6.1 Dietary Protein Flashcards
What are essential amino acids?
They must be supplied by the foods people consume
What are conditionally essential amino acids?
They are amino acids that are normally non essential but essential under certain cpndotopms eg PKU or if the diet cannot supply the amino acid
What are non essential amino acids?
ALso called dispensable amino acids, the are hte ones that the body can create
Which amino acids are essential and which non essential?
What is the condensation reaction for the formation of the peptide bond?
- Condensation reactions involve the formation of a peptide bond between two amino acids
- The –OH group from the acid end and the –H from the amino end (NH2) join and breakaway as H20,
leaving a new bond joining the two amino acids.
What is the structure of proteins? Four levels
What are the four different bond types in a polypeptide?
- Hydrophobic Interactions: These amino acids orient themselves towards the centre of the polypeptide to avoid water
- Disulphide Bridge: The amino acid cysteine forms a bond with another cysteine through its R group
- Hydrophilic Interactions: These amino acids orient themselves outward to be close to the water
- Ionic bonds: positively and negatively charged R groups are attracted to one another
What is the difference between protein peptide and polypeptide?
- Protein is generally used to refer to the complete biological molecule in a stable conformation, whereas peptide is generally reserved for a short amino acid chain often lacking a stable three- dimensional structure.
- However, the boundary between the two is not well defined and usually lies near 20–30 amino acids.
- Polypeptide can refer to any single linear chain of amino acids, usually regardless of length, but often implies an absence of a defined conformation
What happens in protein denaturation?
- Functional protein showing a quaternary structure
- Heat, acid or other conditions alters the intramolecular bonds of the protein
- Unfolding of the polypeptide structure which results in loss of function
How is protein digested in the stomach?
- Partial breakdown (hydrolysis) of proteins begins in the stomach.
- Hydrochloric acid denatures proteins so that digestive enzymes can attack the peptide bonds. Hydrochloric acid activates the digestive enzyme, pepsin, from its inactive form (pepsinogen)
- Pepsin cleaves large polypeptides into smaller polypeptides and some amino acids.
How is protein digested in the small intestine?
- In order to protect the proteins of the small intestine, proteases are stored as inactive proenzymes. The pancreas stores trypsin as trypsinogen and chymotrypsin as chymotrypsinogen.
- Once chyme enters the small intestine, enteropeptidases converts trypsinogen to the active form trypsin.
- Trypsin then binds to chymotrypsinogen to the active chymotrypsin
- Trypsin and chymotrypsin breaks down protein to oligo-, tri- and di-peptides. These are further broken down to single
amino acids by intestinal peptidases
How is protein absorbed during digestion?
- Specific carriers in the membranes actively transport amino acids (and some di- and tri-peptides) into the intestinal cells.
- Intestinal cells may use the amino acids for energy or to synthesise new proteins
- Amino acids not needed by intestinal cells are transported to the surrounding capillaries where they head to the liver and cells throughout the body for protein synthesis.
What are fibrous proteins?
What are structural proteins?
How are proteins synthesised?
- Synthesis of protein is determined by genetic information (DNA). The DNA code is transferred to the cytoplasmic ribosomes by messenger RNA (mRNA).
- Transfer RNA (tRNA) lines up amino acids and brings them to the messenger RNA.
- The ribosomes move along the mRNA and read the code and join specified amino acids together in the order dictated by the code to make a specific protein molecule.
How is sickle cell anemia the result of a sequencing error?
- Sequencing errors can cause altered proteins to be made.
- An example is sickle-cell anaemia, where valine replaces glutamic acid in the amino acid sequence of two of the polypeptide chains.
- As a result of this one alteration, the haemoglobin shape is altered (disc-shape to crescent or sickle- shape) and this interferes with the red blood cell’s ability to carry oxygen.
What are some of the roles of protein in the body?
Protein is constantly being broken down and new types are synthesised in the body for:
1) structural purposes such as growth and replacement of proteins deteriorating with time
2) enzymes
3) hormones
4) fluid balance in the body
5) acid – base balance
6) antibodies for immune function
7) transport
8) source of energy and glucose
9) blood clotting
how does protein provide building blocks of most of the body structures?
- (eg. muscles, blood, skin, bone, hair)
- Collagen (protein matrix) → Bone, ligaments, artery walls, scars
- Replacement of dead or damaged cells (skin cells life span 30 days, GI tract cells replaced every few days, hair and fingernails continue to grow)
How do enzymes facilitate chemical reactions?
- Proteins catalyse chemical reactions including anabolic enzymes and catabolic enzymes
How do proteins act as hormones?
- Chemical messenger molecules produced in endocrine glands (ie. pituitary) as well as some organs (ie pancreas).
- Some hormones are lipids but many are proteins ie; thyroxine, oxytocin, insulin and glucagon
How do proteins regulate fluid balance?
- Proteins regulate the quantity of fluid in blood, cells and interstitial space.
- Fluid flows freely between compartments, but proteins cannot. Proteins are trapped primarily within cells and to a lesser extent plasma
- Cells attract water as fluid follows protein gradient via osmosis.
What is the role of proteins as antibodies?
- Giant protein molecules that combat antigens (foreign invaders)
- Without sufficient protein, the body can’t manufacture its army of antibodies
How do proteins act as acid-base regulators?
- Proteins act as acid – base “buffers”. They take up or release H+ from body fluids
- Under acidic conditions (low pH), there are many H + ions in the fluid. Protein absorbs the H + making less H + available in the fluid and pH rises (ie. less acidic). Under alkaline conditions pH is high ie few H +, so proteins release H + and pH lowered (ie more acidic).
- Prevents acidosis and alkalosis which can be life-threatening.
How are proteins involved in transport around the body?
- Carrier proteins in blood for transporting lipids, fat soluble vitamins, oxygen and minerals.
- Proteins attached to lipoprotein particles help suspend the particle in water (blood), so the fat rich particle can travel around the body
- Act as pumps in cell membranes, transferring compounds from one side of the cell membrane to the other. Eg. active transport of sodium and potassium
How are proteins a source of glucose and energy?
Proteins will be sacrificed to provide energy and glucose during times of starvation or insufficient carbohydrate intake.
How are proteins involved in blood clotting?
- During blood vessel injury, the protein collagen is exposed
- Platelets adhere to the exposed collagen
- Substances are secreted that induce platelets to aggregate and initiate a cascade of reactions leading to the formation of a blood clot
- Process results in formation of fibrin strands (protein) that
- cross link platelets and red blood cells to form a stable clot
- Fibrinogen and prothrombin are two of the clotting factor proteins found in blood
How does protein turnover occur?
- Protein turnover creates ‘free’ amino acids.
- Amino acid pool is made of degraded proteins and those from dietary protein intake.
- Can be used to make new proteins or nitrogen removed so the amino acid can be used as an energy source.
What is the nitrogen balance?
- In a healthy adult, when protein degradation = protein synthesis, ‘Nitrogen balance’.
- In childhood, pregnancy and recovery from illness, people are likely to be in positive nitrogen balance (taking in more protein nitrogen than being excreted: Nin> Nout).
- Negative nitrogen balance occurs in illness, starvation, injury (losing more protein nitrogen than being consumed; Nin< Nout).
How does deamination of amino acids occur?
Amino acids are striped of their amino group, resulting in ammonia and a keto acid. Keto acids can be used for energy metabolism (TCA cycle) or fat production.
How is ammonia converted to urea?
Excess ammonia is toxic (upsets acid-base balance). The liver combines ammonia with CO2 to make urea, a much less toxic compound.
How can a nitrogen source be used to synthesise non essential amino acids?
Cells can make non-essential amino acids from a keto acid and from a nitrogen source (Eg. ammonia)
How does transamination to synthesise non-essential amino acids occur?
The body can transfer amino groups (-NH2-) from an amino acid to a keto acid, forming a new non- essential amino acid and a new keto acid. Transamination requires the coenzyme vitamin B6
Which protein sources are the most well absorbed?
Animal proteins are 90–99% absorbed.
Plant proteins are 70–90% absorbed. S
oy and legumes are 90% absorbed.
Other foods consumed at the same time can affect digestibility
How do animal foods compare to plant foods in terms of their protein quality?
- Animal foods contain all the essential amino acids and are generally ‘high quality’ (complete proteins).
- Plant foods are diverse in content, and tend to be limiting in one or more essential amino acids (incomplete proteins).
- The best guarantee of amino acid adequacy is to eat foods containing high-quality proteins or mixtures of foods containing complementary proteins that can each supply the amino acids missing in the other.
What is MARASMUS (form of protein energy malnutrition)?
What is kwashiorkor (form of protein energy malnutrition)?
