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What are the five primary functions of lipids in the human body?
Provide and store energy, Cushion and protect internal organs, Aid in the absorption of fat-soluble vitamins (A, D, E, K), Provide essential fatty acids, Contribute to cell membrane structure and hormone production.
What is the primary lipid component of cell membranes?
Phospholipids
How are phospholipids structured?
They consist of a hydrophilic “head” (phosphate group) and two hydrophobic “tails” (fatty acid chains).
What is cholesterol’s specific function in the body?
Cholesterol is the precursor for bile acids, vitamin D, and steroid hormones.
Why is cholesterol considered non-essential?
The body can synthesize it internally (mainly in the liver), so it does not have to come from the diet.
Which lipid is the most abundant in our diet and serves as the primary storage form of fat in our bodies?
Triglycerides are both the most abundant dietary lipid and the main storage form of fat in our bodies.
What is the chemical structure of a triglyceride?
A triglyceride consists of a glycerol “head” molecule bonded to three fatty acid “tails.”
What is the structure and state of saturated fatty acids at room temperature?
Have no double bonds in their carbon chains; they are typically solid at room temperature.
What is the structure and state of unsaturated fatty acids at room temperature?
Have one or more double bonds; they are typically liquid at room temperature.
What is the role of bile acids in fat digestion?
Bile acids (produced by the liver, stored in the gallbladder) emulsify large fat droplets into smaller ones to aid digestion.
What is the role of lipase in fat digestion?
Lipase (primarily pancreatic lipase) chemically breaks down fats (triglycerides) into free fatty acids and monoglycerides.
What are the two essential fatty acids, and which one is most recommended to increase in the typical American diet?
omega-3 and omega-6. Omega-3 is recommended
What is the primary site in the gastrointestinal tract for fat absorption?
The small intestine
Name the four major lipoproteins
Chylomicrons, VLDL, LDL, HDL
Which lipoprotein contains the highest percentage of triglycerides?
Chylomicrons
Which lipoprotein has the highest percentage of protein?
HDL
Which lipoprotein is responsible for picking up cholesterol from body cells and returning it to the liver?
HDL (“good” cholesterol) picks up cholesterol from cells and returns it to the liver.
According to the Acceptable Macronutrient Distribution Range (AMDR), what is the recommended percentage range for dietary lipids?
20% to 35% of total calories should come from lipids (fats).
How do you calculate minimum fat grams for someone on a 3,600-calorie diet, given the lower AMDR limit of 20%?
3,600 calories × 0.20 = 720 calories from fat.
720 ÷ 9 (cal/g) = 80 grams of fat
What is a primary dietary source of trans fats?
Partially hydrogenated oils
Why are trans fats considered harmful?
Trans fats raise LDL (bad) cholesterol and lower HDL (good) cholesterol, contributing to increased risk of heart disease.
What is a cis unsaturated fatty acid?
The hydrogen atoms are on the same side of the double bond (naturally occurring).
What is trans fatty acid?
The hydrogen atoms are on opposite sides of the double bond (often produced by partial hydrogenation).
What was one of the most important findings of the Bogalusa Heart Study led by Dr. Gerald Berenson?
It showed that heart disease begins in childhood, demonstrating that signs of atherosclerosis can be found in very young individuals.
What is atherosclerosis?
long-term, inflammatory disease where arteries narrow and lose elasticity due to plaque buildup.
How does atherosclerosis develop?
It begins with the infiltration of LDL into the arterial lining, triggering an inflammatory response and plaque formation.
What are some modifiable risk factors for cardiovascular disease (CVD)?
High LDL cholesterol.
Low HDL cholesterol.
Smoking.
Physical inactivity.
Obesity.
Poor diet (high in saturated/trans fats).
High blood pressure.
Diabetes or poor blood glucose control.
What dietary suggestion is recommended regarding saturated fat intake to reduce CVD risk?
Keep saturated fat as low as 7% of total calories, but do not completely eliminate all saturated fat from the diet.
List some main functions of proteins in the body.
Enzyme and hormone production.
Tissue structure (muscles, bones, skin, etc.).
Transport of nutrients.
Immune function (antibodies).
Fluid balance maintenance.
What unique structural feature differentiates one amino acid from another?
The side chain (R-group) is unique for each amino acid.
What is the primary role of amino acids?
Their primary role is to serve as building blocks for proteins.
How do amino acids form protein?
Amino acids are linked by peptide bonds to form proteins.
What is protein denaturation?
process in which a protein’s three-dimensional structure unravels, losing its function.
What factors can cause protein denaturation?
It can be caused by heat, acid, alcohol, or mechanical agitation.
What is the main purpose of protein turnover in the body?
allows the body to continually break down and rebuild proteins, making it possible to adapt to changing needs and maintain healthy tissues.
How do you calculate the protein RDA (Recommended Dietary Allowance) for a healthy adult?
0.8 g of protein per kg of body weight per day.
For example, a 154 lb adult:
Convert pounds to kg: 154 ÷ 2.2 ≈ 70 kg.
Multiply by 0.8 g/kg: 70 × 0.8 = 56 g of protein/day.
What is the recommended protein intake for elderly individuals over 65 years old to maintain lean body mass?
1.2 g/kg/day is recommended for older adults to help maintain lean body mass.
Where does protein digestion begin?
It begins in the stomach with acidic juices and pepsin starting to break down proteins.
What happens during protein digestion?
In the small intestine, proteases (enzymes) break proteins into individual amino acids, which are then absorbed into the bloodstream.
What are the possible fates of amino acids in the body once absorbed?
Used to make new proteins.
Used to produce energy if needed.
Converted to glucose or fat (if excess).
What is nitrogen balance?
Nitrogen balance compares the amount of nitrogen (from protein) entering the body versus leaving.
What is a positive nitrogen balance?
A positive nitrogen balance occurs when intake exceeds excretion, typically seen during growth, pregnancy, or muscle building.
What are complete proteins?
Complete proteins contain all essential amino acids in the right proportions.
Where are complete proteins primarily found?
They are primarily found in animal-based foods such as eggs, meat, fish, and dairy.
What is a common misconception about combining incomplete proteins?
You must eat all incomplete proteins together at one meal to form a complete protein.
What is actually true about incomplete proteins?
Complementary proteins can be combined over the course of a day to ensure all essential amino acids are consumed.
What is Kwashiorkor?
Primarily protein deficiency with adequate calories; symptoms often include edema (swollen belly), muscle wasting, and enlarged fatty liver.
What is Marasmus?
Deficiency of both calories and protein; symptoms include severe wasting of muscle and fat, stunted growth, and overall emaciation.
What is energy metabolism in the human body?
It is the process of breaking down fuels (glucose, fatty acids, and amino acids) to generate ATP and storing excess fuels when not immediately needed.
What makes ATP the “energy currency” of the cell?
ATP stores and transfers energy within cells, Its high-energy phosphate bonds release energy when broken, and this energy powers various cellular processes (muscle contraction, active transport, etc.).
Which cell organelle is primarily responsible for producing ATP?
The mitochondria are the main sites of ATP production in cells.
What are the coenzymes NADH and FADH2, and what is their primary role?
They are electron carriers that transport electrons and hydrogen ions (H+) to the electron transport chain, where ATP is generated.
How do glucose, fatty acids, and amino acids enter the citric acid cycle for ATP production?
All energy-yielding nutrients are first converted to acetyl-CoA, which then enters the citric acid cycle.
Briefly outline the three main steps of glucose metabolism.
Glycolysis (in the cytosol)
Citric Acid Cycle (in the mitochondrial matrix)
Electron Transport Chain (in the inner mitochondrial membrane)
What are its primary products of the citric acid cycle?
3 NADH
1 FADH2
2 CO2
1 GTP (which can convert to ATP)
What is β-oxidation, and where does it occur?
β-oxidation occurs in mitochondrial matrix and is the process of breaking down fatty acids in the mitochondria to two-carbon acetyl-CoA units.
How many acetyl-CoA molecules are generated from a 20-carbon fatty acid during β-oxidation?
A 20-carbon fatty acid yields 10 acetyl-CoA molecules, as each pair of carbons becomes an acetyl-CoA
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