BSCI 170 - Midterm 2 Flashcards

What does the biomembrane do?

Separates living cytoplasm from nonliving environment (essential for life)

Why is the biomembrane unique?

semi-permeable membrane - controls movement of materials across it

what is the fluid-mosaic model?

the current model for biomembrane structure

what are the critical features of the fluid-mosaic model?

• membranes primarily composed of phospholipids (organized in a bilauer) with proteins and carbohydrates attached

• lipids are in a fluid state (not a rigid barrier)

• kinks in tail prevent tight packing of fatty acids (unsaturated)

• proteins are dispersed in the membrane / free to float in the lipid fluid

• tails are hydrophobic but heads are hydrophilic

what does the amount of fluidity in a membrane depend on?

temperature: as temp. decreases, so does fluidity

what is transition temperature?

Tm: the temperature at which the membrane undergoes fluid-to-solid phase change

• Tm could be affected by changing the lipid structure of the membrane

What does a viscous (thick, sticky) membrane have?

saturated hydrocarbon tails (no C=C - no kinks)

What does a fluid membrane have?

unsaturated hydrocarbon tails (C=C - kinks)

What does increased number of C=C do to Tm?

Lower Tm - makes it easier to melt the membrane and increase fluidity

What is cholesterol made of?

it is a lipid so its made up of hydrocarbons, an OH group, and a hydrophobic tail.

What is a special property of cholestrol?

it is soluble in the hydrophobic core of the membrane bilayer (does have one polar region - OH group)

• IS ABLE TO INTERACT with the hydrophobic tails and alters interactions between adjacent fatty acid chains to maintain membrane fluidity

How does cholesterol affect membrane fluidity?

• reduces membrane fluidity at moderate temperatures; hinders solidification of membrane at lower temperatures

• a fluidity buffer

what do variations in lipid compositions of cell membranes of different species mean?

means that lipid compositions have adapted to specific environmental conditions (in places where temp. varies, lipid compositions are able to change depending on the temperature)

what are integral membrane proteins?

• proteins that are permanently attached to the cell membrane

  • tightly integrated into membrane structure

what is the most common type of integral membrane proteins?

• transmembrane proteins: proteins that pass all the way through the membrane (outside to inside cell)

• amphipathic: function on both sides of the membrane

what are anchored membrane proteins?

proteins covalently attached to lipid heads, they insert into membrane

not exposed to hydrophobic region

what are peripheral membrane proteins?

• loosely bind to integral proteins or to lipids

• removed without destroying the membrane

• function on only one side of the membrane - not embedded in membrane

what are membrane carbohydrates?

• short chains of monosaccharides added to protein or lipid (glycosylation)

• attachment occurs in rough ER and golgi apparatus

• are generally found on the outer membrane layer

what are the two types of membrane carbohydrates?

glycoprotein (bound to protein) or glycolipid (bound to lipids)

give one example of membrane protein function

• HIV must bind to the immune cell surface protein CO4 and coreceptor CCR5 in order to infect a cell

• HIV cannot enter the cells of resistant individuals that lack CCR5

What is selective permeability?

membrane lipids allow unlimited passage of some substances but limited or not passage of other substances

what is diffusion

movement of molecules from higher concentrations to lower concentrations

when does diffusion stop?

when it reaches equilibrium

what type of molecules pass through the membrane easily?

smaller and more hydrophobic molecules diffuse across the membrane more rapidly

• hydrophobic molecules - easily diffuse

• small, uncharged polar molecules - mostly diffuse

• large, uncharged polar molecules - rarely diffuse

• ions - never diffuse

what is the problem we encounter with selective permeability?

• most biologically significant molecules are large and either polar/charged

how do we allow biologically significant molecules to pass through?

• multi-pass, integral membrane (transmembrane) evolved to aid transport of polar or charged molecules

  • create a favorable interior for polar molecules to pass through hydrophobic membrane

what are channel proteins

• integral membrane proteins that allow specific molecules to pass through rapidly

  • tend to have hydrophilic pores + have no specific binding to one molecule

what are carrier proteins?

• integral membrane proteins that facilitate movement of specific molecules across the membrane by binding to them and undergoing conformational changes to shuffle them across (slower than channel proteins)

• specific binding to solute; like an enzyme has a specific substrate

what is passive transport?

• transport is “downhill” - driven by the direction of the electrochemical gradient

• higher to lower

what is active transport?

• transport where energy is added (ATP)

• “uphill” - going against gradient

• low to high

• only carriers - not channels (channels are always passive)

  • carriers can be active or passive

what are solutes?

things that are dissolved in water

how do we balance different solutes’ concentration

sometimes, instead of moving the solutes, water moves across the membrane

what is osmosis?

• passive movement of water across a membrane

what is a primary active transporter?

• uses ATP to transport molecule against concentration gradient

what is a secondary active cotransporter?

• uses stored potential energy of the electrochemical gradient of one molecule to transport another

what special channels does water use to move across the membrane?

aquaporins

if membrane is permeable to solute…

…then solute will go from high to low solute concentration

if membrane is permeable to water…

… then water will move from low to high solute concentration

what does isotonic mean?

solution around cell has the same solute concentration as inside the cell (no net movement of water)

what does hypotonic mean?

• solution around cell has a lower solute concentration than inside the cell

  • water moves into the cell, causing it to swell - why we use saline in IV rather than H2O which could burst the cells.

what does hypertonic mean?

• solution around cell has a higher solute concentration than inside the cell

  • net movement of water out of the cell

what is facilitated diffusion?

passive transport that is aided by proteins (channels and carriers)

what does a uniporter system mean?

a single thing is being moved across the membrane

what is a ligand gated channel mean?

proteins that open/close in response to ligands (a sort of stimulus molecule)

what is an electrically gated channel?

only a certain amount of charge is going to open up this channel

what is a mechanically gated channel?

channels that only open when stretched

what is cotransport?

• some transport proteins can move more than one substance at a time

• symport - two molecules the same direction

• antiport - two molecules in opposite directions

• can be passive or active

what is ATP hydrolysis?

ATP = ADP + Pi

what functions can ATP hydrolysis provide the energy for?

provides the energy to actively move two substances in two different directions - cotransport

what can be stored in an ion gradient?

• energy supplied by ATP hydrolysis to transport one ion

what process can stored potential energy drive?

• the active transport of another solute with a separate cotransport protein

what is bulk transport?

• large proteins, such as proteins and polysaccharides, move by bulk transport

  • exocytosis: secretion (release of material)

  • endocytosis: mechanism for bringing material into the cell

what is phagocytosis (a type of endocytosis - bulk transport)

• cellular eating

• cell engulfs a particle into a vesicle

what is pinocytosis? (a type of endocytosis - bulk transport)

• cellular drinking

• “gulp” of fluid taken into vesicle

• nonspecific uptake of solubilized material

what is receptor-mediated endocytosis?

• used to bring in specific molecules

• ligands bind to specific receptors

• transferred to lysosome for digestions

• a selective form of endocytosis that enables cells to internalize large quantities of specific substances.

what is cell signaling?

• communication between cells in a multicellular organism

• coordinates biochemical, mechanical, reproductive, and other essential activities

what is juxtacrine signaling?

• communication between cells right next to each other

what is paracrine signaling?

communication between cells near each other

what is synaptic signaling?

electrical signal triggers release of neurotransmitter, which diffuses across synapse

what is endocrine signaling?

signaling between distant cells

what happens after a signal is sent?

all cells in range receive the signal

only cells with a receptor tuned to the specific signal can respond to the signal

what does responding to a signal mean?

responding means changing some cellular activity (ex: gene expression, enzyme activity, cell division)

what does interaction between a receptor and its signal (ligand) do?

when a signaling molecule (ligand) binds to a receptor, it causes the receptor to change shape - affects the receptor’s function

are most chemical signals hydrophilic or phobic?

hydrophilic: most need to help to pass through membrane (help from receptors, which are transmembrane proteins)

what kind of transport is NA+/K+?

primary active transport - antiporter

what are water soluble signals?

• signaling molecules (hydrophilic) that dissolve in water - cannot pass through membrane, so they bind to receptors

what are lipid-soluble signals?

signaling molecules (hydrophobic) that dissolve in lipids - easily pass through membrane

what is intracellular signaling?

• mechanism by which cells respond to their environment + communicate (signals are triggered by external stimuli)

• intracellular receptors are receptors found in the cytoplasm or nucleus - signal must be very small and hydrophobic to reach them

what is a ligand-gated ion channel?

ligand has to bind to part of the channel to open it, allowing specific ions to pass through

what is a g-protein-coupled receptor?

receptors that activate G proteins when a ligand binds to them. this triggers a signaling pathway.

what is an enzyme-linked receptor?

an enzyme that happens to be a transmembrane protein (gets activated by a ligand)

what does the reception of a signal trigger and what is it called?

reception → transduction → response: signal transduction pathway (a series of biochemical reactions that lead to a cellular response.)

what does signal transduction usually include?

involves the activation or inactivation of enzymes

• involves phosphorylation (adding a phosphate to activate the protein)

• involves dephosphorylation (removing a phosphate to inactivate the protein)

what is protein kinase?

general name for an enzyme that helps catalyze the addition of a phosphate group from ATP to a protein (key part of phosphorylation)

can a single cell have more than one kinase?

yet, may have several hundred different kinases (each with different substrates and activation profiles)

how can phosphorylation be reversed?

phosphorylation can be reversed by dephosphorylation, which is done by phosphotases (removes the phosphate group from a protein, helping it return to its original conformation so the protein can be reused)

what are second messengers?

small nonprotein molecules + ions

activated by the initial signal (first messenger) and carry instructions through the cell

what is the most common second messenger?

cyclic AMP - hydrophilic.

• helps cell pass on signals from the receptor to other parts of the cell, often by activating enzymes

• ATP + Enzyme Adenyl Cyclase → cyclic AMP

how is cyclic AMP destroyed?

by phosphodiesterase (PDE) → breaks phosphodiester bond cyclic AMP has

what does protein kinase A do (PKa)

an enzyme activated by cyclic AMP that adds phosphate groups to proteins (phosphorylation), which changes their activity.

what type of responses of cellular signaling?

changes in gene expression, enzyme activity, motor activity, cytoskeletal structure, etc..

what can fine tuning of a cellular response lead to?

amplification, regulation, termination

what is amplification

a small signal leads to a large response

different cells can respond to the same signal…

in different ways - one signal is tied to different signaling pathways in different cells

what is termination

every response must be limited in duration

what are catabolic reactions accompanied by

the transfer of electrons between reactants

where exactly is energy stored

in chemical bonds (covalent > weak) in electrons (as potential energy)

• if electrons are rearranged/released, potential energy can be reduced

what is combustion

rapid chemical combination with oxygen (oxidization - a reaction with O2)

• exergonic

what is the formula for oxidation-reduction reaction

Ared + Box → Aox + Bred

Na + Cl → Na+ + Cl-

sodium is losing an electron (OIL) - oxidation

chlorine is gaining an election (RIG) - reduction

CH4 + 2O2 → CO2 + energy + 2H2O

CH4 loses bonds with hydrogen to become CO2 (oxidation/reducing agent)

2O2 gains bonds with hydrogen to become 2H20 (reduced/oxidizing agent)

what is an oxidizing agent?

substance that gains electrons

what is a reducing agent?

substance that donates electrons

can oxidation/reductions occur in isolation?

no - if one is oxidized, the other must be reduced

do electrons move alone

rarely - most of the time they combine with protons as they move

the molecule ____ is usually the more reduced one

______ is a really good oxidizing agent

1) hydrogen

2) oxygen