Ns 1150 Prelim 2

What are the three main classifications of carbohydrates?

Monosaccharides, disaccharides, polysaccharides

Name the three monosaccharides.

Glucose, fructose, galactose

What is the main function of glucose?

Serves as the essential energy source for all body functions and physical activity

What are disaccharides and how are they formed/broken down?

Pairs of monosaccharides; formed by condensation reactions, broken down by hydrolysis

Name the three disaccharides and their monosaccharide components.

Maltose = glucose + glucose; Sucrose = glucose + fructose; Lactose = glucose + galactose

What percentage of U.S. adults are lactose intolerant?

About 25%

What are oligosaccharides and how are they digested?

Chains of 3-10 monosaccharides; humans lack enzymes to digest some, so gut bacteria break them down in the large intestine

What are polysaccharides and which are the three main types?

Chains of monosaccharides; glycogen, starches (amylose & amylopectin), and fiber (soluble & insoluble)

Where is glycogen stored in the body?

In animals, mainly liver and skeletal muscle

Name major dietary sources of carbohydrates.

Fruits, vegetables, grains, legumes, milk (contains lactose); animal flesh has little to none

Approximate grams of CHO per serving in milk, vegetables, fruits, and starches?

Milk ~12g, vegetables ~5g, fruits ~15g, starches ~15g

What is the main CHO in milk?

Lactose (glucose + galactose)

What are examples of complex carbohydrates?

Starches (wheat, rice, potatoes, legumes), glycogen, dietary fiber

Difference between whole grains and refined grains?

Whole grains contain bran, germ, and endosperm; refined grains remove bran & germ, losing fiber, vitamins, minerals, and antioxidants

What is high-fructose corn syrup (HFCS) and its composition?

Made from corn starch; ~55% fructose and 45% glucose (vs sucrose at 50/50)

What health issues are linked to excess fructose?

MASLD (metabolic dysfunction-associated steatotic liver disease), increased TG, LDL-C, and visceral fat

Where does carbohydrate digestion begin?

In the mouth with salivary amylase

Why is there no carbohydrate digestion in the stomach?

Acid halts enzymatic activity

Which enzymes in the small intestine break down carbohydrates?

Pancreatic amylase and brush-border enzymes maltase, lactase, and sucrase

Which carbohydrate forms can be absorbed into the bloodstream?

Only monosaccharides

Through what cells are monosaccharides absorbed in the intestine?

Enterocytes

How do fructose and galactose get processed in the liver?

Converted into glucose or glycogen (except excess fructose)

What are the three main metabolic fates of glucose?

used for fuel (glycolysis, Krebs cycle, oxidative phosphorylation), glycogenesis, lipogenesis

What happens to excess glucose when glycogen stores are full?

Converted into fatty acids and triglycerides via lipogenesis

Why is glucose essential for the brain and red blood cells?

Brain/CNS rely primarily on glucose; RBCs use glucose anaerobically as their main fuel

What are the energy reserve functions of glycogen?

Maintains steady blood glucose levels, prevents protein breakdown by reducing gluconeogenesis

What are the roles of soluble and insoluble fibers?

Soluble fiber slows glucose absorption and improves gut health; insoluble fiber increases stool bulk and reduces transit time

What is the RDA for carbohydrate intake?

130 g/day for adults & children (higher in pregnancy/lactation)

What are the guidelines for added sugars?

≤10% of total kcals, ideally

What is the Acceptable Macronutrient Distribution Range (AMDR) for carbohydrates?

45-65% of daily energy intake

For a 2,000 kcal diet, how many grams of carbs is recommended?

~225-325 g CHO/day

What is the adequate intake (AI) of fiber?

Women: 21-25 g/day; Men: 30-38 g/day

What is the 1st Law of Thermodynamics?

Energy can change forms but cannot be created or destroyed.

What are the main macronutrients that provide energy?

Carbohydrates, lipids (fats), and proteins.

What are catabolic pathways?

Metabolic reactions that break down larger molecules into smaller ones, releasing energy.

What are anabolic pathways?

Metabolic reactions that build larger molecules from smaller ones, requiring energy.

Give examples of catabolic pathways.

Glycolysis, β-oxidation, lipolysis, proteolysis.

Give examples of anabolic pathways.

Gluconeogenesis, glycogenesis, lipogenesis.

What is glycolysis?

Breakdown of glucose into two pyruvate molecules (catabolic).

What is β-oxidation?

Breakdown of fatty acids into acetyl-CoA (catabolic).

What is gluconeogenesis?

Synthesis of glucose from noncarbohydrate sources (anabolic).

What is glycogenesis?

Formation of glycogen (anabolic).

What is lipogenesis?

Synthesis of fatty acids and triglycerides (anabolic).

What is ATP and what does it do?

Adenosine triphosphate; it stores and transfers energy for cellular work.

How is ATP produced?

Energy from catabolic reactions is captured in ATP's high-energy phosphate bonds.

How is energy released from ATP?

By hydrolysis of ATP → ADP + Pi, releasing ~7.3 kcal/mol.

How is ATP used in metabolism?

It transfers energy from catabolic to anabolic reactions to make unfavorable reactions favorable.

What is the central metabolic intermediate that links major energy pathways?

Acetyl-CoA.

What are the two possible fates of Acetyl-CoA?

(1) Used for fat synthesis (lipogenesis), (2) enters oxidative phosphorylation to generate ATP.

Where is glycogen primarily stored?

In the liver and skeletal muscle.

Where are triglycerides primarily stored?

In adipose tissue, muscle, and serum.

Can amino acids be stored in the body?

No; during starvation, muscle protein is broken down to generate energy.

What is oxidative phosphorylation?

The primary ATP-producing process at rest and during steady-state exercise (>3 minutes).

Where does oxidative phosphorylation occur?

In the mitochondria.

Which substrates does oxidative phosphorylation primarily use?

fats and carbohydrates.

What are the two subsystems of oxidative phosphorylation?

Aerobic glycolysis (CHO → pyruvate → acetyl-CoA) and aerobic lipolysis (fatty acids → acetyl-CoA).

What are the three main steps of aerobic carbohydrate oxidation?

Glycolysis, TCA (citric acid) cycle, and electron transport chain (ETC).

What happens during the TCA cycle?

Acetyl-CoA is oxidized, generating NADH, FADH2, and GTP (an ATP equivalent).

What is the role of NADH and FADH2?

They carry high-energy electrons to the electron transport chain to power ATP synthesis.

Where are the ETC complexes located?

In the inner mitochondrial membrane (Complexes I-V).

What happens in the ETC?

Electrons are transferred from NADH/FADH2 through carriers, creating a proton (H⁺) gradient.

What is the role of oxygen in oxidative phosphorylation?

Final electron acceptor; combines with hydrogen to form H₂O.

How is ATP synthesized in mitochondria?

Proton gradient drives ATP synthase (Complex V) to generate ATP.

How many ATP are produced from aerobic metabolism?

Approximately 36-38 ATP per glucose molecule (varies by cell type and shuttle system).

Where are triglycerides stored and broken down?

In adipose tissue and muscle; lipolysis breaks them into glycerol and fatty acids.

What happens to fatty acids during aerobic lipolysis?

They are activated, transported into mitochondria, and undergo β-oxidation to form acetyl-CoA.

How many acetyl-CoA molecules are produced from an 18-carbon fatty acid?

9 acetyl-CoA, along with 8 NADH + H⁺ and 8 FADH₂.

What is energy metabolism?

The sum of all chemical reactions that convert nutrients into usable energy.

What is energy balance?

The relationship between energy intake and energy expenditure.

List the three components of total energy expenditure.

Basal metabolism, thermogenesis, and physical activity.

What is basal metabolic rate (BMR)?

Energy required to maintain basic body functions (e.g., respiration, circulation, digestion).

What is thermogenesis?

Energy cost of food processing (digestion, absorption, transport, storage).

What is physical activity in energy expenditure?

Energy used for all voluntary body movements.

Name factors that increase or decrease BMR.

Genetics, age, sex, growth, body weight, body composition, and energy restriction.

How can energy expenditure be measured?

By assessing oxygen consumption, carbon dioxide production, and heat released.

What is calorimetry?

The science of measuring energy change in a system by tracking heat exchange.

What is a bomb calorimeter used for?

Measures the energy (heat of combustion) of food or nutrients.

How much energy (kcal/g) do macronutrients yield?

Carbs: 4 kcal/g, Fat: 9 kcal/g, Protein: 4 kcal/g, Alcohol: 7 kcal/g.

What is indirect calorimetry?

Estimates energy expenditure by measuring respiratory gas exchange (O₂ consumed and CO₂ produced).

What is the Respiratory Exchange Ratio (RER)?

RER = VCO₂ / VO₂; indicates the proportion of carbohydrate vs fat being oxidized for energy.

What does an RER of 1.0 indicate?

Pure carbohydrate oxidation.

What does an RER of 0.7 indicate?

Pure fat oxidation.

What are the three main health effects of excess sugar consumption?

Dental cavities, nutrient deficiencies, and obesity.

How do sugars contribute to dental cavities?

Bacteria ferment sugars, producing acids that erode enamel; sugary, low-pH drinks worsen this.

How do added sugars cause nutrient deficiencies?

They displace nutrient-dense foods in the diet.

What factors contribute to obesity?

Genetic, metabolic, cultural, behavioral, and socioeconomic factors.

What is monogenic obesity?

Obesity caused by single-gene mutations affecting appetite and satiety regulation (e.g., POMC, NPY, LEP, LEPR, MC3R).

What causes energy imbalance leading to obesity?

High intake of energy-dense, high-fat/sugar foods and low physical activity.

What does positive energy balance lead to?

Weight gain.

What does energy balance lead to?

Weight maintenance.

How has global obesity changed since 1990?

Adult obesity more than doubled; adolescent obesity quadrupled; >2.5 billion adults overweight (WHO 2025).

How many children under 5 were overweight in 2024?

About 35 million.

How many children/adolescents aged 5-19 were overweight in 2022?

Over 390 million worldwide.

What diseases are associated with obesity?

Chronic noncommunicable diseases (CVD, diabetes, some cancers).

What is glucose homeostasis?

The hormonal and neural regulation that maintains steady blood glucose levels.

What are GLUT transporters?

Proteins that facilitate glucose uptake into cells via facilitated diffusion.

Which GLUT transporter is insulin-regulated?

GLUT4, found in muscle and adipose tissue.

What organs are the primary players in glucose homeostasis?

Pancreas (insulin, glucagon) and liver (stores/releases glucose).

What are the two main pancreatic cell types involved in glucose regulation?

Beta cells (insulin) and alpha cells (glucagon).

What is insulin's role?

Promotes glucose uptake into cells and energy storage as glycogen and fat.