Amino Acids, Proteins & DNA ORGANIC

Question 1

What are amino acids?

Answer 1

Organic compounds containing two functional groups: a basic amino group and acidic carboxylic acid group

Question 2

Do amino acids act as an acid or a base? Why?

Answer 2

Amphoteric - can act as both
Due to presence of both basic and acidic groups

Question 3

How many naturally occuring amino acids are there?

Answer 3

20

Question 4

What are 2-aminocarboxylic acids?

Answer 4

Type of amino acids in which amine is bonded to carbon next to COOH group

Question 5

Is the R group acidic or basic?

Answer 5

Can be acidic, basic or neutral

Question 6

How do amino acids undergo acid-base reactions?

Answer 6

Amines react with acids
Carboxylic acids with bases

Question 7

What is a zwitterion?

Answer 7

An ion with both a positive and negative charge

Question 8

How do amino acids form zwitterion?

Answer 8

Interact intramolecularly

Question 9

How will amino acids exist in water?

Answer 9

As zwitterions with both acidic and basic properties

Question 10

What will solution of amino acids in water act as?

Answer 10

Buffer solution - resisting any changes in pH when small amounts of acid/alkali added

Question 11

What happens when acid is added to solution of amino acids in water?

Answer 11

pH lowered
-COO⁻ of zwitterion will accept H⁺ ion to reform -COOH
Zwitterion becomes positively charged

Question 12

What happens when base is added to solution of amino acids in water?

Answer 12

pH raised
-NH₃⁺ of zwitterion will donate H⁺ ion to form -NH₂
Zwitterion becomes negatively charged

Question 13

What is the isoelectric point of an amino acid?

Answer 13

pH adjusted so negatively charged and positively charged ions balance so amino acid exists as neutral zwitterion

Question 14

What reacts to form dipeptide?

Answer 14

-NH₂ of one amino acid reacts with COOH group of another in condensation reaction

Question 15

What is a polypeptide?

Answer 15

Many amino acids joined together in long chain molecule

Question 16

What is the primary structure of a protein?

Answer 16

Sequence of amino acids bonded by covalent peptide bonds

Question 17

What is the secondary structure of a protein?

Answer 17

Weak negatively charged nitrogen and oxygen atoms interact with weak positively charged hydrogen atoms to form hydrogen bonds

Question 18

What two shapes can form within proteins due to hydrogen bonds?

Answer 18

α-helix
β-pleated sheet

Question 19

What forms α-helix shape?

Answer 19

Hydrogen bonds form between every fourth peptide bond between oxygen of carboxyl and hydrogen of amine

Question 20

What forms β-pleated sheet shape?

Answer 20

Protein folds so two parts of polypeptide chain are parallel enabling hydrogen bonds to form between parallel peptide bonds

Question 21

Which bonds does the secondary structure relate to?

Answer 21

Hydrogen bonds between amino and carboxyl - the “protein backbone”

Question 22

How can the hydrogen bonds in protein backbone be broken?

Answer 22

High temperature or pH change

Question 23

What is the tertiary structure of a protein?

Answer 23

Further conformational change of secondary structure leads to additional bonds forming between R groups

Question 24

What type of bonds are seen in tertiary structure?

Answer 24

Hydrogen
Disulphide
Ionic
Weak hydrophobic interactions

Question 25

Where do hydrogen bonds form in tertiary structure in proteins?

Answer 25

Between R groups

Question 26

Where do disulphide bonds form in tertiary structure in proteins?

Answer 26

Between cysteine amino acidsd

Question 27

Where do ionic bonds form in tertiary structure in proteins?

Answer 27

Between charged R groups

Question 28

Where do hydrophobic interactions form in tertiary structure in proteins?

Answer 28

Between non-polar R groups

Question 29

What bonds are seen in primary structure of proteins?

Answer 29

Peptide

Question 30

What bonds are seen in secondary structure of proteins?

Answer 30

Peptide Hydrogen

Question 31

What bonds are seen in tertiary structure of proteins?

Answer 31

Peptide Hydrogen Disulphide Ionic Hydrophobic interactions

Question 32

What is the hydrolysis of proteins?

Answer 32

Reverse reaction of condensation - peptide link broken and water added

Question 33

How can hydrolysis of proteins be carried out by chemicals?

Answer 33

Concentrated hydrochloric acid used and mixture boiled for hours as reaction is slow

Question 34

How can amino acids be identified?

Answer 34

Thin layer chromatography

Question 35

What is used to stain amino acids in TLC?

Answer 35

Ninhydrin

Question 36

Why is a stain used in TLC?

Answer 36

Amino acids are colourless

Question 37

What is calculated from TLC plate?

Answer 37

Rf value of compounds

Question 38

What is the calculation for Rf?

Answer 38

Rf = distance travelled by component / distance travelled by solvent

Question 39

Why may a further technique need to be used after TLC to identify amino acids?

Answer 39

Some amino acids have very similay values in same solvent

Question 40

What further technique can be used after TLC to identify amino acids?

Answer 40

Two dimensional TLC

Question 41

What is different about two dimensional TLC?

Answer 41

Same plate run through two different solvents

Question 42

What are enzymes?

Answer 42

Biological catalysts

Question 43

What do enzymes catalyse?

Answer 43

Metabolic reactions

Question 44

What is the shape of an enzyme's active site determined by?

Answer 44

Tertiary structure of protein

Question 45

What is meant by receptors?

Answer 45

Proteins found on enzymes, cell membranes or DNA

Question 46

How do most drugs work?

Answer 46

Bind to receptors stopping normal biological activity and interrupting development of disease

Question 47

How do drugs bind to receptors?

Answer 47

Intermolecular forces or ionic bonds

Question 48

What is DNA?

Answer 48

A polynucleotide made of many nucleotides bonded together in long chain

Question 49

What is meant by stereoselective?

Answer 49

Describes the site where drug binds to biomolecule in which only one orientation is accepted

Question 50

What is a nucleotide?

Answer 50

Monomer containing a phosphate group, 2-deoxyribose and a nitrogenous base

Question 51

What four varieties of nitrogenous base are there?

Answer 51

Adenine Guanine Cytosine Thymine

Question 52

What is DNA polynucleotide strand made of?

Answer 52

Alternating deoxyribose sugars and phosphate groups covalently bonded together to form sugar-phosphate backbone

Question 53

What are the covalent bonds in the sugar-phosphate backbone of DNA known as?

Answer 53

Phosphodiester bonds

Question 54

How are DNA polynucleotide strands held together?

Answer 54

Hydrogen bonds between nitrogenous bases

Question 55

What DNA base pairs are seen in complementary base pairing?

Answer 55

adenine - thymine guanine - cytosine

Question 56

What types of nitrogeneous bases are adenine and guanine?

Answer 56

Purine

Question 57

What types of nitrogeneous bases are cytosine and thymine?

Answer 57

Pyrimidine

Question 58

How many hydrogen bonds form between adenine and thymine?

Answer 58

Two

Question 59

How many hydrogen bonds form between guanine and cytosine?

Answer 59

Three

Question 60

What structure is DNA said to have?

Answer 60

Double helix

Question 61

What allows DNA strands to separate during cell division?

Answer 61

Weak hydrogen bonds between base pairs more easily broken than covalent in sugar-phosphate strands

Question 62

What type of drug is cis-platin?

Answer 62

Anti-cancer

Question 63

What shape is cis-platin?

Answer 63

Square planar

Question 64

How does cis-platin treat cancer?

Answer 64

Binds to nitrogen atoms on DNA bases Passes through cell membrane and undergoes ligand exchange where chlorine replaced with water Nitrogen better ligand than water so dative covalent bonds form with cis-platin Cis-platin distorts shape of DNA and prevents replication

Question 65

What adverse effect does cis-platin have?

Answer 65

Binds to all cells (healthy and cancerous) and affects replication including hair follicles