3.13- Amino acids, proteins and DNA

Question 1

What is the general structure of an amino acid

Answer 1

Amino acids contain an amine group and a carboxylic acid group to the same carbon

Question 2

What is the optical acitivity of amino acids

Answer 2

All amino acids except for glycine are chiral because there are four different groups around the C, They rotate plane polarised light

Question 3

What is a zwitterion

Answer 3

The amino acid always exist as a dipolar zwitterion, the zwitterion have a postive end with the NH3+ and a negative end with the CO2- ion

Question 4

Explain the acidity and basicity of amino acids in different pH solutions

Answer 4

The amine group is basic and the carboxylic acid group is acidic

If they are in a alkaline solution of a high pH the zwtitterions will be only negative CO2- , if in an acidic solution with a low pH the zwitterions will be only positive NH3+

Question 5

What happens to the extra carboxylic acid or amine groups that are attached to the different carbons

Answer 5

They willl also react and change form in alkalie and acidic conditions

Question 6

What is a dipeptide

Answer 6

Dipeptides are a simple combination of molecules of two amino acids with one amide link, for any 2 amino acids there are two possible combinations of the amino acids in the dipeptide

Question 7

What are some of the other reactions of amino acids

Answer 7

They can also go under esterfication

With a reaction with alcohol or acyl chloride they can react to form an ester

Question 8

What can you use to hydrolyse di peptites/proteins

Answer 8

You canuse concentrated hydrochloric acid or concentrated strong alkalis, they can be hydrolysed and split back into thier constituent amino acids

Question 9

WHat is the primary structure of proteins

Answer 9

It is the sequenze of the 20 different natrually occuring amino acids joined together by condensation reactions with peptide loinks

Question 10

What is the secondary structure of protein, alpha helix

Answer 10

Held in a corkscrew shape with hydrogen bonds between the H of -N - -H+ group and the -O of C +=O of the fourth amino acid along the chain, the R groups ar all pointed to the outside of the helix

Question 11

What is the secondary structure of protiens, pleated sheet

Answer 11

The protein chain folds into parallel strands side by side, ther protein chain is held into the pleated shape by hydrogen bonds between the H of the N-H group and the O of C=O of the amino acid much further along the chain in the parallel region

Question 12

What is the tertiary structure of proteins

Answer 12

The tertiary structure is just the folding of the secondary structure inro more complex shapes, it is held in shape by the interactions betwen the R side grop sin more distant amino acids, there are many different types of interactions like hydrogen bonding, sulfur bonds and ionic intercations

Question 13

Where does ionic interactions occur in tertiary protein structures

Answer 13

There could be a transfer of H+ from COOH to the NH2 groups as it is in simple amino acids

Question 14

Where could sulfur bridges be formed in a tertiary protein

Answer 14

With two cysteine side chains that are close together, due to folding in the protein chain they can react to form a sulfure bridge which is a covalent bond

Question 15

What is an enzyme

Answer 15

Enzymes are proteins, they have active sites which are ustuall a hollow in the globular protein structure into which a substrate molecule can bond to the amino acid side chain, throughout a variety of interactions like all of the intermolecular forces and ionic interactions

Question 16

What properties do substrates need to have to bond to the enzyme correctly

Answer 16

The interactions need to be strong enough to hold the substrate for long enough for the enzyme catalysed reaction to occur but weak enough for the product to be released

They also have to have the right shape with the correct positions of functional groups (lock and key hypotheses)

Question 17

Explain how a stereospecific active site works

Answer 17

If there is a substrate that is chiral, it is likely that only one of the enantiomer will be able to fit in the enzyme so only one isomer will be catalysed, this is becuase the substrate functional groups do not line up with the enzyme functional group so they are unable to form bonds unlike the other enatiomer

Question 18

What is an enzyme inhibitor

Answer 18

They work by blocking the active site, they bind t the active site strongly so stopping the substrate attaching to the enzyme

Question 19

Give the names of the 6 different molexules present in DNA

Answer 19

. Phosphate ion
. 2-Deoxyribose aka pentose sugar

Bases-

. Adenine
.Guanine
.Thymine
.Cytosine

Question 20

What is a nucleotide

Answer 20

A nucleotide is made up from phosphate ion bonded to 2-deoxyriose which is in turn onded to one of the four bases

Question 21

How do the pentose sugar and the phosphate group bond

Answer 21

There is a sugar phostophate sugar phosphate polymer chain which bases attached to the sugars

The bonds are betweeh the 2 OH bonds in each molecule

Question 22

How does dna exist

Answer 22

There are 2 complementary starnds of the polymer chain in a form of the doule helix . the A must be matched to T and C to G

Question 23

How does cisplatin work as an anticancer drug

Answer 23

2 chlorides ions are displaced and the molecule joins on the DNA, in doing this stops the replication of cancerous cells. However it can also prevent the replication of healthy cells by bonding on to the healthy DNA which may lead to side effects like hair loss.