Protein (Post-Midterm) Flashcards
(116 cards)
1
Q
What is the main difference between proteins and carbohydrates or fats?
A
Proteins consist of 16% nitrogen (or 6.25g nitrogen) and are not stored in the body for energy.
2
Q
What is the recommended macronutrient intake of protein?
A
Protein should make up 10-35% of macronutrient intake.
3
Q
What percentage of the human body is made up of protein?
A
Protein makes up 40% of skeletal muscle, 25% of body organs, and 35% of skin and blood.
4
Q
What are the three main functions of proteins?
A
: Proteins have structural, regulatory, and energy functions.
5
Q
What are examples of structural proteins?
A
Examples of structural proteins include actin (contractile), myosin, collagen, elastin, and keratin.
6
Q
What are examples of regulatory proteins?
A
Examples of regulatory proteins include enzymes, catalysts hormones, and transporters.
7
Q
What is the primary structure of a protein?
A
The primary structure refers to the sequence of amino acids in a polypeptide chain.
8
Q
What is the secondary structure of a protein?
A
The secondary structure refers to the local folding patterns of the polypeptide chain, such as alpha-helix and beta-pleated sheet.
9
Q
What is the tertiary structure of a protein?
A
The tertiary structure refers to the overall three-dimensional shape of a protein, which is determined by interactions between amino acid residues.
10
Q
What is the quaternary structure of a protein?
A
The quaternary structure refers to the arrangement of multiple polypeptide chains in a protein complex.
11
Q
What are essential amino acids?
A
Essential amino acids are amino acids that cannot be synthesized by the body and must be obtained from the diet.
12
Q
What is the primary function of protein digestion?
A
The main goal of protein digestion is to transform proteins into amino acids, dipeptides, or tripeptides.
13
Q
What enzyme is responsible for protein digestion in the stomach?
A
Pepsin, activated by hydrochloric acid, hydrolyzes peptide bonds in proteins.
14
Q
Where does major protein digestion occur in the digestive system?
A
Major protein digestion occurs in the small intestine.
15
Q
What are the end products of protein digestion?
A
The end products of protein digestion are free amino acids, dipeptides, and tripeptides.
16
Q
What are the exogenous sources of amino acids in the diet?
A
Exogenous sources of amino acids include animal-sourced foods (meat, poultry, fish, dairy, eggs) and plant-sourced foods (soy milk, tofu, grains, legumes, nuts, and seeds).
17
Q
What are the endogenous sources of amino acids in the GI tract?
A
Endogenous sources of amino acids in the GI tract include desquamated mucosal cells and digestive enzymes and glycoproteins secreted by various organs.
18
Q
What is the function of enteropeptidase in protein digestion?
A
Enteropeptidase, released from the brush border membrane in the small intestine, activates trypsin, which further activates other pancreatic enzymes involved in protein digestion.
19
Q
How are pancreatic enzymes released during protein digestion?
A
Pancreatic enzymes are released as zymogens, inactive forms that require activation.
20
Q
What is the role of aminopeptidases, dipeptidylaminopeptidases, and tripeptidases in the small intestine?
A
These brush border enzymes hydrolyze peptides into free amino acids, dipeptides, and tripeptides for absorption.
21
Q
Protein structural function
A
Contratile proteins (actin, myosin) in cardiac, skeletal, and smooth muscles
Fibrous proteins (collagen, elastin, keratin) in bone, teeth, skin, strong structure
22
Q
Protein regulatory function
A
Enzyme/ catalyst: for reactions and rate of reaction, act as cofactor
Hormones/ messengers: chemical messengaers like insulin, glucagon, that regulate metabolic processes
Transporters: regulate nutrient entry in cell membrane, in blood (albumin, transferrin), immunoglobins, and buffers
Fluid balance: attracts water and contributes to osmotic pressure
23
Q
Protein energy function
A
Source of energy during excessive intake, metabolized energy (TCA cycle, gluocneogenesis, fatty acid synthesis)
24
Q
Protein digestion in oral cavity
A
Mechanical breaking down of protein containing food (teeth, tongue, saliva), preps food for stomach
25
Protein digestion in stomach
Release of HCl from parietal cells (through gatrin, acetylcholine, and histamine) to denature and unfold protein, does not break down peptide bonds
Pepsingen from chief cells (through HCl, pepsin) hydrolyzes peptide bonds into free amino acids
26
Protein digestion in small intestine
Secretin and cholescystokinin stimulate secretion of pancreatic juice from acinar cells with bicaronate, digestive enzymes, water, electrolytes
Stimulates secretion of enteropeptidase from brush border that breaks peptide bondsinto amino acids, dipeptides and tripeptides (with peptidases)
27
What are the different absorption mechanisms for the end-products of protein digestion?
- Amino acid transport and peptide transport.
- Amino acid transport occurs along the small intestine, while peptide transport has lower affinity for peptides longer than 3 amino acids.
28
What are the physiologic consequences of incomplete protein digestion?
Incomplete protein digestion can lead to acute immune reactions, development of sensitivity to polypeptides, and idiosyncratic drug reactions.
29
What is the beneficial effect of breastmilk versus infant formula for the prevention of symptoms?
Breastmilk can reduce the risk of developing allergy disease in infants compared to infant formula.
30
What are the alternatives for breastmilk in infants with a high risk of atopic diseases?
Hydrolyzed proteins in infant formula can be considered as an alternative for breastmilk in infants with a high risk of atopic diseases.
31
Describe the different fates of absorbed amino acids and di-/tripeptides.
Absorbed di-/tripeptides are cleaved to free amino acids in enterocytes, which are either used by enterocytes or transported in the portal blood.
32
Which amino acids are majorly metabolized in the enterocyte?
Glutamine, glutamate, aspartate, arginine, and methionine.
33
What is the significance of these essential amino acid pathways in case of intestinal injury?
In case of intestinal injury, arginine becomes a conditionally essential amino acid, and patients may require arginine or citrulline supplementation in their diet.
34
Describe the function of glutamine in intestinal cell metabolism.
Glutamine is a primary source of energy, stimulates GI mucosal cell proliferation, prevents atrophy of gut mucosa, and creates a barrier against bacterial translocation.
35
Describe the function of glutamate in intestinal cell metabolism.
Glutamate is used for energy and the formation of proline, ornithine, and glutathione.
36
What is the end product of protein digestion?
Amino acids, dipeptides, and tripeptides.
37
Explain the absorption mechanisms for peptides and amino acids.
- Peptides are absorbed through peptide transporters, with lower affinity for peptides longer than 3 amino acids.
- Amino acids require carriers for active transport, using specific transport systems.
38
What are the consequences of proteins entering the bloodstream bypassing the usual absorption mechanisms?
Consequences include acute immune reactions, sensitivity to polypeptides, and idiosyncratic drug reactions.
Due to polypeptides or proteins directly entering blood stream, through leaks in epithelial cells or vesicles
39
Who are the vulnerable population groups for proteins entering the bloodstream bypassing the usual absorption mechanisms?
Those with atopic heredity, infants who receive infant formula and are not solely breast-fed, and those with certain GI tract diseases.
40
How are di- and tripeptides hydrolyzed in enterocytes?
Di- and tripeptides are hydrolyzed to free amino acids by aminopeptidase in enterocytes.
41
What happens to absorbed amino acids in enterocytes?
Absorbed amino acids are either used by enterocytes for protein synthesis, nitrogen-containing compounds, and energy, or transported in the portal blood.
42
What is the primary source of energy in intestinal cell metabolism?
Glutamine is the primary source of energy in intestinal cell metabolism.
43
Which amino acids are required for the synthesis of glutathione?
Glutathione is formed from glutamate, glycine, and cysteine.
44
What is the significance of methionine in intestinal cell metabolism?
Methionine is a precursor for S-adenosylmethionine (SAM), which is involved in various metabolic reactions, including DNA methylation.
45
Describe the process of cysteine formation.
Cysteine can be formed from methionine via the trans-sulfuration pathway, which is vitamin B-6 dependent.
46
What are the major metabolites of methionine in the enterocyte?
Methionine is transformed into cysteine and S-adenosylmethionine (SAM), which is involved in various metabolic reactions.
47
What are the roles of glutamine in intestinal cell metabolism?
Glutamine has trophic effects, stimulates GI mucosal cell proliferation, prevents atrophy of gut mucosa, and acts as a barrier against bacterial translocation.
48
What are the roles of glutamate in intestinal cell metabolism?
Glutamate is involved in energy production, formation of proline and ornithine, and the synthesis of glutathione and taurine.
49
Role of aspartate
Used in intestinal cell as source of energy, can be transanimated into oxaloacetate in TCA cycle, or ornithin into urea cycle
50
Role of arginine
Formed in kidneys, forms citrulline which is essential
51
Peptide transport
Best for peptides with 3 or less, transported by PEPT1 into enterocytes with protons to be cut into amino acids
Na+ is brought in to remove H+, then ATPase removes Na+ to reduce concentration
52
Active amino acid transport systems
Uses Na+ and H+, X and ASC transport systems
53
Passive amino acid transport system
Functions as exchangers or uniporters, uses diffusion, L, y, b, t, asc transport systems
54
What happens to free amino acids during postabsorption, and what percentage is used by the intestine?
Free amino acids are either used by enterocytes or transported to the liver via the portal vein. Approximately 30-50% of amino acids are used by the intestine.
55
What is the primary function of the liver in amino acid metabolism during a meal?
The liver, during a meal, serves as the primary site of amino acid uptake, monitoring their passage from the gut to peripheral circulation, utilizing amino acids for protein synthesis, and acting as the main site of amino acid catabolism.
56
Describe the interorgan amino acid transport and its purpose in the fed-fast cycle.
Interorgan amino acid transport occurs at all stages of the fed-fast cycle, providing amino acids for protein synthesis and other functions to extrahepatic tissues. Amino acids not needed in these tissues are moved into the blood.
57
What are the regulatory effects of insulin on protein anabolism, and when is protein synthesis increased?
Insulin, in response to carbohydrate and protein ingestion, promotes cellular amino acid uptake, stimulates transcellular movement of amino acid transporters to the membrane, inhibits amino acid oxidation, and stimulates protein synthesis. Protein synthesis is increased, particularly during the fed state.
58
What is the fate of dietary proteins that are not needed, and what is the role of amino acids from endogenous proteins in anabolism?
Dietary proteins not needed are catabolized. Amino acids from endogenous proteins are primarily used in anabolism, contributing to the formation of various proteins in the body.
59
List some important plasma proteins synthesized in the liver and their functions.
Important plasma proteins synthesized in the liver include albumin, transthyretin/prealbumin, VLDL, HDL, ceruloplasmin, transferrin, prothrombin, immunoglobulins, acute phase proteins, among others, with diverse functions such as nutrient transport, blood coagulation, and immune response.
60
Explain the effects of different types of dietary proteins on plasma amino acids (whey vs. casein)
Plasma amino acid concentrations increase after a meal, and the change depends on the type of dietary protein consumed. Whey protein leads to a fast, high, and transient increase, while casein protein results in a slower, lower, and prolonged increase.
61
How do fast and slow proteins modulate postprandial protein accretion, and when is each type recommended?
Fast proteins (e.g., whey) lead to immediate utilization for energy and increased protein synthesis. Slow proteins (e.g., casein) inhibit protein breakdown and are recommended before exercise and during periods of decreased protein breakdown, such as during sleep.
62
What happens during metabolism with excess protein intake, and what are the potential consequences?
Excess amino acids from dietary protein are catabolized, with 20% used for protein formation in the liver. Excessive levels of amino acids can lead to neurological problems due to the absence of protein storage in the human body.
63
Describe the process of protein catabolism and the role of ubiquitin.
Protein catabolism involves the constant breakdown of proteins, especially during starvation or low carbohydrate intake. Ubiquitin marks proteins for degradation, and the result is small peptides and amino acids.
64
What are the pathways of amino acid catabolism and their dependence on the type of amino group?
Amino acid catabolism involves transamination and deamination, with the pathway dependent on the type of amino group. Some amino acids cannot be used in certain carbon skeleton pathways.
65
Explain transamination and its significance in the synthesis of non-essential amino acids.
Transamination transfers the -NH2 group from one amino acid to an alpha keto acid, involving amino acids like alanine, glutamate, and aspartate. It is crucial for the formation of non-essential amino acids.
66
What is the significance of deamination in amino acid catabolism, and provide an example.
Deamination involves the release of -NH2 group in the form of ammonia. An example is the deamination of serine or threonine, where ammonia enters the urea cycle for excretion.
67
Differentiate between deamidation and deamination, and where does deamidation occur?
Deamidation involves the loss of an amide functional group in the side chain of glutamine and asparagine. It occurs in extrahepatic tissues where the urea cycle is absent.
68
Explain the pathways for ammonia removal in skeletal muscle and the role of glutamine.
Skeletal muscle uses pathways like the formation of glutamate and glutamine for ammonia removal. Glutamine carries ammonia out of cells, especially to the liver, kidney, and intestine.
69
Describe the alanine-glucose cycle between the liver and muscle.
The alanine-glucose cycle involves transamination of glutamate to alanine in the muscle, release of alanine into the blood, uptake by the liver, and catabolism of alanine for glucose formation during fasting or between meals.
70
What is the purpose of the urea cycle, and what happens to urea synthesized in the liver?
The urea cycle in the liver facilitates nitrogen excretion. Urea synthesized in the liver is secreted into the blood, with 75% traveling to the kidney for excretion through urine and 25% secreted into the intestinal lumen.
71
How is impaired urea cycle related to hyperammonemia, and what are the consequences?
Impaired urea cycle leads to hyperammonemia, causing brain malfunction and coma. Treatment includes a nitrogen-restricted diet, acidifying the GI tract with drugs like lactulose, and antibiotics.
72
What are the uses of carbon skeletons of amino acids, and how are they utilized in the body?
Carbon skeletons of amino acids can be used for energy, glucose formation, ketone bodies, cholesterol, and fatty acids, depending on the energy and protein intake in the body.
73
Explain the concept of nitrogen balance and its relation to protein turnover.
Nitrogen balance represents the equilibrium between nitrogen intake and excretion. Protein turnover occurs as the body rapidly catabolizes dietary amino acids
74
Albumin and function
plasma protein used in fluid balance and indicator of visceral protein status
Transport proteins for nutrients (Ca, Zn, vitamin B-6), and drugs and hormones
75
Prealbumin and functions
Transports thyoid hormone (T4, THYR) and vitamin A, more sensitive indicator of visceral protein status
76
What are the anabolic pathways of the liver?
Formation of purine and pyrimidine (for DNA and RNA)
Other nirogen containing compounds like antioxidants, fatty acid transporters, neurotransmitters and phospholipids
77
What is anabolism, and when is it higest?
Formation of protein and other compounds, and more active after meal ingestion
78
What is catabolism and when is it highest?
The breakdown of proteins to amino acids, and amino acids to amino groups and carbon skeletons
- higher during starvation stimulated by glucagon (uses amino acids as source of energy), low carbohydrate intake, excess protein intake
79
What are the nutritionally essential components of proteins? Why is dietary protein required, and what are its primary roles?
Proteins are essential for their 20 amino acids, contributing to various physiological functions. Dietary protein is crucial for supplying nitrogen for amino acid synthesis, including essential amino acids. Adequate protein intake supports growth and maintenance throughout the life cycle.
80
What is the significance of the 20 amino acids in protein nutrition?
How does dietary protein supply essential amino acids?
The 20 amino acids in proteins are vital for various bodily functions. Essential amino acids must be obtained through the diet since the body cannot synthesize them independently. Dietary protein is essential for supplying these amino acids, ensuring a balanced composition
81
How does an adequate protein intake support growth and maintenance?
How do protein requirements differ between infants and adults?
Adequate protein intake is necessary for growth and maintenance. Infants require a higher proportion of protein for growth, while adults need protein for maintenance and repair. This difference in protein requirements reflects the varying needs during different stages of the life cycle.
82
Explain the concept of protein as the primary source of nitrogen in foods and excreta.
What is the nitrogen content in proteins, and how is it measured?
Proteins are the primary source of nitrogen in foods and excreta. Approximately 16% of proteins consist of nitrogen by weight. Nitrogen is measured as an indirect method to quantify protein content, providing insights into the protein composition of various food sources.
83
Describe the recommended protein intake for infants aged 0-6 months.
How are protein requirements determined for different subgroups?
Recommended protein intakes vary based on age, body size, physiological state, and energy intake. For example, the AI for infants (0-6 months) is 1.52 g/kg/day, while the RDA for adults is 0.8 g protein/kg body weight/day.
84
Explain the calculation for nitrogen balance, including nitrogen ingestion and losses.
How is nitrogen balance assessed, and what are the implications of zero, positive, and negative nitrogen balance?
Nitrogen balance is calculated by subtracting nitrogen losses from nitrogen ingestion. Nitrogen losses occur through urine, feces, and skin. Nitrogen balance is crucial, with zero indicating a balance between intake and losses, positive indicating retention (e.g., during growth), and negative indicating losses (e.g., during trauma or inadequate dietary intake).
85
Provide examples of how nitrogen balance studies can be applied in a clinical setting.
What are the limitations of nitrogen balance studies?
Nitrogen balance studies are applied to assess protein adequacy in hospitalized patients, especially in scenarios like muscle wasting in cancer patients. However, these studies have limitations, including potential overestimation of nitrogen retention rates and the inability to account for amino acid balance.
86
Compare traditional methods and new methods, such as Indicator Amino Acid Oxidation (IAAO), for defining protein requirements.
What are the advantages of IAAO in vulnerable populations?
Traditional methods assume nitrogen balance equates to body protein needs. Newer methods, like Indicator Amino Acid Oxidation (IAAO), focus on the carbon skeleton of amino acids. IAAO is rapid, ethical, and applicable in vulnerable populations such as pregnancy and childhood.
87
What are the potential symptoms of protein excess, focusing on renal function and cardiovascular health?
Excessive protein intake may lead to dehydration, increased kidney workload, renal function deterioration, kidney stone formation, and potential links to cardiovascular disease and cancer.
88
Is there a tolerable upper intake level established for protein?
While there's no established upper limit, the acceptable macronutrient distribution range suggests 10-35% of total energy from protein.
89
Describe the acceptable macronutrient distribution range for protein.
What historical evidence exists regarding potential harm from excessively high protein intake?
The acceptable macronutrient distribution range recommends 10-35% of total energy from protein. Historical evidence, like "Rabbit Starvation," indicates potential harm with very high protein intake, although insufficient data exist on exceeding 35% caloric intake.
90
Explain the characteristics of Kwashiorkor, its causes, and symptoms.
Which demographics are most likely affected
Kwashiorkor occurs when a child receives sufficient calories from carbohydrates but inadequate protein, leading to poor visceral protein status, edema, and other symptoms. It typically happens when the second child is born, and there's no adequate alternative to breast milk for the first child.
91
Describe the causes and symptoms of marasmus.
How does marasmus affect visceral protein status?
Marasmus results from chronic insufficient energy and protein intake, leading to underweight, emaciation, muscle wasting, and depletion of adipose tissue. Unlike Kwashiorkor, visceral protein status is normal or closer to normal.
92
Explain the concept of PEM and its manifestations.
PEM manifests as stunting, wasting, and overweight conditions. Each form requires treatment with an emphasis on protein and energy intake.
93
What are the current methods for determining protein requirements?
How do newer methods, like IAAO, suggest changes to protein intake recommendations?
Current protein recommendations based on nitrogen balance and factorial methods may be underestimated. Newer stable isotope-based methods, like IAAO, suggest higher protein requirements. These recommendations have implications both locally and internationally.
94
Why are higher protein intakes from food sources recommended?
How do protein sources vary in terms of amino acid content and quality?
Higher protein intakes from diverse food sources are recommended due to variations in amino acid content and quality. Different protein sources offer different nutritional benefits.
95
Discuss factors that influence protein requirements.
How do energy intake levels affect protein requirements?
Factors such as age, body size, physiological state, and energy intake influence protein requirements. Athletes and individuals with chronic illnesses may have different protein needs.
96
Explain the significance of IAAO-based protein requirements.
How might these new requirements impact vulnerabe populations?
IAAO-based protein requirements indicate that current protein intake recommendations may be inadequate. These requirements have negative implications for vulnerable populations, including the elderly and pregnant women.
97
How do protein requirements have both local and global implications?
What organizations might be involved in addressing protein needs on a global scale?
: Protein requirements have implications both locally and globally, involving organizations like the World Food Programme, World Health Organization, and FAO. Adequate protein intake is crucial for global health.
98
Compare traditional and newer methods for defining protein requirements.
Why is the IAAO method considered a rapid and ethical approach, especially in vulnerable populations?
Newer methods, like IAAO, focus on the carbon skeleton of amino acids and provide rapid, ethical insights into protein requirements. IAAO suggests changes to protein intake recommendations, although these changes are not yet universally accepted by DRI.
99
What is the Chemical or Amino Acid Score used for?
It is used for the analytical determination of the amino acid composition of a test protein.
100
How is the Protein Digestibility Corrected Amino Acid Score (PDCAAS) calculated?
PDCAAS is calculated as the amino acid score multiplied by true digestibility.
101
What is the Protein Efficiency Ratio (PER)?
PER is the gains in body weight (in grams) divided by the grams of protein consumed, measured using animal models.
102
What does Biological Value (BV) measure?
BV measures the amount of retained amino acids (utilized by the body) relative to the amino acids absorbed in the gastrointestinal tract.
103
What is Net Protein Utilization (NPU)?
NPU measures how well ingested protein is digested, absorbed, and utilized by the body, considering protein digestibility and nitrogen losses.
104
What are the disadvantages of using animal models in protein evaluation?
Animals have different growth rates and maintenance requirements compared to humans.
105
What are some disadvantages of the methodology in protein evaluation?
The methodology doesn't account for nitrogen loss through hair and nails and uses only one source of protein, not a combination of foods.
106
Why are proteins considered nutritionally essential?
Proteins are essential for providing amino acids, including both the synthesis of non-essential amino acids and the supply of essential amino acids.
107
What factors determine the quality of a protein?
The quality of a protein, or its nutritional value, depends on the amount and proportion of essential amino acids, protein digestibility, and amino acid availability.
108
What characterizes high-quality or complete proteins?
High-quality or complete proteins contain all essential amino acids in approximate amounts needed by humans. Examples include animal sources (except gelatin), soy protein, and quinoa.
109
What distinguishes low-quality or incomplete proteins?
Low-quality or incomplete proteins lack sufficient amounts of one or more essential amino acids. Sources include most plant sources (except soy protein and quinoa).
110
Define the term "limiting amino acid."
The limiting amino acid is the essential amino acid present in the lowest amount in the food relative to the requirement for this amino acid in the human body.
111
How can mutual supplementation address limiting amino acids?
Mutual supplementation involves combining protein sources to compensate for limiting amino acids, ensuring complementary amino acid patterns. For example, legumes (high in lysine) can be combined with grain products (low in lysine).
112
Explain the concept of protein digestibility.
Protein digestibility refers to the amount of amino acids absorbed after ingesting a given protein. It varies between animal (90-99%) and plant (70-90%) proteins due to enzyme inhibitors in plant sources.
113
How can amino acid availability be diminished during food processing?
Amino acid availability can decrease due to extensive heating, the Maillard reaction in the presence of sugars, and oxidation of amino acids during food processing.
114
Describe the procedures involved in calculating Amino Acid Score.
The Amino Acid Score involves quantifying essential amino acid concentrations in the protein, comparing them to a reference protein (e.g., egg protein), and identifying the limiting amino acid.
115
Define Protein Efficiency Ratio (PER) and its measurement.
PER is the gains in body weight (in grams) per grams of protein consumed. It is measured using animal models, assessing body weight changes before and after a protein intervention.
116
Differentiate between Biological Value (BV) and Net Protein Utilization (NPU).
BV measures amino acids retained in the body, while NPU considers protein digestibility and nitrogen losses, providing a more comprehensive evaluation of protein utilization.
