Section 8 - Amino Acids, Proteins and DNA Flashcards

1
Q

What makes amino acids amphoteric?

A

They have a basic amino group (NH2) and an acidic carboxyl group (COOH).

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2
Q

What kind of isomerism do amino acids display?

A

Optical - they have a chiral carbon.

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3
Q

Which amino acid does not display isomerism?

A

Glycine - its R group is another hydrogen/

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4
Q

What is a zwitterion?

A

A dipolar ion - it has a positive and negative charge in different parts of the molecule.

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5
Q

What is the isolectric point?

A

The pH when the average overall charge of the amino acid is zero.

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6
Q

What is a suitable way to identify unknown amino acids?

A

Thin-layer chromatography.

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7
Q

What is the name for condensation polymers of amino acids?

A

Proteins

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8
Q

What is the link in a protein chain?

A

Peptide link

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9
Q

What are the conditions for hydrolysis of proteins?

A
  • hot aqueous 6M HCl acid
  • heat
  • reflux
  • 24 hours
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10
Q

What is the primary structure of a protein?

A

The sequence of amino acids in the polypeptide chain.

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11
Q

What is the secondary structure of a protein?

A

The shape of the chain - the peptide links form hydrpgen bonds creating either an alpha helix (spiral) or beta-pleated (folded) sheet.

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12
Q

What is the tertiary structure of a protein?

A

The extra bonds formed between different parts of the polypeptide chain, which gives the protein a 3-dimensional shape.

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13
Q

Which types of bonds help to keep proteins in shape?

A

Hydrogen and Disulfide bonds.

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14
Q

How do hydrogen bonds form in proteins?

A

They exist between the -OH and -NH2 groups.

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15
Q

How do disulfide bonds form in proteins?

A

Cysteine contains a thiol group (-SH). These can lose their H atoms and join together forming a disulfide bond, linking together parts of the protein chain.

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16
Q

Which factors can affect the formation of hydrogen and disulfide bonds?

A
  • temperature
  • pH
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17
Q

Define enzymes

A

Biological catalysts which speed up chemical reactions

18
Q

What type of reactions do enzymes catalyse in the human body?

A

Metablolic reactions

19
Q

What is an active site?

A

The area on an enzyme that the substrate fits into so that it can interact with the molecule.

20
Q

Why are enzymes stereospecific and what does this mean?

A

They have chiral centres and only one enantiomer of a substrate will fit into the active site.

21
Q

What is an inhibitor?

A

A molecule which has a similar shape to the substrate which bonds to the active site but doesn’t react - just blocks the substrate from getting in.

22
Q

What is the amount of enzyme inhibition affected by?

A
  • how strongly the the inhibitor bonds to the active site
  • the relative concentrations of inhibitor and substrate
23
Q

How do inhibiting drugs work?

A
  • block active site of enzyme and stop it working
  • eg. some antibiotics block the active site of enzymes in bacteria which make their cell walls so that eventually they burst.
24
Q

Why is it a problem if inhibiting drugs are chiral?

A

Active sites of enzymes are stereospecific

25
Q

What does DNA stand for?

A

deoxyribonucleic acid

26
Q

What is DNA made from?

A

Lots of monomers called nucleotides

27
Q

What are nucleotides made up from?

A
  • phosphate group
  • pentose sugar
  • base
28
Q

How is the sugar-phosphate backbone bonded?

A

Covalent bonding

29
Q

How is the sugar-phosophate backbone formed?

A

Condensation Polymerisation

30
Q

What is the structure and bonding of DNA?

A

It has a double-helix structure which is held together by hydrogen bonds between the bases.

31
Q

What does Adenine pair with?

A

Thymine

32
Q

What does guanine pair with?

A

Cytosine

33
Q

What atoms do hydrogen bonds form between in DNA?

A

Polar positive Hs (an H bonded to anything highly electronegative eg. N) and the lone pair on a nearby O or N atom.

34
Q

How many hydrogen bonds can A and T form?

A

2

35
Q

How many hydrogen bonds can G and C form?

A

3

36
Q

What is cisplatin?

A

An anti-cancer drug which is a complex of platinum (II) with two chlorine ligands and two ammonia ligands in a square planar shape.

37
Q

What causes cancer?

A

Cells in the body dividing uncontrollably and forming tumours

38
Q

How does cisplatin work?

A
  • an N atom on a guanine base in DNA forms a co-ordinate bond with cisplatin’s Pt ion, replacing one of the Cl ion ligands.
  • a second N atom from a nearby guanine can bond to the Pt and replace the second Cl ion.
  • this causes the strands to kink so the DNA can’t unwind and be copied properly - so the cell can’t replicate.
39
Q

What is the problem with cisplatin?

A

It can bind to DNA in normal cells too, eg hair cells and blood cells, which have to replicate frequently.

This means it causes hair loss and suppresses the immune system.

40
Q

How can you reduce the side effects of cisplatin?

A
  • give low doses
  • target it to the tumour