Module 2: Chapter 5

Contents of the cell membrane

lipids, proteins, carb chains, glycolipids, glycoproteins, cholesterol.

Phospholipids (PLs)

- hydrophilic head (H-bond)
- hydrophobic tails (LDF)
- amphipathic

In aqueous environments PLs

spontaneously arrange with polar regions on the outside and nonpolar on the inside (head-tail-tail-head)

PLs: Shapes

- micelle: big head, single tail
- bilayer
- liposome: enclosed bilayer sphere formed in neutral conditions

Membrane structure: Movement

move within plane, rotate vertically, and fluid

Membrane structure: Fluidity factors

- US FAs: double bonds/kinks, looser packing -> increases fluidity
- S FAs: no double bond/kinks, tighter packing -> decreases fluidity
- cholesterol: 30% of mem mass, amphipathic -> decreases fluidity

Membrane proteins: Transporters

move charged and large particles across the membrane

Membrane proteins: Receptors

detect critical features of the environ; easy signal detectors in cytoplasm

Membrane proteins: Enzymes

functions as a catalyst to increase rate of rxn

Membrane proteins: Anchors

attaches to other proteins to help maintain structure

Integral vs peripheral proteins

- I: permanently attached to mem, CANNOT separate w/o destruction
- P: temporarily attached to mem, CAN separate w/o destruction
- both: act as transporters

Integral proteins: Transmembrane

- span across the bilayer
- 2 hydrophilic and 1 hydrophobic region
- allow for diff functions ie. acting as receptors

Peripheral proteins: info

- inside or outside
- interact via H-bonds
- transmit external signals
- assist other proteins with lipid rafts

Fluid mosaic model of the membrane

lipid bilayer is a fluid structure that allows molecules to move laterally in the membrane; made up of proteins and lipids

Plasma membrane

acts as boundary and maintain intercellular conditions

Facilitated diffusion vs active transport

- FD: transport molecules via channels with gradient
- AT: transport molecules via carriers against gradient (ATP!)
- both: transport large/polar/charged molecules in PL bilayer

Types of membrane transporters: Channel

openings that allow specific molecules inside the membrane

Types of membrane transporters: Carrier

binds, changes configuration and allows molecule transport

Types of membrane transporters: Aquaporins

type of channel that allows water movement across membrane via FD

Osmotic conditions

- hypertonic: too much solute
- hypotonic: too much water
- isotonic: equal parts water and solute

AT: Primary active transport

form of AT that DIRECTLY uses ATP; ie. Na + K pump

AT: Secondary active transport

- transporter proteins build up ion concen'n gradient
- motive force drives transport
- primary transport -> chemical gradient -> movement against gradient

Structures that help change cell shape

- plants: central storage vacuole (turgor pressure)
- animals: contractile vacuoles

Plant cell wall thingz

have polysaccharides in walls ie. cellulose

Fungi cell wall thingz

have chitin and other sugars

Bacteria cell wall thingz

polymers of a.acids and sugars, peptidoglycan

Cell shape/size maintenance factors

- AT regulates solute concen'n
- cell walls provide structure
- vacuoles

Prokaryote vs eukaryote organization

- E have nucleus, P have plasmids and DNA in nucleoid
- E have sterols, P have hopanoids
- E size > P size
- P lack extensive internal compartmentalization
- P absorb nutrients from environment for metabolism

Endomembrane system: Organelles

- nuclear envelope
- ERs
- Golgi apparatus
- lysosomes
- plasma membrane
- vesicles

Exocytosis vs Endocytosis

- Ex: expel contents out of membrane
- En: bring contents into membrane
- both: use vesicles to transport

Endomembrane system: Nucleus

- stores genetic material of cell
- has two membranes; nuclear envelope and pores
- allow movement of info ie. transcriptional factors

Endomembrane system: ERs

- single membrane, attached to nucleus, transport, have lumens
- Rough ER: ribosomes/protein synthesis
- Smooth ER: lipid synthesis

Endomembrane system: Golgi body

- sort and modify proteins/lipids from ER (ie. glycosylation)
- site of carb synthesis
- sometimes recycles things by redirecting transport to ER

Endomembrane system: Lysosomes

- specialized vesicles from Golgi that degrade macromolecules
- proton pumps maintain pH, transporters move degraded matter out
- ideal internal pH = 5

Protein sorting

- direct proteins to cyto, lumen, endomembrane sys or out of cell
- Cytosol ribo pros: no signals, remain in cytosol
- Mem-bound ribo pros: have signal sequences, get recognized and sorted

Protein sorting: Signals

- no signal -> cytosol
- amino acid signal -> mito or chloro
- nuclear localization signal -> nucleus

SRP signal interactions

- SRP binds to a.acid chain, halts translation
- SRP binds to SRP receptor on ER membrane
- ribosome connects with ER, polypeptide chain goes through ER channel
- chain enters ER space it can stay, go to other organelle's lumen, exit cell

Signal anchor sequence (SAS)

- pros goes through channel until SAS sequence is reached
- ER channel releases protein in membrane space
- translation occurs, it stays in membrane

Mitochondrion

- double membrane
- harness energy from macro and turn into ATP
- site of cellular respiration

Chloroplast

- triple membrane (in, out, thylakoid)
- capture solar energy and turn into sugars
- site of photosynthesis; done via pigment network