Protein Flashcards
What do amino acids comprise of?
A nitrogen group (amine group)
A carbon skeleton
An acid group
A side chain (R) which determines structure/function/class
What are the 3 classes of essentiality in amino acids?
Non-essential: can be synthesised by the body
Essential: body cannot produce them, so must be sources from diet
Conditionally essential: essential at particular points in the lifespan (e.g. histidine in infancy, tyrosine in patients with PKA)
Explain the processes by which protein is digested and absorbed in the body
mechanical digestion in the mouth by teeth
gastrin release in response to food
gastrin signals HCl production and pepsinogen secretion
HCl denature protein in the stomach and activated pepsinogen to pepsin
Pepsin cleaves peptides to shorter fragements
Secretin and CCK are secreted and stimulate pancreas to release proteases: trypsinogen, chymptrypsin and carboxypeptidase
these activated enzymes breakdown peptides into dipeptides and AAs ready for absorption
AAs then enter bloodstream
Once in the amino acid pool what are the potential fates of AA’s?
- synthesis of proteins for cell structure, immune function, enzymes and hormones
- energy production from AA carbon skeletons
- synthesis of non-protein nitrogen containing compounds
- ketone production
- fat production when in excess
- glucose production from carbon skeletons of some AAs by gluconeogensis
Explain what happens in amino acid deamination
Amino acids are converted to pyruvate, acetyl CoA, intermediates of the CAC or oxaloacetate for gluconeogensis
- removal of amine group
- amine group is converted to ammonia then urea
- carbon skeletons of ketogenic AAs form acetyl coa and enter CAC
- carbon skeletons of glucogenic AAs form pyruvate to fuel energy production. Forms oxaloacetate for gluconeogensis in fasted state
Explain what happens in amino acid transamination
When additional non-essential amino acids are required in the amino acid pool
- transfer of an amine group from one AA to a new carbon skeleton to form a new AA
Vitamin B6 is an important cofactor
What are the 9 functions of protein in the body?
1) Rigid structure and contraction
- collagen, keratin and muscle fibres
2) Transport of nutrients
- membrane transporter proteins
- albumin/hemeoglobin
3) Hormone and Neurotransmitters
4) Acid/Base Balance
- proteins act as buffers as they are negatively charged
5) Immune Function
- antibodies are made from AAs
6) Fluid Balance
- blood pressure forces fluid out of capillaries, plama albumins and globulins attract back into capillary
7) Forming Glucose
- gluconeogensis used carbon skeleton of glucogenic AAs
8) Providing Energy
- 17kJ/gram
9) DNA Product Formation
- DNA is expressed into functional body proteins
What are the 4 levels of protein structure?
Primary: simple sequence of AAs
Secondary: shape of the molecule caused by weak H bonds
Tertiary: 3-D folding from interactions between R groups which determines shape of molecule
Quaternary: interactions between 2 or more polypeptide chains
Give an example of an inborn error of protein metabolism?
Sickle cell anemia
One code of AA sequence can change entire protein
Explain protein denaturing and in what conditions this occurs
Altering of the proteins 3-D structure
Occurs in acid/alkaline conditions, heat, enzymatically
HCl does this in the stomach
What is the AMDR for protein?
15-25% of total energy intake
Explain the body’s nitrogen balance
Nitrogen accounts of 16% of amino acid weight
How much you use your amino acids determines how much nitrogen you excrete
- if synthesising new proteins you excrete less nitrogen as you do no deaminate
- when not using carbon skeletons for gluconeogensis and ketosis you deaminate and nitrogen is excreted
Measured by comparing protein intake and nitrare excretion
When does a positive nitrogen balance exist?
During growth, pregnancy, recovery from illness, athletic training
When does a negative nitrogen balance exist?
Inadequate protein intake
Bed rest
Increased protein loss
What is a complete protein?
Contains all essential amino acids
What are complementary proteins
When two foods are incomplete but together contain all essential AAs
What is Biological Value
How efficiently the dietary protein is converted to body proteins. Needs all EAAs in the right ratio for a high score
Nitrogen retained/ nitrogen absorbed x100
What has a biological value of 100?
Egg white
What is a chemical score?
mg of each EAA per gram of test food/ mg of each EAA per gram of reference food
The lowest measured ratio is the limiting amino acid
What is PDCAAS?
Chemical score x digestibility
Explain what occurs in Coeliac disease
The body has an immune response to gluten
There is an over production of zonulin, which loosens the tight junctions between cells and allows gluten fragments to cross and trigger an immune response in the enterocyte
Over time this damages enterocyte and flattens villi
What is Kwashiokor?
The specific malnutrition of protein and only moderate energy deficiency. Includes:
- mild weight loss
- edema
- maintenance of some muscle
- 60-80% growth
What is Marasmus?
Protein and energy malnutrition. Involves:
- severe weight loss
- muscle wasting
- severe growth impairment
