proteins and amino acdis Flashcards
functions
digestive enzymes
antibodies
support regulation and expression of dna and rna
support muscle contraction and movement
hormones
move essential molecules around the body
source of energy- 1g protein provides 4kcal
structure
proteins are large molecules made up of amino acids
joined by peptide bonds
amino acids
consists of a central carbon bound to:
hydrogen
nitrogen containing amino acid group
carboxylic acid group
R group/ side chain which makes it unique
types of amino acid
essential- indispensable- cannot be synthesised by the human body, adequate dietary intake needed
non essential- dispensable- can be synthesised by the human body
conditonally indispensable- essential- body cannot produce sufficient amounts of some dispensible amino acids
dietary protein will contain a diverse mix of both essential and non essential
digestion and absorption- mouth
mechanical breakdown - takes less than 1 min
D&A- stomach
chemical digestion- hydrochloric acid denatures proteins- unfolding 3D structure to reveal polypeptide chain- enzymatic digestion by pepsin forming shorter polypeptides, assisted by chyme
D&A- small inestine
protein digestion- digestion by pancreatic enzymes (trypsin, chymotrypsin) and other digesting enzymes proteases lead to the formation of tripeptides, dipeptides and amino acids
D&A- intestinal lining
once inside the enterocytes, tri and dipeptides are broken down into single amino acids which are absorbed into the bloodstream + taken up by target tissue
dietary protein recommendations
reference nutrient intake for average weight adults is 0.75g/kg BW
=45g/d for average female (60kg)
protein needs differ
higher for some populations
-growing children and adolescents
-women who are pregnant/lactating
-athletes
-older adults
kwashiokor
protein deficiency
subcutaneous fat is preserved
oedema is present
6months to 3 yo
enlarged fatty liver
muscle wasting mild or absent
will have larger tummy
marasmus
protein and energy deficiency
common in infants <1yo
subcutaneous fat not preserved
oedema absent
no fatty liver
severe muscle wasting
excessive protein intake
very high protein diets can be harmful
extra protein not used efficiently by body
may impose metabolic burden on bones, kidney and liver
large amounts of protein associated with increased risk of coronary heart disease and cancer
protein quality
proteins can be ran by quality- how many AA are present in a biologically available format
dependent on the proportion of protein derived AA from D&A
digestibiloty of indispensable amino acids
protein complementation
combining incomplete protein sources to provide all 9 essential amino acids
complementation does not have to be done at the same time to meet protein needs- can be done in 24 hour period
eg beans and vegetables are limited in methionie so can complement with grains, nuts and seeds
protein quality scoring
PDCAAS- protein digestibility amino acid score- based on the quality of faecal digestibility (rodent model)
DIAAS- digestible indispendable amino acid score- AA qualoty of food proteins based on ileal digestibility (pig model)- from ileum
WHO recommends DIAAS as is more accurate sample
When looking at protein quality, PDCAAS and DIAAS will result in different digestibility scores- limitation to both methods= only considers raw form of food and only 1g of the food which is different to how much will be consumed
protein digestibility
fraction of protein that is available for absorption once it has been ingested
skeletal muscle maintenance + growth
body protein is concentrated in skeletal muscle
skeletal muscle accounts for ~50% of total body protein, largest resevoir for amino acids
protein and ageing muscle
sarcopenia- biological ageing process is associated with a gradual loss of skeletal mass and function
normally begins age 40-50 and lasts to age 70
associated with reduced mobility, loss of independence and increased mortality
in sarcopenia- muscle has more fatty tissue in it
optimal protein intake (older adults)
for healthy older adults- 1-1.2g/kg bw per day
for older adults with acute/chronic illness- 1.2-1.5g/kg bw
daily physical activity is recommended for all older adults as well as resistance training
nutrition in combination with exercise is considered optimal for maintaining muscle function
higher protein needs
older adults have higher protein needs
skeletal muscle is comprised of muscle proteins that are continuously being remodelled
a key metabolic process of muslce remodelling is muslce protein synthesis (MPS) where AA are incorporated inot new functional muscle proteins
older adults have resistance to the positive effects of dietary protein on the synthesis of protein- anabolic resistance
anabolic resistance
MPS- muscle protein synthesis- increases in net gain in muscle protein
MPB- muscle protein breakdown
response to anabolic stimulus (MPS and MPB) is greater in young compared to elderly which can explain muscle loss- in older adults there is less MPS in response to stimulus
animal protein pros
source of high quality dietary protein for a large proportion of the global population, contain ideal combination of indespensable AA + unlikely to elicit any specific AA deficiences, highly digestible, contributes to micronutrient intake (eg vit b12)
animal protein cons
red and processed meat can increase risk of colorectal cancer, animal production is associated with greenhouse production and nitorgen pollution, unsustainable burden on global resources inclduing land and fresh water
