Lecture 1 Outline (Ch. 5)

I. Membrane Structure

II. Permeability

III. Transport Across Membranes

A. Passive

B. Facilitated

C. Active

D. Bulk

Membrane structure

1915, knew membrane made of lipids and proteins

• Reasoned that membrane = bilayer

Where to place proteins?

Lipid layer 1

Lipid layer 2

Proteins

Membrane structure

• freeze fracture

• proteins intact, one layer or other

• two layers look different

Membrane structure

Experiment to determine membrane fluidity:

• marked membrane proteins mixed in hybrid cell

Membrane structure

Membrane fluidity

• phospholipid f.a. “tails”: saturation affects fluidity

• cholesterol buffers temperature changes

Membrane structure

“fluid mosaic model” – 1970s

• fluid – phospholipids move around

• mosaic – proteins embedded in membrane

Membrane structure

• cell membrane – amphipathic - hydrophilic & hydrophobic

• membrane proteins inserted, also amphipathic

Membrane structure

hydrophilic

hydrophilic

hydrophobic

Membrane Proteins

Membrane proteins:

- transmembrane – span membrane

Integral: inserted in membrane

Peripheral: next to membrane- inside or outside

• Two transmembrane proteins: different structure

Bacteriorhodopsin: proton pump

Membrane structure

Bacterial pore protein

Membrane Proteins

Movement of molecules

Simple Diffusion: most basic force to move molecules

• Disperse until concentration equal in all areas

• Small, non-polar molecules OK

ex. steroids, O2, CO2

Movement of molecules

Cell membranes only allow some molecules across w/out help:

• No charged, polar, or large molecules

ex. sugars, ions, water*

Transport Across Membranes

Types of transport:

A. Passive transport

- Simple diffusion

- Facilitated diffusion

- Osmosis

B. Active transport

C. Bulk transport

• Energy Required?

• Directionality?

• DOWN concentration gradient

• molecules equally distribute across available area by type

Passive Transport - Simple Diffusion

- non-polar molecules (steroids, O2, CO2)

• NO ENERGY required

• DOWN concentration gradient

• molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein.

Passive Transport – Facilitated Diffusion

• NO ENERGY required

• osmosis – movement of water across cell membrane

• water crosses cell membranes via special channels called aquaporins

Passive Transport - Osmosis

• moves into/out of cell until solute concentration is balanced

Passive Transport - Osmosis

equal solutes in solution as in cell

more solutes in solution, than in cell

fewer solutes in solution, than in cell

In each situation below, does water have net movement, and which direction:

• tonicity – # solutes in solution in relation to cell

- isotonic – equal solutes in solution

- hypertonic – more solutes in solution

animal cell

plant cell

- hypotonic – fewer solutes in solution

Passive Transport - Osmosis

Paramecium example

• regulate water balance

• water into contractile vacuole

– water expelled

• pond water hypotonic

Passive Transport - Osmosis

Scenario: in movie theater, watching a long movie.

You are: drinking water

You are: eating popcorn

What happens to your blood?

What happens to your blood?

Passive Transport - Osmosis

• transport proteins

a. ion pumps (uniporters)

• Ex. Na-K ion pump

- Na+ ions: inside to out

b. symporter/antiporter

- K+ ions: outside to in

Active Transport

• UP/AGAINST concentration gradient

• ENERGY IS required

• antiporter: two molecules move opposite directions (UP gradient)

c. coupled transport

• ATP used pump H+ ions out

*gradients – used by cell for energy potential

• against concentration and charge gradients

Active Transport - uniporter

• Ex. proton (H+) pump

• uniporter: ONE molecule UP gradient

Active Transport – coupled transport

• Ex. Active glucose transporter

• Na+ diffusion used for glucose active transport

• Na+ moving DOWN concentration gradient

• Glucose moving UP concentration gradient

• coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions)

• phagocytosis – “food” in

• pinocytosis – water in

• Molecules moved IN - endocytosis

Bulk Transport• ENERGY IS required

• Several or large molecules

Bulk Transport

• receptor-mediated endocytosis

– proteins bind molecules, vesicles inside

• Molecules moved OUT - exocytosis

Self-Check

Type of transport

Energy required?

Movement direction?

Examples:

Simple diffusion no Down conc. gradient O2, CO2, non-polar molecules

Osmosis

Facilitated diffusion

Active transport

Bulk transport

Lecture 1 Outline (Ch. 6)

I. Energy and Metabolism

II. Thermodynamics

A. 1st Law – conservation of energy

B. 2nd Law - entropy

III. Free Energy

IV. Chemical Reactions

V. Cellular Energy - ATP

VI. Enzymes

A. Function

B. Regulation

What is Energy?

The capacity to cause change

Energy

Where does energy on earth come from originally?

40 million billion calories per second!

Metabolism

Metabolism –chemical conversions in an organism

Types of Energy:

- Kinetic Energy = energy of movement - thermal

- Potential = stored energy - chemical

Potential energy can be converted to kinetic energy (& vice versa)

Potential Energy Kinetic Energy

Thermodynamics

Thermodynamics – study of energy transformation in a system

Laws of ThermodynamicsLaws of Thermodynamics:: Explain the characteristics of energy

1st Law:

• Energy is conserved

• Energy is not created or destroyed

• Energy can be converted (Chemical Heat)

2nd Law: • During conversions, amount of useful energy decreases

• No process is 100% efficient

Thermodynamics

Energy is converted from more useful to less useful forms

• Entropy (measure of disorder) is increased

Metabolic reactions: Chemical reactions in organism

Anabolic = builds

up molecules

Metabolism

Two Types of Metabolic Reactions:

Catabolic = breaks

down molecules

Chemical Reactions:

• Like home offices – tend toward disorder

Chemical Reactions

Chemical Reactions:

• Endergonic – energy required to complete reaction

• Exergonic – energy given off

Exergonic

Endergonic

Chemical Reactions

Chemical Reaction:

• Process that makes and breaks chemical bonds

+Reactants

+Products

Two Types of Chemical Reactions:

1) Exergonic = releases energy

2) Endergonic = requires energy

Chemical Reactions

2. Endergonic reactions: “Energy in”

•Products have more energy than reactants

•Requires influx of energy

1. Exergonic reactions: “Energy out” • Reactants have more energy than products• Reaction releases energy

Chemical Reactions

Chemical Reactions

• Exergonic reaction • Endergonic reaction

release free energy

spontaneous

intake free energy

non-spontaneous

Glucose CO2 + H20 CO2 + H20 Glucose

Activation Energy: Energy required to “jumpstart” a chemical reaction

• Must overcome repulsion of molecules due to negative charged electrons

Nucleus Repel Nucleus

Nucleus Repel Nucleus

ActivationEnergy

ActivationEnergy

Chemical Reactions

Exergonic Reaction: – Reactants have more energy than products

But will sugar spontaneously burst into flames? Activation energy:

Make sugar and O2 molecules collide

Chemical Reactions“Downhill” reactions

sugar + O2

water + CO2

Cellular Energy - ATP

• ATP = adenosine triphosphate

• ribose, adenine, 3 phosphates

• last (terminal) phosphate - removable

• ATP hydrolyzed to ADP

ATP + H2O ADP + Pi

• Energy released, coupled to another chemical reaction

Cellular Energy - ATP

• stores 7.3 calories per mole

• ATP regenerated

• need 7.3 kcal/mol to build ATP

• cells power building ATP by coupling to exergonic reactions

- cellular respiration

Cellular Energy - ATP

Enzymes

Energy of activation (EA)

• reactants – absorb energy called: EA

• Reach EA, reaction proceeds (limiting step)

Exergonic – energy given off

• EA from ambient heat usually insufficient

• This is GOOD!

Enzymes

Enzymes

• lower EA

• only for specific rxns

• cell chooses which reactions go forward!

enzymes:

-do speed up rxn would occur anyway

-do not make endergonic exergonic

Enzymes

• enzyme – specific to substrate

• active site – part of enzyme -substrate

• binding tightens fit – induced fit

• form enzyme-substrate complex

• catalytic part of enzyme: converts reactant(s) to product(s)

Enzymes

Enzymes

• substrate(s) enter

• Enzymes lowers EA by:

• products formed

-template orientation

-stress bonds

-microenvironment

• enzyme reused

• What factors might affect enzyme activity?

Enzymes

• inhibitors:

• Drug – blocks HIV enzyme at the active site

Feedback Inhibition:

Enzymes

Like your furnace:

Detector

warm room

Furnace turns on

Room is warm

cold room

Lecture 1 Summary1. Membrane composition and function (Ch. 5)

- Phospholipids and cholesterol- Integral and peripheral proteins

2. How molecules cross membranes (Ch. 5)- Passive Transport- Active Transport- Bulk Transport

3. Energy (Ch. 6)- Types, conversion

4. Metabolic/chemical reactions (Ch. 6)- Catabolic/Endergonic- Anabolic/Exergonic

5. ATP (Ch. 6)

6. Enzymes (Ch. 6)- Purpose- Function- Regulation