Cell Boundaries

Chapter 6

What are boundaries? We have borders

surrounding countries

We have boundaries on a playing field

Why are borders important?

What are the borders of a cell?

Cell membrane Thin, flexible barrier

Cell wall Plant, algae, fungi, prokaryotes Strong supporting layer

Cell Membrane What does it do for cell?

Controls what goes in and out Regulates molecules moving from one liquid side of the

cell to the other liquid side of the cell

Protects Supports

Cell Membrane Lipid bilayer

What are lipids? What does bi- mean? What’s a layer?

A cell membrane is made of two

layers of lipid molecules

Cell membrane Phospholipids bilayer

Made of a negatively charged phosphate “head” PO4

3-

Attracts water because the phosphate is charged (-)

Water is a polar , slightly positive ends and slightly

negative ends

Attached to the phosphate group are 2 fatty acid chains Hydrophobic= don’t like water So the inside of the cell

membrane doesn’t let water in but the outside allows cells to be dissolved in aqueous environments

http://upload.wikimedia.org/wikipedia/commons/3/3a/Cell_membrane_detailed_diagram_4.svg

Other things in the membrane…

Proteins embedded in lipid bilayer

Carbohydrates attached to proteins

So many different molecules in membrane, we call it a “mosaic” of different molecules

Proteins

Proteins help things get across membrane

Kinda like a pump

Carbohydrates…

Chemical identification cards

“ID” card of cell Helps individual cells

id each other

Cell Walls

Outside cell membrane (does NOT replace membrane!!!)

Plants, algae, fungi, prokaryotes

Have pores to allow things in

Function: SUPPORT and PROTECT

Cell walls made of…

Protein and carbs Plant cell walls made

up of CELLULOSE This is a tough

carbohydrate Wood and paper

A biological membrane Cells exist in liquid environments Things need to get in and out of cell Different ways to do this….

The Cell Membrane

Concentration (conc.) Solution

Mix of 2 or more substances Solutes

Substance dissolved in solution Concentration

Molarity (M) is # of Moles of a substance per liter of solution 6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc)

Moles is a unit for measuring EXTREMELY small things is mass of SOLUTE in a given volume of solution (g/L) What is the concentration of 12 grams of salt dissolved in 3

liters of water? 12g/3L= 4g/L

Diffusion Particles constantly move Collide randomly Spread out randomly Diffusion is moving from area of HIGH conc. to

area of LOW conc. This is what we call the CONCENTRATION

GRADIENT

Equilibrium

When the conc. Of a system is the same throughout

(same conc. on both sides)

What’s this have to do with cells?

Cell have liquid inside and are found in liquid environment

We have substances (solutes) inside and outside cell

Unequal concentrations means we get DIFFUSION!!!

B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy

What happens when we reach equilibrium?

Particles continue moving across membrane but in both directions!***No more changes in concentration

Problems for diffusion…

Things too large Charged molecules

Positive/negative Opposites attract but likes do not… These all present serious problems for

things getting across membranes…

If things can cross a membrane we call the membrane PERMEABLE

If things canNOT cross a membrane we call the membrane IMPERMEABLE

Biological membranes are…

SEMI-PERMEABLE Aka… Selectively permeable Cell membranes are picky

Osmosis Water (H2O) can pass

easily through most biological membranes

Def: Diffusion of Water

through a semi-permeable membrane

How Osmosis works… We have water molecules and some

other molecules, let’s say sugar If we have more water on one side of the

membrane (HIGH conc. of H2O), then the water will diffuse across…

Membrane will let water thru but not sugar

Water can move back and forth (not sugar)

Water moves from areas of HIGH conc. To areas of LOW conc.

Water moves across till equilibrium is reached Isotonic:

when conc. Of both solutions is equal Hypertonic: “above strength”

When we begin with more sugar in water More concentrated sugar solution on side A

Hypotonic: “below strength” When we end with less sugar Dilute sugar solution on side A

Osmotic Pressure

Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall

Cell wall does NOT allow cell to expand past a certain size

How do big molecules diffuse across a membrane so quickly if the membrane is selectively permeable?

Facilitated Diffusion What does facilitate mean? Proteins are the extra help “escorts” across the membrane We call these protein channels…

Allow specific things thru

Facilitated Diffusion (continued)

FAST SPECIFIC Still diffusion

so we only see it from high concentration to low

Does NOT require energy

What about when we want to go against the concentration?

(From low concentration to high?)

What do we need???

ENERGY!!!!

ACTIVE transport Process that moves molecules against the concentration

gradient Requires ENERGY A protein pumps small molecules and ions across a cell

membrane against the conc. Gradient Electrochemical gradient

membrane potential To pump large molecules and clumps…

2 other processes: Exocytosis Endocytosis The can change shape of membrane

Types of Active transport

Molecular Transport When small ions and molecules are carried

across membrane Endocytosis

Endo- means…. -Cyto- means… -sis mean….

Exocytosis Exo- means…. -Cyto- means… -sis mean….

Molecular Transport

Proteins are used to pump small molecules and ions across membrane even against the conc. Gradient

The cell devotes a lot of ENERGY to pumping things across membrane

Potassium, calcium, and sodium are some things that need to pumped across

Endocytosis When cells need to take in large material Process of taking material into the cell by

process of infolding, or pockets, of the cell membrane

Pocket breaks loose from cell membrane and forms a vacuole or vesicle inside the cell

Two Types… Phagocytosis Pinocytosis

Two types of endocytosis:1. Phagocytosis

“cell eating” Extensions of cytoplasm surround the particle

and package it within a food vacuole Cell then engulfs the package Amoebas

2. Pinocytosis “cell drinking” When cell needs to take up liquid Tiny pockets in cell membrane form Fill with liquid Then pinch off to form vacuoles inside of cell

Exocytosis Exo- means… Cyto means… Sis means… When cell releases large amounts of material Excretes stuff Membrane of vacuole surrounding particle

inside cell fuses with the cell membrane The contents in vacuole are then forced out of

the cell We see this in removal of water by contractile

vacuoles

MEMBRANE MAMBO!!!