All of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.ll of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.
Many enzymes that occur in certain tissues are found in blood plasma at higher levels when the cancer involves that tissue. Enzymes are usually measured by determining the rate at which they convert a substrate to an end product, while most tumor markers of other types are measured by a test called an immunoassay.
Enzymes are biological molecules that catalyse (speed up) chemical reactions. Enzymes are specificâthey will only work on particular molecules. For example, the enzyme sucrase will only bind with and break bonds in sucrose, not any other type of sugar.nother characteristic of enzymes is that they can be re-used over and over again. A single enzyme will typically catalyse around 10,000 chemical reactions per second. This means that only a tiny amount of enzyme is needed to have a huge effect on a reaction.