Chapter 5: The Working Cell

In the lab, you use a special balloon that is permeable to water, but not sucrose, to make an "artificial cell." The balloon is filled with a solution of 20% sucrose and 80% water and is immersed in a beaker containing a solution of 40% sucrose and 60% water. Which of the following will occur?

Water will leave the balloon.

exergonic reaction

a chemical reaction that releases energy

endergonic reaction

a chemical reaction that requires a net input of energy

coenzyme

a cofactor that is an organic molecule.

solution

a liquid containing a uniform mixture of substances

entropy

a measure of disorder

An enzyme speeds up reactions by lowering the

activation energy

Substrates bind to an enzyme's ________ site.

active

An enzyme is specific because the shape of its __________ matches only particular reactants.

active site

The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of

active transport.

Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.

actively pump water back into their cells to counter its loss due to osmosis

transport protein

allows solute molecules to enter the cell.

receptor-mediated endocytosis

an endocytotic mechanism in which specific molecules are ingested into the cell.

Membrane phospholipids

are able to drift about in the plasma membrane

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?

cellular respiration

Heating inactivates enzymes by

changing the enzyme's three-dimensional shape.

noncompetitive inhibitor

does not enter the active site, instead it binds to the enzyme somewhere else, a place called an allosteric site, and its binding changes the shape of the enzyme so that the active site no longer fits into the substrate.

When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will

exhibit a net movement to the side with lower free water concentration.

the plasma membrane

has receptors for chemical messages, plays a role in signal transduction, and forms a selective barrier around the cell.

Which of these are by-products of cellular respiration?

heat and water

contractile vacuole

helps one-celled organisms pump out extra water

ion channels

how charged particles like Na+ and K+ move across membranes

A plant cell placed in a(n) ____________ solution will lose water and plasmolyze.

hypertonic

The ideal osmotic environment for a plant cell is a(n) _________________ environment.

hypotonic

You know that a cell is in a(n) _____ solution because if the cell _____.

hypotonic ... swelled

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles

An enzyme _____.

is an organic catalyst

Some protozoans have special organelles called contractile vacuoles that continually eliminate excess water from the cell. The presence of these organelles tells you that the environment

is hypotonic to the protozoan.

When molecules move down their concentration gradient, they move from where they are ____________ to where they are ____________________

more concentrated; less concentrated

Which of the following is highest in chemical energy?

one molecule of glucose

plasmolysis

plant cells wilting due to a loss of water

Chemical energy is a form of _____ energy.

potential

Most of the functions of a cell membrane, including transport and enzymatic function, are performed by

proteins

channel proteins

proteins used during facilitated diffusion

competitive inhibitor

reduces an enzyme's productivity by blocking substrate molecules from entering the active site

What name is given to the reactants in an enzymatically catalyzed reaction?

substrate

induced fit

the change of shape of the active site of a enzyme, caused the entry of the substrate, so that t=it binds more snugly to the substate.

Osmosis can be defined as

the diffusion of water.

solvent

the dissolving agent in a solution

Energy is conserved. This means that in any system, _____.

total energy input equals total energy output

what is the behavior of molecules in an isotonic solution

water molecules move in and out of the cell at the same rate.

how much sugar is there in a 100 mL of a 10% aqueous sugar solution

10 grams

Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer?

Na+ (ions and polar molecules)

hypertonic solution

There is a greater concentration of solute outside the cell so water moves out of the cell.

Which of these is exhibiting kinetic energy?

a space station orbiting Earth

An enzyme is considered a(n) ___________ because it speeds up a chemical reaction without being used up.

catalyst

Pinocytosis

cell drinking

cytolysis

cells bursting from excess water pressure inside them

During enzymatic reactions, substrates are converted to products. A property of enzymes that facilitates this reaction is that they are catalysts and therefore _____.

change the rate of a reaction without being consumed by the reaction

how can temperature affect an enzyme's function

chemical reactions speed up as temperature is increased, so in general, catalysis will increase at a higher temperature. However, each enzyme has a temperature optimum and beyond this point the enzyme's functional shape is lost.

A(n) ________________ , which is often a vitamin, binds to an enzyme and plays a role in catalysis.

coenzyme

equilibrium

concentration of molecules is the same throughout the space

The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

endocytosis.

When water moves toward the solution with the _____ solute concentration, the solution is _____.

greater ... hypertonic

In cellular respiration, most energy is released and transferred to ATP when _____

high-energy electrons "fall" to lower energy levels

difussion

passive transport from an area of high to an area of low concentration

Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of

passive transport.

Facilitated diffusion is a type of _____.

passive transport. The cell is not expending energy to move the particles across the membrane

A white blood cell engulfing a bacterium is an example of _____

phagocytosis

turgic

pressure produced by water pushing outward against the cell wall of plant cells

Reactions can be exergonic or endergonic. Which of these reactions is endergonic?

protein synthesis

Most enzymes are _____.

proteins

Overall, membranes seem to have a great deal in common, but on closer inspection it is revealed that membranes of different cells have unique properties. What is the primary component of membranes that gives membranes cell-specific properties?

proteins

Most of a cell's enzymes are

proteins.

hypotonic solution

solute concentration is higher inside the cell than outside so water moves into the cell

the concentration of a solution is the measurement of the amount of

solute in a fixed amount of the solution

first law of thermodynamics

states that the energy in the universe is constant. Energy can be transferred and transformed, but it cannot be created or destroyed.

In a catalyzed reaction, a reactant is often called a(n)

substrate

What affects an enzyme's function

temperature and pH of its environment. When its conformation is significantly altered because of temperature or pH variation, it may no longer catalyze and become denatured

concentration gradient

the difference in the concentration of molecules across a distance

phagocytosis

the process wherein a cell binds to the item it wants to engulf on the cell surface and draws the item inward while engulfing around it. cell eating.

substrate

the specific reactant that an enzyme acts on

thermodynamics

the study of energy transformations that occur in a collection of matter

solute

the substance dissolved in a solution

passive transport

transport that doesn't require energy

ionic bond

when 2 ions of opposite charges attract each other

What controls the direction of a molecule, such as oxygen, involved in passive transport?

the direction of the oxygen concentration gradient

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

hydrolysis

In active transport

molecules move across the plasma membrane against their concentration gradient.

does osmosis occur if a cell is placed in an isotonic solution

No, because the water isn't moving from an area of high to low concentration. No net movement of water.

active site

a pocket or groove on the surface of the enzyme formed by only a few amino acid. It is the space where a substrate fits into.

Cholesterol molecules

helps to stabilize the structure of the plasma membrane

endocytosis

type of active transport that moved large particles into a cell through vesicles.

feedback inhibition

a method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme pathway.

Which of the following processes can move a solute against its concentration gradient?

active transport

There is a net diffusion of water out of an animal cell when it is placed in a(n) _________ solution.

hypertonic

An animal cell placed in a(n) _________ solution will gain water, swell, and possibly burst.

hypotonic

The ______________ between an active site and its substrate often strains bonds and helps the reaction proceed.

induced fit

enzymes

molecules that function as biological catalysts, increasing the rate of a reaction without being consumed by the reaction

Enzymes work by _____.

reducing activation energy

carrier proteins change ______________ in order to move materials like glucose across cell membranes

shape

exocytosis

Active transport that uses vesicles to remove wastes and cell products from a cell. A vesicle fuses with the plasma membrane and releases content outside the cell

A child is brought to the hospital with a fever of 107°F. Doctors immediately order an ice bath to lower the child's temperature. Which of the following statements offers the most logical explanation for this action?

Elevated body temperatures may denature enzymes. This would interfere with the cell's abilities to catalyze various reactions.

Which of the following statements regarding enzyme function is false?

Enzymes are used up when they catalyze a chemical reaction, so must be synthesized for each new chemical reaction.

Which of the following statements regarding enzymes is true?

Enzymes catalyze specific reactions.

Which of these is hydrophobic like the interior of the plasma membrane?

Lipid soluble molecules

what are solutions

a mixture in which one or more substances are uniformly distributed in another subtrance

metabolic pathway

a series of chemical reactions that either builds a complex molecule or breaks sown a complex molecule into simpler compounds

sodium potassium pump

active transport pump that helps move materials from low to high concentrations.

High temperatures or changes in pH can ______________ an enzyme, causing it to lose its shape and biological activity.

denature

The movement of molecules from an area of higher concentration to an area of lower concentration is called _____

diffusion

osmosis

diffusion of water across a membrane

facilitated diffusion

diffusion that doesn't require extra energy but uses transport proteins

The fluid mosaic model describes the plasma membrane as consisting of

diverse proteins embedded in a phospholipid bilayer.

How does pH affect an enzyme's function

each enzyme function best within a certain pH range. When pH changes, the active site progressively distorts and affects enzyme function

Small, nonpolar, hydrophobic molecules such as fatty acids

easily pass through a membrane's lipid bilayer.

"Conservation of energy" refers to the fact that _____.

energy cannot be created or destroyed but can be converted from one form to another

second law of thermodynamics

energy conversions increase the entropy of the universe

isotonic

equal solute concentration inside and outside of the cell so water moves at equal rates

A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of

facilitated diffusion.

In oil-based liquids, phospholipids are arranged so that their _____ face outward and their _____ are orientated inward.

hydrophobic tails ... hydrophilic heads

As a result of its involvement in a reaction, an enzyme _____.

is unchanged

A plant cell surrounded by a(n) ___________ solution will be flaccid (limp).

isotonic

The ideal osmotic environment for an animal cell is a(n) ____________ environment

isotonic

What happens to the turgor pressure inside a cell that placed in a hypertonic solution

it decreases as water diffuses outside of its environment.

When an enzyme catalyzes a reaction,

it lowers the activation energy of the reaction.

what happens when an animal cell gains too much water

it lyses.

what happens when a cell is places into a hypertonic solution

it shrinks

what happens when a cell is places into a hypotonic solution

it swells

what is the energy that drives diffusion

kinetic

what states of matter can solutions be compose of

liquids, solids, or gasses

In a hypotonic solution, an animal cell will

lyse

cofactors

nonprotein helper, which many enxymes require, that bind to the active site and function in Catalysis

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis

All cells are enclosed by a plasma membrane that is similar in ________ and ________.

structure . . . function

The energy required to initiate an exergonic reaction is called

the activation energy.

activation energy

the amount of energy needed for reactant molecules to move "uphill" to a higher-energy, unstable state so that the "downhill" part of a reaction can begin.

You can recognize the process of pinocytosis when _____.

the cell is engulfing extracellular fluid

the catalytic cycle

the enzyme starts with an empty active site. Sucrose enters the active site, attacking by weak bonds. The strained bond of sucrose reacts with water and the substrate is converted (hydrolyzed) to the products glucose and fructose. The enzyme releases the products and emerges unchanged from the reaction.

Plasma membranes are selectively permeable. This means that

the plasma membrane allows some substances to enter or leave a cell more easily than others.

The active site of an enzyme is

the region of an enzyme that attaches to a substrate.

phosphorylation

the transfer of a phosphate group, usually from ATP, to a molecule. Nearly all cellular work depends on ATP energizing other molecules by this method.

energy coupling

the use of energy released from the exergonic reactions to drive essential endergonic reactions- is a crucial ability of all cells. ATP molecules are the key.

Water crosses the plasma membrane

through facilitated diffusion or diffusion.

active transport

transport across cell membranes that require energy of ATP

Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient.

transport proteins . . . down