roles of membranes and their structure Flashcards
is it true that biological membranes have different roles depending on whether they are on the outer surface of the cell-plasma membrane or within the cell
yes it is true
what are the two main types of biological membranes
-plasma membrane-(the cell-surface membrane that surrounds the cell
-intracellular membranes
what is the name for membranes contained within the cell
intracellular membranes
are all membranes partially permeable
yes
What is the role of membranes on the surface of cells-the plasma membrane
-acts as partially permeable barrier, controlling the substances that enter an leave the cell/controls enxhange of materials between the internal cell environment an the external environment
-acts as a site of cell signalling/cell communication
explain how the plasma membrane is a site of cell signalling
The cell-surface membrane has receptors which bind to hormones or other chemicals like drugs which triggering a response in the cell
what is the role of membranes within cells
-form concentration gradients in the cell
-they compartmentalize the cell
-they form organelles like vesicles, which they use to transport substances within the cell
-also form lysosomes, which they use to break down worn-out organelles and to engulf and kill pathogens
-site of chemical reactions
-provide attachment sites for enzymes-meaning they separate organelles from the cytoplasm
what is compartmentalisation
it is the separation of organelles and their contents from the cytoplasm via the formation of membrane-bound compartments known as organelles
How can substances cross the partially permeable membranes,both on the surface of the cell and within the cell
-via diffusion
-facilitated diffusion
-active transport
-osmosis
what is the name of the model that describes how biological molecules are arranged to form cell membranes
Fluid Mosaic model
why are cell membranes described as fluid
The phospholipids are free to move within the phospholipid bilayer in relation to each other,giving the membrane flexibility
Why are cell membranes described as a mosaic
desribed as mosaic because the protein molecules are scattered throughout the phospholipid like tiles in a mosaic
-also they have different sizes,positions and shape like tiles in a mosaic
what biological molecules make up the phospholipids bilayer
-phospholipids
-cholesterol
-glycoproteins
-glycolipids
-carrier proteins
-channel proteins
how do phospholipids arrange in water
they form a bilayer
what is the structure of phospholipids
consists of hydrophilic phosphate head and hydrophobic fatty acid tails
explain how phospholipids arrange to form a bilayer
the hydrophilic phosphate heads are attracted to water so face outward and towards it to form hydrogen bond switch surrounding water molecules, allowing membranes to play a role in compartmentalization
the hydrophobic fatty acid tails are repelled by water so face outwards and towards each other creating the hydrophobic core of the phospholipid bilayer
whats the role of the hydrophobic core
it acts as a barrier to water-soluble substances,
it means that water-soluble substances like glucose cannot leak out the cell and unwanted water-soluble substances cannot get in
can phospholipids be chemically modified to act as signalling molecules
yes,they move within the bilayer activating molecules like enzymes
what type of biological molecules does cholesterol fall into
lipids
what is the role of cholesterol.Explain it
it regulates the stability and fluidity of cell membranes.At low temperatures, cholesterol prevents phospholipids’ hydrophobic fatty acid tails from packing too closely together.This increases the fluidity of cell membranes
At high temperatures, cholesterol binds to the hydrophobic fatty acid tails,this stabilises the phospholipids and causes them to pack closely together, reducing the fluidity of cell membranes and increasing their stability.
where is cholesterol present in the phospholipid bilayer
between the hydrophobic fatty acid tails of phospholipids
is cholesterol only hydrophilic
no
cholesterol has one hydrophilic end which interacts with the hydrophilic phosphate heads of phospholipids and they have a hydrphobic end which interacts with the hydrophobic fatty acid tails of phospholipids
does high concentrations of cholesterol in the membrane make it fluid or rigid
rigid
what else does cholesterol control
the impermeability of mebranes to ions and polar molecules,as the membranes become more fluid they become less impermeable to ions and polar molecules as the hydrophobic fatty acid tails of phospholipids are further apart
what are the two types of protein present in the phospholipid bilayer
-intrinsic proteins
-extrinsic proteins
are lipid-soluble molecules able to pass through the membrane
yes,they diffuse by simple diffusion
state two differences between intrinsic and extrinsic proteins
-intrinsic proteins are embedded in both sides of the bilayer, whereas extrinsic proteins are embedded in one
-intrinsic proteins have hydrophobic R groups on their surface, whereas extrinsic proteins have hydrophilic R groups on their surface
what is the role of intrinsic proteins
they are channel and carrrier proteins and transport water soluble substances across the membrane
how do channel proteins also known as pore protein transport charged/polar molecules through the membrane
-they form a hydrophilic channel in the cell membrane
It allows the passive movement, down the concentration gradient of charged/polar molecules only through
how do carrier proteins transport charged/polar molecules through the membranes
they change shape to transport polar/charged particles across the membrane by both passive and active movement of charged/polar molecules across the membrane
do channel protein move molecules through active or passive movemnt
passive meant down concentration gradient so no energy is required
do carrier proteins move molecules by active or passive movement
both active and passive
whats meant by passive movement
movement down the concentration gradient so no energy is required
are they specific to a particular ions/molecule
yes
What is meant by active movement
movement across the concentration gradient so energy is required
whats the role of glycoproteins
-act as antigens thus they play a role in the recognition of cells as self or non-self
-play a role in cell signalling/communication between cells
-acts as receptors, binding sites for hormones
- play a role in cell adhesion, binding to other cells to hold them together in a tissue
-attach to water molecules to stabilise membranes
what are glycoproteins
proteins with a carbohydrate chain attached to them
whats type of chain is attatched to the glycoprotein
carbohydrate chain/sugar chain
are glycoprotein intrinsic or extrinsic proteins
intrinsic
where are extrinsic proteins located
embedded in one side of the bilayer
what r groups do extrinsic proteins have on their surface
hydrophilic ,interact with the polar phosphate heads of phospholipids and with intrinsic proteins
what is the role of extrinsic proteins
they function as enzymes and catalyse reaction inside cells
what are glycolipids
a lipid with a carbohydrate chain attached to it
what chain do glycolipids have attached to them
carbohydrate chain
what is the role of glycolipids
-act as receptors ,binding sites for specific hormones
-act as antigen thus play a role in the recognition of cells as self and non-self
role of protein in membranes
-allow polar ,charged particles to pass through the membrane
role of phosospholipids
acts as barrier to water soluble substances
how do hormones cause a reaction on cells
cell-surface receptors are specific ,hormones bind to complementary receptors which triggers a reaction
explain structure of a membrane bilayer
-contain phospholipids, hydrophilic phosphate heads facing outwards and hydrophobic fatty acids tails facing inwards and towards each other
-it contains intrinsic and extrinsic proteins
-glycolipids and glycoproteins stick out the surface of the membrane/bilayer
-cholesterol between fatty acid tails of phospholipids
describe whats meant by communication between cells
molecules released by one cell .That molecule then attaches to receptors of another cells, causing a change in that cell
describe how a molecule is released from one cell and then makes a difference in another
-the signal molecule is released by one cell via exocytosis
-the glycoproteins and glycolipids in the membrane of the target cell act as receptors
-the receptors on the target cell are specific and are complementary to the shape of the signal molecule
-the attachment of the signal molecule to the receptors causes a change inside the cell
is it true that each transport protein is specific to an ion/molecule
yes
