Lecture 4 – Lipoproteins, Metabolism and Metabolic Rate

1) What are lipoproteins? Which lipoprotein is used the absorb lipids from the GI tract?

Lipoproteins are lipid-protein packages that transport lipids through the blood. Chylomicrons absorb lipids from the GI tract.

2) Where are VLDLs, LDLs, and HDLs made in the body?

VLDLs, LDLs, and HDLs are all made in the liver.

3) What type of lipid would you mostly find within the VLDLs? What about the LDLs?

VLDLs contain mostly triglycerides, while LDLs contain mostly cholesterol.

4) VLDL’s drop off their lipids primarily within which type of tissue? Which cells of the body will pick up LDLs for the cholesterol inside?

VLDLs drop off lipids primarily in adipose tissue. LDLs are picked up by all body cells for membranes and by testes, ovaries, and adrenal glands for hormone production.

5) HDL’s function to ‘oppose’ both VLDLs and LDLs. What does this mean?

HDLs oppose VLDLs and LDLs by collecting excess lipids and carrying them back to the liver for recycling.

6) Define: metabolism, catabolism and anabolism.

Metabolism is all biochemical reactions in the body. Catabolism breaks molecules down, and anabolism builds larger molecules from smaller ones.

7) What are enzymes needed for and what are cofactors?

Enzymes speed up metabolic reactions. Cofactors (inorganic or organic) are substances required for enzyme function.

8) Glycolysis is considered anaerobic respiration because it doesn’t matter if the cell has oxygen available or not, glucose can be broken down into pyruvate. If the cell doesn’t have enough oxygen available what does this pyruvate get turned into? What if the cell does have oxygen available?

Without oxygen, pyruvate becomes lactic acid. With oxygen, it becomes acetyl CoA and CO₂.

9) What product from the intermediate is the substrate for the citric acid cycle?

The intermediate stage produces acetyl CoA, which enters the citric acid cycle.

10) What is the function of NAD+?

NAD⁺ acts as a coenzyme that carries hydrogen ions and electrons for ATP production.

11) If blood glucose is low, the body can use triglycerides for energy. What must happen to glycerol before it can be used as energy? What must happen to the fatty acids first?

Glycerol must undergo gluconeogenesis to become glucose, while fatty acids undergo beta oxidation to form acetyl CoA.

12) While proteins are not normally used for energy, they can be. What must occur first before an amino acid can enter any of the stages of cellular respiration?

Amino acids must undergo deamination to remove the amine group, forming ketoacids that enter cellular respiration.

13) For how long after a meal is your body in the fed (absorptive) state? What hormone is released during this state?

The fed (absorptive) state lasts about 4 hours after a meal, and insulin is released.

14) This hormone stimulates the storage of nutrients by the body. How? What three things are stimulated during the fed state?

Insulin promotes nutrient storage by stimulating glycogenesis, lipogenesis, and protein synthesis.

15) The body enters the fasting (post absorptive) state how long after eating? What hormone is released during this state?

The fasting (post-absorptive) state begins after 4 hours, and glucagon is released.

16) What is the glucose sparing effect?

The glucose-sparing effect shifts energy use from glucose to fatty acids, preserving glucose for neurons.

17) What does ghrelin do? What does Leptin do?

Ghrelin increases hunger, while leptin promotes satiety (feeling full).

18) How does decreased sleep affect each of these hormones?

Decreased sleep raises ghrelin and lowers leptin, increasing hunger.

19) What two organs/tissues release leptin and how does a high amount of leptin in the blood affect hunger levels?

Stomach and adipose tissue release leptin. Excess leptin causes leptin resistance, reducing fullness signals and increasing hunger.

20) Define metabolic rate. How does this relate to calories?

Metabolic rate is the energy used per time, measured in calories.

21) What is a calorie?

A calorie is the amount of heat needed to raise 1 g of water by 1°C; 1,000 calories = 1 kilocalorie = 1 Calorie.

22) What is the basal metabolic rate and how does this compare to the total metabolic rate?

Basal metabolic rate (BMR) is energy used at rest, while total metabolic rate (TMR) includes BMR plus physical activity.

23) What are the two ways we can measure BMR?

BMR can be measured by a calorimeter (direct heat) or respirometer (oxygen consumption).

24) What causes variations between individuals’ basal metabolic rate

BMR varies with age, lean body mass, gender, and hormone levels (especially thyroid hormones).

25) Total metabolic rate varies because of ….

TMR varies with muscle activity, food intake, and environmental conditions.

26) How do we maintain core body temperature?

Core body temperature is maintained by balancing heat production and loss, controlled by the hypothalamus.

27) What effectors are used by the nervous system to control body temperature?

The nervous system controls sweat glands, skeletal muscles, and blood vessels to regulate temperature.

28) What hormones can affect body temperature? Which one is the most significant?

Epinephrine, norepinephrine, growth hormone, testosterone, and thyroid hormone affect body temperature; thyroid hormone is the most significant.