NS lec 12

CORNELL RED CROSS CLUB BLOOD DRIVES

• Event Dates and Locations:
  • October 2nd (Thursday):
    • Time: 1:00 PM to 6:00 PM
    • Location: Toni Morrison Multipurpose Room
    • Incentive: Donate and receive a $10 Amazon gift card
  • October 20th (Monday):
    • Time: 11:30 AM to 4:30 PM
    • Location: Stocking Hall 148
    • Incentive: Donate and receive a $10 e-gift card + a chance to win a $5000 prize
  • October 30th (Thursday):
    • Time: 1:00 PM to 6:00 PM
    • Location: Biotechnology Building G-10
    • Incentive: Donate and receive a $10 e-gift card + a chance to win a $5000 prize

PHYSICIAN ASSISTANT ASSOCIATE CLUB (PPAAC)

• Joining Information:
  • Weekly Meetings: Wednesdays 4:45-5:45 PM
  • Location: Rockefeller Hall 110
  • Purpose:
  • Network with others interested in the Pre-PA track
  • Learn about opportunities for Patient Care Experience (PCE) and certifications
  • Participate in panels with current PA students and admissions officers

EXAM REMINDER

• Exam 2 Date:
  • Scheduled for next week (October 8, 2025)

PROTEINS OVERVIEW

Learning Objectives

• Describe the structure of amino acids, defining essential, nonessential, and conditionally essential amino acids.
• List the functions of proteins in the human body.
• Summarize the process of protein digestion and absorption, along with the role of key organs and secretions.
• Explain the concept of protein complementation and the risks of inadequate protein intake.

Definition of Proteins

• Proteins are complex molecules made of amino acids joined together by peptide bonds.

Protein Structure

• Primary Protein Structure: Sequence of a chain of amino acids.
• Secondary Protein Structure: Local folding of the polypeptide chain into helices or sheets (e.g., α-helix, β-pleated sheet).
• Tertiary Protein Structure: Three-dimensional folding pattern of a protein due to interactions between side chains.
• Quaternary Protein Structure: Protein structure consisting of more than one amino acid chain.

Peptide Bonds

• To form proteins, amino acids are linked via peptide bonds:
  • Dipeptide: 2 amino acids linked (AA-AA)
  • Tripeptide: 3 amino acids linked (AA-AA-AA)
  • Polypeptide: Several amino acids linked together.
• Proteins may consist of hundreds (e.g., actin) to thousands (e.g., myosin) of amino acids.
• The human genome encodes approximately 20,000 unique proteins.

From Dietary Amino Acids to Functional Proteins

• Key components:
  • Ribosome: Site of protein synthesis
  • mRNA: Messenger RNA that carries genetic information
  • tRNA: Transfer RNA that brings amino acids to the ribosome
• Central Dogma of Molecular Biology:
  • Transcription: DNA to mRNA
  • Translation: mRNA to protein

Major Functions of Proteins and Amino Acids

• Structure and motion (e.g., collagen, keratin)
• Transport (e.g., hemoglobin, albumin)
• Communication (e.g., hormones, neurotransmitters)
• Catalysis (e.g., enzymes)
• Protection (e.g., antibodies)
• Regulation of fluid balance and pH

Amino Acids

Components of Amino Acids

• Structure includes:
  • A central carbon
  • An amino group (-NH2)
  • A carboxylic acid group (-COOH)
  • R-group (side chain) which differentiates amino acids

Amino Acid Classification

• Essential Amino Acids (9 total): Must be obtained from diet
• Nonessential Amino Acids (11 total): Can be synthesized by the body
  • Conditionally Essential: Some nonessential amino acids become essential under certain circumstances

Properties of Side Chains

• Amino acids can be classified based on their R-groups:
  • Basic, sulfur-containing, cyclic, neutral, aromatic, acidic, and amide groups

Dietary Amino Acids Table

• Essential Amino Acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine
• Nonessential Amino Acids: Alanine, Arginine, Asparagine, Aspartic acid, Glutamic acid, Glutamine, Cysteine, Glycine, Proline, Serine, Tyrosine

PROTEINS IN FOOD AND DIETARY RECOMMENDATIONS

Food Sources

• Complete Proteins: Foods containing all nine essential amino acids
  • Sources: Animal-derived foods (meat, milk, fish, eggs)
• Protein Content in Common Foods:
  • Fats and Sweets: ~0g/serving
  • Milk and Milk Products: ~8g protein/serving
  • Vegetables: ~2g/serving
  • Animal Source Foods: ~7g protein/1 ounce
  • Fruits: 0g/serving
  • Starches: ~3g protein/serving; beans (1/2c): ~7g protein/serving

Protein Quality

• Quality depends on whether the protein source provides all essential amino acids in adequate amounts.

Complete vs. Incomplete Proteins

• Complete Proteins:
  • Foods that contain adequate amounts of all nine essential amino acids (most animal proteins, some plant proteins such as soy, quinoa, hempseed, buckwheat, chia seeds).
• Incomplete Proteins:
  • Foods that lack one or more essential amino acids (most plant proteins, e.g., grains like wheat, corn, rice).
  • Example: Corn is low in lysine and tryptophan.

Protein Complementation

• The process of combining incomplete protein sources to provide all essential amino acids in adequate amounts.
  • Example: Eating corn and beans together.

Recommendations

• Recommended Dietary Allowances (RDA):
  • Expressed as grams per day:
  • 56 g/day for males
  • 46 g/day for females
  • Expressed as grams per kilogram of body weight per day (g/kg/day):
  • 0.8 g/kg/day for healthy adults
• Acceptable Macronutrient Distribution Range (AMDR):
• For adults, 10-35% of daily calories should come from protein.
• Protein grams per day for different weights:
  • 100 lb = 36 g
  • 150 lb = 55 g
  • 200 lb = 72 g
• RDAs increase during periods of growth (infants, children, pregnancy, lactation, athletes).

Current American Protein Intake

• Protein intake is approximately 15% of total energy intake for both men and women:
  • US adults consume about 100 g/day for men and 70 g/day for women.

Expert Opinions on Protein Needs for Athletes

• DRI Committee: No changes to RDA for adult athletes.
• International Society of Sports Nutrition: Suggests 1.4 to 2.0 g/kg/day for athletes may improve training adaptations; higher intakes (>3.0 g/kg/day) may benefit composition for resistance training.
• Academy of Nutrition and Dietetics: Endurance and strength training athletes may need 1.2-2.0 g/kg/day.

Case Study

• Sarah, a cross-country runner weighing 145 pounds: Calculate her estimated protein needs based on the different recommendations.

DIGESTION AND ABSORPTION OF PROTEINS

Overview of Protein Digestion

• Occurs in the stomach and small intestine.
• Stomach: Gastric cells release gastrin, causing gastric juices to be secreted.
  • Hydrochloric acid (HCl) denatures proteins and converts pepsinogen to pepsin, initiating digestion.
• Small Intestine:
  • Partially digested proteins stimulate release of secretin and CCK hormones; pancreatic proenzymes like chymotrypsinogen are activated and digest polypeptides into smaller units (tripeptides, dipeptides, and free amino acids).

Digestion in the Stomach

• Protein digestion begins with HCl and pepsin.
  • HCl denatures proteins (unfolds) and activates pepsin from pepsinogen.
  • Pepsin breaks down proteins into smaller polypeptides (proteolysis).

Digestion in the Small Intestine

• Enterocytes release CCK, stimulating release of pancreatic proteases (e.g., trypsinogen, chymotrypsinogen).
  • Enteropeptidase activates trypsinogen and chymotrypsinogen to trypsin and chymotrypsin.
  • Final digestion results in free amino acids and di- and tri-peptides.

Absorption of Amino Acids

• Most amino acids are absorbed in the duodenum.
• Two transport mechanisms:
  • Passive transport
  • Active transport (e.g., PepT1 H+/peptide co-transporter for dipeptides and tripeptides)
• Amino acids cross the basolateral membrane into circulation via capillaries, eventually entering the liver through the portal vein.

Summary of Macronutrient Digestion

• Provides a complete overview of digestion processes for carbohydrates, lipids, and proteins.

Nutritional Actions by Organ/Gland

CLOSING

• Final Note: Have a good day!