Chapter 5

Why are membranes selectively permeable?

to regulate transport across cellular boundaries.
it allows some substances to cross it more easily than others
the cell can maintain an internal environment that is different from its external environment

What are the roles of phospholipids, proteins, and carbohydrates in membranes?

Phospholipids make up the phospholipid bilayer and exists as a stable boundary between two aqueous environments.
Membrane proteins can function as enzymes to speed up chemical reactions, act as receptors for specific molecules, or transport materials across the cell membrane
Carbohydrates covalently linked to proteins (glycoproteins) or lipids (glycolipids) are also a part of cell membranes, and function as adhesion and address loci for cells.
The Fluid Mosaic Model describes membranes as a fluid lipid bilayer with floating proteins and carbohydrates.

How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution and be able to predict the effect of different environments on the organism.

Isotonic: no net movement of water; water diffuses in both directions at the same rate and the volume of the cell is stable
Hypertonic: the water moves to the solution that is hypertonic; cell shrivels up
Hypotonic: water moves out of the solution that is hypotonic and into the cell; the cell expands

How electrochemical gradients and proton gradients are formed and function in cells

The electrical and concentration gradients of a membrane tend to drive sodium into and potassium out of the cell, and active transport works against these gradients. To move substances against a concentration or electrochemical gradient, the cell must utilize energy in the form of ATP during active transport.
- the ion's concentration gradient and electrical force
-drives diffusion of ions across the membrane

the proton gradient may be used as an intermediate energy source for heat and flagellar rotation. It results from the higher concentration of protons outside the inner membrane of the mitochondria than inside the membrane, and becomes the driving force behind atp synthesis/hydrolysis.

The three stages of cell communication: reception, transduction, and response

Reception: detection of the chemical signal

Transduction: convert the signal into a form that can bring about specific cellular sepnsonse; typically requires a signal transduction pathway

Response: can be almost anything; catalysis by an enzyme, rearrangement of the cytoskeleton, activation of specific genes in the nucleus.

How a receptor protein recognizes signal molecules and starts transduction

Receptor molecules called ligands must be of complementary shape to a specific site on the receptor; like a lock and key.
F-PROTEIN COUPLED RECEPTORS (GPCR)
-works w/ the help of a g-protein which uses the energy of GTP
-the ligand binds to the GPCR and causes its shape to change slightly
- then the GPCR binds w/ the G-protein and activates it with GTP

LIGAND-GATED ION CHANNELS
- the ligand causes a change in the shape of the gate; the gate opens and allows ions to flow freely across the membrane
- when the ligand dissociates from the receptor, the gate closes
- extremely important in the nervous system

How a cell signal is amplified by a phosphorylation cascade.

Defined as the activation of proteins by addition of removal of phosphate groups or other messenger molecules.
can greatly amplify the signal and provide more opportunities for coordination and regulation.
The original signaling molecules sends information, but doesn't actually enter the cell.

An example of a second messenger and its role in a signal transduction pathway.

-cyclic AMP (cAMP) and calcium ions
- allow for massive amplification of the signal
- typically, the second messengers activate a protein kinase that begins the phosphorylation cascade.

How a cell response in the nucleus turns on genes whereas in the cytoplasm it activates enzymes.

Nucleus:
- many pathways ultimately regulate protein synthesis by turning on or off specific genes in the nucleus.
- this is achieved by transcription factors that are necessary to begin the first step of protein synthesis
Cytoplasm: signaling may regulate the activity of a protein rather than its synthesis, which affects cellular activity in the cytoplasm.

What apoptosis means and why it is important to normal functioning of multicellular organisms.

the death of cells that occurs as a normal and controlled part of an organism's growth or development.

Developmental changes, removes old, damaged or infected cells, removes cells that have DNA damage and removes immune cells that attack self cells

Selective Permeability

allows some substances to cross the membrane more easily than others
allows the cell to maintain an internal environment that is different from its external environment

amphipathic

Most membrane proteins and phospholipids are amphipathic
Phospholipids both a hydrophilic region and a hydrophobic region.
B/c membrane proteins can be amphipathic, they can reside in the bilayer with their hydrophilic regions protruding

Fluid mosaic model

Cellular membranes are fluid mosaics of lipids and proteins
The model is not a static structure; it is a mosaic of protein molecules bobbing and the membrane moves around like waves

Integral proteins

Go at least part way into the hydrophobic interior
Most are transmembrane, but proteins determine the membrane's fucntion

Peripheral proteins

they are not embed in the lipid bilayer
- loosely bound to the surface of the lipid bilayer
- often attached to the cytoskeleton or fibers of the ECM (extracellular matrix)

6 major functions of membrane proteins

- Transport
- Enzymatic activity
- Attachment to the cytoskeleton or ECM (extracellular matrix)
- cell to cell recognition
- Intercellular joining
- Signal transduciton

Glycolipids

Membrane carbohydrates that are covalently bonded to lipids.

Glycoproteins

A protein with one or more covalently attached carbohydrates.

Transport proteins

- Span the membrane
- May provide a hydrophillic channel across the membrane that is selective for a particular solute (passive)
- May shuttle solutes across by changing shape via the use of ATP (active).
- allow polar molecules and ions to cross the membrane w/o having contact with the hydrophobic interior region

Aquaporins

a specialized transport protein for water molecules

Diffusion

- the movement of particles of any substance so that they spread into the available space.
- each molecule moves randomly, yet diffusion of a population of molecules is directional
- type of passive transport (no energy needed)

Concentration gradient

Substances diffuse down their own concentration gradient; Not affected by the gradients of other substances
represents potential energy and drives diffusion

Passive transport

diffusion of a substance across a membrane with no energy investment
This process is effective as long as the membrane is permeable to the substance
doesnt need energy b/c the concentration gradient already represents potential energy

Osmosis

- similar to diffusion, but refers to the movement of water across a membrane (rather than solutes or particles) to come to equilibrium
- the difference in free water concentration drives osmosis

Tonicity

- the ability of a surrounding solution to cause a cell to gain or lose water
- Partially dependent on the concentration of the solutes that cannot cross the membrane (then the water has to move)

Isotonic

- No net movement of water
- Water diffuses in both direction at the same rate
- volume of the cell is stable

Hypertonic

- "hyper" means more solutes
- Water moves to the solution that is hypertonic
- Water moves out of the cell

Hypotonic

- "hypo" means less solutes
- Water moves out of the solution that is hypotonic
- water moves into the cell

Osmoregulation

The control of water balance in organisms living in hypertonic, hypotonic, or terrestrial environments.

Turgid

Distended or swollen, especially due to high fluid content.

Flaccid

(adj.) limp, not firm or strong (If a plant is not watered enough, its leaves become droopy and flaccid.)

Plamolysis

The "shrinkage" of a cell's contents in a hypertonic solution, but not the entire cell because of its rigid, external cell wall

Facilitated diffusion

- Passive transport (no ATP used)
- speeds transport of a solute but doesn't alter the direction of movement

Ion channels

-When open allow for passage of certain ions down
-electrochemical gradient, creates an electric current
- channel proteins that transport ions

Gated channels

many ion channels function as gated channels these channels open or close depending on the presence or absence of a chemical or physical stimulus

Active transport

- uses energy to move solutes AGAINST THEIR GRADIENTS
- Active \= use of ATP
- moves solutes against their concentration gradients, moving solutes from an area of lesser concentration to an area of greater concentration.

Sodium-potassium pump

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

Membrane potential

-The voltage across a cell's plasma membrane.
- small but significant
- acts like a battery, an energy source that affects the traffic of all charged substances (ions) across the membrane
- inside is negative compared to outside
- favors that passive transport of cations into the cell and anions out of the cell

Electrochemical gradient

- drives the diffusion of ions across the membrane
- made of up of the ion's concentration gradient and electrical force

Electrogenic pump

- helps store energy that can be tapped for cellular work
- can function as the generator of ATP during cellular respiration
- A transport protein that generates voltage across a membrane, causing a net separation in charge.

Proton pump

An electrogenic pump that works largely with H+ ions.

Cotransport

- uses ATP
- one solute is pumped against the concentration gradient across the membrane
- as it diffuses back into the cell, it carries another solute with it

Exocytosis

- occurs when the cell secretes biological molecules through the fusion of vesicles with the plasma membrane
- a transport vesicle buds from the Golgi, to the membrane, and the two membranes fuse, effectively dumping the contents of the vesicle into the outside of the cell

Endocytosis

- the reverse of exocytosis
- cell takes in molecules by forming new vesicles from the plasma membrane
- a small area of the plasma membrane sinks inward, forming a pocket. The pocket pinches in and forms a vesicle containing material that was once outside of the cell
- mechanism for rejuvenating the plasma membrane
- Three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis

Phagocytosis

A type of endocytosis
Cellular eating
Cellular process of engulfing food and encapsulating it in a vacuole.

Pinocytosis

A type of endocytosis
Cellular drinking
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Receptor-mediated endocytosis

- acquisition of bulk quantities of specific substances
- receptor proteins are exposed to the extracellular fluid. Specific solutes bind to the sites. the proteins then cluster in pits that form vesicles containing the bound molecules

Local regulators

Used in local communication between cells
- can be direct contact through gap junctions or plamodesmata
A chemical messenger that influences cells in the vicinity.

Hormones and endocrine signaling

- used by long distance signaling (endocrine signaling)
- specialized cells release molecules of hormones
- travel through the body via the circulatory system
- reach target cells that recognize and respond to the hormone

Cell signaling

cell-to-cell communication allows the cells to coordinate their activities
Cellular response to signaling can be divided into three stages:
- reception
- transduction
- response

Reception

- detection of the chemical signal
- signaling molecule receptor
- tyrosine, kinase, G-protein coupled receptor

Transduction

- convert the signal into a form that can bring about specific cellular responses
- typically requires a signal transduction pathway
Can involve:
- phosphorylation cascade
-second messengers
- adenylyl cyclase
-cAMP, Ca2+, IP3

Response

- can be almost anything
- catalysis by an enzyme, rearrangement of the cytoskeleton, activation of specific genes in the nucleus

Signal transduction pathway

A series of steps linking a mechanical or chemical stimulus to a specific cellular response.
- leads to the regulation of one or more cellular activities

Ligand

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

G-protein coupled receptor

- works with the help of a G-protein which uses the energy of GTP
- binding of the ligand tot he GPCR causes its shape to change slightly
- the GPCR then binds the G-protein and activates it with GTP
- The G-protein leaves the receptor and binds to an enzyme, activating it by changing its shape
- The activated enzyme triggers the next step in cellular response

G-Protein

helps GPCR function and uses GTP

Ligand-gated ion channel

- another class of membrane receptors
- ligand causes a change in shape of athe gate
-the gate opens, allowing ions to flow freely across the membrane
- when the ligand dissociates from the receptor, the gate closes
- extremely important in the nervous system

Protein kinase

- enzymes that transfer the phosphate groups from ATP to proteins
- widely involved in transduction pathways
- addition of phosphate group changes the form of the protein from inactive to active

Protein phosphatases

reverse kinases
- removing the phosphate from proteins, turning off the pathway when the initial signal is no longer present

Second messengers

- cyclic AMP (cAMP) and calcium ions
- allow for massive amplification of a signal
activate a protein kinase that begins phosphorylation cascade

Why are membranes selectively permeable?

to regulate transport across cellular boundaries.
it allows some substances to cross it more easily than others
the cell can maintain an internal environment that is different from its external environment

What are the roles of phospholipids, proteins, and carbohydrates in membranes?

Phospholipids make up the phospholipid bilayer and exists as a stable boundary between two aqueous environments.
Membrane proteins can function as enzymes to speed up chemical reactions, act as receptors for specific molecules, or transport materials across the cell membrane
Carbohydrates covalently linked to proteins (glycoproteins) or lipids (glycolipids) are also a part of cell membranes, and function as adhesion and address loci for cells.
The Fluid Mosaic Model describes membranes as a fluid lipid bilayer with floating proteins and carbohydrates.

How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution and be able to predict the effect of different environments on the organism.

Isotonic: no net movement of water; water diffuses in both directions at the same rate and the volume of the cell is stable
Hypertonic: the water moves to the solution that is hypertonic; cell shrivels up
Hypotonic: water moves out of the solution that is hypotonic and into the cell; the cell expands

How electrochemical gradients and proton gradients are formed and function in cells

The electrical and concentration gradients of a membrane tend to drive sodium into and potassium out of the cell, and active transport works against these gradients. To move substances against a concentration or electrochemical gradient, the cell must utilize energy in the form of ATP during active transport.
- the ion's concentration gradient and electrical force
-drives diffusion of ions across the membrane

the proton gradient may be used as an intermediate energy source for heat and flagellar rotation. It results from the higher concentration of protons outside the inner membrane of the mitochondria than inside the membrane, and becomes the driving force behind atp synthesis/hydrolysis.

The three stages of cell communication: reception, transduction, and response

Reception: detection of the chemical signal

Transduction: convert the signal into a form that can bring about specific cellular sepnsonse; typically requires a signal transduction pathway

Response: can be almost anything; catalysis by an enzyme, rearrangement of the cytoskeleton, activation of specific genes in the nucleus.

How a receptor protein recognizes signal molecules and starts transduction

Receptor molecules called ligands must be of complementary shape to a specific site on the receptor; like a lock and key.
F-PROTEIN COUPLED RECEPTORS (GPCR)
-works w/ the help of a g-protein which uses the energy of GTP
-the ligand binds to the GPCR and causes its shape to change slightly
- then the GPCR binds w/ the G-protein and activates it with GTP

LIGAND-GATED ION CHANNELS
- the ligand causes a change in the shape of the gate; the gate opens and allows ions to flow freely across the membrane
- when the ligand dissociates from the receptor, the gate closes
- extremely important in the nervous system

How a cell signal is amplified by a phosphorylation cascade.

Defined as the activation of proteins by addition of removal of phosphate groups or other messenger molecules.
can greatly amplify the signal and provide more opportunities for coordination and regulation.
The original signaling molecules sends information, but doesn't actually enter the cell.

An example of a second messenger and its role in a signal transduction pathway.

-cyclic AMP (cAMP) and calcium ions
- allow for massive amplification of the signal
- typically, the second messengers activate a protein kinase that begins the phosphorylation cascade.

How a cell response in the nucleus turns on genes whereas in the cytoplasm it activates enzymes.

Nucleus:
- many pathways ultimately regulate protein synthesis by turning on or off specific genes in the nucleus.
- this is achieved by transcription factors that are necessary to begin the first step of protein synthesis
Cytoplasm: signaling may regulate the activity of a protein rather than its synthesis, which affects cellular activity in the cytoplasm.

What apoptosis means and why it is important to normal functioning of multicellular organisms.

the death of cells that occurs as a normal and controlled part of an organism's growth or development.

Developmental changes, removes old, damaged or infected cells, removes cells that have DNA damage and removes immune cells that attack self cells

Selective Permeability

allows some substances to cross the membrane more easily than others
allows the cell to maintain an internal environment that is different from its external environment

amphipathic

Most membrane proteins and phospholipids are amphipathic
Phospholipids both a hydrophilic region and a hydrophobic region.
B/c membrane proteins can be amphipathic, they can reside in the bilayer with their hydrophilic regions protruding

Fluid mosaic model

Cellular membranes are fluid mosaics of lipids and proteins
The model is not a static structure; it is a mosaic of protein molecules bobbing and the membrane moves around like waves

Integral proteins

Go at least part way into the hydrophobic interior
Most are transmembrane, but proteins determine the membrane's fucntion

Peripheral proteins

they are not embed in the lipid bilayer
- loosely bound to the surface of the lipid bilayer
- often attached to the cytoskeleton or fibers of the ECM (extracellular matrix)

6 major functions of membrane proteins

- Transport
- Enzymatic activity
- Attachment to the cytoskeleton or ECM (extracellular matrix)
- cell to cell recognition
- Intercellular joining
- Signal transduciton

Glycolipids

Membrane carbohydrates that are covalently bonded to lipids.

Glycoproteins

A protein with one or more covalently attached carbohydrates.

Transport proteins

- Span the membrane
- May provide a hydrophillic channel across the membrane that is selective for a particular solute (passive)
- May shuttle solutes across by changing shape via the use of ATP (active).
- allow polar molecules and ions to cross the membrane w/o having contact with the hydrophobic interior region

Aquaporins

a specialized transport protein for water molecules

Diffusion

- the movement of particles of any substance so that they spread into the available space.
- each molecule moves randomly, yet diffusion of a population of molecules is directional
- type of passive transport (no energy needed)

Concentration gradient

Substances diffuse down their own concentration gradient; Not affected by the gradients of other substances
represents potential energy and drives diffusion

Passive transport

diffusion of a substance across a membrane with no energy investment
This process is effective as long as the membrane is permeable to the substance
doesnt need energy b/c the concentration gradient already represents potential energy

Osmosis

- similar to diffusion, but refers to the movement of water across a membrane (rather than solutes or particles) to come to equilibrium
- the difference in free water concentration drives osmosis

Tonicity

- the ability of a surrounding solution to cause a cell to gain or lose water
- Partially dependent on the concentration of the solutes that cannot cross the membrane (then the water has to move)

Isotonic

- No net movement of water
- Water diffuses in both direction at the same rate
- volume of the cell is stable

Hypertonic

- "hyper" means more solutes
- Water moves to the solution that is hypertonic
- Water moves out of the cell

Hypotonic

- "hypo" means less solutes
- Water moves out of the solution that is hypotonic
- water moves into the cell

Osmoregulation

The control of water balance in organisms living in hypertonic, hypotonic, or terrestrial environments.

Turgid

Distended or swollen, especially due to high fluid content.

Flaccid

(adj.) limp, not firm or strong (If a plant is not watered enough, its leaves become droopy and flaccid.)

Plamolysis

The "shrinkage" of a cell's contents in a hypertonic solution, but not the entire cell because of its rigid, external cell wall

Facilitated diffusion

- Passive transport (no ATP used)
- speeds transport of a solute but doesn't alter the direction of movement

Ion channels

-When open allow for passage of certain ions down
-electrochemical gradient, creates an electric current
- channel proteins that transport ions

Gated channels

many ion channels function as gated channels these channels open or close depending on the presence or absence of a chemical or physical stimulus

Active transport

- uses energy to move solutes AGAINST THEIR GRADIENTS
- Active \= use of ATP
- moves solutes against their concentration gradients, moving solutes from an area of lesser concentration to an area of greater concentration.

Sodium-potassium pump

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

Membrane potential

-The voltage across a cell's plasma membrane.
- small but significant
- acts like a battery, an energy source that affects the traffic of all charged substances (ions) across the membrane
- inside is negative compared to outside
- favors that passive transport of cations into the cell and anions out of the cell

Electrochemical gradient

- drives the diffusion of ions across the membrane
- made of up of the ion's concentration gradient and electrical force