The Cell, Cell Theory, & Inside The Cell

Chapter 7

Robert Hooke

• 1663

• Used a small hand held “microscope” to

view small chambers within cork

• Called these chambers “Cells”

Anton Van Leeuwenhoek

• 1675

• Dutch lens maker

• Took a close look at the pond water

through a better microscope that he made

by himself

• Saw things moving

• He called it "animalcules"

• These were single celled organisms

The Cell Theory

• This story all starts with a dinner conversation between 2 friends

• Theodore Schwann, an animal scientist who believed that all animals were made of cells

• Mathias Schleiden, a plant scientist who believed all plants were made of cells

• Bringing this up during dinner, the two scientists began to devise the cell theory

The Original Theory

• These two scientists devised one of the best “Life” theories

• The original cell theory stated these 3 ideas:

– 1. The cell is the unit of structure, physiology, and organization in living things

– 2. The cell retains a dual existence as a distinct entity and a building block in the construction of organisms

– 3. Cells form by free-cell formation, similar to the formation of crystals

1. The cell is the unit of structure,

physiology, and organization in

living things

• This basically means that:

–All living things are made of cells

• Our current belief is, “If it doesn’t have

cells, it isn’t classified as what we currently

consider alive in the scientific community

2. The cell retains a dual existence

as a distinct entity and a building

block in the construction of

organisms

• This basically means that:

–Cells are the basic units of structure and function in living things

• Cells are THE MOST basic building blocks of life

– If you get any smaller than a cell, you are no longer dealing with something that is ALIVE

3. Cells form by free-cell formation,

similar to the formation of crystals

• This basically means that:

– Cells (and life) form very similar to the way

salt crystal form on your skin after you swim in

the ocean

– They Spontaneously Generate themselves

– Is this true???

Spontaneous Generation

• Years ago, it was generally believed that life just “formed” in lower life forms

• A mouse formed from leaving cheese in a barn

• Mold formed from leaving food out in the sun

• They just appeared

• This was the current scientific belief at that time

Theory

• Again, this is an excellent example of how

a theory can be WRONG!

• Schwann and Schleider were very

intelligent men, who came up with a great

theory

• BUT, the third rule was VERY WRONG

Rudolf Virchow

• Rudolf Virchow corrected this third rule

with his research on cellular reproduction

• He concluded that a cell only arises

from pre-existing cells

• Cells ONLY come from other cells

• Generally, they only come form the same

type of cell as well

The Last 2 Rules

• (NOT IN YOUR BOOK)

• Various other scientists worked together and decided on the last 2 rules that are not in your book (No single scientist is credited for these last two rules)

• 4. Cells contain hereditary information which is passed from cell to cell during cell division

• 5. All cells are basically the same in chemical composition

Current CELL THEORY

• 1. All living things are made up of cells

• 2. The cell is the structural & functional

unit of all living things

• 3. All cells come from pre-existing cells by

division

• 4. Cells contain hereditary information

which is passed from cell to cell during cell

division

• 5. All cells are basically the same in

chemical composition

Scientist Method• After his death on August 30, 1723, a member of

the Royal Society wrote... "Antony van Leeuwenhoek considered that what is true in natural philosophy can be most fruitfully investigated by the experimental method, supported by the evidence of the senses; for which reason, by diligence and tireless labour he made with his own hand certain most excellent lenses, with the aid of which he discovered many secrets of Nature, now famous throughout the whole philosophical World". No truer definition of the scientific method may be found.

Advances in Technology

• Through the advances in technology made

by Anton van Leeuwenhoek science was

able to move through new doors

• Of course, since he advanced the science,

he had first dibs on the discoveries

More Cells?

• Are the cells in our bodies the only type?

• -Animal Cells

• -Plant Cells

• -Protist Cells

• -Fungal Cells

• Bacterial Cells

To Nucleus or not to Nucleus?

• When we get into the various structures found inside the cell, we will learn about an organelle called a nucleus

• It is the largest and most important organelle in many cells

• It controls the other parts of the cell & controls reproduction

• Its presence or absence is one of the MOST important distinguishers between the different types of cells

To Nucleus

• If a nucleus is present, the cell is called

Eukaryotic

• Every cell in our bodies have a nucleus

• That is why we are called Eukaryotic

Organisms

• Most of the organisms that are considered

“Highly Evolved” are Eukaryotes

Not to Nucleus

• If there is no nucleus present, it is a

Prokaryotic Cell

• These are much simpler cells

• They are much more likely to be free-living

as a single cell, then a eukaryotic cell

– If a cell is Free-living, it can survive as just a

single celled organism– Sometimes a single, prokaryotic cell can be parasitic also

Review

• What did Anton van Leeuwenhoek do?

• What is spontaneous generation?

• What is the cell theory?

• What are the 5 steps of the cell theory?

• What were the three rules of the cell theory devised by Schwann and Schleiden?

• What is the name for a cell with no nucleus?

• What is the name for a cell with a nucleus?

• What did Rudolf Virchow do?

Inside the Cell

Thanks to the selective permeability of the

phospholipid bilayer and the activity of

membrane transport proteins, the plasma

membrane creates an environment that is

different from conditions outside the cell.

Plasma Membrane

• What does it mean to be selectively permeable?

• What is a membrane transport protein?

• The job of the plasma membrane is to separate the cell from the world

• If it does its job correctly, the outside world will have very little affect on the cell

• What is the plasma membrane made out of?

Diffusion• In a solution, particles are ALWAYS

moving

• Under normal pressure, particles try to

spread out evenly across a solution

• As a result, particles tend to move from

high concentration to lower concentration

– This decreases collision

• This is the process of Diffusion

• Once the concentration is the same

throughout, it is called Equilibrium

Facilitated Diffusion

• Water and small molecules can diffuse

across the lipid bilayer in the plasma

membrane, but what about large

molecules like glucose???

– These large molecules require doors in the

plasma membrane called protein channels

– By limiting the amount of these large protein

channels, the cell can control how much

glucose enters the cell

Active Transport Diffusion

• Both diffusion and facilitated diffusion do not

require energy to move particles into and out of

cells

• However, some particles do require energy to

allow them to cross the cell membrane

• These particles use transport protein pumps that

use cell energy (ATP) to allow items to enter the

cell or leave the cell

• Often times this against a concentration gradient

– From low concentration to high concentration

Cytoplasm

• The contents inside the cell that are not the nucleus are collectively termed Cytoplasm

• Often times it is considered just the jelly like material surrounding the organelles, but aside from the nucleus it contains the organelles

• The fluid portion of the cytoplasm is called the cytosol

• It contains HIGH levels of solutes (dissolved substances) and is therefore hypertonic relative to most environments

• This causes water to enter the cell via osmosis

Osmolarity & Tonicity

• Osmosis is the movement of water from

an area of high water concentration (low

solute concentration) to an area of lower

water concentration (higher solute

concentration)

• Tonicity is relative to view point

• ALWAYS consider if you are considering

the cell or solution when deciding tonicity

Osmolarity & Tonicity

• 3 different tonicities:

– HYPERTONIC solution: There is more dissolved

substances and less water OUTSIDE the cell than

inside the cell, therefore water EXITS the cell via

osmosis pressure through the lipid bilayer

– HYPOTONIC solution: There is more dissolved

substances and less water INSIDE the cell than

outside the cell, therefore water ENTERS the cell via

osmosis pressure through the lipid bilayer

– ISOTONIC solution: There is THE SAME AMOUNT

of dissolved substances and water outside the cell as

inside the cell, therefore water move equally

throughout the cell and the pressure does not change

Osmolarity & Tonicity

• The reason osmosis works the way it does is that water moves through the semi-permeable membrane through very small gaps in between the lipid bilayer

• Once in the area of high solute concentration, the water molecules bond, bind, or are attracted to the various solute

• Now, they are to large to fit back through the semi-permeable membrane

Tonicity to a Cell

• The solution a cell is in and its relative

tonicity to a cell is essential to the survival

of a cell

• This regulation is one of the most

important aspects of the plasma and cell

membrane

The Organelles

• NOT ALL CELLS ARE THE SAME

• But they do have a very similar chemical makeup and mechanism

• Cells make up nearly every part of everything that is alive or ever has been alive, therefore to understand cells is to understand life

The NUCLEUS• Structurally, the nucleus is composed of three

main parts:– The nucleolus: which contains and forms the large

and small ribosomes, RNA, DNA, and proteins

– The nuclear envelope: allows the nucleus to control the rest of the cell, such as by sending out ATP. The envelope will let molecules like ATP through but will keep other things in or out, so the nucleus is isolated from the cytoplasm.

– The chromatin: (meaning "colored substance") contains DNA and proteins formed into packets of code called chromosomes

• Heterochromatin: One section of the chromatin that is highly compacted, supercoils

• Euchromatin: Area of chromatin that is composed of long, unwound, filamentous strands

The NUCLEUS

• The largest organelle inside the cell

• Causes a cell to be Eukaryotic or Prokaryotic (Presence or absence of a nucleus)

• Only found one per Eukaryotic cell

• Often considered the brain or central organelle of the cell

• Major purpose is cell control and reproduction

Eukaryotic vs. Prokaryotic

• As just mentioned, if a cell has a nucleus it

is considered Eukaryotic, and higher

evolved

– IE: Humans, Animals, Plants

• If it lacks a nucleus it is considered

Prokaryotic and is less involved

– IE: Protists, Bacteria

Ribosomes

• Assemble Proteins

– It translates Messenger RNA (mRNA) into a polypeptide chain (e.g., a protein). It can be thought of as a factory that builds a protein from a set of genetic instructions

• Comprised of two subunits:

– Each subunit contains a large RNA molecule and several different protiens

– Small subunit

– Large subunit• In Eukaryotes, the large subunit also contains two

small RNA molecules – In Prokaryotes it has only one small

Rough Endoplasmic Reticulum

• Though many ribosomes are found floating freely in the cytosol, there are some associated with membranes

• Hundreds of thousands of ribosomes are attached to a network of membrane bound sacs & tubules called the R.E.R.

• It is attached to the outer membrane of the nuclear envelope

• From there, the layers of sacs extend into the cytoplasm

Rough Endoplasmic Reticulum

• reticulum is a network of tubules, vesicles and sacs that are interconnected.

• They may serve specialized functions in the cell including protein synthesis, sequestration of calcium, production of steroids, storage Endoplasmic and production of glycogen, and insertion of membrane proteins

• Most of the proteins made in the R.E.R. are destined for the cell membrane or beyond

Smooth Endoplasmic Reticulum

• Location of lipid processing

– Area of the cell where fats are made

• Many of these lipids will be shipped to the

cell membrane to repair the lipid bilayer or

stored as fats in the body

• Very similar in structure to the RER but

lacks ribosomes

• The smooth ER also plays a role in

detoxification of drugs and alcohol in the

cell

Golgi Apparatus

• In most cases, the products from the R.E.R.

pass through the Golgi Apparatus before they

reach their final destination

• The Golgi Apparatus is the equivalent of a mail

depot for the cell

• It is here that the items that are leaving the cell

are sent for packaging and shipping.

• If it leaves the cell, it goes through the Golgi

• Remember, the cells make what the body uses,

but each cell type is fairly unique to its job

Lysosomes• These are the cell’s clean up crew and first line

of defense

• Lysosomes are golgi vesicles that are filled with

enzymes that have a low pH (acidic)

• Lysosomes use these enzymes to break down

lipids, carbohydrates, and proteins inside of the

cell

• They clean up the “junk” that would otherwise

build up inside of the cell

• They also are essential for destroying foreign

material inside of the cell

Vacuoles• Vacuoles are simply membrane bound storage

containers within a cell

• They can store water, salts, proteins, and

carbohydrates

• In plants there is a Large Central Vacuole

inside of the cell that is filled with water

– This LCV is what gives non-woody plants

Turgor pressure which is what allows them

to stand up.

– If a plant wilts, its LCV is low on water causing

a low turgor pressure

Mitochondria• The powerhouse of the cell

– This is the area where chemical compounds

found in food are converted into useable ATP

– in a process called the Kreb’s cycle (Chptr 9)

• They are essential to the cells energy

process

• They are enclosed in two membranes

– The inner membrane is folded up inside of the

organelle

• Mitochondria have circular “prokaryote-

like” DNA

Mitochondria

• Mitochondria also reproduce on their own

within your cells

– They reproduce faster when there is a higher

demand for ATP and shrink away and

disappear if that demand is low

• Mitochondria are also all derived from the

cytoplasm of the ovum (egg).

– You get your mitochondria from your mom

• Would you expect muscle cells to have a

lot of mitochondria????

Chloroplasts

• Chloroplasts are the organelle that

captures the suns energy and converts it

into chemical energy

• This is how plants make glucose

• They, like mitochondria, have two

membranes, prokaryotic DNA, and

reproduce individually within a cell

• The inner membrane contains chlorophyll

which give leaves their green color

Fall

• As the suns energy grows weaker (further

away) during the months of fall, the

chloroplasts become less necessary

• As the chloroplasts begin to shrink away,

other pigments that where hidden in a

plant become visible

• These pigments were always there, but

they were covered by the numerous

chlorophylls

• This is why leaves change color in the fall

Endosymbiotic Theory• Endosymbiosis is when an organism

engulfs a smaller organism (to eat it), but

rather than eating it, the prey organism

becomes part of the predator.

• This happens when the prey organism

offers something to the predator

• It is believed this happened early in

Eukaryotic evolution with the mitochondria

and chloroplast

– Prokaryotic DNA, Double membraned,

reproduces on its own inside the cell