Protein Intro
Exam Grades and Overview
Exam three has been graded and is ready for review; grades will be posted soon.
Overall assessment of the exam grades indicates they look relatively good.
No determination yet on whether a grading curve will be applied.
Students will review the exams together on Thursday.
Transition to Protein Discussion
The lecture is transitioning to the topic of proteins, following previous discussions on carbohydrates and lipids.
Focus will include:
Similar biochemical pathways related to proteins as discussed for carbohydrates.
Specific roles of amino acids, including how they are utilized in the body and how they influence various metabolic processes.
Protein Requirements
Daily Protein Needs
Current Recommended Dietary Allowance (RDA) for protein is set at:
0.8 grams per kilogram of body weight
Conversion: 1 kilogram = 2.2 pounds.
The lecturer believes this RDA is relatively low and emphasizes that protein requirements can vary.
Factors include:
Activity levels
Age (increased needs during growth and development stages).
The primary purpose of the RDA is to prevent deficiencies rather than optimize health.
RDA is set to meet the needs of 95% of healthy adults.
Importance of Protein
Protein serves multiple critical functions in the body including:
Muscle Protein Synthesis
Synthesis of enzymes and hormones
Building structural compounds.
The synthesis of proteins is contingent upon:
Signaling mechanisms that indicate when proteins are needed (stimulus).
Energetics that permit the synthesis of proteins.
Proper digestion and availability of amino acids.
Necessity of Amino Acids
Gene Expression
The primary biological reason for protein intake is to support gene expression.
Proteins are synthesized based upon whether the corresponding genes are activated.
Each protein's production is a product of gene expression, which is influenced by:
Biological signals
Availability of nutrients
Energy levels in the body.
Daily Gene Expression Requirements
The lecturer theorizes that an average adult requires approximately 300 grams of protein to meet gene expression demands over a day.
Actual average protein intake tends to be much lower:
Adult women often consume around 70-80 grams.
Adult men typically consume 100-110 grams.
The concept of an amino acid pool is introduced, which indicates that while amino acids are not formally stored, they can be sourced from muscle tissue when necessary.
Protein Turnover
Proteins in the body are continually replaced through turnover:
On average, there is a cycle where about every protein is replaced approximately four times a year.
Different tissues have varying turnover rates, e.g., muscle proteins versus structural components like ligaments.
Key hormones involved in protein turnover include cortisol, which influences proteolysis (protein breakdown).
Protein Demand in Aging and Health
Sarcopenia
Sarcopenia refers to the loss of skeletal muscle mass and function associated with aging.
Maintaining protein intake is crucial for reducing risks related to age, such as:
Increased risk of fractures (e.g., hip fractures)
Infections and surgical recovery also require adequate protein intake due to the high demand for amino acids in immune responses.
Quality of Life
Protein is essential for:
Mobility
Responding to physical demands without the risk of injury.
Overall quality of life as one ages.
Dietary and Nutritional Considerations
Recommended protein intakes may vary based on:
Body size
Activity levels
Specific fitness or health goals.
The lecturer argues for a protein-centric approach to nutrition, emphasizing the importance of both protein quantity and quality.
For vegetarian or vegan diets, the quality of protein is crucial for meeting nutritional needs.
Essential vs. Non-essential Amino Acids
Definitions
Essential Amino Acids (EAA): Amino acids that cannot be synthesized by the body and must be obtained from the diet (9 in total).
Non-essential Amino Acids (NEAA): Amino acids that can be synthesized by the body (11 in total).
Conditionally Essential Amino Acids: Amino acids that are normally non-essential but become essential under specific conditions (e.g., illness, stress).
Consequences of Deficiencies
Inadequate intake of essential amino acids can hinder protein synthesis leading to:
Impaired enzyme production
Reduced effectiveness in metabolic pathways.
Cells utilize internal resources to find missing amino acids when they are deficient in dietary intake (e.g., scavenge within the cellular pool).
Signaling Mechanisms for Protein Use
The body requires specific signals to regulate when and how much protein is synthesized:
Hormones and other signals direct protein metabolism based on activity levels and dietary intake.
In the event of insufficient amino acids from the diet, signaling mechanisms will prioritize the breakdown of muscle tissue to meet urgent protein demands.
The Role of Amino Acids in Gene Expression
Amino acids, particularly leucine, methionine, and lysine, are crucial for maintaining protein synthesis:
Leucine: Stimulates muscle protein synthesis and is essential for maintaining lean body mass, especially in inactive states.
Methionine: Required for the initiation of protein synthesis and plays a vital role in the one-carbon cycle, essential for DNA synthesis.
Protein Structure and Function
Description of Proteins
Proteins are assembled from amino acids linked by peptide bonds between the amino group and carboxylic acid of each amino acid.
Structural Levels
Primary Structure: The sequence of amino acids.
Secondary Structure: The folding patterns (e.g., alpha helices, beta sheets) due to hydrogen bonding between side chains.
Tertiary Structure: The overall three-dimensional shape of the protein influenced by interactions among the side chains.
Quaternary Structure: Complex formed by the assembly of multiple polypeptide chains.
Protein Creation & Functionality
Protein functionality depends on its ability to fold correctly into a three-dimensional shape, facilitated by the ribosomes and endoplasmic reticulum.
Denaturation occurs during digestion, and only properly folded proteins perform biological functions.