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