A lipoprotein is a biochemical assembly that contains both proteins and lipids and may be structural or catalytic in function. Lipoproteins may be enzymes, proton pumps, ion pumps, or some combination of these functions.

Examples include the high density and low density lipoproteins of the blood and the transmembrane proteins of the mitochondrion and the chloroplast.

The lipids are often an essential part of the complex, even if they seem to have no catalytic activity themselves. To isolate transmembrane lipoproteins from their associated membranes, detergents are often needed.

All cells need fats and, for all animal cells, cholesterol to build the multiple membranes which cells use to both control water, and water soluble elements, and to organize their internal structure and protein enzymatic systems.

Regulation of Cholesterol

Biosynthesis of cholesterol is directly regulated by the cholesterol levels present, though the homeostatic mechanisms involved are only partly understood. A higher intake in food leads to a net decrease in endogenous production and vice versa.

The main regulatory mechanism is the sensing of intracellular cholesterol in the endoplasmic reticulum by the protein SREBP (Sterol Regulatory Element Binding Protein 1 and 2). In the presence of cholesterol, SREBP is bound to two other proteins: SCAP (SREBP-cleavage activating protein) and Insig-1.

When cholesterol levels fall, Insig-1 dissociates from the SREBP-SCAP complex, allowing the complex to migrate to the Golgi apparatus, where SREBP is cleaved by S1P and S2P (site 1/2 protease), two enzymes that are activated by SCAP when cholesterol levels are low.

Physiology of Cholesterol

Cholesterol is primarily synthesized from acetyl CoA through the HMG-CoA reductase pathway in many cells/tissues. About 20–25% of total daily production (~1 g/day) occurs in the liver, other sites of higher synthesis rates include the intestines, adrenal glands and reproductive organs.

For a person of about 150 pounds (68 kg), typical total body content is about 35 g, typical daily internal production is about 1 g and typical daily dietary intake is 200 to 300 mg. Of the 1,200 to 1,300 mg input to the intestines (via bile production and food intake), about 50% is typically reabsorbed into the bloodstream.


Cholesterol Biochemstry

Cholesterol is a steroid lipid, found in the cell membranes of all body tissues, and transported in the blood plasma of all animals. Most cholesterol is not dietary in origin, it is synthesized internally.

It is present in higher concentrations in tissues which either produce more or have more densely packed membranes; for example the liver, spinal cord, brain and atheroma.

Cholesterol plays a central role in many biochemical processes, but is best known for the association of cardiovascular disease with various lipoprotein cholesterol transport patterns in the blood.

The name originates from the Greek chole- (bile) and stereos (solid), as researchers first identified cholesterol in solid form in gallstones.

Heart disease is caused by narrowing of the coronary arteries that feed the heart. Like any muscle, the heart needs a constant supply of oxygen and nutrients, which are carried to it by the blood in the coronary arteries.

Cholesterol in Children

Many people assume that high cholesterol is a problem that affects middle-aged adults only. In fact, many people don’t even worry about their cholesterol when they are younger, eating all the fatty convenience foods they want, assuming that their early diet makes no difference.

Nothing could be further from the truth. More children today suffer from high cholesterol. In fact, the numbers of children who are taking cholesterol drugs is on the rise! Some studies have suggested that a childhood of poor eating choices can contribute to higher cholesterol later in life.

Besides this, many of the eating habits learned in childhood affects eating in adulthood. Children who are used to eating high-fat foods and convenience foods are more likely to make the same choices as adults. Switching to healthy foods in adulthood may be harder for children who have made less-than-heart-healthy food choices all their lives. For all these reasons, controlling food intake and lifestyle choices even in early life can contribute to life-long heart health and good cholesterol levels.


A low cholesterol diet is achieved by eating foods low in saturated fat and concentrating on the following:

• Use herbs instead of salt in cooking.

• Consume fat free, skim, or 1% dairy products

• Watch out for bottled and canned drinks and especially for sports beverages – many are very high in sodium, calories, and sugars.

• Choose only lean meats. Enjoy white meats, fish, and poultry rather than red meats.

• Eat plenty of fish

• Enjoy only skinless poultry
• Select plenty of whole grain foods

• Eat lots of fruits

• Read food labels and choose foods low in fats (especially saturated, polyunsaturated, and hydrogenated fats), sodium, and cholesterol

• Choose fresh rather than processed, spiced, prepared, pickled or tinned foods. If you cannot find fresh produce out of season, try frozen foods that have no sauces or other ingredients added.

Lean Meat

When you have chosen your lean cuts of meat, you can make these foods even healthier by reducing the amount of fat you use in preparing them. For example, marinating poultry and other meats in lemon juice and fresh dill or in pureed fruits and vegetables is a heart-friendly way to get plenty of flavor into your cooking without adding fat.

At many fish shops, you can get planks of cedar that are perfect for baking or grilling fish – simply place the fish on the cedar, cover with lemon juice and possibly herbs and grill or bake until done.

All meat processed in plants which sell their products across State lines must, under Federal law, be inspected for wholesomeness by USDA’s Food Safety and Inspection Service. This mandatory inspection program is paid for by tax dollars.

Smoothies and Deserts

Combine your favorite fresh fruits in a blender with fresh fruit juice and a small squirt of honey. Combine until blended. This makes an excellent and very healthy snack. It can also be a great quick breakfast on days when you are in a rush.

Experiment with different fruit combinations to find different tastes. Chilling or even freezing some of the fruit before serving can produce a nice chilled drink that is perfect for summer. If you are craving desserts, you can add a small amount of very low fat frozen yogurt to this recipe and use frozen fruits to get a tasty and heart-friendly alternative to ice cream and other desserts.

Desserts and Snacks:

Limiting desserts and snacks in general can help you control your weight and your calories intake and so keep your heart healthy. If you absolutely crave a dessert or snack, though, try to stave off the craving with fresh fruit.