Chapter 2 Flashcards
An organelle is
an internal functional structure
that is located within the cytosol of a cell that carry out specialized functions.
- Some isolate harmful substances or provide environments for reactions not possible in the cytosol.
- some manage transport & maintain fluid balance in the cytosol.
- shapes of some organelles=elaborate cuz each organelle is adapted to perform a specific function
Plant cells differ from animal cells BECAUSE
plants and animals have very different
requirements for obtaining food and energy.
fungi have many of the same organelles as plants & animals . Fungi-like animals are heterotrophic, while the protist kingdom includes both heterotrophs and photosynthetic autotrophs
The most complex of all cells are
those of some single celled protists.
plasma membrane is
a dynamic (characterized by constant change-GOOGLE) barrier that surrounds the cytosol of the cell
- maintains an internal environment that allows
the organelle to carry out its particular function.
- control the amounts and types of substances that move in and out of the cell
The nucleus is
an organelle that contains & protects almost all the DNA (genetic material) in a eukaryotic cell
–> keeps DNA away from activity of the cytosol & from the metabolic reactions that might damage it
- Small amounts of DNA are present in 2
other organelles= chloroplasts & mitochondria
The nuclear envelope is
a two-layer membrane that surrounds the nucleus of a eukaryotic cell –> conists of 2 lipid bilayers folded together
- the outer layer connected to the endoplasmic reticulum (ER).
- Various proteins like receptors & transporters, are embedded in these bilayers. Others collect in tiny
pores that span the membrane
–> they help facilitate molecule transport across the nuclear membrane
Transport Across the Nuclear Membrane
Like other membranes, the nuclear envelope permits water and gases to cross freely,
- other substances require specific transporters and pumps located across the nuclear membrane to move between the nucleus and the cytosol.
- This selective transport system controls the entry and exit of molecules, ensuring the appropriate molecules involved in processes like DNA transcription into RNA and protein synthesis move in and out at the right times.
Nuclear membrane: Regulation and Protection of DNA
By regulating what molecules cross the nuclear membrane, the cell safeguards its DNA and controls RNA and protein production.
Proteins attached to the inner surface of the nuclear envelope help organize and anchor DNA, and play a role in passing DNA to daughter cells during mitosis.
Nucleolus
The nucleus also contains at least one nucleolus
(plural: nucleoli), a dense irregularly shaped region where subunits of ribosomes are assembled from proteins and RNA.
Nucleoplasm is
is a viscous fluid that is similar to cytosol located in the nucleus contains nucleoplasm, which is enclosed by the nuclear envelope.
The Endomembrane System is
a group of interacting organelles between the nucleus & the plasma membrane
- main function is to make lipids, enzymes,
and other proteins for secretion or insertion into cell membranes
- other specialized functions include destroying toxins & recycling wastes
- The components of the endomembrane system vary among different types of cells, but the most
common components are: Nucleus, the ERs, Golgi body, & vesicles
The Endoplasmic Reticulum is
a membrane-bound organelle that is folded into flattened sacs and tubes, and is an extension of the nuclear envelope
Rough ER
- areas of endoplasmic reticulum with ribosomes attached to the surface
- 1000s of ribosomes are attached to the outer surface of rough ER –> ribosomes synthesize polypeptide chains, which are released into the interior of the ER. Inside the ER, the proteins fold and take on their complex structure.
- Some of these proteins become part of the ER membrane, & others are sent to different cell parts.
- Cells that produce, store, & secrete large amounts of protein, such as gland cells in the pancreas, contain a lot of rough ER. –> Ex, ER-rich gland cells in the pancreas make and secrete enzymes that help to digest food in the small intestine.
Two kinds of ER—rough ER and smooth ER—are named for their _______________________________________
appearance in electron micrographs
smooth ER
areas of the endoplasmic reticulum without attached ribosomes
- does not make proteins
- Some of the polypeptides made in the rough ER end up in the smooth ER as enzymes
–>These enzymes produce most of the cell’s membrane lipids.
- They also break down carbs, fatty acids, & some drugs & poisons.
Vesicles are
a small, membrane-bound, saclike organelles, organelle that may transport, store, or digest substances within a cell
- are many types of vesicles with many different functions
- Some types transport proteins from one organelle to another, or to and from the plasma membrane
A peroxisome is
a type of vesicle
- contains enzymes that digest fatty acids & amino acids
- Peroxisomes form & divide on their own and have a variety of functions like inactivating hydrogen peroxide, a toxic by-product of fatty acid
breakdown
- Enzymes like catalase, in the peroxisomes convert hydrogen peroxide to H2O & O2, or they use hydrogen peroxide in reactions that break down alcohol & other toxins
Vacuoles
- a type of vesicle in both plant and animal cells
a liquid-filled organelle that stores waste and aids in cellular metabolism and water balance - Vacuoles seem empty under microscope but act like “trash cans,” isolating and disposing of wastes, debris, and toxic materials.
- fluid pressure keeps structures firm
Vacuoles: plants vs animals
- Plant cells have a large central vacuole where amino acids, sugars, ions, wastes, & toxins accumulate in a water-filled space.
- The fluid pressure inside the central vacuole helps keep plant cells, and structures like stems and leaves, firm.
- Usually, the central vacuole takes up 50 to 90 % of the cell’s interior
- Plant cells have bigger vacuoles than animal cells as they need to store food & water. This is cuz plants don’t have the ability to move freely like animals. (GOOGLE)
Lysosomes are
a small vesicle that contains digestive enzymes that aid in waste disposal
- its a type of vesicles that contain powerful digestive enzymes
- They fuse with vacuoles that carry particles or molecules for disposal, such as worn-out cell components.
- Lysosomal enzymes empty into these vacuoles and digest their contents.
A Golgi Body is
an organelle with folded membranes that usually looks like a stack of pancakes where the final packaging of proteins occurs
- Enzymes in a Golgi body put finishing touches on polypeptide chains and lipids that have been
delivered from the ER.–> They attach phosphate groups or sugars, & they cleave certain polypeptide chains.
- The end products (membrane proteins, proteins for secretion, and enzymes) are sorted & packaged into new vesicles that carry them to the plasma membrane or to lysosomes
- vesicles like lysosomes are found near it
Mitochondria are
The mitochondrion (plural: mitochondria) is an organelle with two membranes; the site of most
ATP synthesis during aerobic cellular respiration
- In plants & animals, most ATP is produced in a series of reactions that occur inside the mitochondria & require O2 from the breath u take
- These reactions can extract more energy from organic compounds than any other metabolic pathway.
The number of mitochondria varies based on….
the type of cell and the type of organism
- Cells that have a very high demand for energy tend to have many mitochondria.
- Ex, a single-celled yeast (a type of fungus) may have only one mitochondrion, whereas a human skeletal muscle cell may have a >= 1000.
Mitochondria Structure
Typical mitochondria=1-4 μm in length, few are as long as 10 μm.
- some are branched
- can change shape, split in two, and fuse together
- A mitochondrion has 2 membranes: 1 highly folded inside the other
–> This arrangement creates 2 compartments:
1) the mitochondrial matrix= the interior of the mitochondrion
2) the intermembrane space= the space between the 2 mitochondrial membranes
Mitochondria resemble… Elaborate
bacteria in size, form, and biochemistry
- They have their own DNA, which is similar to bacterial DNA
- They divide independently of the cell
& have their own ribosomes
- Such clues led to the widely accepted
endosymbiosis theory. –> mitochondria evolved from aerobic bacteria that took up permanent residence inside a host cell.
A plastid is
a membrane-bound organelle that is involved in photosynthesis & storage in plants and algae
- Chloroplasts, chromoplasts, & amyloplasts are common types of plastids.
A chloroplast is
a double-membrane-bound organelle that contains enzymes & pigments that are used to perform
photosynthesis in eukaryotic cells
- Most chloroplasts= oval or disk shape.
- the 2 outer membranes enclose a semifluid interior
called the stroma. (fluid-filled space that is
surrounding the grana - where
light-dependent reactions of
photosynthesis take place)
- The stroma contains enzymes and the chloroplast’s DNA.
- In the stroma, a 3rd highly folded membrane forms a single compartment.
- In many ways, chloroplasts resemble photosynthetic bacteria. Like mitochondria, they may have evolved by endosymbiosis.
A Chromoplast is
an organelle that makes & stores pigments other than chlorophyll
- They have an abundance of orange & red carotenoids, the pigments that colour many flowers, leaves, fruits, and roots. –> These colourful pigments are revealed in the autumn, when the chlorophyll in some plant leaves is broken down (due to lack of sunlight ig) & the bright fall colours of yellows, oranges, & reds are visible.
- The carotenoids are also visible in fruits. Ex, as a tomato ripens, its green chloroplasts are converted to red chromoplasts, & its colour changes
An amyloplast is
an unpigmented plastid (an organelle) that stores starch grains
- They are abundant in the cells of stems, tubers (underground stems), & seeds.
- In some plant cells, amyloplasts function as gravity-sensing organelles
The Cytoskeleton is
a dynamic system of protein filaments that provides cell structure, helps with cell division, and enables the
cell and inner organelles to move around
- between nucleus and plasma membrane
- Parts of the cytoskeleton reinforce,
organize, and move cell structures, and often the whole cell.
- Some cytoskeleton structures are permanent, whereas others only form at certain times
A microtubule is
a long, hollow cylinder that consists of subunits of the protein tubulin. –> part of cytoskeleton
- form a dynamic scaffolding for many cellular processes, rapidly assembling when they are needed and disassembling when they are not.
- Ex, some microtubules assemble before a eukaryotic cell divides, separate the cell’s duplicated chromosomes, & then disassemble. —> spindle fibres=are made of microtubules
A microfilament is
a fibre structure made from actin that is part of the cytoskeleton & is located in the cytosol of cells –> they strengthen or change the shape of eukaryotic cells.
- Actin microfilaments form at the edge of eukaryote cell, & drag or extend it in a certain direction
- In muscle cells, microfilaments of myosin & actin interact to bring about contraction
Intermediate filaments
the most stable part of a cell’s cytoskeleton.
- They consist of fibrous proteins, each with a globular head and tail and a rodlike centre.
- strengthen and maintain cell and tissue structures and are the toughest of the cytoskeleton filaments.
- r in the cytosol & nucleus of most animal cells.
- r more permanent fixtures of cells than microfilaments & microtubules (GOOGLE)
Organized arrays of microtubules are found in eukaryotic ____________ & _________
flagella(singular: flagellum), cilia (singular: cilium)
A flagellum is
a whiplike tail that is used in propulsion of both prokaryotic & eukaryotic cells
- Ex, a sperm has a flagellum
- longer & less abundant than cilia
cilia are
tiny hairlike structures that propel motile cells through fluid and stirs fluid around stationary cells
-move water and mucus in eukaryotes –> Ex, coordinated motion of cilia on cells that line your airways sweeps particles away from your lungs
- used for movement of prokaryotic cells
Structure of Flagella & Cilia
Both are whiplike structures made of organized arrays of microtubules.
- Microtubules arranged in a special array run lengthwise through flagella and cilia, stabilized by protein spokes and links.
- These microtubules originate from a centriole, located below the structure once it forms.
Pseudopods
- AKA “false feet”
temporary irregular lobes that bulge outward to move and feed on prey - formed by amoebas and other types of eukaryotic cell
- elongated microfilaments force the lobes to advance in a steady direction.
A cell wall is
a porous structure that surrounds the plasma membrane that protects, supports, & gives shape to the cell
- found in plant cells & in many protist & fungal cells
- Water & many solutes easily cross it on the way to and from the plasma membrane.
- The cell wall has a primary wall and develops a secondary wall during later stages of growth
Cell wall: primary wall is
a cellulose coating that surrounds a plant cell.
- It’s thin and pliable allowing the growing plant cell to enlarge.
- At maturity, the cells in some plant tissues stop enlarging and start secreting a material onto the
inner surface of the primary wall. –> This material forms a firm secondary wall
Cell Wall: Secondary wall is
a coating that is added to a plant cell wall; it is more rigid and often thicker than the primary cell wall
Also, some plant cells are covered in an outer _________ _______ which helps …..
waxy cuticle
protect exposed surfaces of soft parts of the plant and limits water loss on hot, dry days.
extracellular matrix (ECM) is
a molecular system that supports and protects a cell; a cell’s environment
( is a network of proteins and other molecules that surround and support cells in tissues. GOOGLE)
- This non-living, complex mixture of fibrous proteins and polysaccharides is secreted by cells and varies with the type of tissue
- It supports & anchors cells, separates tissues, and functions in cell signalling.
- The primary cell wall is a type of ECM, which is mostly cellulose in plants.
- The ECM of fungi is mainly chitin.
Extracellular Matrix (ECM) in Animals
- In most animals, the ECM consists of various kinds of carbohydrates and proteins.
- ECM is the basis of tissue organization, and it provides structural support.
–> Ex, bone is mostly ECM –> Bone ECM is mostly collagen, a fibrous protein, and it is hardened by mineral deposits. - Other protective structures, such as an insect exoskeleton or a bivalve shell, are also examples
of ECM
A cell junction is
a structure that allows cells to interact with each other and the surrounding environment
- In multicellular organisms, cell junctions are structures that connect a cell to other cells and to the environment.
- Cells send and receive ions, molecules, and signals through some junctions.
- Other junctions help cells recognize and stick to each other and to the ECM
Cystic Fibrosis (CF) is
a genetic disorder that impairs the lungs and gastrointestinal tract.
- caused by mutations in the gene that codes for the (cystic fibrosis transmembrane conductance regulator) CFTR protein.
- In CF, this process is disrupted, leading to thick, sticky mucus in lungs and gastrointestinal tract.
- When this happens in the lungs, breathing becomes difficult because mucus blocks the airways. –>this buildup of mucus also makes CF patients at risk for bacterial infections.
- In the GI system, thick mucus can clog pancreatic ducts, blocking enzymes that would normally enter the small intestine. –> This can destroy pancreas & thus the ability to produce necessary digestive enzymes. –> CF patients take dietary supplements to survive
CFTR’s function in healthy cells
- CFTR functions as a membrane transport protein in healthy cells. –> It moves chloride ions (Cl⁻) out of cells lining the lungs and intestinal tract into the mucus.
- This creates an electrical gradient that pulls sodium ions (Na⁺) in the same direction.
- The movement of Na⁺ and Cl⁻ causes water to flow into the mucus by osmosis, keeping it hydrated.
Cystic Fibrosis Treatment
Patients may have lung transplants as the disease progresses, but no cure
- CF is caused by a defect to a single gene= hope is in gene therapy to correct the CFTR gene mutation in the affected cells –> There are many technical hurdles
- 1 in 3900 Canadian children are born with Cystic Fibrosis
- treatment of CF patients is slowly improving but average lifespan = 40 years.
Why is one of the key factors in the evolution of the cell the development of the cell membrane?
- The semipermeable plasma membrane regulated the intake of nutrients & the elimination of waste
- also maintained a controlled environment for metabolic processes.
- Internal membranes later evolved, allowing compartmentalization of cellular functions –> enabling more complex processes to occur within cells.–>Ex, The nuclear envelope found in eukaryotic cells.
The Fluid Mosaic Model is
the idea that a biological membrane are not rigid and consist of a fluid phospholipid bilayer, in which proteins are embedded and float freely
–> Membranes are described as a fluid because the lipid & protein molecules are generally free to move laterally within the two layers.
- wide array of proteins = mosaic
Lipid molecules in cell membranes characteristics
- are highly dynamic or fluid, which is critical for membrane function.
- The lipid molecules exist in a double layer, called
a bilayer, that is less than 10 nm (nanometres) thick - Millions times/second, the lipid molecules may
vibrate, flex back and forth, spin around their long axis, move sideways, and exchange places within the same half of the bilayer
Proteins in cell membranes
Membranes contain a mosaic= wide assortment of proteins
- Some proteins are involved in transport and attachment.
- Others are enzymes that are used in a variety of biochemical pathways.
- Cuz the proteins are larger than the lipid molecules, they move more slowly in the fluid environment of the membrane.
- small number of membrane proteins anchor cytoskeleton filaments to the membrane, & thus do not move
Several of the lipid and protein components of some membranes have carbohydrate groups linked to them, forming _____________ and ________________ that face the exterior of the cell
glycolipids, glycoproteins
- These molecules often play a role in cell recognition and cell–cell interactions. (rmr lego analogy)
A glycolipid is
any membrane lipid that is bound to a carbohydrate
- can contain saturated & unsaturated components (Ms. Akhtar)
A glycoprotein is
a membrane component that contains a sugar/ carbohydrate bound to an amino acid
The plasma membrane is
the outer cell membrane (AKA cell membrane) & is responsible for regulating the substances moving in & out of the cell
Myelin is
a membrane that functions to insulate nerve fibres, is composed mostly of lipids (18 % protein and 82 % lipid)
Membrane asymmetry
- important characteristic of membranes
The proteins & other components of one half of the lipid bilayer differ from those that make up the
other half of the bilayer
–> Thus, proteins and components in the outer half perform different functions than those in the inner half. For instance… - External half: Contains glycolipids and glycoprotein
- Internal half: Contains cytoskeleton bound to proteins.
Membrane Asymmetry: Hormones & growth factors
- Hormones and growth factors bind to receptor proteins found only on the external surface, initiating signaling cascades inside the cell.
- Their binding triggers changes to distinctly different
protein components found on the inner surface of the membrane, spurring a cascade
of reactions that send a signal within the cell
–> Ex, Serotonin, a neurotransmitter, communicates between nerve cells, and its imbalance can lead to depression.–> Drugs can regulate serotonin levels to treat depression symptoms.
The Role of Phospholipids in cell membranes
The dominant lipids found in membranes= phospholipids
- A phospholipid = two fatty acid tails, which are usually linked to glycerol, a phosphate group, & a polar compound like choline
- This composition is vital for membrane function –> The fatty acid tails= hydrophobic & phosphate head= hydrophilic
- In H2O, phospholipids form a bilayer—two lipid molecules thick.
- This bilayer forms spontaneously cuz hydrophobic tails cluster together, & hydrophilic heads interact with H2O.
- The bilayer structure represents the lowest energy state, making it the most stable & likely arrangement.–>The formation of the bilayer structure is spontaneous because it lowers the overall energy of the system by avoiding unfavorable hydrophobic interactions with water and maximizing favorable hydrophilic interactions –> Essentially, its the least the energy costing configuration, thus it is favoured
The fluidity of the lipid bilayer is dependent on____________________________________________
on how tightly the lipid molecules can pack together.
Two factors influence packing: lipid composition and temperature
- Saturated fatty acids (no double bonds) have straight shapes, allowing tight packing.
- Unsaturated fatty acids (with double bonds) have bent shapes (rmr kinks), resulting in looser packing.
- Membranes remain fluid over a range of temperatures but can form a semisolid gel at lower temperatures.
- @ any given temp, fluidity of a membrane is related to the degree to which the membrane lipids are unsaturated. The more unsaturated a membrane is, the lower its gelling temperature
Sterol is
a type of steroid (4 attached carbon rings) with an OH group at one end and a non-polar hydrocarbon chain at the other
Besides lipids, a group of compounds called __________ also influence membrane fluidity
sterols
- Cholesterol, a sterol, is found in animal cell membranes but not in plant or prokaryotic membranes.
- At high temp, sterols reduce membrane fluidity by restraining lipid movement.
- At low temp, sterols prevent the membrane from becoming a non-fluid gel by filling spaces between lipid molecules and keeping them apart.
- Sterols act as membrane stabilizers, ensuring proper membrane function across temperature changes.
Membrane proteins can be separated into the following four functional categories. List Them.
- Transport
- Enzymatic Activity
- Triggering Signals
- Attachment & Recognition
All of these functions may exist in a single membrane, & one protein or protein complex may serve more than one of these function
The Role of Membrane Proteins: Transport
- Many substances can’t freely diffuse through the lipid bilayer of membranes.
- Instead, some compounds can cross the membrane through hydrophilic protein channels
- Certain membrane proteins can undergo shape changes to shuttle molecules across the membrane from one side to the other.
Ms.Akhtar
Passive Transport= no ATP needed –> material travels with help of concentration gradient (high conc to low conc)
Active Transport= ATP needed –> material needs to travel against concentration gradient, & therefore u need energy
The Role of Membrane Proteins: Enzymatic activity
Some membrane proteins, such as those associated with respiration and photosynthesis, are enzymes.
The Role of Membrane Proteins: Triggering signals
- Membrane proteins may bind to specific chemicals, such as hormones.
- Binding to these chemicals triggers changes on the inner surface of the membrane, starting a cascade of events within the cell
The Role of Membrane Proteins: Attachment & recognition
- Membrane proteins exposed to both internal and external surfaces serve as attachment points for cytoskeletal elements and extracellular matrix components.
- they play roles in cell–cell recognition and help bond cells to the extracellular matrix.
- Ex, surface proteins can recognize elements of disease-causing microbes that may try to invade cells,
triggering an immune response.
Beyond function, all membrane proteins can be separated into 2 additional categories. List them
Integral & Peripheral membrane proteins
An integral membrane protein is
a protein that is embedded in the lipid bilayer
- All integral membrane proteins have at least one region that interacts with the hydrophobic core of the membrane.
- However, most integral proteins are transmembrane proteins –> they span the entire membrane bilayer (vertically, Im pretty sure?) and have regions that are exposed to the aq environment on both sides of the membrane
A peripheral membrane protein is
a protein on the surface of the membrane
- do not interact with the hydrophobic core of the membrane
- Peripheral proteins are held to membrane surfaces by non-covalent bonds (hydrogen bonds and ionic bonds) –> usually by interacting with exposed portions of integral proteins as well as directly with membrane lipid molecules
- Most peripheral proteins are found on the cytosol side of the membrane.
–> Some peripheral proteins are part of the cytoskeleton. Ex, microtubules, microfilaments, intermediate filaments, & proteins that link the cytoskeleton together.
- These proteins hold some integral membrane
proteins in place via these interactions
The transmembrane exchange of materials is not limited to the outer surface of the cell. Elaborate.
- many substances must be able to cross the organelle membranes in eukaryotes.
- In mitochondria & chloroplasts, chemical reactions take place in the internal fluids, separated from cytosol by 2 or 3 membrane layers.
–>for these reactions to occur, reactants must be able to enter the organelle, while products must be permitted to leave.
Passive Transport is
the movement of a substance across a membrane without spending energy
- Diffusion drives passive transport
Diffusion is
the net movement of a substance from a region of higher concentration to a region of lower concentration. –>occurs cuz molecules are in constant motion & in an ideal closed environment, tend to become uniformly distributed in space.
- the primary mechanism of solute movement in cells & between cellular compartments separated by a membrane.
- As diffusion proceeds, there is a net movement of molecules in one direction until the concentrations on both sides of the membrane are equal.
The rate of diffusion depends on….
the concentration diff, or concentration
gradient, that exists between two areas or across a membrane.
- The larger the gradient= faster the rate of diffusion
Dynamic Equilibrium is
the state in which continuous action results in balanced conditions –> However, there is no net change in concentration
- after the conc of molecules or ions is = in both regions, the molecules or ions continue to move from one region to another
Membranes have selective permeability, which means?
which means that some molecules can diffuse very rapidly across a membrane while other molecules are unable to transit the membrane without assistance
What factors determine the ease with which a molecule or ion can move across a membrane?
Size & Charge
There are 2 types of passive transport. List them
simple diffusion and facilitated diffusion
Simple diffusion is
the ability of small & non-polar substances to move across a membrane unassisted
- Ex, O2 and CO2, are readily soluble in the hydrophobic interior of a membrane & move rapidly from one side to the other
- Non-polar steroid hormones & non-polar drugs can also cross a membrane easily
- Small uncharged molecules, such as H2O & glycerol, even though they are polar, are still able to move quite rapidly across a membrane. –> but less than O2 & CO2 i think
- In contrast, most membranes r basically impermeable 2 large molecules & ions. –> relative to
transport of water, the movement of small ions is about one-billionth the speed.
Facilitated Diffusion is
the facilitated transport of ions & polar molecules through a membrane via protein complexes that span the membrane –> happens cuz the slow rate of simple diffusion of these substances may not keep up with the demand that metabolic processes
- Although facilitated diffusion involves specific transporters, movement of the molecules & ions is still driven by diffusion based on a concentration gradient across the membrane. –> When equilibrium is reached, facilitated diffusion stops.
transport proteins are
an integral membrane protein that carry out facilitated diffusion of molecules to cross a membrane
- Many transport proteins r very selective about which solutes they carry. –> Ex, those that carry glucose r unable to transport fructose, which is structurally very similar. –> This specificity allows for tight control over what gets in and out of cells & cellular compartments. - The types of transport proteins that r present in the plasma membrane & on the outer membrane of mitochondria depend ultimately on the type of cell & growth conditions
- There are 2 types of transport proteins: channel proteins & carrier proteins
A channel protein is
a hydrophilic pathway in a membrane that enables H2O & ions to pass through
- Other channel proteins facilitate the transport of ions such as Na+, K+, Ca2+, & Cl-
- Most of these ion channels, occuring in all eukaryotes, are voltage-gated channels–> switching between open & closed states in response to membrane voltage changes or signal molecules.
- In animals, voltage-gated ion channels r critical for nerve conduction & control of muscle contraction.
- Malfunctioning ion channels in humans can cause muscle ion channel diseases, leading to symptoms like muscle stiffness or weakness.
A Carrier protein is
a protein that binds to a molecule and transports it across the lipid bilayer
- Each carrier protein binds to a specific solute, like a glucose molecule or a particular amino acid, & transports it across the lipid bilayer
- Diffusion= driving mechanism for moving a solute down its concentration gradient, but it would not be able to move through the membrane without carrier proteins.
- When transporting, the carrier protein changes shape, allowing the solute to move from one side of the membrane to the other
Osmosis is
the passive diffusion of water across a membrane
- In living cells, the inward or outward movement of H2O by osmosis develops forces that can cause cells to swell or shrink.
- H2O always diffuses from an area of lower solute concentration (high water concentration) to an area of greater solute concentration (low water concentration) & is thus influenced by any diff or change in solute concentration on either side of a membrane.
Tonicity (slideshow)
Refers to the concentration of solutesActive Membrane Transport
- a relative term comparing two different solutions
hypotonic
the property of a solution that has a lower solute concentration than another solution
- If the solution that is surrounding a cell contains dissolved substances at lower
concentrations than they are in the cell, the solution is said to be hypotonic to the cell.
- When a cell is in a hypotonic solution, H2O enters by osmosis and the cell tends to swell –> Animal cells in a hypotonic solution may actually swell to the point of bursting.
hypertonic
the property of a solution that has a higher solute concentration than another solution
- an organism in a solution that contains salts or other molecules at higher concentrations than they are in its body must expend energy to replace the H2O that is lost by osmosis
Isotonic
the property of a solution that has the same solute concentration as another solution
- The concentration of water inside & outside cells is equal
active transport is
the movement of substances across membranes against their concentration gradient using pumps
- it is an energy-dependent process, usually ATP, to pump molecules across a membrane.
–> Scientists estimate that about 25 % of a cell’s energy requirements are for active transport.
- Using “pumps,” active transport is able to concentrate specific compounds inside cells & push others out
–> Ex, in muscle cells, the calcium ion conc in one compartment can be as much as 30 000 times as great as the calcium ion concentration in another
compartment. –> Such a huge concentration difference, which is necessary for normal muscle function, is established & maintained through active transport
Primary Active Transport
All primary active transport pumps move positively charged ions, such as H+, Ca2+, Na+, & K+, across membranes.
- These pumps establish their own conc gradients that are crucial for cellular functions.
- H+ (proton) pump: in the plasma membrane pushes H+ ions from the cytosol to the cell exterior. This pump temporarily binds to a phosphate group removed from ATP during the pumping cycle
- Ca2+ (calcium) pump: Pumps calcium from the cytosol to the cell exterior and into the ER vesicles.
- Na+/K+ (sodium–potassium) pump: located in plasma membrane pushes 3 Na+ ions out of the cell and 2 K+ ions into the cell, simultaneously.
https://www.youtube.com/watch?v=7NY6XdPBhxo
Voltage (an electrical potential difference) across the plasma or internal membrane is
a difference in electrical charge on either side of the membrane.
- This diff results from an unequal net distribution of the many cations & anions
- Differences in the various ion concentrations are the result of both passive & active transport, & chem reactions that take place on both sides of the membrane
- The combined effects of the voltage and the differences in ion conc create an electrochemical gradient.
An electrochemical gradient is
a form of stored potential energy that can be used for other transport mechanisms.
- Ex, the electrochemical gradient across the plasma membrane is involved in the movement of ions associated with nerve impulse transmission
- created by the combined effects of a diff in electrical
potential energy (voltage) & a diff in the conc gradients of ions
https://www.youtube.com/watch?v=7NY6XdPBhxo
Secondary Active Transport
- Secondary active transport uses the concentration gradient of an ion, created by a primary pump, as its energy source.
- Ex, the driving force for most secondary active transport in animal cells is the high outside/low inside Na+ gradient set up by the sodium–potassium pump
- Secondary active transport refers to the movement of molecules across a cell membrane using the energy derived from the movement of ions down their concentration gradient, which was initially established by a primary active transport pump (like the sodium–potassium pump). The process does not directly use ATP, but rather the energy stored in these ion gradients.
2 mechanisms facilitate secondary active transport: List them & elaborate
symport & antiport
SYMPORT
- In symport, the solute (the molecule being transported) and the driving ion (like Na+) move through the same membrane channel in the same direction.
- The movement of the driving ion down its gradient provides the energy needed to bring the solute along with it against its conc gradient
- Ex, the sodium-glucose symporter, which uses the Na+ gradient to transport glucose into cells.
ANTIPORT
- In antiport, the driving ion moves in one direction through the membrane channel, while another molecule (solute) is transported in the opposite direction.
- The energy released by the driving ion moving down its concentration gradient powers the active transport of another molecule against its own gradient.
- Ex, in Na+/Ca2+ antiport, Na+ moves into the cell while Ca2+ is pumped out.
- The ion moving down its electrochemical gradient= the driving ion because it is movement of this ion that drives the uphill movement of another ion/molecule (driven ion/molecule)
The largest molecules that can be transported across a cellular membrane by passive or active transport are…
about the size of amino acids or monosaccharides such as glucose.
What are the 2 mechanisms by which eukaryotic cells can export and import larger molecules .
exocytosis & endocytosis
- Exocytosis & endocytosis also contribute to the back-and-forth flow of portions of actual membranes between the endomembrane system & the plasma membrane.
- Both exocytosis and endocytosis require
energy. –>both processes stop if the ability of a cell to make ATP is inhibited
Endocytosis
- IMPORT is done by endocytosis= carry proteins, larger aggregates of molecules, or even whole cells from cell exterior into cytosol
- Takes place in most eukaryotic cells
STEPS
1) proteins & other substances are trapped in a pit-like depression that bulges inward from the plasma membrane
2) The depression then pinches off as an endocytic vesicle
3) rmr the cytosol side of the lipid bilayer becomes the outer layer of the vesicle & the extracellular side of the lipid bilayer becomes the inner layer of the vesicle. (from video)
https://www.youtube.com/watch?v=3ztyiciTDsc
Exocytosis
- EXPORT of materials is done by exocytosis= primarily
secretory proteins & some waste from the cytosol to cell exterior - All eukaryotic cells secrete materials outside the cell through exocytosis
- Ex, glandular cells in animals secrete peptide hormones or milk proteins, & cells lining the digestive tract secrete mucus & digestive enzymes.
- Ex, plant cells secrete carbs to build strong cell walls.
STEPS
1) secretory vesicles move through the cytosol & contact the plasma membrane
2) The vesicle membrane fuses with the plasma membrane, releasing the contents of the vesicle outside of the cell
https://www.youtube.com/watch?v=3ztyiciTDsc
Endocytosis takes place in most eukaryotic cells by one of three distinct but related pathways (there r 3 types of endocytosis). List them.
- pinocytosis
- receptor-mediated endocytosis
- Phagocytosis
Pinocytosis
- simplest of the 3 endocytosis pathways.
- it’s the bulk-phase endocytosis aka pinocytosis, meaning “cell drinking”
- extracellular water is taken in, along with any molecules that happen to be in solution in the water
- No binding by surface receptors takes place
Receptor-mediated Endocytosis
- the molecules to be taken in are bound to the outer cell surface by receptor proteins –> The receptors bind to only certain molecule, usually proteins or molecules carried by proteins.
- After binding, the receptors collect into a pit coated with a network of proteins on the cytosol side, called clathrin
- The coated pit then breaks free of the membrane to form a vesicle
- In cytosol, the vesicle loses its clathrin coating & may fuse with a lysosome. –> Lysosome enzymes then digest the cargo, breaking it down into molecules that r useful to the cell.
Phagocytosis
- the pathway in which cells engulf bacteria, parts of dead cells, viruses, or other foreign particles.
- most commonly performed by a macrophage, a type of white blood cell that helps to fight infection by engulfing invading organisms or particles.
