Cell membrane (1st year) Topic 2 Flashcards
What is the plasma membrane?
The plasma membrane of the cell separates the internal contents of the cell from its external environment. It only allows specific substances to enter or leave the cell.
It is differentially permeable
Mention some functions of the plasma membrane.
1) It separates the contents of the cell from its external environment.
2) Communicates with other cells.
3) Regulates the exchange of substances in and out of the cell between the cytoplasm and its external environment.
4) Chemical reactions occur on it.
5) It acts as a receptor site to recognize external stimuli.
What is the plasma membrane made up of?
Phospholipids
What are phospholipid molecules made up of ?
Hydrophilic polar phosphate heads and hydrophobic non-polar fatty acid tails.
How do phospholipid molecules arrange themselves within the cell?
In a single layer they arrange themselves.The hydrophilic phosphate head spread over the surface of the water, whilst the hydrophobic fatty acid tails arrange themselves away from the water,forming a bilayer.
What can we also find on the surface of the plasma membrane?
Glycolipids,glycoprotein,cholesterol, proteins
What is a glycolipid?
carbohydrate + lipid
contains polar and non-polar parts
Also contains carbohydrate side chains which is used for cell signalling.
What is a glycoprotein?
carbohydrate + protein
can be amphipathic (having both polar and non-polar regions). Also contains carbohydrate side chains used for cell signalling
What is cholesterol?
Slightly similar to lipids.
It is slightly polar at one end
What can we call the plasma membrane instead of a phospholipid bilayer?
The fluid mosaic model
What are micelles?
Micelles are spherical structures that form in water which has its hydrophilic phosphate head molecules pointing outward (water-loving),whilst its hydrophobic fatty acid tails pointing inward (water-hating). These structures are important for the absorption of fats in living organisms. They form if there are phospholipids present in large amounts.
What are polar molecules?
Electrons are unevenly distributed, due to the difference in electronegativity between the atoms. Polar molecules never mix with non-polar molecules.
What are non-polar molecules?
Electrons are evenly distributed. No electronegativity between the atoms,therefore there are no charges.
What is freeze-fracturing?
This technique has allowed us to better understand how proteins fit into the phospholipid bilayer. First cells are rapidly frozen ,then the surfaces are cut with a sharp metal blade, and this allows the insides to be examined.
Do phospholipid molecules stay still in the cell?
No,they are constantly moving which means they are fluid.
Differentiate between saturated and unsaturated fatty acid tails.
The fatty acid tails in the plasma membrane can be either saturated or unsaturated. When fatty acid tails are unsaturated,they are more fluid and they move more. The more unsaturated a fatty acid tail is,the more fluid it is. Unsaturation means that there is the presence of double bonds. If a fatty acid tail is bent,it is because it is unsaturated.If it is straight it means that it is saturated.
Mention the different proteins that can be found on the plasma membrane
Integral (intrinsic) proteins: embedded within the membrane)
Transmembrane proteins (proteins that span the width of the entire membrane
Extrinsic (peripheral) proteins: attached to the membrane’s surface
What is the main function of cholesterol in the plasma membrane?
To avoid the phosopholipids from sticking to eachother,therefore making them more fluid. Cholesterol also makes membranes flexible and stable.Also reduces the escape of polar molecules through the membrane.
Can the proteins within the membrane have hydrophilic and hydrophobic regions?
Yes,some parts of a protein can have hydrophilic regions and other parts can have hydrophobic regions within the same protein.
How can we further classify these types of proteins? Specifically the transmembrane.
Channel proteins and carrier proteins
What are carrier and channel proteins?
They are proteins which are responsible in the selective transport of polar molecules and ions across the membrane through facilitated diffusion or active transport.
Can you mention some functions of these proteins within the plasma membrane?
They can be used as receptor molecules to act as receptor sites for cell signalling between cells. For example hormones are chemical messengers which circulate in the blood and bind to specific target cells which have the correct antigens.
Proteins also take part in energy transfer systems in process like photosynthesis and respiration.
What is an antigen?
A cell identity marker. For example glycolipid or glycoprotein.
Draw a diagram of a phosopholipid bilayer,showing cholesterol,protein with labelling
Cells need essential substances like glucose,oxygen,amino acids etc and need to get rid of toxins like carbon dioxide. How do these material pass into and out of the cell through the plasma membrane? Mention 4 transport mechanisms.
Diffusion
Osmosis
Active transport
Bulk transport (endocytosis or exocytosis)