Biol 40 Chapter 6 and 7 Review

Lipids, Membranes, and the 1st cells + inside the cell

What separates life from nonlife?

Plasma Membrane: serves as a selective barrier from damaging chemicals and substances

Lipids

umbrella term for carbon-containing compounds characterized by their lack of solubility in water

Why are lipids not soluble?

this is a result of their nonpolar hydrocarbons

Hydrocarbons

molecules containing only hyrdrogen and carbon (nonpolar due to electronegativities)

Fatty acid

simple lipid made of a hydrocarbon chain bonded to a polar carboxyl functional group (-COOH)

Cis Fatty Acid

hydrogens are on the same side of the chain, creating a kink in the chain that promotes fluidity and thus increases solubility

Trans Fatty Acids

hydrogens are on opposing sides of each other resulting in a straight, rigidly packed chain that decreases solubility

Unsaturated fats

a hydrocarbon chain with 1+ double bonds (trans and cis fats fit into this category)

Saturated fats

hydrocarbon chain consisting of only single bonds (waxes)

waxes

saturated lipids that have extremely long hydrocarbon tails; forming stiff solids at room temperature

oils

highly unsaturated lipids that are liquid at room temperature

how can unsaturated lipids be converted into saturated lipids?

this is done by breaking down double bonds and adding hydrogen atoms via hydrogenation

steroids

lipids distinguished by their bulky four-ring structure

• differ from each other by the functional groups attached to different carbons in hydrophobic rings

• ex: estrogen, testosterone, and cholesterol (important component in plasma membrane)

fats

nonpolar molecules composed of 3 fatty acids that are linked to a 3-carbon molecule called glycerol 

• frequently referred to as triglycerols or triglycerides

• if glycerol-linked fatty acids are polyunsaturated the resulting triglycerides are liquid at room temp (fats can store up to 2x as much chemical energy as carbohydrates due to their bonds)

• fats form when a dehydration reaction occurs between a hydroxyl group of glycerol and the carboxyl group of a free fatty acid (fats are NOT polymers and fatty acids are NOT monomers)

phospholipid

consist of glycerol that is linked to a phosphate group and 2 hydrocarbon chains of either isoprenoids or fatty acids (phosphate group is also bonded to a small organic molecule that is charged or polar)

• phospholipids with fatty acid tails are found in bacteria/eukarya

• phospholipids with isoprenoid tails are found in domain archaea

• phospholipids are a crucial part of the plasma membrane

lipid roles

• store chemical energy

• act as pigments to trap sunlight

• vitamin in cellular processes

• serve as signals between cells

• waterproof coating on cells/skin

• cell membranes

amphipathic

contain both a hydrophobic (nonpolar) and hydrophilic (polar) region (phospholipid’s hydrophilic phosphate head and hydrophobic lipid tail)

phospholipid phosphate head

• hydrophilic

• polar

• faces solutions in lipid bilayers

phospholipid lipid tails

• hydrophobic

• nonpolar

• face the inside of a membrane in lipid bilayers

micelles

tiny spherical aggregates created when the hydrophilic heads of lipids face outward and interact with water while their hydrophobic tails face inward and interact with each other

lipid bilayer

when lipid molecules align in paired sheets, heads facing the surrounding solution while tails face each other

what kind of molecules can and can’t pass through a selectively permeable membrane?

CAN: small, nonpolar substances are permitted across the membrane (ex: O2 or CO2)

CANT: large, polar substances are NOT permitted across the membrane (ex: C6H12O6)

What happens to permeability as temperature decreases?

Molecules begin to move slowly and become less fluid:

• lipid bilayers begin to solidify and permeability will decrease

• as temp increases permeability will increase

diffusion

spontaneous movement of molecules and ions across a membrane along with the concentration gradient (molecules move from areas of high concentration to low concentration)

passive transport

substances diffusing across a membrane without an outside energy source, at equilibrium this movement will not stop but continues at random

osmosis

diffusion that is specific to water

• only unbound water molecules are capable of diffusion

• shrinks or bursts the volume of cells

hypertonic

solution outside of the cell has a higher concentration of solute than the inside, this causes water to move out of the cell and the cell will SHRINK

hypotonic

solution outside of the cell has a lower concentration than the inside of the cell, water will move from outside of the cell to the inside, BURSTING the cell

isotonic

solute concentration is equal (no change in cell’s volume)

proto cells

vesicle-like structures that harbor nucleic acids

fluid-mosaic model

membranes are a dynamic and fluid mosaic of phospholipids and different types of proteins

ion channels

specialized pore-forming proteins

• ions diffuse from high to low concentration

• electrochemical gradients

channel proteins

pore-like channels in cell membranes

• aquaporin - allow water across the membrane

• gated channels - open or close in response to a signal (binding of a substance or change in electrical charge)

• passive transport

facilitated diffusion

when transmembrane proteins assist in passive transport

carrier proteins

used to facilitate diffusion of substances (act as bridges across membranes)

active transport

transport AGAINST the gradient that requires energy (ATP)

• active transport proteins = pumps

• sodium potassium pump

sodium potassium pump

• sodium ions are in higher concentration on the outside of the cell than on the inside (+)

• potassium ions are in higher concentration on the inside of the cell than on the outside (-)

• the pump sends three sodium ions (Na+) out of the cell and 2 potassium (K+) ions into the cell

secondary active transport

ATP doesn’t directly engage, but provides energy as gradient that powers movement of different solute against its gradient

Pulse Chase Experiment

• Pulse: expose cells to radiation of modified amino acid for a short time

• Chase: end pulse by removing radiation and replacing w/ normal molecule, follow moelcule’s track throughout the cell at set times

• Purpose: mark a population of molecules over a set interval of time and follow their fate over that time

Describe how proteins enter the endomembrane system

1. Protein synthesis begins on a free ribosome in the cytosol, ribosome synthesizes the endoplasmic reticulum signal sequence using info fromt he mRNA

2. Signal sequence binds to a signal recognition particle (SRP) - a complex of RNA + protein - the SRP causes protein synthesis to stop

3. Ribosome + signal sequence + SRP moves to rough endoplasmic reticulum membrane where it attaches the SRP receptor

4. Once the lock (receptor) and key (SRP) connect, the SRP is released and protein synthesis continues through translocon

5. Growing protein is fed into ER lumen, ER sequence is removed

endoplasmic reticulum → golgi apparatus → plasma membrane

glycosylation

addition of 1+ carbohydrate groups — result is referred to as a glycoprotein

cis face of golgi apparatus

where the protein enters, immature

trans face of golgi apparatus

where the protein exits, matured and ready to go to plasma membrane

exocytosis

process in which vesicle membrane and plasma membrane make contact, fuse, and the vesicle lets it’s contents exit the cell

endocytosis

cell taking in material from the outside

receptor mediated endocytosis

uses receptors to bind to macromolecules outside of the cell

early endosome

where cargo is delivered

late endosome

acidified + matured; eventually a lysosome

phagocytosis

brings small cells/food particles inside of the cell through the plasma membrane, engulfing it and delivering it to the lysosome

autophagy

portions of the cytoplasm, including damaged organelles are enclosed in a membrane and delivered to the lysosome

actin filaments (microfilaments)

• fibrous structures made of globular protein subunits (actin)

• smallest, but most abundant (5-10%) protein in animal cells

• exhibits polarity

• structure: two coiled strands

• function: maintain cell shape by resisting tension, move cells via muscle contraction, divide animals cells in two, move organelles + cytoplasm in plants, fungi, animals cause by MYOSIN (motor protein) + actin interaction

intermediate filaments

• serve solely a structural role in eukaryotes

• does not exhibit polarity

• structure: cable like

• function: maintain cell shape + anchor nucleus / other organelles

• nuclear lamins: form a dense mesh in nuclear envelope that anchors chromosomes, nucleus, etc

microtubules

• largest, assembled from subunits of 2 closely related proteins, alpha tubulin + beta tubulin, that under normal conditions exists as stable protein dimers — two parts

• tubulin dimers polymerize in a head-to-tail fashion via non-covalent bonds forming thin chains — protofilaments

• structure: hollow tubes

• function: maintain cell shape via resisting COMPRESSION, move cells via flagella or cilia, move chromosomes in cell division, provide tracks for intracellular transport

• exhibits polarity: + ends growing faster like actin!

• motor proteins move vesicles along microtubules: KINESIN (every step requires energy)

microtubule organizing center (MTOC)

• where the + ends of microtubules grow out of

• most animals have just 1 MTOC near nucleus

• centrosome: MTOC site in animal cells, centrioles: 2 bundles of microtubules

flagella

moves entire cell, consist of several microtubules that move the cell by whipping back and forth + is surrounded by the plasma membrane

cilium (cilia)

moves entire cell, short, hair like projections on eukaryotes

axoneme

the characteristic 9×2 arrangement of microtubules in flagella + cilia — 9 microtubules PAIRS + 2 central microtubules

• basal body: where the 9 axoneme doublets originate

• the beating of cilia requires energy

dynein

motor protein in axoneme doublet arms that require ATP to undergo conformational/shape changes

• transport vesicles

• dynein "arms “walk” on adjacent doublets