Cell membrane and structure Flashcards
Where can cell mambranes be found?
Cell surface membranes surround cell.s
Many organelles are also surrounded by membranes, dividing the cell into different compartments and acting as a barrier between the organelle and the cytoplasm.
Both are partially permeable.
Describe the arrangement of molecules in the membrane.
In the model, phospholipid molecules form a continuous, double layer (bilayer).
This bilayer is ‘fluid’ because the phospholipids are constantly moving.
Describe the roles of different proteins in the cell membrane.
Proteins are scattered through the bilayer, like tiles in a mosaic. These include channel proteins and carrier proteins, which allow large molecules and ions to pass through the membrane. Receptor proteins on the cell-surface membrane allow the cell to detect chemicals released from other cells. The chemicals signal to the cell to respond in some way, e.g. the hormone insulin binds to receptor proteins on liver cells, which tells the cells to absorb glucose.
What else do you need to remember about proteins in the cell mambrane?
Some proteins are able to move sideways through the bilayer, while others are fixed in position.
Some proteins have a polysaccharide (carbohydrate) chain attached these are called glycoproteins.
What do you need to remember about lipids in the cell membrane?
Some lipids also have a polysaccharide chain attached - these are called glycolipids.
What are the roles of the different components of the cell membrane?
The different components of cell membranes have different roles
Phospholipids Form a Barrier to Dissolved Substances
Cholesterol Gives the Membrane Stability
What do you need to rememnber about the structure of phospholipids?
The head is hydrophilic — it attracts water.
The tail is hydrophobic — it repels water.
Diagram of a cell membrane
How does the arrangement of phospholipid molecules affect the movement of substances across cell membranes?
Phospholipids automatically arrange themselves in a bilayer (double layer), with their heads facing outwards and their hydrophobic tails facing inwards. This means the centre of the bilayer is hydrophobic, so it acts as a barrier to water soluble substances,e.g. ions.
What is cholesterol and where is it found
Cholesterol is a lipid found in all cell membranes - except bacterial cell membranes.
What is the role of cholesterol in the cell membrane?
Cholesterol. Cholesterol molecules fit between phospholipids, binding to the hydrophobic tails and causing them to pack more closely together. This restricts their movement, making the membrane less fluid/more rigid.
Cholesterol helps maintain the shape of animal cells (which don’t have cell walls). When is this particularly important?
In cells that aren’t supported by other cells e.g. red blood cells, which float freely in the blood.
According to the fluid mosaic model, how are proteins arranged in the membrane surrounding a mitochondrion?
In a mitochondrial membrane, as in all cell and organelle membranes, proteins are scattered through the phospholipid bilayer like tiles in a mosaic. Some proteins are able to move sideways through the bilayer.
What can the permeability of a cell membrane be affected by?
different conditions: temperature and solvent concerntration
Why can beetroot cells be used to investigate the permeability of the cell membrane is affected by changes in conditions?
e.g. temp.
Plce 5 diff. test tubes containing beetroot and 5cm3 of water in a water bath, each at a diff. temperture, for the same length of time.
Remove the betroot to leave just the coloured liquid.
Use a colorimeter to measure permeability.
The table shows the results of an investigation into the effect of pH on the permeability of beetroot cell membranes. Give a conclusion that can be drawn from the results in the table.
As the pH increases, the absorbance decreases. This means that less pigment was released by the beetroot as the pH increased, so the beetroot cell membranes were less permeable at a higher pH.
