesicle
LDL receptor is recycled to membrane, LDL releases cholesterol in the cell
this is bad cholesterol- we are able to bring those into our cells only if LDL receptor on surface of our cells binds LDL and does this process of bringing LDL in, then have to send empty receptor back to plasma membrane to pull in more LDL** if don’t make enough of these LDL receptors can’t pull LDL into their cells enough which means they have way too much LDL suck in blood stream meaning they have really really high cholesterol as a result of this receptor problem* cells need cholesterol in membrane good side to cholesterol; bad side is that it can contribute to deposits in the arteries that narrow the arteries, athroschlorisis narrowing and hardening of arteries there are a bunch of things that happen in that situation, inflammation whole process LDL sticks to the spot and creates a plaque and if that plaque gets too big, it can block off an artery and cause heart attack!! If going for artery heading toward brain or heart, can choke off blood supply to an important organ, lifetime of eating very fatty foods or having high cholesterol in general can raise the risks of clogged or blogged arteries so the real danger is in terms of cardiovascular disease*
tight junctions
A tight seal that does not allow passage of materials between cells
Seals off body cavities such as intestines and stomach
Important in blood-brain barrier
very important- seal in lumens! individual cells that make up lumen means space in between cells so specific molecule could slip right through, if toxin not a good thing to happen enter straight into blood stream, so this makes sure seal off different separate environments. prevents anything from slipping through in those cells there* so they essentially block this from happening make sure nothing slips through cells into blood stream, meaning if molecule wants to get into cell very selective process if particular channel or transporter can go right through and enter cell if it wants to
gap junctions
A protein channel (hole) between cells
Allows ions and small molecules to move freely, permits electrical coupling (e.g., heart) need ions to move from one cell to another!
Allows for cell to cell communication!
- Meaning if a molecule in the cell is connected via gap junction can just pass through neighboring cell through gap junction and you are in as long as small enough to get through gap junction
- Heart really utilizes this!
Action potential of cardiac muscle cell is signal to have heart contraction, would not want some cells to be activated to have an action potential, if have all different parts of heart activated firing different action potentials, heart having different contractions all over th place and will not get good pumping of heart, want one cardiac muscle cell firing action potential, that sodium will flow into cell, nice strong contraction heart pumps all at once and get nice efficient blood contraction*
Bone also can use this
cell surface area and volume
Surface area of a sphere is 4πr2
Volume of a sphere is 4πr3/3
As radius increases, volume increases faster than surface area
Surface area: volume ratio is a limit to cell size
Surface area supports key cell processes (e.g., transport of things across a membrane)
Beyond a certain surface area: volume ratio, cannot sustain the metabolism of the cell
Cell indentations increase surface area (e.g., microvilli of intestinal epithelial cell)
Skinny and flat cells maximize surface area: volume ratio (e.g., neuron)
things to remember:
- All transcription takes place in nucleus
- All translation begins in the cytosol
- if you are cytosolic protein, you finish translation in the cytosol**
- but if you are a secreted protein, transmembrane protein, lysosomal protein= you will finish translation in the ROUGH ER*** or ER/golgi resident*
how do we know to finish translation in rough ER?
- what do paritcular amino acids have to be shipped over to finish translation
- they have a signal sequence, differentce btw two! if no singal sequence nno indicaton to cell they are going anywhere, will just finish translation in ctyolsol
- BUT if happen to be translating mrna strand and a cople of amino acids end up translating happen to be signal sequence, that is indciation will be shipped over to rough er to finish translation!
- if secreted protein, lysozomal protein distinct signal sequence* so in case of secreted protein or lysozomal protein the signal sequence will be the first amino acids
- signal sequence 1. first couple of amino acids that get translated, 2. signal is removed when translatin is complete you chop it off!
- signal sequence is literallya couple amino acids cell recognizes as signal sequence, distnct combination that happens to get recognized as a signal sequence
membrane bound protein signal sequence
- doesnt have to be first couple of amino acids that gets translated, can be anywhere in amino acid sequence, doesn’t have to be finally hit signal sequence indication to finish translation at rough ER
another thing to note about membrane bound proteins is signal sequence can appear several times in amino acid sequence whereas previously it only appeared once
- can appear severeal times in the amino acid sequence
- signal remains as membrane bound part of protein
eurkartyoic cell biology
cytoslic pathway vs secretory pathway
once finally sent out to cyutosol why only produces one protein product, once sent out mRNA will bind to free ribosome, depending on i fyou stay there bound to that free ribosome is if you do or do not have a signal sequence, if no signal sequence finish translation onf ree ribosome in cytosol wil not go anywhere….
secretory pathway will be endoplasmic R and golgi apparatus, how to package up proteins into vesciles to be sent to outside of cell, or can be fused with the membrane because as we will talk about its pretty hard to get across the membrane, we have a very nonpolar region; making a peptide which happens to have some polar amino acids in it, there is no way its getting outside of the cell
or making particular protein embedded in membrane need some way to weave self inside and otuside membrane, so how does the cell overcome that? follow secretory pathway! take free ribosome once produce that signal sequence of a couple of amino acids cell will recognize that, has a signal sequence recognition particle takes free ribosome and directs it, detors over to rough ER*, free ribosome docks at rough ER to continue translation pushes it into lumen of er or weave peptide insie and outside of membrane so that once it is done we can then ship that finished product, package it up in vesicles from one structure to the next
protein translation at the rough ER
ex. secreted protein
once that particular strand of amino acids is strung together through translation happen to create a signal sequence those free ribosomes can get directed to ER where it will then dock, first couple of amino acids translated were the signal sequence, signal sequence will be embedded in the membrane of the ER here membrane is cytosol of cell, Endoplasmic reticulum will get embedded into the membrane of the ER
- composed of nonpolar or hydrophobic amino acids becuase otherwise would not be able ot exist and not be very happy being in that inner portion, nonpolar amino acids
- once have signal sequence resumse rest of transaltion, see growing strand being pushed into lumen of ER; acting as achor for peptide, need whole protein to be in lumen, embed signal sequence into membraen of ER to push transaltion into lumen so then once done can then remove it and have final protein product* needs to get packd into vesicle then dumped otuside of cell
translation of membrane bound protein
- ribosome directed over to ER here is its mRNA that it has been reading, steps will look the same, said signal sequence doesnt have to be the same amino acid some getting translated, then hit signal sequence which directs you over to rough er, once signal sequence embedded in membrane continue
- once hit signal sequence and every time push translation to the other side of the membrane here, look on image, how get for instance a channel, channels usually composed of proteins how you get them woven in and out of the membrane, because otherwise it would be very hard to get passed those phospholipids have translation pore to weave peptide in and out of membrane
- so signal sequence DOES NOT GET REMVED* green lines and protein woven in and out of membrane here, can still form those vesicles and this will ultimately fuse with plasma membrane to have final locatioN!
- ex. in image, phospholipids that make up membrane will pinch off and fuse with next structure
which cell is exterior outside of cell for protein trafficking?
it will be hte ER lumen side! not cytosol, can think of environment as Er lumen as synonymis with otuside of cell, environments are very very similar, whatever is cytosol will remain cytosol side!
plasma membrane
- dont want fatty acids to stack up and pack together super tightly with saturated fatty acids very tight can rupture cell, want give with membranes so why cell will add cholesteroL!!! to make sure that those fatty acid tales do not pack together!
- cholesterol is really a cool molecule, not only prevents them from sticking together and keeps if fluid, stabilizing this membrane on both ends, when it gets very hot stops it from melting/ keeps them in tact
- at the same time, if very cold stops it from being too rigid b/c of tendency to stack up! so very very great buffer for membrane, does more than inc fluidity maintains that fluidity at all temperatures very similar to a buffer in a sense, stabilizes membrane and increases its fluidity
components of plasma cell membrane
- phospholipids
- 2 choleserol- stabilizes membrane and increases fluidity
- fatty acid tails cannot pack up as nice and neat because of cholesterol molecule getting in the way, keeps quite fluid
- proteins- allow membrne to be dynamic structure, get things across, and allow movement of certain things across membrane but not all things, allows membrane to be a dynamic structure, can transport polar proteins etc
- ex. channels can be selective only allowing a certain ion to get across, once charged ion can be allowed to get through membrane once shown, or don’t even have molecules get across cell, bind to receptro G proteins then activating a whole chain of response inside of the cell to have your desired effect there
- carbohydrates- serve as unique cell surface markers, find only on extracellular side**** will not be finding them in intracellular side*
colligative properties 1
properties that depend on the number of solute paritcles but not on their identity
4 colligative propertes: 1. freezing point, 2. vapor pressure, 3. boiling point, 4. osmotic pressure
change on addition of solute:
if have water then add salt to it, what will happen to these colligative properties- in case of Fp will always dec**
vapor pressure= decreased
boilin gpoint= ALWAYS INC
osmmotic pressure= always increased
Q what side does water/osmosis go towards? 1 M sucrose vs 1 M NaCl?
will go to side B! because it has more particles, van hoff ffactor will be 2 vs side A is 1 here!
dont forget van hoff factor!
need to know water will go towards NaCl becuase its whichever one has higher van hoff factor is where wate rwill go towards!
sucrose i nthis case only has 1 mol of particles, sodium chloride would have 2 moels
these two have same tonicity- those have to od with concentrations, they do start off with same concetrations but NaCl will ionize; so cant say one is hypertonic one hypo b/c they have hte same concetration! this is about osmosis!
osmotic pressure 2
RULE: OSMOTIC PRESSURE= PARTICLE CONCENTRATION
when see this think always water driven toward more concentrated area** all abotu particle concentraiton, high particle concentraiton ewater will be driven toward that side, low concetration will not be driven and will remain where it i sat driven where it is currently sitting!
why need 0.9% NaCl in bags, if alter from that will take on too much water or lose water*** so need to make sure when giving IVs or any sort of injections you get this right otherwise big lawsuit on your hand!
adenyl cyclase
- as alpha subunit dissociates and travels down to adenylyl cyclase and turns that protein on saying hey now operate you can now work!
- adenylyl cyclase- takes atp and converts it into cyclic amp**** so in cell start to see rising levels of cyclic amp** so levels start to drastically increase insdie of our cell
- cAMP then goes around adn starts to ativate cAMP dependent* protein kinases (kinase phosphoralytes* ) so goes around phosphoralting all these diff enzymes
- one way can regulate enzymes is add a phosphate group onto those enzymes or remvoe it, so if have this protein kinase going around adding phospahte groups turns on or off enzymes! so essentially changed enzyme activity in teh cell
- ligand didn’t ven have to come across our membrane here, just boudn ourselves to protein linked receptor and caused all these things to take place
ephinephrine signaling
ex. of g protein
when ephinephrine is released glucose concentration is= release epin. when LOW blood glucose levels!
so epinehprhine can act as ligand and bind to G protein linked receptor, step 1 in this case; causing gdp to dissociate off of alpha subunit 2. gtp binds to alpha subunit
- once gtp is bound to alpha subunit, alpha subunit goes and turns on adenylyl cyclase takes atp and covnerst to camp
- atp converted to camp
- camp goes around and phiosphoraltes enzymes, truning on enzymes that cause us to break down glycogen stores inc amount doing in that case and turning off enzymes forming glycogen*** which makes sense if releasing ephinephrine as a result of low blood glucose levels, dont want to take little bit of glucose in blood will drop even lower, so want to break down glycogen stores so can get glcusoe up in blood
g-protein mediated signal transduction steps!
remember cyclic amp is second messenger!
microfilaments 2
proteins: made of actin- muscle contractions use this actin
diameter: small *smallest
uses: muscle contraction, pseudopod formation, cell adhesions, cytokinesis, help cell move
- thinest of 3, often found beneath cell ’s plasma membrane where they strengthen it and give it shape
- quite strong even though thin and flexible
take out if do not need to know-filamentous actin= F-actin, made up of globular actin G-actin monomers, rate limiting step in actin filament formation, once nucleation has occurred can
-an monomers of actin will join together to form an actin polymer, then twist together to form an actin filament INVOLVED IN GROSS MOVEMENT OF CELL** they are dynamic* what we mean by that is they can lengthen and shorten very frequently, become longer in process known as actin polymerization* and actin depolymerization = helps to move the cell, so one example of where these help gross movement of cell is during cell division, cell will be pinched in the way and then eventually separate into two different cells, microfilaments help cell make pinched shape and move to create two separate cells*
also in an amoeba cell, we will say that it is trying to capture that piece of food to do that has to extend its pseudopods in that direction and move it around that molecule, what helps pseudopods move those microfilaments*
Golgi apparatus
is a membranous structure involved in protein translocation within the cell and in facilitating protein secreation at hte plasma membrane
When vesicles bud off from the ER, where do they go? Before reaching their final destination, the lipids and proteins in the transport vesicles need to be sorted, packaged, and tagged so that they wind up in the right place. This sorting, tagging, packaging, and distribution takes place in the Golgi apparatus (Golgi body), an organelle made up of flattened discs of membrane. THINK MAIL CENTER/UPS
The receiving side of the Golgi apparatus is called the cis face and the opposite side is called the trans face. Transport vesicles from the ER travel to the cis face, fuse with it, and empty their contents into the lumen of the Golgi apparatus.
As proteins and lipids travel through the Golgi, they undergo further modifications. Short chains of sugar molecules might be added or removed, or phosphate groups attached as tags. Carbohydrate processing is shown in the diagram as the gain and loss of branches on the purple carbohydrate group attached to the protein.
Finally, the modified proteins are sorted (based on markers such as amino acid sequences and chemical tags) and packaged into vesicles that bud from the trans face of the Golgi. Some of these vesicles deliver their contents to other parts of the cell where they will be used, such as the lysosome or vacuole. Others fuse with the plasma membrane, delivering membrane-anchored proteins that function there and releasing secreted proteins outside the cell.
Cells that secrete many proteins—such as salivary gland cells that secrete digestive enzymes, or cells of the immune system that secrete antibodies—have many Golgi stacks.
integrins
Integrins bind to ECM, specficially collagen and fibronectin, while Cadherins just bind cells together.
facilitate adhesion
Integrins anchor the cell to the extracellular matrix. In addition, they help it sense its environment.
They can detect both chemical and mechanical cues from the extracellular matrix and trigger signaling pathways in response.
Blood clotting provides another example of communication between cells and the extracellular matrix. When the cells lining a blood vessel are damaged, they display a protein receptor called tissue factor. When tissue factor binds to a molecule present in the extracellular matrix, it triggers a range of responses that reduce blood loss. For instance, it causes platelets to stick to the wall of the damaged blood vessel and stimulates them to produce clotting factors.
Signal peptides
Proteins destined for any part of the endomembrane system (or the outside of the cell) are brought to the ER during translation and fed in as they’re made.
The signal peptide that sends a protein into the endoplasmic reticulum during translation is a series of hydrophobic (“water-fearing”) amino acids, usually found near the beginning (N-terminus) of the protein. When this sequence sticks out of the ribosome, it’s recognized by a protein complex called the signal-recognition particle (SRP), which takes the ribosome to the ER. There, the ribosome feeds its amino acid chain into the ER lumen (interior) as it’s made.
WHAT IS IMPORTANT IS SIGNAL PEPTIDE IS AT THE BEGINNING BECAUSE RIBOSOME MOVES TO ER BEFORE TRANSLATION IS FINISHED** NEED TO KNOW AT N BEGINNING OF PROTEIN***
In some cases, the signal peptide is snipped off during translation and the finished protein is released into the interior of the ER (the lumen). In other cases, the signal peptide or another stretch of hydrophobic amino acids gets embedded in the ER membrane. This creates a transmembrane (membrane-crossing) segment that anchors the protein to the membrane.
for image: https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/protein-targeting-and-traffic
Transport through the endomembrane system
In the ER, proteins fold into their correct shapes, and may also get sugar groups attached to them. Most proteins are then transported to the Golgi apparatus in membrane vesicles. Some proteins, however, need to stay in the ER and do their jobs there. These proteins have amino acid tags that ensure they are shipped back to the ER if they “escape” into the Golgi.
In the Golgi apparatus, proteins may undergo more modifications (such as addition of sugar groups) and before going on to their final destinations. These destinations include lysosomes, the plasma membrane, and the cell exterior. Some proteins need to do their jobs in the Golgi (are “Golgi-resident), and a variety of molecular signals, including amino acid tags and structural features, are used to keep them there or bring them back^33cubed.
If they don’t have any specific tags, proteins are sent from the Golgi to the cell surface, where they’re secreted to the cell exterior (if they’re free-floating) or delivered to the plasma membrane (if they’re membrane-embedded). This default pathway is shown in the diagram above for a membrane protein, colored in green, that bears sugar groups, colored in purple.
Proteins are shipped to other destinations if they contain the right molecular labels. For example, proteins destined for the lysosome have a molecular tag consisting of a sugar with a phosphate group attached. In the Golgi apparatus, proteins with this tag are sorted into vesicles bound for the lysosome.
cytoskeleton job graph
shape and look of microtubules vs microfilaments vs intermediate filament
LDL receptor image
chart of molecules
cytoskeleton job graph 2
intermediate filament image
Eukartyoic cells have 3 types of cytoskeleton
microfilaments structure image
microfilaments function image
WHere is sodium more highly concentrated, inside or outside the cell?
Antiporters move two different ions or molecules in opposite directions across a membrane. Here, we know that sodium’s concentration gradient is used to power the movement of calcium. Since sodium tends to be far more highly concentrated outside the cell (due to the action of the sodium-potassium pump), it will flow inward when allowed to move down its gradient. Since Na+ and Ca2+ move in different directions, calcium ions must exit the cell.
