Transcript Cells - lhsbiocaine

Unit 2: Cells
Part II: Prokaryotes vs. Eukaryotes
Prokaryotes vs. Eukaryotes
 The differences between these
organisms go well beyond the presence
or lack of a nucleus
 This is the first major division of living
things on earth – a very fundamental
difference indeed
 We can no longer think of prokaryotes as
primitive and eukaryotes advanced
Prokaryotes vs. Eukaryotes
 No nucleus
 “Naked” DNA in a DNA
loop and plasmids
 Small ribosomes (70s;
50s/30s subunits)
 Cell walls made of
peptidoglycans
 Flagella not made of
microtubules
 No EMS (endomembrane system)
 Double membrane bound
nucleus
 DNA organized into
chromosomes
 Large ribosomes (80s;
60s/40s subunits)
 Cell walls made of
cellulose (plants) or chitin
(fungi or protist)
 Flagella made of
microtubules
 EMS present
Prokaryotes: Diversity
 The first forms of life were likely very similar to
modern bacteria
 Rapidly evolving, but surprisingly nearly
unchanged over billions of years
 Prokaryotes can be found in literally every
environment and in every available niche on
the planet
 Prokaryotes split into to major groups:
 Archaebacteria - extremophiles
 Eubacteria – “true” bacteria
Prokaryotes: Structure
 DNA Loop: a long single fiber in the cytoplasm
which contains almost all of the genetic material
(the rest is in plasmids); genes are usually kept
small and devoid of introns (extra non-coding bits
of DNA) – highly efficient
 Ribosomes: freely floating in cytoplasm
(unbound); site for protein synthesis
 Antibiotics like tetracycline bind to the prokaryotic
ribosome and interfere with the bacteria’s ability to
produce proteins
Prokaryotes: Structure
 Cell Wall: provide the cell with shape and
structure, and some minimal protection against a
hostile environment; most prokaryotes have them
 Capsule: jelly-like coating that surrounds the cell
wall; only some prokaryotes have them; 4
functions of a capsule:
 Prevents cell from drying out
 Helps cells stick together or on other surfaces (tissues
of other organisms)
 Helps prokaryotes slide on surfaces
 Keeps some bacteria from being destroyed by the host
organism
Prokaryotes: Structure
 Flagella: solid crystal proteins that stick
through the holes in the cell membrane and
spin like propellers for locomotion (very
different structure from eukaryotic flagella)
 Pilli: short bristle-like appendages which
have 2 functions:
 Attach bacteria to surfaces
 Assist in the transfer of DNA from one
bacterium to another
Prokaryotes: Shape
 Eubacteria typically come in one of 4
shapes:
 Coccus (pl. cocci): spere shaped
 Advantage: less distortion in a dried out organism
 Bacillus (pl. bacilli): rod shaped
 Advantage: high surface area
 Spirillum (pl. spirilla): spiral/helical shaped
 Advantage: highly motile (corkscrew motion)
 Spirochete(s): spiral shaped cells with
flagella inside the cell membrane
Prokaryotes: Movement
 Chemotaxis: movement of an organism
toward or away from a chemical
 Positive chemotaxis: chemicals that attract
organisms toward them are called
attractants
 Negative chemotaxis: chemicals that repel
organisms are called repellants
 Runs and twiddles
Prokaryotes: Survival
 When environmental conditions are
unfavorable, bacteria become inactive.
 Some species form endospores (thick
wall surrounding genetic material
 Endospores go dormant until conditions
are favorable
 Endospores can survive very harsh
environmental conditions
 Boil water 2x
Prokaryotes: Reproduction
 Asexual Reproduction
 Binary Fission: single loop of DNA is copied,
both attach to cell membrane; the cell divides
by pinching off between the two loops.
 Sexual Reproduction
 Conjugation: a bridge is formed between cell
pili; F plasmid (F=fertility, ~ 25 genes) injected
with F pilus; new plasmid is recombined into
bacterial DNA
Conjugation
Prokaryotes: Reproduction
 Transformation: a living bacterium
absorbs the genetic material of a dead
cell or “naked” genetic material in the
environment
 Transduction: transfer of DNA from a host
to another cell by means of a virus
Prokaryotes: Metabolics
 Heterotrophs: must eat to acquire food
 Photoheterotrophs: can use light to product
ATP, but must get organic carbon from
another source
 Chemoheterotrophs
 Saprobes: decomposers that absorb nutrients
from dead organic material
 Parasites: absorb nutrients from the body fluids
of living hosts
 Phagotrophs: ingest food and digest it
enzymatically within cells or multiple cellular
bodies
Prokaryotes: Metabolics
 Autotrophs: can produce their own food
 Photosynthetic autotrophs (phototrophs): organisms
that harness light energy to drive the synthesis of
organic compounds from CO2
 Chemosynthetic autotrophs (chemotrophs):
organisms that use energy from specific inorganic
substances to produce organic molecules from CO2
and provide life processes
 Chemoautotrophs: organisms that need only CO2 as
the carbon source; they obtain energy by oxidizing
inorganic substances like hydrogen sulfide,
ammonia, ferrous or other ions
Prokaryotes: Oxygen
 Prokaryotic oxygen requirements can be
used to classify prokaryotes:
 Obligate aerobes: use oxygen for cellular
respiration and cannot survive without it
 Facultative anaerobes: will use oxygen if
present, but can grow by fermentation in an
environment void of oxygen
 Obligate anaerobes: cannot use oxygen and
are killed by it
Prokaryotes: Archebacteria
 Archebacteria lack peptidoglycan in their
cell walls
 Archebacteria have a unique lipid
composition in their cell membranes
 Archebacteria have a different rRNA
structure than eubacteria and eukaryotes
 Most Archebacteria live in extreme
environments
Prokaryotes: Archebacteria
 Examples (subgroups):
 Methanogens: use elemental hydrogen (H2)
to reduce CO2 into methane (obligate
anaerobes)
 Extreme Halophiles: live in high salinity
environments
 Thermoacidophiles: require environments
that are hot and acidic
Eukaryotes: Diversity
 Protists: single celled, mostly
heterotrophic eukaryotic organisms
 ie – amoeba, euglena, diatoms, etc…
 Fungi: mostly multicellular, heterotrophic,
sessile eukaryotic organisms
 ie – mushrooms, molds, rusts (the living
kind)
Eukaryotes: Diversity
 Plants: multicellular, autotrophic
(photosynthetic), sessile eukaryotic
organisms
 ie – trees, grasses, bushes, shrubberies
 Animals: multicellular, heterotrophic,
mostly motile eukaryotic organisms
 ie – sponges, mollusks, fish, insects,
reptiles, amphibians, birds, mammals
Eukaryotes: Structure
 Nucleus
 Contains primary DNA in the
form of chromatin which can
be packaged into
chromosomes for cellular
reproduction
 Bound by a double membrane
(nuclear envelope) with
nuclear pores for the
exchange of RNA
Eukaryotes: Structure
 Nucleolus
 Dense, irregularly shaped body in the
nucleus
 Makes and stores RNA
 Forms new ribosomes
Eukaryotes: Structure
 Mitochondrion (pl. mitochondria)
 Generate ATP (adenosine triphosphate – a
high energy molecule for cellular energy)
 Double membrane; inner membrane =
cristae, where much of cellular respiration
takes place
The area inside the cristae is
called the matrix
Contain their own DNA
Why?
Eukaryotes: Structure
 Plastids
 Leucoplasts – found in
roots and tubers
 Chromoplasts – contain
accessory pigments
 Chloroplasts – contain
chlorophyll pigments,
found in leaves and stems
and are the primary
photosynthetic organelle
Eukaryotes: Structure
 Ribosomes
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Non membrane-bound
Site for protein synthesis (very numerous)
Translate mRNA code into proteins
Made of RNA and proteins
3 Types
 70s - found in prokaryotes
 70s (o) – associated w/ eukaryotes’ ER
 80s – found in cytoplasm of eukaryotes
Eukaryotes: Structure
 Endoplasmic Reticulum
 Provides internal framework, support
 Provides transportation and temporary storage
for organic compounds
 Provides surface area for the synthesis of
organic compounds
 Rough – contains ribosomes, site of protein and
glycoprotein synthesis (usually for secretion)
 Smooth – no ribosomes, synthesize, secrete, and/or
store carbohydrates, steroids, hormones, lipids, or
other non-protein products
Eukaryotes: Structure
 Golgi (complex, apparatus, bodies)
 Flattened membranous sacs stacked together
 Sacs are called cisterna
 Interiors are called the lumen
 Cis face = forming face (input)
 Trans face = maturing face (output)
 Functions: breaks down glycoproteins,
concentrates materials into vesicles, forms the
cell wall, and produces lysosomes
Eukaryotes: Structure
 Lysosomes
 Vesicle w/ highly reactive enzymes which can
break down proteins, nucleic acids, and lipids
 Contain 2 or more hydrolases (enzymes)
 Proteases
 Nucleases
 Lipases
 Acidic environment (pH 5) where enzymes
work best
 “Suicide Bags” = programmed cell death
Eukaryotes: Structure
 Peroxisomes
 Contain oxidative enzymes which transfer H
from various substances to oxygen
 Purines, fats, alcohol, poisons, hydrogen
peroxide can all be broken down by
peroxisomes
Eukaryotes: Structure
 Vacuole
 Membrane bound body with little or no
internal structure
 Vacuoles hold substances (varies from one
cell to another)
 Water, food, waste, pigments, enzymes
 Formed by the pinching of the cell
membrane
 Very large in plant cells (central vacuole),
smaller in animal cells
Eukaryotes: Structure
 Cytoskeleton
 Used to hold and change shape
 Used for internal organization
 Used for movement of molecules and/or
movement of the cell
 Made of smaller organelles
 Microtubules
 Actin Fibrils
 Intermediate Fibrils
Eukaryotes: Structure
 Cell Wall
 Maintains cell shape, protection, prevents
excessive uptake of water
 Made of polysaccharide cellulose embedded
in a matrix of other polysaccharides and
protein
 Walls of different cells glued together by
middle lamella
 Strengthens with age: secondary walls
Eukaryotes: Structure
 Cell Membrane (or Plasma Membrane)
 Semi-permeable membrane surrounding all
cells
 Made of phospholipids, proteins, cholesterol,
carbohydrates, glycoproteins, and
glycolipids
Eukaryotes: Structure
 Cell Membrane
 Fluid-Mosaic Model
 Must be fluid to work properly
 Cholesterol controls fluidity based on temperature
 A mosaic of proteins is embedded and dispersed in
the lipid bilayer
 Integral proteins – inserted into the membrane
 Peripheral proteins – not embedded, attached to
membrane surface
Eukaryotes: Function
 Movement of substances across the cell
membrane
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Bulk Flow
Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Vesicle Mediated Transport
Cell-Cell Junction
Eukaryotes: Function
 Bulk Flow
 molecules move all together in the same
direction due to force from hydrostatic
pressure
 Diffusion (no energy)
 The movement of molecules from high
concentration to low concentration with no
energy requirement (small molecules only)
Eukaryotes: Function
 Osmosis (no energy)
 Special case of diffusion: movement of water
across the membrane from high water
potential to low water potential
 Facilitated Diffusion (no energy)
 Polar molecules cannot get through by
diffusion, so cells use integral membrane
proteins to transport them in/out
 Transport proteins are highly selective
 Uniport, symport, and antiport proteins
Eukaryotes: Function
 Active Transport (energy)
 When a substance is moved across the
membrane against it’s concentration
gradient
 Requires energy and membrane proteins
Eukaryotes: Function
 Vesicle-Mediated Transport
 Vesicles/vacuoles can fuse with the cell
membrane
 Exocytosis: expulsion of contents outside
the cell
 Endocytosis: bringing in outside molecules
 Phagocytosis (cell eating)
 Pinocytosis (cell drinking)
 Receptor-mediated endocytosis
Eukaryotes: Function
 Cell-Cell Junction
 Cells organized into tissues must
communicate with each other
 Chemical signals (exocytosis from one,
endocytosis into the next)
 Other junctions
 Desmosome
 Tight junction
 Gap junction
 plasmodesma