Protein Synthesis And Degradation

Front 1

۞ -----Introduction

Back 1

• Adequate protein is necessary for growth
• If either protein or energy are low, poor growth
• Loss of < 30% of body protein mass results in ~ 80% survival
• Loss of > 30% of body protein results in ~ 20% survival

Front 2

۞ ---- distribution of proteins

Back 2

• Make up about 17% of body mass
• Protein functions include


*******In times of stress, muscle proteins are used before the proteins in vital organs such as liver and intestines

Collagen is preserved because it is difficult to degrade

Front 3

۞ -----Function of proteins

Back 3

o Maintain body structure – collagen
o Facilitate mobility – actin and myosin for muscle contractions
o Transport – oxygen transported by Hg, membrane transport
o Metabolism – enzymes
o Regulation – growth factors
o Immune functions – immunoglobulins

Front 4

۞ -----Nitrogen balance

Back 4

Proteins contain about 16% nitrogen

• Nitrogen balance = Nitrogen intake – Nitrogen excretion


• Positive nitrogen balance
o Protein intake exceed excretion = protein for growth


• Negative nitrogen balance
o Protein excretion exceeds intake = body proteins are lost

Front 5

۞ -----Dynamic Protein Assessment

Back 5

Constant Protein turnover: ( includes protein synthesis and degradation)
Average adult makes and degrades equivalent of 400 gms of protein per day (100 gms from diet and 300 gms body proteins)

Front 6

۞ -----Regulation•
**anabolic hormones – increase protein synthesis

Back 6

o insulin – stimulates protein synthesis

o growth hormone – long-term regulation of growth (high in children)

o testosterone - male sex hormone –promotes especially muscle protein. Synthetic testosterone - anabolic steroids, used to build muscle

Front 7

۞ -----Regulation
****catabolic hormones – increase protein breakdown

Back 7

o cortisol (adrenal cortex) decreases protein synthesis and increases protein degradation in muscle. Increased synthesis of enzymes involved in amino acid oxidation


o glucagons – promotes gluconeogenesis


o epinephrine at high levels depressed protein degradation in the whole body and the muscles may be reduced limiting protein loss

Front 8

۞ -----Regulation

****Cytokines----catalolic

Back 8

o Peptides produced by cells of the immune system (macrophages), high in injury and inflammation

o associated with catabolism of body protein

Front 9

۞ -----PROTEIN METABOLISM

Back 9

** post emal anabolism
** brief net loss of protein
** starvation: liver glycogen gonne-----muscle protein used to meet demand for glucose-------prolonged starvation could lead to depletion of muscle protein

----ketone bodies are formed from fat-- can cross the the blood brain barrier and be used by the brain for energy--