Lecture 13 Protein-AA Function, Structure and Categorization

Question 1

Protein Functions

Answer 1

• **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)

Question 2

Why do we need to acquire protein from the diet?

Answer 2

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

Question 3

How is obligatory protein lossed?

Answer 3

• through epithelia
• through urine/ feces
• synthesis of non protein substances

Question 4

Basic structure of AA

Answer 4

Question 5

What are the essential AA?

Answer 5

• histidine
• isoleucine
• leucine
• lysine
• methionine
• phenylalanine
• threonine
• tryptophan
• valine.

Question 6

What are the AA?

Answer 6

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)

Question 7

Describe the primary structure of AA

Answer 7

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

Question 8

How do AA join together?

Answer 8

1. 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
2. A peptide bond forms between the two AA, creating a dipeptide

Question 9

Describe the secondary structure of AA

Answer 9

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

Question 10

Describe the tertiary structure of AA

Answer 10

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

Question 11

Describe the quaternary structure of AA

Answer 11

Interaction between multiple poly-peptide chains
* In addition there are often non protein components called prosthetic groups.

Question 12

Acronym to remember the essential AA

Answer 12

Help In Learning These Little Molecules Proves Truly Valuable

Question 13

What AA are semi-essential?

Answer 13

cysteine and tyrosine
* cys is made from Met
* tyrosine is made from Phe

Question 14

What makes the “non-essential” AA conditionally essential?

Answer 14

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

Question 15

What conditionally essential AA are sometimes underdeveloped/ have insufficient synthesis?

Answer 15

• cysteine
• glutamine
• glycine
• tyrosine
• arginine

Question 16

When is it common to have underdeveloped AA synthesis?

Answer 16

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

Question 17

When is there a need for increased requirement of conditionally essential AA?

Answer 17

stress, injury, surgeries
* glutamine

Question 18

What are the functions as glutamine?

Answer 18

• 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

Question 19

What conditionally essential AA is commonly needed due to to decreased synthesis?

Answer 19

arginine
* preterm infants cannot synthesize arginine
* adults it is synthesized in the urea cycle; in stress states there is decreased synthetic capacity

Question 20

What are some functions of arginine?

Answer 20

• DNA synthesis
• urea metabolism
• CVD implications when there is no production

Question 21

Where is arginine mainly synthesized?

Answer 21

SI and kidney

Question 22

What is a common example of a conditionally essential AA that may have defective synthesis?

Answer 22

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