Chapter 9 + Quiz Questions Flashcards by Halle Johnsen

What are the 6 membrane functions?

1) Separate cells from the external medium to create an intracellular environment of unique and defined composition.
2) Allow selective transport of substrates in and out of the cell.
3) Provide a location for specialized pathways and processes
4) Rapid changes in electric potential across the membranes of
neurons as basis of the nervous system.
5) Localization of receptors to facilitate response to physiological signals.
6) Mediate cell-cell recognition and interaction

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What are 8 membrane characteristics?

1) Membranes are sheet-like structures, two molecules thick, that form closed boundaries between compartments.
2) Membranes consist of mainly of lipids and proteins, with
carbohydrates linked to these molecules.
3) Membranes are built from amphipathic molecules.
4) Membranes are largely impermeable to polar molecules.
5) Specific membrane proteins mediate particular biological
functions.
6) Membranes are self-assembling, non-covalent structures.
7) Membranes are fluid and dynamic structures.
8) Membranes are highly specialized in their composition and
distribution (asymmetric)

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Membrane formation is a consequence of the ..?

Amphipathic nature of the membrane lipids

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These molecules in self-assemble through the ____ _____

hydrophobic effect

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The structure formed depends on the ____ of cross-sectional areas of the polar head group and the hydrophobic tail

ratio

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Fatty acids favor formation of ______; lipids with two hydrocarbon tails tend to form _____

micelles, bilayers

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Exposure of hydrophobic tails at the edge of the bilayer to water is energetically _______

unfavorable

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Flat bilayer sheets are unstable and spontaneously form membrane _____. These are the basis of cells and organelles

vesicles

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Lipid bilayer membranes have a very low ______ to ions and most polar molecules

permeability

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Permeability of small molecules is correlated with their relative ____

solubility in water

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Some small ___-____ gases and small ____ molecules can pass directly through the membrane

non-polar, hydrophobic

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The cell membrane can represent a critical barrier for polar drugs intended for ______ targets

intracellular

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Encapsulation of a drug within a liposome can facilitate ____ across the membrane

transport

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Liposomes can also be used to target ____ cells or organelles

specific

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Membranes are primarily composed of __ and ____

lipids, proteins

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More active membranes have a higher ratio of ____ to ____

protein, lipid

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Composition of membrane components can be _____, in
particular for prokaryotes

dynamic

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Membranes are dynamic structures due to the nature of the ___-_____ interactions

non-covalent

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Lipids and proteins freely ____ in the plane of the membrane

diffuse

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Lateral movement of proteins and lipids within the membrane is very _____

rapid

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Movements across the membrane is _____

restricted

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Transbilayer movement requires a ____ head group to pass through hydrophobic environment

polar

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Uncatalyzed rate of lipid molecule crossing from one sheet to the other (flip-flop diffusion) is very ___

slow

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What are flippases?

Translocation of lipids from one side of bilayer to the other is catalyzed by enzymes

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Lipid composition of the inner and outer sheets of the bilayer can be different, allowing for ______ of the membrane faces

specialization

Cells need to maintain an appropriate levels of _____ _____

membrane fluidity

Membranes undergo _____-dependent phase transitions

temperature

Membranes undergo temperature-dependent phase transitions. What happens to the membrane when the temperature is below, above, or at the phase transition temperature?

Below: membrane is too solid Above: membrane is too fluid At the: the hydrocarbon chains are partially ordered but lateral diffusion is still possible

Animals use _____ to mediate membrane fluidity

cholesterol

While the basic features of the bilayer are simple and consistent, there are mechanisms to enable specialization: what are 3 of them?

1. Composition of Membrane Components 2. Distribution of Membrane Components 3. Specialized Membrane Regions

In the mechanisms that enable specialization, what entails Composition of Membrane Components?

Lipids and Proteins

In the mechanisms that enable specialization, what entails Distribution of Membrane Components?

Static and Dynamic

In the mechanisms that enable specialization, what entails Specialized Membrane Regions?

Lipid Rafts

The lipid composition of membranes ____ across species and cell types

varies

____ ____ arise from the spontaneous association of lipid molecules whose hydrocarbon tails are of similar length

Lipid rafts

The longer, saturated hydrocarbons of sphingolipids form stable associations making the lipid rafts ___ and more ____ than the rest of the membrane

thicker, ordered

____ are docking points in lipid-anchored proteins that contain long-chain saturated fatty acid anchors

Rafts

The lipid-linked proteins that associate with rafts often serve ____ functions

signaling

Three categories of membrane proteins are defined based on different mechanisms of association with the membrane:

1) Peripheral 2) Lipid-anchored 3) Integral membrane

What kind of membrane proteins associate with the membrane through electrostatic or hydrogen-bonding interactions?

Peripheral

What kind of membrane proteins can dock to either membrane lipids or integral membrane proteins?

Peripheral

The bulk of the ____ membrane proteins is in the cytosol or extracellular space

peripheral

Changes in pH or ionic strength often releases these proteins from the membrane..?

Peripheral

Covalently attached ___ can anchor proteins to the membrane

lipids

Protein modifications are sometimes ______, allowing for regulation of cellular location

reversible

Proteins with ____ chain hydrocarbons always are on the inner face

single

_____ membrane proteins are immersed in, and usually span, the membrane

Integral

In what kind of membrane proteins are the positioning within a membrane specific and directional?

Integral

Integral membrane proteins tend to be of three varieties:

1) Single pass α-helical 2) α-helical bundles 3) β-barrels

In the integral membrane proteins, charged residues are located mostly within the ____ and ______ portions of the protein

intra, extracellular

Residues with non-polar side chains dominate ____ the hydrophobic slab of the bilayer

inside

Membrane spanning regions can be predicted from the..?

amino acid sequence

Stretches of ___ hydrophobic residues in a row are likely membrane spanning

~20

A hydropathy index looks at the _____ characteristics of a protein to predict transmembrane regions

hydrophobic

Side chains within the transmembrane region tend to be ___-_____, however the carbonyl and amide groups of each peptide bond are ____

non-polar, polar

Polar unpaired carbonyl and amide groups in the bilayer core are energetically _______

unfavorable

______ and ____ groups of the protein backbone within the bilayer have to be hydrogen-bonded

Carbonyl, amide

What are the four Categories of Membrane Transport?

1) Simple Diffusion 2) Facilitated Diffusion (carriers, channels) 3) Active Transport (primary, secondary) 4)Ion Transporters

Their direction and rate of movement is determined by their concentrations on either side of the membrane. What Kind of transport is this?

Simple Diffusion

____ can only result in the net movement down a concentration gradient

Diffusion

Membrane transporters lower the activation energy barrier of crossing the bilayer in what kind of transport?

Facilitated Diffusion

The activation energy for removing the hydration shell from a polar solute and transferring it into the non-polar environment in the core of the bilayer is very ____

high

Membrane transporters _____ the activation energy for crossing the membrane by replacing the hydration shell with interactions with polar groups along the transfer path in the protein interior

lower

Does the following occur in Channels or Carriers: Membrane pores transport molecules down concentration gradient

Channels

Does the following occur in Channels or Carriers: high conductance rates because they bind the substrate very weakly

Channels

Does the following occur in Channels or Carriers: no saturation?

Channels

Does the following occur in Channels or Carriers: membrane proteins that undergo substrate-induced conformational change, or membrane repositioning, to release substrate to the other side of the membrane

Carriers

Does the following occur in Channels or Carriers: slower because they bind the substrate quite strongly

Carriers

Does the following occur in Channels or Carriers: saturation

carriers

What is uniport?

Transport of a single molecule

What is the difference between antiporters and symporters?

Antiporters move molecules in different directions. Symporters move molecules in the same direction

In diffusion, co-transport through antiport or symport depends on the..?

Charge of the molecules in order to have a net neutral change

In secondary active co-transport, system couples a molecule moving down its gradient to..?

one moving down its gradient

What is active transport?

The input of energy that allows movement of molecules against concentration gradients

What is primary active transport, and what does it include?

It is driven by direct source of energy (ATP) and includes P-type, V-type, and ABC Transporters

What is secondary active transport?

Couples the movement of one molecule down its concentration gradient within the movement of another molecule down its gradient

What is P-Type ATPase? (x4)

1) Cells maintain high gradients of Na+ outside the cell and K+ inside the cell 2) The gradient control cell volume, electrical excitability, and enables uptake of nutrients through secondary active transport 3) Na+, K+ ATPase uses the energy of ATP hydrolysis to pump three Na+ out of the cell and two K+ into the cell 4) Undergoes a phosphorylated intermediate

What is the V-Type ATPase? (x2)

1) Use the energy of ATP to move protons against a concentration gradient 2) Acidification of organelles

What are ABC transports? (x3)

1) Contain ATP-binding domains (ATP-Binding Cassette) 2) Transport of a variety of biomolecules out of the cell against a concentration gradient 3) Multi-drug resistance protein pumps drugs out of the cell rendering the drugs ineffective

What is secondary active transport?

1) The movement of glucose up its concentration gradient is enabled by the movement of Na+ ions down their concentration. 2) Active transport of glucose depends on the action of the Na+-K+ ATPase to establish the gradient of Na+ ions

___ channels enable rapid movement of ions across the membrane

Ion

Actions of ion channels can cause changes in _____ _____ in neurons.

membrane potential (action potentials)

Ion channels are tightly _____; voltage-gated channels and ligand-gated channels

regulated

Ion channels differ from ion transporters (like the N+,K+ ATPase) in three ways:

1) Faster 2) No saturation limits 3) Gated/Regulated

Ion channels are highly ______ for the molecule to be transported

selective

Selectivity filter discriminates K+ and Na+ based on their ability to shed ____ _______ to form electrostatic interactions within backbone carbonyls

water molecules

As K+ ions enter the filter, the electrostatic repulsion from other incoming K+ ions helps to push the flow of ions from ____ to ____the cell

inside, outside

Which type of transporter is involved in establishing and maintaining membrane potential?

P-type ATPases

The fluid mosaic model refers to..?

the freedom of movement of membrane proteins and lipids within the plane of the membrane

Which is an example of symport?

Glucose uptake into intestinal epithelial cells

Molecule X is transported into the cell in a manner that requires a specific protein, at a rate that depends on the extracellular concentration of X, and with an upper limit to the rate of transport. What type of transport system is likely responsible for transport of X?

Diffusion through a carrier

Uptake of glucose into intestinal epithelial cells is an example of..?

Secondary active transport

The movement of non-polar gases across a membrane reflects..?

Simple diffusion

Chapter 9 + Quiz Questions Flashcards

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