Prokaryotes and Eucaryotes Flashcards
Prokaryotes: Nucleoid
nuclear area - contains a single long circular molecule of double-stranded (ds) DNA, “chromosome”. - No histone proteins associate with chromosome
Prokaryotes: Plasmid
extra small circular, dsDNA molecules - replicate independently of chromosome (Fig. 4.6) - usually contain 5 to 100 genes which are usually not essential for survival of the bacteria - may carry genes for antibiotic resistance, tolerance to toxic metals, production of toxins, synthesis of enzymes - horizontal gene transfer via conjugation
Ribosome
sites of protein synthesis
70S
ribosomes composed of 2 subunits: 50S + 30S subunits - Each subunit is composed of a set of proteins complexed with one or more ribosomal RNAs (rRNA).
“S” =
Svedberg units: measurement of mass based on density gradient centrifugation.
Inclusions:
reservedeposits(nutrients)withinthecytoplasm
Types of inclusions:
Metachromatic granules: volutin
eserve of inorganic phosphate (polyphosphate) that can be
used in the synthesis of ATP
- “change color” = named b/c sometimes stain red with certain
blue dyes such as methylene blue
- are found in algae, fungi, protozoans, and bacteria.
- are characteristic in Corynebacterium diphtheriae, the causative agent of dipththeria.
Polysaccharide granules:
consist of glycogen and starch - iodine + starchgranules appear blue
Lipid Inclusions:
stores lipid
- can be stained with fat-storage dyes such as Sudan dyes
- found in various species of Mycobacterium, Bacillus, Azotobacter, Spirillum.
Sulfur Granules:
stores sulfur
- can serve as source of energy
- bacteria in the genus Thiobacillus derive energy by oxidizing sulfur and sulfur containing compounds.
Carboxysomes
contain the enzyme ribulose 1,5-diphosphate
carboxylasecarbon dioxide fixation
- enzyme is necessary for bacteria that use carbon dioxide as
their source of carbon for photosynthesis.
- are found in nitrifying bacteria, cyanobacteria, and thiobacilli.
Gas Vacuoles:
hollow cavities used to maintain buoyancy
- found in many aquatic procaryotes, including cyanobacteria,
anoxygenic photosynthetic bacteria, and halobacteria
- allows organism to remain at the depth in the water appropriate for them to receive sufficient amounts of oxygen, light, and nutrients.
Endospores
specialized “resting” cells found with bacterium - Unique to bacteria
- are formed when nutrients are depleted and when water is
unavailable
- are highly durable, dehydrated bodies with thick walls or
additional layers
- are formed inside the bacterial cell membrane by
sporulation or sporogenesis).
- can survive extreme heat, lack of water, and exposure to
toxic chemicals and radiation
- certain gram (+) bacteria such as those of the genera Clostridium and Bacillus form endospores
- gram (-) generally do no have endospores
Endospores can be: location
- terminally located (at one end)
- subterminally located (near one end)
- centrally located inside the vegetative cell.
Sporogenesis or sporulation:
process of spore formation
1st stage of sporogenesis, a newly replicated bacterial chromosome and a small portion of the cytoplasm are
isolated by a spore septum.
- The spore septum becomes a double-layered membrane called a forespore.
- Thick layers of peptidoglycan are laid down between the two membrane layers.
- A thick spore coat of protein forms around the outside membrane (this coat is responsible for the resistance of endospores to many harsh chemicals.
- When the endospore matures, the vegetative cell wall dissolves (lyses) and the endospore is
released.
- Endospores contain DNA, small
amounts of RNA, ribosomes,
enzymes, and a large amount of small molecules
- Endospores can remain dormant for a long time…1000s of yrs.
sporeulation stage 1
sporulation stage 2
sporulation stage 3
sporulation stage 4
sporulation stage 5
sporulation stage 6
Germination
return of the endospore to vegetative state
- triggered by physical and chemical damage to the endospore’s coat
b. Endospore’s enzymes break down the extra layers surrounding the endospore, water enters, and metabolism resumes. - One vegetative cell forms one endospore.
- Endospores are important clinically because they are resistant
to the processes that normally kill bacteria;
General Characteristics:Eukaryotes
- Greek for “true nucleus”
- include algae, protozoans, fungi, plants, and animals
- typically larger and structurally more complex than the prokaryotic cell
- contain membrane bound organelles – specialized structures that perform specific functions
- genetic material is organized into chromosomes by closely associating with histones and other proteins
- DNA housed in nucleus
Flagella and Cilia:
- used for locomotion & moving substances - flagella are long projections
- cilia are short numerous projections
- eukaryotic flagella move in a wave-like manner but prokaryotic flagella rotate
flagella and cilia contain cytoplasm and enclosed by plasma membrane
- are arranged in 9 (pairs) + 2 arrangement of microtubules - microtubules composed of tubulin protein
Cell Wall:
- Algae and all plants have cell walls composed of cellulose
(polysaccharide)
- Some fungi have cell walls containing cellulose.
- Most fungi have cell walls composed of chitin (polysaccharide), a polymer of N-acetylglucosamine (NAG) units.
- cell walls of yeasts contain the polysaccharides glucan and mannan
- protozoans have a flexible outer covering (pellicle) instead of a typical cell wall
Plasma Membrane
- functionally and structurally very similar to prokaryotic cells - in addition to phospholipids and proteins, eukaryotic
membrane contains carbohydrates (not found in prokaryotes)
- carbohydrates function in cell to cell recognition and provides
adherence for bacteria
Endocytosis:
is the packaging (internalization) of extracellular material for import into the cell.
- Membrane surrounds a particle and encloses it and brings it into the cell.
- There are three forms of endocytosis: – receptor-mediated endocytosis
– phagocytosis
– pinocytosis
Receptor-Mediated Endocytosis
Specific for a target molecule
Binding of ligand (target) to receptor triggers internalization of receptor and target in a coated vesicle
Coated vesicle fuses with a lysosome, freeing target from the receptor
Target molecule enters the cytoplasm through diffusion or active transport
Receptors can be recycled
Phagocytosis (“cell eating”)
The cell extends a pseudopod around a solid object
The pseudopod engulfs the object, forming a vesicle
The vesicle fuses with lysosomes to digest the object
Usually NOT for nutrition in human cells; phagocytize bacteria, cell debris, and foreign particles
Some specificity involved
Example: macrophages
Pinocytosis (“cell drinking”)
Similar to phagocytosis, except that the material ingested is liquid and molecules that are dissolved in the liquid
Verynonspecific
Nutrients (lipids, sugars, amino acids) enter the cytoplasm via diffusion or active transport
Pinocytotic vesicle returns to the surface
Morecommonthanphagocytosis
Exocytosis
Essentially, the reverse of endocytosis:
- a vesicle within the cell fuses with the plasma membrane and releases contents into the extracellular space.
- the released material may be a product of the cell (protein, hormone, etc.) or waste product from endocytotic vesicles or lysosomes.
Cytoplasm
The cytoplasm consists of cytoplasmic fluid (cytosol), organelles, and cytoskeletal elements
- located between plasma membrane and nucleus
- cytoskeleton contains:
- microfilaments: made of actin proteins; involved in cell mobility, contraction
- intermediate filaments: provide cell stability, anchor proteins to plasma membrane
- microtubules: made of tubulin; maintain cell shape, form the mitotic spindle during cell division, transport substances within the cell
microfilaments
ade of actin proteins; involved in cell mobility, contraction
intermediate filaments:
provide cell stability, anchor proteins to plasma membrane
microtubules
made of tubulin; maintain cell shape, form the mitotic spindle during cell division, transport substances within the cell
Nucleus
houses the cell’s hereditary information (DNA) - has a nuclear envelope - a double membrane with pores
- nuclear pores allow for nucleus to communicate with cytoplasm
- Nucleoplasm - matrix within the nuclear envelope -Nucleolus: center for the synthesis of ribosomal
RNA and ribosomal subunits
- DNA have histone and nonhistone proteins associated with it - chromatin vs chromosome
Chromatin
DNA and its associated proteins (histones) in the
uncondensed form
Chromosome
coiled chromatin in short, rod-like bodies during nuclear division (mitosis or meiosis)…condensed form
Nucleosome
DNA wrapped around 8 Histones; basic structural units of chromosome
Ribosomes
sites for protein synthesis; found in cytoplasm or on rough ER
80S ribosome composed of:
large subunit (60S): composed of 3 rRNAs and 50 proteins - small subunit (40S): composed of 1 rRNA and 33 proteins
- Chloroplasts and mitochondria contain 70S ribosomes, like the procaryotes.
Ribosomes are found in two places:
Membrane attached
- Are bound to the rough endoplasmic reticulum (ER)
- Proteins that are in the secretory pathway are synthesized by these ribosomes
– Membrane unattached
- Are free in the cytosol
- Proteins in the non-secretory pathway are synthesized by these ribosomes
Membrane attached
- Are bound to the rough endoplasmic reticulum (ER)
- Proteins that are in the secretory pathway are synthesized by these ribosomes
– Membrane unattached
- Are free in the cytosol
- Proteins in the non-secretory pathway are synthesized by these ribosomes
- Golgi Apparatus/Complex:
- consists of 4 - 20 flattened sacs (cisterns) stacked one on
top of the other with expanded ends.
- Functions:
1. modify proteins: glycoproteins, lipoproteins, etc. 2. package proteins: - secretory proteins in secretory vesicles sent out of cell via exocytosis
- proteins that are membrane bound
- proteins to be remained in the storage vesicles (i.e. lysosomes)
- Golgi Apparatus/Complex: functions
- Functions:
1. modify proteins: glycoproteins, lipoproteins, etc. 2. package proteins: - secretory proteins in secretory vesicles sent out of cell via exocytosis
- proteins that are membrane bound
- proteins to be remained in the storage vesicles (i.e. lysosomes)
Mitochondrion
power house
- have a double membrane similar to plasma membrane
- outer membrane is smooth
- inner membrane arranged in a series of folds called cristae; folds increase surface area for chemical reaction to occur
- function is to synthesize ATP along inner membrane during cellular respiration
- matrix: center of mitochondrion
- contain 70S ribosomes, DNA of its own, and the machinery to
transcribe and translate the information encoded by their DNA - can self replicate independent of the cell
Chloroplast
only in cells that can do photosynthesis
- are contained in algae and green plants
- are membrane-bounded structures that contain the pigment chlorophyll and the enzymes required for photosynthesis
- The chlorophyll is contained in flattened membrane sacs called thylakoids.
- stacks of thylakoids are called grana
- contain 70S ribosomes, DNA, and enzymes involved in
protein synthesis
- can self replicate on its own within the cell.
thylakoids
The chlorophyll is contained in flattened membrane sacs inside the chloroplast
grana
stacks of thylakoids inside chloroplast
Lynn Margulis
championed the Endosymbiotic Hypothesis, which held that eukaryotic mitochondria and chloroplasts were originally prokaryotes (theory of Endosymbiosis )
- first expanded on this idea in 1981; was treated like a heretic
Suggested:
(a) mitochondria were descended from an aerobic bacterium
(b) chloroplasts from a phytosynthetic
cyanobacterium
Endosymbiosis
An ancient, anaerobic eukaryote engulfed an aerobic eubacterium
Aerobic respiration yields way more ATP (= cellular energy) than less efficient anaerobic respiration
Instead of eating this engulfed cell, they struck up a partnership, or symbiosis
- bacterium got a safe place to live, steady supply of carbon compounds from its host cell
- eukaryote got a more efficient form of
metabolism = lots of extra ATP
Evidence for Endosymbiosis
- mitochondria and chloroplasts have their own circular chromosomes encoding genes needed to replicate their DNA
- reproduce by binary fission, like bacteria
- same size as bacteria
- have their own ribosomes for protein synthesis, which are very similar to bacterial ribosomes
- each is surrounded by a double membrane, consistent with proposed engulfing mechanism (end up with 1 membrane from bacterium, plus 1 layer of the host’s membrane)
Lysosomes
are membrane-bound vesicles which contain hydrolytic enzymes. Their function is to digest foreign substances and cell debris; can digest bacteria
Peroxisomes
are membrane-bound vesicles which contain enzymes which break down fatty acids, amino acids, and hydrogen peroxide.
Centrioles
- Are found in pairs
- They direct the formation of the mitotic spindle during
cell division; also contribute to the structure of cilia and flagella.
- Composedofmicrotubulesin9+0array;9triplets
Algae and all plants have cell composed of ?
cellulose
(polysaccharide)
Most fungi have cell walls composed of
chitin (polysaccharide),
a polymer of N-acetylglucosamine (NAG) units.
cell walls of yeasts contain
the polysaccharides glucan and mannan
protozoans cell wall ?
have a flexible outer covering (pellicle) instead of a typical cell wall
