The Amazing Cell Membrane

First a little chemistry

All matter in the universe consists of elements

An element is a pure substance

Examples of elements needed for life:Carbon C*Hydrogen H*Oxygen O*Nitrogen NPhosphorus PSulfur S

An atom is the smallest part of an element

Can only be seen with the most powerful microscope

Atoms join together to form molecules.

Examples:

Oxygen we breathe is a molecule made up of 2 oxygen atoms: O2

Water is 2 hydrogens with 1 oxygen: H2O

Sugar is a much bigger molecule: C6H12O6

How many atoms in one sugar molecule?

Practice counting atoms

HNO3

H2SO4

C5H10P3O2

How to write 6 carbons, 12 hydrogens, 1 nitrogen and 4 oxygens

Important molecules for life

1. Water!

We take it for granted, but water has many unique properties that support life.

You are 60% water (H2O)

In fact, scientists who look for life on other plants focus on places where water does or used to exist

Organic molecules

Organic = contains carbon and found in living things

Why carbon? There’s lots of carbon in the universe(It’s the second largest component of you, after water)

It can make many different kinds of molecules

Four types of organic compounds found in living things

Carbohydrates Lipids Proteins Nucleic Acids

These are called macromolecules

Macro = giant (opposite of micro)

Cell Membrane

Made primarily of lipids

Lipids don’t dissolve in water.

So they won’t dissolve in

the aqueous (water based)

environment of your cells.

This is how the lipid looks in the membrane:

2-D version

Proteins are embedded in the membrane

Why are the proteins there?

They help certain molecules that are needed by the cell but can’t get through the lipids to enter the cell

Review

What elements are important for living things? How do you read a chemical formula (like C4HNO3)? What molecule is most common in living organisms? What is an organic compound? What four types of organic compounds are found in

living organisms? Why is life carbon-based? What two macromolecules are found in cell

membranes? Why are cell membranes made primarily of lipids? Why do cell membranes have proteins inserted

among the lipids?

What is the main job of the cell membrane?

To regulate what enters and leaves the cell!

What kinds of molecules have to enter the cell?

Small inorganic molecules like O2, CO2, and H2O

Ions like Na+ (sodium) and K+ (potassium) Nutrients that your cell will use for building

blocks or energy like carbohydrates, lipids, and proteins

Cell membrane is semipermeable

Semi = partly

Permeable = lets stuff go through it

So semipermeable means some stuff can go through the membrane – and some stuff can’t go through at all or can’t go through without help.

Function

Transport of materials across the membrane

Passive transport Active transport

No Energy Required! Energy Required!

Passive transport

Diffusion Facilitated Diffusion Osmosis

Equilibrium (everything is balanced)

Simple Diffusion

Solutions and solutes

A solvent is a substance that can dissolve other substances.

Ex: water—universal solvent (it can dissolve lots of things)

A solute is the substance

that dissolves

Ex: salt or sugar A solution is an evenly

distributed mix of solvent and solute

More vocabulary

Concentration: the amount of solute in solution, expressed as mass/volume—such as grams/liter (g/l)

Concentration Gradient: a gradual change in concentration from one area to another

Cell membrane

Solute moves DOWN concentration gradient

from area of HIGH concentration (many molecules per mL) to area of LOW concentration (fewer

molecules per mL)

Diffusion through a membrane

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Facilitated diffusion

Facilitated = helped

Some molecules are helped by channel or carrier proteins

Channel – a tunnel for substances like glucose

Facilitated diffusion

Carrier protein – changes shape to facilitate molecule passing through

Facilitated diffusion also involves moving across a concentration gradient (from high to low)—like diffusion, does not require energy

Review

What is the main job of the cell membrane? What does it mean to say the cell membrane is

semipermeable? What kinds of molecules need to enter the cell? What are the two types of transport and how are they

different? What are the three types of passive transport? Describe simple diffusion How is facilitated diffusion different from simple

diffusion? What kind of molecule does the facilitating?

Osmosis

Osmosis = diffusion of water through a cell membrane

Osmosis: diffusion of water—from high water/low solute to low water/high solute

Three osmotic conditions

Isotonic: iso = the same

--two solutions have the same solute concentration

--so the water flow between them is in equilibrium: no net movement

Cell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

What is the direction of water movement?The cell is at equilibrium.

Three osmotic conditions

Hypertonic: hyper = higher than--comparing two solutions, the one with a higher solute concentration is hypertonic to the other: it will gain water --so water will flow into the hypertonic solution

Salt sucks! So whichever is saltier will draw more water—why you want to drink more when you eat salty things.

In our lab, the syrup was hypertonic because it was more sugary than the egg so the egg lost water and shrank while the syrup became more watery.

Cell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

copyright cmassengale

Three osmotic conditions

Hypotonic: hypo- = lower than

--comparing two solutions, the one with the lower solute concentration is hypotonic to the one with higher solute concentration: it will lose water

--so water will flow out of the hypotonic solution

In our lab, the distilled water was hypotonic to the egg so water flowed into the egg and the egg swelled up.

Cell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement? copyright cmassengale

What is the direction of water movement?