A&P 2 Lec: Carbs, Lipids, Proteins & Metab states

What are the four primary steps in the metabolism of carbohydrates for energy production?

1. Glycolysis

2. Acetyl CoA formation

3. Citric Acid Cycle

4. Electron-Transport Chain and Chemiosmosis

Why is amino NH₂, so toxic to cells?

Ammonia is highly toxic to cells because it can disrupt pH and cellular metabolism. The body quickly converts it into urea, which is much less toxic and can be safely excreted in urine.

Which hormone tells your brain how much fat you have in your body?

Leptin, as it is secreted by adipose (fat) tissue and signals the brain to help regulate appetite and energy balance

The only hormone that causes proteins to breakdown for fuel production is __.

Cortisol

Which hormone promotes protein synthesis and inhibits protein breakdown?

Insulin

PYY is released when?

Released by the gut after eating, reducing appetite

Who would most likely be in positive nitrogen balance and why?

Pregnant women, athletes, and adolescents are typically in positive nitrogen balance because their bodies are growing or repairing tissue.

When does negative nitrogen balance occur?

When more nitrogen is excreted than ingested, so the body is breaking down more protein than it is making

What are the 3 food intakes?

• Dietary protein

• Dietary carbohydrate

• Dietary triglyceride fat

What are the 4 absorbable units?

• Amino acids

• Glucose

• Fatty acids

• Monoglycerides

Losing electrons = ? Gaining electrons = ?

Losing electrons = Oxidation

Gaining electrons = Reduction

Glycolysis does not need oxygen, so?

It happens in both aerobic and anerobic conditions

What is glycolysis?

Process that breaks glucose into 2 pyruvate in the cytosol; produces 2 ATP and 2 NADH.

What is an example of anaerobic fermentation? What is an example of aerobic respiration?

Anaerobic: Glycolysis

Aerobic: ETC, Citric Acic Cycle

What is anaerobic fermentation?

Reduces pyruvic acid to lactic acid in the absence of oxygen

What is the purpose of fermentation?

To regenerate NAD+ so glycolysis can continue

What is Acetyl-CoA?

A molecule formed from pyruvate that enters the citric acid cycle

What is the citric acid cycle?

A cycle that produces 6 NADH, 2 FADH₂, 2ATP, and 4CO₂ from Acetyl-CoA.

What is the total ATP breakdown of Glycolysis, Citric Acid, and ETC?

• Glycolysis: 2 ATP

• Citric Acid Cycle: 2 ATP

• ETC (oxidative phosphorylation): ~28 ATP

  • Total = 32 ATP per glucose

How many ATP were made by substrate phosphorylation?

The first 4 ATP

How many ATP were made by oxidative phosphorylation?

The next 28 ATP

In which specific part of the cell does glycolysis occur?

The cytoplasm.

In which specific part of the cell does aerobic respiration take place?

Mitochondria

Under anaerobic conditions, pyruvic acid is reduced to _____.

Lactic acid

What is the final electron acceptor in the ETC?

Oxygen

What are amino acids used for?

To build body proteins (structural or secretory products)

What is glucose used for?

For glycogen storage in our liver and muscles and used as metabolic fuel in cells

Where is fatty acids stored?

Adipose tissue

How do we get rid of amino acids (nitrogen)?

Urea, using the restroom

Substrate-level phosphorylation vs oxidative phosphorylation?

Substrate level is direct production of ATP during glycolysis and the citric acid cycle.

Oxidative is ATP production using the electron transport chain and oxygen.

What is formed when oxygen accepts electrons?

Water (H₂O)

Under aerobic conditions, pyruvic acid is oxidized to _____ and H₂O

CO₂

Glycogenesis

The synthesis of glycogen from glucose for storage

• Example: Storage of sugar in the liver and skeletal muscle.

Glycogenolysis

The breakdown of glycogen into glucose

• Example: Releasing stored sugar from the liver during fasting.

Gluconeogenesis

The synthesis of glucose from non-carbohydrate precursors, such as amino acids or fatty acids.

• Example: In the liver and the kidneys

Lipolysis

The breakdown of triglycerides into fatty acids and glycerol.

Lipogenesis

The metabolic process of forming triglycerides from fatty acids and glycerol for storage in adipose tissue.

Beta-oxidation

The breakdown of fatty acids into Acetyl CoA molecules to enter the Citric Acid Cycle to produce ATP energy

The metabolic process of forming ketone bodies from excess Acetyl CoA is called _____.

Ketogenesis

Which primary hormone stimulates the process of lipogenesis?

Insulin

Difference between liver glycogen and skeletal muscle glycogen?

Liver glycogen can break down into glucose that goes into the blood stream, but skeletal muscle glycogen stays in the muscle and is used for energy for the muscle

What are the many ways to stimulate fat breakdown (lipolysis)?

• Epinephrine

• Norepinephrine

• Glucocorticoids

• Thyroid hormone

• GH

Protein synthesis is?

The building of protein from amino acids for storage

Proteolysis

The breakdown of proteins into their constituent amino acids, which can occur during digestion or fuel for gluconeogenesis during stress

The process of removing an amino group (NH₂) from an amino acid is known as _____.

Deamination

The process of transferring an amino group (NH₂) from one molecule to another to create a new amino acid is called _____.

Transamination

During Glycolysis, Glucose is converted to _____.

Pyruvate

Why is excess amount of lipid soluble vitamins dangerous and how can it lead to toxicity?

Unlike water-soluble vitamins, which are easily excreted in urine when you have too much, fat-soluble vitamins (like A, D, E, and K) get stored in fat tissue and the liver. Over time, they can build up to toxic levels.

The process of adding an amino group (NH₂) to a molecule is called _____.

Amination

In the urea cycle, ammonia (NH₃) is combined with CO₂ to produce _____ as a waste product.

Urea

Which hormones are the primary stimulants for protein synthesis?

Stimulated by growth hormone, thyroid hormone, and insulin

How long does the absorptive (fed) state typically last after a meal?

Approximately 4 hours.

The postabsorptive (fasting) state generally begins when the stomach and intestines are _____.

Empty

Which hormone is the dominant regulator of the absorptive state?

Insulin, to promote lower blood glucose levels

Which hormone is the dominant regulator of the postabsorptive state?

Glucagon.

How does insulin affect blood glucose levels?

It decreases blood glucose concentration by increasing cellular uptake.

What stimulates glycogenesis?

Insulin

What is the effect of a high-protein, low-carb meal on insulin and glucagon secretion?

It stimulates the release of both hormones to maintain adequate glucose levels for the brain.

If we were starving, what would our body go for first for metabolic fuel?

1. Carbohydrates

2. Fat

3. Protein

Which metabolic pathways are stimulated by insulin?

Glycolysis, glycogenesis, lipogenesis, and protein synthesis.

Which metabolic pathways are stimulated by glucagon?

Glycogenolysis, gluconeogenesis, and lipolysis.

Which metabolic pathways are stimulated by cortisol?

Gluconeogenesis, protein breakdown (proteolysis), and lipolysis.

Which metabolic pathways are stimulated by epinephrine?

Glycogenolysis, lipolysis, and (in muscle) glycolysis.

Which metabolic pathways are stimulated by growth hormone?

Lipolysis and protein synthesis (and decreased glucose uptake).

Which hormone promotes energy storage and lowers blood glucose?

Insulin

Which hormone primarily raises blood glucose during fasting?

Glucagon

Which glucocorticoid hormone is released during stress to promote protein catabolism?

Cortisol

Which hormone is responsible for the “fight or flight” response?

Epinephrine

Which hormone promotes growth and increases fat breakdown?

Growth hormone

What is the main goal of absorptive state?

To store nutrients and build energy reserves approximately 4 hrs during & after a meal

What is the main goal of the post absorptive state?

To maintain blood glucose levels and provide energy using stored fuels such as glycogen & fat due to stomach & intestines being empty

• approximately more than 4 hrs after a meal

Which pathways are active during the absorptive vs postabsorptive state?

1) Glycolysis, glycogenesis, lipogenesis, and protein synthesis.

2) Glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis.

Which pathways are inhibited by insulin and glucagon?

1) Catabolic pathways (breakdown pathways)

2) Anabolic pathways (storage/building pathways)

Kinase vs Phosphatase

Kinase: Adds phosphate

Phosphatase: Breaks down phosphate

Glucose-sparing effect

Where free fatty acids are oxidized by liver to ketone bodies which other cells absorb and use as their source of energy (leaving glucose for the brain)

What are the effects on target cells?

• Increases cellular uptake of glucose, causing blood glucose to decrease

• Stimulates glucose oxidation, glycogenesis, and lipogenesis

• Inhibits gluconeogenesis

• Stimulates active transport of amino acids into cells and promotes protein synthesis

• Acts on the brain as an adiposity signal

Cachexia

Extreme wasting away associated with chronic diseases like cancer, involving loss of appetite and altered metabolism.

_________ and ________ hydrolyze fat and concert glycerol to glucose?

Adipocytes and Hepatocytes

When is protein used as fuel?

When glycogen and fat reserves are depleted

Which branch of the nervous system regulates the postabsorptive state alongside glucagon?

The sympathetic nervous system.

In postabsorptive state, as blood glucose decreases and insulin decreases, what happens?

The pancreatic alpha cells secrete glucagon

• Promotes glycogenolysis and gluconeogenesis

  • ↑ blood glucose level

Protein is NOT broken down unless?

Starvation/stress (cortisol) is present

Under the conditions of injury, fear, anger, and other forms of stress, which system is activated and promotes glycogenolysis and lipolysis?

Sympathoadrenal system

The sympathetic nervous system innervates what tissue?

The adipose tissue

What stores the MOST energy?

Fats store the MOST energy because they are more reduced than carbohydrates or proteins

Does cortisol raise or lower blood glucose?

Raise

The adrenal gland zone that releases cortisol is the _____.

Zona fasciculata

Why does growth hormone secretion increase when blood glucose levels drop rapidly?

To oppose insulin and increase blood glucose concentration.

Metabolic rate

The total amount of energy liberated in the body per unit of time (e.g., kcal/day or kcal/hr)

Which instrument measures metabolic rate indirectly by calculating oxygen consumption?

A spirometer.

Which instrument measures metabolic rate directly by measuring heat production in a closed chamber?

A calorimeter.

What does the metabolic rate depend on?

Physical activity, mental state, absorptive or postabsorptive status, thyroid hormone, and other hormones

Basal metabolic rate (BMR)

The baseline energy expenditure of a person who is relaxed, awake, fasting, and at a comfortable temperature.

What is the estimated average BMR for an adult male?

2,000 kcal/day, but slightly less for a woman

Total metabolic rate (TMR)

The sum of the BMR and the energy required for voluntary activities like exercise

What factors raise TMR?

• Physical activity, pregnancy, anxiety, fever, eating, catecholamines and thyroid hormones

• High in children and decreases with age

What factors lower TMR?

• Apathy, depression, and prolonged starvation

• As one reduces food intake, the body reduces its metabolic rate to conserve body mass, making weight loss more difficult

True or False: Skeletal muscles share the glucose broken down from their glycogen stores with other organs.

False.

Which enzyme converts glucose to glucose 6-phosphate in all cells and traps glucose inside the cell?

Hexokinase.

Which enzyme, found in the liver, kidneys, and intestinal cells, removes phosphate from G6P to release free glucose into the blood?

Glucose 6-phosphatase.