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AQA A-Level Chemistry+ > 3.13 > Flashcards

3.13 Flashcards

1
Q

what are the two functional groups of amino acids?

A

NH2 and COOH (amine and carboxylic acid)

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2
Q

How many are naturally occurring amino acids there in the human body?

A

20

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3
Q

What type of amino acids are found in the body?

A

alpha amino acids

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4
Q

What does this mean about the structure

A

It means NH2 is always on the carbon next to COOH

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5
Q

Draw general formula for alpha-amino acids.

A
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6
Q

Are alpha-amino acids chiral?

A

Yes

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7
Q

Why are alpha-amino acids chiral?

A

One carbon has 4 different substituents (except glycine where R=H)

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8
Q

Which enantiomer do alpha-amino acids exist as in nature?

A

(-) enantiomer

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9
Q

How can amino acids be synthesized industrially?

A

RCHO + NH4CN –> RCH(NH4)CN via Nucleophillic addition

RCH(NH2)CN + HCl + 2H2O –> RCH(NH2)COOH + NH4Cl

(Hydrolysis, HCL is dilute)

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10
Q

How can amino acids be synthesized industrially?

A

RCHO + NH4CH —> RCH(NH2)CN via nucleophilic addition

RCH(NH2)CN + HCl + 2H2O —> RCH(NH2)COOH + NH4Cl (hydrolysis, HCl is dilute)

Need to reflux the reaction mixture

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11
Q

Is the product from amino acid being synthesized naturally optically active?

A

No

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12
Q

Why is the product from amino acid being synthesized naturally optically active?

A

A racemic mixture is formed as the CN_ ion can attack from above or below the planar C=O bond with equal likelihood. An equal amount of each enantiomer is formed, so no net effect on plane polarised light.

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13
Q

In what form do amino acids exist as solids?

A

Zwitterions (ionics lattice)

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14
Q

What consequences does amino acid solids have?

A

High M.P. and B.P.’s

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15
Q

What colour are most zwitterions at room temperature?

A

White solids

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16
Q

Do zwitterions dissolve in water?

A

Yes

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17
Q

Do zwitterions dissolve in non-polar solvents?

A

No

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18
Q

Why do/don’t zwitterions dissolve in non-polar solvents?

A

Zwitterions have polar bonds

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19
Q

Define a zwitterions

A

Ions which have a permanent positive and negative charge, but are overall neutral.

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20
Q

How do zwitterions occur in amino acids?

A

COOH is de-protonated —> COO_

NH2 is protonated —> NH3+

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21
Q

What happens to amino acids in acidic conditions?

A

Gains a proton at the NH2 group.

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22
Q

What happens to amino acids in alkaline conditions?

A

Loses a proton at the COOH group.

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23
Q

What is the peptide linkage?

A

CONH

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24
Q

What is a dipeptide? Draw a general one for amino acids

A

Two amino acids bonded together (a dimer).

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25
Q

What name is given to amino acid chains up to 50 amino acids long?

A

Polypeptides

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26
Q

What is the name given to chains of more than 50 amino acids?

A

Proteins

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27
Q

What are polypeptides and proteins found in?

A

Enzymes

Wool

Hair

Muscles

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28
Q

What is the process by which polypeptides and proteins are broken down into their constituent amino acids?

A

Hydrolysis

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29
Q

What conditions are needed for hydrolysis to occur?

A

6 mol dm_3 HCl

Reflux for 24 hours

30
Q

What is the primary structure of a protein?

A

The sequence of amino acids along the protein chain

31
Q

How is the primary structure of a protein bonded?

A

The sequence of amino acids along the protein chain

32
Q

How is the primary structure represented?

A

Sequence of 3 letter abbreviations of the amino acids

33
Q

How can the primary structure of a protein by broken?

A

Hydrolysis

6M HCl

24-hour reflux

34
Q

What is the secondary structure of a protein chain?

A

The shape of a protein chain

35
Q

What is the two option of the secondary structure?

A

Alpha-helix shape

Beta-pleated sheets

36
Q

How is the secondary structure held together?

A

Via hydrogen bonds

E.g. C=O and N-H groups

37
Q

What is the tertiary shape of a protein?

A

Alpha-helix/Beta-pleated is folded into a complex 3D-shape

38
Q

How is the tertiary structure held together?

A

Hydrogen bonding

Ionic interactions between R groups

Sulfur-sulfur bonding (disulfide bridges)

van der Waal forces of attraction

39
Q

Why is the tertiary structure important?

A

The shape of protein molecules is vital to their function

E.g. enzymes

40
Q

How many amino acids can be attracted to each other?

A

Hydrogen bonding

Ionic interactions between groups on side chains

Disulfide bridges, so 2S atoms oxidized to form an S-S bond

41
Q

What is wool? How is it held together?

A

Protein fiber with secondary alpha-helix structure; held together by by hydrogen bonds

42
Q

What do wool’s structure and bonding mean for wool’s properties?

A

Can be stretched, H-bonds extend

Release it and it returns to its original shape

Wash too hot and H-bonds break permanently

43
Q

How do you calculate an Rf value?

A

Distance moved by that substance divided y the distance moved by the solvent front

44
Q

How can Rf values to used to identify which amino acid are which?

A

Compare the experimental Rf value to known values of the same solvent

Or run pure amino acids in the same in the same solvent nda compare resultsto identify amino acids

45
Q

How do you find the primary structure of a protein?

A

Reflux with 6M HCl and reflux for 24 hours

Carry out TLC to find the number and type of amino acid present

46
Q

How do you find the structure of the secondary and tertiary protein?

A

X-ray diffraction

47
Q

What is an enzyme?

A

A protein-based catalyst that speeds up bodily reactions by factors of 10^10

48
Q

How many reactions is each enzyme designed to catalyze?

A

One reaction they are very specified

49
Q

What is the structure of the enzyme?

A

Globular protein with a crevice in it, known as an “active site”

50
Q

How does the enzyme’s structure help it function?

A

The reacting molecules fit precisely into the active site and held at the exactly right orientation to react.

The lock and key hypothesis.

51
Q

How else do enzymes increase the rate of reaction?

A

Reacting molecules through the intermolecular forces form temporary bonds to the enzyme at the active site.

This weakens the bonds in the molecules, promotes electron movement and lowers the activation energy.

52
Q

What does the stereospecificity of enzymes mean?

A

Active sites are so selective of the shape of substrates that only reactions involving one enantiomer are catalyzed

53
Q

What does stereospecificity mean for most naturally occurring molecules?

A

most naturally occurring molecules only occur as one enantiomer due to stereospecific enzymes

54
Q

How are enzymes denatured?

A

Conditions of pH

55
Q

How does enzyme inhibition work?

A

A molecule with a very similar shape and structure to the substrate is devised

The molecule binds to the enzymes active site.

The molecule blocks the active site.

Therefore the active site cannot absorb the substrate, so the reaction cannot be catalyzed.

56
Q

An example of a drug that works through enzyme inhibition?

A

Penicillin

57
Q

What structure does DNA take?

A

A polymer with 4 monomers; they can be combined diferently

58
Q

What constitutes a nucleotide?

A

A phosphate ion

2-deoxyribose

A base (guanine, cytosine, adenine and thymine)

59
Q

Draw a nucleotide.

A
60
Q

What forms between bases of adjacent nucleotides?

A

H-bonding

61
Q

Hoe does DNA polymerize?

A

OH on the phosphate group

OH on Carbon-3 of 2-deoxyribose

react to eliminate a molecule of H2O

62
Q

What kind of polymer does the polymerization of DNA lead to?

A

condensation of a polymer chain

the backbone of sugar and phosphate molecules, with bases attached

63
Q

What defines the properties of the DNA molecules?

A

the order of the bases

64
Q

Why does DNA have a double helix shape?

A

exists as 2 strands

these 2 strands are held together by hydrogen bonding (C, G, T, and A)

The complementary DNA molecule has bases that hydrogen bonding in the same order to those on the the other molecule

65
Q

How is DNA copied when cells divide?

A

H bonds break between pairs

covalent bonds in polymer chains interact

the sequence of bases is maintained

separate nucleotide molecules that have been created to move hydrogen bonds to their relevant bases

They then polymerise

66
Q

Draw the structure of cisplatin

A
67
Q

What is cisplatin’s function? How does it do this?

A

Anti-cancer drug

Bonds to strands of DNA in order to distort the shape and prevent cell replication.

It bonds to N atoms at 2 adjacent Guanine molecules

The N atoms replace the Cl_ ligands in a ligand substitution reaction

68
Q

Why are Cl_ ions able to be replaced by N in the base?

A

N atoms on the Guanine base have lone pairs of electrons that can coordinately bond to the Pt on

N atoms have better ligands than Cl_ , so replace them

69
Q

What are the drawbacks of using cisplatin?

A

Affects healthy cells that replicate quickly

Damage kidneys

70
Q

What happens when excess bromoethane is added to an amino acid?

A

CH3Br is in excess

so every H on the N atom and the lone pair n the N atom is replaced by CH3 group

quarternary ammonium ion

(makes a salt with Br_)

71
Q

What happens if an amino acid is added to an excess of methanol in the presence of concentrated of sulphuric acid?

A

Methyl ester forms with COOH group

—–>

COOCH3

NH2 is protonated by the acid

—–>

NH3+

AQA A-Level Chemistry+ (23 decks)

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