Exam 2: Chapter 7, Proteins Flashcards
(27 cards)
What is the general structure of a proten/amino acids?
- Comprised of amino acids
- Nitrogen (amino) group
- Carboxyl (acid) group)
- Hydrogen
- Side chain (R)
What are essential and non-essential amino acids, and how many of each are there?
There are 11 nonessential amino acids, which the body can produce.
There are 9 essential amino acids that must be consumed from our diet, because they cannot be synthesized in the body.
Describe transamination
Transfer of an amino group from an amino acid to a carbon skeleton to form a new amino acid
Describe deamination
- Amino acid losing an amino group
- Amino group is incorporated into urea in the liver
- Excreted in urine
What is the difference between complete and incomplete proteins?
Complete Proteins
- adequate amounts of all of the essential amino acids
- animal proteins
Incomplete Proteins
- inadequate amounts of one or more of the essential amino acids
- plant proteins (except soybeans)
What foods can we pair together to get a complete protein?
Rice and beans.
Understand transcription and translation of proteins, and where these processes take place.
- Amino acids are linked by peptide bonds to form proteins
- Synthesis of protein determined through gene expression
- DNA transcription phase
- DNA code transferred from the nucleus to the cytosol via messenger RNA (mRNA)
- mRNA translation phase
- tRNA and ribosomes
- DNA-coded instructions determine shape, and thus function of proteins
Protein organization
- Primary Structure
- Order of amino acids determines shape
- Secondary Structure
- Weaker bonds between nearby amino acids form spiral or pleated sheet shape
- Tertiary Structure
- 3D folding determines function
- Quaternary Structure
- When 2 or more separate polypeptides interact to form a large, new protein.
- Example: Hemoglobin
What is protein quality?
Protein quality is determined by the food’s digestibility and amino acid composition compared with a reference protein that provides the essential amino acids in amounts needed to support growth.
The four ways to calculate protein quality:
- Biological Value (BV): Egg white has the highest BV →100
- Protein Efficiency Ratio (PER)
- Chemical Score
- Protein Digestibility Corrected Amino Acid Score (PDCAAS)
Protein quality definitions and formulas:
- Biological value (BV):
Definition:
A measure of how efficiently the absorbed food protein is converted into body tissue protein.
Formula:
To calculate BV = Nitrogen retained (g) / Nitrogen absorbed (g) x 100
Protein quality definitions and formulas:
- Protein efficiency ratio (PER):
Definition:
Compares the amount of weight gain by a growing lab animal consuming a standard amount of the protein, with the weight gain by an animal consuming a standard amount of a reference protein (casein).
Formula:
To calculate PER = Weight gain (g) / Protein consumed
Protein quality definitions and formulas:
- Chemical score:
Definition:
The amount of each essential amino acid in a gram of food protein being tested is divided by the “ideal” amount for that amino acid in a gram of the reference protein (usually egg protein). Scores range from 0-10.
Protein quality definitions and formulas:
Protein Digestibility Corrected Amino Acid Score (PDCAAS):
Definition:
The most widely used measure! This score is derived by multiplying a food’s chemical score by its digestibility.
Formula:
- Wheat has a chemical score of 0.47 and its digestibility is 0.90
- What is the PDCAAS of wheat?
- 0.47 x 0.90=0.42
Positive Nitrogen Balance:
Protein intake exceeds protein losses (ex: periods of growth and recovery from injury, illness, etc.)
Negative Nitrogen Balance:
Protein losses exceed protein intake (ex: inadequate protein intake accompanied by a serious, untreated illness)
Understand how to calculate grams of protein and calories from protein if given a nitrogen value
- Nitrogen makes up about 16% of the weight of an amino acid (16/100=6.25)
- Therefore, nitrogen intake multiplied by 6.25 provides an estimate of protein intake
Formula: Nitrogen (g) x 6.25= Protein (g)
Example: I consumed 20 g of nitrogen from my diet. How many grams of protein is this?
20 (g) Nitrogen x 6.25= 125 g protein
Understand how to calculate protein needs using the RDA
- AMDR (IOM): 10-35% kcal
- Adult RDA
- 0.8g/kg healthy body weight
- Recovery states
- 0.8 –2.0 g/kg body weight
Digestion and Absorption of Proteins (Overall Process)
- For some foods, the 1st step in protein breakdown takes place during cooking → Cooking denatures protein
- Enzymatic digestion of protein begins in the stomach
- Hydrochloric acid denatures protein
- Pepsin begins enzymatic digestion
- Small intestine
- Secretin and CCK released; stimulate release of pancreatic proteases (trypsin, chymotrypsin, carboxypeptidases)
- Amino acids absorbed into the portal vein
What is usually the first step of protein breakdown?
For some foods, the 1st step in protein breakdown takes place during cooking → Cooking denatures protein
What enzymes are involved in digestion of proteins in the stomach?
- Enzymatic digestion of protein begins in the stomach
- Hydrochloric acid denatures protein
- Pepsin begins enzymatic digestion
What enzymes are involved in digestion of proteins in the small intestine?
- Small intestine
- Secretin and CCK released; stimulate release of pancreatic proteases (trypsin, chymotrypsin, carboxypeptidases)
After digestion in the small intestine, amino acids are absorbed into the
portal vein
Digestion of protein, simplified. Just understand the chart.
