Chapter 6 - Protein Flashcards
How many different amino acids are used to make proteins?
20
Define
Protein
Large complex molecules composed of amino acids
What element is protein the primary source of in our diets?
Nitrogen
How many essential amino acids are there?
9; histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
What is the structure of an amino acid?
What reaction occurs to link amino acids together?
Condensation reaction (removal of water)
What does the sequence of amino acids in each protein determine?
Its unique shape and function
What does it mean if an amino acid is conditionally essential?
Nonessential amino acids that become essential in certain circumstances, such as illness or pregnancy
Acronym for essential amino acids: These Ten Valuable Amino Acids Have Long Preserved Life In Man
- Tryptophan
- Threonine
- Valine
- Arginine (conditional)
- Histidine
- Lysine
- Phenylalanine
- Leucine
- Isoleucine
- Methionine
How many amino acids are in a dipeptide? Tripeptide? Polypeptide?
2, 3, >50
What is the primary structure?
- sequence of amino acids joined together
- weak attraction within chain: H+ on one amino acid attracts O- on nearby amino acids
- Determines the type of protein and the way it folds
What is the secondary structure?
- weak attraction within chain: H+ on one amino acid attracts O-on nearby amino acids
What is the tertiary structure?
- hydrophilic and hydrophobic side chains
- disulphide bridges
- Twists and folds in chain, which are joined together by the disulphide bridges
What happens to the structure and function of a protein if it gets damaged?
Regardless of what level the protein is damaged, it may result in a non-functional proten
What is a sequencing errors?
Changes in protein structure and function; sickle cell anemia is an example as it has one different aa from a regular hemoglobin
What happens when a protein is dentaured and when does it occur?
- Denaturation is the loss of structure (unfolding); its a reduction in solubility and functionality
- It occurs >60 degrees, and at acidic pH
What happens to protein in the mouth?
Chewing and crushing moisten protein-rich foods and mix them with saliva to be swallowed
What happens to protein in the stomach?
Hydrochloric acid (HCl) uncoils protein strands and activates stomach enzymes (protein turns into smaller polypeptides)
What does HCl do in the stomach?
- Denatures protein structure
- Activates pepsinogen to pepsin
What happens to proteins in the small intestine and with the pancreas?
Pancreatic and small intestinal enzymes split polypeptides further:
* polypeptides into tri, dipeptides and aas
Then enzymes on the surface of the SI cells hydrolyze the peptides and absorb them:
* Peptides into amino acids
What does Pepsin do in the stomach?
- Cleaves proteins to smaller polypeptides and some free amino acids
- Inhibits pepsinogen synthesis
Why is pepsin released as pepsinogen?
prevents the auto-digestion of protective proteins in the lining of the digestive tract
Define
Pepsin
A gastric enzyme that hydrolyzes protein. Pepsin is secreted in an inactive form, pepsinogen, which is activated by hydrochloric acid in the stomach.
What does enteropeptidase do?
In the SI, it converts pancreatic trypsinogen to trypsin
What does trypsin do in the SI?
- Inhibits trypsinogen synthesis
- Cleaves peptide bonds next to the amino acids lysine and arginine
- Converts pancreatic procarboxypeptidases to carboxypeptidases
- Converts pancreatic chymotrypsinogen to chymotrypsin
What does chymotrypsin do in the SI?
-
Cleaves peptide bonds next to
the amino acids phenylalanine, tyrosine, tryptophan, methionine, asparagine, and histidine
What does carboxypeptidases do in the SI?
-
Cleave amino acids from the acid
(carboxyl) ends of polypeptides
What does Elastase and Collagenase do in the SI?
- Cleave polypeptides into smaller polypeptides and tripeptides
What does Intestinal tripeptidases do in the SI?
- Cleave tripeptides to dipeptides and amino acids
What does Intestinal dipeptidases do in the SI?
- Cleave dipeptides to amino acids
What does Intestinal aminopeptidases do in the SI?
Cleave amino acids from the amino ends of small polypeptides (oligopeptides)
How are the three ways proteins gets absorbed?
- Brush Border Membrane Na+ dependent transporters
- BBM Na+- independent transporters
- Basolateral Membrane
How do BBM Na+ dependent transporters work?
- Works with a sodium electrochemical gradient
- Bind Na+ which causes confirmational change, bind aa, and then sodium and aa get transported into the intestinal cell
How does protein absorption within intestinal cells?
- Cytoplasmic peptidases hydrolyze di, tripeptides to amino acids
- It is absorbed where it enters the hepatic portal vein
What happens to intact proteins in protein absorption?
- generally not absorbed due to BBM peptidases
- no transporters on BL membrane for proteins
- proteins can not permeate between intestinal cells
Where does protein go in postprandial metabolism?
ex. 30g meal
- 10g to synthesis and turnover
- 4g to intestine
- 4g to the muscle/kidney/adipose
- 12g to the liver where its turned into urea
Acronym for Protein Functions
- Structure
- Hormone
- Immunity
- Transport
- Sensation
- Movement
- Enzymes
What is the function of enzymes?
- Needed for chemical reactions
- Brings substances together (synthesis) or break them down (catabolic)
What is the function of hormones?
- Messengers in the body; they can target cells to alter metabolism, and regulate function
ex. insulin, glucagon, GIP
How do proteins function as transporters?
- Important in the transport of nutrients in the body (ex. lipoproteins)
- Proteins in cell membranes transport substances in and out of the cell
How do proteins function in fluid and electrolyte balance?
- Proteins attract water
- The correct balance between intracellular and extracellular proteins is needed to create fluid balance
How does edema occur?
This occurs when extracellular plasma proteins are low. This results in protein moving into the interstitial space of tissues, which draws water into it, into the tissue in particular, and causes it to swell
How do proteins act as buffers?
- They can accept and release hydrogen ions to maintain pH in body fluids within a narrow range
What occurs to proteins and the body if there is extreme pHs?
The proteins can be denatured and cause acidosis/alkalosis
How do proteins function as antibodies?
- antibodies are produced by B-cells in response to antigens, xenobiotics, allergens
- Required to protect against disease, provides immunity
- Protein is important in immune function (Maintaining all epithelial barriers) (immune cell synthesis and function)
Where are epithelial barriers found?
Skin, GIT, Respiratory, Reproductive
When is protein used for energy?
When there is an inadequate supply of dietary carbohydrates
How is protein used as an energy supply? (I.e. there is insufficient carbs)
- Glucogenesis used the carbons from aas to make glucose
- Nitrogen is then excreted in urine
Where are amino acids stripped to become glucose?
Either the pyruvate or TCA cycle
Define
Amino Acid Pool
Amino acids derived from the diet or protein degradation
What does protein synthesis and degradation determine in metabolism?
Determines the nitrogen balance, which is a marker of protein synthesis or breakdown
What is a limiting amino acid?
If just one amino acid that is needed to make a protein is not available, the protein will not be synthesized. That aa which is not available is considered limiing
What are common examples of limiting amino acids?
Lysine, Methionine, Threonine, Tryptophan
What five things regulate muscle protein synthesis?
- Insulin
- Testosterone
- Growth Hormones
- Some AAs
- Contraction and stretch
What three things regulate muscle protein degradation?
- Glucagon
- Epinephrine
- Mediators of inflammation
Define
Protein Turnover
Synthesis of new protein to replace degraded protein
Protein turnover accounts for what percentage of resting energy expenditure?
10-25%
What does nitrogen balance or maintenance mean?
Nitrogen intake (synthesis) = Nitrogen loss (degradation)
When does positive nitrogen balance occur?
During growth, pregnancy, and/or replenishment
When does negative balance occur?
During Starvation/Malnutrition, Injury, Illness
How do amino acids turn into urea in the liver?
Ammonia is produced from deaminated aas; this combines with CO2 to make Urea
If amino acids are not oxidized immediately for energy, what can they be used for?
- Gluconeogenesis
- Fatty acid synthesis (ketogenic aas turn into Acetyl CoA for the FA synthesis)
How much of our body protein turns over each day?
0.2-0.4%
What are protein requirements based upon?
Ensuring there is enough protein to replace losses, sustain turnover, and help growth
What is the RDA for protein?
0.8g/kg of body weight
What is the protein recommendation for athletes?
1.2-1.7g/kg
How much should protein contribute to total energy intake?
10-35%
What is a complete/high-quality protein?
A protein source which has all essential amino acids in sufficient amounts; animal sources are complete
What is the digestibility of differing protein sources?
- Animal sources: 90-99%
- Plant sources 70-90% (soy/legumes 90%)
What does the Protein Digestibility-Corrected Amino Acid Scores (PDCAAS) mean?
Between 0 and 1; 1 is for the sources that are most digestible and most balanced for essential aa content
What effect does protein have on heart disease?
Diets that are high in animal protein associated with elevated cholesterol; homocysteine levels in blood increase risk of CVD
This is why its recommeneded that meat intake is limited
What effect does protein have on cancer?
- High red meat or processed meat consumption is positively associated with risk of colon cancer
- Cooking meat at high temperature or over open flame can create carcinogens such as heterocyclic amines
What effect does protein have on osteoporosis?
Calcium excretion increased with high protein intake
* need a high Ca:ptn ratio to balance and protect bones from Ca depletion
What effect does protein have on kidney disease?
Protein does not cause kidney disease but people with chronic kidney disease have to monitor protein intake
Define
Plant-Based Diet
A diet of mostly plant foods with limited intake of animal products is associated with reduced risk of chronic disease
Define
Complementary Foods
protein sources (foods) that together supply all 9 essential amino acids.
Define
Protein-energy undernutrition (PEU)
A disorder caused by inadequate intake of protein, energy, and nutrients
Who is predominantly affected by PEU?
Children; 4:1 ratio
What are the two common forms of severe PEU?
Marasmus and Kwashiorkor
What is Marasmus?
Severe inadequate intake of protein, energy, and other nutrients
* Caused by starvation or malabsorption
What are the symptoms of marasmus?
- Severe wasting of muscle and adipose tissue
- Stunted physical growth and brain development
- Anemia
- Fluid and electrolyte imbalances
What is Kwashiorkor?
recent or acute extremely low protein intake and food deprivation following weaning, complicated by infections
What is the symptoms of kwashiorkor?
- Some weight loss and muscle wasting
- Edema and fatty liver
- Retarded growth and development
- Skin sores and brittle hair
What is the difference between marasmus and kwashiorkor?
Kwashiorkor is acute, while marasmus is chronic. Kwashiorkor also has edema and fatty liver, and a higher risk of mortality. Overall, marasmus is an adaptation while Kwasiorkor is a complication
What prevents adaptation to PEU in Kwashiorkor?
The response to the infection uses energy and protein which prevents the lowering of energy expenditure and protein turnover.
Globally, what are the most common deficiencies?
Protein-energy, iron, Vitamin A, and iodine
What nutrients are predominantly involved in immune function?
- Protein
- Vitamin A
- Vitamin C
- Zinc
What is PEM?
Protein energy malnutrition
Who at risk of PEM in Canada?
- Those in poverty, homeless, isolated rural areas
- Elderly
- People with EDs; drug and alcohol addictions
- People living with muscle wasting conditions
How should the adequate amount of protein be determined?
By looking at gram requirements vs. calorie % requirements; 50g = 10% of energy but you may need 100+ g
