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Biochemistry > Proteins > Flashcards

Proteins Flashcards

1
Q

Urea cycle is also known as

A

Ornithine cycle ( first member of the reaction is ornithine )

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2
Q

2 nitrogen atoms of the urea formed are derived from two different sources ,name the sources

A

One from ammonia
Other directly from alpha amino group of aspartic acid

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3
Q

What is the step 1 in urea cycle

A

Formation of carbamoyl phosphate

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4
Q

Step 2 in ornithine cycle

A

Formation of citrulline

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5
Q

Which step in the ornithine cycle is the formation of urea

A

Step 5

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6
Q

Step 3 in urea cycle

A

Formation of argininosuccinate

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7
Q

Step 4 in ornithine cycle is

A

Formation of arginine

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8
Q

Cytoplasmic enzyme involved in the synthesis of pyrimidine

A

Carbomyl phosphate synthestase II

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9
Q

Rate limiting step in urea cycle

A

CPS-I

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10
Q

Explain the first step in urea cycle

A

One molecule ammonia condenses with CO2
Presence of 2 molecules of ATP
To form carbonyl phosphate
Enzyme :CPS-(mitochondrial enzyme )
Irreversible and allosterically regulated

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11
Q

In what aspects does CPS I differ from CPS II

A

Site Mitochondria , cytoplasm
Pathway urea ,pyrimidine
Positive effector NAG , nil
Source of N ammonia , glutamine
Inhibitor nil , CTP

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12
Q

Where does the second reaction of ornithine cycle take place

A

Mitochondrial (just like 1st)

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13
Q

Which are two mitochondrial steps in urea cycle

A

First 2

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14
Q

How is citrulline formed in the urea cycle

A

Carbamoyl group transferred to NH2 group of ornithine
By ornithine transcarbamoylase (OTC)

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15
Q

Which product in urea cycle leaves the mitochondria

A

Citrulline leaves to the cytoplasm

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16
Q

Citrulline is present in

A

Milk
Not present in tissue proteins or blood

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17
Q

What is an inhibitor of step 3 of urea cycle

A

Ppi ( inorganic pyrophosphate)

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18
Q

How is argininosuccinate formed

A

One molecule of aspartic acid adds to citrulline forming C-N bond , second nitrogen of urea.
Catalyzed by : argininosuccinate synthetase
Needs hydrolysis of ATP to AMP level (2 high energy phosphate bonds are utilized )

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19
Q

Inhibitor of cps II

A

CTP

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20
Q

Argininosuccinate is cleaved by what in the fourth step of urea cycle

A

Argininosuccinate lyase (argininosuccinase )

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21
Q

Argininosuccinate is cleaved to what

A

Arginine and fumarate , argininosuccinase is inhibited by fumarate

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22
Q

How is the inhibition of argininosuccinase avoided

A

Cytoplasmic localization of the enzyme

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23
Q

Which step in urea cycle involves aspartic acid

A

Step 3

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24
Q

Other purposes of fumarate formed during the formation of arginine

A

Funneled into tca cycle to be converted to malate and then to oxaloacetate to be transaminated to aspartame

25
Q

How is the urea cycle linked to TCA cycle

A

By fumarate

26
Q

Citrulline +aspartate ——>
Summary of 3rd and 4th step

A

Arginine +fumarate

27
Q

Donation of amino group by asparate takes place in which reaction other than urea cycle

A

Purine nucleotide synthesis

28
Q

The final reaction in ornithine cycle / urea cycle

A

Hydrolysis of arginine to urea and ornithine
By arginase

29
Q

Why does the ornithine return mitochondria after the formation of urea

A

To react with another carbonyl phosphate and cycle is proceeds

30
Q

Which component is a catalyst that gets used and regenerated in urea cycle

A

Ornithime

31
Q

Energetics of the urea cycle

A

Consumes 4 high energy phosphate bonds
1NADH is produced (=2.5 ATP)
Hence net energy expenditure = 1.5 high energy phosphates

32
Q

Why is it called the urea bicycle

A

Urea cycle and TCA cycle are interlinked

33
Q

What in the urea cycle produces 1NADH

A

Fumarate in 4th step converted to malate , malate when oxidized to oxaloacetate

34
Q

When is the activity of urea cycle elevated

A

During starvation , to meet the increased rate of protein catabolism

35
Q

What are the types of regulation of urea cycle

A

Coarse and fine regulation

36
Q

The one group not carried by tetra hydro folic acid (THFA)

A

Methyl group

37
Q

Which nitrogen atoms of THFA carry the one-carbon groups

A

N5 , N10 atoms of THFA

38
Q

The one carbon groups are contributed to the 1C pool by

A

Amino acids

39
Q

What is transamination

A

Exchange of alpha amino group between one alpha amino acid and another alpha keto acid
The reaction is readily reversible .

40
Q

Common example of transamination

A

Interchanged between alanine and glutamic acid .
(Almost all cases , amino group is accepted by alpha ketoglutaric acid so glutamic acid is formed )

41
Q

Enzymes catalyzing the transamination reaction as a group are called
And the prosthetic group in it

A

Amino transferases
Pyridoxal phosphate

42
Q

Ammoniagenesis helps in excretion of

A

Hydrogen ions

43
Q

What is chemical name of glutathione

A

Gamma-glutamyl-cysteinyl- glycine

44
Q

Miester cycle is also known as

A

Gamma glutamyl cycle

45
Q

Glycine can be synthesised by

A
  1. By glycine synthase enzyme
    2.from serine( serine hydroxy methyl transferase )
  2. From glyoxylic acid (glycine transaminase)
  3. From threonine (threonine aldolase)
  4. From choline
46
Q

Different degradation processes of glycine

A

Glycine cleavage
Serine formation
Transamination reaction
Oxidative deamination

47
Q

End product of transamination of glycine by glycine transaminase

A

Glyoxylate + glutamate

48
Q

in collagen , every third amino acid is

A

Glycine

49
Q

Primary structure of protein.

A

Denotes number and sequence of amino acids in the protein
Higher levels of organisation are decided by the primary structures

50
Q

Secondary structure of proteins

A

Preserved by non covalent forces or bonds like hydrogen bonds , electrostatic bonds , hydrophobic interactions and van der waals forces
Different secondary structure - alpha helix , beta sheet , bends , loops , disordered regions

51
Q

What causes phenylketonuria

A

Inability to convert phenylalanine to tyrosine. due to absence/ deficiency of phenyl alanine hydroxylase

52
Q

Normal blood phenylalanine & abnormal PKU blood level

A

1 to 2 mg /dl
PKU > 20mg/ dl

53
Q

Manifestations of PKU

A

Mental retardation
low iq
Seizure
irritation
Failure to walk
hypopigmentation
Eczematous dermatitis
Mousy odor (lactic odour )

54
Q

Define transamination

A

Process of transfer of amino group from an amino acid to a keto acid converting the original keto acid to a new amino acid and the origin amino acid o a new keto acid
Without the liberations of ammonia

55
Q

Examples of transamination

A

Aspartate + alpha ketoglutarate <——> oxaloacetate + glutamate
(AST)
Alanine + alpha ketoglutarate <—>Pyruvate + glutamate
ALT (alanine transaminase )

56
Q

Alpha helix

A

*Most common secondary structure found in proteins
* Seen in hemoglobin , myoglobin , alpha keratin , collagen
* right handed coiled structure
*stabilised by extenisve hydrogen bonding
*hydrogen bonds are parallel to the alpha helix
*bonds are individually weak , collectively maintain helical structure
*Each turn of helix contains 3.6 amino acid residues and each amino acid is separated by a distance of 1.5 A°

57
Q

Denaturation of proteins

A
  • process of disorganisation of native protein structure
    *loss of 2° 3° 4° structures without breaking primary structure
    *causes unfolding of 3 dimensional proteins
    PRIMARY STRUCTURE MAINTAINED BY STRING COVALENT PEPTIDE BONDS. higher structures - weak non-covalent bonds
58
Q

Alkaptonurea
Metabolic defect :

A

lack of homogentisate oxidase enzyme

Biochemistry (10 decks)

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