Chapter 7 - Protein Objectives: Review the basic structure of proteins and their component amino...
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Transcript of Chapter 7 - Protein Objectives: Review the basic structure of proteins and their component amino...
Chapter 7 - ProteinObjectives:• Review the basic structure of proteins and their component amino
acids
• Learn which are the essential amino acids and why
• Understand that there are various amino acid “pools” within the body including dietary and body tissue pools
• Learn how amino acids can be used for
The synthesis of new proteins for growth or replacement of cellular proteins
Production of important non-protein nitrogen containing molecules
Oxidation as an energy source
Synthesis of glucose, ketones or fatty acids
• Understand how the liver and muscle handle amino acid metabolism, and how brain function is closely related to some amino acid metabolism
• Learn how to determine the “quality” of the protein you eat, what the recommended intakes are and why
Fig. 7-1, p. 175
Functional roles of proteins:
Structural organization
Table 7-1a1, p. 178
Table 7-1a2, p. 178
Table 7-1b, p. 179
Key Ideas: the tertiary structure of a protein is determined by its amino acid composition and amino acid side chain chemistry determines what our bodies can do with them metabolically
Sources of Protein
Exogenous Sources• Animal products such as meat, poultry, fish, and
dairy products (not including butter, sour cream, or cream cheese)
• Plant products such as grains, grain products, legumes, and vegetables
Endogenous Sources• Desquamated mucosal cells (50g protein/day)• Digestive enzymes and glycoproteins (17g/day)
(total daily requirement for protein for males is 56g/day, for females it is 46 g/day)
Table 7-2, p. 182
Digestion of Proteins – pepsin only works on exogenous proteins, all other enzymes work on both exogenous and endogenous proteins
Step 1
Amino acid transporter
Cytosol
Intracellular amino acid metabolism
Na+ /K +
ATPase
Step 2
Cell membrane
Step 3
Step 4
Step 5
Aminoacid Amino
acid
Aminoacid
Aminoacid
Aminoacid
Fig. 7-6, p. 183
Na+
Na+
Na+
Na+
Na+
Na+
Table 7-3, p. 184
Amino Acid Supplements
• Amino acids that use the same carrier system may create, depending on the amount ingested, a competition between the amino acids for absorption
• Supplements may result in impaired or imbalanced amino acid absorption
• Some amino acid supplements can cause serious illness
•L-tryptophan
•L-phenylalanine
• Some amino acids are useful
•L-lysine
PeptideCarrier
Lumen(small intestine)
Brush borderMembrane
K1 K1
Na1
Na1
Basolateral Membrane
Enterocyte
Na1
Na1
H1H1
H1H1
PeptidePeptide
Fig. 7-7, p. 184
Na1
Na1
Na1
Na1
Na1
Na1
K1 K1
Required forsome aminoacid transport
AminoAcid
Enterocyte
Lumen
AminoAcids
BasolateralMembrane
Carrier
Brush bordermembrane
Aminoacids
ADP 1
ATP
Pi
Peptides
Fig. 7-8, p. 185
Table 7-4, p. 185
Fig. 7-9, p. 186
Many dietary amino acids are used by enterocytes and never make it into the circulation. This is an example of the fates of glutamine in the enterocyte.
Fig. 7-10, p. 186
Reduced Glutathione can also be made from glutamine in enterocytes
Metabolic Fates of Amino Acids
• Synthesis – Plasma proteins (albumin, retinol-binding protein, acute phase
proteins, heat shock proteins) – Nitrogen containing non-protein compounds (glutathione,
carnitine, creatine, carnosine, choline)– Purines and pyrimidines
• Catabolism
•Transamination and deamination to keto-acids
•Energy
•Glucose
•Ketone bodies
•Cholesterol
•Fatty acids
•Ammonia disposal – urea cycle
Synthesis of plasma proteins
Synthesis of nitrogen containing, non-protein compounds
• Glutathione
• Carnitine
• Creatine
• Carnosine
• Choline
• Purine and pyrimidine bases
Table 1. Effect of Oral Creatine Supplementation on Specific Activities
Activity Summary of Studies CommentsStationary cycling sprints
Several studies support an ergogenic effect in repeated sprints but are not convincing for single sprints
Field studies with bicycles on a track are needed to simulate actual competition
Running sprints (repeated or single)
Conflicting results regarding performance enhancement
Speculation is that weight gain offsets any potential benefit
Swimming sprints (repeated or single)
Conflicting results regarding performance enhancement
Speculation is that weight gain offsets any potential benefit
Weight lifting
Some evidence of an ergogenic effect
Whether creatine supplementation truly increases muscle synthesis is being investigated. Creatine-induced weight gain may make true double-blindness difficult to achieve
Fig. 7-16, p. 192
Pyrimidine synthesis
Fig. 7-17a, p. 193
Purine synthesis from ribose phosphate
Fig. 7-17b, p. 193
Gout
Fig. 7-20, p. 195
Amino Acid Metabolism
• Deamination or transamination
• Nitrogen recycling/disposal via urea cycle
• Use of remaining carbon skeletons
Fig. 7-21, p. 196
Deamination
Urea
Fig. 7-22, p. 196
Transamination
Fig. 7-23, p. 197
A typical blood chemistry panel might include the following tests:
General Metabolism
Kidney Function
Electrolytes Liver Function Thyroid Pancreas
GLU (Glucose)LDH (Lactate dehydrogenase)CPK (Creatine phosphokinase)
BUN (Blood Urea Nitrogen)CREAT Creatinine
Na (Sodium)K (Potassium)Cl (Chloride)CA (Calcium)PHOS Phosphorus
ALP (Alkaline phosphatase)ALT (Alanyl amino transferase)ALB (Albumin)GGT (Gamma-glutamyl transpeptidase)SGPT (Serum glutamate pyruvate transaminase)TP (Total Protein)CHOL (Cholesterol)GLOB (Globulin)TBILI (Total Bilirubin)
T3 Triiodothyronine)T4 Thyroxine
AMY (Amylase)LIP (Lipase)
Fig. 7-24, p. 199
Fate of carbon skeletons from amino acids
If acetylcoA is abundant, but oxaloacetate is not
glucogenic
ketogenic
Metabolic fates of selected amino acids
• Phenylalanine – tyrosine, melanin, thyroid hormones, L-dopa, dopamine, norepinephrine, epinephrine, acetyl coA
• Tryptophan – serotonin, melatonin, picolinate, NAD+, nicotinamide, NADP+, acetylcoA, pyruvate, xanthurenic acid
• Methionine – homocysteine, spermidine, tetrahydrofolate, taurine, sulfate, succinylcoA
• Lysine – carnitine, acetylcoA• Threonine – succinyl coA, pyruvate, acetaldehyde
Fig. 7-31, p. 207
Fates of amino acids not used for the synthesis of body proteins
How do organs other than the liver get rid of the ammonia biproduct of amino acid metabolism?• Ammonia to glutamate to glutamine
(glutamine synthetase; ATP; Mg2+ or Mn2+)
• Alanine to pyruvate to glucose (transamination)
• Branched chain amino acids to glutamate to glutamine to alanine (transamination)
Fig. 7-34, p. 209
Alanine-glucose cycle
Fig. 7-38b, p. 213
Fig. 7-38c, p. 213
Kidneys prefer:
Glycine, alanine, glutamine, glutamate, phe, and aspartate
From these it produces:
Arginine, histidine, serine and maybe tyrosine
It is the only organ other than the kidney that has gluconeogenic enzymes and is critically important during fasting.
Table 7-5, p. 214
You can also excrete urea via the skin, and can lose nitrogen via hair and skin cell loss. These losses are referred to as insensible nitrogen losses.
Fig. 7-38a, p. 213
How to Determine Protein Quality?
• Digestibility• Composition with respect to indispensable
amino acids– High quality or complete– Low quality or incomplete
• Quantitative evaluation methods– Amino acid score– Digestiblity corrected amino acid score– Protein efficiency ratio– Nitrogen balance– Biological value– Net protein utilization
Table 7-6, p. 220
Table 7-7, p. 222
FoodServing
Weight in grams
Protein grams % Daily Value
Hamburger, extra lean
6 ounces 170 48.6 97
Chicken, roasted
6 ounces 170 42.5 85
Fish 6 ounces 170 41.2 82
Tuna, water packed
6 ounces 170 40.1 80
Beefsteak, broiled
6 ounces 170 38.6 77
Cottage cheese
1 cup 225 28.1 56
Cheese pizza 2 slices 128 15.4 31
Yogurt, low fat 8 ounces 227 11.9 24
Tofu 1/2 cup 126 10.1 20
Lentils, cooked 1/2 cup 99 9 18
Skim milk 1 cup 245 8.4 17
Split peas, cooked
1/2 cup 98 8.1 16
Whole milk 1 cup 244 8 16
Lentil soup 1 cup 242 7.8 16
Kidney beans, cooked
1/2 cup 87 7.6 15
Cheddar cheese
1 ounce 28 7.1 14
Macaroni, cooked
1 cup 140 6.8 14
Soymilk 1 cup 245 6.7 13
Egg 1 large 50 6.3 13
p. 227a
p. 227b
p. 228