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Basic Principles Of Medicine 1-FTM 1 > DLAproperties Of Amino Acids > Flashcards

DLAproperties Of Amino Acids Flashcards

1
Q

Where are peptide bonds formed?

A

Between the a-carboxyl group of one amino acid and the amino group of another

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2
Q

How are peptide bonds formed?

A

The process of translation

Exception is the synthesis o& the tripeptide glutathione

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3
Q

What are the characteristics of the peptide bond?

A
  • The peptide bond has partial (40%) double-bond character
  • Peptide bond is rigid and planar
  • the peptide bond is uncharged but polar
  • The —C=O and —NH groups of the peptide bond May form hydrogen bonds
    • May form repetitive hydrogen bonds
    • Stabilizes the a-helical and B-sheet structures
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4
Q

Describe the configuration of the peptide bond

A
  • Trans configuration minimizes steric hindrance
  • Side chains are in trans configuration
  • Rotation is possible at the a-carbons
  • Peptide bonds do not break during denaturation of proteins
    • Denaturation involves changing the conformational shape of a protein
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5
Q

Aspartate and glutamate have…

A

Negative (acidic) side-chains at physiological pH (pk about 4)

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6
Q

What are the precursors to biologically active amines?

A

The a-amino acids are precursors for many biological active amines

The amino group is retained (amines) and the a-carboxyl group is enzymatically removed as CO2 (decarboxylated)

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7
Q

What is GABA?

A

A neurotransmitter

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8
Q

What is histamine ?

A

Mediated allergic and inflammatory responses, gastric secretion and neurotransmission

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9
Q

How is GABA formed?

A

GABA(y-aminobutyric acid) is formed by decarboxylation of the a-carboxyl group of glutamate

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10
Q

How is histamine formed?

A

Formed by decarboxylation of histidine by histidine decarboxylase

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11
Q

What are the functions of serotonin ?

A
  • Pain perception
  • Affective disorders
  • Regulation of sleep, temperature and blood pressure
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12
Q

Explain the transformation of tryptophan to serotonin

A
  1. Tryptophan+ tetrahydrobiopterin —> 5-hydroxytryptophan and dihydrobiopterin (+H2O) by hydroxylase
  2. 5-hydroxy-tryptophan —> serotonin by aromatic amino acid decarboxylase PLP
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13
Q

How does Prozac (fluoxetine) work as an antidepressant?

A
  • Prozac (fluoxetine) as a selective serotonin reuptake inhibitors (SSRI)
    • An antidepressant drug that blocks serotonin elimination from synaptic cleft

Enhances the action of the neurotransmitter

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14
Q

What are the Catecholamines?

A

Dopamine, tyrosine, and epinephrine are formed from tyrosine

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15
Q

Summarize dopamine formation

A
  • Tyrosine is hydroxylated to dihydroxy-phenylalanine (L-DOPA)
  • L-DOPA is decarboxylated to dopamine, the first Catecholamine
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16
Q

What are dopamine functions?

A

Dopamine can act as neurotransmitter or it can be used as an intermediate for the synthesis of norepinephrine and epinephrine

Dopamine and norepinephrine are mainly neurotransmitters in the brain and the autonomic nervous system

Epinephrine and norepinephrine may also act as hormones

17
Q

What are the functions of epinephrine?

A

Epinephrine and norepinephrine are released inti the blood from the adrenal medulla during stress situations

Epinephrine (fight or flight) leads to:
-Release of glucose from the liver

  • Release of fatty acids from fat cells
  • Elevated blood pressure
  • Increased heart output
18
Q

Describe positive and negative charges in amino acids at neutral pH

A

The a-amino acid carboxyl group is negatively charged at:
-physiological pH

-The pKa for the a-carboxyl groups is about 2

The amino group of the a-amino acids is positively charged

  • At physiological pH
  • The pKa for the a-amino group is about 9-10

Some amino acids have a side chain that may carry a charge at physiological pH

19
Q

How is a swifter ion formed?

A

At physiological pH, a possible charge of the side chain will determine the overall charge of an amino acid

If the side chain doesn’t have a dissociable proton, then a zwitterion is formed at ~neutral pH; the amino acid carries no net charge

20
Q

What are the positive/basic side chains amino acids?

A

Sometimes histidine, dependent on exact pH

Arginine (Arg)and lysine (Lys)(pKa for both above 10)

Histidine (his) pKa about 6

21
Q

Explain the titration curve of alanine

A

Alanine has two ionizable groups= two pkas

Two pKa gives two buffering regions

Some aa will have 3 pKas due to the ionizable nature of their side chains

  • aa capable of acting as either an acid or base - amphoteric
  • Most aa are not soluble as physiological buffers as pKas are too high or low I.e. ~2.3 or 8-9
22
Q

What defines the buffer region of an amino acid?

A

The pKa defines the buffer region

The pI is the isoelectric point- no net charge

23
Q

Explain the histidine side chain buffer

A

-The histidine side chain has an imidiazole ring (pKa 6) which allows buffering of a possible drop in intracellular pH, which is normally about pH 7

  • The pKa of histidine May be shifted in proteins to 6-7 due to local chemical environment of the protein
    • Histidine would then be even more favorable to buffer the normal pH inside of cells
24
Q

What are the main blood buffer systems?

A
  • Phosphate buffer
  • Hb buffer in RBC (hemoglobin is rich in histidine side chains)
  • Bicarbonate buffer in plasma
25
Q

What are the general structure of amino acids?

A

An a-carbon atom -assymetric (except in glycine)-linked to:
-A Carboxylic acid group

  • An amino group
  • An H atom
  • A variable R group (side chain): any molecule can replace the ‘R’. For instance glycine simply has an -H instead and alanine a -CH3
  • In total there are 22 different R-groups and different three letter abbreviations to represent the amino acid (Asn, Glu)
26
Q

Explain the stereochemistry of Amino Acids

A

19 of the common amino acids are chiral (glycine aren’t chiral)

2 non-superimposable mirror images -stereoisomers

  • D & L forms based on the glyceraldehyde rule
  • Determined by the position of the -amino group, instead of -OH
  • Naturally occurring proteins are L-amino acids
  • Rare-D-amino acids in some antibiotics & peptidoglycan of bacterial cell wall
27
Q

How is proline different from amino acids ?

A

It has secondary amino group and it’s side chain forms a rigid ring structure

28
Q

How do peptide bonds formed with proline take a specific shape?

A
  • Lead to bends in the protein chain
  • Collagen is rich in proline residues
  • Interrupt the a-helical structure
  • Proline is an a-helix breaker
29
Q

What amino acids have nonpolar, aliphatic side chains?

A

Glycine, alanine and proline

30
Q

What amino acids have nonpolar, aliphatic side chains(branched ) ?

A

Valine, leucine, and isoleucine

31
Q

What amino acids have aromatic side chains ?

A

Phenylalanine, tryptophan, and tyrosine

32
Q

Contrast Trp and Tyr have UV light absorbance.

A

UV light absorbance by aromatic amino acids

Absorbance at 280 no is approximately 4x higher for TRP than for TYR

-Phenylalanine doesn’t show much absorbance

33
Q

What are the sulfur containing methionine and cysteine ?

A

Methionine and cysteine

Methionine is also grouped under nonpolar side chains

Cysteine is grouped under uncharged polar side chains at neutral pH

34
Q

Describe cysteine

A

Contains a sulfhydryl group

2 cysteine residues can be used to form a disulfide bond

2 “free” cysteine May oxidize to form cystine

35
Q

What are the polar uncharged amino acids:

A

asparagine and glutamine

Asparagine is a derivative of Aspartate

Glutamine is a derivative of glutamine

36
Q

What are the polar, uncharged amino acids?

A

Serine, threonine

Serine & threonine residues contain a hydroxyl group

May be:

  • Phosphorylated
  • Glycosylation

Basic Principles Of Medicine 1-FTM 1 (39 decks)

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