Chapter 3 Cell Structure

Question 1

Prokaryote

Answer 1

• DNA is not enclosed within a nucleus
• Usually DNA is arranged as one circular chromosome
• They lack membrane- enclosed organelles
• Single celled organisms: Bacteria, Archaea

Question 2

Eukaryotes

Answer 2

• DNA is found in the nucleus: surrounded by a nuclear membrane
• DNA arranged as multiple chromosomes
• They have membrane-enclosed organelles
• Single celled or multicellular organisms
• Ex. Algae, Protozoa, Fungi, Plants, Animals

Question 3

Morphology (Shape ) of Bacteria

Answer 3

• Coccus (Pl. Cocci) = Spherical
• Bacillus (Pl. Bacilli) = Rod Shaped
• Vibrio = Curved
• Spirillum (Pl. Spirilla) = Spiral Shaped
• Spirochete = Corkscrew Shaped

Question 4

Bacterial Cell External Structures (Capsules and Slime Layers)

Answer 4

• Sticky, gelatinous layer external to the cell
• Composed of polysaccharide, protein or both
• If layer is organized and firmly attached to the cell wall = Known as a capsule
• If layer is unorganized and loosely attached to the cell wall = Known as a Slime Layer
• In some bacteria capsules play a role in virulence
• Protection against phagocytosis (Ex. Streptococcus pneumoniae. With Capsule = causes disease and without = no disease)

Question 5

Slime Layers

Answer 5

• Often allow bacteria to attach to surfaces
• Medical implants, water pipes, teeth
• Example: Streptococcus mutans
  Makes polysaccharide slime from sucrose
  Attaches to teeth, which can lead to cavities

Question 6

Flagella (Flagellum)

Answer 6

• Long protein appendages
• Used in motility
• Semi-rigid, helical turns like a propeller
• Bacterial cells have four typical arrangements of flagella:
  1) Monotrichous = a single polar flagellum
  2) Lophotrichous = Two or more flagella originating form opposite poles
  3) Peritrichous = Flagella distributed all over the cell

Question 7

Flagellar Motility

Answer 7

• Flagella turn causing cell to move in one direction -“run”

- Periodically flagella reverse direction causing a random change in direction -“Tumble”

Question 8

Flagella allow chemotaxis

Answer 8

• Movement toward or away from a stimulant
• Toward a nutrient (attractant)
• Away from a toxin (repellent)
• Ex. E. coli will move toward glucose
• Flagellar protein can be used to distinguish among stains of species = E.coli

Question 9

Fimbriae and Pili General Info

Answer 9

• Short, hair-like appendages

- Hollow

Question 10

Fimbriae

Answer 10

• Allow the cell to adhere to surfaces
• Contribute to pathogenicity
• Example: Some stains of E.coli have fimbriae that allow them to attach to the intestinal wall

Question 11

Pili

Answer 11

• Allows attachment of two bacteria to each other
• Involved in transferor genetic material between bacteria
• Ex. E.coli’s sex pilus

Question 12

Bacteria Cell Wall

Answer 12

• Semi-rigid structure giving shape to the cell
• Major function is to prevent rupture of the cell - protects against environmental changes
• Useful in the identification of bacteria (Gram Stain)

Question 13

Bacteria Cell Wall Composed of the Complex macromolecule

Answer 13

• Peptidoglycan
• Which is a mesh-like structure composed of polysaccharide and amino acids
• Polysaccharide portion is composed of two alternating monosaccharides:
  1) N-acetyl glucosamine (NAG)
  2) N-acetyl muramic (NAM)
• Peptide portion composed of short chains of amino acids

Question 14

A generalized View of Peptidoglycan

Answer 14

• Polysaccharide chains run parallel
• Peptide chains link polysaccharides together
• Forms a mesh-like net surrounding the cell

Question 15

The Gram Positive Cell Wall

Answer 15

• Made of thick layers of peptidoglycan outside of plasma membrane
  1) Also contains teichoic acids
  2) Wall teichoic acids: attached to the peptidoglycan
  3) Lipoteichoic acids: attached to plasma membrane and extend through the peptidoglycan
• Gram positive bacteria have only one membrane = cytoplasmic membrane

Question 16

The Gram Negative Cell Wall

Answer 16

• Thin peptidoglycan layer that is sandwiched between two membranes
• Outer membrane of lipids (phospholipids), proteins and lipopolysaccharides (LPS)
• Polysaccharide portion of LPS is composed of O-Sugars (Useful for distinguishing gram negative bacteria)
• Lipid portion of LPS is toxic
• Referred to as endotoxin

Question 17

What’s so Special About Peptidoglycan?

Answer 17

• Completely different from anything found in animal cells
• Many antibiotics have been discovered that act against peptidoglycan
• Example: Penicillin - inhibits production of peptidoglycan
• Also degraded by one of our own natural defences: Lysozyme (Found in tears, saliva, mucous)

Question 18

The Cytoplasmic Membrane

Answer 18

• Composed of phospholipid bilayer
• Serves as a semi-permeable barrier
• Selectively allows inflow and outflow of materials
• Exists in a semi-fluid state

Question 19

Antimicrobial Agents

Answer 19

• Alcohols disrupt the membrane

- Can be used as a disinfectant

Question 20

Internal Components Cytoplasm

Answer 20

• The substance inside the plasma membrane
• Is about 80% water
• Contains most of the ‘stuff’ needed for life
  1) Sugars, amino acids, nucleotides etc.
  2) Enzymes
  3) Some functional structures

Question 21

The Nucleoid

Answer 21

• Contains the bacterial chromosome (DNA)
• All genetic information required for cell’s structures and functions
• Not surrounded by a nuclear membrane
• May also contain plasmids:
  Smaller double stranded DNA molecules
  Contain non-essential genes (Genes for antibiotic resistance)

Question 22

Ribosomes

Answer 22

• Site of protein synthesis (translation)
• Made of protein and ribosomal RNA (rRNA)
• Two parts:
  30S subunit
  50S subunit
  Together form the complete 70S ribosome

Question 23

Ribosomes of Bacteria differ from Eukaryotic Ribosomes

Answer 23

• Eukaryotes have 80S ribosomes
• Several antibiotics target bacterial ribosomes
• Ex. Streptomycin, Erythromycin
• Prevent the bacteria from making new proteins

Question 24

Storage Granules (Inclusion Bodies)

Answer 24

• Usually deposits or granules of nutrients, stored for later use
• Examples: Sulfur granules, polysaccharides (glycogen), Lipid inclusions, enzymes, magnetite
• Variety of inclusion bodies occur in different bacterial species - can serve as a basis for identification

Question 25

Endospores

Answer 25

• Formed only by Gram positive bacteria
• Special resting structure - allows bacteria to enter dormant state
• Extremely durable: Resists heat, desiccation, chemicals, radiation, etc. (Some can survive in boiling water)
• Remains dormant until good growth conditions occur - can form a new population

Question 26

Sporulation

Answer 26

1) Cell replicates its DNA
2) Septum forms, dividing the cell into unequal compartments
3) Larger compartment engulfs the smaller
4) Peptidoglycan and other protective material forms around the forespore (Spore Coat)
5) Finished spore is freed from the mother cell as the mother cell dies

Question 27

Eukaryotic Cell Structure

Answer 27

• Includes microorganisms: Algae, fungi, protozoa
• Higher organisms: Plants and animals
• Larger and more complex than prokaryotes
• Genetic material is housed in a nucleus
• Membrane bound organelles

Question 28

Cytoplasmic Membrane (Eukaryotic)

Answer 28

• Same basic structure as in prokaryotic cells
• Contains phospholipids, proteins, and sterols
• Sterols make membrane relatively rigid compared to bacteria

Question 29

Cell Wall (Eukaryotic)

Answer 29

• Not all eukaryotes have cell wall - allows endocytosis
• Simple structure compared to bacteria
• Made of:
  Cellulose (algae, plants)
  Chitin (fungi)

Question 30

Cytoplasm (Eukaryotic)

Answer 30

• Substance inside the plasma membrane, but outside the nuclear membrane
• Cytoplasm has complex internal structure - cytoskeleton
• Protein filaments on the inside of the plasma membrane
• Provides support and shape
• Transports substances through the cell

Question 31

Ribosomes (Eukaryotic)

Answer 31

Larger and heavier than bacterial ribosomes = 80S

Question 32

Membrane Bound Organelles (Eukaryotic)

Answer 32

• Structures with specialized functions
• Not present in bacteria
• Examples:
  1) Nucleus: compartment holding genetic material
  2) Mitochondria: site of energy production
  3) Chloroplasts: site of photosynthesis in algae and plant cells

Question 33

Appendages External to the Cell

Answer 33

Flagellum and Cilia
- Long flexible projections that contain protein and cytoplasm
- Move in a whip-like fashion
- Can be used for:
Motility
Sweeping material past stationary cells