prokaryotes

1
Prokaryotes and Viruses
2

• Prokaryotes
• Describe and relate the structure and roles of
  different components of prokaryotic cells.
  (including capsule, cell wall, the cell membrane,
  invaginations, flagella, bacterial chromosome,
  plasmids, glycogen granules and lipid droplets)
•  
• Interpret information, pictures, diagrams and
  electron micrographs to identify eukaryotic and
  prokaryotic cell components and organelles

3
Prokaryotic Cells Textbook Pages 30-31
4
Prokaryotes

• Theyre everywhere! Biomass is 10x eukaryotes
• Can thrive in many different environments
• Useful for biological research
• Can cause disease
• No membrane-bound organelles
• Nucleoid (not nucleus)
• Usually very small (eg. Escherichia coli -
  cylindrical rod c 2 x 1 ?m)
• Mostly unicellular
• Diverse habitat
• strong acid
• boiling water
• absence of oxygen
• Divide by binary fission Bacteria Growth -
  YouTube
• A boundary membrane and a rigid cell wall

5

• A prokaryotic cell has three architectural
  regions
• on the outside, flagella and pili project from
  the cell's surface
• enclosing the cell is the cell envelope generally
  consisting of
• a cell wall
• The cell wall consists of peptidoglycan in
  bacteria
• a plasma membrane
• a capsule
• inside the cell is the cytoplasmic region that
  contains
• the cell genome (DNA)
• ribosomes and various sorts of
• invaginations
• lipid droplets
• glycogen storage granules

6

• Cell wall
• Rigid structures around the outside of the cell
• Allow cells to survive in adverse conditions
• Provide support to cells that lack a cytoskeleton
• Helps with classification of bacteria
• Shape of cell
• Gram ve/Gram ve

• Cell wall Gram staining
• Developed by Hans Christian Gram in 1884
• Classifies bacteria according to their cell wall
  structure and reaction to certain dyes
• Uses crystal violet/iodine
• Some bacteria retain the Gram stain Gram
  Positive
• Others lose the stain, during the decolourising
  process and appear red when they are counter
  stained with safrannin - Gram Negative

7
Prokaryotic Cells

• Cell membrane
• Encloses everything in the cell
• Surrounds the cytoplasm
• Made of lipid (fat) and protein
• Selectively permeable - controls what enters and
  leaves the cell
• Site of attachment of other structures e.g.
  flagella

http//torresbioclan.pbworks.com/w/page/22377072/c
ell20membrane20-20team20sMART
8
Prokaryotic Cells

• Cell membrane - invaginations
• Indents in the cell membrane
• Thought to provide surface for specialised
  functions of the bacteria
• E.g. Respiration
• Photosynthesis
• Cell membrane is the site of many cellular
  activities in bacteria

9
Prokaryotic Cells

• Bacterial genetic material
• Bacteria have single circular chromosome ie a
  closed loop
• Chromosome is made of double stranded DNA
• DNA in the bacterial cell is generally confined
  to this central region - nucleoid
• Though it isn't bounded by a membrane, it is
  visibly distinct (by transmission microscopy)
  from the rest of the cell interior.

10
Prokaryotic Cells

• Bacterial genetic material
• Bacteria also have DNA in the form of plasmids
• these are NOT part of the main chromosome
• Not essential for survival
• Information in plasmids is for extras, such as
  the ability to resist antibiotics.

11
Prokaryotic Cells

• Bacterial genetic material

http//sandwalk.blogspot.com/2009/03/on-evolution-
of-bacterial-chromosomes.html
12
This plasmid, designed by scientists from wild
type, has penicillin resistance (AmpR) and
kanamycin resistance (KanR). It also has sites to
allow transfer of genes from other species.
13
Prokaryotic Cells

• Prokaryotic cells reproduce by binary fission
• Very quickly! WCYDWT Bacteria - YouTube
• Ecoddington14

14
Prokaryotic Cells

• Glycogen granules and lipid droplets

• Nutrients and energy reserves may be stored in
  the cytoplasm in the form of glycogen, lipids,
  polyphosphate, or in some cases, sulphur or
  nitrogen.

15
Prokaryotic Cells

• Glycogen granules black
• Fat droplets - red

http//picasaweb.google.com/lexkatedra.bt/LAM0607
16

• Capsule
• A gelatinous capsule is present in some bacteria
  outside the cell wall.
• The capsule may be polysaccharide (pneumococci),
  polypeptide as (bacillus anthracis) or hyaluronic
  acid as in streptococci
• The capsule is antigenic
• The capsule has antiphagocytic function so it
  determines the virulence of many bacteria
• It also plays a role in attachment of the
  organism to mucous membranes.

17

• Flagella
• Flagella are
• the organelles
• of cellular mobility
• They arise from cytoplasm and extrude through the
  cell wall
• They are long and thick thread-like appendages,
  protein in nature
• Only found in some bacteria

18
(No Transcript)
19
Prokaryotic Cells

• Flagella
• Flagella are responsible for movement in motile
  bacteria
• Moves a bacterium by rotating like a propeller
• Distribution can help to identify bacteria
• http//youtu.be/2P9hvlsF9_c
• flagella - YouTube

20
Prokaryotic Cells

• Fimbriae and Pili
• Short hair-like projections
• Fimbriae more numerous and shorter
• Used to fasten cell to surface
• Or to other cells during conjugation

21
Prokaryotic Cells

• Ribosomes
• Give the cytoplasm of bacteria a granular
  appearance in electron micrographs
• Smaller than the ribosomes in eukaryotic cells
• Similar function in translating the genetic
  message in messenger RNA into the production of
  peptide sequences (proteins).

22
Prokaryotic Cells

• Ribosomes

http//train-srv.manipalu.com/wpress/?p124385
http//emp.byui.edu/wellerg/cell/ribosomes.htm
23

• Ribosomes
• Prokaryotes have 70S ribosomes,
• small (30S) subunit
• large (50S) subunit
• Eukaryotes have 80S ribosomes
• small (40S) subunit
• large (60S) subunit
• bacterial 70S ribosomes are vulnerable to to
  antibiotics while the eukaryotic 80S ribosomes
  are not exploited by scientists

24
Cell structure Structure Function
Cell wall Made from peptidoglycan (contains amino acids and carbohydrates) Keeps substances out, stops cell from bursting by osmosis
Plasma membrane Made from phospholipids and proteins Partially permeable
Nuclear material Long circular DNA, no proteins attached Contains genes needed for growth and reproduction
Plasmid Small, circular piece of DNA Carries additional genes, e.g. antibiotic resistance
Capsule Slimy layer outside the cell wall Protects against drying out and can help evade immune system
Ribosome Makes RNA and protein Protein synthesis
Flagellum Only in some bacteria, rigid corkscrew shape Helps bacterium move through fluids
25
Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Cell wall
Bacterial chromosome
Capsule
0.5 µm
Flagella
(a)
A typical rod-shaped bacterium
(b)
A thin section through the bacterium Bacillus
coagulans (TEM)
26
Structure Flagella Function(s) Swimming movement Main chemical composition Protein
Pili Pili Pili
Sex pilus Stabilizes mating bacteria during DNA transfer by conjugation Protein
Common pili or fimbriae Attachment to surfaces protection against phagotrophic engulfment Protein 
Capsules (includes "slime layers" and glycocalyx) Attachment to surfaces protection against phagocytic engulfment, occasionally killing or digestion reserve of nutrients or protection against desiccation Usually polysaccharide occasionally polypeptide
Cell wall Cell wall Cell wall
Gram-positive bacteria Prevents osmotic lysis of cell protoplast and confers rigidity and shape on cells Peptidoglycan (murein) complexed with teichoic acids
Gram-negative bacteria Peptidoglycan prevents osmotic lysis and confers rigidity and shape outer membrane is permeability barrier associated LPS and proteins have various functions Peptidoglycan (murein) surrounded by phospholipid protein-lipopolysaccharide "outer membrane"
Plasma membrane Permeability barrier transport of solutes energy generation location of numerous enzyme systems Phospholipid and protein
Ribosomes Sites of translation (protein synthesis) RNA and protein
Inclusions Often reserves of nutrients additional specialized functions Highly variable carbohydrate, lipid, protein or inorganic
Chromosome Genetic material of cell  DNA
Plasmid Extrachromosomal genetic material DNA
Table 2. Summary of characteristics of typical
bacterial cell structures

27

• Viruses
• Explain why viruses are not classified as living
  organisms.
• Describe the structure of a virus particles and
  relate to replication within cells.
•  
• Compare and contrast eukaryotes, prokaryotes and
  viruses.

28

• Viruses (Pages 30-31 of textbook)
• Non-cellular. Typical size range 20-300nm.
• Contain no cytoplasm or organelles.
• No chromosome, just RNA or DNA strands.
• Covered in protein coat.
• Depend on cells for metabolism and reproduction.

29

• Viruses are a group of unique particles that
  infect every type of living organism, from
  bacteria to flowering plants, and mammals.
• They cause death and countless suffering to
  humans.
• Viruses occur in two phases
• The extracellular phase is non-reproducing and
  contains few, if any enzymes.
• During the intercellular phase, the virus exists
  mainly as replicating nucleic acids which take
  over the metabolic machinery of the host to
  synthesise new viruses.
• Viruses can only reproduce inside living cells.
  They use a variety of strategies to enter a cell.
• The viral DNA is incorporated into the host cell
  DNA where it acts as a gene producing new viral
  proteins.
• Thousands of new viruses are produced which
  eventually burst out of the host cell.
• Viruses can not be classified into any of the
  five kingdoms. It is difficult to decide whether
  they are living or non-living.

30
(No Transcript)