Chapter 9: Cell Communication, Chapter 5: Membrane Structure and Function, Chapter 4 - Living Eukaryotic Cell, BIOL 1001-Chapter 4: Prokaryotes, Eukaryotes & S:V Ratio, nucleic acids, proteins, Chapter 3: Carbohydrates and Lipids, BIOL 1001-Chapter 2...

Consider the following materials that must cross the membrane. For each, tell how it is moved across. A. CO2 B. Glucose C. H+ D. O2 E. H2O

A. Simple diffusion B. Transport proteins C. Transport proteins D. Simple diffusion E. Simple diffusion and protein channels (aquaporins)

signal integration

interaction of signals from two or more different cell-surface receptors that merge to activate the same response in the cell

intercellular communication

interactions between cells using chemical signals

Axon

A threadlike extension of a neuron that carries nerve impulses away from the cell body.

second messenger

- small molecules that propogate a signal after it has been intiated by the binding of a ligand to a receptor - middleman

Describe how cholesterol affects membrane fluidity.

At relatively high temperatures—at 37°C, the body temperature of humans, for example—cholesterol makes the membrane less fluid by restraining phospholipid movement.

Binding initiates a signaling pathway (2nd step of cell communication)

- 2nd-messenger enzymes and activated proteins interact w/ specific proteins to cause changes in cell environment

Internal receptors

- Found in cytoplasm - Respond to hydrophobic ligand molecules that travel across membrane - bind to proteins that act as mRNA synthesis regulators - Initiates transcription (DNA --> mRNA), affects GE

How an enzyme-linked receptor works

- Ligand binds to the extracellular domain - signal is transferred through membrane and an enzyme is activated - Enzyme sets of chain of events (cell response)

cell surface receptors

- Membrane-anchored proteins that bind to external ligand molecules - Performs signal transduction - Allows ligands to interact with cell w/o entering - Malfunction = abnormal cell functioning (hypertension, cancer, etc.)

Three types of protein filaments that make up the cytoskeletons

- Microtubules - Actin Filaments - Intermediate filaments

Water soluble ligands

- polar, cannot pass through cell membrane w/o help - Bind to extracellular domain of cell-surface receptors - Usually small molecules, peptides, or proteins

paracrine signaling

- Signal released from a cell has an effect on neighboring cells. - move by diffusion through extracellular matrix - quick responses that don't last long - usually nerve cells

Common second messengers

- calcium ions (release insulin, cause muscle contractions) - cyclic AMP (activates A-kinase enzyme) - Inositol phospholipids - diacylglyerol (DAG)

structure of a nerve cell

- cell body - dendrite - axon

Autocrine signaling occurs during

- early development of a cell (ensures proper tissue development and function) - During pain and inflammatory response - Programmed cell death

Enzyme-linked receptors

- intracellular domains that are associated w/ an enzyme - large extracellular and intracellular domains - Membrane-spanning region consists of a single alpha-helical region of a peptide strand

Propagation of a signal (1st step of cell communication)

- ligand binds to a receptor - extracellular domain undergoes conformational changes - Leads to activation of intracellular domain + proteins

hormones

- ligands released in endocrine signaling - travel to target cells through bloodstream - become diluted in blood, act on cells in low concentrations

Steroid hormones

- lipids w/ hydrocarbon skeleton + 4 fused rings w/ specific functional groups - Bind to carrier proteins to be soluble in blood - estrogen, testosterone, cholesterol

Phosphorylation

- one of most common CHM mods that occurs in signaling pathways - Phosphate (PO_3) groups are added to molecules (often serine, threonine, and tyrosine residues) - Phosphate replaces hydroxl group of protein

Membrane proteins are the mosaic part of the model. Describe each of the two main categories: A. Integral proteins B. Peripheral proteins

A. Penetrate the hydrophobic interior of the lipid bilayer B. Appendages loosely bound to the surface of the membrane, often to exposed parts of integral proteins

3 categories of cell surface receptors

1) Ion-channel linked 2) G-protein linked 3) Enzyme linked

3 components of cell surface receptors

1) extracellular domain (enternal, ligand-binding region) 2) transmembrane domain (hydrophobic, membrane-spanning region) 3) intracellular domain

G protein cycle

1) ligand binds to G-protein 2) G-protein alpha subunit exchanges GTP for GDP 3) Alpha subunit dissociated from beta subunit and y subunit triggers a cell response

The sodium-potassium pump is an important system for you to know. Use the following diagram to understand how it works. Use these terms to label the figures, and briefly summarize what is occurring in each: extracellular fluid, cytoplasm, Na+, K+, ATP, ADP, P, and transport protein.

1. Na+ binds to the sodium-potassium pump. 2. This stimulates phosphorylation of the pump. 3. The pump changes shape and releases Na+ to the outside. 4. The new pump shape now has an affinity for K+, and binds them. This triggers the dephosphorylation of the pump 5. This causes the pump to change shape again, and release K+ to the inside. 6. In the new shape, the pump will now bind Na+ again.

Define isotonic

A solution with the same concentration of solutes as the cell it surrounds. There will be no net movement of water across the plasma membrane. In an isotonic environment, the volume of the animal cell is stable.

gap signaling

A cell targets an adjacent cell connected with gap junctions

autocrine chemical signaling

A cell targets itself with ligands

Cytosol description

A central region that coordinates many metabolic activities

What is a ligand? What do ligands have to do with receptor-mediated endocytosis?

A ligand is a molecule that binds specifically to another molecule, usually a larger one. Human cells use receptor-mediated endocytosis to take in cholesterol for membrane synthesis and the synthesis of other steroids. Cholesterol travels in the blood in particles called low-density lipoproteins (LDLs), each a complex of lipids and a protein. LDLs bind to the LDL receptors on plasma membranes and then enter the cell by endocytosis. The LDLs thus act as ligands.

What is meant by membrane fluidity? Describe the movements senn in the fluid membrane.

A membrane is held together primarily by hydrophobic interactions, which are much weaker than covalent bonds. Most of the lipids and some of the proteins can shift about laterally—that is, in the plane of the membrane. The lateral movement of phospholipids within the membrane is rapid.

Function of signal transduction

A membrane protein (receptor) may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external messenger (signaling molecule) may cause the protein to change shape, allowing it to relay the message to the inside of the cell, usually by binding to a cytoplasmic protein.

Describe how decreasing temperature affects membrane fluidity.

A membrane remains fluid as temperature decreases until finally the phospholipids settle into a closely packed arrangement and the membrane solidifies. The temperature at which a membrane solidifies depends on the types of lipids it is made of.

Ligands

A molecule that binds specifically to a receptor site of another molecule.

Function of enzymatic activity

A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway.

Function of transport

A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Other transport proteins shuttle a substance from one side to the other by changing shape. Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane.

Define hypotonic

A solution with less solutes than the cell it surrounds. The cell will swell and lyse (burst).

Define hypertonic

A solution with more solutes than the cell it surrounds. The cell will lose water, shrivel, and probably die.

Define each of the following, and give a specific cellular example: A. Exocytosis B. Endocytosis C. Receptor-mediated endocytosis D. Phagocytosis E. Pinocytosis

A. The cellular secretion of biological molecules by fusion of vesicles containing them with the plasma membrane B. Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane C. The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances D. A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and certain immune cells of animals. E. A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes

Describe active transport. What type of transport are involved, and what is the role of ATP in the process?

Active transport is a type of membrane traffic during which the cell must expend energy. The transport proteins involved are called carrier proteins. ATP supplies the energy for most active transport.

Peter Agre received the Nobel Prize in 2003 for the discovery of aquaporins. What are they?

Aquaporins are channel proteins that facilitate the passage of water molecules through the membrane of certain cells.

Phospholipids are amphipathic. Explain what this means.

Amphipathic means that the phospholipid has both a hydrophilic region and a hydrophobic region.

Kinase

An enzyme that transfers phosphate ions from one molecule to another

Dendrites

Branchlike parts of a neuron that are specialized to receive information.

Distinguish between glycolipids and glycoproteins.

Glycolipids: Membrane carbohydrates covalently bonded to lipids Glycoproteins: Membrane carbohydrates covalently bonded to proteins

Distinguish between channel proteins and carrier proteins.

Channel proteins function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane. Carrier proteins hold on to their passengers and change shape in a way that shuttles them across the membrane.

What is cotransport? Explain how understanding it is used in our treatment of diarrhea.

Cotransport is the coupling of the "downhill" transport of one substance to the "uphill" transport of another substance against its own concentration gradient. Normally, sodium in waste is reabsorbed in the colon, maintaining constant levels in the body, but diarrhea expels waste so rapidly that reabsorption is not possible, and sodium levels fall precipitously. To treat this life-threatening condition, patients are given a solution to drink containing a high concentration of salt (NaCl) and glucose. The solutes are taken up by sodium-glucose cotransporters on the surface of intestinal cells and passed through the cells into the blood.

The region that is outside the organelles but inside the plasma membrane

Cytosol

Define passive transport

Diffusion of a substance across a biological membrane; cell does not have to expend energy to make it happen

Small hydophobic ligands

Directly diffuse through the plasma membrane

signal transduction

Extracellular signals are converted to intracellular signals

What is facilitated diffusion? Is it active or passive? Cite two examples.

Facilitated diffusion is the phenomenon during which polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. Facilitated diffusion is considered passive transport because the solute is moving down its concentration gradient, a process that requires no energy.

Cite two lines of evidence that were inconsistent with the Davson-Danielli model.

First, inspection of a variety of membranes revealed that membranes with different functions differ in structure and chemical composition. A second, more serious problem became apparent once membrane proteins were better characterized. Unlike proteins dissolved in the cytosol, membrane proteins are not very soluble in water because they are amphipathic. If such proteins were layered on the surface of the membrane, their hydrophobic parts would be in aqueous surroundings.

the organelle that consists of a stack of flattened membranes, each enclosing a single compartment

Golgi apparatus

What are the two types pf receptors?

Internal and cell-surface

Define flaccid

Limp

What is membrane potential? Which side of the membrane is positive?

Membrane potential is the voltage across a membrane, which ranges from about -50 to -200 millivolts (mV). The minus sign indicates that the inside of the cell is negative relative to the outside.

Function of intercellular joining

Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions.

Function of attachment to cytoskeleton and ECM

Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins. Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes.

Define plasmolysis

Phenomenon during which the plant cell shrivels, and its plasma membrane pulls away from the wall.

The genetic material of a eukaryotic cell is housed in the

Nucleus

Where is the cytoskeleton mainly found in eukaryotic cell

Nucleus Cytosol

Are the processes you described in question 26 active or passive transport? Explain your response.

Passive transport. With regard to membrane potential, because the inside of the cell is negative compared with the outside, the membrane potential favors the passive transport of cations into the cell and anions out of the cell.

Why does the red blood cell burst when placed in a hypotonic solution, but not the plant cell?

Plant cells have a cell wall and animal cells do not. Plant cells are turgid (firm) and generally healthiest in a hypotonic environment, where the uptake of water is eventually balanced by the wall pushing back on the cell.

An organelle in the eukaryotic cells that contains most of the cells genetic material is the

nucleus

Major functions of the nucleus

Protecting the genome Gene regulation

The currently accepted model of the membrane is the fluid mosaic model. Who proposed it? When? Describe this model.

S. J. Singer and G. Nicolson proposed the fluid mosaic model in 1972. In this model, the membrane proteins reside in the phospholipid bilayer with their hydrophilic regions protruding.

signaling pathway

Sequence of linked reactions, triggered by activation of a receptor protein, that relays information within a cell

Describe how phospholipids with unsaturated hydrocarbon chains affect membrane fluidity.

The membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails. Because of kinks in the tails where double bonds are located, unsaturated hydrocarbon tails cannot pack together as closely as saturated hydrocarbon tails, and this makes the membrane more fluid.

Function of cell-cell recognition

Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells.

Function of the rough endoplasmic reticulum

Sorts proteins that are destined for other locations

endocrine signaling

Specialized cells release hormone molecules into vessels of the circulatory system (bloodstream) to reach target cells

Describe the Davson-Danielli model.

The Davson-Danielli model of membrane structure suggested that the membrane might be coated on both sides with hydrophilic proteins, with a phospholipid bilayer between two layers of proteins.

Use as many words are possible from the previous list to describe why a carrot left on the counter overnight become limp. Underline or highlight each word you use.

The cells of the carrot contain more water than the surrounding air, and therefore water will leave the carrot cells. The cells are hypotonic to the surrounding air. As water leaves the carrot cells, they will become flaccid as plasmolysis occurs. The water is leaving the cells by osmosis; the solutes remain in the cells.

Define osmosis

The diffusion of water across a selectively permeable membrane

Define diffusion

The movement of molecules of any substance so that they spread out evenly into the available space

Define concentration gradient

The region along which the density of a chemical substance increases or decreases

The organelle that plays a role in sorting proteins that are destined for the Golgi apparatus, lysosomes, vacuoles, plasma membrane, or outside of the cell is th

rough endoplasmic reticulum

Membrane carbohydrates are important in cell-cell recognition. What are two examples of this?

Two examples include the sorting of cells into tissues and organs in an animal embryo, and the rejection of foreign cells by the immune system.

What are the two forces that drive the diffusion of ions across the membrane? What is the combination of these forces called?

Two forces drive the diffusion of ions across a membrane: a chemical force (the ion's concentration gradient) and an electrical force (the effect of the membrane potential on the ion's movement). This combination of forces acting on ions is called the electrochemical gradient.

Define turgid

Very firm

Are transport proteins specific? Cite an example that supports your answer.

Yes. A transport protein is specific for the substance it translocates, allowing only a certain substance to cross the membrane. For example, a specific water carrier protein in the plasma membrane of red blood cells transports glucose across the membrane.

Dimer

a compound whose molecules are composed of two identical monomers

G-protein linked receptors

bind a ligand and activate a membrane protein called a G-protein

ion-channel linked receptors

bind a ligand and open a channel through the membrane that allows specific ions to pass through

target cells

cells that have receptors for a particular hormone

The complex of DNA and proteins in a eukaryotic cell is referred to as

chromatin

The membranes of the endoplasmic reticulum form which of the following

cisternae fluid filled tubules

intracellular communication

communication within a cell

The smooth ER is ___ with the rough ER

continuous

The location of the cytoskeleton is primarily in the ___ but also in the nucleus along the inner nuclear membrane.

cytosol

The endoplasmic reticulum is a network of

membranes

The double membrane structure that surrounds the nucleus is the

nuclear envelope

receptors

proteins on target cells that receive chemical signals

Synapse

the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

examples of endocrine signals

thyroid gland, hypothalamus, pituitary gland

Dimerization

two receptors bind to each other to form a stable complex called a dimer