Biochemistry: Citric Acid Cycle and Metabolism

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Questions and Answers

What is the first substrate of the citric acid cycle?

Pyruvate

Fatty acids

Acetyl CoA

Citrate (correct)

What molecule is produced during the decarboxylation phase of converting pyruvate to acetyl CoA?

NADH

CO2 (correct)

GTP

Acetyl CoA

How many molecules of CO2 are produced in one cycle of the citric acid cycle?

2 (correct)

Which reduced coenzymes are produced during the oxidation of glucose in the citric acid cycle?

3 NADH and 1 FADH2 Signup and view all the answers

What process occurs during the oxidation phase of converting pyruvate to acetyl CoA?

Removal of H atoms Signup and view all the answers

What is the role of norepinephrine released from sympathetic fibers in adipose tissue during the fasting state?

Stimulates lipolysis Signup and view all the answers

Which hormone is NOT involved in influencing metabolism during the fasting state?

Insulin Signup and view all the answers

What percentage of blood cholesterol is derived from dietary sources?

15% Signup and view all the answers

Which of the following is a function of the liver?

Detoxification of drugs Signup and view all the answers

What is the primary source for synthesizing most of the body's cholesterol?

Acetyl CoA in the liver Signup and view all the answers

What is a major function of Vitamin B1 (thiamine) in the body?

Coenzyme used in removing CO2 from organic compounds Signup and view all the answers

Which vitamin is primarily associated with skin lesions such as cracks at the corners of the mouth?

Vitamin B2 (riboflavin) Signup and view all the answers

Which of the following dietary sources is primarily associated with Vitamin B3 (niacin)?

Nuts, meats, and grains Signup and view all the answers

What are the potential symptoms of Vitamin B5 (pantothenic acid) deficiency?

Fatigue, numbness, and tingling of hands and feet Signup and view all the answers

Vitamin B2 (riboflavin) serves as a component of which coenzymes?

FAD and FMN Signup and view all the answers

What is the energy value of carbohydrates and proteins per gram?

4 kcal/g Signup and view all the answers

Which nutrient is primarily responsible for making ATP in cells?

Glucose Signup and view all the answers

Which of the following food groups is NOT part of USDA's MyPlate?

Meats Signup and view all the answers

What is one primary role of soluble fiber in the diet?

Lowers blood cholesterol levels Signup and view all the answers

What is the primary function of the electron transport chain (ETC) in oxidative phosphorylation?

To directly use oxygen to form water Signup and view all the answers

Which of the following sources contains the most kilocalories per gram?

Lipids Signup and view all the answers

Which molecules provide the high-energy electrons needed for the electron transport chain?

NADH and FADH2 Signup and view all the answers

What happens to excess glucose in the body?

It is converted to glycogen or fat Signup and view all the answers

Which of the following describes what occurs at complex IV of the electron transport chain?

Electron pairs combine with protons and oxygen to form water Signup and view all the answers

What role do cofactors play in the electron transport chain?

They participate in the oxidation and reduction reactions Signup and view all the answers

Which dietary principle emphasizes the consumption of junk food?

Avoid junk food Signup and view all the answers

Which type of carbohydrate provides roughage that aids in defecation?

Cellulose Signup and view all the answers

What is the outcome of chemiosmosis in oxidative phosphorylation?

Synthesis of ATP by adding Pi to ADP Signup and view all the answers

During which phase of oxidative phosphorylation is the proton gradient established?

Phase 1, where electrons are transferred through the ETC Signup and view all the answers

Which of the following best describes the nature of the complexes involved in the electron transport chain?

They consist of clusters of proteins that alternate between being oxidized and reduced Signup and view all the answers

Which two components derived from the Krebs cycle can return to participate in glycolysis and further cycles?

NAD+ and FAD Signup and view all the answers

What is the primary goal of the fasting state?

To maintain blood glucose within normal range Signup and view all the answers

Which process first mobilizes stored glucose to maintain blood glucose levels during fasting?

Glycogenolysis in the liver Signup and view all the answers

What occurs as a result of inadequate insulin production in diabetes mellitus?

High blood glucose levels Signup and view all the answers

What is the primary source of blood glucose during prolonged fasting?

Catabolism of cellular protein Signup and view all the answers

Which message reflects the role of insulin in the fed state?

Insulin directs nearly all events of the fed state. Signup and view all the answers

Which of the following processes provides glycerol for gluconeogenesis during fasting?

Lipolysis in adipose tissues Signup and view all the answers

What is the result of excessive glucose excretion in urine due to high blood glucose levels?

Dehydration and increased urination Signup and view all the answers

During fasting, what is the significance of sparing glucose for organs like the brain?

To maintain energy supply for glucose-dependent organs Signup and view all the answers

Study Notes

Chapter 24: Nutrition, Metabolism, and Energy Balance

Video Connection (Career Connection): Understanding how the body converts nutrients to energy helps advise patients on dietary choices for peak performance.

Part 1-Nutrients

Nutrient: Substance in food needed for growth, maintenance, and repair.
Five Categories:
- Macronutrients: Carbohydrates, lipids, proteins (make up most of diet)
- Micronutrients: Vitamins and minerals (equally important, small requirements)
Essential Nutrients: Approximately 40 molecules must be provided by diet; cannot be synthesized in adequate amounts.
Water: Accounts for ~60% by volume of food.
Energy Value: Measured in kilocalories (kcal).
- 1 kcal = 1 Calorie (C)
- Carbohydrates and proteins: ~4 kcal/g
- Lipids: ~9 kcal/g
USDA's MyPlate: Guidelines represented as portions on a dinner plate.
Basic Dietary Principles:
- Eat only what you need
- Eat plenty of fruits, vegetables, and whole grains
- Avoid junk food

Part 2-Metabolism

Metabolism: Sum of all biochemical reactions in the body that involve nutrients, constantly building up (anabolism) and breaking down (catabolism)
Energy for essential activities: Used even at rest (breathing, absorbing nutrients from food).

24.1 Carbohydrates, Lipids, and Proteins Supply Energy and Are Used as Building Blocks

Dietary Sources (Carbohydrates):
- Primarily plants (except for milk sugar [lactose] and small amounts of glycogen)
- Sugars (monosaccharides and disaccharides): fruits, sugarcane, sugar beets, honey, milk
- Starch (polysaccharide): grains and vegetables
- Insoluble fiber (cellulose): increases stool bulk, facilitates defecation
- Soluble fiber (pectin): reduces blood cholesterol levels
Carbohydrate Uses in the Body:
- Glucose: primary carbohydrate molecule used by cells to make ATP
- Fructose and galactose are converted to glucose before entering circulation.
- Many cells use fat for energy, but neurons and RBCs rely entirely on glucose.
- Excess glucose can be converted to glycogen or fat for later use.
- Carbohydrates also build nucleic acids and cell's glycocalyx.
Dietary Requirements (Carbohydrates):
- Recommended daily intake: 45-65% of total calories (e.g., ~46% for typical American adult).
- Should mostly consist of complex carbohydrates (whole grains, vegetables), rather than simple (monosaccharides and disaccharides).
- Eating large amounts of refined, sugary foods can lead to obesity and nutritional deficiencies.
- Starchy foods are often less expensive than high-protein foods.
Dietary Sources (Lipids):
- Primarily triglycerides (neutral fats).
  - Saturated fats: meat, dairy, coconut
  - Trans fats: hydrogenated oils (e.g., margarine, shortening)
  - Unsaturated fats: seeds, nuts, olive oil, most vegetable oils
- Cholesterol: egg yolk, meats, organ meats, shellfish, milk products
- Liver makes ~85% of blood cholesterol.
- Linoleic acid (omega-6): a component of lecithin
- Linolenic acid (omega-3): fatty acid
Lipid Uses in the Body:
- Adipose tissue: protective cushioning, insulation, energy storage.
- Phospholipids: essential part of myelin sheaths (neurons) and cell membranes
- Cholesterol: stabilizes cell membranes; precursor of bile salts and steroid hormones
- Prostaglandins: regulatory molecules from linolenic acid, play a role in smooth muscle contraction, blood pressure regulation, and inflammation.
- Triglycerides: major energy source for skeletal muscle.
- Fatty acids help the body to absorb fat-soluble vitamins.
Dietary Requirements (Lipids):
- Fats: 20-35% of total caloric intake.
- Limit intake of saturated fat to ≤10% of total fat intake.
- Cholesterol does not need to be part of your diet.
Dietary Sources (Proteins):
- Animal products (eggs, milk, fish, most meats) and soybeans provide complete proteins.
- Legumes, nuts, and cereal grains contain incomplete proteins.
- Combined, cereal grains and legumes provide all essential amino acids.
Essential Amino Acids:
- Histidine and arginine: Essential in infancy but not in adults
- Other essential ones: Tryptophan, methionine, valine, threonine, phenylalanine, leucine, isoleucine, and lysine.
Protein Uses in the Body:
- Structural materials: keratin (skin), collagen/elastin (connective tissue), muscle proteins
- Functional molecules: enzymes and protein hormones, control various activities.
- Multiple factors determine whether amino acids synthesize new proteins or are used for energy (ATP).
- All amino acids needed to build a particular protein must be present at the same time.
- If insufficient amounts of one or more amino acids in a protein exist, amino acids are used as energy rather than being used for the construction of a new protein.
- The requirements of adequate caloric intake determine whether a given protein will be used for energy or stored.
Dietary Requirements (Proteins):
- Needs to supply essential amino acids (and make non-essential ones).
- Amount needed depends on age, size, metabolic rate, current nitrogen balance.
- Rule of thumb: daily intake of 0.8 g per kg body weight.

Part 3-Energy Balance

Energy intake: Energy liberated during food oxidation.
Energy output includes:
- Heat (about 60%)
- Work (driven by ATP)
- Stored fat/glycogen
Heat energy cannot be used by cells for work, but is essential for maintaining body temperature to allow metabolic reactions to occur efficiently.
Body Mass Index (BMI):
- Formula based on height/weight
Overweight: (BMI = 25-30)
Obesity: (BMI > 30)
Risk factors (obesity-related diseases): Chronic low-grade inflammation, impaired insulin function, type 2 diabetes, osteoarthritis, atherosclerosis, hypertension, heart disease, and cancer.
Basal Metabolic Rate (BMR):
- reflects the minimum energy to perform essential activities
Influenced by:
- age/sex
- body fat content
- body temperature
- stress
Thyroxine: Increased O2 consumption, and heat production influencing BMR.
Fasting State/Postabsorptive State: When the GI tract is empty and stored energy is broken down to meet the metabolic demands of the body.
Goal: Maintain blood glucose levels in a normal range (70 -110 mg/100 mL).
- Sources of blood glucose:
  - Glycogenolysis in the liver (immediate reserve)
  - Glycogenolysis in skeletal muscle (begins before liver glycogen is depleted)
  - Lipolysis in adipose tissue and liver (producing glycerol to enter gluconeogenesis in liver
  - Amino acid catabolism of lean muscle tissue (gluconeogenesis)
Glucose sparing: During prolonged fasting, the body uses more non-carbohydrate fuels to conserve glucose. Brain use for glucose while other cells switch to fatty acids/ketone bodies for fuel.
Hormones & Neural Controls (Fasting State):
Glucagon: Raises blood glucose, a hyperglycemic hormone. Released in response to low blood glucose. Targets liver and adipose tissues triggering glycogenolysis/gluconeogenesis.
Sympathetic nervous system: Releases norepinephrine, stimulating lipolysis in adipose tissue, and adrenaline releasing epinephrine from the adrenal medulla which mobilizes fat and promotes glycogenolysis.
Other Hormones: Growth hormone, thyroxine, sex hormones, and corticosteroids influence metabolism and nutrient flow.
Core and Shell Temperatures:
- Body's core (highest temperature) includes the organs within the skull, thoracic, and abdominal cavities.
- Body's shell (lowest temperature in most circumstances) is mainly located on the skin.
Mechanisms of Heat Exchange:
- Radiation
- Conduction
- Convection
- Evaporation
Role of Hypothalamus:
- Main integrating centre for thermoregulation in the anterior region (in specific) of the brain's hypothalamus.
- Receives afferent information from peripheral thermoreceptors (shell), and the sensitive central thermoreceptors within the core including the anterior hypothalamus to blood temperature. -Initiates heat-loss or heat-promoting activities according to the inputs received.
Clinical-Homeostatic Imbalances:
- Hyperthermia
- Hypothermia
- Diabetes mellitus- Inadequate insulin production, or abnormal receptors leaving blood glucose unavailable to most cells. Resulting in high blood glucose levels, glucose in the urine, and metabolic acidosis.
- Metabolic syndrome- A cluster of 5 risk factors affecting heart disease, & stroke, and escalating the risk of type 2 diabetes.

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Description

Test your knowledge on the citric acid cycle and its role in metabolism. This quiz covers key concepts such as substrates, products, and hormonal influences during the fasting state. Gain a deeper understanding of how energy is produced and utilized in biological systems.