Structure and Function of the Cell

Cells make up all living things

Cells are the basic unit of life

Cells

Tissues

Organ systems

Organs

Organisms

CELL THEORY• 1665 – Robert Hook - Looked at cork,

gave the little chambers the name “cells”

CELL THEORY

1674 – Anton Van Leeuwenhoek - first to look at living cells

- saw “animalcules” or little animals

CELL THEORY

1838 – Schleiden - All plants are made of these Cells

1839 – Schwann - All animals are made of these cells

1855 – Virchow –Noticed that Cells make more of

themselves.

FINAL CELL THEORY

• All living things are made up of one or more cells

• Cells are the basic unit of structure and function in living things

• Cells come from previously existing cells – NO spontaneous generation!

Prokaryotes Vs. Eukaryotes

Prokaryotes:

- literally means “before nucleus”

- primitive single celled life, the first!

- example: bacteria

- still has DNA just not enclosed in a nucleus

Prokaryotes Vs. EukaryotesEukaryotes:

- literally means “true nucleus”

- DNA enclosed by the nuclear membrane

- Can be single celled like protists (amoebas, paramecium)

- Or can be part of a multicellular organism like: plants, animals or fungi

Prokaryotes Vs. EukaryotesEukaryotes:

- significantly larger than prokaryotic cells

- have many more organelles than prokaryotic cells

How do we study cells?

• Microscopy – using a device that magnifies an image of a very small specimen

– Magnification:

– Resolution:

Here’s our specimen, but what’s wrong?

Magnify, still no good?

Increase resolution

Light microscopy

• Pros: more affordable– Easier prep– Can observe living cells

• Cons: – More limited in terms of

Mag/Res

Lightmicroscopy

Electron microscopy

• Pros: – Significantly greater

mag/res

• Cons: – Specimen Prep is much

more involved– Specimen prep will kill

specimen, no live observations

Electron microscopy

*Color is added, EM’s Only see produce black And white images

All cells must perform the same few functions to stay alive

BUT, since they have different organelles, they might go about it differently

I. All cells must control what enters and exits a cell

II. All cells must convert the energy in nutrients to into energy it can use

III. All cells must make, modify and ship proteins to where they need to go

IV. All cells must be able to store nutrients, digest large molecules and recycle damaged organelles

V. All cells must grow and divide

VI. All cells have a particular shape and can move IF THEY NEED TO

We will be starting with function I

Plasma Membrane

Phospholipid bilayer that surrounds all cells and certain organelles within the cell

Phospholipid

Hydrophilic Phosphate head

Hydrophobic Fatty acid Tails

Remember the Triglycerides?What’s the difference?

In water what will happen?

Water on outside of cell

Water on outside of cell

Also Water on Inside of cell

Double layer allows:

• All hydrophobic parts to be away from water

• All hydrophilic parts to be near water

Membrane – more than just phospholipids

A little more than just phospholipids

Plasma membrane contains:

Proteins embedded in phospholipid bilayer;

Cholesterol tucked between fatty acids

Carbohydrate chains

Why proteins?

• Proteins increase contact with water and act as channels through which certain molecules can pass

Why cholesterol?• Cholesterol keeps the membrane fluid and

flexible; prevents solidification

Why Carbs? Carbohydrate chains act as cell “ID” tags.

Fluid Mosaic Model: theory that describes the composition of the membrane

- Fluid because it is flexible; p-lipids and proteins can shift position

- Mosaic because it is made of many small molecules that work together as a whole

Membrane acts as a semi-permeable barrier (think bouncer!)

some stuff passes right through the phospholipids:

- small, hydrophobic, uncharged

some stuff can’t:

- ions (Na+, Cl-, K+, Ca++) - polar molecules (Sugars, Amino Acids)

- large nonpolar

But don’t we need these?!?! We’re getting there….

? ?

There are two general categories of transport:

Passive transport: The easy way; no energy required; molecules just flow

naturally across

Active Transport: the hard way; energy required; molecules need to

be pushed or carried across

BROWNIAN MOVEMENT

Molecules are ALWAYS moving

Passive Processes: No energy needed

• Diffusion: Movement of solutes from areas of high concentration to areas of low concentration until concentrations are equal.

• Concentration Gradient = differences in Concentration

Gaseous Diffusion

High Conc. Low Conc. No membrane needed

Think of it as molecules spreading out!

Progression of Liquid Diffusion

High Conc. Low Conc.

?

Facilitated Diffusion – movement of solute from high concentration to low concentration BUT requires

transport protein to move molecule that are too big or polar to get

through the bilayer on their own

Glucose is too big to fit through phospholipids and will be diffused through a transport protein to get

into the cell

Osmosis – A Passive Process where water moves across a cell membrane from an area that is hypotonic (lots of water, little solute) to an area that is hypertonic (little water, lots of solute)

think of the water as trying to dilute the concentrated side to make the concentration even

Weak Iced Tea Strong Iced Tea

Move water until you get

Two perfect Iced teas

Tonicity – term used to compare the concentration of one solution to another - will determine where water goes

3 ConditionsHypotonic

IsotonicHypertonic

The solution with the higher concentration is called Hypertonic.

The solution with the lower concentration is called Hypotonic

If the concentrations are equal, they are called isotonic

20% Salt Solution

10% Salt Solution

Which is Hypertonic?

Inside is Hypertonic

10% Salt Solution

20% Salt Solution

Which is hypertonic?

?Outside is Hypertonic

20% Salt Solution

20% Salt Solution

Isotonic:

Isotonic

CrenationC

ytol

ysis

Comparing Cell types chart

PlasmolysisVs.

Turgidity in Plant cells

- Turgor pressure: Pressure that the water INSIDE the cell puts on

the cell wall. Supports plant

A B A B

Active TransportCell must use energy to force molecules to move across the

membrane from a low concentration to a high

concentration. Usually used to move ion and since ions can not go through the phospholipids requires a transport protein

Active Transport:

Vesicle TransportVesicle transport is different from Diffusion, Osmosis, facilitate diffusion and active transport in that we are moving large quantities (many molecules) rather than individual molecules. The cell must package the material in a vesicle and bring it in or out of the cell depending on the goal.

• Making a vesicle requires the cell to exert energy in the form of ATP, but we don’t have to concern ourselves with concentration differences. The two types of vesicle transport depend on direction -

• Moving materials into a cell in a vesicle is called endocytosis. Moving materials out of a cell is called exocytosis.

Bulk transport into cell

Endocytosis

Phagocytosis

Pinocytosis

(SOLIDS)

(LIQUIDS)

Phagocytosis: “cell eating” large proteins, dead cells, bacteria substances WAY too big for even a protein;

Making/moving a vesicle requires energy ATP

Pinocytosis: Cell drinking; bulk ingestion of liquids

Particularly important in kidney and intestinal cells

Exocytosis – Bulk Transport out of cell

Way of releasing large quantities of stuff from the cell including : Hormones, mucus and cell wastes

NEEDS ATP