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Biochemistry > Aminoacids > Flashcards

Aminoacids Flashcards

1
Q

Proteins. 3 points

A

.Proteins are of paramount importance for biological systems
.All the major structural and functional aspects of body are carried out by protein molecules
.All proteins are polymers of amino acids linked by peptide bonds

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2
Q

Total aa present in nature

A
  1. Only 20 of them are seen in human body
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3
Q

First aa to be discovered

A

Asparagine

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4
Q

First aa to be isolated

A

Leucine

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5
Q

20th aa

A

Threonine

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6
Q

21st aa

A

Selenocysteine

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7
Q

Exception for alpha amino acids

A

Proline
GABA
Beta alanine

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8
Q

Classification of aa(4)

A

Structure
Side chain
Metabolism
Nutritional requirements

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9
Q

Simple

A

Glyicine
Alanine

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10
Q

Branched chain

A

Valine
Leucine
Isoleucine

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11
Q

Hydroxy aa

A

Serine
Threonine

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12
Q

S containing

A

Cysteine
Methionine

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13
Q

Amide group

A

Asparagine
Glutamine

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14
Q

Monoamino dicarboxylic

A

Aspartic acid
Glutamic acid

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15
Q

Dibasic monocarboxylic

A

Lysine
Arginine

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16
Q

Aromatic

A

Phenylalanine
Tyrosine

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17
Q

Heterocyclic

A

Tryptophan
Histidine

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18
Q

Imino acid

A

Proline

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19
Q

DERIVED AA
found in proteins

A

Hydroxy proline and hydroxy lysine-
Important components of collagen

Gamma carboxylation of glutamic acid residues of proteins - important for clotting process

Ribosomal proteins and histones - aa ext methylated and acetylated

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20
Q

Not seen in proteins

A

During metabolism of proteins
Orinithine
Citruline
Homocysteine
Thyroxine may be considered as derived from tyrosine

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21
Q

Non alpha aa

A

Gaba - glutamic acid
Beta alanine - pantothenic acid n coA

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22
Q

Special groups
ARGININE
PHENYLALANINE
TYROSIN
TRYPTOPHAN
HISTIDINE
PROLINE

A

GUANIDIUM
BENZENE
PHENOL
INDOLE
IMIDAZOLE
PYRROLIDINE.

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23
Q

Non polar side chain

A
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24
Q

Polar.
Uncharged /nonionic

A
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25
Q

Polar.
Charged/ionic

A
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26
Q

Purely ketogenic. Why

A

Leucine.
Because leucine is converted to ketone bodies during metabolism

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27
Q

Keto and gluco. (5)

A

Lysine
Isoleucine
Phenylalanine
Tyrosine
Tryptophan.
In humans lysine predo ketogenic
During metabolism part of carbon skeleton of these aa will enter ketogenic pathway and other half glucogenic pathway

28
Q

Purely glucogenic

A

All the 14 remaining.
Enter only into glu path

29
Q

Essential/ indispensable

A
30
Q

Partially/semi essential/ semi indespensable

A
31
Q

Non essential/ dispensable

A
32
Q

Tasteless

A

Leucine

33
Q

Bitter

A

Isoleucine
Arginine

34
Q

Flavouring agent

A

Sodium glutamate

35
Q

Artificial sweetner. Contains

A

Aspartame
Aspartic acid phenylalanine

36
Q

MP
Solubility

A

High. > 200c
Soluble in polar. Insoluble in non

37
Q

Sweet

A
38
Q

Amoholyte

A

Aa can exist as ampho or zwitter ions in soln depending on the ph of the medium

39
Q

Isoelectric point(4)

A

The ph at which the molecule carries no net charge is knows as

In acidic solution they are cationic form and in alkaline behave as anions

At iso aa will carry no net charge all the groups are ionized but the charges will cancel each other

Therefore at at this point
No mobility in an E
Solubility minimum
Buffering capacity minimum

40
Q

Buffering action!!

A

At isoelectric point minimum
Maximum in and around pk1 or pk2

41
Q

Optical activity (3)

A

Aa having an assymetric C atom exhibits OA
Glyicine simplest aa. No assymetric c atom. Shows no OA
All others are O active

42
Q

Optical isomers / mirror image forms produced with reference to alpha carbon atom
Which occurs naturally

A

D and L.
L isomers - natural aa

43
Q

D aa are seen in

A

Small amounts in
Microbes and constituents of certain antibiotics such as
GRAMICIDIN - S
POLYMYXIN
ACTINOMYCIN -D
VALINOMYCIN
bacterial cell wall peptidoglycans

44
Q

Isoleucine and threonine OA

A

2 optically active centres
4 diastereo isomers

45
Q

Optical isomers are used extensively in medicine. Explain

A

Approx 50% of marketed drugs are chiral

2 forms must be distinguished because they may differ in dosages effectiveness side effects and indicated use

Examples
Ethambutol
1- treat tuberculosis
1- cause blindness

Naproxen
1- treatment for arthritis
1- liver poisoning

46
Q

General reactions of aa

A

Due to carboxyl group (2)
Due to amino group(3)
Due to side chains(4)

47
Q

Decarboxylation(3)

A

The amino acids will undergo
alpha decarboxylation to form the corresponding amine

Thus some important amines are produced
from amino acids.

For example,

Histidine → Histamine + CO2
Tyrosine → Tyramine + CO2
Tryptophan → Tryptamine + CO2
Lysine → Cadaverine + CO2
Glutamic acid → Gamma amino
butyric acid (GABA) + CO2

48
Q

Amide formation (4)

A

The -COOH group of
dicarboxylic amino acids (other than alpha
carboxyl) can combine with ammonia to form the
corresponding amide.
For example,

Aspartic acid + NH3 → Asparagine
Glutamic acid + NH3 → Glutamine

These amides are also components of protein
structure.
The amide group of glutamine serves
as the source of nitrogen for nucleic acid synthesis.

49
Q

Transamination(3)

A

The alpha amino group of
amino acid can be transferred to alpha keto acid to
form the corresponding new amino acid and alpha
keto acid.

This is an important reaction
in the body for the inter-conversion of amino acids
and for synthesis of non-essential amino acids.

Ast increases in MI
Alt increases in liver disease

50
Q

Oxidative deamination(2)

A

The alpha amino group
is removed from the amino acid to form the
corresponding keto acid and ammonia

In the body Glutamic acid is the most common
amino acid to undergo oxidative deamination.

51
Q

Transdeamination(3)

A

Most of the aa transfer their amino group to alpha keto glutaric acid to form glutamic acid.

Glutamic acid undergoes oxidative deamination to release ammonia.

The two reactions are metabolically coupled

52
Q

Formation of carbamino compound (3)

A

Carbon
dioxide adds to the alpha amino group
of amino acids to form carbamino compounds.

The reaction occurs at alkaline pH and serves as
a mechanism for the transport of carbon dioxide
from tissues to the lungs by hemoglobin

Hb—NH2 + CO2 →
Hb—NH—COOH (Carbamino-Hb)

53
Q

Transmethylation(2)

A

The methyl group of Methionine,
after activation, may be transferred to an acceptor which
becomes methylated

Methionine + Acceptor → Methylated Acceptor +
Homocysteine

54
Q

Ester formation by OH group(3)

A

The hydroxy
amino acids can form esters with phosphoric acid.

In this manner the Serine and Threonine residues
of proteins are involved in the formation of
phosphoproteins.

Similarly these hydroxyl groups
can form O-glycosidic bonds with carbohydrate
residues to form glycoproteins.

55
Q

Reaction of the amide group (1)

A

The amide groups
of Glutamine and Asparagine can form N-
glycosidic bonds with carbohydrate residues to form
glycoproteins.

56
Q

Reactions of SH group (3)

A

Cysteine has a
sulfhydryl (SH) group and it can form a disulphide
(S-S) bond with another cysteine residue.

The two
cysteine residues can connect two polypeptide
chains by the formation of interchain disulphide
bonds or links

The dimer formed by
two cysteine residues is sometimes called Cystine
or Dicysteine.

57
Q

Which structure of protein is responsible for biological activity?

A

Primary? In text

58
Q

Domain (11)

A

Compact globular functional unit of protein

Relatively independent region of protein and may represent a functional unit

Defined as stable units of protein structure that could fold autonomously

Each domain forms a compact 3 dimensionsal structure

Molecular evolution uses domains as building blocks

Domains vary in length from between 25 to 500 aa.

Domains are stabilised by metal ions or disulphide bridges

Provide specific catalytic binding sites as found in E or regulatory proteins

Usually connected w relatively flexible areas of protein

Immunoglobulin contains specific domains

Form functional units such as calcium binding domain of calmodulin

59
Q

PRIMARY STRUCTURE (4)
BRANCHED AND CIRCULAR PROTEIN

A

Denotes the no. And sequence of aa in the protein

Higher levels of organisation are decided by the primary structure.

Generally polypeptide chains are linear
Branching points may be produced due to interchain disulfide bridges
Interchain and intrachain

Very rarely protein maybe present in circular form eg Gramicidin

Each polypeptide chain has a unique amino acid sequence decided by genes

Primary structure maintained by covalent peptide bonds.

60
Q

Pseudopeptide / isopeptide

A

Gamma carboxyl group of glutamic acid may enter into peptide formation
Eg Glutathione ( Gamma glutamyl cystenyl glyicine)

61
Q

MOTIF

A

In a Protein a structural motif is a superstructure

Found in proteins and E with dissimilar functions

Two proteins may share the same motif yet lack appreciable primary structure similarity

Examples :
Beta hairpin
Helix loop helix
Zinc finger
Helix turn helix

62
Q

Formation of ammonia

A

Liberated from aa and nitrogenous compounds

produced in intestine by bacteria metabolism and also in kidney for maintenance of extra cellular ph

at physiological ph NH4+ formation is favoured by a factor of 100:1.free ammonia can diffuse across membranes but not NH4+

first step in catabolism of aa is to remove amino group as ammonia. this is the major source of ammonia.

small qties from catabolism if purine and pyramidine bases

highly toxic to nervous. detoxification is by conversion to urea and ex through urine

63
Q

Source and fate of ammonia

A
64
Q

Transamination
Reaction
E
Prosthetic group
Rever/irrever
Example

A

Exchange of alpha amino group between one alpha amino acid and another alpha keto acid forming a new alpha amino acid

.aa1 + ka2 = aa2+ ka1

Aminotransferases

Plp

Readily reversible

.

65
Q

Biological significance of transamination (3)
Exception

A

First step of catabolism
NH3 removed and carbon skeleton of aa enters into catabolic pathway

Synthesis of non essential aa
From keto acids
Pyruvate (t) alanine
Oaa aspartic acid
Alpha getoglutarate glutamic acid

Interconversion of aa

Lysine threonine and proline are not transaminated. They follow direct degradative pathways.

66
Q

Clinical significance of transamination

A

Ast and alt are induced by glucocorticoids which favor gluconeogenesis
Markers of liver injury

Biochemistry (5 decks)

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