Chapter 7 Protein Flashcards
What elements are protein made of?
Carbon, hydrogen, and oxygen. Some contains nitrogen and mineral sulfur.
What is the building block of protein?
Amino acid.
The structure of amino acid
A central carbon bonded with 4 groups of elements.
What are the four groups elements bond with the carbon?
Nitrogen(amino) group, acid (carboxyl) group, hydrogen, and a side chain(R)
How many amino acids does body need?
20 different animo acids.
Nonessential amino acids
11 amino acids that we do not need to get from food, because our bodies can produce them by other amino acids we consume.
Essential amino acids
The amino acid that body cannot produce, and we can only get from food.
Why body cannot synthesize essential acids?
Because body cannot make carbon skeleton, cannot attach the group to the carbon skeleton, or cannot do the whole process fast enough to reach the need.
Conditional Essential amino acid
Some nonessential amino acid will be classified as conditional essential amino acid during the infancy, disease, or trauma.
Transamination
The process of body synthesizing nonessential amino acids.
Transamination involves
One amino acid lose an amino group and form another amino acid. Eg. One acid donates an acid group to another amino group’s carbon skeleton to becomes a nonessential acid.
Deamination
One amino acid lose an amino group but does not transfer it to another amino acid.
The transportation of animo acids
The amino acids incorporated in the urea of liver, and transported in the bloodstream, and go into the kidney, and excreted in the urine.
When the amino acid breaks down
To amino-free carbon skeleton, it is used as energy or synthesized into other compounds, such as glucose.
Difference between animal protein and plant protein
Animal protein contains all 9 essential amino acids, but plant protein doesn’t.
Classification of dietary protein
Animal protein is complete protein. Plant protein is incomplete protein, because it contains amount limited 1 or more amino acids.
Limiting amino acid
The essential amino acid in smallest supply in a food or diet in relation to body needs is called the limiting amino acid. 木桶原理中的短板
Complementary protein
Two or more plant proteins combine together to compensate the deficiency of each protein.
Do complementary proteins eat in one meal?
No, but the protein should be balanced over a day to provide sufficient amino acid to body. For non vegetarians, it is better to have small amount of animal protein.
Peptide bond
—CO—NH— 肽键
Joining the body of peptide can form
dipeptide, tripeptide, oligopeptides(4-9 peptides), and polypeptides(10 or more)
What kind of protein is most in body?
Polypeptides, ranging from 50 to 2000 animo acids. Body can synthesize many proteins by joining different combinations of of amino acids with peptide bond.
Gene expression
The process determine the synthesis of protein in body.
When does gene expression begin?
It begins when the DNA replicate.
What is gene served as?
It is served as a template to guide the duplication of genetic info carried by DNA.
Structure of DNA
DNA is a double-stranded, helical form. Each strand contains four nucleotides核苷酸.
4 nucleotides
A (adenine), G(guanine), C(cytosine), T(thymine)
Relation between 4 nucleotides
They are bind to each other, A and T, C and G.
Codons
Sequence of 3 nucleotides per unit of instruction which dictate where the amino acids should be placed in a protein and in which order. These nucleotides units are called codons.(密码子)
How many codons do amino acids have?
Some amino acids have only one codon, whereas most of the amino acids have 6 codons.
What is the result of mistake order or type of amino acids?
Profound health consequences.
Where is the protein synthesis?
Ribosomes in cytosol of cells.
RNA
DNA is in the nucleus. DNA code used to synthesize certain protein should be transferred from the nucleus to the cytosol to allow for such synthesis. The transfer is the job of messenger RAN.
DNA transcription
In order to produce RNA, DNA unwind its supercoiled state to let the enzyme read the code and transcribe it to a complementary single-strand mRNA molecule, called primary transcript.
The mRNA in the cell undergoes the process
Remove any parts of DNA which that do not code for the synthesis of protein.
mRNA translation
The RNA goes to ribosome and ribosome read the codons on the RNA and translate those instructions to produce a specific protein.
The process of synthesis of protein
It starts at a specific starting of RNA and continues until a specific ending codon is reached, such as UAA, UAG, or UGA.
tRNA (transfer RNA)
One key participant in protein synthesis in cytosol. The tRNA unit takes amino acids to the ribosomes as needed in during protein synthesis. The tRNA has a complementary code to mRNA. Numerous tRNA carriers are presented during protein synthesis to continually supply the ribosomes with needed amino acid.
Primary structure of protein
The sequential order and strong peptide bonding of amino acids in a polypeptide chain, called primary structure. It determine the shape of protein.
Once after the synthesize of polypeptide is completed
Indicates by the ending codons, it is released from the ribosome, as is the mRNA. And the polypeptide twisted into a complex 3-dimensional structure.
What does DNA code determine?
The shape and the function of the protein.
Secondary Structure
Amino acids must be accurately positioned in order to let the amino acids interact and fold correctly into the intended shape for the protein. This allows weaker chemical bonds to form between amino acids near each other and stabilize the structure. This spiral-like sheet is called secondary structure.
Tertiary structure
The 3-dimensional folding of a protein is tertiary structure.. It determines the overall shape and physiological function of protein.
Denaturation of protein
Exposure to acid or alkaline enzymes, solutions, heat, or agitation can change the structure of protein, leaving it to a denatured state. Alternative of protein’s 3-dimensional structure is called denaturation.
The benefit and harm of denature
Eg. The secretion of HCl change the structure of protein, but it make it easier to be broken down and digested. Also the heat will kill the bacteria in the food and make food taste better. But during the illness, changing of gastrointestinal acid, body temperature will make some protein lose their function.
Protein turnover
Proteins in body are in a constant state of broke down, rebuilding, and repair. It is a process that cells can increase the production of protein they need, and reduce the production of the protein not currently need.
The supply of protein
Proteins are supplied from food and recycling and reutilizing of amino acids that break down of food protein.
How much protein comes from animal source?
70% in North America, and 35% worldwide.
Why plant protein is better than animal protein?
It contains no cholesterol and little saturated fat.
How to evaluate the quality of protein?
The digestibility, the composition of amino acids compare to reference protein that provide essential amino acids in amount needed to support growth.
The digestibility of animal proteins and plant proteins.
Digestibility of animal acid is 90% to 100%, plant protein is 70%.
Concept of protein quality applies only occur
when the intake of protein equal or less than the need.
When protein intakes exceed the need
The efficiency of using protein decreases, because when the protein need is met, the remaining amino acids are used as energy.
Biological Value(BV)
It is a measure that how efficiency absorbed protein from food convert to the tissue protein.
Formula of BV
BV = Nitrogen retained/Nitrogen absorbed X 100
The BV of plant and animal protein
The BV of plant protein is much lower than animal protein.
Protein Efficiency ratio (PER)
The weight gain when a animal consume a standardized amount of protein compares to the weight gain when a animal consume a standardized reference protein.
What does FDA use of PER?
Set standard for the labeling of food intended for infants.
Formula of PER
Weight gain/Protein consumed
Chemical Score
The amount of essential protein in a gram of protein is divided by the ideal amount of amino acid in a gram of reference protein.
Protein Digestibility Corrected Amino Acid Score (PDCAAS)
Use the most widely. Chemical Score X digestibility.
A protein lack any of the 9 essential amino acid is 0, because the chemical score is 0.
Which protein has the highest BV?
Egg white protein.
Three good source of protein
Soy, edamame, peanut butter.
Negative nitrogen balance
When protein intake is less than the protein loss, it is negative protein balance. It usually happens on individuals who eating inadequate protein during illness or injury and those in diseases that increase protein breakdown.
Postitive nitrogen balance
When protein intake is more than loss. Usually happens on individuals during the period of growth and recovery from injury, illness, and trauma. And hormones insulin, growth hormone, and testosterone all stimulate the synthesis of protein for building tissue.
Why we use nitrogen to determine the protein?
Nitrogen is easy to quantified, it can be measured. And nitrogen is approximately 16% of protein.
Estimate protein intake
Nitrogen X 6.25 = Protein (g)
Why is it difficult to measure nitrogen balance?
Because it need the nitrogen of all the food intakes and nitrogen loss in 24 hours. It is not feasible outside the hospital. So it is easier to calculate RDA.
Recommended Intake of Protein
0.8 g/kg body weight for most adults. 10 to 35% of energy should come from protein.
56g/day for men, 46g/day for women.
RIP for people during injuries or athletes
2.0g/kg body weight
Digestion of protein
- During the cooking, the tough connected tissue is softened in meat.
- Some proteins are broken down by stomach acid, pepsin. But it can only break a few peptide bonds.
- In stomach. Protein is partially digested by enzyme pepsin and HCl.
- In pancreas. Further protein is digested by the enzyme produced by pancreas in small intestine.
- In small intestine. The final digestion. Breaks into amino acid.
- Liver. Amino acids are absorbed into the portal system from here. From here to enter the bloodstream.
- Large intestine. Some protein is present in feces.
Digestion during the infancy
Some small protein can be absorbed by GI tract directly.
When can infants use common allergenic food?
After 12 months.
Functions of protein
- producing vital body structure. 2. maintaining fluid balance. 3. Contribute acid-base balance（pH）. 4. forming enzymes, hormones, neurotransmitters. 5. Contributing o immune function. 6. Transporting nutrients. 7. forming glucose. 8. provide energy.
PEM
Protein-Energy Malnutrition. Usually occurs as marasmus and kwashiorkor.
Marasmus
Developed slowly from severe deficiency of energy. Overtime, this leads to extreme weight loss, muscle and fat loss, and growth impairment.
Kwashiorkor
Occurs more rapidly in response of to a severe deficit of protein, typically accompanied with underlying infections and disease.
Reason of kwashiorkor
The mother of a 12-18 month year old child is pregnant or have already given birth again, there is not sufficient milk for elder child. So the child change the diet abruptly to the gruel and root.
Kwashiorkor can be cured
If children are helped in time—infections are treated and have diets contains ample proteins and energy and other essential nutrients—the disease process can be reverse and grow again.
Marasmus
Result of chronic PEM. It is caused by diets containing deficient of proteins, energy, and other nutrients.
How much protein is suggested to intake
no more than 35% of energy intake
Kidney and high protein intake
High intake of protein will cause the overburden of kidney. And water is needed for kidney to excrete urea. So low protein with adequate fluid is recommended.
