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Ch. 7 Protein

Structure of Proteins (4)
1. The structure of proteins enables them to perform many vital functions
2. Proteins contain nitrogen, unlike CHO and fat.
3. Amino acids are the building block.
4. 20 different amino acids exist.
Proteins: description & function
1. A protein is a polymer constructed from amino acid monomers
2. Proteins perform most of the tasks the body needs to function
- They are the most elaborate of life's molecules
- There are many types of proteins
• Enzymes are proteins that allow specific chemical reactions to occur - (dehydration or hydrolysis)
- Without enzymes most of the chemical reactions that all life needs would not occur
Types of Protein (7)
1. Contractile (ex. muscle)
2. Defensive (ex. antibodies)
3. Enzymes (ex. dehydrogenase)
4. Signal (ex. Insulin)
5. Storage (ex. Ovalbumin-egg white)
6. Structural (ex. Hair)
7. Transport (ex. Hemoglobin)
Proteins: detailed structure
1. Amino acids are subunits (monomers) of proteins.
- A central carbon atom with bonds to a hydrogen atom, an amino group -NH2, an acidic group - COOH, and an R (remainder) group (only thing that different)
• Peptide Bond - Covalent bond between two amino acids.
- Peptide - Two or more amino acids bonded together.
- Polypeptide - Chain of many amino acids joined by peptide bonds.
Proteins: The Monomers = Amino Acids
All proteins are constructed from a common set of 20 kinds of amino acids - three are shown here. There is a list of all 20 in the book
AA consists of:
- A central carbon atom attached to:
• an amino group Side
• a carboxyl group
• a hydrogen
• and a side group that is variable among all 20
- called the "R" group
AA properties
- The properties of the amino acid depends upon which functional group is the R-group
• Acidic, basic, hydrocarbon, polar, etc
Functional Groups and Isomers
1. Functional groups are specific combinations of bonded atoms that always react in the same manner, regardless of the particular carbon skeleton.
- Determine polarity of organic molecule
-Hydrophobic or hydrophilic
- Determine ionic character of organic molecule
-Acidic or basic
Proteins as polymers
1. Cells link amino acids together by dehydration synthesis
- The resulting bond between them is called a peptide bond
essential AA
1. 9 amino acids are essential
- The human body cannot make them
- They must be supplied in the diet
2. 11 amino acids are nonessential
- If not supplied in the proper amount by the diet, the body can synthesize them
3. Under special circumstances, a nonessential amino acid can become essential - CONDITIONALLY essential amino acids
- In times of stress and disease
- Nonessential amino acid that is needed in greater amounts than the body can produce it
Recycling AA
1. The body can recycle amino acids from proteins no longer needed.
2. These amino acids can be used to build new proteins, or provide energy if glucose is lacking in the diet.
Protein: 4 levels
1. Primary - Sequence of amino acids.
2. Secondary - Polypeptide coils or folds in a particular fashion.
3. Tertiary - Folding and twisting that results in final three- dimensional shape of a polypeptide.
4. Quaternary - Consists of more than one polypeptide.
AA: how do they build proteins?
1. Amino acids link into long strands that coil and fold to make a wide variety of different proteins.
2. Several strands may cluster together into a functioning unit, or a metal ion (mineral) or a vitamin may join to the unit and activate it. This is the use of many vitamins
The variety of proteins (4)
1. Each type of protein has a distinctive sequence of amino acids and so has great specificity
2. Like letters in the alphabet, the sequence of amino acids determines the identity of the protein.
3. The variety of possible sequences for amino acid strands is tremendous.
4. A single human cell may contain as many as 10,000 different proteins, each one present in thousands of copies.
Inherited AA sequences (5)
1. The sequence of amino acids in a protein is determined by heredity
2. If an incorrect amino acid is inserted, the result can be disastrous to health.
3. In sickle-cell disease, a glutamic acid in one strand is replaced with a valine.
- Analogous to spelling a word wrong - it no longer makes "sense"
4. Genes determine the sequence of amino acids in each finished protein.
5. Genetic information in a cell goes from DNA->RNA
- DNA is transcribed into messenger-RNA and translated into the amino acid sequence of a protein
AA: results of slight changes
1. A slight change in the primary structure of a protein affects its ability to function
- Affects its shape, charge, acidity, etc
- The substitution of one amino acid for another in hemoglobin causes sickle-cell disease
nutrients & gene expression (2)
1. Every cell nucleus contains the DNA for making every human protein, but cells do not make them all.
- Some genes are "expressed" and others are not depending on the cell type. only proteins needed
• For example, only cells of the pancreas express the gene for the protein hormone insulin.
2. Nutrients do not change DNA structure, but they greatly influence genetic expression
- Example: Too much vitamin A can harm a fetus.
what determines protein shape?
1. The function of a protein is dependent on its shape
2. The final shape of a protein is determined by its
primary structure (sequence of amino acids)
because this determines which R groups interact.
3. A protein's shape is also sensitive to the surrounding environment
- Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape
• Secondary, tertiary, and quaternary interactions and structure are disrupted
- This is called denaturation
- Without the proper shape, proteins lose their functions
denaturation of proteins
1. Proteins can be denatured (distorted in shape) by heat, radiation, alcohol, acids, bases, or the salts of heavy metals.
- During digestion, stomach acid denatures proteins, permitting digestive enzymes to make contact with the peptide bonds and cleave them.
- During cooking, denaturation also occurs.
digestion & absorption of proteins
1. Proteins (enzymes) activated by stomach acid, digest proteins from food, denatured by acid.
2. The mucus coating secreted by the stomach wall protects its own proteins from attack by either enzymes or acid.
• pH of stomach acid is 1.5.
denaturation: what happens (4)
1. Loss of 3-D shape
2. Loss of Function
3. Necessary for Digestion of proteins (1st thing that happens is denaturation
4. Environmental conditions
• temperature
• pH
• chemicals
protein digestion
1. By the time most proteins enter the small intestine, they are denatured and broken into smaller pieces.
- A few are single amino acids
- Most are large strands called polypeptides (but not full proteins)
2. In small intestine, pH rises by the action of bicarbonate, and enzymes (protease) continue digesting the strands into single amino acids or di- and tripeptides.
what happens to AA after protein digested (2)
1. The cells of the small intestine complete digestion, absorb amino acids and some larger peptides, and release them into the bloodstream for use by the body's cells.
2. Practically speaking, all proteins ingested are denatured and digested
- No pills can "aid digestion"
- Specific foods containing enzymes will not "digest the cells in your body"
AA absorption: overview (3)
1. Absorbed by cells of small intestine
• A few Larger molecules absorbed
• Hormones or allergens
2. separate sites for absorption of each AA
3. Released into the bloodstream
• Carried to the liver
Roles of proteins in the body (3)
1. Proteins are versatile, unique, and play important roles in the body
2. Proteins have been called "the primary material of life"
3. **The body makes enzymes, hormones, and chemical messengers of the nervous system from its amino acids
proteins: supporting growth & maintenance
The body needs dietary amino acids daily to grow new cells and to replace worn-out ones
- The entire process of breakdown, recovery, and synthesis is called protein turnover
Proteins: building enzymes, hormones & other components
1. Enzymes work as biological catalyst
• They speed up the rate of chemical reactions
• They participate in, but are not changed by the reactions
AA sequence of human insulin (4)
1. Some hormones are proteins
2. Chemical messengers made in many parts of the body that act on other tissues
3. Secreted in response to conditions that require regulation
4. Each hormone effects a specific organ or tissue and elicits a specific response
proteins: building antibodies
1. Antibodies are proteins that defend against foreign proteins and other foreign substances within the body (antigens)
• Part of the immune system
cell membrane protein functions (5)
Membrane proteins have a variety of functions:
- Channel Proteins
- Carrier Proteins
- Cell Recognition Proteins
- Receptor Proteins
- Enzymatic Proteins
proteins: maintaining fluid & electrolyte balance (4)
1. Proteins help regulate the body's electrolytes & fluids
2. Channel Proteins - Involved in passage of molecules through membrane.
3. Carrier proteins - Combine with substance to aid in passage through membrane
• cell may use energy to accomplish this = active transport
proteins: maintaining acid-base balance (4)
1. Proteins buffer the blood against excess acidity or alkalinity.
2. Acid - substance that releases hydrogen ions into watery solutions
3. Base (or alkali) - substance that accept hydrogen ions from solutions
4. Buffer - substance that opposes changes in pH (measure of how strong an acid or base is)
- accepts hydrogen ions when in excess
- Donates them when there is a deficit
proteins: blood clotting (2)
1. Proteins that clot the blood prevent death from uncontrolled bleeding.
2. Platelets release molecules that convert fibrinogen into fibrin
- Fibrin is a threadlike protein
- Fibrin forms a dense network to create a patch
proteins: functions (9)
1. Regulation of gene expression
2. Providing structure and movement
• Muscle tissue
• Other structural proteins
- collagen
3. Building enzymes, hormones, & other compounds
4. Building antibodies
5. Transporting substances
• Hemoglobin and lipoproteins
6. Maintaining fluid and electrolyte balance
• Edema
7. Maintaining acid-base balance
8. Blood clotting
9. Providing energy and glucose
proteins: providing energy & glucose (3)
1. When insufficient carbohydrate and fat are consumed to meet the body's energy need, food protein and body protein are sacrificed to supply energy.
3. The nitrogen part is removed from each amino acid, and the resulting fragment is oxidized for energy.
3. No storage form of amino acids exists in the body.
the fate of AA: general (3)
When an amino acid arrives in a cell, it can be:
- Used as is to build protein
- Altered somewhat to make another needed
compound, such as the vitamin niacin
- Dismantled to use its amine group to build a nonessential amino acid
• The remaining carbon, hydrogen and oxygen atoms can be converted to glucose or fat
the fate of AA: no glucose or fatty acids (2)
- The cell strips the amino acid of its amine group (nitrogen part) and uses the remainder of its structure for energy
- The amine group is excreted from the cell and then from the body in the urine
the fate of AA: surplus of energy (3)
In a cell that has a surplus of energy and amino acids, the cell
- takes the amino acid apart
- excretes the amine group
- converts the rest to glucose or fat for storage
AA are wasted when... (4)
- Energy is lacking from other sources.
- Protein is overabundant.
- An amino acid is oversupplied in supplement form.
- The quality of the diet's protein is too low (too few essential amino acids).
why do people take supplements? (3)
- Athletes take them to build muscle
- Dieters may take them to speed weight loss
- To strengthen their nails, relieve pain, and depression
protein supplements (4)
Protein supplements, including whey protein:
- Are popular with athletes
- Are not necessary for well-fed athletes
- Are not better than ordinary foods
- May place a burden on the kidneys to excrete excess nitrogen/urea
AA supplements (3)
- The body is designed to handle whole proteins best
- No level of amino acid supplementation can be assumed safe
- Much is still unknown, and there is no guarantee of their safety or effectiveness
food protein: quality, use & need (3)
1. The body's use of a protein depends in part on the user's health.
2. To be used efficiently, protein must be accompanied by ample carbohydrate and fat, vitamins and minerals.
3. Protein is influenced by a protein's digestibility and its amino acid** composition.
Protein-rich food: easiest to digest (3 in order)
Digestibility of protein varies from food to food.
1. Amino acids from animal proteins are most easily digested and absorbed (over 90%)
2. Amino acids from legumes are next (80 to 90%)
3. Amino acids from plant foods vary (70 to 90%)
Cooking with moist heat can improve digestibility whereas dry heat methods impair it.
AA composition: 2 types
1. High-quality proteins - provide enough of all of the essential amino acids needed to make new proteins
2. Low-quality proteins - do not provide all the essential amino acids (1 or more)
- If a nonessential amino acid is unavailable from food, the cell synthesizes it
- If the diet fails to provide an essential amino acid, the cells begin to conserve the amino acid and reduce their use of amino acids for fuel.
complementary proteins (3)
1. If a person does not consume all the essential amino acids it needs, the body's pools of essential amino acids will dwindle until body organs are compromised. (blood proteins go first)
2. Proteins lacking essential amino acids can be used only if those amino acids are present from other sources.
3. Complementary proteins - two or more proteins which together provide all the essential amino acids
essential AA: how many & how to get (4)
1. There are eight essential amino acids.
2. Different foods contain different ones.
3. Complementary proteins
4. Many "traditional" diets include mixtures of foods that provide "complete" proteins
• Beans and rice
• Beans and corn
• Peanut butter sandwich
complementary proteins (2)
1. Mutual supplementation of two or more foods
2. essential amino acids missing from one food can be provided by another
proteins: intakes (5)
1. The DRI recommendation for protein intake depends on size and stage of growth
2. DRI recommended intake is 0.8 gram per kilogram of body weight
3. Minimum is 10 percent of total calories
4. Athletes may need slightly more (1.0 gram per kg)
5. Vegetarians: 1.8 grams per kg
protein: how to calculate your needs
The DRI recommended intake is 0.8 g/kg To figure your protein need:
1. Find your body weight in pounds
2. Convert pounds to kilograms (by dividing pounds by 2.2)
3. Multiply kilograms by 0.8 to find total grams of protein recommended
nitrogen balance
Protein recommendations are based on nitrogen balance studies, which compare nitrogen excreted from the body with nitrogen ingested with food.
protein deficiency & excess (2)
1. Protein deficiencies and energy deficiencies are the world's leading form of malnutrition
2. Both protein deficiencies and excess are of concern, & need to be addressed separately
effects of too much protein
Protein-eneregy malnutrition (PEM) is the most widespread form of malnutrition in the world today.
PEM takes two different forms:
- Marasmus
- Kwashiorkor
Extreme food energy (including low-protein) deficiency
- Common in children - Muscle wasting - Impairments
- Disease conditions - Preventing death • Heart failure
2. The extreme loss of muscle and fat characteristic of marasmus is apparent in this child's matchstick arms
1. Kwashiorkor is the Ghanaian name for "the evil spirit that infects the first child when the second child is born."
- Each baby is weaned from breast milk as soon as the next comes along. The older baby no longer receives breast milk and is given a watery cereal with scant protein of low quality.
2. Kwashiorkor - low protein and/or low protein quality
- Weaning of babies - Fluid balance is diminished - Changes in body - Risk of infection
3. The edema and enlarged liver characteristic of kwashiorkor are apparent in this child's swollen belly.
PEM at home (7)
PEM is not unknown in the United States, where millions live on the edge of hunger.
- Inner cities
- U.S. Indian reservations
- Rural areas
- Some elderly people
- Hungry and homeless children
- People suffering from anorexia nervosa
- People with wasting illnesses such as AIDS, cancer, or drug and alcohol addictions
Protein: too much protein?
There is no benefit from eating excess protein
- Kidney & liver problems - Bone calcium loss
- Heart disease
- Cancer
protein: kidney disease (3)
1. Animals fed experimentally on high-protein diets often develop enlarged kidneys or livers.
2. In human beings, a high-protein diet increases the kidneys' workload but this alone does not appear to damage healthy kidneys or cause kidney disease.
3. In people with kidney problems, a high-protein diet may speed the kidneys' decline.
protein: adult bone loss (3)
1. Evidence is mixed about whether high intakes of protein from animal sources, especially when accompanied by low calcium and low fruit and vegetable intakes, may accelerate osteoporosis.
2. Feeding purified proteins to human subjects causes calcium to be spilled from the urine.
3. Too little protein may weaken the bones in malnourished elderly individuals.
protein: heart disease (2)
1. Foods rich in animal protein tend to be rich in saturated fat ---> Heart disease
2. Protein metabolism creates the amino acid
Homocysteine --->
- High blood levels correlated with heart disease and stroke
- Also related to smoking, drinking, coffee and B vitamin deficiencies
protein: Cancer
1. As for heart disease, the effects of protein on cancer causation cannot be easily separated from the effects of fat
2. Population studies suggest a correlation between high intakes of fatty and well- cooked red meats and processed meats and some types of cancer, particularly of the digestive tract, breast, and prostate.
protein: intakes
Health risks may follow the overconsumption of protein-rich foods.
Health recommendations advise between 10 and 35 percent of energy intake.
protein rich foods (2)
1. Protein is critical to nutrition
2. Displacement of other necessary foods
Advantages of legumes (5)
1. Protein quality of legumes is almost comparable to meat.
2. Vitamin and mineral source
3 Soybeans - complete protein. soy protein can be considered equivalent to meat. so can well chosen complementary proteins
4. Fiber
5. Low Fat
vegetarians: benefits & pitfalls
In affluent countries, people who eat vegetarian diets suffer less often from chronic diseases than people whose diets center on meat.
vegetarian: positive (3)
1. Strong evidence links vegetarian diets with reduced incidences of chronic diseases.
- Some benefits include
• Less obesity • Defense against certain cancers
• Less heart disease • Less high blood pressure
• May help prevent diabetes, osteoporosis, diverticular disease, gallstones, and rheumatoid arthritis
2. Some of these effects may arise more from what vegetarians include in the diet than from what they omit.
- abundant fruit, legumes, vegetables, and whole grains
3. Other health behaviors associated with being vegetarian: typically - Non-smoking - Non-drinking
- More physically active
• Even when these are factored in, vegetarian diets still show benefits
meat eaters: positive & negative
1. A balanced, adequate diet in which lean meats and seafood, eggs, and milk play a part in addition to fruits, vegetables and whole grains can be very healthy.
2. True meat lovers who shun all vegetables have no adequate substitutions for these foods (unlike vegetarians who can find suitable replacements for meat).
3. Critical times in life when animal protein may be needed -->Pregnancy and infancy Childhood
Adolescence Aging
support during critical times
1. Both meat eaters and lacto-ovo vegetarians can rely on their diets during critical times of life.
2. A vegan diet can pose challenges. Why?
3. Meat provides abundant iron, zinc, and vitamin B12 needed by everyone, but in particular by pregnant women, children, and adolescents.
poorly planned meat eaters (4)
- Vitamin A (high in plant products)
- vitamin C (fruits)
- Folate (B vitamins comes from grains
- fiber, among others