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A Level Biology OCR > Proteins > Flashcards

Proteins Flashcards

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1
Q

What are proteins

A

They are polymers of about 20 naturally occurring amino acids

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2
Q

What is the general formula of an amino acid

A

DRAW IT

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3
Q

What elements are found in proteins

A

carbon, hydrogen, oxygen, nitrogen and sometimes sulfur

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4
Q

What happens at PH 7 to amino acids

A

Both the amine and carboxyl groups on the amino acid become ionised

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5
Q

What does an ionised amino acid look like

A

DRAW IT

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6
Q

How are amino acids grouped

A

They are grouped according to the properties of the R side chain. Whether they are acidic, basic, polar or non polar.

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7
Q

How are amino acids denoted

A

They are given both 1 letter and 3 letter abbreviations

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8
Q

How are amino acids joined together

A

they are commonly joined together by amide linkage which is known as a peptide bond.

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9
Q

What does a peptide bond look like

A

DRAW IT

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10
Q

What are proteins in terms of amino acids and bonds

A

They are long polymers of amino acids linked together by peptide bonds, and are always written with the n terminal towards the left.

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11
Q

What type of reaction forms the peptide bonds

A

It’s a condensation reactions as water is also formed

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12
Q

Where does this reaction occur

A

It occurs on the ribosome where proteins are synthesised in the cell.

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13
Q

What is it called when two amino acids are bonded and when 3 amino acids or more are bonded

A

Two - dipeptide
Three - polypeptide

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14
Q

What needs to happen in order for a polypeptide to be called a protein

A

It must fold into a complex 3D shape. Once it is folded it can carry out its function and is now referred to as a protein.

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15
Q

What is the reaction called to break the peptide bond and what is needed for it to occur

A

It is called a hydrolysis reactions and to break the peptide bond a molecule of water is added. This is carried out by the protease enzyme.

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16
Q

What is the primary structure

A

The specific order of amino acids in a polypeptide

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17
Q

What does the primary structure do and why is this important

A

It helps to determine the 3D shape of the protein molecule. The shape of a protein is critical for its function.

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18
Q

how is the primary structure determined and how does a change in it affect the protein

A

it is determined by the DNA sequence of the gene coding for the polypeptide. A change in the amino acids will greatly affect the shape of the protein preventing it from carrying out its function.

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19
Q

how does the secondary structure of a protein form

A

It forms as a result of hydrogen bonding between different amino acids in the chain

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20
Q

What are the partial charges in the peptide bond

A

Hydrogen in the peptide bonds has a partial positive charge and the oxygen in the bond has a partial negative charge.

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21
Q

What do these partial charges do

A

The positive and negative charges can attract each other and hydrogen bonds form between amino acids in the polypeptide chain.

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22
Q

What do the hydrogen bonds that are formed do

A

They cause the polypeptide chain to twist and fold into shapes.

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23
Q

What are two common types of secondary structure and what are they

A

Alpha helices - polypeptide chains twisted into a helical shape held in place by hydrogen bonds

Beta plated sheets - Polypeptide chains folded into a flat sheet-like structure, held in place by hydrogen bonds

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24
Q

What does the secondary structure depend on

A

It depends on the primary structure in that region

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25
Q

What is the tertiary structure

A

The overall 3D shape that the polypeptide chains twisted into

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26
Q

Where are the forces responsible for the tertiary structure from and therefore how does this relate to the primary structure

A

The forces form between the R groups on amino acids in the polypeptide chain. So the type of bonding depends on the specific amino acids in the chain (primary structure).

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27
Q

When does the tertiary structure from

A

Once the secondary structure forms the polypeptide continues folding forming the tertiary structure.

28
Q

What is the first bond/ force that is responsible for the tertiary structure

A
  1. Hydrogen bonds (which are weak bonds easily broken by changes in PH and temperature)
29
Q

What is the second bond/ force that is responsible for the tertiary structure

A

Ionic bonds (between amino acids with charged groups which attract holding parts of the chain together)

30
Q

What is the third bond/ force that is responsible for the tertiary structure

A

Disulphide bonds (between two R groups containing sulfur atoms, forming a covalent bond). These are very strong bonds.

31
Q

What is an interaction that can also determine protein structure and how do they do so

A

Hydrophilic and hydrophobic interactions
Hydrophobic reactions occur as many amino acids have uncharged R groups so are non-polar amino acids, which cluster together repelling water molecules. These are called hydrophobic interaction and are found in the centre of proteins away from water molecules.
Hydrophilic amino acids tend to be found on the surface of proteins so they can interact with water molecules.
These interactions are weak.

32
Q

What is a difference between the tertiary and quaternary structure

A

if these bonds form on the same chain they are tertiary and different chains/subunits they are quaternary.

33
Q

What is the quaternary structure

A

Some proteins consist of more than one polypeptide chain working together as a large molecule , held together in a precise structure. The quaternary structure shows how these chains/subunits are arranged to form a 3.D structure.

34
Q

What are polypeptide chains in the quaternary structure called

A

They are called subunits

35
Q

What does the quaternary structure only apply to

A

Proteins with at least two subunits

36
Q

What holds together the subunits

A

They are held together by ionic bonds, hydrogen bonds and disulfide bonds.

37
Q

What can the quaternary structure also involve

A

The addition of non-amino acids derived groups known as prosthetic groups. The quaternary structure shows the position of the prosthetic groups.

38
Q

What do the prosthetic groups do and what are proteins called that have them

A

They help the proteins carry out their functions.
Proteins are called conjugate proteins if they have them.

39
Q

What are globular proteins

A

Globular proteins are proteins with a spherical mass and specific 3D shape. They fold up so that the hydrophilic groups are on the surface (can interact with water molecules) and the hydrophobic groups are inside the molecule (so they can’t interact with water molecules).

40
Q

What is a feature of globular proteins

A

They are soluble in water

41
Q

What is haemoglobin

A

Haemolglobin is a globular protein with a quaternary structure.

42
Q

What does haemoglobin consist of

A

It consists of 4 polypeptide subunits forming a large molecule. It has 2 alpha subunits and 2 beta subunits.

43
Q

What is the purpose of haemoglobin

A

IT blinds to O2 in the lungs and then releases it to body tissues.

44
Q

What is the prosthetic groups of haemoglobin

A

It has 4 haem prosthetic groups, that contain iron Fe2+, one haem per polypeptide, oxygen binds with iron, so because of the prosthetic groups 4 oxygen molecules can be carried.

45
Q

What is a special feature of haemoglobin and what is it held together by

A

When oxygen attaches to haemoglobin its quaternary structure slightly changes making it easier for more oxygen to attaches.
Haemoglobin, is held together by hydrogen bonds.

46
Q

What is insulin

A

It is a globular protein and a hormone carried in the bloodstream that regulates glucose in the blood.

47
Q

What does insulin consist of

A

It consists of two polypeptide chains linked by disulfide bonds.

48
Q

How does insulin carry out its function

A

It binds to specific receptor molecules which are proteins found on the cell membranes of target cells.
The shape of insulin means that it fits perfectly into the receptor and slight changes can prevent effective binding.

49
Q

What is lysozyme

A

It is a globular protein and is found in saliva and tears and is used to catalyse the breakdown of a molecule in bacterial cell walls. Helping to defend against bacteria.

50
Q

What is a feature of lysosome and how does its structure help to achieve this

A

Lysozyme is a specific enzyme, so it only reacts with a specific substrate molecule. This is because it consists of a single polypeptide chain that folds to form a groove along the surface, this is called the active site. The substrate fits perfectly into the active site. This makes the enzyme highly specific.

51
Q

What are fibrous proteins

A

Fibrous molecules that form long chains or fibres (like ropes).
Their fibrous nature makes them insoluble in water, also contributing to this is the fact that they have lots of hydrophobic R groups on the amino acids.

52
Q

What are fibrous proteins used for

A

They are useful for structure and support for example in bones, tendons and walls of blood vessels.

53
Q

What is collagen

A

A fibrous protein found in tendons (connect muscles to bones), ligaments (connect muscles to each other) and is also found in the skin.

54
Q

What is the structure of collagen

A

It forms a triple helix of polypeptide chains. In the collagen every 3rd amino acid is glycine where the R group is a hydrogen atom. So it has the smallest R group of all amino acids allowing for polypeptides to wrap tightly around each other.

55
Q

What are collagen chains held together by and what does this do? What also forms between chains

A

They are held together by hydrogen bonds which help to stabilise the quaternary structure of the protein. Crosslinks also form between the chains making them strong.

56
Q

What does collagen group together to form

A

Large number of helices join together to form fibrils and micro fibrils, where the molecules are staggered so there are no weak points.

57
Q

What is keratin

A

A fibrous protein found in hair, fingernails, and the outer surface of skin.

58
Q

What are the properties of keratin

A

It is very strong and insoluble in water.

59
Q

What is the structure of keratin

A

It consists of two long stranded molecules. And a high proportion of the amino acids are cysteine which can form disulfide bonds, these bonds are very strong covalent bonds and as it contains lots of them, it makes keratin very strong.

60
Q

What is elastin

A

It is a fibrous protein which the skin contains lots of, which helps to make the skin supple and elastic.

61
Q

Where is elastin found

A

It’s also found in artery walls, where they stretch when blood pleases through the artery, and recoil in between pulses helping the artery to return to the original shape.

62
Q

What are the properties of elastin and what causes it

A

The hydrophobic regions in elastin associate causing molecules to group together. When stretched they move apart and stay attached at crosslinks. After stretching molecules re associate springing back together, making it very elastic.

63
Q

How are proteins broken down

A

They are broken down by protease which are enzymes that catalyse the reverse reaction - turning peptides into amino acids.
A water molecule is used to break the peptide bond in a hydrolysis reactions, reforming the amino acids.

64
Q

What is the test used for proteins

A

The biuret test

65
Q

What are the stages of the biuret test

A
  1. Sample mixed with an equal volume of NaOH solution
  2. 1% of copper sulfate solution added a few drops at a time until the sample solution turns blue
  3. Solution is mixed and left to stand for 5 minutes
66
Q

What is the positive test for the biuret test and why does it occur

A

It goes from blue to violet
Peptide bonds form violet coloured complexes with copper ions in alkaline solutions.

67
Q

What is the biuret reagent made out of

A

A mixture of copper sulfate solution and an alkali is called a biuret reagent.

A Level Biology OCR (19 decks)

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