Bio quiz 4

fluid mosiac

used to describe a cell membrane.

Membrane is not rigid, phospholipids can move sideways within their layer, flexible.

Also has many different components, including phospholipids, cholesterol, different types of proteins, carbohydrates, and different types of lipids

hydrophobic interactions

_ are primarily what hold the membrane together, rather than the strong covalent bonds between phospholipids.

Interactions aren’t rigid (between hydrophobic tails), and membrane can remain intact while its molecules move.

membrane proteins

_ are proteins embedded in or associated with the membrane. They are generally much larger phospholipids, moving slower.

Some drift, moving around with the membrane

Some are attached to the cytoskeleton, held relatively stationary

Some are attached to the extracellular matrix (ECM), held in place

Some move directionally along cytoskeletal fibers by motor proteins

Larry Frye and Michael Edidin experiment

experiment that proved membrane proteins can move. Took cells from a mouse and human, fused them together, and formed one hybrid cell containing both types of membrane proteins. Overtime, the proteins of both cells mixed together, providing at least some membrane proteins are capable of lateral (sideways) movement within the plasma membrane.

slows, solidify, fluid

as temperature decreases, molecular movement _, and eventually, the membrane can _ and become too rigid.

likewise, in a higher temperature environments, membranes can become too _.

saturated fatty acid, less

the fatty acid whose hydrocarbon tail has no carbon-carbon double bonds, allowing tails to pack closely together without kinks, making the membrane _ fluid

unsaturated fatty acid, more

the fatty acid whose tail contains one or more carbon-carbon double bonds, creating a kink in the hydrocarbon tail. They are not as tightly packed, allowing for a _ fluid (moving) membrane.

Important as in low temperatures, phospholipid tails are prevented from packing as tightly, allowing a membrane to remain fluid at a lower temperature before solidifying.

membrane lipid composition

organisms can adapt their membrane composition by altering their _, allowing them to maintain the proper level of membrane fluidity.

Occurs when a cold environment can make membranes too rigid, whereas a warm environment can make membranes too fluid.

cholesterol

At high temperatures, _helps prevent the membrane from becoming too fluid by restraining phospholipid movement.

At low temperatures, _ gets between phospholipids that want to pack tightly together, preventing them from packing too closely.

Serves as a buffer for changes in membrane fluidity.

rigid, fluid

If a membrane becomes too _:

• permeability (what enters and exits the cell) changes

• membrane proteins may not function properly

• enzymatic (catalyst) proteins in the membrane may become inactive

However, if it’s too _, membrane proteins may also be unable to function properly.

proteins

_ determine most of the membrane’s functions as they can perform specific jobs. They can:

• transport substances

• receive signals

• catalyze reactions

• identify cells

• attach cells to other structures

• connect the membrane to the cytoskeleton

• help cells communicate

2 identical cell membranes can have different functions by containing different _.

integral membrane proteins, transmembrane

Amphipathic proteins that penetrate into the hydrophobic interior of the phospholipid bilayer, embedded in the membrane.

Many are _ proteins, meaning they span the entire membrane and are exposed to both the inside and outside of the membrane

• The portion of the protein inside the membrane need to be compatible with a hydrophobic environment (contains non-polar amino acids that often form an alpha-helix).

• The portion of the proteins exposed to the cytosol and extracellular fluids contain hydrophilic region. Some form hydrophilic channels, allowing hydrophilic substances such as ions, water, and other hydrophilic molecules to pass through

peripheral membrane proteins

proteins that are loosely attached to the membrane surface (inside and outside). May attach to phospholipids or exposed portions of integral proteins.

cytoplasmic side

The _ of the membrane refers to the side facing inside the cell. here, some membrane proteins attach to the cytoskeleton, which helps hold these proteins in specific positions.

extracellular matrix (ECM)

The _ is located outside an animal cell, containing materials outside cells that provide structural support and organization. Some membrane proteins attach to the _, helping give animal cells a stronger framework than the plasma membrane alone can provide.

membrane carbohydrates

_ are carbohydrates generally located on the extracellular surface. They are usually relatively short branched chains that contain fewer than 15 sugar units.

• These can be attached to lipids, forming glycolipid (carbohydrate + sugar).

• Most can also attach to proteins, forming glycoproteins (carbohydrate + protein)

These are important as they allow for cell-cell recognition.

extracellular surface

the _ refers to the outside-facing surface of the plasma membrane

cell-cell recognition

allows for cells to distinguish one type of cell from another. important for both embryonic development and the immune system

embryonic development

during development, cells need to sort themselves into appropriate tissues and organs. Cell recognition helps them determine which neighboring cells they should interact with. This exemplifies _

immune system

Your _ needs to distinguish your own cells from foreign cells. Cell-surface molecules (membrane carbohydrates) help with this recognition.

asymmetric

Because a cell has two sides, the extracellular side and the cytoplasmic side, the membrane is therefore _. This means the 2 sides have different arrangements. Examples:

• the 2 lipid layers can have different lipid compositions

• proteins have specific orientations

• carbohydrates are primarily located on the extracellular surface

The membrane’s _ arrangement is established as the membrane is being built and processed through the ER and Golgi, which help determine the organization and orientation of lipids, proteins, and carbohydrates. Its organization is established during the construction and processing/trafficking of membrane components .

membrane traffic

refers to substances constantly moving into and out of the cell

selectively permeability

Defined as the membrane allowing some substances to cross more easily than others. This is essential to life because the cell needs to control what’s inside and outside.

Depends on both the phospholipid bilayer and transport proteins.

permeability

how easily a substance can pass through a barrier. high _ means a substance crosses easily, while low _ means a substance has difficulty crossing.

supramolecular structure

the biological membrane is an example of a _. A _ is a structure made when many individual molecules organize together into a larger structure (emergent properties)

emergent property

an _ is a property that appears when individual components are organized together.

Ex: many phospholipids form a membrane

“form fits function”

meaning: the structure of something helps explain what it’s capable of doing

ions

_ are charged particles. Cells need specific concentrations of these _. Therefore, the cell may need to:

• allow an _ to enter

• prevent an _ from entering

• allow an _ to leave

• prevent an _ from leaving

Membranes control all of this

hydrophobic

_ substances interact favorably with the _ interior of the membrane. They can dissolve into the lipid portion of the membrane, therefore being able to cross.

Non-polar, _ molecules cross the lipid bilayer relatively easily and don’t require a transport protein to cross.

polar, ions

_ molecules, including water, have more difficulty crossing membranes due to their hydrophilic properties. The larger the molecule, the harder it is to cross.

_ are charged, interacting strongly with surrounding water molecules. They form a shell of water around themselves, making it extremely difficult for them to enter the hydrophobic interior of the membrane, even more than polar molecules.

channel proteins

a type of transport protein that forms a hydrophilic passage (tunnel) through the membrane, allowing specific substances to pass through without directly interacting with the hydrophobic membrane interior

aquaporins

a type of channel protein that facilitates the movement of water across membranes (specialized hydrophilic pathway for water).

A single _ allows 2 billion water molecules per second.

Most consist of 4 identical polypeptide subunits, which each form a channel, each allowing water molecules to pass through in single file.

carrier protein

another type of transport protein. creates an opening in the membrane (revolving door). They:

• bind/hold onto its specific substance

• changes shape

• moves the substance across the membrane

• releases it on the other side

Can participate in:

• facilitated diffusion: substance moving down its gradient without energy

• active transport: substance being moved against its gradient using energy

transport proteins

proteins that transport substances into and out of the cell. Two main types include channel and carrier proteins.

They recognize particular substances, allowing them in. Only substances that fit the appropriate interaction can use that transporter.

They usually transport one specific substance or small group of related substances.

Form fits function: Can reject structural isomers as _ have a particular 3D structure (think lock and key)

glucose carrier protein

A _ is a transport protein that allows glucose to cross the membrane, making glucose cross approximately 50,000 times faster than it would individually.

structural isomers

Molecules that have the same molecular formula but different arrangements of atoms. Chemically similar, but not identical

ex: glucose and fructose

concentration gradient

a difference in concentration of one substance between 2 regions (more molecules somewhere than another place). Each substance has it's own _, diffusing accordingly and independently of the concentration gradients of other substances.

Molecules tend to move from regions of higher concentration to lower concentration when they can move freely.

determines directions molecules move

passive transport

transport of molecules that does not require the cell to expend metabolic energy to drive the transport. They move according to their gradient (generally high→low)

• channel proteins

• some carrier proteins (when moving down the gradient)

active transport

transport of molecules that requires the cell to expend metabolic energy to drive the transport. Can move substances against their gradient (generally low→high)

• some carrier proteins (when moving up the gradient)

thermal energy

energy that keeps the particles in matter in constant motion. Even if a substance appears still, its molecules are moving around randomly.

diffusion

the movement of particles so that they spread out into available space.

Though individual molecules move randomly, the overall population of molecules can show a directional movement as most move from a region of higher to lower concentration.

Occurs spontaneously, meaning it occurs without the cell needing to supply energy to make it happen, as molecules already have thermal energy and are already moving randomly.

A form of passive transport as ATP is not required.

dynamic equilibrium

as molecules undergo diffusion, eventually, there should be an equal concentration in both regions. This is where you obtain _.

Molecules are still in motion, but move at an equal rate from one region to the other. Therefore, there is no net movement in either direction.

cellular respiration

_ is an example of cell diffusion, as cells require O2 for it. The outside of a cell has higher O2 ratings and therefore O2 diffuses inside. The concentration gradually increases as the concentration gradient continues, continuing as long as _ keeps consuming O2, not stopping as it continues being consumed.

osmosis

the diffusion of free water (water that doesn’t interact with other molecules, less solute) across a selectively permeable membrane. water moves towards the side with higher solute concentration (low free water)

tonicity

the ability of a surrounding solution to cause a cell to gain or lose water (what happens to the cell). Determined by:

• Solute concentration (how much solute is present)

• membrane permeability (can that solute cross the membrane?)

nonpenetrating solutes

a solute that cannot cross the membrane (affects where water moves instead).

• If the surrounding solution has more _ than the cell, water leaves the cell

• If the surrounding solution has less _ than the cell, water enters the cell

isotonic solution

An _ has approximately the same effective concentration of nonpenetrating solutes as the cell, so water moves in and out at equal rates (dynamic equilibrium)

No net water movement, cell remains stable

hypertonic

the surrounding solution has a higher concentration of nonpenetrating solutes than the cell, so water moves outside the cell.

• Animal cell: leads to the shrinking, and often damaging or dying, of animal cells (lack a cell wall)

• Plant cell: water leaves the shell, makes cell shrink, causing its plasma membrane to pull away from the cell wall

hypotonic

the surrounding solution has a lower concentration of nonpenetrating solutes than the cell, so water moves inside the cell.

• Animal cell: leads to the swelling, and often the lyse (burst) of animal cells

• Plant cells: have a rigid cell wall, resisting expansion

turgor pressure, turgid

as water enters, cell contents push outward against the cell wall. The cell wall pushes back. This pressure is known as _. Eventually, the cell becomes very firm. This state is called _, which represents a generally healthy state.

Many plants rely on these cells for mechanical support. A plant’s cells contain enough water to maintain pressure against their cell walls, allowing them to stay firm upright.

flaccid

When a plant cell and its surroundings are isotonic, there’s no net tendency for water to enter, becoming _, or limp. This can cause plants to wilt.

plasmolysis

occurs when water leaves the shell in a hypertonic environment, making the cell shrink and causing its plasma membrane to pull away from the cell wall. this is:

water loss → _ → wilting → potentially cell death

osmoregulation

the regulation of solute concentrations and water balance. Necessary as cells can’t tolerate unlimited water gain or loss.

too much water → swelling → possible lysis

too little water → shrinking → damage/death

contractile vacuole

A _ collects excess water and expels it from the cell.

water enters the cell → _ removes excess water → cell doesn’t burst

facilitated diffusion

diffusion of a substance (crossing the membrane) that is helped by a membrane transport protein

The transport protein helps, doesn’t power (passive transport)

simple diffusion

diffusion of a substance (crossing the membrane) that is done directly through the lipid bilayer (a type of passive transport)

only applies to non-polar molecules

ion channels

channel proteins that transport ions (selective; might let K+ through but not Na+)

gated channels

ion channels with a “gate” that can open or close in response to a stimulus, meaning the cell can control when an ion is allowed through

Important in the nervous system, as nerve cells depend on controlled movement of ions across their membranes. They can generate and reset electrical signals by opening and closing ion channels.

electrical stimulus

a type of stimuli that can open a gated channel, responding to changes in electrical conditions

ex: a nerve cell’s ion channel can open in response to an _, which helps restore the cell’s ability to fire another signal

chemical stimulus

a type of stimuli that can open a gated channel, responding to changes in chemical conditions.

A specific substance binds to the channel, acting as a signal to open or close the channel. Isn’t necessarily the substance being transported

ATP

most active transport gets its energy from _, the cell’s major usable energy molecule formed in the mitochondria.

It powers transport by transferring its terminal phosphate group direct to the transport protein, which can cause the protein to change shape. This shape change allows the protein to move a substance across the membrane.

ATP hydrolysis

when ATP is broken down and energy is released, this is called _. This energy can be used to perform cellular work

ATP → ADP + phosphate + energy

sodium-potassium pump

a form of active transport that moves 3 Na+ out and 2 K+ in for every cycle of the pump. Requires ATP, which changes the pump shape.

Important as both Na+ and K+ are both positively changed ions, and 3 positive charges exit while only 2 enter again. The net charge concludes that a +1 charge leaves the cell, making the inside of the cell relatively more negative compared to the outside.

membrane potential

all cells have a difference in electrical charge across their plasma membrane, known as the _. It is the electrical difference between the inside and outside of the cell.

The inside is generally more negative relative to the outside, approximately -50 to -200 mV (negative sign indicating the inside is relatively negative to the outside)

Cations are electrically attracted toward the negative interior, encouraging cations into the cell.

Anions are repelled by the negative interior, so anions tend to go out of the cell.

voltage

a form of electrical potential energy. When opposite charges are separated, there is stored potential energy (like a battery)

difference in potential energy in 2 points

electrochemical gradient

Ions are affected by both a chemical force (concentration gradients) and an electrical force (due to their charges). Together, this is called the _.

For ions, we can’t simply say they move down their concentration gradient (as with regular molecules). Instead, we determine where concentration is higher AND where the electrical charge attracts or repels the ion.

Ions move according to their _. When chemical and electrical forces oppose one another, the overall movement depends on the combined _, and may require active transport to maintain the desired gradient.

electrogenic pumps

a pump that contributes to the voltage across the membrane

ex: the sodium-potassium pump (in animal cells)

proton pump

electrogenic pump found in plants, fungi, and bacteria. The _ actively transports H+ out of the cell.

think: a positive charge is moved outside the cell, creating an electrical difference across the membrane

1. The cell uses ATP to pump H+ out

2. A difference in H+ concentration is created

3. H+ now wants to move back down its gradient

4. the cell can harness that movement to perform work

The resulting H+ gradient, using ATP, stores usable energy in a gradient that can later be used for other cellular work.

Cotransport, cotransporter

_ is a type of protein gradient, defined as the movement from one substance down its gradient provides energy to move another substance against its gradient. When one substance goes downhill, the energy is used to push another uphill. The protein responsible for this is called a _, which transports 2 substances together, one moving down its gradient while the other moves against its gradient.

sucrose

Plant cell example of cotransport. A plant uses ATP to power a proton pump that moves H+ out of the cell, creating a large H+ gradient. The outside now has a higher concentration of H+ outside than inside the cell, so H+ wants to move back in. Plant walls also want _ to enter (for non-photosynthetic tissues that also require sugar), but that would be against its concentration gradient. Also that’d normally require energy, the plant uses the H+ gradient to allow both H+ and _ into the cell simultaneously. The energy from H+ moving downhill drives sucrose uphill.

glucose

Animal cell example of cotransport, including Na+ and _. Inside an intestinal cell, Na+ concentration is relatively low, whereas outside, Na+ concentration is relatively high. Na+ wants to enter the intestinal cell. This downhill movement of Na+ brings _ into the cell simultaneously, despite _ moving against its own concentration gradient. This increases the concentration of solutes inside the intestinal cell, allowing water to follow them through osmosis, allowing the body to absorb water much more effectively.

_ eventually enters the blood through facilitated diffusion (moving down its concentration gradient) while Na+ is pumped out using active transport.

vesicles

proteins, polysaccharides, and large particles are too large to pass through a channel or carrier protein. Therefore, they rely on _, a small membrane-bound sac, for transportation.

bulk transport

Instead of a molecule going through a membrane, the cell’s molecule goes:

molecule → inside vesicle → vesicle moves → vesicle interacts with membrane

Called _ because the cell is moving a large amount of material at once.

Requires energy as the cell has to rearrange the membrane, form vesicles, move vesicles, and fuse membranes or pinch membranes off (active cellular processes).

exocytosis

a vesicle that releases its materials outside the cell is referred to as _.

Golgi apparatus

vesicles commonly come from the _, which processes and packages molecules. Once the _ has packaged something that needs to leave the cell, a piece of the _ membrane can bud off.

transport vesicle

a vesicle that moves molecules within the cell between internal compartments (i.e carrying proteins from the ER to the Golgi apparatus). Contains material that needs to be transported

secretory vesicle

a vesicle that moves molecules out of the cell or to the cell membrane via exocytosis

microtubules

secretory vesicles arrive at the plasma membrane by traveling along _, a part of the cytoskeleton that serves as tracks inside the cell.

fuse

when a vesicle membrane comes into contact with the plasma membrane, specific proteins help the two membranes interact, allowing them to _, or to become one continuous membrane, after the materials inside the vesicle are secreted. The vesicle membrane becomes part of the plasma membrane.

secretion

a cell produces something and releases it

endocytosis

occurs when a cell wants to bring material into the cell using a vesicle.

pocket

During endocytosis, the plasma membrane begins to bend inward, forming a _. The material outside the cell becomes trapped inside this _. It gets deeper, until eventually, the membrane pinches off, forming a new vesicle that is now inside the cell containing material that was originally outside.

phagocytosis

a form of endocytosis, “cellular eating.” Refers to the cell taking in large particles. During _, the cell surrounds a large particle and brings it inside a vesicle.

Especially useful for cells that need to engulf large particles

pinocytosis

a form of endocytosis, “cellular drinking.” Refers to a cell taking in extracellular fluid and dissolved substances. The plasma membrane forms a small pocket, the fluid gets trapped, the pocket pinches off, and now the cell has a vesicle containing fluid from outside

receptor-mediated endocytosis

_ is the most selective form of endocytosis. Instead of the cell grabbing whatever happens to be nearby, it uses receptors

receptor

a protein that specifically binds to a particular molecule

LDLs (low-density lipoproteins)

Located outside the cell membrane, _ grab onto cholesterol (which is needed for membrane synthesis and making other steroids) and carries cholesterol through the bloodstream.

LDL receptors

The cell has special proteins on its plasma membrane called _, which bind with the LDL. Once bound, the cell brings the LDL using receptor-mediated endocytosis.

Think: lock

familial hypercholesterolemia

an inherited condition called _ that causes individuals to have very high levels of cholesterol in their blood. this is caused by their LDL receptor proteins being defective or missing, so LDL can’t effectively enter the cell and remains in the blood.

atherosclerosis

the cholesterol carried by LDL can accumulate in the bloodstream and contribute to _, which involves buildup of lipids within blood vessel walls. This buildup can narrow the blood vessel, making it harder for blood to flow through. This can cause serious cardiovascular problems (including heart damage or stroke)

membrane recycling/remodeling

endocytosis and exocytosis happen continually and balance each other.

Exocytosis adds membrane (vesicle membranes fusing with the membrane)

Endocytosis removes membrane (plasma membrane folds inward and pinches off, forming a vesicle)

The fairly constant total amount of plasma membrane is called _ and happens continually in most eukaryotic cells.

cell signaling

different cells need to coordinate things like when to:

• grow

• divide

• make proteins

• release substances

• use energy

• respond to changes

• communicate with other cells

This coordination is possible because cells communicate with one another, known as _. Essentially, one cell sends a signal, another receives it, and the receiving cell changes its activity.

local signaling

occurs when the receiving cell is very close to the signaling cell

gap junctions, plasmodesmata

a form of local signaling where cells are connected to one another with direct contact. In animal cells, these are called _, while in plant cells, they’re known as _.

cell-cell recognition

animals can also communicate through direct contact between cell-surface molecules (i.e the carbohydrates on the outside of plasma membranes). this is called _, essentially interacting through molecules on their surfaces.

secreted signaling molecules

cell’s don’t necessarily have to touch. A signaling cell can release a signaling molecule into its surroundings, which can then travel to another cell. If the signaling molecules only travel a short distance, it’s a type of local signaling. This exemplifies _.

paracrine signal, local regulator

a form of local signaling in animals is _. Here, a cell releases a signaling molecule that travels a short distance and a nearby cell responds. This signaling molecule is called a _ because it affects nearby cells.

growth factor

an important type of a local regulator, which stimulate nearby cells to grow or divide. One signaling cell can release _s that affect many nearby cells simultaneously.

synaptic signaling, neuron, neurotransmitters

a type of local signaling that occurs in the nervous system. A nerve cell is called a _, which has an electrical signal that travels along it. When that electrical signal reaches the end of the neuron, it causes the neuron to release _, which are chemical signaling molecules that diffuse across the synapse to reach the target cell.

synapse, synaptic cleft

the neurotransmitter has to cross a tiny gap between the signaling neuron and the target cell. This gap is called the _, which is the junction/communication region, and the tiny space between cells is the _. The neurotransmitters, after diffusing across the _ to reach the target cell, bind to receptors on the target cell and trigger a response.