Lecture 5 Flashcards
1
Q
What are some of the functions of proteins?
A
- Associated with strength and muscle
- Wound healing
- Have a structural role and a functional role in cells
2
Q
In what foods can protein be found?
A
Milk, eggs, legumes and many whole grains
Excess meat may result in high saturated fat intakes
2
Q
Some proteins are working molecules. List them (6)
A
Enzymes
Antibodies
Transport vehicles
Hormones (not all are proteins – e.g., sex hormones made up of sterol (lipid)
Cellular “pumps” – what gets in and out of a cell
Oxygen carriers (e.g., hemoglobin)
3
Q
Some proteins are for structure. In what (7)?
A
Tendons
Ligaments
Scars
Fibres of muscles
Cores of bone & teeth (collagen matrices – minerals cling onto making structures stronger)
Filaments of hair
Materials of nails
4
Q
What is the structure of proteins? What are they made up of?
A
- Made of carbon, hydrogen, and oxygen (like fat and carbohydrates)
- Contain nitrogen
- Some amino acids also contain sulphur
5
Q
Proteins are composed of amino acids. How can these make all the proteins?
A
The amino acids in a strand of protein are different from one another – not identical like starch
20 different amino acids make up most of the proteins of living tissue (A protein strand can contain 50 to 1000 amino acids. So many different combinations).
6
Q
What is the structure of amino acids?
A
An amine group at one end - nitrogen-containing part
An acid group at the other end
A distinctive side chain (group) attached to the carbon at the center of the backbone which gives it its identity & chemical nature.
Must understand the structure of an amino acid. The “backbone” is the same for all amino acids. The side chain differs from one amino acid to the next. The nitrogen is in the amine group
7
Q
What are some of the things side chains make the amino acids differ in?
A
Size, shape, electrical charge (Going to contribute to the shape and behaviours of the protein (repel, attract, neutral))
8
Q
What does it mean for an amino acid to be essential or indispensible?
A
Cannot be synthesized at all by the body or cannot be synthesized in sufficient amounts
Can only be replenished from foods
The body cannot make the proteins it needs to do its work without the essential amino acids
The body can make the other amino acids from fragments derived from carbohydrate or fat to form the backbones & nitrogen from other sources
9
Q
What does it mean for an amino acid to be nonessential or dispensible?
A
Amino acids that can be synthesized by the body
The body can make these from fragments derived from carbohydrate or fat to form the backbones
Nitrogen from other sources (e.g., dismantling amino acids)
10
Q
What does it mean for an amino acid to be conditionally indispensible/essential?
A
An amino acid that is normally nonessential
in circumstances when the need exceeds that body’s ability to produce it, it must be supplied by the diet (e.g., tyrosine)
11
Q
Describe what it means by “amino acids are recycled”
A
Body makes some amino acids but also breaks down proteins to reuse those amino acids:
- Food proteins (after digestion) & body proteins (after their cellular work) are dismantled freeing their amino acids
- Recycling system provides access to amino acids for energy when needed
12
Q
Cells can use amino acids for energy if required. Like when?
A
Tissues can break down their own proteins in time of fuel or glucose deprivation
Working proteins are sacrificed
Priority system by the body to select tissue proteins to dismantle (most dispensable proteins used first and structural proteins of certain organs are guarded until their use is forced by dire need)
13
Q
What is a peptide bond?
A
Connects one amino acid to another
Formed between the amine of one amino acid and the acid group of the next amino acid through a condensation reaction
Forms a chain of amino acids with side chains bristling out from the backbone
14
Q
What is the primary structure?
A
The chain is the primary structure.
15
Q
What is the secondary structure?
A
Determined by weak electrical attractions within the chain
Positively charged hydrogens attract nearby negatively charged oxygen
Sections of the chain may twist into a helix or fold into a pleated sheet giving proteins strength and stability
16
Q
What is the tertiary structure?
A
Long polypeptide chains twist and fold into a variety of complex tangled shapes
Side groups may attract or repel each other
Side groups may be hydrophilic or hydrophobic (therefore the chain folds so hydrophilic side groups are on the surface near water & hydrophobic side groups are hidden in the middle)
Disulfide bridges also determine tertiary structure
Shape gives characteristics
17
Q
What are quaternary structures?
A
Interactions between 2 or more polypeptides
Some polypeptides work together in large complexes
Some proteins strands function alone while other proteins are composed of several strands
18
Q
What is hemoglobin?
A
A large globular protein that carries oxygen and is made up of four polypeptide chains
19
Q
Proteins perform different tasks dictated by their shape, such as?
A
- Globular proteins are water soluble, such as some proteins of the blood
- Some proteins form hollow balls & carry/store materials in their interior
- Some proteins are much longer than they are wide like the proteins of tendons
20
Q
What is collagen?
A
A protein from which connective tissues are made (tendons, ligaments, scars & the foundations of bones & teeth)
Acts like glue between cells
Elasticity in blood
21
Q
What is insulin
A
As we know, it helps regulate blood sugar
Produced by the pancreas
Helps cells use sugar
22
Q
What are enzymes?
A
Protein catalysts (facilitates a chemical reaction without being altered in the process)
23
Q
What can be said about inherited amino acid sequences?
A
For each protein there exists a standard amino acid sequence
A sequence which is specified by heredity. Wrong amino acid can be disastrous to health (sickle cell anemia)
24
What is sickle cell disease?
Need to know it is the replacement of one amino acid to the other, altering the protein’s shape and its function (unable to carry oxygen efficiently), alters blood cells which can lead to blood clotting, strokes, and potentially early death.
25
Every human cell contains the DNA for making every human protein but cells do not contain every protein. How does the cell know to either express or suppress certain genes?
In general, cells monitor nutrient concentrations in the fluids surrounding them and triggers a cascade of molecular events inside the cell that ultimately leads to expression or suppression of certain genes
26
What are some examples of suppression or expression of certain genes?
Pancreas: Responds to internal molecular messages generated when blood glucose is overabundant by synthesizing insulin
Hemoglobin: When body's iron stores run low, immature red blood cells respond by reducing hemoglobin synthesis. In contrast, abundant iron stimulates hemoglobin synthesis by immature red blood cells
27
What is the denaturation of protein, what causes it, and why is it important?
The irreversible change in a protein's shape
Can be caused by heat (cooking), acids, bases and alcohols
Denaturation is important to the digestion of food protein (stomach acids open up a protein's structure, allows digestive enzymes to make contact with the peptide bonds & cleave them).
28
Why are proteins digested?
Each protein performs a particular task in a specific tissue. Proteins eaten must be broken down and absorbed. Amino acids then are arranged into specific human body proteins.
29
How do some proteins digest others in the acidic stomach (pH of 2)?
Certain acid-tolerant proteins (many of which are enzymes), digest proteins from food that have been denatured by acid. The coating of mucus secreted by the stomach wall protects its proteins from attack by either acids or enzymes.
30
How is protein digested in the mouth?
Protein is crushed by chewing & moistened with saliva
Not really an enzymatic digestion happening yet
31
How is protein digested in the stomach?
Acid helps to uncoil the protein's tangled strands so that the stomach's protein-digesting enzyme can attack the peptide bonds.
Lining is protected from acid & enzymes by a mucus coating secreted by stomach cells
32
What is the stomach's protein-digesting enzyme, which works best in an acidic environment?
Pepsin
It cleaves amino acid strands into polypeptides and a few amino acids.
33
How are proteins digested in the small intestine? What happens to proteins of different sizes?
Receives small denatured pieces of protein from the stomach (most are polypeptides, a few are single amino acids)
Alkaline juices from the pancreas neutralize the acid delivered by the stomach (pH increases to about 7 -- neutral)
Cells lining the small intestine have enzymes on their surfaces that split most tri & dipeptides into single amino acids, which are then absorbed.
Some di & tripeptides are absorbed into cells where they are split into single amino acids before being released into the bloodstream
A few larger peptide molecules can escape the digestive process altogether and enter the bloodstream intact
34
What are the protein-digesting enzymes from the pancreas & small-inestine and what do they do?
Proteases
Continue breaking down protein until nearly all that is left are dipeptides, tripeptides, or single amino acids
35
Does taking enzyme help?
No. Even the stomach's digestive enzymes are denatured and absorbed when their jobs are through as amino acids.
36
Do predigested proteins (amino acid supplements) help protect the digestive system from overworking?
No. The healthy digestive system easily handles whole proteins
Single amino acid supplements may compete for absorption sites or overwhelm a carrier resulting in possible deficiency in another amino acid
37
What happens to amino acids in the bloodstream? Where are they taken (2)?
Carried to the liver
Used by the liver or released into the blood to be taken up by other cells
38
What happens when amino acids are for the liver?
Used in protein synthesis, used for energy, or used to synthesize a nonessential amino acid and released into bloodstream for cells
39
What happens when amino acids are used by the cells?
Use the amino acids to make proteins for their own use, make proteins that are released into the lymph or blood for other uses. When necessary, body cells can use amino acids for energy
40
What are the roles of protein in the body (6)?
- Supporting growth and maintenance
- Building enzymes, hormones, and other compounds (amino acids & antibodies)
- Maintaining fluid and electrolyte balance
- Maintaining acid-base balance
- Clotting of blood
- Providing energy and glucose (when insufficient carb and fat)
41
The continuous breakdown & synthesis of body proteins involving the recycling of amino acids is what? And how many grams per day?
Protein turnover (300-400g/day)
42
Amino acids are not only building blocks for protein. Which ones are examples of this?
Tyrosine is a component of both epinephrine and norepinephrine and is used to make both melanin and thyroxine
Tryptophan serves as a starting material for serotonin and niacin
43
Proteins are also antibodies. What are they produced by and what are they?
The immune system
Large proteins of the blood
44
What is edema?
The swelling of body tissue caused by the leakage of fluid from blood vessels
Seen in protein deficiency and other conditions
Caused by the failure of any part of the fluid balance system
45
How do proteins support growth and maintenance?
amino acids must be continuously available to build the proteins of new tissue -- embryo and growing child, muscles of an athlete in training, new blood to replace losses, scar tissue, new hair & nails) (protein helps replace worn out cells & cell structures (red blood cells, cells lining the intestinal tract, skin cells
46
How do proteins maintain fluid and electrolyte balance?
too much fluid in a cell, cell ruptures; too little fluid in a cell, cell unable to function; water can diffuse freely into & out of cells, but proteins can't but they attract water so by maintaining stores of internal proteins & of some minerals, cells retain the fluid they need; fluid is kept within blood vessels by proteins that are too large to freely move across capillary walls so the proteins attract and hold water within the vessels, preventing the water from freely flowing into the spaces between cells.
47
How do proteins maintain acid-base balance?
preventing acidosis or alkalosis in the blood. Normal processes of the body continually produce acids which are compounds that release hydrogens and bases which are compounds that accept hydrogens, so protein buffers pick up and release hydrogens when needed in the bloodstream
48
An amino acid that arrives at a cell can be used in one of what three ways?
1. Used to build part of a growing protein
2. Altered to make another needed compound
3. Dismantled to use its amine group to build another amino acid
Remainder can be used for fuel or converted to glucose or fat.
(carbon, hydrogen and oxygen can make glucose or fat)
49
If the cell is starved for energy & lacking glucose and fatty acids, what will happen to the amino acid?
The amine group will be removed & the remainder used for energy
The amine group will ultimately be excreted as urine
50
If the body has a surplus of amino acids and energy, what will happen to the amino acid?
The amino group will be excreted
The remainder can be used for energy or converted to glucose or fat for storage
51
Define "wasted amino acids"
Amino acids not used to build protein or make other nitrogen containing compounds
52
When do amino acids get wasted (4)? *
1. The body does not have enough energy from other sources
2. The body has more protein than it needs
3. The body has too much of any single amino acid, such as from a supplement
4. The diet supplies protein of low quality, with too few essential amino acids
53
To prevent wasting of dietary protein & permit the synthesis of needed body protein, what should the diet look like?
- Dietary protein must be adequate in quality
- The diet must supply all of the essential amino acids in the proper amounts
- Enough energy-yielding carbohydrate and fat must be present -- protein sparing
54
What does the body's response to protein depend on (3)?
- The body's state of health
- Other nutrients and energy taken with the protein
- The protein's quality
55
How does the state of health affect the body's response to protein?
Malnutrition (undernutrition) and infection may greatly increase need for protein
Undernutrition: secretion of digestive enzymes slows as the tract's lining degenerates
Infection: extra protein is needed for enhanced immune function
56
How does protein quality affect the body's response to protein (2) (what is it influenced by)?
Influenced by:
A protein's digestibility
- Animal sources (90+%) are more easily digested & absorbed than those from plant sources (legumes 80-90%; grains and other plant foods 70-90%).
A protein's amino acid composition
- Cells need a full array of amino acids from food, their own amino acid pool (those dissolved in the body's fluids that provide cells with ready raw materials from which to build new proteins or other molecules), or from both.
57
Define high-quality proteins
Dietary proteins containing all of the essential amino acids in relatively the same amounts that human beings require
May also contain nonessential amino acids
58
If an amino acid is nonessential, what does that mean if not available from food?
If not available from food, the cell can synthesize it & continue attaching amino acids to the protein strand being manufactured.
59
If the diet fails to supply enough of an essential amino acid, what happens within a single day?
Limiting the breakdown of their working proteins
Reducing their use of amino acids for fuel
60
How does limiting amino acids affect protein synthesis?
An essential amino acid present in an insufficient amount limits the body's ability to build protein (like when making muffins) but normal protein-related activities resume when limiting amino acid is available
61
What happens if the shortage of an amino acid is chronic?
Cells begin to break down their protein-making machinery
- When intake becomes adequate, synthesis will lag until the protein-making machinery can be rebuilt
- Until then, cells function less & less efficiently
62
What happens to partially completed proteins?
Not kept for completion later. They are dismantled & the amino acids are returned to circulations so they are available to other cells. If not soon used for protein synthesis, they are stripped of their amine groups & the residue is used for other purposes.
63
What are complementary proteins?
2 or more proteins whose amino acid assortments complement each other in such a way that the essential amino acids missing from one are supplied by the other
Doesn't need to be in the same meal
Literally the same thing as mutual supplementation
64
What are some examples of complementary proteins?
Oatmeal and milk
rice and beans
pasta, vegetables and parmesan cheese.
65
How much protein do people really need?
DRI committee recommends for adults, 0.8/kg body weight/day (RDA).
10%-35% of total calories (AMDR)
Athletes may need more
(Most people in Canada receive more protein than is required)
66
What is nitrogen balance?
The amount of nitrogen consumed compared with the amount excreted in a given time period
Under normal circumstances, healthy adults are in nitrogen equilibrium = zero balance (in = out)
Positive balance (in > out)
Negative balance (in < out)
67
What happens in positive nitrogen balance and what are some examples of places where this would occur? *
More protein is synthesized by the body than is degraded
Nitrogen intake exceeds excretion
Healthy growing children and adolescents, pregnant women, people recovering from a protein deficiency
68
What happens in negative nitrogen balance and what are some examples of places where this would occur? *
The body degrades more protein than it synthesizes
The body loses nitrogen as it breaks down muscles and other body proteins
Starving or severe stresses (e.g., burns, injuries, infections, and fever)
69
What is protein-energy undernutrition (PEU, PEM)? And what are the two parts of it?
World's most widespread malnutrition problem
Marasmus & Kwashiorkor
69
What is marasmus?
Chronic inadequate food intakes
- Shriveled and lean all over
- Inadequate energy, vitamin, mineral & protein intake
70
What is Kwashiorkor?
Severe acute malnutrition
- Swollen belly & skin rash
- Too little energy and protein to support body functions
- Typical when a new sibling is introduced
71
Without adequate nutrition, what happens with marasmus?
- Muscles, including the heart muscles, waste & weaken
- Brain development is stunted & learning is impaired
- Metabolism is so slow that body temperature is subnormal
- Little or no fat under the skin to insulate against the cold (just skin & bones)
- Child engages in as little physical activity as possible, not even crying for food
- Body cuts down on protein expenditure not needed for the heart, lungs & brain to function
- Growth ceases
- Skin loses elasticity & moisture - sores develop & fail to heal
- Digestive enzymes are in short supply
- Digestive tract lining deteriorates & absorption fails
- Blood proteins, including hemoglobin, are no longer produced - child becomes anemic & weak
- Antibodies are degraded to provide amino acids for other uses, - target for infection
72
What happens with Kwashiorkor?
Baby is weaned from breast milk when next child born (breast milk: high-quality protein
watery cereal: low in protein low quality protein)
Symptoms resemble those of marasmus. Often without severe wasting of body fat
Proteins & hormones that previously maintained fluid balance are diminished. Fluids leak out of the blood & accumulate in the belly & legs, causing edema
Belly often bulges with a fatty liver. Lack of the protein carriers that transport fat out of the liver
Fatty liver loses some of its ability to clear poisons from the body, prolonging their toxic effects
Without sufficient tyrosine to make melanin, the child’s hair loses its normal colour
Inadequate protein synthesis leaves the skin patchy & scaly & sores fail to heal
73
What does PEU or PEM look like in Canada?
Poverty of unaffordable food costs
Many elderly people
Unhoused children and adults
Those with anorexia nervosa
Infants -- over-diluted formula
Toddlers - replacing their milk with un-enriched, protein-poor "health food" rice drinks, almond drinks
Wasting diseases such as AIDS & cancer
Addiction to drugs and alcohol
74
What can be said about hungry children (3)?
- Do not learn as well as fed children
- Are not as competitive
- Are ill more often
- Have higher absentee rates from school and cannot concentrate for long
75
What happens if proteins are overconsumed?
- No health benefits
- May pose health risks for the heart, kidneys, and bones
76
Diets high in protein-rich foods can have what negative effects on the body?
- Animal protein sources in particular can be high in saturated fat, which may increase LDL cholesterol (which increases risk of heart disease)
- A high-protein diet can worsen existing kidney problems & may accelerate a decline in only mildly impaired kidneys (controlled protein diet)
- Mixed evidence on high protein diets accelerating bone loss
77
What can be said about the process of digesting protein?
Protein is satiating
Protein has the highest thermic effect of food (digestion takes more energy than with carbs or fat)
78
Food richest in protein carry with them a characteristic array of vitamins and minerals, including what?
- Including vitamin B12 & iron
- Tend to lack vitamin C and folate
79
What can be said about protein foods and obesity?
They are high in kcal which can lead to obesity
80
Legumes are excellent sources of ___, ___, ___, and lack ___, ___, ___.
Many B vitamins
Iron
Calcium
Vitamin A
Vitamin C
Vitamin B12
81
What are some ways to get enough but not too much protein?
Balance amino acids in legumes using grains & vegetables
Soybean protein is comparable to meat (too much can inhibit iron absorption, so add small amounts of meat &/or foods rich in vitamin C)
82
What is a lacto-ovo vegetarian?
includes dairy products and eggs but excludes animal flesh and seafood
83
What is a lacto-vegetarian?
includes dairy products but excludes eggs, animal flesh and seafood
84
What is an ovo-vegetarian?
Includes eggs but excludes milk products, animal flesh, and seafood
85
What is a pesco-vegetarian?
excludes animal flesh but eats seafood - pescatarian, pescetarian, pescotarian
86
What is a vegan?
includes only food from plant sources and excludes all food from animal sources – also called a strict vegetarian
87
What is a flexitarian?
Includes primary plant-based foods but animal products such as meat and fish are eaten occasionally
88
What are some reasons for vegetarianism?
Preference
Convenience
Advertising
Availability
Economy
Emotional comfort
Habit
Positive associations
Social pressure
Values or beliefs
Weight
Nutritional value
89
What are the benefits (effects on body) of well-planned vegetarian diets?
Lower obesity rates
Lower heart disease rates
Lower high blood pressure rates
Lower cancer rates
Higher life span
90
Why is it hard to study the reduced incidences of chronic disease?
Vegetarians often have higher intakes of vegetables and fruit
Vegetarian diets often contain more fibre, potassium, several vitamins associated with reduced disease risk
Vegetarians generally smoke less, use alcohol less, more physical activity
91
What can be said about body weight and meat consumption?
Intake of what else is body weight correlated with?
Weight increases as frequency of meat consumption increases
Lower body weights correlated with high intakes of fibre and low intakes of fat
92
Why do people consuming plant-based diets die less often from heart disease and related illnesses than meat-eating people?
- Plant-based diets are generally lower in saturated fat & cholesterol than mixed diets
- Plant-based diets generally contain unsaturated fats that are associated with lower risk of heart disease
- Vegetarian diets are generally higher in dietary fibre
- Vegetables may lower disease risk because of phytochemicals
93
So, when soy protein replaces animal protein, what is reduced?
Total blood cholesterol
LDL cholesterol
Triglycerides
Blood pressure
94
What aspects of vegetarian diet & lifestyle lead to them having lower blood pressure & lower rates of hypertension?
Diet: high in fibre, fruits, and vegetables
Lifestyle factors: appropriate body weight, smoking and alcohol intake raise blood pressure, physical activity lowers blood pressure
95
What aspect of vegetarian diets may lead them to having significantly lower rates of some cancers than the general population?
May be the abundance of vegetables and fruit rather than the exclusion of animal products
96
Colon cancer appears to correlate with moderate-to-high intakes of what?
Alcohol
Total food energy
Fatty red meats & processed meats (but not poultry or fish)
97
Poorly planned vegetarian diets are at risk of inadequate what (7)?
Protein
Iron
Zinc
Calcium
Vitamin B12
Vitamin D
Omega-3s
98
Poorly planned omnivorous diets may be insufficient in what?
Vitamin A
Vitamin C
Folate
Fibre
99
What is the RDA for protein for vegetarians?
Some suggest it should be higher because of lower digestibility of plant proteins, but it is still 0.8g/kg.
100
What does the DRI committee recommend for iron intake for vegetarians?
Iron can be a problem even for meat eaters
Should be increased to 1.8x the general RDA
Absorption of iron from plants is enhanced by vitamin C consumed with iron-rich foods
101
For a vegetarian to meet zinc needs, what is recommended?
Eat a variety of nutrient-dense foods
Maintain an adequate energy intake
Include whole grains, nuts, legumes
102
Similar to iron, meat is zinc's richest source. Why can it be a concern for vegetarians?
Soy interferes with its absorption
Can be a problem for growing children but few vegetarian adults are zinc deficient
103
What can be said about vitamin B12 and deficiencies?
Requirement is small, but significant amounts are found ONLY in animal-derived foods
Vegans must rely on B12-fortified foods or supplements
104
What can be said about vitamin D and deficiencies?
Animal foods such as milk and butter are fortified
Margarine and some milk alternatives are fortified
Fatty fish are sources of Vitamin D
Supplements may be needed if vitamin-D fortified foods are not used & limited sun exposure
105
Vegetarian diets typically provide enough omega-6 fatty acids but often lack omega-3 fatty acids. What does this mean?
This imbalance slows production of EPA and DHA
Without fish or eggs in the diet, intake of EPA and DHA falls short
106
A vegetarian's diet should include good sources of _____ because it is an essential nutrient. What are some sources of omega 3's?
Linolenic acid
Canola oil, flax seed, walnuts, and soy
107
What are the overall recommendations for planning a vegetarian diet?
Choose fresh, whole foods
Avoid reliance on heavily processed convenience foods that contain added sugars, salt, saturated fats and trans fats
Soy, beverage & tofu fortified with calcium, vitamin D & vitamin B12 can substitue for cow's milk products
Dark green vegetables and legumes help meet iron & zinc needs
To ensure adequate intakes of vitamin B12, vitamin D, and calcium, select fortified foods or use supplements daily.
