sp2010 chapter 5 old

Chapter 5

The Working Cell

Cell ActivitiesCells have three basic

types of activities1. transport2. chemical

3. mechanical

Cell Activites

Transport Activities

Transport Mechanisms

Transport Mechanisms I. Passive transport

Passive transport mechanisms do not require the cell to input any

energy.It is dependent on two things:

1. The innate energy and movement of atoms and molecules

2. A concentration gradient

Transport MechanismsI. Passive transport

All atoms and molecules are in a constant state of motion.

Large molecules move slower than small ones.

Warm molecules move faster than cold ones.

Gases are more active than liquids which are more active than solids, but

all molecules move.

Transport Mechanisms I. Passive Transport

A concentration gradient occurs as molecules spread out into a space.

According to Newton’s Laws of motion, an atom or molecule moves in a straight line until it collides with

another force that causes it to change direction.

Transport MechanismsI. Passive transport

All passive transport mechanisms are really variations of diffusion.

Diffusion refers to a movement of molecules from an area of greater concentration to an area of lesser

concentration along a concentration gradient.

If the molecules are in an idealized closed system, they will ultimately

spread out and become equally dispersed throughout the space.

Passive Transport Mechanisms

A. Simple diffusionSimple diffusion is the diffusion of molecules as they move through open

space or through a membrane.As with all diffusion, the molecules

move from an area of greater concentration to an area of lesser

concentration.

Transport MechanismsA. Simple Diffusion

Initially the molecules are highly concentrated in one area.

As they move, they bump into each other and the confining

walls of their space.

A. Simple diffusionWhen we open a perfume bottle in a room, the aromatic molecules begin to

move out of the bottle and into the larger space. This is an example of

simple diffusion.Oxygen moves out of the lung and into

the blood by simple diffusion.Also, carbon dioxide moves out of the

blood and into the lung by simple diffusion.

A. Simple diffusion

Passive Transport MechanismsB. Osmosis

Osmosis is the diffusion of water through a membrane.

The process depends on the concentration of the molecules

dissolved in the water since these molecules exert osmotic pressure.

However, the dissolved molecules do not pass through the membrane during

the process of osmosis.

During osmosis, water will move to the side of the membrane with the most

concentrated solution (the saltier side).Although, when we label a solution, we label it according to the concentration of the solute (dissolved material), not the

solvent (water).A 10% salt solution is 90% water. It is

important to keep this in mind when discussing osmosis.

Also, in considering osmosis, it is important to understand that we are

comparing the solution outside the cell (A) to the solution inside the cell (B). In other words, we compare the solutions

on either side of the membrane.

If the two solutions are equal in concentration, than A is isotonic to B

and B is isotonic to A.“iso” means “the same” and “tonic”

refers to the saltiness (or solutes).A=0.9% solutes

B=0.9%solutes

Isotonic isotonic

If solution A has a higher concentration of solutes than solution B, A is hypertonic to B.

“hyper” means “more than”At the same time, solution B is hypotonic to A.

“hypo” means “less than”

A=10% solutes

B=0.9%solutes

hypertonic hypotonic

Passive Transport MechanismsB1. Osmosis

This is a U shaped tube with a membrane inside, at the bottom of the U, separating

side A from side B.

membrane

Side A has a concentration of 10% purple molecules

(the blue dots are water).Side B has a concentration of

20% purple molecules.A is hypotonic to B.B is hypertonic to A.

Since side B is the “saltier” side, water moves from side A to side

The solution level in side B rises while the solution

level in side A drops.

B. How Osmosis affects cells

The solution (cytoplasm) inside most cells has a concentration of

approximately o.9%.Although this does vary some, for our purposes, we are going to consider this concentration a constant for all cells.

B2. Osmosis in Animal CellsWhen a blood cell is placed into a solution

with a concentration of 0.9% salt, the solutions inside and outside of the cell are isotonic to each other. Water moves into

and out of the cell at an equal rate. The cell is not affected by this solution. It remains

normal and functional.

B2. Osmosis in Animal Cells

B2. Osmosis in Animal CellsWhen a blood cell is placed in a 10% salt solution, the outside solution is hypertonic to the solution inside the cell. The solution inside the cell is hypotonic to the outside solution. Water will move out of the cell at a faster rate than it moves into the

The cell shrinks as it loses water. Finally, the cell collapses. This

collapse is called crenation. In this form, the cell can no longer function

and will die.

B2. Osmosis in Animal Cells•When an animal cell is placed in

distilled water, the solution inside the cell is hypertonic to the outside solution. The outside solution is

hypotonic to the solution inside the cell. Water moves into the cell at a

faster rate than it moves out.

•The cell swells and swells and swells and eventually ruptures.

•The rupturing of a cell is called lysis.

D.I. water

Should you look for this cell under the microscope, you would only find little bits of membrane, or, more likely, nothing at all.

B3. Osmosis in Plant Cells

•A plant cell in a hypertonic solution will lose water mainly from its central

vacuole.

•The central vacuole shrinks, the cell membrane collapses and all the

organelles inside the membrane get crowded together. This is called

plasmolysis.

In general, the size of the cell does not change because the cell wall is

rigid and does not collapse. However, in this condition, the cells have no

pressure to hold up the leaves of the plant. It wilts.

•A plant cell in a hypotonic solution will take

water into the central vacuole.

B3. Osmosis in Plant Cells•The vacuole swells, pushing the cell membrane against the cell wall. All the organelles are pushed out to the periphery of the cell. This is called

turgor.•This is the ideal condition for the plant because it creates a pressure in the cells

which allow them to hold up their leaves and flowers.

The cell does not rupture because the cell wall is rigid and creates an opposing pressure that equalizes with the osmotic pressure.

D.I. water

Passive Transport MechanismsC. Dialysis

Dialysis is the movement of particles across the membrane.These particles are pulled through the membrane with

water that is diffusing through.

Passive Transport MechanismsC. Dialysis

D. Carrier Facilitated DiffusionCarrier facilitated diffusion relies not only on the concentration of particles on

either side of the membrane. Carrier facilitated diffusion requires a

membrane carrier protein to carry the particles across the membrane.

Still, it is a diffusion process and does not require an input of energy from

D. Carrier Facilitated Diffusion

Active Transport Mechanisms

II. Active TransportUnlike passive transport, active transport

does require an input of energy from the cell.

Another important difference between active and passive transport mechanisms is

that active transport can move particles against the concentration gradient, from an area of lesser concentration to an area of

greater concentration.

II. Active TransportIn situations where the cell needs to take in

all the particles it can despite concentration, it is important to have this option.

As you take in and digest nutrients, the cells that absorb the nutrients may start out with a lesser concentration, but as more and more

move into the cell, the concentration becomes greater inside the cell, but the cell still needs

to continue taking in more.

A. Typical Active TransportLike carrier facilitated diffusion, typical active transport requires a membrane carrier protein to bring the particles across the membrane.

However, ATP is required to activate the carrier and bring the

particle across.

Active Transport

ATP ATP

Active Transport

ADP + P

Active Transport

B. Co-TransportCo-transport is similar to typical

active transport except, in this case, a second type of particle attaches itself to the original particle and both are pulled

through the membrane at the same time (piggyback).

B. Co-Transport

ATP ATP

B. Co-Transport

ADP + P

B. Co-Transport

C. Exchange pumpAnother example of an active

transport mechanism is the exchange pump.

This process involves moving one type of molecule to the inside of the cell while moving a different type of molecule to the outside of the cell.

C. Exchange pump When a nerve or muscle cell becomes

electrically charged, sodium ions rush out of the cell and potassium ions rush in (by diffusion).

In order for these cells to come back to their resting state, the ions must be returned to their

original place.The Na+/K+ pump pulls sodium ions into the

cell and potassium ions are pulled out of the cell.

C. Exchange pump

ATP ATP

C. Exchange pump

ADP + P

C. Exchange pump

Transport by VacuoleIII. Transport by Vacuole

Large molecules and cells cannot pass through the membrane by passive or

active transport.The only way to bring these into the cell

is by forming vacuoles.The cell also transports large molecules

out of the cell by vacuole. These mechanisms require the cell to expend a considerable amount of energy.

Transport by VacuoleA. Endocytosis

The process of bringing cells and large molecules into the cell by vacuole is called Endocytosis.

There are 3 forms of endocytosis.1. Phagocytosis means “cell eating”.2. Pinocytosis means “cell drinking”. 3. Receptor (membrane) mediated

endocytosis which uses receptor proteins on the membrane to initiate

the reaction.

Transport by VacuoleA1. Endocytosis/Phagocytosis

Cells like your white blood cells often take in bacterial cells to protect you from infection. Other cells (especially unicellular organisms or protozoa) take in small cells as food. In order to bring in a complete cell, the cell

membrane rises up, surrounds and engulfs the cell.

Also, phagocytosis may bring in large chunks of materials like splinter fragments.

Transport by VacuoleA1. Endocytosis/PhagocytosisAs the membrane closes over the

material to come in, membrane touches membrane and the

molecules reorganize so that the inner membrane forms a vacuole inside the cell that separates from

the membrane.

Transport by VacuoleA1.

Endocytosis/Phagocytosis

Transport by VacuoleA2. Endocytosis/Pinocytosis

Taking in fluid requires a different approach.

The cell membrane invaginates forming an inpocket.

As the pocket forms, it creates a vacuum that sucks the extracellular fluid along with

large molecules into the pocket.The membrane then closes over the top and pinches off the vacuole inside the cell.

Endocytosis/Pinocytosis

Transport by VacuoleA3. Endocytosis/Receptor

MediatedReceptor Mediated Endocytosis is

much like pinocytosis, but more specific.

Receptors in the membrane attract and capture specific molecules, although

extracellular fluids do enter the newly forming vacuole as well.

MediatedY Y Y Y Y

Mediated

Transport by VacuoleB. Exocytosis

The process of releasing vacuole-encased molecules from the inside of the cell is

called Exocytosis. The vacuole is formed within the cell and

then fuses with the cell membrane as it releases its

contents.

As the cell forms proteins and other materials for export out of the cell, the endoplasmic reticulum or the golgi package these materials in

vacuoles.This vacuole moves through the cell

until it reaches the cell membrane.

As the vacuole bumps into the cell membrane, membrane touches

membrane and the molecules reorganize.The membrane of the vacuole is

incorporated into the cell membrane and as the membrane stretches out, the

materials inside the vacuole is left on the outside of the cell.

EnzymeActivities

Energy and the Cell Energy

Energy = the capacity to do work.Kinetic energy = energy of motion or energy used to do

work.Potential energy = stored energy.

Energy and the CellLaws of ThermodynamicsThere are 2 laws of physics that concern energy transformations.

They are called the Laws of Thermodynamics.

Energy and the Cell1st Law of

Thermodynamics =Energy conservation

the amount of energy and matter in the universe is constant;

It can neither be created nor destroyed…it can change form.

Energy and the Cell2nd Law of Thermodynamics =

the Law of Entropy (chaos) The universe is moving towards entropy

or energy in the universe is becoming

more chaotic.Energy transfers or transformations

are not 100% efficient. Some energy is always lost in the

form of heat.

Energy and the Cell Chemical reactions

Endergonic reactions= require energyExergonic reactions= release energy

Exergonic reactions often drive endergonic reactions.

This is called Energy or reaction coupling.

ATP ADPCO2 + H2O Glucose + O2

Chemical ReactionsThe chemical reactions in the cell

are collectively called metabolism or metabolic reactions.There are 2 forms of metabolism1. anabolic reactions – build large

molecules from smaller ones. 2. catabolic reactions – break down

large molecules into smaller ones.

Chemical ReactionsTypical reactions

Substrate(s) (reactants) are converted to product(s)

+anabolic

catabolic

Chemical ReactionsEnzymes

Catalyst - speeds up the rate of a reaction

Biological catalyst - a catalyst that is safe to use in a living cell.

Enzymes are biological catalysts.

Enzymes are not changed by the reaction.

Can be used again and again

enzyme

Substrates are converted to product with the help of the enzyme

Enzymes

Enzyme at the start of the

reaction

Unchanged Enzyme at the

end of the reaction

Metabolic PathwayMetabolic pathway = a

series or chain of reactions.

Product of one reaction becomes substrate for next+ + +

A + B F + GD + EC

Metabolic PathwayEach reaction has a separate

enzyme.

Enz 1 Enz 2 Enz 3+ + +A + B F + GD + EC

Metabolic PathwayAlternate pathways are determined by enzymes

If Enzyme 3 is present, D will be converted to F and G the original pathway will be completed with

these final products. But if Enzyme 4 is present D will be converted to W and X and the alternate pathway

will occur, resulting in the final products Y and Z.

Enz 1 Enz 2 Enz 3+ + +A + B F + GD + EC

W + X Y + Z

EnzymesEnzymes :

1. are biological catalysts.2. are usually made at least

partly of protein.3. are substrate specific.

4. can be induced or inhibited.

EnzymesGeneralized enzyme

structure

Apoenzyme = protein part of

the enzyme

Coenzyme (organic) or

cofactor (inorganic) =

non-protein part of the enzyme

Active Site = where the substrate fits into the

enzyme

Allosteric site = where the enzyme is activated

or deactivated

enzyme

EnzymesActivation of an enzyme

An enzyme may be activated by placing an activator molecule into the allosteric site. This process

causes the shape of the active site to change so that the substrate can fit

into the active site.

EnzymesActivation of an enzyme

This is called positive allosterism.Without the activator molecule, the active site remains closed off so that

the substrate cannot fit into it.

structure

Inactive enzyme

activator

substrate

structure

activated enzyme

activator

substrate

structure

activated enzyme

activator

substrate

EnzymesInhibition of an enzyme

An enzyme may be inhibited by placing an inhibitor molecule into the allosteric site. This process

causes the shape of the active site to change so that the substrate can no longer fit into the active

EnzymesInhibition of an enzyme

This is called negative allosterism.

Without the inhibitor molecule, the active site remains open so that the substrate fits into it.

Enzymes

Example of negative allosterism

EnzymesHow an Enzyme Works1.E + S The substrate bumps into the

enzyme and aligns with the active site.2.E-S complex The substrate fits into the active site, and the enzyme shifts,

stressing the bonds of the substrate.3.E + P The products are formed and

released.4.The enzyme returns to its original shape

and can be used again.

EnzymesHow an Enzyme Works

EnzymesHow an Enzyme WorksAll enzymatic reactions require some

energy to get them started. This energy is called the energy of activation.

Enzymes reduce the energy of activation so that it takes much less energy to get the reaction going. Once started, the

reaction will continue on its own steam.

Enzymes

EnzymesFactors that affect the rate

of an enzymatic reaction 1. temperature

2. pH3. enzyme concentration

4. inhibitors

Enzymes1. Temperature profile

Every enzyme has a temperature profile. This profile is a graph

showing at what rates the reactions take place at various temperatures.

The temperature profile generally forms a “bell-shaped” curve.

Enzymes 1. Temperature profile

The peak of the curve represents the optimal temperature. This is the

temperature at which the reaction rate is fastest.

As temperature cools from optimal, molecules slow down and do not

encounter each other as often or with as much energy, so the reaction rate slows

down until the reaction no longer occurs. This temperature is called the minimal

temperature.

As temperature becomes warmer than optimal, enzymes begin to change shape. This change

in shape is called denaturing the enzyme. If the temperature gets too warm, the enzyme

changes so radically that the substrate can no longer fit into the active site. The reaction rate is then 0 (no reaction occurs) and the enzyme is

irreversibly denatured. This temperature is called the

maximal temperature.

The range of temperatures between the minimal and maximal is called the functional range. This is the range of

temperatures within which the enzyme works.

Minimal temperature

Maximal temperature

Functionalrange

Enzymes1. Temperature profileEvery enzyme has a unique

profile based on the type of organism it is found in and/or the location in the organism where it

does its work.

Enzymes1. Temperature profileAmong mammals, smaller mammals tend to have higher

normal body temperatures than larger mammals. As a result, one

would expect the optimal temperature for a small mammal

to be at a higher temperature than the optimal for larger mammals.

Cold blooded animals do not regulate their body temperatures as closely as mammals, so their functional range may be broader

than that for mammals.The enzymes that work in cells all over the

body also need a broader functional range.Enzymes that work outside the body

(digestive enzymes of fungi or the enzymes that work in the testes) usually have a

cooler optimal temperature than enzymes that work inside the body.

Temperature in oC

Temperature Profile for various enzymes

Enzymes 2. pH profile

As with temperature, enzymes have a pH profile. This profile is a

graph showing at what rate the reaction takes place a various pHs.This profile also, generally forms

a “bell-shaped” curve.

Enzymes2. pH profile

The peak of the curve represents the optimal pH. This is the pH at which the

reaction rate is fastest. As the pH becomes more acidic or more

basic than optimal, the enzyme begins to denature.

When the enzyme no longer functions, it is irreversibly denatured. The points where this occurs will be the minimal

and maximal pH and the range between the two is the functional pH range.

Enzymes2. pH profile

Minimal pH Maximal pHFunctional range

Enzymes 2. pH profile

Every enzyme has a unique profile based primarily on where in the organism it functions.

A blood enzyme has a very narrow range that is slightly basic.

Stomach enzymes have a very low pH optimal.Pancreatic enzymes work best at a neutral pH.

Catalase, which breaks down hydrogen peroxide, has a broad range of pHs at which it works, since it must work in every cell of the

Enzymes 3. Enzyme Concentration

The concentration profile for enzymes is quite different than the temperature and pH profiles. Initially, there is a steep positive correlation

between enzyme concentration and reaction rate, but at a certain point, using more enzyme cannot make the rate go faster and the curve levels off

into a plateau. There is no minimal or maximal concentration. The optimal concentration occurs just before the

plateau.

Enzymes3. Enzyme concentration

Enzymes4. Inhibitors

The more inhibitor present, the slower the reaction rate.

2 typesa. Competitive inhibitors

b. Non-competitive inhibitors

Enzymes 4a. Competitive Inhibitors

A competitive inhibitor partially mimics the substrate molecule and blocks the active site.

This inhibition is temporary since the inhibitor can move into or out of the active site.

The substrate and the inhibitor compete with each other for access to the enzyme.

Often competitive inhibitors are produced by the body to slow down the speed of a reaction.

Enzymes 4b. Non-competitive

InhibitorsA Non-Competitive inhibitor blocks the allosteric site or removes co-enzyme or co-

factor from the enzyme. A blocked allosteric is sometimes

temporary and reversible.A removed co-factor or co-enzyme destroys

the enzyme and is permanent.

EnzymesInhibitors

MechanicalActivities

Mechanical Activities Mechanical activities of the cell

involve movement of some sort.At the cellular level, mechanical

activities would include the following:cytoplasmic streaming amoeboid movement

The beating of cilia and flagellaThe movement of centrioles, microtubules

and chromosomes during cell division

Mechanical Activities Other cell-level mechanical

activities include the following:The movement of RNA out of the

nucleus.The movement of vacuoles,

mitochondria, plastids and other organelles.

Endocytosis and exocytosis are transport activities with a mechanical aspect.

Mechanical Activities Mechanical activities at the organism level

might include: Muscle contraction allowing gross

movement of the body.Peristaltic contractions of the digestive tract

The pumping action of the heartThe movement of blood through the vessels.

The movement of air into and out of the lungs.

Mechanical Activities

Most mechanical activities require ATP breakdown and the cells must

metabolize foods in order to maintain a constant supply of the

sp2010 chapter 5 old

transport activities

osmosis osmosis

diffusion of molecules

example of simple diffusion

reallyvariations of

solutes b

process of osmosis

solution b ishypotonicto

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