Chapter 4: Cell membranes and transport Flashcards
What is the function of the Cell Surface Membrane
The Structure of cell surface membranes allows movement of substances between cells and their surroundings and allows cells to communicate with each other by cell signaling
Describe the fluid Moisaic membrane
It is a biological model that describes the structure of the cell membrane. It is descried as fluid because both phospholipids and proteins can move about by diffusion
Describe the other components of the fluid moasic membrane
- The Carbohydrate component of the glycolipids and glycoproteins protrude out into the extracellular environment
- The hydroxyl points point out into the solution in order for it to be soluble.
- There are also Cholesterol molecules, intrinsic and extrinsic proteins and a glycocalyx
Describe the significance of double bond kinks in the hydrocarbon chains of the phospholipid.
They play a major role in the fluidity of the cell membrane. The more double bonded kinks there are, the more fluid will be the cell membrane.
Describe how an unsaturated hydrocarbon s affects the fluidity of a cell membrane
The more unsaturated, the more fluid the membrane. The more single bonds there are in the the hydrocarbons, the more unsaturated it will be.
Name the types of proteins found in the proteins.
- Intrinsic proteins
- Transmembrane proteins
- Extrinsic proteins
What are intrinsic proteins and how do they stay intact
They are found in the inner layer
They stay intact because the hydrophobic regions repels from the water.
They may be found on the inner layer, outer layer or may span the whole membrane.
What are transmembrane proteins? Describe their structure.
They are proteins that span the whole membrane.
The hydrophobic regions which cross the membrane are often made up of one or more alpha chains
Why does intrinsic proteins stay so well in the membrane?
The hydrophobic region made from hydrophobic amino acids are next to the hydrophobic fatty acid tails and are repelled by the watery environment on either side of the membrane.
Explain why the phospholipid molecules are arranged as they are.
The hydrophilic regions, made from hydrophilic amino acids, are repelled by the hydrophobic interior of the membrane and therefore face into the aqueous environment inside or outside the cell, or line hydrophilic pores which pass through the membrane.
What are extrinsic proteins? Describe how these proteins maybe held in the membrane.
These are found on the inner or outer surface of the membrane. Many of these are a bound to the intrinsic proteins. Some are held in other ways e.g by binding to molecules insides or outside the cell or to phospholipids
What differentiates glycoproteins and glycolipids from other proteins and lipids?
They both have branching carbohydrate chains that faces the outside of the membrane.
What is the total thickness of a membrane?
7 nm on average including the cholesterol
What is the primary role of phospholipids?
The form the bilayer which is the basic structure on the membrane
Why is it difficult for polar molecules to pass through the phospholipid bilayer?
What is the consequence of said characteristic?
The tails of the phospholipids are non polar so it is difficult for polar molecules to pass through.
It allows the phospholipid bilayer to act as a very effective bilayer to water soluble molecules. Therefore amino acids and proteins will not leak out of the cell and unwanted molecules may not enter.
What are the ways that a phospholipid could be modified so that it becomes a signalling molecule?
- They may move about the membrane it self to activate other molecules.
- They maybe hydrolysed to release small water soluble signalling molecules.
What is cholesterol?
a small, lipid-related molecule with a hydrophilic
head and a hydrophobic tail which is an essential constituent of membranes, particularly in animal cells, conferring fluidity, flexibility and stability to the membrane
Describe the presence of cholesterol in Animals, plants and prokaryotes.
Animals: They have a very high abundance of cholesterol, almost having as much cholesterol as they have phospholipid.
Plant cells: Its much less common but still there.
Prokaryotes: Never have cholesterol
How does cholesterol affect the fluidity of a cell membrane?
At low temperatures, cholesterol increases the fluidity of the cell membrane, preventing it from becoming too rigid.
What is the benefit to a cell of having cholesterol in its phospholipid hilayers
It ensures that a cell can survive at a colder temperature and its helps stabilise the cell at a higher temperature when the cell could become too fluid.
It also improves the mechanical stability of the membrane, preventing it from breaking off too quickly.
The hydrophobic regions of cholesterol prevents ions from leaking off the membrane.
How do glycoproteins and glycolipids improve the stability of a membrane
The carbohydrate chains project into the watery surroundings of the cell and form hydrogen bonds.
What is the glycocalyx? How is it different between plants and animals?
The Carbohydrate chains projecting out create a sugary coating called the glycocalyx.
In animal cells, it is mainly glycoproteins but in plant cells it is mainly glycoproteins.
What are the 3 main groups of signalling receptors on the cell surface membrane?
- The signalling receptors.
- The receptors involved in endocytosis
- The receptors involved in cell adhesion.
How does the signalling receptors work?
These receptors recognise messenger molecules like hormones and neurotransmitters.
When the messenger molecules binds to the receptor, a series of chemical reactions is triggered inside the cell.
How do receptors to be responsible for endocytosis work?
These bind to molecules that are parts of the structures to be engulfed by the cell surface membrane.
What are antigens?
A substance that is foreign to the body and stimulates an immune response.
What is the function of a transport protein?
They provide hydrophilic channels or passageways for ions and polar molecules to pass through the membrane.
What is the benefit to a cell of having channel proteins and carried proteins
Channel proteins and carrier proteins are very specific to the ion or molecule that they can transport. Therefore they can control the movements of these ions or molecules into and out of the cell.
What are channel proteins?
The channel protein is a membrane protein of a fixed shape which has a water- filled pore through which selected hydrophilic ions or molecules can pass through.
