Biological Membranes Flashcards
What is the role of PLASMA/CELL SURFACE membranes?
Surrounding all cells, SEPARATING the CELLS CONTENTS from the OUTSIDE WORLD are membranes.
What are membranes found around in eukaryotic cells?
In eukaryotic cells membranes are also found around many organelles.
What are membranes made up of?
Membranes are made up of molecules called phospholipids
What is the role of membranes at the surface of cells?
The plasma membrane has many roles at the surface of cells:
It separates the cell from environment - helps creates concentration gradient
It controls the exit and entry of molecules and ions - provide selective permeability
It’s involved in FACILITATED diffusion, active uptake and osmosis
It’s involved in cell recognition (glycoproteins)
It’s involved in cell to cell attachment (glycoproteins)
It acts as a receptor for hormones over neurotransmitters
What is the role of membranes within cells?
The membrane around many organelles present in eukaryotic cells separate the organelles contents from the cells CYTOPLASM so each organelle is a discrete entity and is able to perform its function
It helps COMPARTMENTALISE/surround organelles e.g. Mitochondria/golgi
It is involved in the ISOLATION of contents e.g. Isolate DNA(nucleus)
It is a SITE for attachment of ribosomes (e.g. Nuclear envelope)
It provides selective permeability
It helps create concentration gradients
What are the differences and similarities between phospholipids and triglycerides?
Differences:
- phosphate group
- 2 fatty acid tails
- 2 ester bonds
Similarity:
Both have glycerol
Both have fatty acid
Both have ester bond
What is a phospholipid molecule made up of?
The phospholipid molecule is made up of :
A Phosphate Glycerol head
Bonded to 2 fatty acid tails
What is hydrophilic and hydrophobic in phospholipid?
Phospholipid head is hydrophilic attracted to water
Phospholipid tail is hydrophobic not attracted to water
What is a polar molecule ?
A polar molecule is any molecule with charge
What is a non polar molecule ?
A non polar molecule is any molecule that DOES NOT have an overall charge
What is the distribution of electrons like in non-polar molecules?
In non-polar molecules the electrons are distributed more SYMMETRICALLY
and thus does not have an abundance of CHARGES at the OPPOSITE sides.
The charges all CANCEL out.
Is the phosphate head polar or non polar?
Polar
Negatively charged
Is the fatty acid tail polar or non polar ?
Non poplar
How is the phospholipid bilayer created?
The cytoplasm inside a cell contains a lot of water,
and so does the fluid outside cells.
Due to this the phospholipid molecules group in order to shield the hydrophobic tails from water
But keeping the hydrophilic heads drawn to water
This causes the phospholipids to arrange themselves in a double layer with the heads facing out toward the water and tails inside form water
This is called a phospholipid bilayer..
What does ‘plasma membranes are partially permeable’ mean ?
Partially permeable means that some substances can pass through others cannot
How thick are cell membranes?
7-10nm
What is the phospholipid bilayer also made up of?
The phospholipid bilayer is also made up of many different types of molecules
What did SINGER and NICHOLSON do in 1972?
In 1972 singer and Nicholson proposed a model of how all the compounds found in cell membranes might be arranges to form a biological membrane.
What is the term fluid mosaic model used to describe?
The term fluid-mosaic is used to describe the molecular arrangements in membranes. The main features are:
- Phospholipid bilayer
- Intrinsic proteins - extend right across the bilayer
- Extrinsic proteins - are partially embedded in the bilayer
What do intrinsic proteins act as?q
Instrinsic proteins which are extend right across the bilayer act as CHANNEL proteins or CARRIER proteins to help move substances across the membrane
What do extrinsic proteins act as?
Extrinsic proteins are partially embedded in the bilayer
These are involved in cell recognition
What does fluid mosaic mean?
Fluid = molecules move around Mosaic = proteins floating amongst phospholipids so it's not just made of phospholipids
Why is the arrangement the fluid mosaic model suggests ideal for cell membranes?
Such an arrangement is ideal for cell membranes as lipid bilayers tend to reseal themselves once disturbed or torn.
There are additional chemical components that make up the membrane:
Glycolipids
Glycoproteins
Phospholipid
Cholesterol molecules
What is the role of glycolipids?
Glycolipids play a part in COMMUNICATION BETWEEN CELLS and CELL TO CELL RECOGNITION
What is the role of phospholipid?
Phospholipids act as a barrier to polar/charged particles
Phospholipids select what enters or leaves the cell
What is the function of glycoproteins?
Glycoproteins have several functions:
- they act as surface antigens and are involved in cell recognition (enabling cells to distinguish self from non-self)
- cell to cell attachment - holds cells together in a TISSUE
They act as a receptor for HORMONES DRUGS TRANSPORT PROTEINS
- cell signalling
What is the role of cholesterol molecules?
Cholesterol molecules are positioned within the bilayer
Cholesterol molecules help STABILISE the membrane by MAINTAINING FLUIDITY
Reducing permeability to polar/charged molecules e.g. After and ionic cannot pass easily
What make up the GLYCOCALYX?
The glycoproteins and glycolipids make up the GLYCOCALYX
What is the glycocalyx?
The glycocalyx is a carbohydrate base covering
that covers the outside of cells
