Protein and Amino acid Metabolism and requirements Flashcards
What amino acids are a precursor of signal transducer?
arginine for nitric oxide synthesis
what are amino acids?
building blocks of protein
What elements do the amino acid structure contain?
carbon, hydrogen, oxygen, nitrogen and some cases, sulfur.
what is the structure of amino acid made of?
α-amino group, α-carboxyl group (acid group) and a side R-chain
what is aspartame?
artificial sweetener
Which combination of aspartame L and D configurations cause sweet taste?
L and L
Which combination of aspartame L and D configurations cause bitter taste?
D and L
L and D
D and D
The amino acid structure give it its properties, what type of properties are there?
- non-polar
- polar
- positive charge
- negative charge
What happens in condensation?
loss of H2O
What are polypeptide chains?
- chains of amino acid
- proteins made of many polypeptides
- have peptide linkages
- amine-carboxyl group linakge with condensation of H2O
What are the causes of protein degradation to amino acids?
- Abnormal proteins (mutant/damaged)
- Short-lived proteins (regulatory proteins/rate-limiting enzymes)
- Long-lived normal proteins (contractile proteins in muscle)
- Membrane proteins (e.g. receptors)
- Endocytose proteins (plasma proteins, hormones, lipoproteins)
- Mitochondrial proteins
What are the 3 pathways of protein degradation to amino acids?
- ubiquitin-proteasome pathway
- lysosomes
- mitochondrial proteases
What switches on the proteasomal pathway?
acidosis in muscle of patients with renal failure
What are the 2 stages in the proteosomal pathway when activated?
- Ubiquitin tagging
2. Proteolytic degradation
What are important regulators of protein metabolism?
- FOXO1
- Smad
- Akt (protein kinase B)
- mTOR
- 4EBP1
- p70S6K
What is FOXO1?
transcription factor
What is Smad?
signal transducer
What is Akt (protein kinase B)?
protein kinase which decrease apoptosis and increase protein synthesis
what is mTOR?
protein kinase that regulates cellular processes
what stimulates mTOR?
leucine metabolite α-ketoisocaproate
What is 4EBP1?
binds to elF4E (eukaryotic translation initiation factor 4E) and stops initiation
what is p70S6K?
increase protein synthesis
Name the levels of protein structure and what each structure is defined as:
primary = amino acid sequence
secondary = α helices, β sheet
tertiary = folded, compact with van der Waals forces and disulphide bridges
quatermary = non-covalent associate of polypetide chains, non-covalent hydrogen bonds/van der Waals forces
What percentage of the protein is in the muscle, skin, bones and the remainder?
muscle = 50% bone = 20% skin = 10% others = 20%
How many proteins are there in the body on a range?
30,000-50,000 proteins
What can all tissues do regarding non-essential amino acids?
- all can make non-AA
- remodel the mix of amino acids
- convert non-AA carbon skeletons into amino acids/other derivatives that have nitrogen
Which organ is the major site of nitrogen metabolism?
liver
when in dietary surplus, potentially toxic nitrogen of amino acids is eliminated via?
- transaminations
- deaminations
- urea formation
What are carbon skeletons generally conserved as?
- carbohydrate, via gluconeogenesis
- fatty acid, via fatty acid synthesis pathways
What are some 3 essential amino acids?
Arginine
Methionine
Phenylalanine
What is arginine and what is it needed for?
synthesised by mammalian cells, but rate insufficient to meet growth needs
what is methionine needed for?
large amounts to produce cysteine if insufficient in diet
what is phenylalanine needed for?
large amounts to form tyrosine, if not adequately supplied in diet
What two amino acids are conditionally essential, and what are they needed for?
arginine = essential in preterm infant glutamine = trauma, cancer
What happens in a diet low in lysine?
lead to incomplete protein synthesis
What is the limiting amino acid in wheat protein?
lysine
What is the limiting amino acid in maize protein?
tryptophan
What is the limiting amino acids in beef protein?
methionine, cysteine
Among vegetable proteins, which has the most complete amino acids?
soya protein
What is PDCAAS?
Protein digestibility corrected amino acid score
How do you calculate PDCAAS?
- Analyse nitrogen content
- calculate protein (N x 6.25)
- Analyse essential amino acid (IAA) content
- Calculate amino acid score (uncorrected)
- Determine digestibility
- Calculate PDCAAS
What is the formula for the amino acid score?
mg of EAA in 1g test protein DIVIDED by mg of EAA in 1g amino acid reference pattern
what is the PDCAAS formula?
= lowest uncorrect EAA ratio MULTIPLIED by true protein digestibility
What is the first step of amino acid catabolism?
removal of nitrogen containing amino group
removal of amino groups of 20 amino acids begins with?
transfer of groups to glutamic acid
What facilitates/catalyses amino acid transfer to glutamate, and what is the process called?
glutamate dehydrogenase
called “oxidative deamination”
what are the products of amino acid catabolism?
alpha-ketoglutarate and ammonium ion (NH4+)
What is the remainder of the carbon skeleton converted to?
- acetyl-coA
- pyruvate
- citric acid cycle intermediate
What are the 3 categories that amino acids fall into?
- glucogenic
- ketogenic
- glucogenic and ketogenic
What are the amino acids that are both glucogenic and ketogenic?
(remember ‘PiTTT’)
- phenylalanin
- isoleucine
- threonine
- tryptophan
- tyrosine
What are the amino acids that are only ketogenic?
- lysine
- leucine
What is the carbon skeleton remnant of ketogenic/lipogenic amino acids?
acetyl coA
What is the carbon skeleton remnant of glucogenic amino acids?
pyruvate, TCA cycle intermediate
What is the metabolic fate of ketogenic/lipogenic amino acids?
TCA cycle, energy production, ketogenesis, lipogenesis
What is the metabolic fate of glucogenic amino acids?
TCA cycle, energy production, gluconeogenesis
What does the greek word “anaplerosis” mean?
fill up
What does the greek word “cataplerosis” mean?
drain out
What is the sole purpose of the urea cycle?
remove ammonia from body
how much % of free ammonia at physiological pH?
1%
What are the dangers of ammonium salts?
- toxic
- causes vomiting
- convulsions
- ultimately coma and death
At what levels of ammonium ion concentration, would it lead to coma and death?
exceeding 250µM.
What ions do ammonium ions mimic?
potassium ions
What do ammonium ions possibly favour?
synthesis of excessive amounts of glutamate and glutamine = have excitatory effects on neural tissues
What is required for removal of urea via kidneys?
urea is soluble but requires appreciable quantities of water
What happens when cytosolic arginine is cleaved?
cleaved by arginase to urea and ornithine
How is citrulline formed in the urea cycle?
- cytosolic ornithine moves to mitochondrial matrix
- condensed with carbamoyl phosphate
What provides the urea cycle reaction its energy?
anhydride of carbamoyl phosphate
Where is citrulline transported to?
cytosol
Where are the two locations of urea cycle?
mitochondria and cytosol
What happens as a result of humans not being able to tolerate high concentrations of essential amino acids?
if not deposited as protein, they are oxidised by high-capacity, highly regulated oxidative pathways
what is the anabolic drive?
essential amino acids regulate protein synthesis and protein degradation
What are the 5 categories of nutrition disorders and nutrition related conditions?
- Malnourishment/undernourishment
- Sarcopenia/frailty
- Overweight/obesity
- Micronutrient abnormalities
- Re-feeding syndrome
Under the malnourishment tree, what are some examples of ‘disease-related malnutrition (DRM) without inflammation’ diseases?
- stroke
- dementia
- parkinson’s disease
- anorexia nervosa
- depression
- malabsorption (coeliac disease, short bowel syndrome)
How do you measure protein requirements via looking at muscle loss/gain?
anthropometry, MRI
How do you measure protein requirements via looking at nitrogen balance?
collect food/urine/faeces
How do you measure protein requirements via looking at protein turnover?
isotopic methods
What is positive nitrogen balance?
intake of N > total N output
What is negative nitrogen balance?
intake of N < total N output
What are some examples of excreted nitrogen compounds?
urea, bacterial protein, ammonia
uric acid, urea, creatinine, protein
required balance of nitrogen intake is?
5mg N/kg/day
Is less or more protein needed for pregnant women?
less
Who may need more protein requirements?
- patients with renal failure
- older people
- obese undergoing weight-loss therapy
