Unit 2: Cell Structure and Function

Cells

basic structural & functional units of every organism

Prokaryotes

(Pro-No): bacteria, DNa in nucleoid region, smaller than Eukaryotes

Eukaryotes

(Eu-Do): fungi, animals, plants, DNA in nucleus, have membrane-boudn organelles

Organelles

membrane bound structures in Eukaryotes

• Endomembrane organelles

• Energy organelles

Endomembrane organelles

• nuclear envelope

• endoplasmic reticulum

• golgi complex

• lysosomes

• vesicles/vacuoles

• plasma membrane

Energy organelles

• mitochondria

• chloroplasts

Compartmentalization

allows for diff metabolic reactions to occur in diff locations

• increases surface area

Nucleus

• has genetic info

• double membrane

• has pores (materials in & out)

• has nucleolus (rRNA is made)

• subunits exit via nuclear pores → turn into ribosomes

Ribosomes

made up of rRNA & protein

• function: make proteins

• locations: Cytosol & ER

Endoplasmic Reticulum

• network of membranous sacs & tubes

• functions: creates membranes, compartmentalize cell

Rough ER

has ribosomes

Smooth ER

• no ribosomes

• creates lipids, metabolizes carbohydrates, cleans cell

Golgi complex

• contains cisternae

• has directionality

• Cis face: receives vesicles from ER

• Trans face: sends vesicles back into cytosol for production

• functions: Receives transport vesicles w/ stuff from ER → Modifies, Sorts, Adds molecular tags, Packages materials that exit membrane via exocytosis

Lysosomes

• hydrolyzes (breaks down) macromolecules in animal cells

• Autophagy: lets cells renew itself

• animal cells

Peroxisomes

• to break things down

• catalyze reactions that produce H2O2 → break it down to H2O

• (similar to lysosomes)

• plant cells

Vacuoles

• storage space

• large vesicles from ER & Golgi

• selective in transport

Food vacuole

form via phagocytosis (cell eating) → then digested by lysosomes

Contractile vacuole

maintain water levels in cells

Central vacuole

(in plants): contain inorganic ions & water

• crucial for turgor pressure

Mitochondria

• site of cellular respiration

• double membrane

• has folds → increase surface area

Mitochondrial matrix

contains:

• enzymes that catalyze(speed up) cellular respiration & produce ATP

• mitochondrial DNA

• ribosomes

Chloroplast

(only plant cells)

• site of photosynthesis

• contains chlorophyll (green pigment)

• has thylakoids & storm

Thylakoids

membranous sacs → organize into stacks (grana)

• Grana: where light dependent reactions occur

Stroma

fluid around thylakoids

• location for Calvin Cycle

• Contains: Chloroplast DNA, Ribosomes, Enzymes

Cytoskeleton

network of fibers throughout cytoplasm

• give structural & mechanical support

• anchor organelles (ensure position)

• allow for movement

Microtubules

hollow, rod-like structure made of tubulin (protein)

• structural support

• cell motility (flagella)

Microfilaments

thin, solid rods made of actin (protein)

• maintain cell shape

• bear tension

• cell motility

• cleavage furrow

Intermediate Filaments

fibrous proteins made up of varying subunits

• structural elements

• maintain cell shape

• anchor nucleus & organelles

• form nuclear lamina (lines nuclear envelope)

Plasma membrane

separates internal & external cell environment

• consists phospholipids (amphipathic): contain head & tail

• forms a bilayer

Fluid Mosaic Model

• temp affects fluidity

• Unsaturated hydrocarbon tails: maintain fluidity at low temps

• Kinked tailed: prevent tight packing of phospholipids (low temp)

• Cholesterol: maintain fluidity at high & low temps

• High temp: reduce movement

Integral proteins

embedded into lipid bilayer (very stuck=very hard to remove)

• amphipathic

Peripheral proteins

not embedded into lipid bilayer (kinda attached→remove themselves from membrane)

• attach to cell → make it do smt → then leave

Membrane carbohydrates

• crucial for cell-to-cell recognition

• acts as a marker for recognition (molecular tag)

Glycolipids

carbohydrates bonded to lipids

• glyco=sugar

Glycoproteins

carbohydrates bonded to proteins

• lets a cell recognize another cell

Cell wall

(only plants)

• provides: shape/structure, protection, control water intake

• consist of cellulose (help plants stay upright)

Plasmodesmata

hole-like structures in cell filled w/ cytosol that connect adjacent cells

Selective permeability

some substances can cross membrane more easily than others

• small, non polar, hydrophobic molecules have easy passage

• large, polar, hydrophilic molecules have hard passage

Passive transport

• high → low

• doesn’t require energy bc solute is moving w/ concentration gradient

• import materials, export waste

Diffusion

constant motion of molecules

• high → low

• move DOWN concentration gradient

• diffuse across membrane

Osmosis

diffusion of water down concentration gradient across membrane (aquaporin)

• low → high

Facilitated diffusion

diffusion of molecules thru membrane via transport proteins

• high → low

• increases diffusion rate for: small ions, H2O, carbohydrates

• transport proteins: channel & carrier

Channel Proteins

provide a channel for molecules & ions to pass

• act as a “gate”

• hydrophilic

• high → low

• no energy needed

Aquaporins

specific channel protein for water

Carrier proteins

undergo conformational changes(shape change) for substances to pass

• need energy

• low → high

Active transport

needs energy bc solute moves against concentration gradient

• Pumps

• Cotransport

• Exocytosis

• Endocytosis

ATP

• Adenosine Triphosphate

• energy source used by cells

Pumps

maintain membrane potential (unequal concentrations of ions across membrane)

Sodium potassium pump

• 3 Na+ pumped out of cell

• 2 K+ pumped into cell

• Result: +1 net charge in extracellular fluid

321 NOKIA

Proton pump

integral membrane protein that builds up a proton gradient

• pumps H+ out of cell

Cotransport

coupling of favorable movement of 1 substance w/ unfavorable movement of another substance

• favorable movement: downhill diffusion

• unfavorable movement: uphill transport

Exocytosis

(exit/OUT) production of molecules via vesicles that fuse to plasma membrane

Endocytosis

(enter/IN) uptake of molecules from vesicles fused from plasma membrane

• phagocytosis

• pinocytosis

• receptor mediated endocytosis

Phagocytosis

cell eats particles later digested by lysosomes

Pinocytosis

nonspecific uptake of extracellular fluid → contain dissolved molecules

Receptor mediated endocytosis

specific uptake of molecules via solute binding to receptors on plasma membrane

• lets cells take BIG amounts of a substance

Tonicity

ability of an extracellular solution to cause a cell to gain or lose water

• depends on concentration

• isotonic, hypertonic, hypotonic

Osmoregulation

cells must be able to regulate their solute concentrations & maintain water balance

Isotonic solutions

equal concentration

• water diffuses in & out of cell at same rate

Hypertonic solutions

lose water to extracellular surroundings

• SHRINK → die

• higher concentration outside cell

Hypotonic solutions

gain water

• SWELL → explode

• lower concentration outside

• maintain turgor pressure

Water potential

physical property, predicts direction water will flow

• high water potential → low water potential

• low solute → high solute concentration

• high pressure → low pressure