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MCAT - Organic Chemistry > Class 4 > Flashcards

Class 4 Flashcards

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1
Q

Are amino acids amphoteric?

A

Yes, they can act as both an acid and a base.

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2
Q

What is the difference between L and D amino acids?

A 
L = amino group on the left
D = amino group on the right
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3
Q

Which form (L or D) is that naturally occurring form of amino acids?

A

L

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4
Q

What is the only amino acid that is achiral?

A

Glycine (Gly)

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5
Q

What amino acid forms disulfide bonds?

A

Cysteine (Cys)

-SH thiols bind

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6
Q

What is the only secondary amino acid?

A

Proline (Pro)

This makes it bulky and formation of hydrogen bonds for secondary structure can be difficult.

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7
Q

How do you form an imine?

A

Carbonyl + NH4Cl -> imine (double bond to N in place of O)

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8
Q

What are the basic steps for amino acid formation?

A

Aldehyde -> imine formation -> KCN adds carbon to become COOH -> H3O+ converts CN to COOH

This will form an L,D racemic mixture!

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9
Q

What is the Gabriel Malonic ester synthesis?

A

A second way to form an amino acid:

Phthalimide -> treat with base pulling an H of N -> treat with malonic ester that has a good LG -> treat with alkyl halide with an R group of interest -> treat with H3O+ -> heat

Will form an L,D racemic mixture!

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10
Q

Lower (even into the negatives) = strong _________.

A

Acids!

Think low pH, low pKa, HIGH Ka

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11
Q

What are the different Ka values for strong and weak acids?

A

Strong acid: Ka > 1; pKa 0

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12
Q

What is the pKa of RCOOH?

and RNH3+?

A

RCOOH: pKa =2

RNH3+: pKa = 9-10

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13
Q

When pH > pKa a group will…

A

be deprotonated

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14
Q

What is the isoelectric point?

A

The pH at which an amino acid has no net charge. 100% will be in the zwitterionic form (+ charge on amino group, - charge on carboxyl group; net charge =0)

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15
Q

How do you calculate the isoelectric point?

A

pI = (pKa1 + pKa2)/2

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16
Q

Acidic amino acids will have a ______ isoelectric point than basic amino acids.

A

Lower

17
Q

If your pH is

A

positive because your solution is more acidic than your molecule and will thus put protons on

18
Q

If your pH is > pI what net charge will your amino acid have?

A

negative because your solution is basic relative to your AA and thus will pull off protons.

19
Q

What are some peptide bond characteristics? Caused by what?

A

Due to resonance:

Partial double bond character
Cannot rotate
Planar
Amide H is slightly acidic

20
Q

What is the difference between D and L carbohydrates?

A

Location of the OH group.
L = OH group on the left
D = OH group on the right

21
Q

What is the naturally occurring form (L or D) of carbohydrates?

A

D

22
Q

Which OH will you look at when trying to determine D or L configuration?

A

Penultimate carbon

23
Q

What does the +/- mean in sugars?

A

direction of rotation of polarized light

24
Q

What is the stereochemical relationship between D and L sugars?

A

Enantiomers

25
Q

When naming sugars what is the main distinguishing feature? How does that affect the name?

A

Aldehyde or ketone.

Aldehyde chain will start numbering with most oxidized carbon.

Ketone will start numbering at the carbon at the end of the chain

26
Q

What is mutorotation?

A

Interconversion of anomers

27
Q

What is your anomeric carbon in a sugar?

A

The carbon of the carbonyl

28
Q

What does it mean if your sugar has a hemiacetal?

A

It is a reducing sugar

Mutorotation occurs

It is in equilibrium with the linear (carbonyl) form

29
Q

What does it mean if your cyclic sugar is an acetal?

A

It is NOT in equilibrium with the linear form

it does NOT mutorotate

and it is a NON-reducing sugar

30
Q

What is Benedict’s test?

How do you know if it is positive?

A

Identifies a reducing sugar via a redox reaction

gain of electrons = reduction

A positive test will yield red precipitate showing that you have a reducing sugar (i.e. aldehyde in equilibrium with hemiacetal)

A negative test indicates no reducing sugar present (i.e. acetal)

31
Q

What is the “ochem definition” of oxidation?

A

Add oxygen or take away hydrogen

32
Q

Do acetals open up into aldehyde or ketones?

A

No

33
Q

In regards to sugars, what is the anomeric carbon?

A

The carbon bonded to TWO oxygens.

34
Q

How do you number sugars?

A
  1. Find the anomeric carbon

2. End of carbon chain closest to that carbon = carbon #1

35
Q

How are fatty acids liberated from triacylglycerols?

A

Saponification (base-mediated ester hydrolysis)

36
Q

What interaction gives stability to micelles and phospholipid bilayers?

A

Van der waals forces (hydrophobic forces) between the fatty acid tails.

MCAT - Organic Chemistry (5 decks)

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