Amino Acids and Peptides

Question 1

What is the 21st amino acid?

Answer 1

Selenocysteine

(that include certain peroxidases and reductases, selenoprotein P1, and the iodothyronine deiodinase responsible for converting the prohormone thyroxine(t4) and t3.

Question 2

The alpha carbon of every amino acid is chiral except

Answer 2

GLYCINE

Question 3

All protein amino acids all share the absolute configuration of L- glyceraldehyde and thus are defined as L- amino acids. TRUE OR FALSE

Answer 3

True

Question 4

Provide monomer units for formation of long polypeptide chains of proteins

Answer 4

L-amino acids and their derivatives

Cellular fxns:
Nerve transmission
Biosynthesis of porphyrins, purines, pyrimidines, urea

Question 5

Cellular fxns of L amino acid

Answer 5

Nerve transmissions

Biosynthesis of porphyrins, purines, pyrimidines, urea

Question 6

Short polymers of amino acids

Answer 6

Peptides

Question 7

Perform roles in neuroendocrine system

Answer 7

Peptides

.. Such as hormones, hormone-releasing factors, neuromedulators, neurotransmitters

Question 8

Only L-amino acids occur in Proteins. TRUE OR FALSE

Answer 8

TRUE

Question 9

Amino acids may have positive or negative charge. TRUE OR FALSE

Answer 9

TRUE

Question 10

pKa values express the strengths of strong acids. TRUE OR FALSE.

Answer 10

FALSE. Weak acids.

Question 11

pKa values do not vary w/ the environment. TRUE OR FALSE.

Answer 11

False. Do vary.

Question 12

At its isoelectric pH (pI), an amino acid bears no net charge. TRUE OR FALSE

Answer 12

True

Question 13

The solubility of Amino Acids reflects their ionic character. TRUE OR FALSE.

Answer 13

TRUE

Question 14

A given amino acid having more than one triplet coding for it.

Answer 14

Redundancy. (Limits the available codons to the 20 amino acids)

Question 15

Humans cannot synthesize 10 of the 20 common L-amino acids. TRUE OR FALSE

Answer 15

TRUE. Thus, human diet must contain adequate quantities of these essential amino acids

Question 16

Nutritionally essential Amino Acids

Answer 16

HILLAMPTTV

Histidine
Isoleucine
Leucine
Lysine
Arginine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine

Question 17

Found in peroxidases and reductase where it participates in the catalysis of electron transfer reactions.

Answer 17

Selenocysteine

Question 18

Not specified by a simple three letter codon unlike the others

Answer 18

Selenocysteine

Question 19

A selenium ion replaces ______ of its structural analog, cysteine.

Answer 19

Sulfur

Question 20

All proteins/amino acids all share the L-glyceraldehyde configuration. TRUE OR FALSE

Answer 20

TRUE. thus are L-amino acids.

Some proteins/amino acids are dextrorotatory/ levorotatory.

Question 21

Amino acids that fulfill roles in metabolic processes

Answer 21

OCA - urea synthesis

Ornithine
Citrulline
Argininosuccinate

Question 22

Other metabolic processes

Answer 22

Tyrosine in thyroid hormone
Glutamate in neurotransmitter
Biosynthesis

Question 23

Both -COOH and R-NH3 are strong acids. True or false

Answer 23

False. Weak acids.

Question 24

Molecules that contain an equal number of ionizable groups of opposite charge and therefore bear NO NET CHARGE (electrically neutral)

Answer 24

Zwitterions

Question 25

At its isoelectric ph (pI), an amino acid bears no net charge. TRUE OR FALSE

Answer 25

True

Question 26

Isoelectric pH

Answer 26

pI - the pH midway between pKa values on either side of the isoelectric species - zwitterions are examples of isoelectric species

Question 27

Net charge depends upon

Answer 27

1) pKa values of its functional groups | 2) pH of its surrounding medium

Question 28

Characteristic pH at which the net electric charge is zero is called

Answer 28

Isoelectric point or "pI"

Question 29

Amino acid at the isoelectric pI is called

Answer 29

Zwitter ion - electrically neutral ( not migrating in an electrical field)

Question 30

Polar environment favors _____ form.

Answer 30

Charged form. | Polar- charged form (Non polar - uncharged form)

Question 31

Non polar environment: A) raises the PKa of a _____ group. B) lowers pKa of ____ group.

Answer 31

A) carboxyl group (making it weaker acid) | B) amino group (making it a stronger acid)

Question 32

Charged functional groups of AA ensure that they are: ________ in polar solvents (ex. ___ and ____) ________ in nonpolar solvents (___, ____, ____)

Answer 32

Soluble ( water and ethanol) | Insoluble (benzene, ether, hexane) BEH

Question 33

Can reinforce/counteract solvent effects

Answer 33

Adjacent charged groups

Question 34

Amino acids do not absorb light and thus are colorless. True or false.

Answer 34

True

Question 35

Ten times more efficient in absorbing light than phenylalanin and tyrosine. Major contributor of protins to absorb light

Answer 35

TRYPTOPHAN (250-290nm)

Question 36

Hydrophobic R groups of alanine, valine, leucine and isoleucine occur primarily in the + AROMATIC R groups of phenylalaninr , tyrosine and tryptophan

Answer 36

Interior of cytosolic proteins

Question 37

Smallest amino acid, often occurs where peptides bend sharply

Answer 37

Glycine

Question 38

Stabilize specific protein conformations via ionic interactions or salt bridges

Answer 38

Charged R groups of basic and acidic amino acids

Question 39

Histidine

Answer 39

Plays unique roles in enzymatic catalysis

Question 40

Plays a role in ezymatic catalysis

Answer 40

Histidine Pka of its imidazole proton permits it to fxn at neutral ph as either a base or acid

Question 41

Most important reaction of amino acids

Answer 41

Formation of peptide bond

Question 42

Chemical reactions exhibit all of its characteristic chemical rxns

Answer 42

- carboxylic acid group (formation of esters, amides, acid anhydrides) - amino groups: acylation, amidation, esterification

Question 43

Alcohol group of SERINE and the primary thioalcohol group of cysteine are excellent

Answer 43

NUCLEOPHILES

Question 44

Amino acid sequence determines primary structure. True or False

Answer 44

TRUE

Question 45

Peptide bond has

Answer 45

Partial Double bond character

Question 46

Peptides are

Answer 46

Polyelectrolytes

Question 47

Noncovalent forces constrain

Answer 47

Peptide conformations

Question 48

Amino acids present in peptides are called

Answer 48

Aminoacyl residues

Question 49

Peptide hormones typically contain ONLY the a-amino acids of proteins. TRUE OR FALSE

Answer 49

True. Other peptides contain non protein amino acids or amino acids linked by ATYPICAL PEPTIDE BOND ex. Glutathione

Question 50

Formation of peptides from amino acid is therefore accompanied by a net loss of one positive and one negative charge per peptide bond formed.

Answer 50

TRUE

Question 51

The physiologically active conformation reflects the collective contributions of the

Answer 51

Amino acid sequence Steric hindrance Non covalent interactions

Question 52

Widely used for detecting amino acids, forms a purple product w/ amino acids and a yellow adduct with imine groups of proline and hydroxyproline

Answer 52

NINHYDRIN

Question 53

Some proteins contain additional amino acids that arise by

Answer 53

Post- translational modification of an amino acid present in the peptide