Lecture 14 Flashcards
8x roles of Proteins
- Building material
- Hormones
- Enzymes- digestive
- Immune Function (Immunoglobulins)
- Fluid Balance (spaces- interstitials., inter/extra cellular spaces, maintin correct fluid volume-maintained by levels of proteins and electrolytes)
- Transporters - nutrients to sites required
- Antibodies
- Sources of Energy (2nd call after glucose/glycogen stores/carbs, convert aa amino acids–> glucose)
Amino acids
Amino group + C + Acid group
-+ side group varies (influential factor giving unique properties)
Non essential amino acids
Essential amino acids
Phenylalanine side chain
CH2 - Benzoate ring
Glycine side chain
H
Alanine side chain
CH3
Aspartic acid side chain
CH2 - COOH
9x essential aa Amino acids
essential = cannot be produced in body- have to be sourced in diet
- histidine (his)^1
- isoleucine (ile)
- Leucine (leu)
- lysine (lys)
- methionine (met)^3
- Phenylalanine (phe)^4
- Threonine (thr)
- Tryptophan (trp)
- valine (val)
8x non-essential aa Amino acids
Can be produced in body from essential amino acids/derived from metabolic products
- alanine (ala)
- asparagine (asn)
- aspartic acid (asp)
- glutamine (gin)
- Glutamic acid (glu)
- Glycine (gly)
- Proline (pro)
- Serine (ser)
Conditionally essential amino acids
=Non-essential amino acids sitting in essential side of aa amino acid table
Tyrosine - in people with phenylketinuria (they have to avoid dietary phenylalanine- cannot make tyrosine)
Arginine - in young infants (part. premature infants). no capacity to manufacture that aa arginine
Rare inborn metabolic errors sometimes make non-essential aa –> essential
Protein formation
Amino acids joined together to form water and Dipeptide
Peptide bond
Di-peptide
Tri-peptide
Polypeptides/proteins
-sequence of aa gives protein’s its function (dictated by DNA and RNA)
e.g. Hb Hemoglobin - polypeptide bound on its self with sulphur bonds, forming protein which attracts Iron and carries O2 around body
Incorrect protein sequences
When amino acid sequence is incorrect in a polypeptide/protein, protein cannot function in normal form
Haemoglobin
Illustration of Polypeptide/protein structure
-one of the four highly folded polypeptide chains that forms the globular hemoglobin protein
-Traps Iron
Heme-the non-protein portion of the hemoglobin- holds iron
The amino acid sequence determines the shape of the polypeptide
Sickle cell anaemia
Protein a/acids sequence in structure incorrect, stopping it from functioning normally
Genetic mutation that stops them from producing correct sequencing to make Hb
-crescent shaped
-reduced capacity to carry O2
Recommended intakes of Protein
RDI: Adults (not children or adlescent)
Males: O.84g/kg/day
Females: 0.75g/kg
Recommmended Percentage: 12-25% of energy intake (4kcal per gram)
(1.6-8 g/kg) - for more active people, protein utilisation/synthesis/turn over increased
Derivation of RDI
- arbitary or established
- balance studies : during WWII where people were starved of specific nutrients in concentration camps, until became deficient, then refeed. once deficiency reversed would call that is the nutrient requirement for that individual
Consuming extra protein supplements for gym
(1. 6-8 g/kg) - for more active people, protein utilisation/synthesis/turn over increased
- can easily increase protein intake
- majority of NZ’s consume 120% more protein than required
- whey protein- from milk products. just use skim milk powder
- build muscle by working fibres and do resistant activity to increase muscle mass (not by consuming more protein)
- But when your physical activity has increased = increased protein turnover = do need to eat more protein (but dont know the impact of eating excessive amount of protein)
- large popn studies done, people eating high amounts of protein, esp. from animal sources/meat have higher risk of CDV and cancer
- also if dont consume enough fluid with them- can result in kidney problems
- some renal stones
Protein quality
High quality proteins - food which supplies the Essential a/acids (varying sources e.g. for vegans)
Digestibility
-Animal (easier digestion and absorption)vs. plant
Amino acid composition
-according to limiting amino acid
“some legumes, nuts, seeds, fish and other seafood, eggs, poultry (e.g. chicken) and/or red meat with the fat removed
-guideline emphasises getting more protein from non-animal sources. and making sure protein makes up a proportionate amount of diet
-recommended to have 1-2 servings of protein daily (not all from meat/mixed sources)
Protein quality sources
Reference protein Complementary protein Legumes: Ile Lys Grains:Met Trp Together: Ile Lys Met Trp -combine different plant based sources and carb sources, to make up all essential aminoacids (dont need to eat animal products to get all essential a/acids) -beans and rice
Protein absorption in mouth
Mouth and salivary glands
Chewing and crushing moisten protein-rich foods and mixing them with saliva to be swallowed
-breaking down fibres assoc with protein (e.g. in meat structure)
-dont produce digestive enzymes in mouth
Protein absorption in stomach
HCl uncoils protein strands and activates stomach enzymes
(pepsinogen –> pepsin)
-protein enzymes secreted into gut in precursor state, otherwise would digest yourself
Protein –Pepsin + HCl –> smaller polypeptides + a/acids(cleaved of pp chain)
-not a huge amount of digestion occurs in stomach, but just enough to be in smaller chain lengths before SI
-mixing of chyme and release signals pancreatic enzymes and intestinal enzymes
Protein absorption in small intestine
Pancreatic enzymes and small intestinal enzymes spit polypeptides further
(Pancreatic Endopeptidases- Trypsin, Chymotripsin and Elastase)
Polypeptides –pancreatic and intestinal proteases –> tripeptides, dipeptides and a/acids
Then enzymes of the surface of the small intestinal cells hydrolyse these peptides and the cell absorb them
(intestinal enzymes specific for chopping up smaller chain lengths of peptides (Tripeptidases, Dipeptidases and aminopeptidases)
Peptides –intestinal tripeptides and dipeptidases –> aminoacid (absorbed)
-cascading event: one enzyme system has to cut up longer chain lengths, have to wait until small chain lengths can start cleaving of a/acids.
-some specific to certain a/acids, only cleave of points of peptide where certain a/acid sits)
HCl and the Digestive enzymes in the Stomach
HCl -denatures protein structure -activates pepsinogen to pepsin Pepsin -cleaves protein to smaller polypeptides and some free a/acids -inhibits pepsinogen synthesis
List of intestinal digestive enzymes
Enteropeptidases Trypsin Chymotrypsin Carboypeptidases Elastase and collagenase Intestinal tripeptidases Intestinal Tripeptidases Intestinal Aminopeptidases
Enteropeptidases in small intestine
-enterokinase
Converts pancreatic trypsinogen to typsin
Trypsin in small intestine
Inhibits trypsinogen synthesis
Cleaves peptide bonds next to the a/acid lysine and arginine
Converts pancreatic procarboxypeptidases to carboxypeptidases
Converts pancreatic chymotrypsinogen to chymotrypsin
Chymotrypsin in small intestine
Cleaves peptide bonds next to the amino acid phenylalanine, tyrosine, tryptophan, methionine, asparagine and histidine
Carboypeptidases in small intestine
Cleave a/acids from the acid (carboxyl) ends of polypeptides
Elastases and collagenase in small intestine
Cleave polypeptides into smaller polypeptides and tripeptides
Intestinal tripeptidases in small intestine
cleaves tripeptides to dipeptides and aminoacids
Intestinal dipeptidases in small intestine
cleaves dipeptides to a/acids
Intestinal aminopeptidases
cleave a/acids from the amino ends of small polypeptides (oligopeptides)
pancreas negative feedback loop
once trypsin is produced
- it stops the production of trypinsogen
- trypsin reaches a certain level, feeds back to pancreas
Disease of pancreas re protein digstion
inability or reduction of pancreatic enzyme secretion
-decrease of digestion and absorption of protein
(no trypsin activation to initiate protein digestion - enzyme cascade)
Protein absorption
Proteins –>
Peptides –>
(most absorption facilitates by sodium of H (active cotransported) )
a) Di and Tripeptides cotransport with H+ (active)
b) Amino acid cotransport with Na+ (acitve)
-ecoport on basalateral mebrane, which swaps sodium with potassium, allows active gradient to occur which allows a/acids and peptides into cell
-some breakdown of di- and tri-peptides by peptidases in the enterocyte itself –> converting them into a/acids
c) Small peptides are carried intact across the cell by transcytosis
-engulfed by membrane and diffuse into enterocyte
All enter venule –> villi –> portal vein –> liver –> changes a/acids structure depending on body requirement
Nitrogen Balance
Nitrogen intake = Rate of Nitrogen expenditure
-majority of people are in balance
Nitrogen balance N in = N out
-measure nitrogen rather than protein, as nitrogen is the products which are measured in uring
gN x 6.25 = g protein
Factors causing negative nitrogen balance
- Decreased protein intake (over the short term) (trying to lose weight, unwell and no appetite)
- Starvation or reduced GI function(decreased protein absorption)
- Injury, trauma or surgical operation
- Illness or infection or burns (up to 70g/d) (esp severe/high percentage of body burns- sometimes the negative nitrogen balance which will kill them. Unable to synthesise enough protein to repair burn damage)
-even if youre desperately to give them nitrogen/proteint through NG tube or vein often cant get enough in to synthesize enough protein to repair burns) - Some post operative conditions
- Many cancers
-Catabolism of cancer= Cakexia (not starvation. caused inflammatory factor produced by the cancer cells, pushing people into hypercatabolic state, cuasing neg nitrogen balance. sometimes hard to correct, even through given medication to try slow down process/high protein diet. so debilitating that kills them) - Lactation
- whenbreast feeding. but temporary and not risky re mortality
Degradation > Synthesis
Factors which cause Positive nitrogen balance
- Increased protein intake (over short term)
-only for a temporary time, as body will always try to return to equilibrium
-temporary +ve n balance, utilise for energy and then will adapt and will start to excrete more nitrogen containing products i.e. urea - Growth
-growth spurts during first 6months of life, prepubertal growth spurt - Pregnancy
- Recovery from illness or trauma
-after being in -ve nitrogen balance. will metabolically start to convert to try increase synthesis synthesis or protein and reduce degradation
-“Ebbing phase”: metabolism changes into positive nitrgoen state to try and get body to equilibriate its nitrogen balance
Synthesis> Degradation
What does nitrogen balance mean
stage of nutrition
whether need to intervene or not
Urinary nitrogen losses to asses protein losses
Record mmol/day Calculate mg/d
24hr urine urea
24hr urine creatine
24hr urine uric acid
Insert into formula and figure out nitrogen balance
-now labs do the calculations
-used in clinical practice esp for patients who are severely traumatised
Protein Energy malnutrition
Infections- Dysentery
Rehabilitation
-not really seen in NZ
-is seen in Aus
The toll of malnutrition
Global deaths of children under 5 years by cause 2008, % of total
-greatest age group effected by malnutrition
8.8 million total deaths per year
-35% of which are due to malnutrition (particularily protein-energy malnutrition)
34% Other
18% Pneumonia
15% Diarrhoea
12% Prematurity
9% Malaria
9% Birth asphyxia
3% HIV/AIDS/Measles
-stats havent changed much even with millenium goals
Malnutrition Infection Cycle
If not much food around
becomes malnourished
susceptible to infection
once got infection and not much food around = makes infection worse
even when try to rehabilitate/feed them, almost missed the boat
-really difficult to eat enough and regain appropriate nutritional status to have appropriate immunity to fend off further nutrition
-this Malnutrition Infection cycle eventually kills them
Marasmus
Severe deprivation, or impaired absorption of protein, energy, vitamins and minerals
Develops slowly(over long periods of time); chronic PEM
-countries experiencing chronic famine due to war/inability to transport food to those who need it.
-diets are poor overall, not just energy
Severe weight loss (chronic)
Severe muscle wasting, with no body fat
Growth:
Kwashiorkor
More acute: occurs where acute shortage of food (esp protein) Older infants and young children (1 to 3 years) (more than adults)
Inadequate protein intake or, more commonly, infections
Rapid onset acute PEM
Some weight loss (not as much as marasmus)
Some muscle wasting, with retention of some body fat
Growth: 60-80% weight for age (effects children’s growth)
Edema
Enlarged fatty liver (collection of water particularily around liver) - characteristic
Apathy, misery, irritability, sadness
Loss of appetite
Hair is dry and brittle; easily pulled out; changes colour; becomes straight
-assoc wih other micronutrient deficiencies (zinc, iron, B vit) - effecting hair and skin
Skin develops lesions (and infections)
Summary
Proteins are made up of AA, 9 of which are essential
Cell Synthesise proteins according to DNA
-sequencing of a/acids important
Protein has many roles in the body
Proteins are constantly synthesised and broken down
This can be tracked by measuring nitrogen balance
Dietary protein adequacy is characterised by AA and protein digestibility of food
