Unit 2: Cell Biology

Cell

• fundamental unit of life

  • defined by cell membrane composed of a phospholipid bilayer that controls what enters + leaves cell

    • semi-permeable

Prokaryote

• type of cell that lacks an internal membrane-bound compartment to house DNA

• NO NUCLEI (organelle)

  • simple → must be SINGLE - cellular

    • single prokaryotic cell = whole prokaryotic organism

• ex: E. coli

• Shared Structures w/ E’s

  • plasma membrane

  • cytoplasm

  • DNA

Eukaryote

• type of cell that contains multiple membrane-bound internal compartments called organelles

• have NUCLEI (organelle)

  • complex → can be single or multi-cellular

• ex:

  • yeast: many single-celled eukaryotic organisms

  • cheek epithelium: part of multicellular eukaryotic organism

*bound = thing that surrounds

• Shared Structures w/ P’s

  • plasma membrane

  • cytoplasm

  • DNA

Compartmentalization

• separates different cellular processes into different isolated physical spaces for optimal safety + efficiency

  • possible because of organelles

Surface Area: Volume Ratio

• intracellular transport

  • nutrients enter cells + travel to mitochondria by diffusion

    • essential to power cellular work

  • small benefit:

    • more efficient at getting nutrients in + out

    • move things around faster

  • large benefits:

    • more valuable structures can fit inside

      • more organelles + mitochondria → more cellular work

    • increased functional complexity + specificity

      • why E’s can do much more than P’s

• Transmembrane Transport

  • structure functions of small intestine + red blood cells (NOTES)

• Cellular Work

  • macro mol’s that do related work functions = held close together (anchored in membrane [chem rxn “workbenches”])

  • more membranes = more work space = more productivity

Organelle

• allow for compartmentalization w/in eukaryotic cells

Plant Cell

Animal Cell

Mitochondrion

• membrane-bound organelle found in eukaryotic cells that does cellular work

  • generates chemical energy for cellular functions

  • convert nutrients to ATP

• big surface area to volume ratio:

  • = more mitochondria can fit in cell → more cellular work can be done

• nutrients enter cells + need to travel to mitochondria by diffusion

  • nutrients = essential to power cellular work

Chloroplast

• specialized cell organelle found in plants that converts sunlight → chemical energy through photosynthesis

Plasma Membrane

• Structure:

  • composed of a phospholipid bilayer, proteins, + other mol’s

    • lipids + proteins = crucial for composition

      • entering + exiting…

• Function:

  • controls transport of materials into + out of cell

    • maintain cellular homeostasis

• present in both prokaryotic + eukaryotic cells

• semi-permeability + fluid mosaic model

  • ex: diagram w/ H2O channel

Cytoplasm

• Structure:

  • thick, jelly-like liquid inside cell containing water + wide variety of macromolecules doing work

    • intracellular space

      • REM: MEANS CELLS ARE NOT ISO W/ PURE 0.0M WATER

• Fucntion:

  • supports chemical reactions needed to sustain life functions

Nucleus

• present in eukaryotic cells (organelles) but not prokaryotic cells

• = large membrane bound organelle in eukaryotic cells

  • stores DNA + controls cellular activities

Phospholipid Bilayer

• major component of plasma membrane

• structure allows for selective permeability w/ NP/P fatty acid tails and phosphate head group

  • polar + hydrophilic head groups on “outside” and NP + hydrophobic tails on inside

    • diagram

• boundary of cell = controls what materials pass through

• enhances liquidity of movement:

  • kinked, unsaturated fatty acid tail makes phospholipid tails harder to stack

  • easier to slide past each other + be more fluid

Fluid Mosaic Modelb

• Fluid:

  • all individual components can keep moving

  • “liquidity”

    • “kinked” unsaturated leg

      • = harder to stack, easier to slide past each other + more fluid

      • b/c double bond makes chain not straight; at least one double bond, and can’t rotate like single bond

    • cholesterol molecules

      • lipids → = happy to be embedded in NP fatty acid tail region

        • BUT: b/c = different shape, add to difficulty of stacking → stay fluid

  • NONE of molecules are covalently attracted

• Mosaic:

  • made of many small pieces

  • membrane is mostly made of phospholipids w/ some cholesterol molecules and proteins (protein channels)

    • all = 1 continuous surface

• diagram

Selective Permeability

• phospholipids + proteins allow plasma membrane to be selectively permeable for different molecules traveling from extracellular space to cell cytoplasm + vice versa

  • molecules transported by energy/ pathway (protein channel)

    • speed of molecules = kinetic energy (their T)

  • molecules blocked

    • cell prevents from entering + exiting b/c important or toxic in certain places

• facilitated by structure of phospholipid bilayers (NP+h-phobic / P+ h-philic)

• let specific molecules through, necessary to maintain cellular homeostasis

  • TRANSPORT

Solvent

• substance that does the dissolving (→ solution w/ solute)

  • present in larger amount

  • usually liquid (H2O) but can be solid/ gas too

Solute

• substance that gets dissolved (→ solution w/ sovent)

  • present in smaller amount

  • solid/ liquid/ gas

    • breaks down → smaller particles

Diffusion

• random movement of chemicals from high concentration area → low concentration area

• movement of particles down their concentration gradient

  • trying to be evenly distributed everywhere

  • more LIKELY to go from high to low concentrations

• two types (w/ + w/o energy)

Osmosis

• facilitated diffusion of water down its concentration gradient across a semi-permeable membrane

  • moves from more solute → less solute

    • = less solvent → more solvent

      • solvent = H2O

• uses a polar pathway to go through b/c only wants to interact w/ polar head groups or itself, so can’t pass through NP fatty acid tail region

  • protein channel = aquaporin (POLAR)

  • water needs to keep moving back + forth to regulate homeostasis

  • won’t get STUCK anywhere

• diagram

Aquaporin

• protein that allows water to enter + exit cell

  • provides a polar pathway for water to move through the hydrophobic region of the semi-permeable membrane

Isotonic

• same concentration of solute in cell and in solution

  • always compare: x = isotonic w/ respect to y

    • net direction of water = equilibrium

• diagram

Hypertonic

• higher solute concentration in x than y

  • solution is hypertonic compared to cytoplasm of cell = solution has more solute

  • cell shrivels b/c water moves out (to higher concentration region)

    • net direction of water = out

• diagram

Hypotonic

• lower solute concentration in x than y

  • solution is hypotonic compared to cytoplasm of cell = solution has less solute

    • cell explodes b/c water moves in (to higher concentration region)

      • net direction of water = in

• diagram

Concentration Gradient

• change in concentration of a solute between two regions

  • molecules naturally move DOWN their CG

    • = high to low concentration (w/o energy)

    • passive transport

  • active transport:

    • molecules move AGAINST their CG

      • = low to high concentration (requires energy)

Passive TRansport

• movement across the cell membrane down the concentration gradient w/o using the cell’s energy

  • energy comes from molecules already moving

    • got from environment + colliding w/ other things

• 2 types

Simple Diffusion

• substance dissolves into plasma membrane

• RULES:

  • substances must be:

    • small (<5 atoms)

    • NP

      • “uninterested” in interacting w/ H2O or pm

      • if P → relations w/ charged material that may anchor it in place

    • net movement down concentration gradient

• ex: CO2

  • can’t control how it moves; just regulate concentrations

Facilitated Diffusion

• substances moved across membrane via a specific protein channel

  • move through hole based on what concentration gradient dictates

    • b/c don’t want to interact w/ NP tail region

• RULES:

  • substance must be:

    • small (<5 atoms)

    • polar or charged (±)

      • makes tethered to one side of membrane

    • moving down concentration gradient

• ex:

  • H2O uses aquaporin

Channel

• protein channels = designed to let specific molecules cross phospholipid bilayer boundary

• SELECTIVE:

  • only certain molecules can pass

• ex:

  • aquaporin for H2O molecules

Active Transport

• substances can be moved across membrane via a specific pump

  • pumps can use ATP as source of energy

• Characteristics for AT:

  • big (>5 atoms)

  • moving UP concentration gradient

  • moving many molecules all at once

    • all make it harder to move molecules → uses CELLULAR ENERGY

  • diagram

Adenosine Triphosphate (ATP)

• energy-storing molecule used to do cellular work

  • major source of cellular energy

    • structure: adenine + ribose + 3 phosphate groups

      • ATP → ADP + Pi

        • break bond b/w ribose and 3 phosphate groups for energy

Pump

• what substances requiring active transport use to cross membrane

• can use ATP as source of energy, “powered” by ATP

  • ~ channels in facilitated diffusion (but not passive)

• used for:

  • pumping big molecules

  • pumping molecules up concentration gradient

Bulk Transport

• Type of active transport

  • uses cellular energy (ATP)

• for HUGE “substances” (like whole cells) that need to enter/ exit cell

• for moving A LOT of any substance into/ out of cell ALL AT ONCE

  • ~ gulp huge thing or lots of little things all at once

• 2 types

Exocytosis

• bulk transport OUT of cell

  • “material” packed into vesicle

  • vesicle fuses to plasma membrane (ATP)

  • contents empty into outside + vesicle becomes part of membrane

• diagram

Endocytosis

• bulk transport INTO cell

  • cell membrane bends inwards to form pit around material

  • “pinches off” to create sealed vesicle of material (ATP)

  • vesicle fuses w/ internal organelles to use content material

• diagram

Vesicle

• small, membrane-bound sac inside/ outside cell that stores + transports material

  • enclosed by 1+ layers phospholipids (separate from cytoplasm)

• allows for transport of materials in bulk transport into + out of cell

  • = “package” + transport uses ATP