How are fatty acids transported across membranes in the body? Urgent: Thank you

Passive transport. There are three types of passive transport: simple diffusion, filtration, and facilitated diffusion.

Simple diffusion: also known as lipid soluble diffusion, refers to the diffusion transport of exogenous chemicals from the high concentration side directly through the biological film to the low concentration side, which is the main way for exogenous chemicals to pass through the biological film. No energy consumption, no carrier.

Filtration: The process of passing through hydrophilic, soluble pores on biofilms. With the help of hydrostatic pressure and osmotic pressure.

Water passes through the micropores in the membrane, and the chemicals are transported. Only polar molecules with a molecular weight of less than 100 and uncharged such as water and ethanol can be passed.

Urea, lactic acid.

and other water-soluble small molecules and gas molecules such as O2 and CO2.

Facilitated diffusion: also known as carrier diffusion, refers to the process of using the carrier to move from the high-concentration side through the biofilm to the low-concentration side. No energy is consumed.

As for the first reason asked by the landlord, the answer is related to the structure of the membrane. For example, in the capillary lymphatic membrane, we know that the main structure that makes up the membrane is the phospholipid bilayer, which consists of a hydrophilic polar head and a hydrophobic non-polar tail. Due to this structural characteristic of membrane lipids, they can automatically coalesce in aqueous solution to form a lipid bilayer.

The simple understanding is that because the membrane contains phospholipids, which are lipids, the biofilm is glycerol.

Lipids such as fatty acids are not excluded, so they do not need to consume energy to enter the membrane.

It should be into the cell, simply spreading.

Free proliferation, assisted proliferation, active transport. Substances move in and out of the cell by simple diffusion, which is called free diffusion. Active transport refers to the process of transporting substances into or out of the cell membrane under the action of energy with the assistance of a carrier against the concentration gradient.

Assisted diffusion is also known as facilitated diffusion and facilitated diffusion.

Free diffusion features

diffusion along a concentration gradient (or electrochemical gradient);

There is no need to provide energy;

Without the assistance of membrane proteins.

This mode of transport does not require the assistance of energy and protein, and it is possible to move across the membrane along the concentration difference.

Assists in diffusion characteristics

Higher than free diffusion transport rate;

the presence of a maximum transfer rate; Within a certain limit, the rate of transport is proportional to the concentration of the substance. If a certain limit is exceeded, the concentration will no longer increase, and the transportation will no longer increase. Because the binding site of the carrier protein on the membrane has reached saturation;

Specific, i.e., binding to a specific solute. There are two main types of such special carrier proteins: ionophores and channel proteins.

There is no need to provide energy;

Under the condition of paraconcentration, a specific protein is required to transport the substance, and this transport protein has a certain specificity, that is, a certain substance can only have a specific protein transport.

Active transport of its features

inverse concentration gradient (inverse chemical gradient) transport (there is also a special case of para-concentration gradient in the small intestine transporting glucose);

requires energy (directly powered by ATP) or is coupled to a process that releases energy (co-transport) and is sensitive to metabolic toxicity;

all have carrier proteins and are dependent on membrane transport proteins;

Selective and specific.

Active transport requires ATP to decompose and then provide energy for this movement, which can transport substances against the concentration difference, while at the same time requiring the assistance of specific transport proteins to complete the transport.

Example: Among the following substances that cannot be transported across the membrane into the cell are ()aLipid molecule cPepsin DThreonine c is right, and there are three main ways for substances to be transported across membranes:

1) Free diffusion: O2, CO2, H2O, alcohols, benzene (2) Active transport: various ions, proteins, amino acids, glucose (3) Assisted diffusion:

Hormones, certain small functional proteins, also have a mode of transport that is not part of the transmembrane: endocytosis and exoflux of cells.

K+ and threonine can be actively transported.

Lipid molecules are the substances required by cells to synthesize the cell membranes of various organelles, so because the cell membrane is selectively permeable, it can choose to absorb some of the small molecules required, so lipid molecules can cross the membrane.

Whereas, pepsin belongs to proteins and is a macromolecular substance. It cannot enter cells by transmembrane transport, and pepsin is produced by cells and excreted into the digestive tract and does not enter any cells, pepsin only catalyzes the breakdown of proteins in food. Pepsin is not a hormone that acts on cells.

Lipids are divided into fats, phospholipids, and sterols.

Fats are broken down into glyceric acid for transport, which is freely diffused across the membrane.

Phospholipids diffuse freely.

Sterols including cholesterol, sex hormones, and vitamin D are all small molecules that diffuse freely.

The above is my own, I think it should be right, and the following is from a high school biology textbook.

The fat in food is digested and absorbed to form chylomicrons in the small intestine, and the triglycerides carried by the chylomicrons are mainly transported to the human adipose tissue through the blood circulation. Triglycerides are the most abundant in adipose tissue, accounting for more than 98% of the total triglycerides in the body. Some of the triglycerides stored in adipose tissue are converted into fatty acids and glycerol by enzymes, which are transported to the liver, where liver cells resynthesize triglycerides and store them, which can also be transported to the bloodstream in the form of very low-density lipoproteins.

Therefore, there are two kinds of triglycerides in the blood, one is exogenous, that is, it is obtained from food; The other is endogenous, i.e., resynthesized in the liver.

Lipids enter the cell and diffuse freely, and phospholipids, the main components of the cell membrane, are chemically similar and soluble with lipids.

Free diffusion, because the cell membrane is mainly made up of phospholipids, which are all lipids.

Free diffusion, as lipids are small molecules.