Biology Test Unit 2

}}Tour of the Cell:}}

• What is a cell?
  • smallest unit of structure and function in all living things
  • performs all the life processes to maintain homeostasis
  • enclosed by membranes that maintain an internal environment and separate them from the external one
• smooth ER: no ribosomes, synthesize lipids, like phospholipids, cholesterol, fatty acids
• rough ER: ribosomes on it, make protein that will be secreted
• ribosome: synthesize proteins by translating code from mRNA to amino acids. made in nucleus. large subunit, mRNA, small subunit. rRNA + protein, do not have membranes
• centriole: made out of microtubules, pair animal cell
• centrosome: microtubule organizing center, makes them specifically during cell division/mitosis
• plasma membrane: controls movement
• cell wall: shape + protection
• cytoplasm: involved in cell metabolism
• cells are small so they can be replaced
• Prokaryotes vs. Eukaryotes:

}}Endosymbiotic Theory:}}

• explains how eukaryotes evolved from prokaryotes

  1. small aerobic prokaryoric cells were engulfed by larger prokaryotes (endocytosis)
  2. the two cells formed a mutualistic symbiotic relationship. host cell helped provide nutrients and the internal cell produced energy
  3. 2 cells became interdependent to survive

• evidence: mitochondria and chloroplasts are membrane bound organelles that

  • are similar in size + shape to prokaryotes
  • each have their own set of circular DNA and ribosomes
  • double membranes
  • divide independently

}}The Cytoskeleton:}}

• a cellular scaffolding or skeleton contained within the cytoplasm to help keep cell shape/structure
• 3 proteins make up the cytoskeleton: microtubules, intermediate fibers, microfilaments
• microtubules: long, hollow tubes made of tubulin
  • provide framework for organelles/ vesicles to move within cell
  • seperate chromatins during cells division
• intermediate fibers: fibrous, rope-like protein keratin
  • stabilizes cell’s structure by resisting tension
  • helps anchor nucleus
• microfilaments: thing, threadlike strands of contractile protein, actin
  • aid in moving the cytoplasm around the cell: cyclosis

}}Cell Junctions:}}

• plasmodesmata: channels between adjacent plant cells that allow chemical messages and nourishment to be shared
• extracellular matrix: sticky layer in animal cells that helps hold cells together. connected by 3 types:
  • tight junctions: bind cells tightly, leakproof
  • anchoring junctions: fasten cells together w/ cytoskeleton fibers, allowing stretching
  • gap junctions: allows neighboring cells to exchange signals + materials

}}Protein Processing + Secretion:}}

DNA → (transcription) copy occurs in nucleus → mRNA leave nucleus through nuclear pores → (translation) attaches to ribosomes → polypeptide

• if mRNA attaches to cytoplasm/ free floating ribosome, protein stays in cell
• if mRNA attaches to rough ER, protein will be secereted
• ribosome: synthesize proteins
• RER: transports and modifies the protein
• transport vesicle: protein is transported here from RER
• golgi apparatus: receives the incoming protein at the cis end, the packages and prepares protein for secretion at trans end.
• secretory vesicle: fuse within cell membrane, releasing the protein outside the cell (exocytosis)
• lysosomes: break down nutrients for use inside cell, digest old cell parts, digest bacteria + virusus in WBC
• proteins secreted: enzymes, hormones, antibodies
• lysosomal storage disorders: genetic disorders that cause lysosomes to be missing one functional enzyme
  • tay sachs: missing an enzyme that breaks down lipids, affects nervous system (lethal)
  • pompe disease: missing an enzyme that breaks down glycogen which is stored in muscle, liver and stops heart (treatable)

}}Why Cells Are Small:}}

• specific cellular structures are used to maximize the exchange of materials with the environment. these structures increase SA:V ratio
  • ex. root hairs: thin extensions of the root that increase the SA for water/mineral absorption
  • ex. alveoli: thin, small sacs in lungs to increase SA to maximize gas exchange
  • villi and microvilli are finger-like projections of the small intestine to increase SA to increase absorption of nutrients into the bloodstream.
• volume grows faster than SA because is it to the third power instead of the second.
• if there is a high ratio, the exchange rate of nutrients will meet the metabolic needs of the cell
• as cell grows, SA:V decreases because V changes faster

}}The Plasma Membrane:}}

• function: a selectively permeable nonpolar barrier that maintains homeostasis by controlling movement into and out of the cell
• structure: phospholipid bilayer with embedded membrane proteins (transmembrane proteins)
• membrane proteins are amphipathic
• fluid mosaic model: lateral movement and bobbing of the membrane proteins within the phospholipid components
• membrane transport:
  • factors that determine how/if a substance will cross cell membrane:
  • polarity/charge: nonpolar, uncharged pass easily
  • size
  • concentration gradient: ions move down or with the concentration gradient without energy
  • does it need a receptor?
• structure and function of the extracellular matrix:
  • structure: collagen, fibronectin, proteoglycan, integrins
  • function:
  • support
  • adhesion
  • regulation
  • movement

}}Functions of Membrane Proteins:}}

• transport proteins: protein carriers and channels, move substances across membrane
• enzymes: catalyzes reactions
• identity markers: carb antenna used to detect surroundings (cell-to-cell recognition)
  • glycoprotein: short polysaccharide attached to protein and if antigen enters the body, the glycoproteins are not recognized so an immune attack will occur (glycolipids do the same thing)
• receptors: receives external signals from ligands (hormones, ions, neurotransmitters) and send info into cell causing signal transductions
• cell junctions: uses peripheral and integral proteins, connects one cell to another (anchoring, gap, tight)
• structure: attachment to cytoskeleton and extracellular matrix (outside of cell), maintains shape

}}Blood Types:}}

• 4 types: A, B, AB, O
• blood types are names for the glycoproteins found on the surface of the red blood cells
• antibodies are made by white blood cells to attack and kill antigens that the body does not recognize
• blood type A:
  • protein A, anitgen A
  • does not recognize protein B
  • anti-body is anti-B
• blood type B:
  • protein B, antigen B
  • does not recognize protein A
  • anti-body is anti-A
• blood type AB
  • protein A and protein B
  • all proteins recognized
  • no antibodies
• blood type O
  • no protein
  • does not recognize protein A or B
  • anti-body is anti-A and anti-B
• Rh factor: postitve blood types can accept negative blood types, but negative blood types can only accept negative negative blood types have anti-Rh antibody
  • postivie blood types have the Rh antigen
  • ex. A+ has protein A and Rh so they can accept O+, O-, A+, A-. A- can only accept O- and A- because they have anti-Rh
• universal donor: O-
• universal recipient: AB+

}}Membrane Transport:}}

• passive transport: does not require energy to move substance across membrane [high] → [low]
  • diffusion and facilitated diffusion are the two types
• active transport: requires energy to move substance across membrane [low] → [high]
  • bulk transport and protein pumps are the two types

}}Diffusion:}}

• the movement of molecules across a membrane from a region of high concentration to low
• ex, smal, lipid soluble, non polar, uncharged molecules like O2 and CO2
• molecules diffuse inside cell
• high concentration outside low concentration inside
• molecules stop moving at equilibrium (equal number of molecules on both sides- no more gradient)
• real life: diffusion of oxygen + CO2 occurs between alveoli and red blood cells, then at our muscle cells
  • blood cells coming from lungs have [high] CO2 and [low] O2
  • muscle cells have the same thing
• what would happen if oxygen reached the equilibirum?
  • we would die because without a gradient oxygen will no longer diffuse into muscle cells

}}Facilitated Diffusion:}}

• the movement of molecules through a membrane using a protein channel or carrier
• ex. substances that are charged, polar, medium size like Na or Cl or glucose
• the inside of the channel or carrier will have charges that will attract the molecules and pull them into the channel

}}Protein Pumps Active Transport:}}

• ions are pumped against the electrochemical gradient
• sodium potassium pump
  • resets cells to resting potential
  • salted bananas: high Na concentration outside cell high potassium concentration inside cell
• ion pumps help create a difference in charge across the membrane (membrane potential- inside of cell neg, outside pos)
• has to go back to resting potential before messages are sent

}}Bulk Transport:}}

• movement of large moelcules (proteins-hormones, enzymes; starch) into or out of the cell using vesicles

  1. exocytosis: moves materials out of the cell using secretory vesicles (ex. hormones, enzymes)

  2. endocytosis: movement of materials into the cell

     1. phagocytosis: moves solid into the cell using pseudopods
     2. pinocytosis: moves liquid into the cell

  3. receptor-mediated endocytosis: require specific receptor proteins that only endocytose a specific molecule that activate the receptors

     1. ex. body cells remove the bad LDL from circulating in the blood by receptor-mediated endocytosis. this reduces the accumulation of dangerous plaques that could block arteries
     2. hypercholesterolemia: no functional LDL receptors→ too much LDL in body

• how glucose gets into the cell:

  • insulin activates the receptor in the membrane, causing a signla transduction, which mobilizes the glucose channel proteins to fuse with the plasma membrane
  • the glucose channels open and allow glucose into the cell
  • the insulin receptors are endocytosed by receptor-mediated endocytosis, breaking down the insulin, and then fuses back to the membrane to replace the receptors in the membrane

}}Cotransport:}}

• type of secondary active transport
• transport protein couples the movement of an ion down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient
• more potential energy builds as H+ ions accumulate
• sucrose utilizes the energy of the H+ ions flowing down the gradient to get into the cell