Cells

I. Introduction – “What is a cell?”

A cell is the smallest unit that can carry out A cell is the smallest unit that can carry out allall the activities necessary for life. (i.e. the activities necessary for life. (i.e. homeostasis, metabolism, reproduction, homeostasis, metabolism, reproduction, heredity, cellular organization)heredity, cellular organization)

MostMost microscopic organisms are made up microscopic organisms are made up of a single cell. of a single cell.

II. Cell Discovery – “Who discovered the cell?”

New information was due largely to the New information was due largely to the advancement of the microscope. advancement of the microscope.

From a simple From a simple magnifying glassmagnifying glass to more to more complex complex compound light microscopescompound light microscopes to the to the latest technology of latest technology of transmission electron transmission electron microscopesmicroscopes and and scanning electron scanning electron microscopesmicroscopes..

a. Robert Hooke (1635-1703)

In 1665, the English In 1665, the English scientist and monk, scientist and monk, observed a thin slice observed a thin slice of cork. of cork.

He described what he He described what he saw as “a great many saw as “a great many little boxes,” which he little boxes,” which he then termed the then termed the cellcell..

b. Anton van Leeuwenhoek (1632-1723)

In 1675, the Dutch In 1675, the Dutch microscope maker, microscope maker, was the first person to was the first person to observe living cells.observe living cells.

For the next 150 years For the next 150 years very little research was very little research was done on cells.done on cells.

c. Robert Brown (1773 - 1858)

In 1827, the English In 1827, the English botanist, botanist, was the first was the first person to see the person to see the nucleus inside cells.nucleus inside cells.

However, by the However, by the time he died no one time he died no one really understood really understood the importance of the importance of his discovery.his discovery.

d.Matthias Schleidan (1804-1881)

In 1838, the German In 1838, the German botanist, observed botanist, observed thousands of plant thousands of plant cells and concluded cells and concluded that that allall plants were plants were composed of cells.composed of cells.

e. Theodor Schwaan (1810-1882)

In 1839, the German In 1839, the German zoologist, came to the zoologist, came to the same conclusion, that same conclusion, that allall animals were animals were composed of cells.composed of cells.

f. Rudolph Virchow (1821-1902)

In 1855, the German In 1855, the German physician, while physician, while studying diseases, studying diseases, determined that cells determined that cells come only from other come only from other cells. (i.e. cells cells. (i.e. cells produce more cells)produce more cells)

III. The Cell Theory – “Why are cells important?”

The observations of these scientists, taken The observations of these scientists, taken together are known as the cell theory:together are known as the cell theory:

1) All living things are composed of one or 1) All living things are composed of one or more cells.more cells.

2) Cells are organisms’ basic units of 2) Cells are organisms’ basic units of structurestructure and and functionfunction..

3)   Cells come only from existing cells.3)   Cells come only from existing cells.

IV. Basic Materials in a Cell – “What is a cell made up of ?”

The 4 Major Organic MoleculesThe 4 Major Organic Molecules

1) Carbohydrates1) Carbohydrates

2) Lipids2) Lipids

3) Proteins3) Proteins

4) Nucleic Acids 4) Nucleic Acids

V. Levels of Cellular Organization -“How are cells organized?”

i)       Cellsi)       Cells

ii)      Tissuesii)      Tissues

iii)     Organsiii)     Organs

iv)     Organ systemsiv)     Organ systems

v) Organisms v) Organisms

VI. Organelles Found in a Typical Cell - “What is in cell?”

OrganellesOrganelles (little organs) are specialized (little organs) are specialized compartments that carry out specific compartments that carry out specific functions within a cell.functions within a cell.

BY UNDERSTANDING THE BY UNDERSTANDING THE STRUCTURESSTRUCTURES IN A CELL, YOU CAN PREDICT THEIR IN A CELL, YOU CAN PREDICT THEIR FUNCTIONSFUNCTIONS..

A. Nucleus

1. Termed the “brain” of 1. Termed the “brain” of the cell.the cell.

2. Used to direct all cell 2. Used to direct all cell activities and serves as the activities and serves as the storage center for the storage center for the cell’s cell’s DNADNA..

3. Contains the 3. Contains the chromosomes (genes). chromosomes (genes).

B. Nucleolus and C. Nuclear Envelope

B1. Stores genetic B1. Stores genetic material such as material such as RNA.RNA...

B2. Site where ribosomes B2. Site where ribosomes are synthesized (made).are synthesized (made).

C1. Double membrane C1. Double membrane around the nucleus is used around the nucleus is used to protect it and allow to protect it and allow nucleic acidsnucleic acids to enter and to enter and leave the nucleus.leave the nucleus.

D. Cell Membrane

1. The 1. The semipermeable semipermeable membranemembrane allows specific allows specific molecules to come in and molecules to come in and out of the cell.out of the cell.

2. They also protect the 2. They also protect the cell and give it support.cell and give it support.

3. The 3. The lipid bilayerlipid bilayer is is made of hydrophilic heads made of hydrophilic heads and hydrophobic tails.and hydrophobic tails.

E. Cytoplasm

1. A jellylike fluid 1. A jellylike fluid within the cell that within the cell that helps to cushion the helps to cushion the cell and other cell and other organelles.organelles.

2. 2. CytosolCytosol is the liquid is the liquid portion, which is in portion, which is in constant motion as the constant motion as the particles move around.particles move around.

F. Mitochondria

1. Often called the 1. Often called the “powerhouse” of the cell “powerhouse” of the cell because it is the place because it is the place where energy/where energy/ATPATP is is converted. (i.e. site converted. (i.e. site where where cellular cellular respirationrespiration occurs) occurs)2. The number of 2. The number of mitochondria in a cell mitochondria in a cell will vary. (i.e. muscle will vary. (i.e. muscle cells have more cells have more mitochondria)mitochondria)

G.Ribosomes

1. These are the most 1. These are the most numerous of the cells numerous of the cells organelles because organelles because they are they sites they are they sites where where proteinsproteins are are created (synthesized).created (synthesized).

H. Endoplasmic Reticulum (ER)

The ER directs the traffic The ER directs the traffic of the many molecules by of the many molecules by creating a series of creating a series of channels that act as a channels that act as a “highway system” though “highway system” though the cytosol.the cytosol.

1. 1. RoughRough (has ribosomes (has ribosomes on it) – synthesizes on it) – synthesizes proteins.proteins.

2. 2. SmoothSmooth ( (nono ribosomes) ribosomes) – synthesizes – synthesizes lipids.lipids.

I. Golgi Apparatus

1. Labels the 1. Labels the proteinsproteins that are to that are to be used inside and be used inside and outside of the cell. outside of the cell.

2. Also packages and 2. Also packages and distributes the distributes the proteinsproteins to specific to specific destinations.destinations.

J. Lysosome

type of type of vacuolevacuole that contains that contains digestive enzymes to digestive enzymes to break down food break down food particles and disease-particles and disease-causing bacteria that causing bacteria that enter the cell.enter the cell.

““Recycling centers” Recycling centers” of the cell.of the cell.

K. Vacuoles

Fluid filled space Fluid filled space that aids in digestion, that aids in digestion, storage, support, and storage, support, and helps maintain water helps maintain water balance.balance.

2. Often stores 2. Often stores enzymes and waste enzymes and waste products.products.

L. Cilia and Flagella

1. They are hair-like 1. They are hair-like projections out of the projections out of the cell membrane.cell membrane.

2. Used for 2. Used for locomotion in locomotion in unicellularunicellular organisms organisms and movement of and movement of materials in materials in multi-multi-cellularcellular organisms. organisms.

M. Centrioles (Animal only)

11. Organizes fibers . Organizes fibers during cell during cell division. (i.e. division. (i.e. mitosismitosis))

2. Always found in 2. Always found in pairs.pairs.

N. Chloroplasts (Plants only)

1. These organelles make 1. These organelles make chemical energy in the chemical energy in the form of sugars, using form of sugars, using air, water, and energy air, water, and energy from sunlight. (i.e. from sunlight. (i.e. photosynthesisphotosynthesis))

2. Found mostly in algae 2. Found mostly in algae such as seaweed and such as seaweed and green plants. green plants.

O. Cell Wall (Plants only)

1. Thick outer layer that 1. Thick outer layer that provides strength by provides strength by making the cell rigid. making the cell rigid.

2. Mostly made of 2. Mostly made of cellulosecellulose but with but with some pores to allow some pores to allow ions and molecules to ions and molecules to pass through.pass through.

P. Large Central Vacuole (Plants only)

Holding tank – stores Holding tank – stores waste products, waste products, nutrients, and water.nutrients, and water.

2. May occupy 2. May occupy between 30% and 90% between 30% and 90% of the cells volume. of the cells volume.

VII. Categories of Cells – “How do cells differ?

1. 1. ProkaryoticProkaryotic ( (First CellsFirst Cells))

a. Small, simple cells that lack a nucleus.a. Small, simple cells that lack a nucleus.

b. b. BacteriaBacteria are living prokaryotes and are are living prokaryotes and are the most numerous.the most numerous.

VII. Categories of Cells – “How do cells differ?

2.2. Eukaryotic Eukaryotic ( (True CellsTrue Cells))a. Large, complex cell that contain a a. Large, complex cell that contain a membrane-membrane-bound compartment called bound compartment called the nucleus.the nucleus.b. Both b. Both plantplant cells and cells and animalanimal cells, cells, although although different themselves, are different themselves, are considered eukaryotic considered eukaryotic since they have a since they have a nucleus.nucleus.

ProkaryoteProkaryote vs.vs. EukaryoteEukaryote

A. NucleusA. Nucleus nonenone yesyes

B. MembraneB. Membrane

bound organellesbound organelles nonenone yesyes

C. Size (microns)C. Size (microns) 1-10µm1-10µm 2-1,000µm2-1,000µm

D. Evolved D. Evolved 3.5bya3.5bya 1.5bya1.5bya

(billion years ago)(billion years ago)

E. Types of cells E. Types of cells bacteriabacteriaplants/animals/fungi plants/animals/fungi

VIII. Theory of Endosymbiosis – “Why do cells differ?”

MitochondriaMitochondria and and chloroplastschloroplasts are are descendants of descendants of prokaryoticprokaryotic cells so it is cells so it is believed that 1.5 billion years ago some believed that 1.5 billion years ago some prokaryotic cells were “swallowed” by prokaryotic cells were “swallowed” by larger cells but were larger cells but were notnot digested. Thus the digested. Thus the prokaryotic cells remained inside the larger prokaryotic cells remained inside the larger cells and gradually lost the ability to live cells and gradually lost the ability to live alone. The partnership that the two cells alone. The partnership that the two cells formed is called formed is called endosymbiosisendosymbiosis..

IX. Limits of Cell Size – “Why are all cells so small?”

1. Since cells are continuously in contact with their 1. Since cells are continuously in contact with their surroundings their parts cannot be to far from the surroundings their parts cannot be to far from the membrane.membrane.

2. Cell volume increases faster than surface area. (i.e. 2. Cell volume increases faster than surface area. (i.e. ratio of surface area to volume limits how large a ratio of surface area to volume limits how large a cell can get):cell can get):

a. Surface area = measurement of exterior of cella. Surface area = measurement of exterior of cell

b. Volume = measurement of interior of cellb. Volume = measurement of interior of cell

Any Questions?

An education is not how much you have committed to memory. It is knowing where to go to find out what you need to know and it is knowing how to use the information that you get.

--William Feather