Cell biology

Cell membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism. s are vital to the way cells function. In animal cells, they form the outer layer of the cell – the ultimate barrier between the inside of the cell and its surroundings. In plant cells, the cell surface membrane is inside a relatively rigid cellulosecellulose
A complex carbohydrate which makes up plant cell walls. cell wall but the properties of the membrane still control much of what moves into and out of the cell. Most of the organellesorganelles
A distinct part of the cell, such as the nucleus, ribosome or mitochondrion, which has structure and function. inside a eukaryoticeukaryotic
Cells that make up animals, plants, fungi and protista. They are three-dimensional, membrane-bound sacs containing cytoplasm, a nucleus and a range of membrane-bound organelles. cell are also membrane-bound. Understanding the properties of cell membranecell membrane
The membrane which forms the boundary between the cytoplasm of a cell and the medium surrounding it and controls the movement of substances into and out of the cell. s is key to understanding how cells work.

The structure of the cell membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.

The cell membranecell membrane
The membrane which forms the boundary between the cytoplasm of a cell and the medium surrounding it and controls the movement of substances into and out of the cell. , however, is more than a simple unit membraneunit membrane
Bilayer of polar lipid molecules in an aqueous environment - the basis of the structure of the cell membrane. . Our current model is of a fluid phospholipidphospholipid
A lipid molecule with a hydrophilic region around the ionic phosphate group and a long hydrophobic hydrocarbon tail that forms a bilayer in aqueous solutions. bilayer with many other molecules associated with it, floating or embedded in the lipid sea. These other molecules include cholesterolcholesterol
A lipid which can be measured in the blood. High levels are linked to an increased risk of cardiovascular disease. , glycolipidsglycolipids
Lipids that have a carbohydrate chain attached to them. The carbohydrate chain is attached to the outside of the cell and is part of the cell recognition system. , proteins and glycoproteinsglycoproteins
Proteins that have a carbohydrate chain attached to them. The carbohydrate chain sticks out of the outside of the cell and is part of the cell recognition system. and they all have different functions in the membrane. This is the fluid mosaic modelfluid mosaic model
Our current model of membrane structure consisting of a fluid phospholipid bilayer with many other molecules (including cholesterol, glycolipids, proteins and glycoproteins) floating or embedded in the lipid sea, all with different functions. of membrane structure and it explains many of the properties of membranes that we can observe experimentally.

The fluid mosaic model of the cell membrane.

• A Phospholipids: lipid molecules with a hydrophilichydrophilic
  Molecules that absorb or dissolve in water - usually polar molecules. ‘head’ region around the ionic phosphate groupphosphate group
  A molecule containing phosphorus and oxygen. and a long hydrophobichydrophobic
  Insoluble in water, repel water. hydrocarbon tail that form a bilayer in aqueous solutions.
• B Cholesterol: a lipid with a steroid ring structure, and hydrophilic and hydrophobic regions. It makes up part of the membrane structure - there may be up to one cholesterol molecule for every two phospholipids. Cholesterol makes the membrane stiffer and more rigid – so the amount of cholesterol in the structure affects the rigidity of the membrane.
• C Glycolipids: lipids that have a carbohydratecarbohydrate
  Energy producing organic compounds which are made of carbon, hydrogen and oxygen. Examples of food containing carbohydrate are rice, pasta, bread and potatoes  chain attached to them. The carbohydrate chain is attached to the outside of the cell and is part of the cell recognition system.
• D Proteins: a wide variety of molecules that carry out many of the very specific functions of the cell membrane. There are integral proteins and peripheral proteins. They can form temporary and permanent channels in the membrane, allowing different molecules to pass in and out of the cell. They may be enzymes involved in active transportactive transport
  The process which uses energy to move substances against a concentration gradient or across a partially permeable membrane using a special transport protein. systems or enzymes linked to biochemical pathways such as photosynthesis or respiration. Proteins also act as receptor molecules for other molecules such as hormones and neurotransmittersneurotransmitters
  Chemicals which are released in a synapse when an action potential reaches the end of one neurone. They cross the synaptic gap and trigger and impulse in the next neurone. .
• E Glycoproteins: proteins that have a carbohydrate chain attached to them. The carbohydrate chain sticks out of the outside of the cell and is part of the cell recognition system.