cells: the living units - blair school...

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Cells: The Living Units

Chapter 3, PPT 1

Cells…What do you know? Cells

Cells are

the structural units of all living things

Cell History

•  Robert Hooke – Observation of plant cells in 1600s

Cell History

•  Schleiden & Schwann – Said living things were composed of cells in 1830s

•  Virchow – Said cells only come from other cells

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Cell Theory 1.  All living things are composed of cells.

–  When you define the properties of a cell, you define the properties of life.

2.  The cell is the basic structural and functional unit of living organisms.

3.  All cells arise from pre-existing cells – Continuity of life has a cellular basis.

Cell Theory Additionally 4.  Organismal activity depends on individual

and collective activity of cells

5.  Biochemical activities of cells are dictated by subcellular structure.

Cells •  Vary in size, shape and function

– Size = 2 micrometers to 40 inches – Shapes = see HW – Functions = so many!

1 micrometer = 1/12,000 of an inch

Generalized, Composite Cell •  But even though they are different, they all

have similarities in common… 1.  Plasma/cell membrane 2.  Cytoplasm 3.  Nucleus

Plasma Membrane

•  Why does a cell have an outer membrane? – Keep some things in,

keep some things out •  Separate the two major fluid

compartments of the body –  Intracellular fluid – Extracellular fluid – Both largely composed of H20

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Plasma Membrane Structure

Phospholipid Bilayer •  Hydrophilic Head

– Phospholipid •  Hydrophobic Tail

– Two fatty acid chains

Phospho = Lipid = Bi =

Hydro = Phobic = Philic =

About Polarity •  What do you know about “poles’? •  What objects have “poles”? •  What does the polarity of a magnet refer to?

– Opposite charges … what do opposite charges do? – Opposites attract!

•  We said water was polar… what did that mean?

Water is Polar

•  What does that mean? •  What causes this? •  Draw it…

Lipids are Nonpolar •  What major organic biomolecule does NOT

disassociate in water? •  Why??

–  It is non-polar, no charges to pull/attract

•  Think back to bio… what makes a duck’s feathers waterproof?

NOTE: § With polar substances opposites attract § With non-polar substances, like attracts like

Let’s play a Game •  If your last name starts with…

– A to G; you are polar and have a negative charge – H to P; you are polar and have a positive charge – Q to Z; you are nonpolar

•  Look around the room for the neon green signs •  Based on what you are, go to the place you

should hang out.

QUIZ TIME

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Can you explain this to someone?

The plasma membrane is composed of a phospholipid bilayer. The hydrophilic head and

hydrophobic tail of this structure separates intracellular and extracellular fluids.

If not, you need to review the material or come see me!!

•  Very thin structure •  Phospholipid bilayer

– A double layer of lipid molecules •  Protein molecules dispersed among the bilayer

– Protein molecules constantly change – Results in a constantly changing mosaic pattern

Plasma Membrane Structure Fluid Mosaic Model

Plasma Membrane Proteins

Two major types •  Integral proteins

– What does integral mean? –  Steady Eddys

•  Peripheral proteins – What does peripheral mean? – Rico Suaves

Integral Protein Structure •  Proteins firmly inserted into the phospholipid

bilayer •  Transmembrane

– Transatlantic flight? – Span the entire width of the membrane and protrude

on both sides

Integral Protein Function Transport things into & out of cell

– They all have hydrophobic and hydrophilic regions •  Channels

– Pores formed in membrane by a cluster of proteins •  Carriers

– Proteins bind to a substance and then move it through membrane

Integral Protein Function Transport things into & out of cell •  Signal transduction

– Receptors that relay messages from hormones and other chemical messengers

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Peripheral Protein Structure •  Attached loosely to integral proteins or

membrane lipids – Easily removed

•  Supporting filaments •  Enzymes •  Mechanical functions

– Shape changers (cell division, muscles)

Peripheral Protein Function

Plasma Membrane Glycocalyx

The sugar coating of our cells! •  Structure

– Glycoproteins & Glycolipids •  Function

– Recognition •  Sperm, bacteria, etc.

Fluid Mosaic Model

Figure 3.3

QUIZ TIME

QUIZ TIME!!! Graded or ungraded?

Individually or as a group?

1.  The plasma membrane separates what? –  Intracellular fluid and extracellular fluid

2.  The intracellular and extracellular fluid are composed of a large amount of what? – H2O

3.  The head of a phospholipid is what? –  Hydrophillic

4.  Bilayer means what? –  Two layers

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5.  Who said cells come from other cells? –  Virchow

6.  What are two of the three components of a composite cell?

–  Plasma Membrane, Cytoplasm, Nucleus

7.  Is the head of the phospholipid on the inside or outside of the plasma membrane?

–  Outside hydrophobic tails line up inside

8.  And what are the proteins doing? –  …

9.  Give one of the three parts of the cell theory.

Cell Theory 1.  All living things are composed of cells. 2.  The cell is the basic structural and functional

unit of living organisms.

3.  All cells arise from pre-existing cells

Plasma Membrane Specializations

•  Microvilli •  Membrane Junctions

Microvilli Structure Microvilli = “little shaggy hairs” •  Minute fingerlike extensions of the plasma

membrane project from free or exposed cell surface

•  Actin core

•  Increase surface area •  Found on absorptive cells; intestinal cells

Microvilli Function

Microvilli in Celiac Disease Membrane Junctions

Three types •  Tight junction •  Desmosome / Anchoring junction •  Gap Junction / Nexus

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Tight Junctions •  Impermeable junction •  Series of integral

proteins fuse together •  Prevents molecules

from passing through extracellular space between adjacent cells

•  Found in epithelial cells lining the digestive tract

Desmosomes •  Anchoring junctions •  Spot welds between cells •  Found in tissues subjected

to great mechanical stress; skin, heart muscle

Gap Junction (aka “nexus”)

•  Communicating junctions between adjacent cells

•  Found in heart and smooth muscle

•  What is that orange thing?

We talked about composite cells. What are they? Cells that have 3 components in common.

What three things?

1. Plasma Membrane 2. Cytoplasm 3. Nucleus

What is the plasma membrane composed of

A bilayer of phospholipids with hydrophilic heads and hydrophobic tails.

The tails are composed of what?

Two fatty acid chains

What are the two types of membrane proteins? Integral (Steady Eddy) Peripheral (Rico Sauve)

Remember what your cells’ sugar coating is called? Glycocalyx

We talked about specializations of the plasma membrane. What are the projections called? Microvilli.. Little shaggy hairs.

How do they help? Increase surface area

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What are the three types of junctions? 1. Tight Junctions 2. Desmosomes 3. Gap Junctions

Why do cells need membrane junctions? They can’t all just be floating out there wherever they want; that would be silly. (Need to communicate, keep things out, be held together)

Plasma Membrane Function

1.  Membrane Transport – Passive – Active

2.  Resting Membrane Potential – Generates – Maintains

Membrane Transport •  Interstitial Fluid

– “Blood bath” – Extracellular fluid that our cells are bathed in – “Feeds” our cells

•  Think about it… – What do our cells need to be fed?

• Amino acids, sugars, fatty acids, vitamins, hormones, neurotransmitters, salts

– What might need to exit them? • Waste products

Selective Permeability Cells have a selectively permeable membrane

–  (aka differentially permeable)

•  Allows some things to pass, but blocks others

– Allows nutrients, etc. to enter cell – Allows waste to exit cell

Membrane Transport

•  Passive – No cellular energy required

• Active – Require cellular energy

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Membrane Transport Passive – no E

Active – need E

•  Diffusion – Simple

• Osmosis – Facilitated

• Carriers • Channels

•  Filtration

Diffusion

•  Molecules and ions scatter evenly throughout the environment

•  Molecules move from an area of higher concentration to an area of lower concentration – Molecules move along (down) the concentration

gradient

•  Can be simple or facilitated

(Passive Transport)

Simple Diffusion Examples •  Molecules and ions scatter evenly throughout the

environment •  Molecules move from an area of higher concentration to

an area of lower concentration –  Molecules move along (down) the concentration gradient


Active – need E




•  Filtration

Simple Diffusion

•  Unassisted diffusion of molecules that are: – Lipid-soluble – Small enough to pass through channels

•  Examples – Osmosis

• Unassisted diffusion of a solvent (often water) through membrane

– Oxygen, carbon dioxide, fat-soluble vitamins

(Passive Transport) Osmosis

•  Osmos = pushing •  Diffusion of a solvent

through a selectively permeable membrane

•  Occurs when solvent (usually water) concentration differs on both sides of cells – Solvent (water) moves

from area of high to low concentration

(A Special Simple Diffusion)

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Osmosis •  If the membrane is

impermeable to solute molecules the volume of the solution will change – Solute (particles) can’t

move, so solvent (water) does


Osmosis (A Special Simple Diffusion)

Osmosis Terms •  Osmolarity

– The number of atoms, ions or molecules present per unit / The total concentration of all solute particles in a solution

•  The greater the osmolarity, the greater the concentration •  The lower the osmolarity, the lower the concentration


Osmosis Terms

•  Hydrostatic pressure – Back pressure exerted by water against membrane

•  Osmotic pressure – Cell’s tendency to resist net water entry

•  Water will diffuse until hydrostatic pressure is equal to osmotic pressure


Tonicity Ability of a solution to change shape (tone) of a cell by altering internal water volume

•  Isotonic –  Same osmolarity (solute conc) inside and outside cell –  Intra- and Extra- cellular concentrations are equal –  No net gain or loss of water in cell

(Osmosis)

Tonicity

•  Hypertonic – Hyper = high, above – Extracellular concentration is higher than intracellular – Cells lose water / shrink

(Osmosis)

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Tonicity

•  Hypotonic – Hypo = low, below – Extracellular concentration is lower than intracellular – Cells gain water / lyse (burst)

(Osmosis)

Osmosis, Osmolarity & Tonicity Review from last class…

…any questions??

Human Tonicity To be isotonic to a human, a solution must be:

–  0.9% saline –  5% sucrose

Think…why does it matter??

(Osmosis)

Hypotonic Hypertonic Isotonic

What is the difference between active and passive transport?

Active requires energy, passive doesn’t In diffusion particles move from an area of __________

concentration to an area of __________ concentration High to low

What two things are required of molecules to enter a cell

via passive diffusion? Lipid-soluble or small

Osmosis is a special type of what?

Passive diffusion (no energy, moving down concentration gradient

Osmosis occurs when particles can or can’t pass through the membrane?

Can’t… the solvent has to pass through If the osmolarity of a solution is high, then the solute

concentration is high or low? High

If there is a large difference in the osmolarity on two sides

of a semipermeable membrane, the osmotic pressure will be low or high?

High If a cell is in a hypotonic solutions, what will happen to it?

Burst / Lyse

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Active – need E




•  Filtration

Facilitated Diffusion •  Molecules cannot pass through the membrane

because they are dissolved in water – Hydrophobic tails won’t allow them to pass

•  Still goes down concentration gradient – From high to low concentration

•  Examples – Sugars, amino acids, ions

(Passive Transport)

Facilitated Diffusion Transport is facilitated (assisted) by integral (transmembrane) proteins

•  Carrier Proteins –  Molecule enters protein –  Binding causes shape

change –  Shape change opens “gate” –  Shields it from non-polar

inner membrane

•  Channel Proteins –  Aqueous channels –  Some are always open –  Some are gated and

controlled by chemical and electrical signals

(Passive Transport) Facilitated Diffusion

Transport is facilitated by integral proteins •  Carrier Proteins

–  Molecule enters protein –  Binding causes shape change –  Shape change opens “gate” –  Shields it from non-polar inner

membrane

•  Channel Proteins –  Aqueous channels –  Some are always open –  Some are gated and

controlled by chemical and electrical signals

(Passive Transport)


Active – need E




•  Filtration

Filtration •  Process that forces water and solutes through a

membrane or capillary wall by hydrostatic pressure

•  Uses pressure gradient - pushes fluid with solute from a higher-pressure area to a lower-pressure area

•  Not selective •  Example

– From capillaries to tissues, makes urine

(Passive Transport)

cells: the living units - blair school...

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