Prokaryotes - tacs.dypvp.edu.in
Transcript of Prokaryotes - tacs.dypvp.edu.in
• Prokaryotes• Single-celled.
• Reproduce by binary fission (another copy by dividing).
• No cell nucleus or any other membrane-bound organelles. DNA travels openly around the cell.
• All bacteria are prokaryotes.
• Eukaryotes• Most organisms that we can see, such as
trees, grass, worms, flies, mice, humans, mushrooms and yeast are eukaryotes.
• Can either be single-celled or multi-celled.
• Can reproduce in one of several ways (Ex. meiosis, mitosis).
• Have cell nucleus within containing its DNA.
• Nucleus most evident distinction between these cell types.
Two Basic Types of Cells
• All cells are surrounded by a plasma membrane.
• The semi-fluid substance within the cell is called “cytosol”, containing the cell
organelles.
• All cells contain chromosomes which have genes in the form of DNA.
• All cells have tiny organelles called “Ribosomes” that make proteins.
1). Prokaryotic and eukaryotic cellsdiffer in size and complexity
Similarities
• A major difference between prokaryotic and eukaryotic cells is the
location of chromosomes.
– In an eukaryotic cell, chromosomes are contained in a true nucleus ).
– In a prokaryotic cell, the DNA is concentrated in the nucleoid) without a membrane
separating it from the rest of the cell.
– In prokaryotic cell, DNA is a single strand or double strand DNA. But in eukaryotic
cell, DNA is double strand.
1). Prokaryotic and eukaryotic cellsdiffer in size and complexity
Differences
• All cells are surrounded by a plasma membrane.
• The semifluid substance within the membrane is the cytosol, containing the organelles.
• All cells contain chromosomes which have genes in the form of DNA.
• All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes.
Prokaryotic and eukaryotic cells differ in size and complexity
• A major difference between prokaryotic and eukaryotic cells is the location of chromosomes.
• In an eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the nucleus.
• In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.
Structure of Prokaryotes
Prokaryotes
Bacteria Archaea
- Exist in extreme environments (hot and salty)
- Exist in most environments
They are differing in some other structural, biochemical andphysiological characteristics
Types of Prokaryotes
Gram positive vs Gram-negative prokaryotes
Bacteria come in two flavors:
Flagella
Pili
Capsule
Plasma Membrane
Cytoplasm
Cell Wall
Lipopolysaccharides
Teichoic Acids
Inclusions
Spores
Bacterial Structures
ProkaryotesRibosomes: • Small electron dense particles• Involved in prt.synthesis• 70 S(30 S + 50S)• Different from host cell ribosomes in SR.• Streptomycin interferes with bacterial metabolism
sparing the host cell ribosomes.• 3 types of RNAs:• Ribosomal, transfer , mRNA• Found within cytoplasm or attached to
plasma membrane.
ProkaryotesCytoplasm:
• Also known as proto-plasm.
• Gel-like matrix of water, enzymes, nutrients, wastes, (organic n inorganic solutes) and gases and contains cell structures like numerous ribosomes and polysomes.
• No ER n memb.bound organelles.• Shows signs of internal mobility like cytoplasmic streaming
, amoeboid movement and formation and disappearance of vacoules.
Location of growth, metabolism, and replication.
Granules or inclusions: Bacteria’s way of storing nutrients. Staining of some granules aids in identification.
Plasma Membrane Separates the cell from its environment. Limits the protoplast Thin n elastic , can be only seen with electron microscope With the exception of mycoplasma , bacterial cytoplasmic memb.lacks
sterol. Phospholipid molecules oriented so that hydrophilic,water-loving
heads directed outward and hydrophobic ,water-hating tails directed inward.
Proteins embedded in two layers of lipids (lipid bilayayer)
FUNCTIONS:
Semipermeable membrane
Housing enzymes for cell wall, outer membrane synthesis, assembly n secretion of extractoplasmic n extracellular substances
Generation of ATP
Cell motility
Mediation of chromosomal segragation during replication
Cell Wall
• Peptido-glycan Polymer (amino acids + sugars)
• Unique to bacteria
• Sugars; NAG & NAM– N-acetylglucosamine
– N-acetymuramic acid
• D form of Amino acids used not L form– Hard to break down D form
• Amino acids cross link NAG & NAM
Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers.
Provides rigid support while freely permeable to solutes.
Backbone of peptidoglycan molecule composed of two derivatives of glucose:
- N-acetylglucosamine (NAG)- N-acetlymuramic acid (NAM)
NAG / NAM strands are connected by inter-peptide bridges.
Prokaryotes – Cell Wall
From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are:
Gram Positive Gram Negative
Prokaryotes - Cell Wall
• 80% Water {20% Salts-Proteins)– Osmotic Shock important
• DNA is circular, Haploid– Advantages of 1N DNA over 2N DNA– More efficient; grows quicker– Mutations allow adaptation to environment quicker
• Plasmids; extra circular DNA– Antibiotic Resistance
• No organelles (Mitochondria, Golgi, etc.)
Cytoplasm
Prokaryotes - GlycocalyxSome bacteria have an additional layer outside of
the cell wall called the glycocalyx.
This additional layer can come in one of two forms:
1- Glycoproteins loosely associated with the cell wall.
- Slime layer causes bacteria to adhere to solid surfaces and helps prevent the cell from drying out.
- StreptococcusThe slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities).
Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque.
Prokaryotes - Glycocalyx
2.Polysaccharides firmly attached to the cell wall.
Capsules adhere to solid surfaces and to nutrients in the environment.
Adhesive power of capsules is a major factor in the initiation of some bacterial diseases.
Capsule also protect bacteria from being phagocitized by cells of the hosts immune system.
Prokaryotes – Surface Appendages
Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces.
Consist of delicate strands of proteins.
Flagella: Long, thin extensions that allow some bacteria to move about freely in aqueous environments.
Endoflagella: Wind around bacteria, causing movement in waves.
• Motility - movement
• Swarming occurs with some bacteria– Spread across Petri Dish
– Proteus species most evident
• Arrangement basis for classification– Monotrichous; 1 flagella
– Lophotrichous; tuft at one end
– Amphitrichous; both ends
– Peritrichous; all around bacteria
Flagella
• Short protein appendages– smaller than flagella
• Adhere bacteria to surfaces– E. coli has numerous types
• K88, K99, F41, etc.
– Antibodies to it will block adherence.
• F-pilus; used in conjugation– Exchange of genetic information
Pili
• Resistant structure– Heat, irradiation, cold– Boiling >1 hr still viable– Takes time and energy to destroy spores
• Location important in classification– Central, Subterminal, Terminal
• Bacillus stearothermophilus -spores– Used for quality control of heat sterilization equipment
• Bacillus anthracis - spores – Used in biological warfare
Endospores
Eukaryotic cell
Cytoplasm = cytosol + organelles
The nucleus• Genes that control the eukaryotic
cells
• Nuclear envelope is a double
membrane, each membrane is
lipid bilayer with proteins
• perforation by pores
• chromatin – DNA, histons,
non-histon protein
• cell division – chromatin
condensate to chromosomes
• the nucleolus – synthesis of
ribosomes components
• The nucleus control protein synthesis by sending molecular messengers in the
form RNA – mRNA - messenger - TRANSCRIPTION
• is synthesized in nucleus according the DNA
• in ribosomes is genetic information translate into the primary structure of a
specific protein - TRANSLATION
• free ribosomes – suspended in the cytosol, function of protein in cytosol
• bound ribosomes are attached to outside membrane network called the
endoplazmatic reticulum;
make proteins destined into membrane and for export from the cell (secretion)
Ribosomes
The endomembrane system
Nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosoms, various
kinds of vacuoles and plasma membrane
• ER consist of a network of
membranous tubules and sacs
called cisternae
• ER is continuous with nuclear
envelope
• Smooth ER - cytoplasmatic
surface lacks ribosomes
• Rough ER – ribosomes are
attached to the cytoplasmatic side
Function of smooth ER – synthesis of lipids (phospholipids, steroids),
metabolism of carbohydrates (glycogen) and detoxification of drugs (barbiturates)
and poisons
Function of rough ER – secretion of proteins, glycoproteins
formation of transport vesicules to other components of endomembrane system
Golgi apparatus – sorting cell products, they are modified and stored (removes
sugar monomers and product diverse oligosaccharides)
two poles are reffered to as the cis face ad trans face
Exocytosis and Endocytosis is transport of large molecules
Cell secretes macromolecules by a fusion of vesicles
with plasma membrane = Exocytosis - budded from
the Golgi – products
Endocytosis – cell takes in macromolecules a particulate matter by
forming new vesicles from plasma membrane
three types :
Phagocytosis – cell engulf a particle
Pinocytosis – cell gulf droplets of
extracellular fluid
Receptor-mediated endocytosis is very
specific – receptor and ligand
Lysosomes are digestive compartments
• membrane bounded sac of
hydrolytic enzymes
• enzymes hydrolyze in acidic
environment (pH 5) proteins,
polysaccharides, fats and nucleic
acids
• function is intracellular digestion of
food particles, smaller organisms and
organic components engulfing by
phagocytosis and own organic old
material by autophagy
Mitochondria and chloroplasts
Vacuoles, vesicles• membrane–bounded sacs
• vacuoles have various functions: food vacuoles
contractile vacuoles
tonoplast
• Convert energy (ATP) that cells use for work
Mitochondria are the sites of cellular respiration
Chloroplasts are sites of photosynthesis
• Semiautonomic organelles, that grow and reproduce within the cell
• contain own DNA (prokaryotic origin)
Mitochondria
• in all eukaryotic cells
• hundreds or thousands
• two membrane, each is
phospholipid bilayer with a
unique collection of embedded
proteins
The outer membrane is smooth, the inner membrane is convoluted with infolding
called cristae
Intermembrane space
Mitochondrial matrix
ChloroplastA member of plant organelles
family called plastids:
leukoplast
chromoplasts
chloroplasts
thylakoids
Inner membranous
system, outside of it
is stroma
• photosynthesis
The cytoskelet• the dynamic networks of
protein fibers extending
throughout the cytoplasm
• Support, motility,
regulation
• microfilaments (2)
• intermediate filaments (3)
• microtubules (1)
1
2
3
3. cell-shape, mechanical support, provides anchorage for many organelles
and cytosolic enzymes
2. the thinnest filaments, twisted double chain of actin subunits, cell-shape, cell
organization, pull a forces, function in muscle, amoeboid movement –
pseudopodia
1. compression-resisting function, dynamic behavior, binding GTP for polymerization,
intracellular transport (associated with dyneins and kinesins, they transport
organelles like mitochondria or vesicles, the axoneme of cilia and flagella, the
mitotic spindle
Centrosomes and Centriolas
• 9 set of triplets microtubules
• tubulin α, β => microtubules
• grow out from a centrosome, within of animal cells
are a pair of centriolas
• cell shape, cell motility, cell division, organelle
movements
Flagella and Cilia
• Unicellular eukaryotic organisms, sperm of animals, algae and some plants
• Cilia occur in large numbers on the cell surface.
• Cilia work like oars:
• Flagella are longer and are usually limited to just one or few
• the motor molecule
called dynein
• basal body identical
to centriole
• 9 doublets of outer
microtubules
• one doublet of inner
microtubule
Flagellum
Microfilaments - Actin filaments
• Molecules of actin – a globular protein G => F fibrilar protein
• Is a twisted double chain of actin subunits
• function is bear tension (pulling forces)
• ameboid movement – extend and contraction of pseudopodia
• maintenance of shape, changes of shape
Plant Cells:
have chloroplast
use photosynthesis
have cell wall
one large vacuole
are rectangular
Animal Cells:
don't have chloroplast
no cell wall
one or more small vacuole
either circular or have irregular shape
Cellulose of plant cell walls helps to plant cells
to allow high pressure to build inside of it,
without bursting. A plant cell has to be able to
accept large amounts of liquid through
osmosis, without being destroyed. An animal
cell does not have this cell wall. If you start to
fill the animal cell with too much distilled water
or other fluid, it will eventually pop.