The Cell

Plant and Animal Cells

• Every living thing on Earth is composed of cells.

• The term cell was first used by Robert Hooke to describe the chambers found in a piece of cork.

• Cells are the smallest living unit of which all organisms are composed

• Cells are classified in many ways• One of the most important

classification methods is by complexity.

Cell Complexity• Simple cells are termed prokaryotic.

• Complex cells are termed eukaryotic.

• On what basis do we classify cells as simple or complex?

Prokaryotic and Eukaryotic Cells

There are two general classes of cells: prokaryotic and eukaryotic.

The evolution of prokaryotic cells preceded that of eukaryotic cells by 2 billion years.

The Cell Timeline

• The major similarities between the two types of cells (prokaryote and eukaryote) are:

• 1.They both have DNA as their genetic material.

• 2.They are both membrane bound.

• 3.They both have ribosomes .

• 4.They have similar basic metabolism .

• 5.They are both amazingly diverse in forms.

• The major and extremely significant differences between prokaryotes and eukaryotes are:

• eukaryotes have a nucleus while prokaryotes do not.

• eukaryotes have membrane-bound organelles prokaryotes do not.

• The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus.

• The organelles of eukaryotes allow them to exhibit much higher levels of intracellular division of labor than is possible in prokaryotic cells.

• Eukaryotic cells are, on average, ten times the size of prokaryotic cells.

• The DNA of eukaryotes is much more complex and therefore much more extensive than the DNA of prokaryotes.

Organism

PROKARYOTIC Mycoplasma genitalum (Bacterium) Helicobacter pylori (Bacterium) Haemophilus influenza (Bacterium) EUKARYOTIC Saccharomyces cerevisiae (yeast) Drosophila melanogaster (insect) Caenorhabditis elegans (worm) Homo sapiens (human) Arabidopsis thaliana (plant)

Number of base pairs (millions)

0.58

1.67

1.83

12

165

97

2900

125

Number of encoded proteins

470

1590

1743

5885

13,601

19,099

30,000 TO 40,000

25,498

Number of chromosomes

1

1

1

17

4

6

23

10

• Prokaryotes have a cell wall composed of peptidoglycan, a single large polymer of amino acids and sugar.

• Many types of eukaryotic cells also have cell walls, but none made of peptidoglycan.

The size of cells

• prokaryotes can vary in size from 0.25 x 1.2 m to 1.5 x 4 m

• average size (E. coli 1 x 3 m)

• eukaryotes are generally larger

• – 200 m in diameter

Prokaryotic Cell

• There are many types of eukaryotic cells but the two most common types are plant and animal cells

• A eukaryotic cell may be divided into major zones.

• These zones are man made divisions used to facilitate the study of cells.

• Animal cells are the cells found in animals. You are made up of trillions of animal cells.

• There are two basic zones of an animal cell:

• Nucleus• Cytoplasm

• Cytoplasm:

• Cytoplasm is the watery-like part of the cell where the action takes place. It is where the nutrients are used.

• Most chemical activity occurs here

• Nucleus: • The nucleus is the brain of the cell.• It controls the cell, and tells it

what to do.• The nucleus also contains the

DNA which is like a blueprint. A blueprint is a plan that people use when they build.

Organelles• In each zone (nucleus or cytoplasm) of an

animal cell (or plant cell) are specialized units called organelles.

• Organelles perform specialized functions

• Most organelles are common to both plant and animal cells but a few are only found in one or the other type.

What organelles are inside the

cytoplasm:

• Organelles in 'higher' eukaryote cells:

• Endoplasmic Reticulum (ER) -This organelle resembles a system of parallel membranes similar to a radiator core.

• The ER is important in protein synthesis.

• It is also a transport network for molecules destined for specific locations within the cell.

• Helps give the cell its shape

There are two types: Smooth ER - Does not have ribosomes on its surface and tends to be more of a tubular network.

• Rough ER - has ribosomes on its surface , and tends to be more in 'sheets'. Very common in the cell and easily seen with an electron microscope.

• Ribosomes –are small spherical structures found in the cell cytoplasm.

• These are the most common organelle found in cells.

• Ribosomes are produced in the nucleus of a cell but are released in to the cytoplasm where they function in protein production.

• Half of the ribosomes are located on the surface of the Endoplasmic Reticulum.

• The other half are 'free' in the cytosol or cytoplasm of the cell.

Cell Theory:

• All organisms are made up of one or more cells.

• The cell is the basic unit of organization of all organisms.

• All cells come from other cells all ready in existence.

What are cells made of?Cells are mostly water. The rest of the present molecules are:

•protein

•carbohydrate

•nucleic acid

•lipid

•other

What are cells made of?

By elements, a cell is composed of:

• 60% hydrogen

• 25% oxygen

• 10% carbon

• 5% nitrogen

• Microtubules - made from tubulin, and make up centrioles,cilia,etc.

• Cytoskeleton - Microtubules, actin and intermediate filaments.

Mitochondria

• Second largest organelle in the cell.

• Has its own unique genetic structure.

• Double-layered outer membrane with inner folds called cristae.

• Energy-producing chemical reactions take place on cristae

• The number of mitochondria in cells is dependent on the type of cell.

• Cells with higher energy requirements have more mitochondria than cells with lower energy needs.

• Cells with higher numbers of cristae also produce more energy than cells with fewer folds or cristae.

• Mitochondria are the site at which cellular respiration takes place.

Golgi Apparatus

The golgi body is responsible for packaging proteins for the cell.

Once the proteins are produced by the rough E.R.they pass into the sack like cisternae ( vesicles) that are the main part of the golgi body.

These proteins are then squeezed off into little spheres( lysosomes) which drift off into the cytoplasm.

What's a Golgi?

• "The golgi apparatus is a part (organelle) of non-bacterial (eukaryotic) cells that is the site of several cell functions, including:

• synthesis of carbohydrates,

• secretion of proteins to the outside of the cell,

• transport of cell wastes to the digestive mechanism of the cell.

• The golgi appartus has been described in many ways but commonly it is described as looking a little bit like a stack of pancakes viewed from the side."

Plastids

• Plastids are a group of organelles found primarily in plant cells.

• Plastids which have color are associated with photosynthesis and exclusively found in plants

•The most common of these plastids are chloroplasts which contain the green pigment chlorophyll.

• Other pigmment containing plastids are called chromoplasts.

• Some chromoplasts contain the following pigments:

•Carotene pigments which are responsible for the orange and red coloration in flowers and fruits.

•Xanthrophylls contain a yellow pigmment.

• Plastids which store starches and other carbohydrates are found in cells

• Amyloplast, occur in plant tissues that do not turn green - a common form, and are used to store starch.

• Leucoplasts are used to store glucose in animal cells.

Lysosomes

• Lysosomes are oval structures that contain a digestive enzyme.

• These organelles serve to defend the cell from pathogenic microorganisms.

• In addition lysosomes are used to breakdown food substance that are trapped in the vacuoles.

• If the contents of a lysosome are accidentally opened the digestive enzymes will destroy the cell. This explains the nickname “suicide sac” .

Plasma Membrane

• Outer membrane of cell that controls cellular traffic

• Contains proteins that span through the membrane and allow passage of materials

• Proteins are surrounded by a phospholipid bi-layer.

A phospholipid bilayer (in water) cannot have a free edge

All bilayers form closed compartments

• Cell membranes are made up of phospholipid molecules (fats) with various large globular protein molecules suspended in them.

• The lipid bi-layer is formed because of the chemical structure of a lipid.

All biological membranes are bilayers of phospholipid.

The proteins in each type of membrane give it its unique properties.

• Since cells are constantly in water, the lipids form a double layer, with the heads towards the water and the tails inside so that they can stay away from the water.

• These bi-layers have proteins scattered about in them.

• Sometimes carbohydrates (sugars) are attached to these proteins.

• ( Carrier molecules)

• A selectively permeable (sometimes called semi-permeable) membrane allows some molecules across but not others.

Plasma Membrane

Electron Microscopic View of the Cell Membrane

Plasma Membrane Structure

OSMOSIS

• When water enters or leaves a cell the process is called osmosis.

OsmosisDiffusion of water through a semi-Diffusion of water through a semi-

permeable membrane from an area permeable membrane from an area where the water molecules are where the water molecules are more concentrated to an area more concentrated to an area where the water molecules are less where the water molecules are less concentratedconcentrated

• This means that water would cross a selectively permeable membrane from a dilute solution (less dissolved in it) to a concentrated solution (more dissolved in it).

SolutionsSolutions

exposed to an isotonic solution cells exposed to an isotonic solution cells will neither lose nor gain waterwill neither lose nor gain water

exposed to a hypotonic solution cells exposed to a hypotonic solution cells will swell due to the uptake of water will swell due to the uptake of water by the cellby the cell

exposed to a hypertonic solution cells exposed to a hypertonic solution cells will shrink due to the loss of water will shrink due to the loss of water from the cellfrom the cell

Solutions

–Hypotonic - solution with lower solute concentration.

–Hypertonic - solution with higher solute concentration.

–Isotonic - both solutions have same concentration

DIFFUSION• Diffusion is the movement of gases

from a high concentration of molecules to a low concentration of molecules.

• Molecules can diffuse across membranes through the pores in the lipid bilayer.

Facilitated diffusion (or facilitated transport)

• Facilitated diffusion (or facilitated transport) is a process of diffusion, a form of passive transport made possible by transport proteins.

• Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane transport proteins.

• Small uncharged molecules can easily diffuse across cell membranes.

• However, due to the hydrophobic nature of the lipids that make up cell membranes, water-soluble molecules and ions cannot do so; instead, they are helped across by transport proteins.

PHOSPHOLIPIDS... • The heads of the PHOSPHOLIPIDS are

composed of glycerol and a phosphate group and like to dissolve in water.

• Phospholipids are polar molecules • These molecules have water tolerant area

called water-loving (or hydrophilic) molecules.

• The tails of the PHOSPHOLIPIDS are mostly fatty acids made up of long carbon and hydrogen chains.

• Carbon and hydrogen chains are not polar and do not like to dissolve in water. Molecules that do not easily dissolve in water are called water-hating (or hydrophobic) molecules.

Active transport

• Active transport requires energy.

• Types of actice transport include:

• Carrier molecules

• Endo and phagocytosis

Pinocytosis and Phagocytosis

• The cell membrane occasionally invaginates or indents to capture extracellular fluids in a process called pinocytosis.

• The invagination becomes pinched off to form a pinocytic vesicle.

• Taking up of solid particles is called phagocytosis. Both pinocytosis and phagocytosis are types of endocytosis, the prefix meaning in.

• Cells may expel liquids or solids by the reverse process, exocytosis, the prefix meaning out.

• The transport vesicle fuses with the cell membrane and opens to expel the contents from the cell.

Plastids

• The most obvious difference between plant cells and other eukaryotic cells is that cells of most plants contain unique organelles called plastids, which include chloroplasts, chromoplasts, and amyloplasts.

• Chloroplasts contain a special pigment known as chlorophyll, which absorbs sunlight energy.

• This sunlight energy is then converted to another form of energy utilizable by other living organisms.

• This energy conversion process is referred to as photosynthesis, which combines carbon dioxide from the air and hydrogen from water to form sugars and other organic compounds.

• Oxygen is returned to the atmosphere as a by product.

• Chromoplasts synthesize and store pigments such as yellow xanthophylls, orange carotenes, and various red pigments.

• Leucoplasts are organelles where animal cells store starches, proteins, and lipids.

Chloroplasts

• Chloroplasts are of central importance to the plant cell.

• They contain chlorophyll which fundamentally converts sunlight into fuel that the mitochondria use for energy, known as photosynthesis.

• Chloroplasts and mitochondria are closely linked to one another, as well as very similar in structure to one another.

The Nucleus

• The cell nucleus is a remarkable structure because it forms the package for our genes and their controlling factors. It functions to:

• Store the genetic information for the cell on the genes of chromosomes

• Controls the activity of cell organelles by regulatory factors released through the nuclear pores

• Produces messenger Ribonucleic acid or mRNA

• Produce ribosomes in the nucleolus

• Organize the uncoiling of DNA for cell division,

• Surrounding the nucleus is the nuclear envelope. It is a double membrane that separates the nucleus from the rest of the cell.

• At some points along the nuclear envelope the inner and outer membrane are joined and they form very small pores..

• Because of these pores, the nuclear envelope, like the cell membrane, is selectively permeable.

• During cell division, the chromosomes shorten by coiling and become thick enough to be clearly visible when they are stained

• It allows the contents of the nucleus, the nucleoplasm, to have a different chemical composition than the rest of the cell.

• Much of the nucleoplasm consists of chromatin, various proteins bound to DNA.

• Usually the chromatin appears as long, thin threads called chromosomes.

The most visible structure in the nucleus is the nucleolus, which functions in the production of ribosomes.

Sometimes, there are two or more nucleoli; the number depends on the species and stage in the cell's reproductive cycle.

• The nucleus also controls the protein synthesis in the cytoplasm. It sends molecular messengers in the from of RNA.

Cell wall• The CELL WALL is a very complex

structure. This structure was first discovered some time in the seventeenth-century, by a scientist named Robert Hooke.

• Hooke cut a thin slice of cork and examined it carefully through a primitive microscope.

• Unfortunately, these cork cells were long dead, and the only remaining structure were the cell walls.

• The main reason for the cell walls being the only organelle left is that it is made up of cellulose.

• Cellulose is a very strong structure that allows for structural support. This is ideal for the cell wall, which function is to prevent water loss from inside the cell, and to provide structural strength to resist dehydration.

• Cell walls are actually composed of three layers, the Primary cell wall, the Secondary cell wall, and the Middle lamella.

• These three layers give an added support and protection to the plant cell, even long after it has died.

• The cell wall is a non-living structure ranging anywhere from 0.1 to several mm thick.

The Primary Cell Wall

• The primary cell wall is the first section of the wall to be laid down by the plant cell.

• This primary cell wall is also able to expand as the cell grows in size.

• This primary cell wall may be impregnated with additional materials (cutin and suberin).

• These materials form a waxy cuticle, this cuticle is impermiable many types of invading particles.

The Secondary Cell Wall• The secondary cell wall is found

between the cell membrane and the primary cell wall.

• The secondary cell wall has a strong and durable matrix that gives the plant cell support and protection.

• However some plants lack the need for a secondary cell wall.

• Such is the case of grasses and other flexible plants instead of the cell walls having three layers it only contains two, the primary cell wall and the middle lamella.

• Wood or other non-flexible plants would be an example of the types of plants that would need a secondary cell wall in the cell.

The Middle Lamella• The primary cell walls of neighboring

cells are not in direct contact with other cells.

• They are are separated by a layer called the Middle Lamella, a layer of a jellylike polysaccharide called pectin.

• The middle lamella sticks the cells together, and acts like a bonding agent or glue. This is so that plant cells can stay more closely together.

Cell Wall Diagram