module 2 - 5.1 structure and function of membranes Flashcards
what does the structure of plasma membranes allow?
allows cells to communicate with each other
what are the 2 types of membranes?
- cell membranes
- cell surface membranes/ plasma membranes
what holds a cell together?
cytoskeleton
which atom is on the end of a fatty acid tail?
oxygen
what is compartmentalisation?
formation of separate membrane-bound areas in a cell
what does compartmentalisation allow for the cell?
- allows different environmental conditions in different parts of the cell
- allows chemical conc. gradient to be made
- allows protection of cellular components
what does a proton pump do inside a membrane?
makes it acidic
what are membranes?
flexible fluid able to break and fuse easily
what are the roles of the cell surface membrane?
- environment
- transport
- cell to cell signalling
- cell to cell joining
- detection of changes in environment
- site of chemical reactions
what does the environment provide for the cell?
provides fixed conditions inside cell cytosol (cytoplasm)
what does transport do for the cell?
provides partially permeable membrane that creates a barrier to some substances, controlling transport of substances in and out of cell
what does cell to cell signalling do for the cell?
has proteins (glycoproteins or lipiproteins) on it which interact with other cells
what is signal transduction?
process of cells responding to substances outside the cell
what does signal transduction do?
detects changes in environment
what do enzymes act as in the membrane?
- site of chemical reactions for the cell
- some proteins in the membrane may be enzymes
what does cell to cell joining allow the cell to do?
tissue formation
is the head of the phospholipid hydrophilic of hydrophobic?
hydrophilic
what is the hydrophilic head made up of?
- phosphate group
- phosphoester bond
- glycerol
is the tail of the phospholipid hydrophilic of hydrophobic?
hydrophobic
what is the hydrophobic tail made up of?
- ester bond
- fatty acid
how are the fatty acid tails positioned?
towards each other they do not overlap e.g.
o==o
o==o
o==o
what is the structure of a phospholipid?
- has a polar head (made of a glycerol and phosphate molecule)
- has 2 fatty acid non-polar tails
- they are amphipathic
what is the arrangement of a phospholipid?
- spontaneously arranged into a bilayer
- hydrophobic tails face inwards, surrounding polar fluids
- 2 hydrophilic heads face outwards, touching extracellular fluids
when do phospholipids form micelles?
when submerged in water
why is a phospholipid amphipathic?
because phospholipids have hydrophilic and lipophilic regions
what does trilaminar mean?
it has 3 layers
which model was proposed by Seymour Singer and Garth Nicolson?
fluid-mosaic model
how is a membrane fluid?
- phospholipids create a viscous (sticky) layer but are free to move within it, relative to each other
- proteins with varying size, shape and position were distributed throughout
how can proteins move in the fluid mosaic model?
freely through the bilayer
what is the ease of the movement of proteins dependent on?
the number of phospholipids with unsaturated fatty acids
what do hydrophobic/ hydrophilic layers do?
restrict entry and exit of substances
when is a phospholipid more fluid?
phospholipids with short or unsaturated fatty acids
how can phospholipids move?
horizontally
how do phospholipids from a bilayer in plasma membranes?
- phospholipids have a polar phosphate group (hydrophobic) that face aq solutions
- fatty acid tails are non-polar, repelled from aq environment
- tissue fluid and cytoplasm are aqueous, phospholipids form 2 layers with hydrophobic tails facing inwards
- hydrophobic phosphate groups face outwards, interact with aq environment by hydrogen bonding
what are intrinsic/ integral proteins?
within the membrane
what type of proteins are intrinsic/ integral proteins?
transmembrane proteins
what are 2 large groups of transmembrane proteins?
channel proteins
carrier proteins
what are channel proteins involved in?
facilitated diffusion
what are carrier proteins involved in?
active transport
where are extrinsic/ peripheral proteins present?
only one side of the membrane
what do extrinsic/ peripheral proteins often have?
amino acids with hydrophilic R groups on the outer surface
what will the amino acids on outer surface of the extrinsic protein bind to?
phospholipid heads or a transmembrane protein
what are glycoproteins?
proteins containing oligosaccharide chains, covalently attached to amino acid R groups
are the polar hydrophilic heads water soluble or water insoluble?
water soluble
are the hydrophobic tails water soluble or water insoluble?
water insoluble
what is the process called when the oligosaccharide chains covalently attach to amino acid R group?
glycosylation
what can glycoproteins be found as?
intrinsic or transmembrane proteins
what are the functions of glycoproteins?
- CELL ADHESION - by tight junctions with proteins: claudin, occluding
- CELL SIGNALLING - e.g receptor proteins for neurotransmitters, hormones and drugs
what are glucolipids?
lipids with monosaccharide or oligosaccharide bound to the lipid
what does oligo- mean?
more than di- and tri- but not as many as poly-
what is the phosphate group in a phospholipid replaced by?
the sugar residue
what are the functions of glycolipids in membranes?
- CELL SURFACE MARKERS for cell to cell signalling
- IMMUNE RESPONSES by acting as antigens (recognition of host cells by viruses)
- ABO BLOOD GROUPS: the 4 main blood types (A, B, AB, O)
what happens during cell to cell signalling?
the saccharide of the glycolipid binds to a specific complementary carbohydrate or carbohydrate-binding protein of a neighboring cell
what are blood types determined by?
by the oligosaccharide attached to a specific glycolipid on the surface of red blood cells (acts as an antigen)
what is cholesterol?
a sterol or modified steriod or type of lipid
what is cholesterol biosynthesized by?
all animal cells
what does cholesterol serve as?
something that comes before the biosynthesis of steroid hormones, bile acid, and vitamin D
what is cholesterol required for?
build and maintain membranes and modulate membrane fluidity
what does the hydroxyl group of each cholesterol molecule interact with?
water surrounding the membrane
(while the bulky steroid and hydrocarbon chain are embedded in the membrane, alongside non-polar fatty acid chains of the other phospholipid)
cholesterol increases membrane packing, what does this do to the membrane?
alters membrane fluidity and maintains membrane integrity so that animal cells don’t need cell walls
what do some transmembrane proteins act as?
enzymes
what are many of the enzymes involved in respiration located as?
transmembrane proteins in the inner mitochondrial membrane
what happens when the formation of ATP from ADP = Pi is energetically unfavourable?
proceed to happen in opposite direction
how do you overcome the formation of ATP from happening in reverse?
ATP synthase couples with ATP synthesis to an electrochemical gradient
what is the electrochemical gradient created by?
the difference in proton (H+) concentration across the inner mitochondrial membrane
what happens during photosynthesis in plants (in terms of ATP)?
ATP is synthesized by ATP synthase using a proton gradient
what is a proton gradient created in?
thylakoid lumen through thylakoid membrane and into the chloroplast stroma
