Plasma Membrane Structure

What is the best definition for the fluid mosaic model as applied to the plasma membrane? - A moving collection of distinct, individual components - A solid aggregation of phospholipids, sterols and proteins - A particular arrangement of glyceroglycolipids, sphingolipids, cholesterol, and glycoproteins - A homogeneous mixture of lipids and proteins

- A moving collection of distinct, individual components; 'Fluid" refers to how the membrane components are in motion and "mosaic" refers to the multitude of phospholipid and protein components within the membrane that together cohesively make the membrane.

Signal transduction

- A series of molecular changes that converts a signal on a target cell's surface to a specific response inside the cell. - Signal receptors; facilitate communication between cells

electrogenic pump

- A transport protein that generates voltage across a membrane - Pumps ions across the membrane

Which of the following statements is true? - Liposomes are lipid bilayers and micelles are lipid monolayers, both which contain membrane proteins - Amphipathic molecules can be used as surfactants to reduce solution surface tension - Micelles are celled in laboratory experiments to replicate the phospholipid bilayer - Micelle size is dependent on temperature and independent of pH

- Amphipathic molecules can be used as surfactants to reduce solution surface tension

Which of the following statements about glycoglycerolipids and sphingolipids are false? Select all that apply. - Both contain two fatty acid tails attached to a glycerol backbone - Both and amphipathic and can be found in lipid rafts - Both may have a carbohydrate head and hydrocarbon chains - They differ from each other in the type of carbohydrate head group attached

- Both contain two fatty acid tails attached to a glycerol backbone - Both and amphipathic and can be found in lipid rafts - They differ from each other in the type of carbohydrate head group attached

Which of the following is true about cholesterol? - Cholesterol increases membrane fluidity at high temperatures and decreases membrane fluidity at low temperatures - Cholesterol increases membrane fluidity at low temperatures and decreases membrane fluidity at high temperatures - Cholesterol increases membrane fluidity at low temperatures and increases membrane fluidity at high temperatures - Cholesterol decreases membrane fluidity at low temperatures and decreases membrane fluidity at high temperatures

- Cholesterol increases membrane fluidity at low temperatures and decreases membrane fluidity at high temperatures

What essential function does a plasma membrane fulfill? Select all that apply. - Establishment of a boundary - Sealing off the cell from its environment - Inhibition of random diffusion - Absorption and secretion regulation

- Establishment of a boundary - Inhibition of random diffusion - Absorption and secretion regulation

Which of the following characteristics would make a molecule amphipathic? - The ability to donate and accept electrons - Containing an amide bond - Having a few charged amine groups on one end and a long series of carbons and hydrogens linked together on the other end - Being comprised mainly of a 4-ring hydrocarbon structure

- Having a few charged amine groups on one end and a long series of carbons and hydrogens linked together on the other end

Which of the following characteristics is LEAST applicable to a phospholipid? - Hydrophilic - Unsaturated in the cis orientation - Amphipathic - Even numbered hydrocarbon chain

- Hydrophilic; Phospholipids are not considered hydrophilic because of their long hydrophobic hydrocarbon chains. Phospholipids that have a polar end and a nonpolar end are amphipathic.

Which of the following changes would most likely cause the melting point of the plasma membrane to decrease? - Increase ratio of unsaturated fatty acids to saturated fatty acids - Increase the ratio of saturated fatty acids to unsaturated fatty acids - Add more glycolipids to the plasma membrane - Increase the temperature of the cell culture

- Increase ratio of unsaturated fatty acids to saturated fatty acids; Saturated fatty acids contain no double bonds, which makes their tails linear and regular. Unsaturated fatty acids, on the other hand, contain at least one double bond, creating bent and kinked tails. This kink interferes with the Van der Waals forces that encourage the hydrophobic lipid tails to pack closely together, resulting in a more fluid membrane.

A researcher notes that there is very little diffusion across the plasma membranes of a particular line of cells. What can the researcher do to improve rates of diffusion across the cell membrane in this cell line? - Use a different medium to culture the cells - Allow cell populations to get larger before splitting the cells into new petri dishes - Increase the incubation temperature - Genotype the cells to look for mutations in transmembrane transport proteins

- Increase the incubation temperature; As temperature increases, membrane fluidity increases. Membrane fluidity makes some space for molecules to diffuse through the membrane, increasing diffusion.

Which of the following descriptions regarding cholesterol's role in plasma membrane fluidity is false? Select all that apply. Cholesterol: - Increases membrane fluidity by interfering with the hydrophobic interactions of the phospholipids - Decreases membrane fluidity by interfering with random horizontal movement of phospholipids - Increases membrane fluidity by promoting hydrophobic interactions between phospholipids and lipid rafts - Decreases membrane fluidity by interfering with close packing of saturated fatty acid tails

- Increases membrane fluidity by promoting hydrophobic interactions between phospholipids and lipid rafts - Decreases membrane fluidity by interfering with close packing of saturated fatty acid tails

Which of the following interventions will decrease the fluidity of the membrane? Select all that apply. - Increasing the number of unsaturated phospholipids in the membrane - Increasing the number of saturated phospholipids in the membrane - Increasing the temperature - Increasing the concentration of scramblases

- Increasing the number of saturated phospholipids in the membrane

Which of the following describes a spontaneous movement of phospholipids in the plasma membrane? Select all that apply. - Moving past other phospholipids in the extracellular leaflet - Moving past other phospholipids in the cytosolic leaflet - Moving from the extracellular leaflet tom the cytosolic leaflet - Moving from the cytosolic leaflet to the extracellular leaflet

- Moving past other phospholipids in the extracellular leaflet - Moving past other phospholipids in the cytosolic leaflet

Which of the following would you NOT expect to find in a sample taken from the plasma membrane of a cell? - Cholesterol - Amino acids - Sphingomyelin - Nucleic acids

- Nucleic acids

Which of the following is NOT a common component of the plasma membrane? - Phospholipids - Sterols - Proteins - Nucleotides

- Nucleotides; Nucleotides are not commonly found in the plasma membrane. RNA is found within the cytoplasm and the nucleus and DNA is found within mitochondria and the nucleus.

During normal digestion, the gallbladder secretes bile that contains amphipathic molecules to aid in the digestion of fats by breaking down larger oil droplets into smaller micelles. How would you expect the amphipathic molecules of these micelles be arranged? - Polar head groups facing outwards and nonpolar tails pointing in towards the middle - Polar head groups facing inwards and nonpolar tails pointing out away from the middle - Both A and B are correct - None of the above

- Polar head groups facing outwards and nonpolar tails pointing in towards the middle; Amphipathic molecules have a polar group and a nonpolar group. In solution, amphipathic molecules gather to form micelles. A micelle is a single-layer lipid aggregate in an aqueous solution. The hydrophilic head region is in contact with the solvent, while the hydrophobic tail region is sequestered in the center of the micelle. This arrangement promotes favorable hydrophilic-hydrophilic and hydrophobic-hydrophobic interactions.

Membrane protein

- Proteins within the phospholipid layer that transport water soluble substances across the lipid bilayer. - Used during active transport

Which of the following characteristics apply to sterols? Select all that apply. - Regulation of membrane fluidity - Sphingomyelin interactions - 4-ring structure - Modified carbohydrate

- Regulation of membrane fluidity - Sphingomyelin interactions - 4-ring structure

Which of the following is a function of the plasma membrane? Select all that apply. - Separate's the cytosol from the extracellular environment - Regulates the entry and exit of molecules to and from the cell - Assists in cell signaling - Inhibits some diffusion

- Separate's the cytosol from the extracellular environment - Regulates the entry and exit of molecules to and from the cell - Assists in cell signaling - Inhibits some diffusion

Which of the following types of movement within the cell membrane are unlikely to occur? Select all that apply. - Spontaneous 180 degree rotation of a phospholipid from the extracellular layer to the cytoplasmic layer - Horizontal translation of phospholipids within their particular section of the bilayer using enzymes known and scramblases - Movement of a phospholipid from the extracellular leaflet to the intracellular leaflet using floppases - Movement of a phospholipids from the intracellular leaflet to the extracellular leaflet using flippases

- Spontaneous 180 degree rotation of a phospholipid from the extracellular layer to the cytoplasmic layer - Horizontal translation of phospholipids within their particular section of the bilayer using enzymes known and scramblases - Movement of a phospholipid from the extracellular leaflet to the intracellular leaflet using floppases - Movement of a phospholipids from the intracellular leaflet to the extracellular leaflet using flippases

cell-cell recognition

- The function of membrane proteins in which some glycoproteins serve as ID tags that are recognized by membrane proteins of other cells. - Carbohydrate chain identifies "self" from "non-self" (viruses)

membrane potential

- The voltage across a cell's plasma membrane - The difference in charge across a cell membrane that is maintained by active transport

Which of the following can be true about glyceroglycolipids and sphingolipids? Select all that apply. - They are amphipathic and found in the plasma membrane - They have glycerol backbone and are modified with a carbohydrate group - They form lipid rafts with cholesterol and have hydrophobic tails - They can be modified with a carbohydrate group and be involved in cell signaling

- They are amphipathic and found in the plasma membrane - They can be modified with a carbohydrate group and be involved in cell signaling

Sodium-potassium pump

A carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

Endocytosis

A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane.

Aquaporins

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Carrier proteins

Bind to molecules and change shape to shuttle them across the membrane

Fill in the blanks for the following statement: _______________ the amount of unsaturated fatty acids will cause membrane fluidity to decrease and increasing the amount of saturated fatty acids will cause membrane fluidity to _______________.

Decreasing; Decrease

function of cholesterol in cell membrane

Increases membrane fluidity; helps membranes stay fluid in cold temperatures when they contract, phospholipids are pushed together, there is less space and movement across the membrane

Charge of a cell

Inside is negative; outside is positive

Examples of Lipid-anchored proteins

Lipid-anchored proteins are covalently bound to single or multiple lipid molecules. This arrangement anchors the protein within the membrane, without having it actually touch the membrane itself. G proteins are intracellular membrane-bound structures that help coordinate the signaling cascade initiated by the G protein-coupled receptors.

Examples of Glycoproteins

Major histocompatibility complex, blood type antigens

Intracellular joining

Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions. This type of binding is more long lasting.

Simple diffusion

Movement of any substance down a concentration gradient; passes between spaces in phospholipids (O2, CO2)

Facilitated diffusion

Movement of specific molecules across cell membranes through protein channels

Passive transport

Movement of substances from high concentration to low down a concentration gradient until the concentrations are equal; spontaneous process requires no energy;

Examples of Peripheral proteins

Peripheral proteins are found within the cytoplasm and are temporarily attached to integral proteins or are associated with peripheral regions of the lipid bilayer. They tend to interact only briefly with the membrane before resuming their function in the cytoplasm. This category includes some enzymes and hormones.

What is the most abundant component in the plasma membrane?

Phospholipids

What are plasma membranes composed of?

Phospholipids, proteins, carbohydrate chains, cholesterol

What kind of biologically relevant molecule is formed through an esterification reaction? - Proteins - Glycogen - Phospholipids - Cholesterol

Phospholipids; Fatty acids can be attached to a glycerol molecule through a process known as esterification. In phospholipids, this happens to two out of the three hydroxyl groups. The remaining hydroxyl group is phosphorylated.

What cannot cross the cell membrane easily?

Polar/hydrophilic molecules cannot cross the hydrophobic membrane (H2O, glucose, amino acids); large molecules physically cannot fit

Channel proteins

Proteins that provide passageways through the membrane for certain hydrophilic (water-soluble) substances such as polar and charged molecules

Examples of Integral proteins

Protons pumps, ion channels, G protein-coupled receptors

3 forms of cell-cell recognition of carbohydrate chains

Self from non-self; blood types; tissue sorting in an embryo

Integral proteins

Span the membrane from top to bottom; if they go all the way through, the hydrophilic tips are exposed to water and the hydrophobic portions are hidden inside

Active transport

The movement of materials from low to high concentrations against/up the gradient; requires energy in the form of ATP; non-spontaneous

Osmosis

The movement of water down a concentration gradient and across a membrane; usually in and out of plant cells

Peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

Membrane vesicles

They carry processed proteins from the exit face of the Golgi complex to the plasma membrane for incorporation into the plasma membrane itself.

Transport proteins

Transport proteins are membrane proteins that form pumps that use ATP to actively transport large molecules across the membrane

True or false: Lipid anchored proteins are not in contact with the plasma membrane.

True; Lipid anchored proteins are covalently attached to a lipid molecule which is then inserted into the cell membrane. The protein itself is not considered in contact with the membrane itself, but rather 'anchored' to it.

What is amphipathic?

having both hydrophilic and hydrophobic parts

what crosses the membrane easily?

non-polar hydrophobic molecules (O2, CO2); small so can diffuse through spaces between phospholipids

Exocytosis

release of substances out a cell by the fusion of a vesicle with the membrane.