Chapter 6

The structural characteristics of transporters, such as size, shape, and charge, determine what they transport—a property called ______________.

The structural characteristics of transporters, such as size, shape, and charge, determine what they transport—a property called specificity.

We say plasma membranes are __________ _____________, meaning they can control what substances pass through them and the direction and rate of transport of these substances.

We say plasma membranes are selectively permeable, meaning they can control what substances pass through them and the direction and rate of transport of these substances.

Membrane transport processes can be labeled as ________ or ________.

Membrane transport processes can be labeled as passive or active

Passive processes do not require any ___________ expenditure or “activity” of the cell membrane—the particles move by using energy that they already have. Active processes, on the other hand, do require the expenditure of metabolic energy by the cell.

Passive processes do not require any energy expenditure or “activity” of the cell membrane—the particles move by using energy that they already have. Active processes, on the other hand, do require the expenditure of metabolic energy by the cell.

In active processes the transported particles are actively “___________” across the membrane. Keep this distinction in mind as we explore the basic mechanisms of cell membrane transport.

In active processes the transported particles are actively “carried” across the membrane. Keep this distinction in mind as we explore the basic mechanisms of cell membrane transport.

The term ______________ refers to a natural phenomenon caused by the tendency of small particles to spread out evenly within any given space. All molecules in a solution bounce around in short, chaotic paths. As they collide with one another, they tend to spread out, or __________.

The term diffusion refers to a natural phenomenon caused by the tendency of small particles to spread out evenly within any given space. All molecules in a solution bounce around in short, chaotic paths. As they collide with one another, they tend to spread out, or diffuse.

Note that during diffusion, molecules move from an area of higher concentration to an area of lower concentration. Another way of stating this principle is to say that diffusion always occurs down a ___________ __________.

Note that during diffusion, molecules move from an area of higher concentration to an area of lower concentration. Another way of stating this principle is to say that diffusion always occurs down a concentration gradient.

Recall that a ____________ is a mixture of one or more solutes and a solvent

Recall that a solution is a mixture of one or more solutes and a solvent

The end result of diffusion is an ____________ in which both solutions have equal concentrations.

The end result of diffusion is an equilibrium in which both solutions have equal concentrations.

Homeostatic mechanisms maintain concentration differences so that diffusion does not stop. This condition of continual, constant diffusion is sometimes called a ____________ equilibrium.

Homeostatic mechanisms maintain concentration differences so that diffusion does not stop. This condition of continual, constant diffusion is sometimes called a dynamic equilibrium.

Movement of particles through the phospholipid bilayer from an area of higher concentration to an area of lower concentration—that is, down the concentration gradient..

What is it? example?

Simple Diffusion. EX. carbon dioxide out of all cells

Passive transport of water through a selectively permeable membrane in the presence of at least one impermeant solute

What is it? Example?

Osmosis. Ex. Water molecules into and out of cells to maintain cell volume

Diffusion of particles through a membrane by means of membrane channels (particles move down their concentration gradient)

What is it? Example?

Channel-mediated passive transport (facilitated diffusion)

Diffusion of sodium ions into nerve cells during a nerve impulse

Diffusion of particles through a membrane by means of membrane carriers (particles move down their concentration gradient)

What is it? example?

Carrier-mediated passive transport (facilitated diffusion)

Diffusion of glucose molecules into most cells

Sometimes molecules diffuse directly through the bilayer of phospholipid molecules that forms most of a cell membrane.

What kind of molecules pass easily?

lipid-soluble molecules can pass through easily. such as oxygen (O2) and carbon dioxide (CO2) can diffuse directly

. When molecules pass directly through the phospholipid membrane, the process is called __________ diffusion.

. When molecules pass directly through the phospholipid membrane, the process is called simple diffusion.

When molecules are allowed to cross a membrane, they are said to __________ the membrane. Thus a membrane is permeable to a molecule only if it can pass through that membrane. We say that a molecule is _________ if it is able to diffuse across a membrane—and it is __________ if it cannot.

When molecules are allowed to cross a membrane, they are said to permeate the membrane. Thus a membrane is permeable to a molecule only if it can pass through that membrane. We say that a molecule is permeant if it is able to diffuse across a membrane—and it is impermeant if it cannot.

____________ is the movement of water through a semipermeable membrane. A semipermeable membrane allows water to pass through the membrane, but blocks the passage of at least one solute. Often, water is able to move across a living membrane that does not allow movement of one or more other substances.

Osmosis is the movement of water through a semipermeable membrane. A semipermeable membrane allows water to pass through the membrane, but blocks the passage of at least one solute. Often, water is able to move across a living membrane that does not allow movement of one or more other substances.

a term meaning “water pore proteins.”

aquaporins

the pressure that prevents the movement of water by osmosis from pure water into the solution.

osmotic pressure

The higher the osmotic pressure of a solution, the ___________ the tendency for water to move into it.

The higher the osmotic pressure of a solution, the greater the tendency for water to move into it.

Osmotic pressure and solution concentration are related. How?

The more concentrated (with impermeant solutes) a solution, the higher is its osmotic pressure. Thus water moves by osmosis from the solution with the lower osmotic pressure (lower concentration) into the solution with the higher osmotic pressure (higher concentration).

A mediated passive transport that is often called ____________ diffusion because the diffusion is facilitated, or helped, by the transporters.

mediated passive transport that is often called facilitated diffusion because the diffusion is facilitated, or helped, by the transporters.

Cell membranes possess protein “__________,” better known as membrane channels . Membrane channels are pores through which water molecules, specific ions, or small, water-soluble molecules can pass.

Cell membranes possess protein “tunnels,” better known as membrane channels . Membrane channels are pores through which water molecules, specific ions, or small, water-soluble molecules can pass.

For example, sodium ions (Na+) pass only through sodium channels, and chloride ions (Cl−) pass only through chloride channels. Recall that water moves through AQPs, which are water-specific channels, during osmosis. AQP channels also may be called aquapores.

The active or “open” state can be almost immediately changed to the “closed” state, or the state can be changed from closed to open, by various triggering mechanisms. Some gated channels are triggered by ?

electrical changes (voltage),

others by light,

and still others by mechanical or chemical stimuli.

Because ions or molecules move down their concentration gradients as they pass through channels, this type of facilitated diffusion is passive and is called __________ ___________ __________ transport.

Because ions or molecules move down their concentration gradients as they pass through channels, this type of facilitated diffusion is passive and is called channel-mediated passive transport.

Molecules may move down their concentration gradient by passing through a different type of membrane transporter called a ___________ ____________.

Molecules may move down their concentration gradient by passing through a different type of membrane transporter called a membrane carrier.

Thus the carrier may facilitate diffusion in a process called carrier-mediated passive transport.

Carrier reactions are sometimes __________ and may thus transport molecules in either direction, depending on the concentration gradient.

Carrier reactions are sometimes reversible and may thus transport molecules in either direction, depending on the concentration gradient.

The adenosine diphosphate (ADP)–adenosine triphosphate (ATP) carrier found in the inner membranes of the mitochondrion transports ADP into and ATP out of the mitochondrial matrix

There are different types of passive transporters, or _________, in membranes.

There are different types of passive transporters, or porters, in membranes.

Some transport only one type of ion or molecule at a time. This type of porter is often called a __________.

Some transport only one type of ion or molecule at a time. This type of porter is often called a uniporter.

__________________ move two or more types of ions or molecules in the same direction through a membrane.

Symporters move two or more types of ions or molecules in the same direction through a membrane.

Symport can also be called ______________.

Symport can also be called cotransport.

This form of transport involves the passing of water and permeable solutes through a membrane by the force of hydrostatic pressure.

filtration

____________ pressure is the force, or weight, of a fluid pushing against a surface.

Hydrostatic pressure is the force, or weight, of a fluid pushing against a surface.

Membrane transporters called membrane __________ are able to carry out a transport process in which cellular energy is used to move molecules “uphill” through a cell membrane.

Membrane transporters called membrane pumps are able to carry out a transport process in which cellular energy is used to move molecules “uphill” through a cell membrane.

Diffusion—a passive process

a. Molecules spread through membranes

b. Molecules move from an area of higher concentration to an area of lower concentration, down a concentration gradient

c. There is no diffusion when concentrations are equal

Simple diffusion

a. Molecules cross through the phospholipid bilayer

b. Solutes permeate the membrane; therefore we call the membrane permeable

Osmosis

a. Osmosis is the movement of water through a semipermeable membrane, which prevents the passage of at least one solute

b. Osmotic pressure is the force that prevents the movement of water by osmosis; it is a measure of the tendency for water to move into a solution

c. Water moves from the solution with the lower concentration of impermeant solutes (lower osmotic pressure) into the solution with the higher concentration of impermeant solutes (higher osmotic pressure). The greater the difference in osmotic pressures between the solutions, the greater is the movement of water

Water moving into or out of cells determines cell volume. Cells placed in a(an)

1. hypertonic solution

2. isotonic solution

3. hyptonic solution

(1) Hypertonic solution shrivel as water flows out of them

(2) Isotonic solution do not change volume

(3) Hypotonic solution swell as water flows into them

Facilitated diffusion (mediated passive transport)

a. kind of diffusion?

b. gradient?

c. energy?

d. types ?

a. A special kind of diffusion in which movement of molecules is made more efficient by the action of transporters embedded in a cell membrane

b. Transports substances down a concentration gradient

c. Energy required comes from the collision energy of the solute

d. Channel-mediated passive transport, Carrier-mediated passive transport

Channel-mediated passive transport

(1) Channels are specific—allow only one type of solute to pass through

(2) Gated channels may be open or closed—may be triggered by a variety of stimuli

(3) Aquaporins (AQPs) are water channels that permit rapid osmosis

Carrier-mediated passive transport

(1) Carriers attract and bind to the solute, change shape, and release the solute out the other side of the carrier

(2) Carriers can be reversible, depending on the direction of the concentration gradient

Role of passive transport processes

Channels and carriers allow membranes to be selectively permeable; one-way transporters may determine direction of transport

Types of passive transport

(1) Diffusion directly across phospholipid bilayer (simple diffusion) or through membrane channels and carriers (facilitated diffusion); driven by concentration gradient of solute (higher concentration toward lower concentration)

(2) Osmosis is passive movement of water through AQPs based on difference in osmotic pressure, moving water from a less-concentrated solution (lower osmotic pressure) to a more-concentrated solution (higher osmotic pressure)

(3) Does not require metabolic energy and moves ions and molecules into and out of cells and organelles to maintain homeostasis

Transport by pumps

a. Pumps are membrane transporters that move a substance against their concentration gradient—opposite of diffusion

b. Examples: calcium pumps and sodium-potassium pumps

allow substances to enter or leave the interior of a cell without actually moving through its plasma membrane

Transport by vesicles

Two basic types of endocytosis

Phagocytosis

Pinocytosis

Two basic types of endocytosis (explain them)

(a) Phagocytosis—“condition of cell eating”; large particles are engulfed by the plasma membrane and enter the cell in vesicles; the vesicles fuse with lysosomes, which digest the particles

(b) Pinocytosis—“condition of cell drinking”; fluid and the substances dissolved in it enter the cell

the plasma membrane “traps” some extracellular material and brings it into the cell in a vesicle

Endocytosis

membrane receptor molecules recognize substances to be brought into the cel

Receptor-mediated endocytosis

Exocytosis

1. Process by which

2. Large molecules are what?

3. provides a way fo?

4. X vesicle that may?

(1) Process by which large molecules, notably proteins, can leave the cell even though they are too large to pass through the plasma membrane

(2) Large molecules are enclosed in membranous vesicles and then pulled to the plasma membrane by the cytoskeleton, where the contents are released

(3) Exocytosis also provides a way for new material to be added to the plasma membrane

(4) Exosome—extracellular vesicle that may pinch off a cell during exocytosis

Role of active transport processes

a. Active transport requires energy use by the membrane

b. Pumps—concentrate substances on one side of a membrane, as when storing an ion inside an organelle

c. Vesicle-mediated transport (endocytosis, exocytosis)—moves large volumes of substances at once using a bag of membrane, as in the secretion of hormones and neurotransmitters

breaks large molecules into smaller ones; usually releases energy

Catabolism

builds large molecules from smaller ones; usually consumes energy

Anabolism

Chemical structure of enzymes

a. Proteins of a complex shape

b. The active site is where the enzyme molecule fits the substrate molecule—a type of lock-and-key model (

____________ regulate cell metabolism

Enzymes regulate cell metabolism

____________ are chemical catalysts that reduce the activation energy needed for a reaction

Enzymes are chemical catalysts that reduce the activation energy needed for a reaction

_______________ usually have an -ase ending, with the first part of the word signifying the substrate or the type of reaction catalyzed

Enzymes usually have an -ase ending, with the first part of the word signifying the substrate or the type of reaction catalyzed

known as oxidases, hydrogenases, and dehydrogenases; energy release depends on these enzymes

Oxidation-reduction enzymes

digestive enzymes belong to this group

Hydrolyzing enzymes—hydrolases; digestive enzymes belong to this group

add or remove phosphate groups

Phosphorylating enzymes—phosphorylases or phosphatases; add or remove phosphate groups

Enzymes that add or remove carbon dioxide

carboxylases or decarboxylases

Enzymes that rearrange atoms within a molecule

mutases or isomerases

________________ add water to a molecule without splitting it

Hydrases add water to a molecule without splitting it

General functions of enzymes

a. Enzymes regulate cell functions by regulating metabolic pathways

b. Enzymes are specific in their actions

c. Various chemical and physical agents known as allosteric effectors affect enzyme action by changing the shape of the enzyme molecule; examples of allosteric effectors include :

(1) Temperature

(2) Hydrogen ion (H+) concentration (pH)

(3) Cofactors

(4) End products of certain metabolic pathways

d. Most enzymes catalyze a chemical reaction in both directions

e. Enzymes are continually being destroyed and continually being replaced

f. Many enzymes are first synthesized as inactive proenzymes

__________ ____________, the pathway by which glucose is broken down to yield its stored energy, is an important example of cell catabolism

Cellular respiration, the pathway by which glucose is broken down to yield its stored energy, is an important example of cell catabolism

cellular respiration has three pathways that are chemically linked

a. Glycolysis

b. Citric acid cycle

c. Electron transport system (ETS)

Pathway in which glucose is broken apart into two pyruvate molecules to yield a small amount of energy (which is transferred to ATP and NAD)

Glycolysis

Glycolysis

1. Pathway in which..

2. Includes many..

3. Aerobic?

4. occurs where?

5. Enzymes may convert?

a. Pathway in which glucose is broken apart into two pyruvate molecules to yield a small amount of energy (which is transferred to ATP and NAD)

b. Includes many chemical steps (reactions that follow one another), each regulated by specific enzymes

c. Is anaerobic (requires no oxygen)

d. Occurs within cytosol (outside the mitochondria)

e. Enzymes may convert some of the pyruvate into lactate, which pools until it can be converted back to pyruvate and used in the aerobic pathway to generate ATP

Citric acid cycle (Krebs cycle)

1. Pyruvate is..

2. the cycle is a repeating..

a. Pyruvate (from glycolysis) is converted into acetyl, which is “picked up” by CoA and enters the citric acid cycle after losing CO2 and transferring some energy to NAD

b. Citric acid cycle is a repeating (cyclic) sequence of reactions that occur inside the inner chamber of a mitochondrion; acetyl splits from CoA and is broken down to yield waste CO2 and energy (in the form of energized electrons), which is transferred to ATP, NADH, and FADH2

Electron transport system (ETS)

1. Energized electrons are …

2. as electrons are shuttled…

3. Protons what?

4. What is formed and how?

a. Energized electrons are carried by NADH and FADH2 from glycolysis and the citric acid cycle to electron acceptors embedded in the cristae of the mitochondrion

b. As electrons are shuttled along a chain of electron-accepting molecules in the cristae, their energy is used to pump accompanying protons (H+) into the space between mitochondrial membranes

c. Protons flow back into the inner chamber through pump molecules in the cristae, and their energy of movement is transferred to ATP

d. Low-energy electrons coming off the ETS bind to oxygen and rejoin their protons to form water (H2O)

Protein synthesis is a central anabolic pathway in cells,

Anabolism

Such bulk transport mechanisms differ from pump mechanisms how?

Such bulk transport mechanisms differ from pump mechanisms in that they allow substances to enter or leave the interior of a cell without actually moving through its plasma membrane

In ____________ the plasma membrane “traps” some extracellular material and brings it into the cell.

In endocytosis the plasma membrane “traps” some extracellular material and brings it into the cell.

In a type of endocytosis called receptor-mediated endocytosis, receptors in the plasma membrane first bind to specific molecules in the extracellular fluid, which triggers endocytosis

The cytoskeleton does all the work by pulling part of the plasma membrane inward, thereby forming a depression, while at the same time pushing the membrane at the edges to form a sort of trap for extracellular material. When the extended edges of membrane fuse, a vesicle forms. The cytoskeleton then pulls the vesicle containing extracellular material inward.

In _________________ , microorganisms or other large particles are engulfed by the plasma membrane and enter the cell in vesicles that have pinched off from the membrane. Once inside, the vesicles may mature to form various types of vesicular organelles, such as lysosomes.

In phagocytosis, microorganisms or other large particles are engulfed by the plasma membrane and enter the cell in vesicles that have pinched off from the membrane. Once inside, the vesicles may mature to form various types of vesicular organelles, such as lysosomes.

______________, or “condition of the cell drinking,” is a similar process in which fluid and the substances dissolved in it enter a cell.

Pinocytosis, or “condition of the cell drinking,” is a similar process in which fluid and the substances dissolved in it enter a cell.

Movement of solute particles from an area of lower concentration to an area of higher concentration (up the concentration gradient) by means of an energy-consuming pump structure in the membrane

What type of active transport? example?

Pumping: In muscle cells, pumping of nearly all calcium ions to special compartments—or out of the cell

Movement of cells or other large particles into cell by trapping it in a section of plasma membrane that pinches off to form an intracellular vesicle; a type of vesicle-mediated transport

What type of active transport? example?

Phagocytosis (endocytosis), Trapping of bacterial cells by phagocytic white blood cells

Movement of fluid and dissolved molecules into a cell by trapping them in a section of plasma membrane that pinches off to form an intracellular vesicle; a type of vesicle-mediated transport

What type of active transport? example?

Pinocytosis (endocytosis), Trapping of large protein molecules by some body cells

Movement of proteins or other cell products out of the cell by fusing a secretory vesicle with the plasma membrane; a type of vesicle-mediated transport

What type of active transport? example?

Exocytosis, Secretion of the hormone prolactin by pituitary cells

______________ is the process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane

Exocytosis is the process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane

the smooth endoplasmic reticulum (SER) membrane concentrates calcium ions inside the SER, where they are stored for later use (as in muscle contraction).

__________________: the chemical reactions that occur in the body.

metabolism: the chemical reactions that occur in the body.

_________ metabolism, then, refers to the chemical reactions of the cell.

Cell metabolism, then, refers to the chemical reactions of the cell.

Enzymes, which are classified as functional ______________,

Enzymes, which are classified as functional proteins,

________________—a chemical that reduces the amount of activation energy needed to start a chemical reaction

catalyst—a chemical that reduces the amount of activation energy needed to start a chemical reaction

___________ are proteins and have the chemical properties of proteins. __________ are usually tertiary or quaternary proteins of complex shape.

Enzymes are proteins and have the chemical properties of proteins. Enzymes are usually tertiary or quaternary proteins of complex shape.

Often, their molecules contain a nonprotein part called a cofactor. Inorganic ions or vitamins may make up part of a cofactor. If the cofactor is an organic nonprotein molecule, it is called a ___________________.

Often, their molecules contain a nonprotein part called a cofactor. Inorganic ions or vitamins may make up part of a cofactor. If the cofactor is an organic nonprotein molecule, it is called a coenzyme.

The _________ __________ is the portion of the enzyme molecule that chemically “fits” the substrate molecule or molecules. Recall that a substrate is the molecule acted on by an enzyme molecule.

The active site is the portion of the enzyme molecule that chemically “fits” the substrate molecule or molecules. Recall that a substrate is the molecule acted on by an enzyme molecule.

All digestive enzymes are classified as _____________ because they catalyze the hydrolysis of food molecules.

All digestive enzymes are classified as hydrolases because they catalyze the hydrolysis of food molecules.

In general, _______________ regulate cell functions by regulating metabolic pathways

In general, enzymes regulate cell functions by regulating metabolic pathways

A molecule or other agent that alters enzyme function by changing its shape is called an ___________ _________________.

A molecule or other agent that alters enzyme function by changing its shape is called an allosteric effector

In the process known as end-product _______________, a chemical product at the end of a metabolic pathway binds to the allosteric site of one or more enzymes along the pathway that produced it and thereby inhibits the synthesis of more product

In the process known as end-product inhibition, a chemical product at the end of a metabolic pathway binds to the allosteric site of one or more enzymes along the pathway that produced it and thereby inhibits the synthesis of more product

Many enzymes are synthesized as inactive _____________. Substances that convert proenzymes to active enzymes are often called ______________.

Many enzymes are synthesized as inactive proenzymes. Substances that convert proenzymes to active enzymes are often called kinases.

Three smaller pathways are chemically linked together to form the larger catabolic pathway known as cellular respiration:

1. Glycolysis

2. Citric acid cycle

3. Electron transport system

_____________ _______________ is the process by which cells break down glucose (C6H12O6), or a nutrient that has been converted to glucose or one of its simpler products, into carbon dioxide (CO2) and water (H2O).

Cellular respiration is the process by which cells break down glucose (C6H12O6), or a nutrient that has been converted to glucose or one of its simpler products, into carbon dioxide (CO2) and water (H2O).

_____________is a catabolic pathway that begins with glucose, which contains six carbon atoms per molecule, and ends with pyruvate, which contains only three carbon atoms per molecule.

Glycolysis is a catabolic pathway that begins with glucose, which contains six carbon atoms per molecule, and ends with pyruvate, which contains only three carbon atoms per molecule.

Glycolysis occurs in the ____________of cells, outside any particular organelle. The cytosol, then, must contain all the enzymes necessary to catalyze each of the reactions that make up the glycolysis pathway

Glycolysis occurs in the cytosol of cells, outside any particular organelle. The cytosol, then, must contain all the enzymes necessary to catalyze each of the reactions that make up the glycolysis pathway