Biology Chapter 3 Notes: Cells
Cells
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all organisms made of cells; most basic unit of life
first used in mid-1600s by Robert Hooke (British scientist); small rooms
Cell theory: all living organisms are made up of one or more cells; cells arise from other, preexisting cells
Prokaryotic Cells
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Does not have a nucleus; DNA simply resides in the middle of the cell
Four basic structures: plasma membrane encompasses the cell (intracellular substances are
within the cell); cytoplasm's jelly-like substance fills the cell; ribosomes makes proteins; one or
more circular loops or linear strands of DNA
may have cell walls to protect and give shape to the cell
pili: Hair-like projections that help cells attach to other surfaces
Flagellum: whip-like projection(s) that aids in cellular movement
diverse metabolically
Endosymbiosis Theory
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a prokaryote entered a larger host prokaryote, eventually their existence became dependant on
each other
Support: chloroplasts and mitochondria are similar in size to prokaryotic cells; have small
amounts of circular DNA simular to prokaryotes; divide by fission like prokaryotes; have internal
structures called ribosomes that are similar to bacteria ones
Invagination
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plasma membrane folds in on itself; other compartments are formed when new membrane
encloses on the folded ones
Eukaryotic Cells
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about 1.5 billion years after prokaryotes
Typical features: DNA contained in nucleus; internal structures into compartments; larger
usually by 10 times; cytoplasm has organelles
Plasma Membrane
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phospholipid bilayer (phospholipids) membrane that holds the contents of a cell in place and
regulates what enters and exits the cell
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Heads of the phospholipids re hydrophilic (polar) and the tails are hydrophobic (non-polar); a
sheet is created
various protein, carb and lipid molecules are also attached to the bilayer
Transmembrane proteins: penetrate right through the lipid bilayer; surface proteins reside on
the inner or outer surface of the membrane; lipids are within the hydrophobic tails
Receptor proteins: bind to chemicals in the cell's external environment; regulate certain
processes within the cell; heart cell receptors bind to adrenaline in times of stress or fright
Recognition Proteins: a fingerprint that makes it possible for the body's immune system to
distinguish the cells that belong inside your body from those that are invaders and need to be
attacked; help cells bind to or adhere to other cells/molecules
Transport proteins: transmembrane proteins that help large/strongly charged molecules pass
through the plasma membrane
Enzymatic proteins (enzymes): accelerate chemical reactions on the plasma membrane's surface
Short Branched Carbohydrate Chains: allows cell to be recognized by other cells like immune sys
Cholesterol: helps membrane maintain its flexibility
Fluid mosaic: plasma membrane comprised of many parts that aren't anchored in place
Faulty membranes: cystic fibrosis (chloride ions are restricted and hard to get mucus out of
lungs)
Beta-blockers: treats anxiety
Have a fingerprint that identifies cells ("I belong here")
Movement of molecules across membranes
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Passive transport: molecular movement occurs spontaneously without input of energy; diffusion
and osmosis
Diffusion: solute is dissolved in a gas or liquid (solvent) and moves from an area of high solute
concentration to an area of a lower concentration; moves down their concentration gradient
Simple diffusion: gets through plasma membranes on their own (O2, CO2)
Facilitative diffusion: Most molecules may be repelled and electrically charged; they need a
carrier molecule to pass/enter
Osmosis: passive diffusion of water across a membrane; water molecules will move to lower
concentration areas; hypertonic solution contains more solutes in extracellular fluid (water
diffuses out); hypotonic solutes contain lower concentrations are lower in extracellular fluid
(water diffuses in); Isotonic (balanced); only determined by the total concentration of molecules
Active Transport: movement of very large molecules or molecules that move against their
concentration gradient; uses up energy and ATP; digestion pushes H+ ions into stomach; when
the transport uses energy directly from ATP to fuel, it is primary active transport; many
transporter proteins use indirect method of fueling activities from ATP and it is called secondary
active transport
Endocytosis and exoctytosis are used for bulk transport of particles: can be receptor mediated
(LDL particles in cholesterol)
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Phagocytosis: large particles are engulfed by cells / Pinocytosis: dissolves particles and liquids
(amoebas, unicellular protists)
Connections between cells
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connections hold the cells in place and enable them to communicate with each other
Tight junctions: water-tight seals around cells and also anchor cells in place; important in the
small intestine because it prevents excess water and bacteria to flow into your cells along with
nutrients
Desmosomes: fasten cells together into strong sheets like a irregular interval of velcro (not
water tight); lines tissue of animal body cavities, muscle tissue, holding fibers together; lack of
this will form blisters
Gap junctions: pores surrounded by special proteins that form open channels between two cells;
secret passageways for nutrients to flow through; cell-to-cell communication; important for the
functioning of hearts; allows cells to recognize when they bump against other cells (contact
inhibition); cancer cells do not have contact inhibition
In plant cells, there are 1,000-100,000 microscopic gap junctions called plasmodesmata
Nucleus
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the nucleus is the largest and most prominent organelle in most eukaryotic cells; generally
larger than any prokaryotic cell
Nuclear membrane (nuclear envelope): separates nucleus from cytoplasm; contains two bilayers
one on top of the other; perforated and covered with tiny pores made from multiple protein
embedded in the phospholipid membranes and spanning both bilayers; pores enable large
molecules to pass in and out the nucleus
Chromatin: prominent structure inside the nucleus; a mass of long, thin fibers consisting of DNA
with some proteins attached to it to keep it from getting impossibly tangled; as DNA directs
activity, chromatin resembles a plate of spaghetti but when cell division time, chromatin coils up
and the threads become shorter and thicker until they become visible as chromosomes
Nucleolus: area near the centre of the nucleus where subunits of the ribosomes are assembled;
ribosomes copy bits of info stored in DNA and use them to construct proteins; ribosomes are
passed through the nuclear pores and into the cytoplasm before they begin production
Cytoplasm and the Cytoskeleton
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form the cell's internal environment (shape/structure) provide its physical support
controls intracellular traffic flow
can generate movement with cilia in unison or flagella
Mitochondria
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power all the reactions in our bodies that make it possible for us to breathe, move and think; allpurpose energy converters and are present in virtually all eukaryotic cells; some cells have 200
mitochondria
mitochondria consume most of the oxygen used by each cell due to energy conversion from
food; produces about 90% of energy our cells need in return
Two separate compartments: intermembrane space and the matrix
has their own DNA; mixed in among approx 3000 proteins; has 2-10 copies of its own little ringshaped DNA; this DNA carries instructions for making 13 important mitochondrial proteins
necessary for metabolism and energy production
our mitochondria come from the mitochondria that were initially present in the mother's egg;
sperm contains DNA but no cytoplasm so no mitochondria; true for most eukaryotes
exercise intolerance can be related to defective mitochondrial DNA
Lysosomes
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round, membrane-enclosed, acid-filled vesicles that function as garbage disposals; enzymes in
lysosomes represent broad spectrum of chemicals designed for dismantling macromolecules
that are no longer needed by cells or by-products of cellular metabolism
50 different enzymes: some enzymes break down lipids, carbs, protein and nucleic acids
lysosomes are frequently also a first step when a cell consumes and begins digesting a particle
of food or invading bacterium (phagocytosis)
Tay-Sachs disease: inability to produce a critical lipid-digesting enzyme; lysosome swells until it
bursts and the cell chokes to death
Endoplasmic Reticulum
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site where cells build proteins and disarms toxins; actual production and modification of
biological molecules are made in the endomembrane system with instructions from the nucleus
takes up nearly 1/5th of the cell's volume; lipids are produced, products for export are modified,
toxic chemicals are broken down and nutralized
Rough ER: contains ribosomes for protein production; primary function is to fold and package
proteins that will be shipped elsewhere in the organism; proteins used within the cell itself are
generally produced on free-floating ribosomes in cytoplasm; pancake stack shaped
Smooth ER: father from the nucleus, lacks ribosomes, slightly different in apperance; branched
tube look-a-like; synthesizes lipids (varies) such as fatty acids, phospholipids, steroids; hormones
are produced inside ovaries and testes; inside liver, fat cells are produced; following production,
the cells are transported
Smooth ER" detoxifying enzymes break down harmful chemicals; proliferated ER can be
beneficial with drugs because it increases capacity for detoxification; may be more and more
drug tolerant over time
Golgi Apparatus
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processes molecules sythesized in the cell (primarily proteins and lipids); site of carb synthesis
including complex polysaccharides found in many plasma membranes; not interconnected
ER transports vesicles into cytoplasm, then to G.A.; vesicles fuse with the G.A. membrane and
dump their contents into a Golgi body; contents visit 4 chambers making slight modifications;
modified molecules moves into cytoplasm
Cell Wall
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made from polysaccharides imbedded with cellulose; some bacteria, protists, and fungi have cell
wall; sometimes there is a secondary cell wall formed; nearly 100 times thicker than plasma
membrane
provides structural strength; water resistance; protection from insects and other animals
primary cell walls touch; plasmodesma connects these cell walls together
50 different enzymes
50 different enzymes
Vacuoles
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Nutrient storage: stores hundreds of dissolved substances including amino acids, sugars, and
ions
Waste management: retains waste products and degrades them with digestive enzymes like
lysosomes
Predator deterrence: nasty-tasting materials that accumulate inside
Sexual reproduction: contain pigments that give some flowers their colours, enabling them to
attract birds/insects to help the plant reproduce by transferring pollen
Physical Support: high concentration of solutes cause water to rush into cells through osmosis;
creates turgor pressure
Chloroplasts
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power-house for plant cells; contains stroma, thylakoid and DNA
each cell in a green leaf has about 40-50 chloroplasts
chloroplasts are oval; critical for photosynthesis