The Working Cell:G: Membrane

Transport &

H: EnzymesChapter 5

Standards Unit G: Membrane Transport• I can recognize the fluid mosaic model and accurately

identify and describe the function of the components.

• I can compare and contrast the various ways substances cross the cell membrane.

• I can recognize the various ways substances cross the membrane and provide examples from the human body for each.

• I can predict changes to a cell mass and size placed in solutions of differing concentrations

• I can use data to create a graph to show the relationship between concentration and mass.

• I can use a graph to extrapolate the concentration that is isotonic to a cell.

MEMBRANE STRUCTURE AND FUNCTION

Crash Course: Membranes and Transport

• 5.10 Membranes organize the chemical activities of cells

Membranes provide structural order for metabolism

The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell

Cytoplasm

Outside

of cell

TE

M 2

00

,00

0

• 5.11 Membrane phospholipids form a bilayer

Phospholipids

Have a hydrophilic head and two hydrophobic tails and are the main structural components of membranes

Phospholipids form a two-layer sheet called a phospholipid bilayer, with the heads facing outward and the tails facing inward

Figure 5.11A

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH

CH

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH3

CH2

CH2

CH3

CH3

CH3N+

O

O O–P

O

CH2CHCH2

C O C O

O O

Phosphate

group

Symbol

Hydrophilic head

Hydrophobic tails

Water

Water

Hydrophilic

heads

Hydrophobic

tails

Figure 5.11B

• 5.12 The membrane is a fluid mosaic of phospholipids and proteins

A membrane is a fluid mosaic with proteins and other molecules embedded in a phospholipid bilayer where the phospholipids are constantly moving and shifting (FLUID)

Membrane proteins are located studded within the membrane giving it a mosaic appearance (MOSAIC) Figure 5.12

Fibers of the extracellular matrix

Carbohydrate

(of glycoprotein)

Glycoprotein

Microfilamentsof cytoskeleton

Phospholipid

CholesterolProteins

Plasmamembrane

Glycolipid

Cytoplasm

5.13 Proteins make the membrane a mosaic of functions

Many membrane proteins function as enzymes

Other membrane proteins function as receptors for chemical messages from other cells

Membrane proteins also function in transport moving substances across the membrane

Figure 5.13B

Messenger molecule

Receptor

Activated

molecule ATP

Figure 5.13C

Figure 5.13A

• 5.14 Passive transport is diffusion across a membrane

In passive transport, substances diffuse through membranes without work (energy) by the cell spreading from areas of high concentration to areas of low concentration

Small nonpolar molecules such as O2 and CO2 diffuse easily across the phospholipid bilayer of a membrane

EquilibriumMembraneMolecules of dye

Equilibrium

Figure 5.14B

Figure 5.14A

• 5.15 Transport proteins may facilitate diffusion across membranes

Many kinds of molecules do not diffuse freely across membranes

For these molecules, transport proteins provide passage across membranes through a process called facilitated diffusion

Figure 5.15

Solutemolecule

Transportprotein

• 5.16 Osmosis is the diffusion of water across a membrane

In osmosis water travels from a solution of lower solute

concentration to one of higher solute concentration

Why would water move in this direction?

Figure 5.16

Lower

concentration

of solute

Higher

concentration

of solute

Equal

concentration

of solute

H2OSolute

molecule

Selectively

permeable

membrane

Water

molecule

Solute molecule with

cluster of water molecules

Net flow of water

• 5.17 Water balance between cells and their surroundings is crucial to organisms The control of water balance is called osmoregulation

Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions

In hypertonic solutions animals cells are shriveled and plants cells are plasmolyzed – why does this happen?

In hypotonic solutions animal cells burst/lysis and plant cells are in turgid (their ideal state) – why does this happen?

In isotonic solutions animal cells are normal, but plant cells are limp – why??

Figure 5.17

Plant

cell

H2O

H2OH2O

H2O

H2O

H2O

H2O

H2OPlasma

membrane

(1) Normal (2) Lysed (3) Shriveled

(4) Flaccid (5) Turgid(6) Shriveled

(plasmolyzed)

Isotonic solution Hypotonic solution Hypertonic solution

Animal

cell

PP PProtein

changes shape

Phosphate

detachesATP

ADPSolute

Transport

protein

Solute binding1 Phosphorylation2 Transport3 Protein reversion4

• 5.18 Cells expend energy for active transport

Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP

Figure 5.18

Fluid outside cell

Cytoplasm

Protein

Vesicle

• 5.19 Exocytosis and endocytosis transport large molecules

To move large molecules or particles through a membrane

A vesicle may fuse with the membrane and expel its contents (exocytosis)

Figure 5.19A

Membranes may fold inward enclosing material from

the outside (endocytosis)

Figure 5.19B

Vesicle forming

Endocytosis can occur in three ways

Phagocytosis

Pinocytosis

Receptor-mediated endocytosis

Pseudopodium of amoebaFood being ingested

Phagocytosis Pinocytosis Receptor-mediated endocytosis

Material bound to receptor proteins

PIT

Cytoplasm

Plasma membrane

TE

M 5

4,0

00

TE

M 9

6,5

00

LM

230

Figure 5.19C

CONNECTION

• 5.20 Faulty membranes can overload the blood with cholesterol

LDL – Low-density lipoproteins – receptor mediated endocytosis

Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors

hypercholesterolemia

LDL particle

Protein

Phospholipid outer layer

CytoplasmReceptor

protein

Plasma

membrane

Vesicle

Cholesterol

Figure 5.20

Standards Unit H: Enzymes• I can relate the function of thyroxin to metabolism.

• I can use words and models to show the lock and key function of enzymes.

• I can describe how co-enzymes and co-factors assist enzymes.

• I can explain how enzymes help our metabolic reactions to occur

• I can model/show how thyroxin production is regulated.

• I can relate protein structure to the denaturation of enzymes and provide examples of conditions that cause denaturation.

• I can represent the rate of enzyme activity graphically.

• Cool “Fires” Attract Mates and Meals Fireflies use light to send signals to potential mates instead of using chemical signals like most other insects

The light comes from a set of chemical reactions that occur in light-producing organs at the rear of the insect

Females of some species produce a light pattern that attracts males of other species, which are then eaten by the female

ENERGY AND THE CELL

• 5.1 Energy is the capacity to perform work

All organisms require energy which is defined as the capacity to do work

Kinetic energy is the energy of motion

Potential energy is stored energy and can be converted to kinetic energy

Figure 5.1A–C

• 5.2 Two laws govern energy transformations

Thermodynamics is the study of energy transformations

• The First Law of Thermodynamics

According to the first law of thermodynamics

Energy can be changed from one form to another

Energy cannot be created or destroyed

Figure 5.2A

• The Second Law of Thermodynamics

The second law of thermodynamics states that energy transformations increase disorder or entropy, and some energy is lost as heat

Figure 5.2B

Heat

Chemical reactions

ATP ATP

Glucose

+

Oxygen

water

Carbon dioxide

+

Energy for cellular work

• 5.3 Chemical reactions either store or release energy

Endergonic reactions absorb energy and yield products rich in potential energy

Figure 5.3A

Pote

ntial energ

y o

f m

ole

cule

s

Reactants

Energy required

Products

Amount of

energy

required

Exergonic reactions release energy and yield products that contain less potential energy than their reactants

• Cells carry out thousands of chemical reactions the sum of which constitutes cellular metabolism

• Energy coupling uses exergonic reactions to fuel endergonic reactions

Figure 5.3B

Reactants

Energy released

Products

Amount of

energy

released

Po

ten

tia

l e

nerg

y o

f m

ole

cu

les

• 5.4 ATP shuttles chemical energy and drives cellular work

ATP powers nearly all forms of cellular work

The energy in an ATP molecule lies in the bonds between its phosphate groups

Phosphate

groups

ATP

EnergyP P PP P PHydrolysis

Adenine

Ribose

H2O

Adenosine diphosphateAdenosine Triphosphate

++

ADP

Figure 5.4A

ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to make molecules more reactive

Figure 5.4B

ATP

Chemical work Mechanical work Transport work

P

P

P

P

P

P

P

Molecule formed Protein moved Solute transported

ADP +

Product

Reactants

Motorprotein

Membraneprotein Solute

+

ATP

ADP + P

Energy for

endergonic

reactions

Energy from

exergonic

reactions

Cellular work can be sustained because ATP is a renewable resource that cells regenerate

Figure 5.4C

• 5.21 Chloroplasts and mitochondria make energy available for cellular work Enzymes are central to the processes that make energy available to the

cell

Chloroplasts carry out photosynthesis using solar energy to produce glucose and oxygen from carbon dioxide and water

Mitochondria consume oxygen in cellular respiration using the energy stored in glucose to make ATP

Bozeman: Enzymes

HOW ENZYMES FUNCTION• 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers For a chemical reaction to begin reactants must

absorb some energy, called the energy of activation

EA barrier

Reactants

Products1 2

Enzym

e

Figure 5.5A

A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction

Figure 5.5B

Reactants

EA without

enzyme

EA with

enzyme

Net

change

in energy

Products

Energ

y

Progress of the reaction

Figure 5.6

Enzyme

(sucrase)Glucose

Fructose

Active siteSubstrate

(sucrose)

H2O

1 Enzyme available

with empty active

site

2 Substrate binds to

enzyme with induced fit

4 Products are

released3 Substrate is

converted to

products

• 5.6 A specific enzyme catalyzes each cellular reaction Enzymes have unique three-dimensional shapes that determine which

chemical reactions occur in a cell

The catalytic cycle of an enzyme

• 5.7 The cellular environment affects enzyme activity

Temperature, salt concentration, and pH influence enzyme activity

Some enzymes require non-protein cofactors such as metal ions or organic molecules called coenzymes

5.8 Enzyme inhibitors block enzyme action

Inhibitors interfere with an enzyme’s activity

A competitive inhibitor

Takes the place of a substrate in the active site A noncompetitive inhibitor

Alters an enzyme’s function by changing its shape

Figure 5.8

Substrate

Enzyme

Active site

Normal binding of substrate

Enzyme inhibition

Noncompetitive

inhibitor

Competitive

inhibitor

CONNECTION

• 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors

• EX: Cyanide is a inhibitor in the cellular respiration reaction in the mitochondria. It causes a build-up of O2 in the blood and ultimately results in suffocation