AR

Unit 2- An Introduction to the Cell

Module 6.1- The cell is the fundamental unit of life

  • the cell is the smallest most basic unit of living organisms
    • the simplest structure that exists as an independent unit of life
  • all living organisms are either unicellular or multicellular
    • Unicellular- single cell
    • Multicellular- more than one cell
  • bacteria, yeasts, and algae are mostly unicellular
  • plants and animals are multicellular, specialized for certain functions
  • a cell can be of many different sizes
  • Cell theory- similarity in the microscopic organization of all living organisms, all organisms are made up of cells, the cell is the fundamental unit of life, cells come from preexisting cells
    • unites all forms of life
  • the fundamental unit of life=simplest entity we can define as living
    • reproduce
    • respond to environment
    • harness energy
    • evolve
  • helps transfer understandings to larger forms

Module 6.2- All cells maintain homeostasis, store and transmit energy, and transfer energy

  • all cells have a discrete boundary that separates the interior of the cell from its external boundary and maintains the inside in life compatible way
  • all cells contain an information molecule that they can use and pass on
  • all cells harness energy and material from the environment

The cell membrane and homeostasis

  • Cell membrane- the boundary between the interior of the cell and the nonliving exterior
  • all cells must continually acquire and exchange ions and building blocks to make macromolecules
  • cells must also release waste out of their membrane
  • inside of the cell doesn’t change much, the specific pH and salt concentration
    • needed for reactions, protein folding, and other functions
  • Homeostasis- the active maintenance of stable internal conditions, maintained by the cell membrane
    • important for cells and organisms
    • temperature, heart rate, blood pressure, blood pH, and water content
    • active energy-using process

Information

  • cells store, use, and transmit info which encodes and determines features
    • archived like a blueprint
  • this DNA must quickly and accurately be copied to daughter cells in reproduction
  • nucleotides are the core-directs protein form
  • proteins make the cell's internal architecture, shape, ability to move, and chemical reactions
  • DNA guides RNA synthesis and RNA directs protein synthesis
  • Ribosomes- complex structure, the site where a protein is assembled, translates RNA, a small unit and a large unit, 3 types of ribosomal RNAs and 20-50 types of ribosomal proteins
  • central dogma- the path from DNA to RNA to protein, the basic flow of info on all cells, a key concept of biology
  • DNA is easily copied/ replicated which makes passing between cells and cells or organisms to offspring easier

Metabolism

  • essential cell feature or transfer from the environment-from sum and chemical compounds
  • Metabolism- the entire set of chemical reactions by which cells transfer energy from one form to another and build and breakdown molecules
  • Adenosine triphosphate (ATP)- a chemical form that stores energy, enables cells to carry out functions
    • used for growing, division, and transfer of substances in and out of cells
  • Catabolism- a set of chemical reactions that break molecules into smaller pieces
  • Anabolism- a set of chemical reactions that build molecules from smaller units, require energy
  • many metabolic reactions have been used for 1000s of years

Modules 6.3- The structure and function of cells are closely related

  • there is a connection between structure and function on all biological levels
  • all cells have specialized shapes for specialized functions

Modules 6.4- Prokaryotes and eukaryotes differ in their internal organization

  • Nucleus- membrane-bound space that contains the genetic material of the cell
    • nuclear membrane- controls substance moving in and out of the nucleus
  • Cytoplasm- the space outside of the nucleus
  • Prokaryotic- cells without a nucleus
  • Eukaryotic- cells within a nucleus

Prokaryotes

  • the first cells
  • most live as a single-celled organism
  • Domain- groups of organisms. bacteria, eukarya, and archaea
  • 2 prokaryote domains- small size, reproduce rapidly, obtain energy and nutrients
    • bacteria- can be good and bad
    • archaea- can tolerate environmental extremes
  • usually, 1-2 macromolecules in diameter, help them absorb nutrients
  • DNA held in the nucleoid
    • one circular DNA molecule arranged in loops
  • plasma membrane surrounding the cell wall- helps keep its shape
  • the bacteria cell wall is thick peptidoglycan or thin lipid layer
  • some archeae and bacteria have flagella- structures of their surface to help them move
  • Plasmids- small circular molecules of DNA, few genes, transformed through pili
    • extend from one cell to another when exchanging plasmids
    • hold info about environmental advantages because it can spread quickly
  • more prokaryotes than eukaryotes
  • bacteria and archaea differ in the cell wall, DNA RNA synthesis, and different eukaryote’s evolution

Eukaryotes

  • evolved later than prokaryotes
  • Eukarya- animals, plants, fungi, protists (single-celled microorganisms)
  • defined by the presence of a nucleus, which houses most of the DNA
  • DNA is a linear molecule rather than circular
  • Nuclear membrane- allows for more complex regulation of gene expression
  • can regulate DNA RNA and RNA protein synthesis
  • Organelles- membrane-defined compartments, that divide cell contents
  • Cytosol- jelly-like material outside of the nucleus and organelles
  • eukaryotic ribosomes are longer than prokaryotes
  • different of lipids in cell membranes between prokaryotic and eukaryotic
  • eukaryotic have cilia
    • Cilia- a rodlike structure that extends from the cells
    • Nonmotile cilia- cilia that don’t move, sensor function
    • Motile cilia- cilia that move

Module 7- Subcellular compartments of Eukaryotes

Module 7.1- The endomembrane system compartmentalized the eukaryotic cell

  • all cells…
    • have a membrane
    • use DNA and RNA
    • carry out metabolic reactions
  • Eukaryotes have a nucleus and many membranes
    • the inside surface area is tenfold greater than a cell membrane
  • Surface area- the total amount of area of the outer surface of an area
  • internal membranes define the subcellular compartments/ organelles, each with a specific function and organization

The endomembrane system

  • membranes are usually connected one way or another by membrane bridges or vesicles
  • Vesicles- small membrane-enclosed sacs that transport substances within a cell or from the interior to the exterior of the cell, form a budding from an organelle
    • take a piece of the membrane and the internal contents of the organelle they derive from
    • fuse with another organelle or the cell membrane to reform a continuous membrane and unload their contents
  • Endomembrane system- made up of interconnected membranes of the cell or connected by vesicles
    • cell membrane, nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles
  • in plants, the endomembrane system is actually continuous between cells through intercellular connections
  • most prokaryotic cells don't have extensive internal membranes, but some photosynthetic bacteria do
  • the endomembrane system divides the cell interior into 2 parts- one inside the compartments defined by these membranes and one outside these compartments
    • separated inside of the membrane and cytosol
  • Cytoskeleton- protects and gives structure to the cell

Nucleus

  • the innermost organelle of the endomembrane
  • protects the DNA
  • Nuclear envelope- defines the boundary of the nucleus, 2 lipid bilayer membranes
  • Nucleolus- makes mRNA and also holds ERNA and rRNA
  • Nuclear pores- perforate the inner and outer nuclear envelope membranes
    • large protein complexes with an inner passageway that regulates which molecules move into and out of the nucleus
    • essential for communication between the nucleus and the rest of the cell
    • ex. proteins that decide gene expression
    • ex. info transfer in DNA depends on RNA movement through these pores
  • Chromatin- DNA or cell information that is ready for use
  • Chromosomes- DNA or information ready for transport around the cell

Endoplasmic reticulum

  • Endoplasmic reticulum (ER)- an organelle that is involved in the production of proteins and lipids, bound with 1 membrane which is continuous with the nuclear membrane
    • produces many of the proteins and lipids used inside and outside the cell
    • transported by vesicles to the cell membrane, other organelles of the endomembrane system, or the cell exterior
  • makes up much of the lipids for the membranes, also quite large in size
  • made up of interconnected tubules and flattened sacs- the interior is called the lumen
  • Lumen- the interior of the organelle or cell
  • it has an extremely convoluted membrane
  • Rough endoplasmic reticulum- studied with ribosomes, the site of RNA protein synthesis
  • larger and more extensive ERs have larger amounts of proteins
  • Enzymes- proteins that speed up rates of chemical reactions
  • all cells have some ER to make transmembrane and organelle proteins
  • Smooth endoplasmic reticulum- the site of fatty acid and phospholipid synthesis
    • predominates in cells specialized for the production of lipids- many synthesize steroid hormones
  • SER contains enzymes that can help detoxify certain drugs and harmful products of metabolism

Golgi apparatus

  • Golgi apparatus- modifies and sorts proteins and lipids produced by the ER, usually where vesicles go after the ER
    • part of the pathway of modification of proteins and lipids
  • function- modifies proteins and lipids, sorting, adds carbohydrates to proteins and lipids
  • Glycoproteins and glycolipids- sacs that make up the majority of the Golgi apparatus
  • Antigens/ recognition factors- carbohydrates added to proteins and lipids, like a badge
  • made up of cisternae sacs that are flattened, many vesicles
  • vesicles move from the ER to the Golgi through cisternae then to the cell membrane or other organelles
  • enzymes chemically modify proteins and lipids as they go through the Golgi
  • predominantly glycosylation, sugars, linked to proteins and lipids, occurs first
    • sugar links completely change the protein and its function
  • Golgi to ER transport happens when proteins are accidentally moved forward and need to move back

Lysosomes

  • Lysosomes- specialized vesicles derived from the Golgi apparatus, degrade damaged and unneeded macromolecules
    • have a key role in intracellular digestion and recycling of organic compounds
    • involved in programmed cell death
  • lysosomes contain a variety of enzymes that break down macromolecules like nucleic acids, lipids, and complete carbs
    • packaged in the Golgi apparatus
  • Golgi sends macromolecules for dehydration to lysosomes via vesicles
  • lysosome interior has a pH of 5 (acidic)
    • protects the outside proteins and organelles because they can’t act in that pH
  • enzymes in lysosomes are synthesized by rough ER, sorted in the Golgi, and then packed into lysosomes
  • proteins embedded in the protein membrane come from the Golgi
    • keep homeostasis and transport

Module 7.2- Mitochondria and chloroplasts harness energy for use by the cell

  • mitochondria and chloroplasts aren’t part of the endomembrane system
    • harness energy for the rest of the cell
  • mitochondria and chloroplasts can grow and multiply independently of the other organelles
    • have their own DNA separate from that of the rest of the cell
  • scientists believe they came from bacteria

Mitochondria

  • Mitochondria- organelles that harness energy from organic molecules like carbohydrates
  • use chemical reactions to break down molecules like other organisms
    • energy is stored as adenosine triphosphate (ATP)
    • drives many chemical reactions- the universal energy currency of the cell
    • growth, division, and moving substances
  • provide eukaryotic cells with most of their usable energy
  • Cellular respiration- a series of chemical reactions in which organic molecules are broken down and the energy is stored as ATP
    • takes place in the mitochondria
  • in cellular respiration, oxygen is consumed and carbon dioxide is released
  • mitochondria are rodshaped with 2 membranes, outer and highly convoluted inner membrane
  • Intermembrane space- space between the inner and outer membranes
  • Mitochondria matrix- space enclosed by the inner membrane
  • cellular respiration happens in steps rather than all at once, energy is therefore not all released at once
    • some steps occur in the cytosol, the mitochondrial matrix, and some along the inner mitochondrial membrane
    • the mitochondrial membrane step makes or releases the most ATP
    • increases surface area for the chemical matching that synthesizes

Chloroplasts

  • mitochondria are present in almost all plant and animal cells
  • plant cells and green algae also have chloroplasts
  • Chloroplasts- organelles that capture sunlight energy to synthesize simple sugars
  • Photosynthesis- the capture of sunlight to synthesize simple sugars
    • carbon dioxide is consumed and oxygen is released
  • chloroplasts are enclosed by a double membrane consisting of an outer and inner membrane
  • Thylakoid- inside of chloroplasts, look like flattened sacs, grouped into structures called grana
  • Grana- in the thylakoid, connected to one another by membrane bridges so they enclose a single, interconnected, compartment
  • photosynthesis has many steps in different locations
  • in the thylakoid, the light from the sun is turned into chemical energy which occurs along the thylakoid membrane
  • Chlorophyll- light-collecting pigment molecule in the thylakoid membrane, green in color
  • the folds of the thylakoid add surface area which increases its function

Module 7.3- The cytoskeleton and cell wall help to maintain cell shape

  • Cytoskeleton- a system of protein filaments, that provides internal support for cells and tracks within the cell for transport of vesicles and other organelles, determines the cell’s shape
    • allow some cells to change shape, move about, and transport substances within the cell
  • some cells have a cell wall outside the cell membrane, which provides structure and support

Cytoskeleton

  • all eukaryotic cells have at least 2 cytoskeletal elements- microtubules and microfilaments
    • long chains of polymers made up of protein subunits
    • allow cells to change shape, move about, and transport substances
  • Microfilaments- present in various locations of cytoplasm, extensively branched just beneath the cell membrane
    • play an important role in maintaining cell shape
    • log bundles form a band that extends around the circumference of epithelial cells
  • Microtubules- hollow tube-like structures, that help maintain cell shape and internal structure
    • in animal cells, they radiate outward from a microtubule organizing center to the cell periphery
    • helps cells withstand compression
    • many organelles tether to these to be guided to organelle arrangements
  • some eukaryotic cells may have cytoskeletal proteins, in cytoplasts and mitochondria

Cell wall

  • present in plants, algae, fungi, and bacteria
  • maintains the cell shape and size, protection, and structure
  • outside the cell membrane
  • rigid and resists expansion
  • Turgor pressure- the force exerted by water pressing against an object, a result of water moving into cells surrounded by a cell wall
    • provides structural support and protection for cells
  • Vacuole- in plants and fungi cells, absorbs water and contributes to turgor pressure
    • why plants wilt
    • can store nutrients, ions, and water
    • why plant cells are usually larger
  • the cell wall is made up of carbohydrates and proteins but its main component is polysaccharide cellulose
  • much algae and plants have cellulose cell walls but some are silicon or calcium carbonate
  • must fungi cell walls are chitin
  • the bacteria cell wall is mostly peptidoglycan
  • animal and plant cells have a cell membrane, mitochondria, an endomembrane system, and a cytoskeleton
  • plant cells have chloroplasts, a cell wall, and vacuoles while animal cells don’t

Module 8- Cell and Organism Size

Module 8.1- Surface area increases more slowly than volume as an object gets larger

  • Volume- the total amount of space an object occupies
  • volume increases more quickly than the surface area
  • Microplasma- a bacteria, the smallest free-living organism
  • prokaryotic cells are usually smaller than eukaryotic

Surface area and volume

  • volume and surface area can be found of any 3D object
  • the surface area describes a flat 2D structure
  • to find volume and surface area one must think of an organism as a geometric shape
  • cube: volume- S^3, surface area- 6S^2
  • Sphere: volume-4/3Pir^3, surface area- 4Pir^2

Surface area to volume ratio

  • a later object has a larger volume-to-surface area ratio than a smaller object

Scaling

  • the volume: the surface area is the reason things are a certain size
  • Isometry- increase in size but shape overall kept
  • Allometry- increase in size and change in shape, what happens in the bio world
  • as 3D objects get bigger the shape does too, balancing the v:as ratio
  • Ex. the increased folds in mitochondria can support a larger volume organism because it increases the surface area without increasing volume

Module 8.2- Diffusion limits the size of prokaryotes

  • most bacteria are tiny, 20-300 nanometers in diameter
  • bacteria are sphere, rod, or spiral-shaped
  • have a larger surface area compared to the volume
    • allows them to take in nutrients and other things through their membranes
  • Diffusion- the movement of molecules from areas of high to low concentration
  • bacteria rely on diffusion to take in molecules and remove waste
  • diffusion is fast over short distances yet incredibly slow and ineffective over long distances
    • why things with larger surface areas compared to volume can use rely on diffusion
  • the biggest bacteria is 100,000,000x larger than the average bacteria and only works because its large vacuole takes up a large amount of space

Module 8.3- Cells and organisms have evolved in ways to circumvent the limits of diffusion

  • eukaryotes are larger meaning they have a larger volume:surface area than prokaryotes
  • internal membranes can be used by larger cells to combat higher v:as ratios
    • highly folded ER, Golgi, mitochondria, and thylakoid

Diffusion in multicellular organisms

  • diffusion supplies key molecules for metabolism
    • constrains the size, shape, and function of cells and organisms
  • humans and other animals have organs that provide a large amount of surface area for oxygen absorption
    • the human lungs have 600 million alreali which have a combined surface area of a tennis court
  • a large surface area and thin walls allow diffusion in large cells

Bulk flow in multicellular organisms

  • Bulk flow- the movement of a fluid driven by pressure differences
    • how oxygen flows to other parts of the body
  • hemoglobin in red blood cells binds to oxygen, then are pumped around by the heart
  • many invertebrate animals lack cell-defined blood vessels so they just pump into the body cavity
  • bulk flow moves nutrients and hormones as well
  • the diaphragm uses bulk flow to move air into the lungs
  • vascular channels powered by evaporation allow bulk flow to move water and nutrients in large plants
  • bulk flow allows plants and animals to have different shapes, sizes, and functions

Module 9- Cell Membranes

Module 9.1- cell membranes are composed of 2 layers of lipids

  • cell membranes separate cells from their external environment and define compartments within eukaryotic cells
  • lipids form a barrier in an aqueous or watery environment
  • the cell membrane is a mix of components- lipids, proteins, and carbohydrates
    • keep the internal environment stable
    • movement of components in and out of the cell
  • phospholipids are made up of a glycerol backbone attached to a phosphate group and 2 fatty acids
    • the head is hydrophilic and the tail is hydrophobic
    • nonpolar and don’t form hydrogen bonds with water
    • called amphipathic- having hydrophilic and hydrophobic regions
  • phospholipids arrange themselves in structures for the heads and tails
    • caused by waters polarity
  • phospholipid tails interact with other fatty acids
    • also caused by waters polarity
  • different head shapes create different sized shapes
  • lipid bilayer- formed by a less bulky head and 2 lipid-tailed phospholipids, chains come together with heads on the outside, form all cell membranes
  • when phospholipids are put in water (pH 7) they form bilayers in a liposome shape
    • spherical structures with an inner and outer space, have a bet input of energy
    • self-healing
    • interacts with watery inside and outside
    • acts as a barrier to polar molecules

Module 9.2- Cell membranes are dynamic

  • membranes are dynamic- lateral movement of lipids and other membrane components
    • help vesicles break off and are absorbed
    • allows shape change, movement, and engulfment of particles
  • Van der Waals forces allow phospholipid tails to associate
    • weak, allowing for movement, can spin and move fat
  • fatty acid tails are flexible and move, form, and reform
  • the membrane is fluid, tail length influences fluidity
    • a longer tail makes the membrane less fluid
    • also influenced by the number of carbon-carbon bonds
    • more double bonds make it unsaturated making it less stable and more fluid
  • cholesterol is amphipathic and participates in the membrane bilayer
    • at higher temperatures, the cholesterol membranes become more stable and less fluid
    • helps temperature not drastically change membrane fluidity (homeostasis)
  • lipid rafts- lipids formed into defined patches
    • bilayers aren’t uniform and rather made up of different rafts
  • lipid flip-flop- spontaneous transfer of lipid between bilayer layers, very rare
    • hydrophilic head would have to pass through the hydrophobic area
    • why different layers have different components

Module 9.3- Proteins and carbohydrates associate with cell membranes

  • Membranes- phospholipids, cholesterol, proteins, and carbohydrates
  • proteins make up to 50% of the mass of red blood cell membranes
  • membrane protein functions: transport molecules, and pass electrons along the membrane in the process of harnessing energy for use by the cell
  • transport proteins-more ions and molecules across the membrane
  • receptor proteins- allowed the cell to receive signals from the environment
    • some act as enzymes and others help maintain structure and shape
  • Integral membrane proteins- permanently associated with the cell membrane and can’t be removed without destroying the membrane
  • Peripheral membrane proteins- temporarily associated with the membrane or integral membrane proteins through weak noncovalent bonds, easily separated
  • Transmembrane proteins- the main type of integral membrane proteins, span the entire bilayer, have 2 hydrophilic regions on either end and a hydrophobic piece in the middle
    • the hydrophobic piece holds the proteins in place
    • act for the outer hydrophilic end to receive signals and send them through the hydrophobic piece
  • peripheral membrane proteins can be associated with internal or external end
    • interact with polar heads of lipids or weak noncovalent interactions with integral membrane proteins
  • peripheral membrane proteins are only transiently associated with the membranes and transmit signals from the environment
  • peripheral membrane proteins help proteins cluster in lipid rafts
  • proteins can freely move in the cell membrane
  • carbohydrates are in the membrane too
  • carbohydrates in the cell membrane are attached to other membrane components via covalent bonds
    • attach to lipids
  • glycolipids- a carbohydrate covalently attached to a lipid
  • glycoproteins- a carbohydrate covalently linked to a proteins
  • glycolipids and glycoproteins are free to move around the membrane
  • fluid mosaic model- inspired by lipids, proteins, and carbohydrates freely moving in the membrane, the lipid bilayer is a structure within which molecules have laterally (fluid) and is a mixture (mosaic of various components)
  • what can pass in and out of a cell independent of what molecules make up the membranes (maintains homeostasis)
  • Liposomes- formed when phospholipids are placed in water with a natural pH, form a spherical shape that resembles a cell
  • Micelle- large headed single tailed lipids packed tightly together into a spherical shape

Module 10- Membrane transport

Module 10.1- Passive transport involves diffusion

  • the cell membrane is selectively permeable to maintain homeostasis
    • due to lipids and embedded proteins
  • polar, charged, and large molecules are generally unable to pass through the membrane on their own
  • nonpolar, uncharged, and small molecules can pass through the membrane on their own
    • because of the nonpolar bilayer interior
  • Proteins and many polysaccharides are too big to cross
  • lipids and small gasses like oxygen and carbon dioxide can pass freely
  • some small uncharged polar molecules can pass too, like water
  • transport proteins move molecules like water, ions, and nutrients

Simple diffusion

  • water at room temperature moves about 500m a second, with 5 trillion collisions per second
    • important for chemical reactions
  • concentration gradient- areas of higher and lower concentrations of a substance
    • cause a net movement of molecules
  • diffusion is the movement of a concentration gradient
  • dynamic equilibrium- the movement of molecules in both directions when in an even concentration
  • Passive transport- when molecules move across a membrane by diffusion
    • results in a difference in concentration
  • simple diffusion- passive transport and moves directly through the membrane
  • steroids, lipids, oxygen, carbon dioxide
  • export waste and take in nutrients

Facilitated diffusion

  • transport proteins are used in simple and passive transport to move molecules
  • transport proteins span the cell membrane and provide a route for substances to enter and exit
  • Facilitated diffusion- diffusion across a cell membrane through a transport protein
    • high to low concentration
  • Channel proteins- a transport protein, provide an opening between the inside and outside of a cell through which certain molecules can pass through
    • depends on shape and charge
  • some transport proteins are gated and respond to a chemical or electrical signal
  • Carrier protein- binds to and then transports specific molecules across the cell membrane
    • either open to the inside or outside of the cell
  • the shape of the carrier protein lets specific molecules through
  • the number and type of transport proteins depend on the cell
  • Aquaporins- allow water to enter or exit the cell by facilitated diffusion
  • Gated channels
    • ligand-gated- open with signal proteins like hormones
    • Voltage-gated- open with an electrical charge like a nerve impulse

Module 10.2- Active transport requires energy

  • Active transport- the movement of a substance against a concentration gradient, requires cellular energy
    • primarily active transport cells use ATP directly to move molecules
  • Secondary active transport- cells use ATP indirectly to move molecules across the membrane

Primary active transport

  • energy in primary active transport comes from the breakdown of adenosine triphosphate (ATP)
  • transport proteins change their shapes and pump molecules against the concentration gradient
  • Antiporters- move molecules against the gradient and across the membrane
  • Symporters- move 2 molecules in our out of the cell

Secondary active transport

  • the move of charged ions across the membrane, through transport proteins, builds a build-up of ions on one side of the membrane
    • causes a store of energy
    • can be used to move molecules from areas of low to high concentrations
  • transport driven by built-up charges and not ATP is the main idea of secondary transport
  • a pump generates a chemical gradient and the membrane acts as a dam to store energy
  • an electrical gradient is caused by a more negative or positive molecule charge on one side
  • Electrochemical gradient- a gradient with both chemical and charge components
  • proteins move from areas of high to low concentrations causing a potential for other molecules to move against the gradient

Module 10.3- Endocytosis and exocytosis move large molecules into and out of a cell

  • all transported molecules end up in the cytoplasm or outside of the cell
  • some cells use vesicles to export or import molecules
    • usually come from the rough ER
  • Vesicles- small spherical organelles that travel between the endomembrane system in eukaryotic cells
  • vesicles bud off and fuse with other cells or organelles releasing their contents
  • Exocytosis- vesicle fuses with the cell membrane and releases its contents into the extracellular space
    • depends on the fluidity and dynamic nature of a membrane
  • exocytosis is used to remove cytoplasmic waste
    • the vesicle fuses with the cell membrane
  • exocytosis is used to deliver proteins to the cell membrane
    • protein embedded in the membrane of the rough ER
    • carry any other of the membrane proteins and fuse with the next membrane
  • Endocytosis- a vesicle buds off from the cell membrane toward the cell interior (invaginates) enclosing material from outside the cell and bringing it into the cell
  • microorganisms and large particles can be ingested by other cells
    • can be transported to lysosomes for digestion
  • endocytosis and exocytosis are ways to transport molecules without going through the membrane
    • only in eukaryotes
  • Molecular motors- associated with the cytoskeleton and move vesicles in the cell
    • much faster than diffusion
  • cytoskeleton helps move vesicles around the cell

Module 11- Water movement: osmosis, tonicity, and osmoregulation

Module 11.1- Osmosis governs the movement of water across the membranes

  • Water balance- how much water is in a cell or organism, a form of homeostasis
  • water levels determine concentrations of ions and solvents
  • water determines the size and shape of a cell
  • many biochemical processes need a specific water concentration
  • water can move via diffusion
  • water concentration often occurs because ions, amino acids, sugars, etc. are dissolved in water
  • Solutes- dissolved in a substance
  • Solvent- liquid a solvent is dissolved in
  • Molarity- molar concentration, the concentration of a solute in a solution, MOL/L, M
  • membranes sometimes split 2 liquids or solutions
  • Permeable- freely allows water and solutes through
  • Impermeable- blocks the diffusion of water and solutes
  • Selectively permeable- lets some solutes and water molecules through but not all
  • a high solute level means a low water concentration and a low solute concentration means a large water concentration
  • Osmosis- the movement of water across areas of selectively permeable membranes in response to a difference in solute concentration
  • if a membrane was permeable to the molecules then it would diffuse on its own, osmosis is needed when the membrane is impermeable to the solute
  • when multiple solutes are present the direction depends on which side has a greater total number of solutes

Module 11.2- Water potential combines all of the factors that influence water movement

  • the cell wall and gravity can exert pressure on water
  • Water potential- all of the chemical and physical forces that affect the movement of water- osmosis, pressure, and gravity
    • helps us understand where water is moving

Osmotic pressures

  • Osmotic pressure- the tendency of water to move from one solution to another with osmosis
  • higher solute means a higher osmotic pressure
  • osmotic pressure is the tendency for a solution to draw water in
  • Hydrostatic pressure- the pressure gravity exerts on a solution
  • when water stops moving the osmotic pressure and hydrostatic pressures are equal
  • waters height and force are used to measure osmotic pressure

Tonicity

  • Tonicity- describes osmotic pressure and direction of water movement
    • how strongly water is pulled into a solution compared to another
  • higher tonicity has a higher solute concentration than another solution
  • Hypotonic solution- a solution with a higher solute concentration than another solution
  • Hypertonic solution- a solution with a lower solute concentration than another solution
  • Isotonic solution- a solution was the same concentration as another solution
  • animal cells try to keep intracellular and extracellular fluids isotonic
  • some protists live in hypotonic environments and use contractile vacuoles to prevent exploding
  • Contractile vacuoles- organelles that take up excess water from inside the cell and expel it into the external environment

Turgor pressure

  • Turgor pressure- the force exerted by water pressing against an object, developed as a result of water moving by osmosis into cells with a cell wall
  • the cell wall presses back on turgor pressure
  • a high turgor pressure makes the cell expand and low turgor pressures make a cell wilt

Water potential

  • water potential uses osmotic pressure, turgor pressure, and gravity to determine which way water will flow
  • water moves from high water potential to low water potential
  • Ψ- water potential symbol
  • Ψp- pressure potential
  • Ψs- solution potential, Ψs= -iCRT, becomes more negative with move solute, negative of the osmosis pressure
    • i- ionization constant, substances that don’t ionize in the water get a 1
    • C- solution concentration, molarity
    • R- pressure constant, 0.0831
    • T- the temperature in kelvin
  • pure water at ground level has a Ψ of 0
  • Ψ= Ψs+Ψp
  • trees for example have lower water potential at the top and pull water up

Module 11.3- Osmoregulation is a form of homeostasis

  • Osmoregulation- regulation of osmotic pressure inside cells and organisms
    • the regulation of water content, keeps the internal fluid in the right concentration
    • a form of homeostasis

Osmoconformers

  • Osmoconformers- keep their internal fluid at the same osmotic pressure as the surrounding environment
    • don’t use very much energy to do this
  • must adapt to the solute concentration of their external environment
    • usually like to stay in places with stable solute concentrations like seawater
  • use energy to regulate the concentration of ions like sodium, potassium, and chloride and molecules like amino acids and glucose
    • have to pump potassium in and sodium out
  • many sea invertebrates are osmoconformers and have high sodium and chloride concentrations
    • need to match the external environment
  • some have high levels of urea
  • Urea- a waste product of many animals’ protein metabolism

Osmoregulation

  • Osmoregulators- water and electrolyte homeostasis by maintaining internal solute concentration different than the environment
  • use energy to pump ions across cell membranes
  • adapt to many different environments
  • marine osmoregulators have lower inner electrolyte concentrations than seawater
  • freshwater osmoregulators have higher electrolyte concentrations than the environment

Module 12- Origin of compartmentalization and the eukaryotic cells

Module 12.1- The organization of the eukaryotic cell helps obtain eukaryotic diversity

  • cell similarities- a cell membrane, DNA, can harness energy from its environment, regulate substances through the membrane
  • prokaryotes- small, with no nucleus, and no internal membrane system, harness carbon, and energy in many ways
  • eukaryotes- larger, have a nucleus, and internal membranes, harness carbon and energy in limited ways
  • eukaryotes are successful because they can form diverse shapes and sizes and multicellular structures
    • engulf other cells, large trees, complex humans

Dynamic cytoskeleton and membranes

  • the cytoskeleton can be remodeled quickly which allows cell shape to change quickly
  • dynamic cytoskeleton requires dynamic membranes to function during remodeling
  • the endomembrane system can quickly change shape as well
  • dynamic continuity- membranes are interchangeable via vesicles
  • mitochondria and chloroplasts have more stable membranes
    • have membrane-embedded proteins that require a stable membrane
  • the cytoskeleton and membrane allow for endocytosis
  • Phagocytosis- a form of endocytosis, eukaryotes surround food particles and package them in vesicles

Energy metabolism

  • passive and active transport are the only ways for prokaryotic cells to take in molecules
    • can metabolize the molecules in many ways to obtain carbon and energy
  • eukaryotes are limited to what the organelles can do
  • some vesicles fuse with lysosomes with enzymes which break down the particles
    • some are processed by the mitochondria
  • multicellularity allows eukaryotes to feed on bacteria, other cells, large food, plants, and animals
    • began predation- increased the complexity of interactions among organisms
  • flexible photosynthetic eukaryotic cells can interact with their environments much more than photosynthetic bacteria
  • many plants have evolved multicellular bodies with many different cells- working together
    • can have leaves high in the sky

Module 12.2- Chloroplasts and mitochondria originated by endosymbiosis

  • chloroplasts are in certain algae and plants
    • use energy from sunlight to build energy-rich carbohydrates
  • mitochondria are in most eukaryotic cells and every multicellular eukaryote
    • the site of cellular respiration, harness energy stored in the carbohydrate and other organic molecules and transfer it to the form ATP

Chloroplasts and mitochondrial origins

  • Symbiosis- the close association between two species
  • Endosymbiosis- when one partner becomes permanently incorporated into their host
  • mitochondria and chloroplasts are double membraned- one membrane of the original bacteria and the second being the membrane from the vesicle from the endocytosis cell

Other symbioses

  • much of the evolution of eukaryotic cells came from formerly free-living organisms
    • symbiosis between bacteria and eukaryotic cells
  • eukaryotes can live in different environments by using bacteria to carry out reactions they couldn’t on their own

Eukaryotic cell origins

  • some think archeal cells first evolved into eukaryotic cells
    • had a nucleus, cytoskeleton, and an endomembrane system but only had a limited way of deriving energy from organic molecules
    • later engulfed a proteobacterium to gain a mitochondria
  • some think an archeal cell engulfed a proteobacterium to gain mitochondria first