Proteins + Amino acids Flashcards
(43 cards)
What’s the energy source from proteins? (kcal)
4kcal per 1g of protein
What are the main roles of proteins?
Provide many essential functions in body…
- Digestive enzymes for chemical reactions
- Immune functions by antibodies
- Regulation of expression of DNA / RNA
- Move blood around body (Hg)
- Bodily functions by hormones
- Contraction of muscles
Describe the structure of a protein
Amino acids bound together via peptide bonds forming a polypeptide (primary structure)
- free amino group (N-terminus) one end
- free carboxyl group (C-terminus) at other end
What are amino acids structure?
A central carbon bound to…
- a hydrogen
- a nitrogen-containing amino group (NH2)
- a carboxylic group (COOH)
- An R group / variable side chain
What are the 2 types of amino acids?
Indispensable (essential) amino acids
Dispensable amino acids
Describe indispensable amino acids and what are conditional indispensable AAs?
They cannot be synthesised by body so adequate dietary intake is required
- such thing as conditional indispensable = usually not essential amino acids except in times of stress / growth / illness
Describe dispensable amino acids
These can be synthesised by the body
What do dietary proteins contain?
Usually a mix of both dispensable and indispensable amino acids
Describe digestion and absorption of proteins
- Mechanical breakdown in mouth (chewing)
- Chemical digestion in stomach - via hydrochloric acid which unfolds 3D structure revealing chain + enzymatic digestion by pepsin forming shorter polypeptides + chyme
- Digestion by pancreatic enzymes (trypsin, chymotrypsin + other proteases) = formation of tripeptides, dipeptides + AAs
- Once inside enterocytes of small intestine, all proteins are broken down to form AAs which are absorbed by blood stream + taken up by target tissues
What is chyme?
Chyme is a mixture comprised of gastric juices + partially digested food which is transported from stomach to small intestine
What are the dietary recommendations of protein (average weight adults - what is this for avg weighed male + female?)
Reference nutrient intake (RNI) for average-weight adults is 0.75g protein / kg of body weight per day
- Females - 45g / day (60kg)
- Males - 56g per day (75kg)
Why would males required more typically + how does protein need change for active individuals?
The greater protein intake for males is required to maintain nitrogen balance for muscle mass
- highly active individuals + growing children + pregnant women require more protein
How is protein intake different between continents?
India + Asia - meeting protein recommendation for an individual weighing 62kg (a lot from plant-based protein)
EU + US - these protein recommendations are sig. exceeded (a lot from animal protein)
What are the 2 kinds of severe acute malnutrition (affected by protein intake)
- Kwashiorkor
- Marasmus
Describe Kwashiorkor in more detail
Cause, age group, subcutaneous fat, oedema, liver, muscle wasting
Cause - protein deficiency
Age group - 6mo -> 3yrs
Subcutaneous fat - preserved
Oedema - present (build-up of fluid in body)
Liver - enlarged fatty liver
Muscle wasting - mild or absent
Describe Marasmus in more detail
Cause, age group, subcutaneous fat, oedema, liver, muscle wasting
Cause - protein + energy deficiency
Age group - < 1 yr
Subcutaneous fat - not preserved
Oedema - absent
Liver - no fatty liver
Muscle wasting - severe
How is excess protein stored?
It is stored as fat or excreted in urine
Why is excess protein a bad thing?
Metabolic burden
- Bones = high protein intake increases calcium excretion = bad bone health
- Kidneys = strain from filtering excess nitrogen
- Liver = overburdened metabolism
Increased disease risk
- heart disease + cancers - high animal proteins (red / processed) = coronary heart disease + some cancers
What could also be an underlying reason for increased disease risk from excess protein intake?
Often due to excess animal protein (red / processed) which often contain high amounts of saturated fats
How are proteins ranked + what is it dependent on?
Based on quality - how many AAs are present in biologically available format (20 key amino acids)
- dependent upon proportion of protein-derived AAs from digestion
- how similar are the AAs to those found in human cells
What is the protein quality score based on?
Amino acid composition, digestibility of essential AAs, human requirement of essential AAs
- PDCAAS - quality based on faecal digestibility
- now replaced by DIAAS - based on ileal digestibility
What are the 2 types of proteins based on quality?
- Complete proteins (high quality) - provide adequate amounts of all 9 essential AAs (e.g. animal proteins, soy, mycoprotein)
- Incomplete proteins (low quality) - do not contain adequate amounts of >1 essential AAs (e.g. nuts, grains, seeds, legumes)
So should you only eat complete proteins?
NO, obviously not!
It is possible to combine incomplete proteins sources to provide all 9 essential AAs
e.g. peanut butter on toast - complementing legumes (PB) with grains (bread) = complete protein
- however protein complementation does not need to be done at same meal to meet protein needs
Where is the largest reservoir for body protein?
Skeletal muscle - accounts for roughly 50% of total body protein
