Amino Acids & Proteins

Question 1

How many naturally occuring amino acids are there?

Answer 1

20.

Question 2

Amino acids are joined together in what type of chains to form proteins?

Answer 2

Polypeptide chains.

Question 3

How long are the polypeptide chains that form proteins?

Answer 3

From a few hundred to over a thousand amino acids long.

Question 4

Every amino acid has the same structure, except for…?

Answer 4

The R group.

Question 5

What part of a protein is involved in reactions with a substrate?

Answer 5

The R group.

Question 6

If the R group is changed, what effect can this have on a protein?

Answer 6

It can destroy the protein.

Question 7

What FOUR atoms or groups are attached to the central carbon atom of an amino acid?

Answer 7

1. A hydrogen atom.
2. A carboxyl group (COOH).
3. An amino group (NH2).
4. An R group.

Question 8

Of the carboxyl group and amino group in an amino acid, which is an organic acid and which is an organic base?

Answer 8

Organic acid - carboxyl group.
Organic base - amino group.

Question 9

What are the three groups of amino acids?

Answer 9

1. Non-polar side chains and hydrophobic.
2. Polar with uncharged side chains.
3. Polar with charged (acidic or basic) side chains.

Question 10

Which group of amino acids is this?:

Alanine, valine, leucine, isoleucine, glycine, proline, methionine, phenylalanine and tryptophan.

Answer 10

Non-polar side chains and hydrophobic.

Question 11

Which two amino acids are aromatics, with ring structures that can be involved in fluorescence?

Answer 11

Phenylalanine and tryptophan.

Question 12

What type of bond joins individual amino acids to form proteins?

Answer 12

Peptide bonds.

Question 13

Methionine contains sulphur. This means that it can be involved in what sort of bonding?

Answer 13

Metal bonding.

Question 14

Which group do these amino acids belong to?:

Serine, threonine, cysteine, tyrosine, asparagnine, glutamine and histidine.

Answer 14

Polar with uncharged side chains.

Question 15

Which group do these four amino acids belong to?:

Aspartate, glutamate, lysine, and arginine.

Answer 15

Polar side chains (charged, either acidic or basic).

Question 16

Name the nine essential amino acids.

Answer 16

Phenylalanine, tryptophan, isoleucine, valine, methionine, lysine, threonine, leucine and histidine.

Question 17

Why are the nine essential amino acids so-called?

Answer 17

They are essential for physiological functions but cannot be synthesised by humans.

Question 18

Kwashiorkor is a condition caused by a diet adequate in ………………. but lacking ……………… .

Answer 18

Carbohydrates, amino acids.

Question 19

All amino acids have chiral centres and are optically active, but are they all R-enantionmers or L-enantiomers?

Answer 19

Amino acids are all L-enantiomers.

Question 20

Are only R-enantiomers or L-enantionmers of amino acids used to make proteins?

Answer 20

Only L-enantiomers of amino acids are used to make proteins.

Question 21

Give an example of why chirality can be important.

Answer 21

Chirality is very important in drug design. For example, the R-enantiomer of prozac is effective, but the L-enantiomer is dangerous.

Question 22

Amino acids are important physiological buffers. What is the function of a buffer?

Answer 22

Buffers are solutions that resist changes in pH upon addition of an acid or a base, keeping enzymatic reactions at a constant pH.

Question 23

What do buffers take up or release in order to maintain enzymatic reactions at a constant pH?

Answer 23

H+ ions.

Question 24

If a solution has a high pH, does it have a lot of H+ ions or very few pH ions in solution?

Answer 24

It has very few H+ ions in solution so it is very basic.

Question 25

Solutions with a low pH have ………………. H+ ions in solution.

Answer 25

Solutions with a low pH have lots of H+ ions in solution and they are very acidic.

Question 26

Are amino acids weak acids or strong acids?

Answer 26

Weak acids.

Question 27

How many titratable protons do amino acids possess?

Answer 27

At least two.

Question 28

What sort of reaction forms peptide bonds? What is released in the reaction?

Answer 28

Peptide bonds are formed in condensation reactions and a molecule of water is released.

Question 29

Peptide bonds are ………… bonds, which restricts …………….. of the polypeptide chain.

Answer 29

Double, rotation.

Question 30

True or false? Proteins can only fold where there is a single bond in the polypeptide chain.

Answer 30

True. Proteins can only fold where there is a single bond because double bonds restrict rotation of the chain.

Question 31

Polypeptide chains can be ……………….. (2D) when a carbon has ………………. binding atoms?

Answer 31

Planar, three.

Question 32

Can polypeptide chains be cis or trans?

Answer 32

Yes, in a planar conformation polypeptide chains can be cis or trans.

Question 33

What is the difference between a cis polypeptide chain and a trans polypeptide chain?

Answer 33

Cis polypeptide chains have the R groups on the same side.

Trans polypeptide chains have R groups on opposite sides.

Question 34

What is a potential problem with cis polypeptide chains?

Answer 34

There can be problems with cis polypeptide chains when the amino acids are large or polar.

Question 35

There can be short peptides as well as polypeptide chains. What function do these short peptides often have in the body?

Answer 35

Short peptides are often used in signalling, where their structure is not very important. Many hormones are short peptides.

Question 36

What are the two forms that polypeptides can fold into to form a secondary structure?

Answer 36

Alpha helices and beta pleated sheets.

Question 37

What type of bonds hold alpha helices and beta pleated sheets together?

Answer 37

Hydrogen bonds.

Question 38

Name some of the forces involved in protein folding.

Hint: there are five main forces.

Answer 38

Hydrophobic interactions, hydrogen bonds, electrostatic attraction, metal ion coordination and covalent bridges (e.g. disulfide bridges).

Question 39

True or false? The three-dimensional shape of a protein has no impact on its function.

Answer 39

False. A protein’s 3D shape is critical to it’s function.

Question 40

Does the primary structure of a protein have any influence on its secondary or tertiary structure?

Answer 40

Yes, the primary structure of a protein dictates its secondary and tertiary structures.

Question 41

As a general rule in biochemistry, when a molecule is produced in several steps, how is overproduction of the end product often prevented?

Answer 41

Usually accumulation of the end product inhibits the first step of production, thus preventing overproduction.

Question 42

If a protein is water soluble, it will fold into compact structures - will the core be polar or non-polar?

Answer 42

Polar.

Question 43

If proteins are identified as follows, what are they being classified by? What does this depend on?:

Structural proteins, enzymes, transport and storage, muscle contraction and mobility, protection, regulation and receptors.

Answer 43

Biological role. This all depends on a protein’s structure.