Structure Snd Function Of Prokaryotic Snd Eukaryotci Cells

Question 1

General structural features of bacterial cells

Answer 1

• Cell shape
• Cell Wall
• Cell membrane(s)
• Capsules
• Pili and/or Fimbriae
• Cytoplasmic inclusions
• Bacterial DNA and nucleic acids
• Ribosomes
• Flagella
• Spores

Answer 2

1) Cell membrane / plasma membrane / inner membrane
Thin structure lying inside the cell wall and enclosing the cytoplasm of the cell.
Role:
1) Selective barrier through which materials exit and enter th cell = selective permeability
2) Large molecules e.g. proteins can not pass through membrane
3) Allows entry of smaller molecules e.g. H20, CO2 and some simple sugars

Question 3

Outer Membrane

Answer 3

Thin structure lying beyond the the cell wall. Only Gram-negative bacteria.
Role:
1) Selective barrier
2) Contains proteins for transport
3) Lipopolysaccharide – bacterial defence 4) Allows selective uptake and efflux

Question 4

Cell wall

Answer 4

Contains peptidoglycan, a network of sugar polymers cross linked by polypeptides. Made of 2 monosaccharides N- acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) which are related to glucose.
Role:
1) maintainscellshape
2) protectsthecell
3) prevents cell from bursting in a hypotonic environment
(Eukaryote cell walls are made of cellulose or chitin)

Question 5

Gram stains

Answer 5

Gram stain=used to classify bacteria by cell wall composition

Gram positive= bacteria have simpler walls with a large amount of peptidoglycan.Peptidoglycan traps crystal violet,which masks the red Saran in dye

Gram negative= bacteria have less peptidoglycan and an outer membrane that contains lipopolysaccharides.Crystal violet is easily rinsed away,revealing the red safrinin dye

Question 6

Capsule

Answer 6

Outer layer of polymer made of extracellular polysaccharide and/or proteins is present in some prokaryotes.
Role:
1) adherence to a substrate, cells, surface such as
teeth (e.g. Streptococcus mutans)
2) protect bacteria from the host immune system such as phagocytosis and complement (e.g. Streptococcus pneumoniae)

Question 7

4) Fimbriae

Answer 7

Hair-like thin appendages
Role: allow attachment to substrates/surfaces or other cells

Question 8

Pili

Answer 8

longer than fimbriae
Role: allow prokaryotes to exchange DNA (conjugation)

Question 9

Correct order of the staining

Answer 9

.

Question 10

Flagella’

Answer 10

• Flagella are long filamentous appendages consisting of a filament, hook and motor.
  -Composed of 42 different types of proteins.
  -Scattered across the surface or concentrated at one or both ends of the cell.
  Role: Movement, Attachment, Secretory apparatus Approx. half of all prokaryotes exhibit taxis - the ability to move toward or away from a stimulus.
  Eg. chemotaxis is the movement toward or away from a chemical stimulus.
  Attachment: for host cell attachment and invasion.
  Secretory apparatus: for proteins involved in pathogenicity (virulence factors)

Question 11

Flagellls and motility

Answer 11

• Rotates clockwise or counter-clockwise by rotation from the motor unit.
• Bacterial flagella rotate to push the cell.
• Motile bacteria exhibit taxis:
positive taxis = movement towards an attractant negative taxis= movement away from a repellent
• Most flagella proteins are modified versions of others with different functions.
• Flagella likely evolved as existing proteins were added to an ancestral secretory system. Exaptation = structures adapted for one function take on new functions.

Question 12

Internal Organisation and DNA=mesosome

Answer 12

1) Mesosome
Bacterial cells may have one or more large, irregular folds.
Role:
• Many functions have been proposed: respiration etc
• Still unknown if cell processing artefacts or true cell structures.

Question 13

Internal organiosdation and dna=nucleoid/nuclear body/dna/chromosome

Answer 13

Prokaryotic genome has less DNA than the eukaryotic genome. Circular continuous chromosome of dsDNA, not contained in a
nucleus but in nucleoid region with no surrounding membrane. Most also have smaller rings of independently replicating DNA
called plasmids. Role:
• DNA replication, transcription.
-Differences between prokaryotes and eukaryotic DNA replication, transcription, and translation allows use of antibiotics to inhibit bacterial growth without harming host.

Question 14

Internal organisation and dna=ribosomes

Answer 14

Cytoplasm of a bacterial cell contains numerous 70S ribosomes (consisting of 50S and 30S subunits). Consists of rRNA and protein.
Role:
• Protein synthesis
• Antibiotic target site: eg. streptomycin can attach to the small subunit and inhibit protein synthesis.

Question 15

Internal organisation and dna -endoscopes

Answer 15

Dormant, tough, non-reproductive structure.
Role:
• Permits survival of nuclear material for later germination.
• To ensure the survival of a bacterium through environmental stress.
• Resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants.
• Commonly found in soil and water, where they may survive for long periods of time

Question 16

Internal organisation and dna =cysts

Answer 16

Azotobacter species and others are known to form cysts. Dormant cells with thickened cells walls
Role:
• Permits survival of nuclear material for later germination.
• To ensure the survival of a bacterium through stress.
• Resistant to desiccation and some chemicals, but cannot withstand high temperatures like endospores.

Question 17

Fungi

Answer 17

• Mushrooms are just the aboveground parts of a vast network of underground filaments.
• Fungal filaments absorb nutrients from the soil, transfer them to trees and receive sugars in return.
• Some even transfer sugars between trees of different species.

• Fungi are diverse and widespread.
• They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients.
• About 100,000 species of fungi have been described.

Question 18

Body structure of fungi

Answer 18

• Most common body structures are multicellular filaments and single cells (yeasts).
• Some species grow as either filaments or yeasts; others grow as both.
• Morphology of multicellular fungi enhances ability to absorb nutrients.
• Body of fungi form networks of branched hyphae adapted for absorption.
• Hyphae have tubular cell walls strengthened with chitin.
• Most fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of organelles.

• Fungal hyphae form an interwoven mass called a
mycelium.
• The structure of a mycelium maximizes surface-to-volume ratio, making feeding very efficient.

Question 19

Hyphae

Answer 19

Adapted for trapping and killing prey

Question 20

Virus

Answer 20

• A virus is an infectious particle consisting of DNA/genes packaged in a protein coat.
• Viruses are much simpler in structure than even prokaryotic cells.
• Viruses cannot reproduce or carry out metabolism outside of a host cell.
• Viruses exist in an area between life-forms and chemicals, leading a “borrowed life”.

Question 21

What causes tobaccco mosaic disease

Answer 21

-extracted sap from tobacco plant with tobacco mosaic disease
-passed sap through a porcelain filter known to trap bacteria
-rubbed filtered sap on healthy tobacco plants
-healthy plants became infected

Question 22

Structure and function of viruses

Answer 22

• Viruses are not cells.
• Small infectious particles consisting of nucleic
acids enclosed in a protein coat (in some cases, a membranous envelope).
• Viruses are obligate intracellular parasites = replicate only within a host cell.
• Each virus has a host range, a limited number of host cells that it can infect.

Question 23

Viral genomes

Answer 23

Double- or single-stranded DNA or RNA.
Viruses are classified as DNA viruses or RNA viruses.
Viruses have between three and 2,000 genes in their genome.

Question 24

Candida and envelopes

Answer 24

•Capsid = protein shell (capsomeres) that encloses the
viral genome.
•Variety of structures = helical or icosahedral.
•Viral envelopes (derived from membranes of host cells) surround the capsids of influenza viruses and many others.
•Viral envelopes = combination of viral and host cell molecules

Question 25

Bacteriophages

Answer 25

Also called phases are viruses that infect bacteria