proteins

Question 1

how are polypeptides made?

Answer 1

amino acids are the basic monomer units that combine to make up a polymer called a polypeptide

Question 2

what do polypeptides combine to form

Answer 2

proteins

Question 3

what provides indirect evidence for evolution

Answer 3

the fact that the same 20 amino acids occur in a living organism provides indirect evidence for evolution

Question 4

what does every amino acid have

Answer 4

a central carbon atom to which is attached to four different chemical groups

Question 5

what are the four different chemical groups amino acids can be attached to

Answer 5

amino group NH2

Carboxyl group COOH

hydrogen atom H

R side group

Question 6

define amino groups

Answer 6

a basic group from which the amino part of the name amino acid is derived

Question 7

define carboxyl groups

Answer 7

an acidic group which gives the amino acid the acid part of its name

Question 8

define the R (side) group

Answer 8

a variety of different chemical groups.

these 20 naturally occurring amino acids differ only in their R (side) group

Question 9

draw the general structure of an amino acid

Answer 9

Question 10

what do two amino acid monomers combine to form

Answer 10

a dipeptide

Question 11

explain a condensation reaction between two amino monomers

Answer 11

the water is made by combining an OH from the carboxyl group of one amino acid with an H from the amino group of another amino acid

the two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other

Question 12

what breaks peptide bonds

Answer 12

a hydrolysis reaction

Question 13

what do we call a chain with many amino acids

Answer 13

a polypeptide

Question 14

define polymerisation in terms of amino acids

Answer 14

through a series of condensation reactions, many amino acid monomers can be joined together in a process called polymerisation

Question 15

what forms the primary structure of any protein
and what is this determined by

Answer 15

the sequence of amino acids in a polypeptide chain.

this sequence is determined by DNA

Question 16

what determines the shape and function of a protein
what does this mean

Answer 16

its primary structure

this means that a change in just a single amino acid in this primary sequence can lead to a change in just a single amino acid in the primary sequence that may stop it from carrying out its function

Question 17

define hydrogen bonds

Answer 17

the hydrogen of the NH group has an overall positive charge while the O of the C=O group has an overall negative charge

these two groups therefore readily form weak bonds called hydrogen bonds

Question 18

what do hydrogen bonds cause

Answer 18

the long polypeptide chain to be twisted into a 3d shape, such as the coil known as an a-helix

Question 19

what can a-helices do

Answer 19

the a-helices of the secondary protein structure can be twisted and folded even more to give the complex, and often specific, 3-D structure of each protein

this is known as the tertiary structure

Question 20

how are tertiary structures maintained

Answer 20

by a number of different bonds

where the bonds occur depends on the primary structure of the protein.

Question 21

what bonds maintain the tertairy structure

Answer 21

disulfide bridges

ionic bonds

hydrogen bonds

Question 22

describe disulfide bridges

Answer 22

they are fairly strong and therefore not easily broken

Question 23

describe ionic bonds

Answer 23

they are formed between any carboxyl and amino groups that are not involved in forming peptide bonds.

they are groups that are not involved in forming peptide bonds.

they are weaker than disulfide bonds and are easily broken by changes in PH

Question 24

describe hydrogen bonds

Answer 24

they are numerous but easily broken

Question 25

explain why the 3-d shape of a protein is important

Answer 25

the 3-d shape of a protein is important when it comes to how it functions

it makes each protein distinctive and allows it to recognise, and be recognised by, other molecules.

it can then interact with them in a very specific way

Question 26

describe the primary structure of a protein

Answer 26

the primary structure of a protein is the sequence of amino acids found in its polypeptide chains.

this sequence determines its properties and shape

following the elucidation of the amino acid sequence of the hormone insulin by Frederick sanger in 1954, the primary structure of many other proteins is now known

Question 27

describe the secondary structure of a protein

Answer 27

the secondary structure is the shape that the polypeptide chain forms as a result of hydrogen bonding.

this is most often a spiral known as the a-helix, although other configurations occur

Question 28

describe the tertiary structure of a protein

Answer 28

the tertiary structure is due to the bending and twisting of the polypeptide helix into a compact structure.

All three types of bond, disulfide, ionic and hydrogen, contribute to the maintenance of the tertiary structure

Question 29

describe the quaternary structure of a protein

Answer 29

the quaternary structure arises from the combination of a number of different polypeptide chains and associated non-protein groups into a large, complex protein molecule

Question 30

explain how we perform a test for proteins

Answer 30

place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature

add a few drops of very dilute 0.05% copper(II) sulfate solution and mix gently

a purple coloration indicates the presence of peptide bonds and hence a protein.

if no protein is preset the solution remains blue