Prokaryotes

Do not have membrane surrounding their DNA

lack a nucleus Lack various internal structures

bound with phospholipid membranes

Are small, ~1.0 µm in diameter Have a simple structure Composed of bacteria and

archaea

Eukaryotes

Have membrane surrounding their DNA

Have a nucleus Have internal membrane-

bound organelles Are larger, 10-100 µm in

diameter Have more complex structure Composed of algae, protozoa,

fungi, animals, and plants

[INSERT FIGURE 3.1]

Structure

Referred to as phospholipid bilayer; composed of lipids and associated proteins

Approximately half composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channels Integral proteins Peripheral proteins Glycoproteins

Fluid mosaic model describes current understanding of membrane structure

Membranes contain a hydrophilic and hydrophobic side

Composed of many different types of proteins

Proteins in the lipid bilayer move freely within the membrane

Thin pliable lipid and protein envelope

that defines a cell.

Phospholipid bilayer

Functions:

Regulates nutrient and water intake

Regulates waste removal Site of prokaryotic respiration Site of prokaryotic flagella

attachment Involved in the distribution of

genetic material during binary fission

Function Energy storage Harvest light energy in

photosynthetic prokaryotes Selectively permeable Naturally impermeable to most

substances Proteins allow substances to

cross membrane Occurs by passive or active

processes Maintain concentration and

electrical gradient Chemicals concentrated on

one side of the membrane or the other

Voltage exists across the membrane

Glycocalyces

Gelatinous, sticky substance surrounding the outside of the cell

Composed of polysaccharides, polypeptides, or both

Types of Glycocalyces

Capsule Composed of organized

repeating units of organic chemicals

Firmly attached to cell surface Protects cells from drying out May prevent bacteria from

being recognized and destroyed by host

Polysaccharides or polypeptides in composition.

Surround the cell wall in some bacteria.

Function:

Protection from phagocytosisOsmotic barrierReservoir for nutrientsVirulence factor

Consist of polysaccharide fibers that extend form the bacterial surface

Functions:

ProtectionAttachmentAssociated with biofilms

Types of Glycocalyces

Slime layer Loosely attached to cell

surface Water soluble Protects cells from drying out Sticky layer that allows

prokaryotes to attach to surfaces

Flagella

Axial Filaments

Pili (Fimbriae)

Flagella

Structures of locomotion

Originate in the plasma membrane

In bacteria rotate like a propellar

Many different arrangements

Flagella Are responsible for

movement Have long structures that

extend beyond cell surface

Are not present on all prokaryotes

Flagella

Structure Composed of filament,

hook, and basal body Flagellin protein (filament)

deposited in a helix at the lengthening tip

Base of filament inserts into hook

Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins

Filament capable of rotating 360º

Arrangements of Flagella

A.Monotrichous

B.Lophotrichous

C.Amphitrichous

D.Peritrichous

Axial filament (endoflagella)

Originates in the cell membrane and transverses the length of the cell in the periplasmic space.

As the endoflagella rotate to move the cell the characteristic shape is formed .

Endoflagella are associated with spirochetes.

Endoflagellum is also know as an axial filament.

Attached to the plasma embrane and transverses the entire cell.

Responsible for the spirochete morphology.

Flagella

Function Rotation propels bacterium

through environment Rotation reversible, can be

clockwise or counterclockwise Bacteria move in response to

stimuli (taxis) Runs Tumbles

Fimbriae and Pili Rod-like proteinaceous

extensions

Fimbriae

Hollow tubes that protrude from some bacteria

Compose of protein

• Fimbriae Sticky, bristlelike

projections Used by bacteria to

adhere to one another, to hosts, and to substances in environment

Shorter than flagella May be hundreds per cell Serve an important

function in biofilms Virulence factor

Pili Tubules composed of pilin Also known as conjugation pili Longer than fimbriae but shorter

than flagella Bacteria typically only have one

or two per cell Mediate the transfer of DNA

from one cell to another (conjugation)

Bacterial Conjugation

Transfer of plasmid DNA from a donor to a recipient.

Process strengthens the bacterial cell and alows for survival in a competitive environment.

1. poly-Beta-hydroxybutyric acid - stores lipids for use in plasma membrane

 

2. glycogen - stores starch like polymer of sugar for energy production

 

3. Polyphosphate granules (metachromatic granules) - storage for phosphates for plasma membrane and the formation of ATP from ADP.

 

4. Sulfur granules - stores sulfur which is necessary for the metabolic reactions in biosynthesis.

Mesosomes - invagination of the plasma membrane that increases the surfaces area of the plasma membrane during binary fission.

The mesosome also serves as a site for the attachment and distribution of genetic material during binary fission.

In prokaryotic cell division, called binary fission.

A diagram of the attachment of bacterial chromosomes, indicating the possible role of the mesosome (an inward fold of the cell membrane) in ensuring the distribution of the "chromosomes" in a dividing cell.

Upon attachment to the plasma membrane, the DNA replicates and reattaches at separate points. Continued growth of the cell gradually separates the chromosomes and allocates chromosome copies to the two daughter cells.

6. gas vacuoles - storage of metabolic gases such as methane or hydrogen gas. The gas vacuoles help in the buoyancy of the cell and aids in it motility.

 

7. ribosomes - responsible for the synthesis of proteins.

 

8. nucleoid material - the genetic material of bacteria, which usually is balled up in the cell. During binary fission the nucleoid material unravels within the cell in order to be copied and distributed to the daughter cells.

 

9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.

 9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.

 

These plasmids may be transferred from one bacterial cell to another by the

F-pili.

10. Endospores - a survival mechanism of certain genera of bacteria such as Clostridium and Bacillus.

The endospores are composed of a complex of dipicolinc acid and calcium and the function of the endospore is to protect the bacterial chromosome.

The endospores are very resistant to heat, desiccation, freezing, and other physical properties such as pesticides, antibiotics, dyes, and acids.

The endospores may remain dormant for many years until the environment becomes suitable to sustain the life of the bacteria.

The endospore will then germinate to form an exact copy of the parent cell that produced it.

 

Fungi, algae, plants, and some protozoa have cell walls but no glycocalyx

Composed of various polysaccharides Cellulose found in plant cell

walls Fungal cell walls composed of

cellulose, chitin, and/or glucomannan

Algal cell walls composed of cellulose, proteins, agar, carrageenan, silicates, algin, calcium carbonate, or a combination of these

 

Three different types of cell walls and their compositions:

 

Fungal cell walls are composed of cellulose and/or chitin.

 

Plant cell walls are composed of cellulose.

 

Algal cell walls are composed of cellulose, silicon, and calcium carbonate.

 

Consist of a lipid bilayer and associated proteins. The Plasma Membrane of Eukaryotic cells resembles and functions in the same manner as the prokaryotic plasma membrane with the following exceptions;

 

Contains high levels of sterols such as cholesterol.

 

No respiratory enzymes are located in the eukaryotic plasma membrane.

Respiration occurs in the mitochondria.

Glycocalyces

Never as organized as prokaryotic capsules

Help anchor animal cells to each other

Strengthen cell surface Provide protection against

dehydration Function in cell-to-cell

recognition and communication

 

Flagella

 

There are several different arrangements of flagella in eucaryotes.

 

This diagram represents a biflagellated eukaryotic cell.

One of the flagella aids in movement laterally and the other aids in up and down movement.

The eukaryotic flagella move like a whip.

See Flagellar handout.

 

Flagella Function

Do not rotate, but undulate rhythmically

Cilia Similar to flagella both structurally and functionally but are much shorter and more numerous.

Cilia are found peritrichously to the cell.

Move in an undulating manner and motility by those organisms with cilia is much more rapid than those with flagella.  

Membranous Organelles

Nucleus Often largest organelle in cell Contains most of the cell’s

DNA Semi-liquid portion called

nucleoplasm One or more nucleoli present

in nucleoplasm; RNA synthesized in nucleoli

Nucleoplasm contains chromatin – masses of DNA associated with histones

Surrounded by nuclear envelope – double membrane composed of two phospholipid bilayers

Nuclear envelope contains nuclear pores

Nucleus - double membraned organelle that houses the genetic material of cell.

Nuclear membrane contains numerous pores through which proteins and RNA can move.

Membranous Organelles

Endoplasmic reticulum Netlike arrangement of flattened,

hollow tubules continuous with nuclear envelope

Functions as transport system Two forms

Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis

Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; transports proteins produced by ribosomes

Endoplasmic reticulum - network of cytoplasmic membranes where lipids and proteins are produced.

 

Smooth ER - synthesis of lipids

 

Rough ER - associated with ribosomes and is responsible for the synthesis of proteins.

.

Membranous Organelles

Golgi body Receives, processes, and

packages large molecules for export from cell

Packages molecules in secretory vesicles that fuse with cytoplasmic membrane

Composed of flattened hollow sacs surrounded by phospholipid bilayer

Not in all eukaryotic cells

Golgi apparatus (dictyosome) is associated with the ER.

It modifies and packages the lipids and proteins manufactured by the ER and places them in vesicles for cellular use.

Membranous Organelles Lysosomes, peroxisomes,vacuoles,

and vesicles Store and transfer chemicals

within cells May store nutrients in cell Lysosomes contain catabolic

enzymes Peroxisomes contain enzymes

that degrade poisonous wastes

Membranous Organelles Mitochondria

Have two membranes composed of phospholipid bilayer

Produce most of cell’s ATP Interior matrix contains

70S ribosomes and circular molecule of DNA

mitochondria - involved in the production of chemical energy in the form of ATP.

Consist of convoluted inner membrane and outer membrane. Invaginations are called cristae and contain enzymes used to synthesis ATP.

All respiratory enzymes are located in the inner membrane of the mitochondria.

Membranous Organelles Chloroplasts

Light-harvesting structures found in photosynthetic eukaryotes

Have two phospholipid bilayer membranes and DNA

Have 70S ribosomes

Endosymbiotic TheoryEukaryotes formed from union of small aerobic

prokaryotes with larger anaerobic prokaryotessmaller prokaryotes became internal parasites

Parasites lost ability to exist independently; retained portion of DNA, ribosomes, and cytoplasmic membranes

Larger cell became dependent on parasites for aerobic ATP production

Aerobic prokaryotes evolved into mitochondria Similar scenario for origin of chloroplasts

Not universally accepted

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