protein and amino acids Flashcards
what is protein a major component of
plant and animal tissue
amino acids are needed in every what
living cell
why do we need a constant supply of protein
as Our bodies constantly make, break down and use proteins so we need protein to replace what we use.
We don’t store amino acids. As although stored in protein the protein always has a function to carry out so isn’t stored
what is excess protein converted into
energy or fat
protein is important in energy gen
if theres not enough protein or in form of glucose in body them what happens to muscles
broken down causing wasting - PEM. This helps to provide our bodys the fuel they need.
Wasting weakens muscles including the heart
insulin is a protein needed as what
a hormone for homeostasis
what is excess protein converted into and used for
proteins converted to glucose to be used as energy. Or to create fatty acids, so is incorporated into our fat store
what is the structure of protein
Made of strings of amino acids linked with peptide bonds.
there are 20 amino acids
R group determines the identity and unique chemical properties of the amino acid
alpha carbon is the central one
Amine group is a nitrogenous group
Proline is only amino acid that rings around the central carbon
what are essential amino acids and how many are there
9
Essential as were unable to synthesis that amino acid so it must come from diet
All 20 amino acids are needed
what are non essential amino acids and how many are there
Non essential – don’t have to get them from the diet as we can biochemically synthesis them
there are 3
explain semi-essential amino acids an dhow many there are
8
Semi essential amino acids we can synthesis but we need something else from the diet, Often another Animo acid to synthesis them
Cystine can only be synthesised if we have methionine (an essential amino acid)
We can only synthesis tyrosine if there’s adequate amount of phenylalanine in diet, (an essential amino acid )
what is Phenylketonuria (PKU)
Autosomal recessive disorder.
Cannot metabolise Phe due to (virtually) absent phenylalanine hydroxylase.
Excess Phe builds up in blood affecting brain development.
Heel-prick blood test in UK
Treatment is a low protein diet (Phe-restricted)
how do peptide bonds form
between CO and NH of 2 amino acids
it produces the product of water
often known as dehydration synthesis of polypeptides
what is the breaking of polypeptide bonds called
hydrolysis
as adds water across the bond
what is an ex of the structure of insulin
Sulphydryl (-SH) groups of 2 cysteine molecules may be oxidised to form a disulphide bridge.
what are the functions of proteins
Enzymes (e.g. amylase) (Anything ending is ase is an enzyme)
Energy source
Transport (e.g. haemoglobin) (eg na/k, channels, etc are all proteins)
Hormones (e.g insulin - released into blood by pancreas) (not all hormones are proteins but lots are)
Movement (e.g. actin & myosin - allow for shape changes in muscles allowing contraction)
Structure (e.g. collagen)
Storage (e.g. ferritin - stores iron in body)
Immunity (e.g. antibodies- for immune response)
Growth, differentiation and gene expression
explain hormones in terms of protein function
Chemical messengers made in one part of the body which act on cells elsewhere, e.g. insulin
hormones can travel slow taking minuets to hours for response
explain immune function in term of protein function
Antibodies are blood proteins which attack and inactivate bacteria.
Antibodies circulate in fluids, destroying targets
We have immune cells which manufacture proteins
Nervous system acts fast in seconds,
explain structural functions of protein
Fibrin in blood (can turn to a solid to clot blood when needed)
Collagen gives skin and bone their elastic strength
Keratin gives hair and nails their strength
nitrogen in protein foods is measured using what method, explain the method
Kjeldahl method.
Developed in 1883 by Johan Kjeldahl
Method used for UK food tables
Digestion
Neutralisation
Titration
name some non amino nitrogen’s
cyanide, nitrate, nitrite, nitrogen gas, azo compounds
what some of the amino nitrogen’s
- Amino acids
most have nutritional value
some excreted (no value) - Peptides, e.g. carnosine
- Nucleic acids
purines, pyrimidines (may be subtracted)
(Some biological amines are derived from nucleic acids )
why do children need more protein
as are growing
explain plant protein compared to animal protein nutrition in the diet
Plant protein has less value then animal protein . As its easier to get all amino acids with eating animal protein. But you can achieve all amino acids with plant diet but need lots more plant material eaten
If a child needs 1 g/kg/day milk/egg protein, they need how much of mixed animal and plant protein, and how much of just plant protein
1.5 g/kg/day mixed animal and plant protein
OR
2.0 g/kg/day plant protein per day
what are the UK DRV requirements for protein based on
on recommendations of FAO/WHO/UNU expert consultation in 1985.
Values based on estimates of amount of high quality egg or milk protein required for N equilibrium.
egg and milk protein are of highest quality
whats the requirement of protein during pregnancy and lactation
Pregnancy: +6 g/day
Lactation:
+11 g/day for 0-6 months
+8 g/day for 6+ months
whats the requirements of protein in g per kg/day
0.75g protein per kg/day
whats the upper limit on protein in g per kg/day
1.5g
whats protein quality determined by
the profile of amino acids, in that food substance
whats high quality protein
supplies all essential aa in the proportions needed by the body.
what is lower quality protein
lacks adequate amounts of one or more essential aa.
what is limiting amino acid protein quality
the essential aa present in the lowest amount relative to the reference protein.
whys the quality of protein in mixed diets not so important
because of ‘complementation’ of different proteins
Mixing protein sources increases the nutritional value of the mixture.
how can we express quality of protein
by comparing amino acid scores
The AA score doesn’t tell us what amino acid is missing tho
what is biological value (BV)of protein
The proportion of absorbed protein retained in the body
how can biological value of protein be calculated
N absorbed
N is nitrogen
examples of Biological values of protein in egg, meat, and wheat products
Egg, human milk 90 – 100 %
Meat, fish 70 – 80 %
Wheat protein 50 %
what is net protein utilisation (NPU), and what does it take into account
The proportion of dietary protein retained in the body
Takes into account digestibility of the protein
how do we calculate Net protein Utilisation (npu)
BV =
N retained X 100
—————-
N intake
NPU = BV x digestibility
explain the indictor of protein quality: Protein Efficiency Ratio (PER)
The gain in weight of growing animals per gram of protein eaten.
explain the indicator of protein quality: Relative Protein Value (RPV)
The ability of a test protein, fed at various levels of intake, to support nitrogen balance, compared with a standard protein.
what is the chemical score
Based on chemical analysis of the protein.
The amount of the limiting amino acid compared with the amount of the same amino acid in egg protein(egg white)
reference protein in calc will be egg protein
how do we calculate chemical store
mg of aa in 1g reference protein (mg/g)
what are DIAAS scores and how do we calculate them
Digestible Indispensable Amino Acid score.
Recommended to replace Protein Digestibility Corrected AA score (PDCAAS)
Reference protein = human milk
DIASS (%) =
100 X (mg of digestible dietary IAA in 1g of dietary protein) in wheat for ex
———————————————————————
(mg of the same dietary IAA in 1g of reference protein)
IAA = indispensable amino acids
DIAAS score will come across more often than other scores
give ex of protein sources of high quality
wholemeal bread
tortilla(maize)
peanuts
peas
roast chicken
baked cod
meat
Peanuts are high quality but not completely high quantity protein as limit an AA
Plant protein generally has lower levels of total protein than animal sources
where do protein sources in Scottish diet come from
Meat & meat products 38%
Cereals & cereal products 23%
Milk & milk products 13%
Fish & fish dishes 8%
Vegetables & potatoes 8%
Vegetables & potatoes 8%
Other(nuts and seeds) 7%
So most of protein source is from high quality meat products
Issue with red meat as protein is its levels of saturated fat and its sustainability, eg co2 emissions with growing that meat, etc
the processing of some plant material can chanage the profile of what
limiting amino acids
such as boiling rice can prevent lysine from being limited
ae red meats higher or lower in protein than white meats
little higher
explain how portion size should be taken into consideration when looking at protein content
Peanuts and meat / fish may have similar protein levels but portion size eat will be different, so will influence the protein levels. So take this into consideration
processing of wheat does what to protein content
reduces the content
how does toasting bread impact protein content
Toasting changes structure of bread which increases protein content, but isn’t always a healthier increase in protein
do softer or hander cheese have more protein
harder the cheese the more protein content
explain body composition between males and females
Women have more body fat than males to protect vital organs around pelvic area and for pregnancy
males have more protein in body than females
males hold more water in body than females
males have less essential fat in body than females
when do we lose bone mineralisation
We lose bone mineralisation as we age, starts in mid / early 20s in males and females
In menopause females lose bone minerals much faster
So why elderly females are at high risk of osteoporosis at old age
when does muscle protein decline
Our peak lean tissue is at age 30, after that age our muscle protein content starts to decline as we age, once were 50 rate of decline dramatically increases, so is why we lose muscle at old age but increase body fat. This leads to sarcopenia. If we lose too much protein then simple activities become difficult
The more muscles used at young age the longer it takes for muscle to reduce
Diet and physical activity prevent this
why do adults require protein
Adults require protein for repair processes
And cos protein is constantly broken down and needing renewed
Need calcium to replace calcium usage as the skeleton isn’t static, and to help repair bone
our dietary protein intake must replace what
what’s being excreted
explain the overview of protein metabolism
10kg protein in body. Protein is constantly degraded and resynthesized.
70g endogenous protein of the 80g from dietary protein is secreted into intestinal lumen, these are then digested and absorbed, the amino acids and dipeptides then go back into this amino acid pool, which is then in equilibrium with the proteins being synthesised and metabolised.
Small faecal loss of 10g a day. This is faecal nitrogen from undigested dietary protein and also from intestinal bacteria, and shed mucosal cells, and protective mucus
Some amino acids are oxidised with carbon skeletons used for glucogenesis or used as fuel. And nitrogen is excreted as urea
how can protein status be assessed
by measuring dietary intake of N compounds and output of N compounds.
Measuring the intake could be done by food dairies
nitrogen output sources
Urine
Faeces
Sweat
Shed skin cells
Hair & nail growth
Blood & tissue loss
Urine and feaces have greatest nitrogenous output
what are urinary nitrogen metabolites, and name and explain some urinary nitrogen metabolites
urinary N metabolites = things in urine that nitrogen is lost via
Urea: main N containing substance.
Uric acid: product of breakdown of purine nucleotides. High blood concentrations lead to gout. Which blocks blood vessels (Uric acids associated with diabetes’s and kidney stones and high sugar intake)
Creatinine: breakdown product of creatine phosphate in muscle. (Amount of creatinine excreted depends upon muscle mass (so why more excreted in men than women))
Creatine: N containing organic acid – helps supply E to cells –mainly the muscle (originates from meat)
Muscle loss increases when ill so you produce more creatinine and creatine
what is nitrogen balance or equilibrium
Intake = excretion (N balance or equilibrium)
So no change in total body content of protein, normal state in adults
whats a positive nitrogen balance
Intake > excretion (positive N balance)
Increase in body protein. Normal in pregnancy and growth
whats a negative nitrogen balance
Intake < excretion (negative N balance)
Gives net loss of nitrogen in body and loss in body protein
when would pos and neg balances of nitrogen occur
Pos nitrogen balance required in childhood as there growing etc
Neg nitrogen balance means ur losing lean tissue mass, so losing protein for muscle and is associated with illness, infection, trauma or inadequate intake
When losing weight we don’t want to lose weight as well as muscle protein
how can protein turnover be measured, and explain this
as half lives
Half life is the teim taken for labelling to fall to half of its original peak. 1 half life = loss from 100 to 50 %, 2 half lives = 50% to 25% etc
theres variation within protein half life
explain dynamic equilibrium in terms of protein turnover
If an isotopically labelled amin acid is given then the process of turnover can be followed, The labelled amino acids are rapidly incorporated into the newly synthesised proteins and are gradually lost as proteins are broken down. The rate at which the label is lost from an individual protein depend son the rate at which the protein is broken down and replaced
more on why do adults need protein
Continual catabolism of tissue proteins creates the requirement for dietary protein.
Also, protein lost in mucus, enzymes and other proteins secreted into the GI tract.
Requirements based on amount needed to maintain N balance.
Intakes above requirements do not result in positive N balance, except after protein loss
why do children need protein
Growing children should be in +ve N balance.
Requirement for growth smaller than for protein turnover.
Protein deficient child: grow slower so stunting of growth.
protein requirements when Recovering from trauma (tissue loss, or surgery) or infection
Patients will be in +ve N balance.
Do NOT require a diet richer in protein than usual.
Semi-essential amino acids (e.g. proline & glutamine) may become more essential in diet
why might people lose protein when ill
change and reduction in protein is due to the prolonged bedrest. So if someone unwell theyre confined to bed and protein loss can be due to wasting or atrophy of muscles that aren’t being used. So muscle protein s changed and reduced as normal but without the stimulus of exercise, less is being replaced so more lost
Protein loss mediated by:
Cortisol
Cytokines
