section 2: biological molecules - topic 5: proteins Flashcards

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1
Q

what are proteins?

A

polymers.

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2
Q

what are the monomers of proteins?

A

amino acids.

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3
Q

what is formed when 2 amino acids join together?

A

a dipeptide.

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4
Q

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

A

a polypeptide.

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5
Q

what are proteins made up of?

A

one or more polypeptides.

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6
Q

what is the general structure of all amino acids?

A

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

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7
Q

what is the difference between different amino acids?

A

the variable group they contain.

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8
Q

what chemical elements do all amino acids contain?

A

carbon.
oxygen.
hydrogen.
nitrogen.

some also contain sulphur.

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9
Q

what are amino acids linked together by?

A

peptide bonds - to form dipeptides and polypeptides.

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10
Q

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

A

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.

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11
Q

what are the 4 structural levels of a protein?

A

primary.
secondary.
tertiary.
quaternary.

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12
Q

describe the primary structure.

A
  • 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.
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13
Q

describe the secondary structure.

A
  • 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.
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14
Q

describe the tertiary structure.

A
  • the coiled or folded chain of amino acids is often coiled and folded more.
  • more bonds form between different parts of the polypeptide chain.
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15
Q

what are the bonds involved in the tertiary structure?

A

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

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16
Q

describe the ionic bonds in the tertiary structure.

A

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

17
Q

describe the disulphide bonds in the tertiary structure.

A

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.

18
Q

describe the hydrophobic & hydrophilic interactions in the tertiary structure.

A

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.

19
Q

describe the hydrogen bonds in the tertiary structure.

A

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.

20
Q

what is the quaternary structure?

A

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.

21
Q

what is the quaternary structure determined by?

A

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.

22
Q

what are the 2 types of proteins?

A

globular.
fibrous.

23
Q

what do globular proteins look like?

A

they are round and compact.

24
Q

what is the structure of a globular protein?

A

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.

25
Q

what are examples of globular proteins?

A

haemoglobin.
insulin.
amylase.

26
Q

describe heamoglobin.

A

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.

27
Q

describe insulin.

A

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.

28
Q

describe amylase.

A

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.

29
Q

what do fibrous proteins look like?

A

they are tough and rope-shaped.

30
Q

what are the 2 properties of fibrous proteins?

A

insoluble.
strong.

31
Q

what kind of protein are fibrous proteins?

A

structural.
- fairly unreactive (unlike many globular proteins)

32
Q

what are examples of fibrous proteins?

A

collagen.
keratin.
elastin.

33
Q

describe collagen.

A

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.

34
Q

describe keratin.

A

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).

35
Q

describe elastin.

A

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.