Membranes Flashcards
Cystic fibrosis
Occurs due to improper gene encoding, leads to impaired lung and gastral impairment, no cure lung transplant is often needed
Cystic fibrosis molecular proplems
No cl leaves cells, so no sodium enters, so no water enters the cells resulting in dry thick mucus build up
Plasma membrane
A semipermeable membrane for the uptake of nutrients and the deposits of waste
Internal membranes
Lead to compartmentalization of processes and increased complexity within a cell
Fluid mosaic model
Current view of the cell membrane. Proteins float around lipids rather than exist in a ridged form
Lipid molecules in the mosaic model
Exist in a bilayer less than 10nm. They vibrate, flex back and forth, spin on their axis, and move sideways to switch places with other lipids
Lipid molecules in the mosaic model don’t
Often switch sides between the two sections of the bilayer
Mosaic aspect of the mosaic model
Occurs because most membranes have many different proteins.
Proteins role in the mosaic model
Transport, attachment, signal, transduction, electron transport and anchor protiens
Anchor proteins
Do not more and anchor the cytoskeleton to the membrane
Movement of proteins
In slow because they are bigger than the lipids.
Lipids and proteins
Are often attached to carbohydrate groups
Mitochondrial membrane
Their main job is electron transport so they are high in protein and low in fat
Plasma membrane composition
Equal parts lipids and proteins
Myelin sheath
Insulates nerve fibers. Is high in fats and low in protein
Protein asymmetry
Proteins on one side of the bilayer are different to those on the other because each side has different functions
Example of protein asymetry
Glycolipids, carbohydrate groups, hormones and growth factors are on the outside while proteins that bind to the cytoskeleton are on the inside
Proof of fluid mosaic
Membranes are fluid and membrane asymmetry
Membranes are fluid experiment
1970 Frye and Edidin grew a human and mouse cell while staining their proteins different colors. When the cells were combined they watched the proteins mix
Membrane asymmetry
Proved using the freezing fracture technique
Freezing factor technique
A block of cells is rapidly frozen in liquid nitrogen and then split open separating the bilayers. With an electron microscope researchers observed different proteins
Lipid fabric of the membrane
The foundation of all biological membranes
Lipids include
Fats; phospholipids and steroids
Phospholipids
Dominant lipid in membranes. They have a head and two long hydrocarbon chains called fatty acids
Membranes can
Adjust to a change in lipids as long as the consistency stays the same
Phospholipid head
Consists of a glycerol linked to an alcohol or amino acid
Amphipathic
All phospholipids are. Contain hydrophobic and hydrophilic parts
Fatty acid chains
Non polar (hydrophobic)
Phosphate containing head
Polar (hydrophilic)
Fatty acids can be…
Saturated and unsaturated
Saturated
All carbons are bound to the max amount of hydrogens
Unsaturated
Includes double bonds between carbons, resulting in kinks in the chain
In water phospholipids can become
Micelle, liposome, of a bilayer. Depends on their concentration and they hydrophobic effect
The hydrophobic effect
Polar molecules reject hydrophobic molecules. The tails hide from the water and the lowest energy state is reached.
Influences of the lipid bilayers fluidity
The fatty acid and temperature
Fatty acids
Saturated are tightly packed and rigid where as unsaturated and loosely packed and have more fluidity
Temperature
If it is cooled the motion slows and then stops leading to a semi solid gel. The more unsaturated the cooler it can get before it hardens.
Too cold problems
Decreased permeability, and inhibited function of attached enzymes and receptors
Too hot problems
The membrane becomes too fluid and Na+, K+, Ca2+ can flow too easily killing the cell
Organisms that cannot control body temperature
Control the permeability of their membranes by changing the amount of saturated and unsaturated lipids there are
Fatty acid biosynthesis
The process of forming fatty acids using desaturases
desaturases
A group of enzymes that take saturated fatty acids and remove a H+ from two carbons and introduce a double bond between them
All fatty acids start
Saturated
desaturase abundance
Multiple are needed to make multiple double bonds. Their production is regulated by gene transcription
Cyanobacterium
A bacteria that shows the relationship between a decrease in temperature and a increase in desaturase transcript, desaturase enzyme and in unsaturated fatty acids
Setrols
Impact membrane fluidity. Ex cholesterol
Cholesterol
Found in animals, not plants or prokaryotes. Acts as a buffer to maintain proper fluidity
Too hot cholesterol
Restrains the movement of lipids
Too cold cholesterol
Goes between fatty acids and prevents them from associating with each other
Membrane protiens
Make each membrane unique
4 types of membrane proteins
Transport, enzymatic, signal, attachment/recognition
Transport
They can provide hydrophilic channels or shuttle molecules
Enzymatic activity
Many enzymes are membrane proteins, such as the respiratory and photosynthetic electron transport chain.
Signal transduction
Carry information from receptor proteins to the inside of the cell
Attachment/recognition
Exposed to the internal and external membrane, attachment points for the cytoskeleton, and cell to cell recognition
Integral membrane proteins
Proteins imbedded in phospholipid bilayer
Transmembrane proteins
IMP that transverse the whole lipid layer, they have domains. Primarily polar amino acids
Transmembrane protein domains
Regions with very different polarity. Made up of nonpolar amino acids that form an alpha helix
Alpha helix
A secondary protein structure
Amino acid structure
A primary structure the allows us the determine the transmembrane protein. Mostly non polar
Length of a lipid bilayer
17-20 amino acids
x-membrane spanning domains
The amount of times that a protein spans the membrane
Polar amino acids
Exposed to an aqueous solution
Peripheral membrane proteins
Extracellular and are held on by hydrogen and ionic bonding with integral proteins and membrane lipid molecules. A mixture of polar and non polar membranes
Peripheral membrane proteins location
The cytoplasm side of the membrane and are part of the cytoskeleton.
Peripheral membrane proteins purpose
Have key enzymes for photosynthesis and cellular respiration
