CHAPTER 4CHARACTERISTICS OF PROKARYOTIC & EUKARYOTIC

CELLS

Questions of ImportanceWhat are the 2 basic cell types?

What are the special characteristics associated with Prokaryotic cells?Can you compare and contrast Prok. & Euk. Cells?

What are the structural differences between a Gram Positive and Gram Negative Cell?

Basic Cell TypesProkaryote: single-celled organisms, and ALL are bacteria.

Termed Prokaryotes because they contain NO nucleus (Pro = before, Karyon = nucleus)Prokaryotes not only lack a nucleus but also lack any membrane bound organelles

Prokaryotes are among the smallest of all organismsProkaryotes are thought to be a good deal older than Eukaryotic cells.

Thoughts are that they have been around for over 4 billion years.

Reproduce by a simple process called binary fission

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Eukaryotic Cells

Eukaryote: single-celled or multi-cellular organisms.Eu = true

Karyon = nucleusEuk. cells possess a nucleus as well as various membrane bound organelles

Euk. cells are larger and more complex than Pro. cellsEukaryotic cells reproduce by a process called Mitosis.

Mitosis is similar to binary fissionSome organisms reproduce by budding

Prok. Vs. Euk. cells

Prokaryotic cells have a single circular chromosome; Eukaryotic cells have paired chromosomes

Prokaryotic cells lack histone proteins; Eukaryotic cells have histone proteins

Prokaryotic - cell wall has peptidoglycan; plant and fungal cells have both cellulose and chitin

ONLY Eukaryotic DNA is in a nucleus surrounded by a nuclear membrane

Prokaryotic DNA is in a nuclear region not surrounded by a membrane

BOTH types have a plasma membrane, DNA, Cell Wall (plant cells), Ribosomes, Cytoplasm

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Prokaryotic Classification

Prokaryotic Cells are usually classified according to:Size

ShapeArrangement

Size: generally 0.5 to 2.0 micrometersAlways exceptions

Shapes:

Arrangement:Diplo- 2 bacteria together

Strepto- chain of bacteriaTetrads – 4 cells arranged in a cube

Staphylo- grape like clusters of bacteriaSarcinae- eight cells arranged in a cube

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Prokaryotic Cell Structures

Structurally, bacterial cells consist of the following:1. Cell membrane, usually surrounded by a cell wall

2. Internal cytoplasm with ribosomes, nuclear region, and in some cases granules and/or vesicles

3. Capsules, flagella, and pili (external)

External Structures of the Prokaryotic Cell

The Cell Wall:Lies outside the cell membrane in nearly all bacteria

Two important functions:1. Maintains the characteristic shape

2. Prevents the cell from bursting when fluids flow into the cell by osmosisCell wall contains Peptidoglycan (murein): The single most important component of cell

wallLarge polymer

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Cell MembraneLiving Membrane that serves as a boundary b/w the cell and outside environment

Phospholipid bilayer embedded with proteinsControls what enters and leaves a cell

Monitors envir. for changesAreas associated w/CM

Periplasmic Space: found in Gram Negative bact.Gap b/w the Cell Wall and CM

Area contains peptidoglycanActive area of metabolism and transport

Outer membrane: found in Gram Negative bacteriaOuter most layer, very similar to CM in structure

Not as selective about what passes through itContains LPS (lipopolysaccharide A)

Endotoxin that is released after death of cellDo some research:

Find out what the effects of Lipopolysaccharide A are to the human body.Glycocalyx

Any substance found external to the cell wallThickest structure is a Capsule

Thinnest layer is the slime layerAll bacteria have at least a thin slime layer

CapsuleProtective coat only found on a few types of bacteria

Prevents phagocytosis by WBCPrevents chemical agents from entering the cell

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Slime Layer

Thinner than a capsuleProtects cell from drying out

Helps trap nutrientsCreates “biofilms”

Can help cells bind together or adhere to objectsDental plaque

Distinguishing b/w cells by their cell wall

Gram-positive Bacteria have a relatively thick

layer of peptidoglycan (60-90%)

Gram-negative Bacteria have a more complex

cell wall with a thin layer of peptidoglycan

(10-20%)

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Extras!!Mycoplasm genus – lack a cell wall

vary in shape due to no cell wall

Acid Fast bacteriaCW is 60% lipid and much less peptidogl.

Growth is relatively slow due lipid contentHard to absorb needed nutrients

Structures of Motility

FlagellaExtensions from the cell membrane through the cell wall

Allow the bacterium to move with speed and purposeBacteria can have one or multiple flagella

Monotrichous – one flagellaAmphitrichous- one at each end

Lophotrichous – two or more at each endPeritrichous – all over the surface

Atrichous – No flagella present

Bacterial MovementChemotaxis

Sometimes bacteria move toward or away from substances in their

environment by this nonrandom process

1. Positive chemotaxis: net result is movement towards the attractant

(nutrients)2. Negative chemotaxis: net result is

movement away from the repellent

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Axial Filaments - aka Endoflagella

Present in spirochetesDue to placement b/w outer sheath and cell wall endoflagella cause a spirochete to

rotate like a corkscrewConjugation Pili

Found only in certain groups of bacteriaThese structures attach two cells and furnish a pathway for the transfer of genetic

materialConjugation allows for the genetic variety in bacterium

Creates the issue of antibiotic resistance

Attachment Pili - aka fimbriaeStructures that help bacteria adhere to a surface

Contribute to the pathogenicity of certain typesSome bact. Adhere to RBCs and cause the RBCs to clump = hemoagglutination

Neisseria gonorrhoeae strains w/out rarely cause gonorrhea, pili needed to attach to epithelial cells or sperm

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INTERNAL STRUCTURES

CYTOPLASMSemi-fluid substance inside the CM

70-80% waterConstant metabolic activity

RibosomesConsist of RNA

Sites of protein synthesisUsually found in chains (polyribosomes)

70S (30S and 50S)Eukaryotes are 80S (antibiotics)

Nuclear Region - aka nucleoidWhere DNA is located

Single circular strandSmaller circular DNA (plasmids) also located here

Plasmids are supplemental DNA (circular)Usually passed to other bacteria during conjugation

Inclusions - AKA granulesSmall bodies in the cytoplasm that are not surrounded my membrane

Each contains specific substances such as glycogen (glucose) and polyphosphate (metabolic reactions), enzymes

EndosporesHelps an organism survive

Not a method of reproductionContain very little water

Highly resistant to heat, disinfectants, radiation, acids etc.Chlorine dioxide gas

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Movement of Substances across the membrane

Understanding movement of materials helps us to understand how cells workPolar and nonpolar molecules pass differently

Large vs. small pass differently2 types of transport

PassivePassive TransportNo energy required

Particles move down a gradientHi to Lo conc.

Simple diffusion-Facilitated diffusion-

Osmosis-

Active TransportEnergy Required

Particles move against the gradientLo to Hi conc.

EndocytosisExocytosis

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