cell membrane Flashcards
- Give the parts of a cell surface
membrane
Phospholipid bilayer, intrinsic proteins, extrinsic proteins, cholesterol, glycolipids, glycoproteins.
- Where is a membrane found?
The cell surface membrane has a single membrane. A double membrane surrounds the nucleus, chloroplasts and mitochondria. The Golgi apparatus, endoplasmic reticulum and vesicles all have a single membrane.
- Why do phospholipids form a bilayer?
The phosphate group is polar, and attracts water. It is hydrophilic head. The fatty acid tails turn away from water, but mixes readily with fats, these are the hydrophobic tails. The two sets of hydrophilic heads point to the outside of the cell surface membrane, attracted to the water on both sides. The hydrophobic tails point into the centre of the membrane, repelled by the water, to form a bilayer.
- What are extrinsic proteins and
intrinsic proteins?
Extrinsic proteins are only found on one side of the plasma membrane. Intrinsic proteins span from one side to the other.
- What are protein channels?
Proteins that form water-filled tubes to allow water-soluble ions to diffuse across the membrane by facilitated diffusion.
- What are carrier proteins?
Proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane by facilitated diffusion.
- What are the functions of proteins in
the plasma membrane?
Provide structural support, act as channel or carrier proteins for facilitated diffusion, allow active transport through carrier proteins, form cell-surface receptors for identifying cells, help cells adhere together, act as receptors for hormones, embedded enzymes, act as antigens for cell recognition.
- What is the function of cholesterol?
Reduces lateral movement of other molecules, including phospholipids, make the membrane less fluid at high temperatures, hydrophobic so prevents leakage of water and dissolved ions from the cells.
- What is the function of glycolipids?
Act as recognition sites, help maintain the stability of the membrane, help cells attach to one another and form tissues.
- What is the function of glycoproteins?
Act as recognition sites, to help cells attach to one another and form tissues, allows cells to recognise each other, for example lymphocytes.
- Why can molecules not move freely
across the plasma membrane?
They may not be soluble in lipids and therefore cannot pass through, they may be too large for the channels, they may have the same charge as a protein channel, so be repelled. Charged ions cannot pass through the hydrophobic tails.
- Why is it called the fluid mosaic model?
Fluid because the individual molecules can move past each other, giving flexibility. Mosaic, because the proteins that are scattered through the bilayer like a mosaic.
- What are the functions of the internal
plasma membranes?
Control entry and exit from organelles. Separate organelles from cytoplasm, so metabolic reactions can occur. Provide internal transport. Isolate enzymes, that could cause damage. Provide surfaces for reactions to occur.
- What is meant by “membrane fluidity”
How much the components of the membrane (phospholipids, proteins etc) move around laterally.
- What factors can affect membrane fluidity?
increased temperatures make the membrane more fluid. Decreases cholesterol content makes the membrane more fluid. Increased number of unsaturated fatty acids in the phospholipids make the membrane more fluid.
