Microbiology Lecture 4: Prokaryotic Cells

What are characteristics of prokaryotic cells?

Lack membrane-bound organelles

DNA is in a single, circular chromosome

Divides by binary fission

What is the diameter and length of most bacteria?

Diameter: 0.2 - 2.0µm

Length: 2-8µm

What are the five different shapes of bacteria?

Coccus, Bacillus, Vibrio, Spirochete, Spirillum

Which bacteria shapes are the most common?

Cocci and bacilli

Which bacteria is characterized by its curved rod shape?

Vibrio

Which bacteria is characterized by a helical and flexible shape?

Spirochete

Which bacteria is characterized by a helical and rigid shape?

Spirillum

Which arrangement of bacteria is characterized by chains?

Strepto

Which arrangement of bacteria is characterized by clusters?

Staphylo

What is the name of a linear arrangement of cylindrical cells?

Streptobacilli

What is glycocalyx?

A sticky, gel-like layer surrounding the cell

What is glycocalyx comprised of?

Polysaccharide, polypeptide, or both

What are the two forms of glycocalyx?

Slime layer and capsule

What are characteristics of the slime layer?

Unorganized, considered a loose shield, protects cell from desiccation and loss of nutrients

What are characteristics of the capsule?

Organized, bound tightly to the cell, has thicker consistency, and protects cell from phagocytes

What are the functions of the glycocalyx?

Protection and attachment to other cells or surfaces

What is flagella?

A long, filamentous appendage that propels bacteria

What are the components of flagella?

Filament, basal body, and hook

What is the function of the basal body?

Anchors the hook and filament into the cell wall and plasma membrane

What are the four types of flagella patterns?

Monotrichous, lophotrichous, amphitrichous, and peritrichous

What is monotrichous?

One flagella located at one site

What is lophotrichous?

Bunches of flagella at one site

What is amphitrichous?

Bunches of flagella at two sites

What is peritrichous?

Random distribution all over the cell surface

What is taxis?

Movement towards or away stimulus

What is chemotaxis?

Movement in response to chemical stimulus

What is phototaxis?

Movement in response to light stimulus

What is fimbriae and its function?

Small, bristle-like fibers on cell surface that adheres to each other and other surfaces

What is pili and its function?

Rigid, tubular structure on cell surface of gram (-) cells that is longer and less numerous than fimbriae

Involved in conjugation

What is conjugation?

The transfer of DNA between bacteria using a pilus

Why is the cell wall so important in prokaryotes?

Provides structural support, protects the fragile cell membrane and interior contents

Also provides immunological differences between strains of bacteria

What is the cell wall composed of in bacteria?

Peptidoglycan - repeating of disaccharides N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) that are crosslinked by short peptide fragments

Why is penicillin an effective general antibiotic?

It interferes with crosslinking, disrupting the cell wall structure

Which genus is penicillin not effective against?

Mycoplasma

What is unique about gram-positive cell walls?

Thick peptidoglycan layer present with teichoic acids

What are teichoic acids and their functions?

Polymers that consist of an alcohol and phosphate that regulate cation movement

Can also be used for identification purposes

What are two types of teichoic acids seen in gram-positive cell walls?

Lipotechoic acids and wall teichoic acids

What is the difference between lipotechoic acids and wall techoic acids?

Lipotechoic acids span the PG layer and are linked/embedded to the cell membrane

Wall teichoic acids are linked to the PG layer

What is unique about gram-negative cell walls?

Thin peptidoglycan layer with an additional outer membrane

Has a higher lipid content and no teichoic acids present

What is the function of the outer membrane layer of the gram-negative cell wall?

Provides additional barrier to antibiotics and enzymes

What does the outer membrane layer of the gram-negative cell wall consist of?

Lipopolysaccharides (LPS) and porins, membrane protein channels

What are the three LPS present in the outer membrane?

Lipid A, Core polysaccharide, and O polysaccharide

What is the function of Lipid A?

The lipid portion that is embedded in top layer of outer membrane

Functions as endotoxin when released at cell death

What is the function of core polysaccharide?

Provides stability by linking the O polysaccharide with the Lipid A

What is the function of O polysaccharide?

Functions as an antigen and can be used for identification

What does the decolorization step in the Gram stain do to gram-negative cells?

Dissolves the outer membrane layer

What is the cell/plasma membrane composed of?

Phospholipids and proteins

What is the phospholipid bilayer?

A two layered arrangement of phosphate and lipid molecules

Which way does the phospholipid head and tail face?

The hydrophobic lipid tail faces inward and the hydrophilic phosphate head faces outward

What is the function of the peripheral protein?

Found along the inner/outer surface, it can catalyze reactions and act as scaffolding

What is the function of integral proteins?

Found going through the membrane, it can act as channels

What is the fluid mosaic model?

Membrane is a fluid structure with a "mosaic" of various proteins embedded in it

What is selective permeability?

Large molecules (eg proteins) cannot pass, but small molecules (eg water, gas) can

What are three passive processes?

Simple diffusion, facilitated diffusion, and osmosis

What is simple diffusion?

Movement of molecules from an area of high concentration to an area of low concentration without channels

Continues until equilibrium is reached

What is facilitated diffusion?

Movement of molecules across cell membranes through either specific or nonspecific protein channels

What is osmosis?

Diffusion of water molecules across a selectively permeable membrane

What happens to water in an isotonic solution?

No net movement; the water moves equally in both directions

What happens to water in a hypotonic solution?

Water moves into the cell, causing it to swell and possibly lyse

What happens to water in a hypertonic solution?

Water moves out of the cell, causing the cytoplasm to shrink

What is active transport?

The use of ATP to move substances against its concentration gradient

What is the cytoplasm of prokaryotes comprised of?

Dense, gelatinous solution of sugars, amino acids, and salts

What percentage of the cytoplasm is water?

70-80%

What is the structure of the chromosome in prokaryotes, and where is it located?

A double strand of circular DNA, it is found in the nucleoid region

What is the importance of plasmids?

Extrachromosomal, plasmids can carry genes for drug resistance and can be transferred between cells

What are the ribosomal subunit sizes in prokaryotes?

Small: 30S

Large: 50S

Complete: 70S

What are endospores?

"Resting" cells that are produced when nutrients are depleted

Which genera produces endospores?

Bacillus and Clostridium

What structures do endospores have to be able to withstand hostile conditions?

Durable, dehydrated cells with thick walls

When does sporulation occur?

Occurs if key nutrients are lacking

What are the steps of sporulation?

(1) Spore septum isolates newly replicated DNA

(2) Thick layer of peptidoglycan forms

(3) Thick spore coat of protein forms

(4) Original cell is degraded

(5) Endospore released

What are unique characteristics of endospores?

Not metabolically active, can be dormant for thousands of years, germination is triggered by damage to endospore coat, and is not a direct means of reproduction

What diseases persisted due to the resistance of their endospores?

Bacillus anthraces: Anthrax

Clostridium: Tetanus

C. diifficle: Pseudomembranous colitis

C. perfringens: Gas gangrene

C. botulinum: botulism

What are characteristics of eukaryotic cells?

Membrane-bound organelles present, typically larger, and more complex

What are characteristics of flagella and cilia in prokaryotes?

Composed of microtubules, which are made of the protein tubulin, that are arranged as 9 pairs in a ring with 2 in the center

What is a difference between flagella movement in prokaryotes vs eukaryotes?

Eukaryotes: moves like a whip in a wave-like fashion

Prokaryotes: rotates

What are the cell walls in eukaryotes made of?

Plants and algae: cellulose

Fungi: chitin, polymer of NAG

What is the eukaryotic plasma membrane composed of?

Different types of proteins, carbohydrates that function as attachment and receptor slides, and sterols (lipids)

How does the eukaryotic cytoplasm differ from prokaryotic cytoplasm?

Presence of cytoskeleton, which provides shape/support and transport

What are the ribosomal subunit sizes in eukaryotes?

Small: 40S

Large: 60S

Complete: 80S

What are characteristics of the nucleus?

Largest of the cell structures, it contains genetic info and is surrounded by a double membrane nuclear envelope

What is the function of the nucleolus?

Site of ribosomal RNA (rRNA) production

What are lysosomes?

Membrane-enclosed vesicles that contain digestive enzymes

Which cells carry many lysosomes?

White blood cells

Where in the mitochondria does cellular respiration occur?

Inner membrane

Which micro/organisms have chloroplasts?

Algae, green plants

What are chloroplasts comprised of?

Chlorophyll and enzymes for photosynthesis

What is the endosymbiotic theory?

Organelles like mitochondria and chloroplasts were once free-living prokaryotes that had been engulfed by larger primitive eukaryotic cells

Evolved into obligatory relationship

What evidence supports endosymbiotic theory?

(1) Chloroplasts and mitochondria resemble size and shape of bacteria

(2) Contains circular DNA

(3) Reproduces independently of host cell

(4) Contains 70S ribosomes