Chapter 5 Gases - Mr. Doyle SUIS Science

Chapter 5

Ground Rules of

Metabolism Sections 6-10

5.6 Cofactors in Metabolic Pathways

• Most enzymes require cofactors

• Energy in ATP drives many endergonic reactions

Table 5-1 p86

Cofactors and Coenzymes

• Cofactors

• Atoms or molecules (other than proteins) that are

necessary for enzyme function

• Example: Iron atoms in catalase

• Coenzymes

• Organic cofactors such as vitamins

• May become modified during a reaction

Catalase and Cofactors

• Catalase is an antioxidant that neutralizes free radicals

(atoms or molecules with unpaired electrons that attack

biological molecules)

• Catalase has four hemes (small organic compound with an

iron atom at its center)

• Catalase works by holding a substrate molecule close to one

of its iron atoms (cofactors)

• Iron pulls on the substrate’s electrons, bringing on the

transition state

Heme

ATP—A Special Coenzyme

• ATP (adenosine triphosphate)

• A nucleotide with three phosphate groups

• Transfers a phosphate group and energy to other

molecules

• Phosphorylation

• A phosphate-group transfer

• ADP binds phosphate in an endergonic reaction to

replenish ATP (ATP/ADP cycle)

Figure 5-18 p87

adenine

three phosphate

groups

ribose

adenine

ribose

AMP ADP

energy in energy out

ADP + phosphate

ATP

A

B

C

Coupled Reactions

Take-Home Message:

How do cofactors work?

• Cofactors associate with enzymes and assist their function.

• Metal ions stabilize the structure of many enzymes. They also

participate in some enzymatic reactions by donating or

accepting electrons

• Many coenzymes carry chemical groups, atoms, or electrons

from one reaction to another

• The formation of ATP from ADP is an endergonic reaction;

ADP forms again when a phosphate group is transferred from

ATP to another molecule – energy from such transfers drives

cellular work

5.7 A Closer Look at Cell Membranes

• A membrane is a continuous, selectively permeable barrier

• A cell membrane is organized as a lipid bilayer with many

proteins embedded in it and attached to its surfaces

Membrane Lipids

• Phospholipid molecules in the plasma membrane have two

parts

• Hydrophilic heads interact with water molecules

• Hydrophobic tails interact with each other, forming a

barrier to hydrophilic molecules

The Fluid Mosaic Model

• Fluid mosaic model

• Describes the organization of cell membranes

• Phospholipids drift and move like a fluid

• The bilayer is a mosaic mixture of phospholipids, steroids,

proteins, and other molecules

Cell Membrane Organization

one layer

of lipids

one layer

of lipids

Membrane Proteins

• Cell membrane function begins with the many proteins

associated with the lipid bilayer

• Peripheral membrane proteins temporarily attach to the lipid

bilayer’s surfaces by interactions with lipids or other proteins

• Integral membrane proteins permanently attach to a bilayer

Types of Membrane Proteins

• Each type of protein in a membrane has a special function

• Adhesion proteins

• Recognition proteins

• Receptor proteins

• Enzymes

• Transport proteins (active and passive)

Types of Membrane Proteins

B Recognition proteins

such as this MHC

molecule tag a cell as

belonging to one’s own

body.

c Receptor proteins such

as this B cell receptor bind

substances outside the

cell. B cell receptors help

the body eliminate toxins

and infectious agents.

D Transport proteins

bind to molecules on

one side of the

membrane, and

release them on the

other side. This one

transports glucose.

E This transport

protein, an ATP

synthase, makes

ATP when

hydrogen ions flow

through its interior.

Extracellular

Fluid

Lipid

bilayer

Cytoplasm

ANIMATED FIGURE: Cell membranes

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videos_animations/membrane_proteins_v3.html

Table 5-2 p88

Take-Home Message:

What is a cell membrane?

• The structural foundation of all cell membranes is the lipid

bilayer

• Adhesion proteins, recognition proteins, transport proteins,

receptors, and enzymes embedded in or associated with the

lipid bilayer impart functionality to a cell membrane

ANIMATION: Lipid bilayer organization




videos_animations/bilayer.html

5.8 Diffusion and Membranes

• Ions and molecules tend to move spontaneously from regions

of higher to lower concentration

• Water diffuses across cell membranes by osmosis

Diffusion

• Diffusion

• The net movement of molecules down a concentration

gradient

• Moves substances into, through, and out of cells

• A substance diffuses in a direction set by its own

concentration gradient, not by the gradients of other

solutes around it

Diffusion

The Rate of Diffusion

• Rate of diffusion depends on five factors

• Size

• Temperature

• Steepness of the concentration gradient

• Charge

• Pressure

Concentration Gradients

• Concentration

• The number of molecules (or ions) of substance per unit

volume of fluid

• Concentration gradient

• The difference in concentration between two adjacent

regions

• Molecules move from a region of higher concentration to

one of lower concentration

Tonicity

• Tonicity

• The relative concentrations of solutes in two fluids

separated by a selectively permeable membrane

• For two fluids separated by a semipermeable membrane, the

one with lower solute concentration is hypotonic, and the

one with higher solute concentration is hypertonic

• Isotonic fluids have the same solute concentration

Osmosis

• Osmosis

• The movement of water down its concentration gradient –

through a selectively permeable membrane from a region

of lower solute concentration to a region of higher solute

concentration

Osmosis

selectively permeable membrane

Membrane Permeability

• Selective permeability

• The ability of a cell membrane to control which substances

and how much of them enter or leave the cell

• Allows the cell to maintain a difference between its internal

environment and extracellular fluid

• Supplies the cell with nutrients, removes wastes, and

maintains volume and pH

Selective Permeability of Lipid Bilayers

gases glucose and

other polar

molecules;

ions

lipid

bilayer water

Effects of Fluid Pressure

• Hydrostatic pressure (turgor)

• The pressure exerted by a volume of fluid against a

surrounding structure (membrane, tube, or cell wall) which

resists volume change

• Osmotic pressure

• The amount of hydrostatic pressure that can stop water

from diffusing into cytoplasmic fluid or other hypertonic

solutions

Effects of Fluid Pressure

Take-Home Message: What influences the

movement of ions and molecules?

• Molecules or ions tend to diffuse into an adjoining region of

fluid in which they are not as concentrated

• he steepness of a concentration gradient as well as

temperature, molecular size, charge, and pressure affect the

rate of diffusion

• Osmosis is a net diffusion of water between two fluids that

differ in water concentration and are separated by a

selectively permeable membrane

• Fluid pressure that a solution exerts against a membrane or

wall influences the osmotic movement of water

3D ANIMATION: Osmosis

videos_animations/Osmosis/osmosis.html

5.9 Membrane Transport Mechanisms

• Many types of molecules and ions can cross a lipid bilayer

only with the help of transport proteins

How Substances Cross Membranes

• Gases and nonpolar molecules diffuse freely across a lipid

bilayer

• Ions and large polar molecules require other mechanisms to

cross the cell membrane

• Passive transport

• Active transport

• Endocytosis and exocytosis

Passive Transport

• Passive transport (facilitated diffusion)

• Requires no energy input

• A passive transport protein allows a specific solute (such

as glucose) to follow its concentration gradient across a

membrane

• A gated passive transporter changes shape when a

specific molecule binds to it

Passive Transport of Glucose

Active Transport

• Active transport

• Requires energy input (usually ATP)

• Moves a solute against its concentration gradient, to the

concentrated side of the membrane

• Calcium pumps

• Active transporters move calcium ions across muscle cell

membranes into the sarcoplasmic reticulum

Active Transport: Calcium Pump

Extracellular Fluid

Cytoplasm



ANIMATED FIGURE: Active transport




videos_animations/active_transport.html

Cotransport

• Cotransporter

• An active transport protein that moves two substances

across a membrane at the same time

• Example: The sodium-potassium pump moves Na+ out of

the cell and K+ into the cell

Cotransport: Sodium-Potassium Pump

Extracellular Fluid

Cytoplasm

ADP

Take-Home Message: How do

molecules or ions cross a cell membrane?

• Transport proteins help specific molecules or ions to cross

cell membranes

• In passive transport, a solute binds to a protein that releases

it on the opposite side of the membrane; he movement is

driven by a concentration gradient

• In active transport, a transport protein pumps a solute across

a membrane, against its concentration gradient; the

movement is driven by an energy input, such as ATP

ANIMATED FIGURE: Passive transport




videos_animations/passive_transport_v2.html

5.10 Membrane Trafficking

• By processes of endocytosis and exocytosis, cells take in and

expel particles that are too big for transport proteins, as well

as substances in bulk

• Requires formation and movement of vesicles formed from

membranes, involving motor proteins and ATP

Exocytosis and Endocytosis

• Exocytosis

• The fusion of a vesicle with the cell membrane, releasing

its contents to the surroundings

• Endocytosis

• The formation of a vesicle from cell membrane, enclosing

materials near the cell surface and bringing them into the

cell

F Some vesicles and their contents are delivered to lysosomes.

lysosome

B The pits sink inward and become endocytic vesicles.

C Vesicle contents are sorted.

Exocytosis

D Many of the sorted molecules cycle to the plasma membrane.

E Some vesicles are routed to the nuclear envelope or ER membrane. Others fuse with Golgi bodies.

Golgi

Endocytosis

A Molecules get concentrated inside coated pits at the plasma membrane.

coated pit

Stepped Art

Figure 5-27 p94

ANIMATED FIGURE: Membrane cycling




videos_animations/membrane_cycling.html

Figure 5-28a p94

plasma

membrane

Figure 5-28b p94

aggregates of

lipoproteins

Three Pathways of Endocytosis

• Receptor-mediated endocytosis • Specific molecules bind to surface receptors, which are

then enclosed in an endocytic vesicle

• Phagocytosis • Larger target particles such as microbes or cellular debris

are engulfed by pseudopods which merge as a vesicle, which fuses with a lysosome in the cell

• Pinocytosis • A less selective endocytic pathway that brings materials

in bulk into the cell

Figure 5-29a p95

A Pseudopods of a white blood cell

surround Tuberculosis bacteria (red).

ANIMATED FIGURE: Phagocytosis




videos_animations/phagocytosis.html

Phagocytosis

B Endocytic vesicle

forms.

c Lysosome fuses with

vesicle; enzymes digest

pathogen.

D Cell uses the

digested material

or expels it.

Membrane Cycling

• Exocytosis and endocytosis continually replace and withdraw

patches of the plasma membrane

• New membrane proteins and lipids are made in the ER,

modified in Golgi bodies, and form vesicles that fuse with

plasma membrane

Forming New Plasma Membrane

Take-Home Message: How do cells take in

large particles and bulk substances?

• Exocytosis and endocytosis move materials in bulk across

plasma membranes

• In exocytosis, a cytoplasmic vesicle fuses with the plasma

membrane and releases its contents to the outside of the cell

• In endocytosis, a patch of plasma membrane sinks inward

and forms a vesicle in the cytoplasm

• Phagocytosis is an endocytic pathway by which cells engulf

particles such as microorganisms

Documents

Chapter 5 Gases - Mr. Doyle SUIS Science