section 2: biological molecules - topic 5: proteins

Question 1

what are proteins?

Answer 1

polymers.

Question 2

what are the monomers of proteins?

Answer 2

amino acids.

Question 3

what is formed when 2 amino acids join together?

Answer 3

a dipeptide.

Question 4

what is formed when more than 2 amino acids join together?

Answer 4

a polypeptide.

Question 5

what are proteins made up of?

Answer 5

one or more polypeptides.

Question 6

what is the general structure of all amino acids?

Answer 6

a carboxyl group (-COOH) and an amino group (-NH2) attached to a carbon atom.

Question 7

what is the difference between different amino acids?

Answer 7

the variable group they contain.

Question 8

what chemical elements do all amino acids contain?

Answer 8

carbon.
oxygen.
hydrogen.
nitrogen.

some also contain sulphur.

Question 9

what are amino acids linked together by?

Answer 9

peptide bonds - to form dipeptides and polypeptides.

Question 10

what type of reaction is it to form dipeptides and polypeptides?

Answer 10

a condensation reaction.
^ a molecule of water is released during the reaction.

the reverse of this adds a molecule of water to break the peptide bond.
- hydrolysis reaction.

Question 11

what are the 4 structural levels of a protein?

Answer 11

primary.
secondary.
tertiary.
quaternary.

Question 12

describe the primary structure.

Answer 12

• this is the sequence of amino acids in the polypeptide chain.
• different proteins have different sequences of amino acids in their primary structure.
• a change in just 1 amino acid may change the structure of the whole protein.
• it’s held together by the peptide bonds between the amino acids.

Question 13

describe the secondary structure.

Answer 13

• the polypeptide chain doesn’t remain flat and straight.
• hydrogen bonds form between the -NH and -CO groups of the amino acids in the chain.
• this makes it automatically coil into an alpha helix or fold into a beta pleated sheet.

Question 14

describe the tertiary structure.

Answer 14

• the coiled or folded chain of amino acids is often coiled and folded more.
• more bonds form between different parts of the polypeptide chain.

Question 15

what are the bonds involved in the tertiary structure?

Answer 15

ionic bonds.
disulphide bonds.
hydrophobic & hydrophilic interactions.
hydrogen bonds.

Question 16

describe the ionic bonds in the tertiary structure.

Answer 16

these are attractions between negatively-charged R groups and positively-charged R groups on different parts of the molecule.

Question 17

describe the disulphide bonds in the tertiary structure.

Answer 17

whenever 2 molecules of the amino acid cysteine come close together, the sulphur atom in 1 cysteine bonds to the sulfur in the other cysteine, forming a disulphide bond.

Question 18

describe the hydrophobic & hydrophilic interactions in the tertiary structure.

Answer 18

when hydrophobic R groups are close together in the protein, they tend to clump together.
this means that hydrophilic R groups are more likely to be pushed to the outside.
^ affects how the protein folds up into its final structure.

Question 19

describe the hydrogen bonds in the tertiary structure.

Answer 19

these weak bonds form between slightly positively-charged hydrogen atoms in some R groups and slightly negatively-charged atoms in other R groups on the polypeptide chain.

Question 20

what is the quaternary structure?

Answer 20

some proteins are made of several different polypeptide chains held together by bonds.

the quaternary structure is the way these polypeptide chains are assembled together.

Question 21

what is the quaternary structure determined by?

Answer 21

the tertiary structure of the individual polypeptide chains being bonded together.
- because of this, it can be influenced by all those bonds (ionic, disulphide, hydrophobic + hydrophilic, hydrogen).

for proteins made from more than 1 polypeptide chain, the quaternary structure is the proteins final 3D structure.

Question 22

what are the 2 types of proteins?

Answer 22

globular.
fibrous.

Question 23

what do globular proteins look like?

Answer 23

they are round and compact.

Question 24

what is the structure of a globular protein?

Answer 24

the hydrophilic R groups on the amino acids tend to be pushed to the outside of the molecule.
- this is caused by the hydrophobic and hydrophilic interactions in the proteins tertiary structure.

this makes globular proteins soluble, so they’re easily transported in fluids.

Question 25

what are examples of globular proteins?

Answer 25

haemoglobin.
insulin.
amylase.

Question 26

describe heamoglobin.

Answer 26

haemoglobin is a globular protein that carries oxygen around the body in red blood cells.

it’s a conjugated protein - means it’s a protein with a non-protein group attached.
the non-protein part = a prosthetic group.

each of the 4 polypeptide chains in haemoglobin has a prosthetic group called haem.
- it’s the iron-containing haem groups that bind to oxygen.

Question 27

describe insulin.

Answer 27

insulin is a hormone secreted by the pancreas - helps to regulate the blood glucose level.

its solubility is important - means it can be transported in the blood to the tissues where it acts.

an insulin molecule consists of 2 polypeptide chains - held together by disulphide bonds.
- when they’re in the pancreas, 6 of these molecules bind together to form a large, globular structure.

Question 28

describe amylase.

Answer 28

amylase is an enzyme that catalyses the breakdown of starch in the digestive system.

it’s made of a single chain of amino acids.
its secondary structure contains both alpha-helix and beta-pleated sheet sections.

most enzymes are globular proteins.

Question 29

what do fibrous proteins look like?

Answer 29

they are tough and rope-shaped.

Question 30

what are the 2 properties of fibrous proteins?

Answer 30

insoluble.
strong.

Question 31

what kind of protein are fibrous proteins?

Answer 31

structural.
- fairly unreactive (unlike many globular proteins)

Question 32

what are examples of fibrous proteins?

Answer 32

collagen.
keratin.
elastin.

Question 33

describe collagen.

Answer 33

collagen is found in animal connective tissues - bone, skin, muscle.

it’s a very strong molecule.

minerals can bind to the protein to increase its rigidity i.e. in bone.

Question 34

describe keratin.

Answer 34

keratin is found in many of the external structures of animals - skin, hair, nails, feathers, horns.

it can either be flexible (as in skin) or hard and tough (as in nails).

Question 35

describe elastin.

Answer 35

elastin is found in elastic connective tissue - skin, large blood vessels, some ligaments.

it’s elastic - allows tissues to return to their original shape after they’ve been stretched.