Membranes Flashcards
(22 cards)
How are composed phospholipids
A hydrophilic polar head composed itself of…
glycerol; the backbone of the phospholipid bilayer
A phosphate group to which is usually linked a charged molecule such as choline, ethanol amine or the amino acid serine.
And a non polar hydrophobic tails; two fatty acids
Are phospholipids hydrophilic or hydrophobic ?
They are amphipathic, meaning that they are both:
Hydrophilic; lipid head loves water
And
Hydrophobic; lipid tails are scared of water
What is the consequence of this property?
Phospholipids molecules either form a Micelle or a phospholipid bilayer according depending on the orientation of the molecule.
How are phospholipid bilayers important ?
They are a major constituent of the cell membrane and provide a permeable barrier as well as a matrix for proteins.
How does the phospholipid bilayer functions ?
It excludes water soluble molecules from the non polar interior of bilayer and cell
Ex: Bilayer of the cell is impermeable to large water soluble molecule such as glucose
What factors affect the fluidity of the membrane ?
- The degree of saturation of the fatty acid tail
- The presence of cholesterol
- Patches of membranes that can be less fluid called lipid rafts and that are formed by cholesterol
What are glycolipids and glycoproteins ? What is their utility ?
They are sugars found on lipids or proteins and that act as identification markers.
What are oligosaccharides . Give an example
Small chains of about three to ten monosaccharides linked together.
Ex: glycoproteins and glycolipids
What constitutes the fluid mosaic model
- Phospholipid bilayers
- Protein
- integral membrane proteins
- peripheral intracellulaire membrane protein - Surface markers
- Cholesterol
What are interagir membrane proteins and their distinction with transmembrane proteins
Protein inserted into the phospholipid bilayer. An integral protein that crosses the bilayer completely is called a trans membrane protein.
What are peripheral membrane proteins ?
Proteins attached to the surface of the phospholipid bilayer or to an integral protein
How are (integral) proteins anchored to the membrane, how are the usually arranged?
A protein region called a transmembrane domain and composed of hydrophilic amino acids anchor the protein to the membrane since the fatty acids of the phospholipids are also hydrophobic
The integral membrane proteins are usually arranged in alpha helixes
Can integral membrane protein form beta sheets ?
Yes, and in such case they form pore through the membrane
What differentiates integral membrane proteins from one another
The number of times the protein crosses the membrane
Ex: a single transmembrane domain can be used to anchor the cytoskeleton on the cell, while multiple membrane domains can be used as surface cell receptors for external molecules such as hormones
What are the functions that proteins can serve in the cell membrane
- Transporter
- Enzyme
- Cell surface receptor
- Cell surface marker
- Cell to cell adhesion
- Attachement to cytoskeleton
What are transporter proteins
Proteins that form a channel or carrier that control the movement in and out of the cell. (Membrane are very specific about what goes in and out)
Give example of transporter proteins
Aquaporins: water channels proteins that facilitate the transport of water
Potassium channels function to facilitate the transport of potassium ions in and out the cell. They are found in most cells but most notably in neurones.
Distinction between channel proteins and carrier proteins
Channel proteins have a hydrophilic interior that provides an aqueous channel through which polar molecule can pass when its open.
Carrier proteins bind to the molecule they assist to carry through the membrane
How can you qualify then ?
You can say it is selectively permeable
How are composed phospholipids
Polar hydrophilic head
1. Phosphate group; the charged polar “head” usually has a charged molecule linked to it, such as volume, ethanol amine or the amino acid serine.
