Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… ·...

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Amino acids have important roles in living organisms Subunits (building blocks) of peptides and proteins Neurotransmitters Metabolic intermediates C NH 3 + O O - glutamate γ-aminobutyric acid (GABA)

Transcript of Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… ·...

Page 1: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

Amino acids have important roles in living

organisms

Subunits (building blocks) of peptides and proteins

Neurotransmitters Metabolic intermediates

C

NH3+

O

O-

glutamate γ-aminobutyric acid

(GABA)

Page 2: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

Proteins are synthesized from 20 ‘standard’ α-amino

acids. Their names have 3- and 1-letter abbreviations.

Alanine Ala A Methionine Met M

Cysteine Cys C Asparagine Asn N

Aspartate Asp D Proline Pro P

Glutamate Glu E Glutamine Gln Q

Phenylalanine Phe F Arginine Arg R

Glycine Gly G Serine Ser S

Histidine His H Threonine Thr T

Isoleucine Ile I Valine Val V

Lysine Lys K Tryptophan Trp W

Leucine Leu L Tyrosine Tyr Y

Page 3: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)
Page 4: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

Amino acid pKa’s vary because of attached functional

groups (microenvironment influences acidity)

Page 5: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

Most amino acids are chiral, and are designated

‘D’ or ‘L’ based on Emil Fischer’s nomenclature

Page 6: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

The ‘Fischer projection’ is a simplified way to

depict stereochemistry

Vertical bonds point

away from viewer

(dashed wedges)

Horizontal bonds

point toward viewer

(filled wedges)

Chiral carbons may

be left out entirely

Fisher projection

Page 7: Amino acids have important roles in living organismsrebecca/153A/W11/Lectures/153A_W11_Lec04… · Amino acids have important roles in living organisms Subunits (building blocks)

How to identify the stereochemistry of an amino

acid (D or L?)

The CORN rule

Fisher projection

1. Orient the structure to look

down the Cα-H bond

2. Follow the other Cα

substituents to spell CORN

(carboxylate, R-group,

amino): counterclockwise is L,

clockwise is D

L-amino acid: D-amino acid:

L-amino acid: D-amino acid:COO

-

R

H+H3N

COO-

R

NH3+

H

If projection is aligned with:

• carbon chain vertical

• carboxylate on top

amino group on left = L

amino group on right = D

C

NH3+

R COO-

HC

NH3+

-OOC R

H

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Nonstandard amino acids are found in modified

proteins and as free metabolites