Unit 2 Exam Nutri Sci Study Guide

Four phases of metabolism

1. Stored proteins/carbs/fats → 2. Break down into amino acids, glucose, glycerol, fatty acids → 3. Energy substrates broken down → 4. TCA cycle harvests energy, electrons transported to produce ATP

Glycemic index definition

The measure of how a carbohydrate-containing food raises blood glucose compared to a reference food (same carb amount)

Glycemic index graph axes

X-axis: Time (hours); Y-axis: Blood glucose levels

Low GI vs. High GI characteristics

Low GI: Slower, flatter blood glucose curve; High GI: Faster, sharper blood glucose peak

Three dietary factors modulating glycemic response

Carbohydrate intake, fiber consumption, meal timing/portions

Two physical factors modulating glycemic response

Exercise/physical activity, body composition (muscle mass vs. fat)

Two ways to manage blood glucose

1. Enhance insulin sensitivity (e.g., aerobic exercise, healthy fats); 2. Reduce glucose spikes (e.g., low GI foods, smaller balanced meals)

Role of aerobic exercise in glucose management

Enhances insulin sensitivity by increasing muscle glucose uptake

Role of high fiber foods in glucose management

Slows digestion, improves insulin response, reduces glucose spikes

Essential amino acids definition

Amino acids that must be obtained from the diet (e.g., tryptophan, isoleucine)

Non-essential amino acids definition

Amino acids the body can synthesize (e.g., arginine, proline)

Semi-essential amino acids definition

Conditionally essential, needed in specific conditions (e.g., cysteine from methionine, tyrosine from phenylalanine)

Transamination process

Moves nitrogen groups between amino acid backbones to form non-essential amino acids

Deamination process

Removes amino group from amino acid, forming ammonia (toxic) → converted to urea in liver → excreted via kidneys

Fates of amino acids

1. Protein synthesis; 2. Non-protein nitrogen compounds

Catabolism

Urea, glucose, ketone bodies, ATP

Amino acid pool

Collection of amino acids from protein turnover and food, used for synthesis or converted to glucose/fat

Metabolic homeostasis

Balance of chemical processes in the body for normal function; disrupted in diseases like diabetes

Protein structure relationship to function

Primary (amino acid sequence) → Secondary (helices/sheets) → Tertiary (3D folding) → Quaternary (protein interactions) determine functions like enzymes, hormones

Central dogma of biochemistry

DNA → transcription → RNA → translation → protein (function)

Transcription process

DNA unzips in nucleus, RNA polymerase makes mRNA copy, mRNA leaves for cytoplasm

Translation process

Ribosome reads mRNA codons, tRNA brings amino acids, forms protein chain until STOP codon

Protein denaturation

Unfolding of protein due to heat, disrupting secondary/tertiary/quaternary structures, inactivating function

Hemoglobin function and structure

Carries oxygen in blood; tetramer with heme (non-protein, holds Fe2+); mutated in sickle cell anemia

Protein functions

Growth/maintenance, enzymes, hormones, antibodies, fluid/electrolyte balance, acid-base balance, transport, energy

Nitrogen balance

Equilibrium where protein intake = output; Positive (intake > output, e.g., pregnancy); Negative (output > intake, e.g., fasting)

Nitrogen balance equation

Protein intake (g)/6.25 - urinary urea N - (0.25 × urinary urea N) - 2 g

Protein quality

Ability of a protein to provide essential amino acids in sufficient amounts

Limiting amino acid

Amino acid in shortest supply, halting protein synthesis unless supplemented

Complete vs. complementary proteins

Complete: Contains all essential amino acids (e.g., soy); Complementary: Two incomplete proteins (e.g., beans + rice) meet needs

Protein digestibility

Measure of amino acids absorbed from a protein source

Biological value (BV)

Percentage of protein nitrogen retained for growth/maintenance after digestion

GI tract: Mouth function

Mechanical breakdown (chewing), saliva with amylase starts starch digestion

GI tract: Stomach function

Secretes acid/pepsin for protein digestion, churns food into chyme

GI tract: Small intestine function

Major site of digestion/absorption, villi/microvilli increase surface area

GI tract: Large intestine function

Absorbs water/electrolytes, forms/stores feces

Peristalsis vs. segmentation

Peristalsis: Propels food; Segmentation: Mixes food for digestion

Common GI problems and nutritional impact

GERD (acid reflux, food restrictions), Celiac (gluten intolerance, malabsorption), Lactose intolerance (low calcium/vitamin D)

Digestion process steps

1. Break down food into monomers (small intestine); 2. Transport across mucosa; 3. Enter blood/lymph

Water/ion absorption (large intestine)

The process by which water and ions are absorbed in the large intestine.

Role of bile in digestion

Emulsifies fats for digestion in small intestine.

Systemic energy balance definition

Balance between energy consumed (food) and energy used (BMR, TEF, activity).

Energy balance equation

Energy in (food intake) = Energy out (body expenditure).

Negative energy balance

Energy out > in, uses stored fat/muscle (e.g., fasting)

Positive energy balance

Energy in > out, stored as fat (e.g., overeating)

Components of energy expenditure

Basal Metabolic Rate (60-75%), Thermic Effect of Food (10%), Physical Activity (15-30%), Adaptive Thermogenesis (variable)

Basal Metabolic Rate (BMR)

Energy for vital functions at rest; modulated by muscle mass, thyroid hormones, age

Thermic Effect of Food (TEF)

Energy for digestion/absorption; highest for protein (20-30%), lowest for fat (0-5%)

Physical activity expenditure

Energy for movement (exercise + NEAT); varies by intensity and body weight

Adaptive thermogenesis

Adjusts energy use for temperature/stress; includes shivering, brown fat heat production

Hormones regulating energy intake

Ghrelin (↑ hunger), Leptin (↓ hunger), Insulin (↓ glucose, fullness), GLP-1 (↓ appetite)

Leptin's systemic effect

Secreted by adipose tissue, signals fullness to hypothalamus, reduces appetite

BMI calculation

BMI = Weight (kg) / Height² (m²); e.g., 70 kg, 1.75 m → 22.86

BMI and disease risk

High BMI associated with diabetes, heart disease, but not definitive for obesity

Metabolism definition

Sum of all chemical reactions in the body to maintain life, including anabolism and catabolism

Anabolism definition

Builds complex molecules from smaller ones, uses ATP (e.g., glycogenesis, protein synthesis)

Catabolism definition

Breaks down complex molecules, releases ATP (e.g., glycolysis, beta-oxidation)

Glycolysis overview

Glucose → 2 Pyruvate in cytoplasm; produces 2 ATP (net) + 2 NADH

Citric Acid Cycle (TCA)

Acetyl-CoA → CO₂, NADH, FADH₂, GTP in mitochondria; feeds ETC

Electron Transport Chain (ETC)

NADH/FADH₂ donate electrons in mitochondria, produce ~28-32 ATP via ATP synthase

Lipid catabolism

Triglycerides → glycerol (glycolysis) + fatty acids (beta-oxidation → Acetyl-CoA); ~100+ ATP per fatty acid

Protein catabolism

Deamination → ammonia → urea; carbon skeleton → pyruvate/Acetyl-CoA/TCA intermediates; ~15-20 ATP per amino acid

Alcohol catabolism

Ethanol → acetaldehyde → acetate → Acetyl-CoA; ~7 kcal/g, inefficient, may lead to fatty liver

Glycogenesis

Glucose → glycogen in liver/muscle, driven by insulin

Lipogenesis

Glucose/fatty acids → triglycerides in adipose tissue, driven by insulin

Gluconeogenesis definition

Creates glucose from non-carb precursors (glycerol, amino acids, lactate) in liver/kidneys

Ketogenesis definition

Produces ketone bodies (acetoacetate, β-hydroxybutyrate) from fatty acids in liver mitochondria

Role of gluconeogenesis in fasting

Maintains blood glucose for brain/RBCs in early fasting (12-48 hours)

Role of ketogenesis in starvation

Provides ketone bodies as alternative fuel for brain/muscles, spares protein after 3-5 days

Fed state metabolism

↑ Insulin, ↓ Glucagon; activates glycolysis, glycogenesis, lipogenesis, protein synthesis

Fasting state metabolism

↑ Glucagon, ↓ Insulin; activates glycogenolysis, gluconeogenesis, lipolysis, ketogenesis

Ketogenic diet metabolism

High fat, low carb; ↑ lipolysis, ketogenesis; ↓ glycolysis, glycogenesis

High-carb diet metabolism

↑ Insulin; ↑ glycolysis, glycogenesis, lipogenesis; ↓ gluconeogenesis, ketogenesis

Intestine role in glucose homeostasis

Absorbs dietary glucose, secretes incretins (GLP-1, GIP) to enhance insulin release

Pancreas role in glucose homeostasis

Beta cells (insulin, ↓ glucose), Alpha cells (glucagon, ↑ glucose)

Liver role in glucose homeostasis

Fed: Glycogenesis, lipogenesis; Fasting: Glycogenolysis, gluconeogenesis, ketogenesis

Muscle role in glucose homeostasis

Fed: Glucose uptake via GLUT4, glycogen synthesis; Fasting: Uses fatty acids/glycogen

Adipose tissue role in glucose homeostasis

Fed: Lipogenesis, fat storage; Fasting: Lipolysis, releases fatty acids/glycerol

Insulin resistance definition

Cells respond poorly to insulin, leading to high blood glucose

Type 1 diabetes definition

Autoimmune destruction of beta cells, no insulin production, onset in childhood

Type 2 diabetes definition

Progressive insulin resistance with relative insulin deficiency, often adult-onset

Factors affecting glycemic response

Insulin sensitivity, genetics, gut microbiome, meal composition, exercise, sleep, stress