Lecture 13 Protein-AA Function, Structure and Categorization Flashcards
Protein Functions
- **movement **(actin-myosin)
- structural proteins (collagen, elastin, keratin, actin, myosin)
- participate in & regulate metabolism (enzymes & hormones)
- transport (Hb, transferrin, albumin, Na/K ATPase pump)
- Communication (hormones)
- Protection against infection (immunoglobulins)
Why do we need to acquire protein from the diet?
No storage form of AA
* Maintain protein balance (>50% of dry body weight)
* essential amino acid supply
* used to make non-essential substances as well
How is obligatory protein lossed?
- through epithelia
- through urine/ feces
- synthesis of non protein substances
Basic structure of AA
What are the essential AA?
- histidine
- isoleucine
- leucine
- lysine
- methionine
- phenylalanine
- threonine
- tryptophan
- valine.
What are the AA?
Non polar side chain - Aliphatic
* Glycine (Gly)
* Alanine (Ala)
* Leucine (Leu)
* Isoleucine (Ile)
Imino
* Proline (Pro)
Aromatic
* Phenylalanine (Phe)
* Tyrosine (Tyr)
* Tryptophan (Trp)
Sulphur containing
* Cysteine (Cys)
* Methionine (Met)
Polar side chain - hydroxyl
* Serine (Ser)
* Threonine (Thr)
* Asparagine (Asn)
* Glutamine (Gln)
Charged side chain - acidic
* Aspartic (Asp)
* Glutamic acid (Glu)
Charged side chain - basic
* Histidine (His)
* Lysine (Lys)
* Arginine (Arg)
Describe the primary structure of AA
The linear number and order of the amino acids present
* Determined by the base pairs in the gene that codes for the protein
* Side chains make the protein unique and determine final protein structure
How do AA join together?
- An OH group from the acid end of one AA and an H atom from the amino group of another join to form a molecule of water
- A peptide bond forms between the two AA, creating a dipeptide
Describe the secondary structure of AA
Folding of protein into organized and predictable patterns
* depends on the constituent AAs & peptide bonds (globular or fibrous) of the primary structure
* Maintained by positive/negative charges, hydrogen bonds → α-helix or β-sheets
Describe the tertiary structure of AA
Additional folding of the protein due to interactions
between the R groups and spatial arrangement of single poly-peptide chains
* hydrogen bonds
* hydrophobic interactions
* van der waals interactions
* disulfide bridge
* ionic bond
Describe the quaternary structure of AA
Interaction between multiple poly-peptide chains
* In addition there are often non protein components called prosthetic groups.
Acronym to remember the essential AA
Help In Learning These Little Molecules Proves Truly Valuable
What AA are semi-essential?
cysteine and tyrosine
* cys is made from Met
* tyrosine is made from Phe
What makes the “non-essential” AA conditionally essential?
somewhat essential because extent of synthesis of some AA depends on dietary supply of precursor AAs &/or biosynthetic capacity
* under-developed/ insufficient synthesis
* increased requirement
* decreased synthesis
* defective synthesis
What conditionally essential AA are sometimes underdeveloped/ have insufficient synthesis?
- cysteine
- glutamine
- glycine
- tyrosine
- arginine
When is it common to have underdeveloped AA synthesis?
neonates
* When born the pathways are not up to speed they get developed so need a good supply of the AA because synthesis is not good yet
When is there a need for increased requirement of conditionally essential AA?
stress, injury, surgeries
* glutamine
What are the functions as glutamine?
- amide N donor for DNA biosynthesis
- precursor for glucose formation
- oxidative fuel for intestinal and immune cells
- improtant for inter-oran transport of N & C, rids tissues of excess NH4 (via glutamate)
may be needed in increased requirement
What conditionally essential AA is commonly needed due to to decreased synthesis?
arginine
* preterm infants cannot synthesize arginine
* adults it is synthesized in the urea cycle; in stress states there is decreased synthetic capacity
What are some functions of arginine?
- DNA synthesis
- urea metabolism
- CVD implications when there is no production
Where is arginine mainly synthesized?
SI and kidney
What is a common example of a conditionally essential AA that may have defective synthesis?
tyrosine due to lacking enzymes
* Phe cannot be synthesized to Tyr because there is no phenylalanine hydroxyalse (PAH) which can cause the condition phenylketonuria (PKU) where there can be a build of Phe and this can be toxic, hence Tyr becomes an essential AA in this case
* Person would take glycomacropeptide (GMP) which has minimal Phe
