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