Proteins

Question 1

What is the chemical used when testing for proteins?

Answer 1

Biuret (blue) which is made up of 1cm^3 of sodium hydroxide - irritant - (to make the test solution alkaline) and drops of copper sulfate down the side of the tube.

Question 2

What is the biochemical test for proteins?

Answer 2

2cm^3 of your sample plus biuret (can be pre-made or you add it separately) Positive result = colour change from blue to purple/violet. Negative result = stays blue.

Question 3

What are the functions of proteins? (general)

Answer 3

Structural components, are membranes and carriers, all enzymes are proteins, antibodies are proteins, many hormones are proteins.

Question 4

What are proteins made up of?

Answer 4

The monomers are amino acids. A dipeptide = 2 amino acids joined together, a polypeptide = more than 2 (21-50) and a proteins are made up of one or more polypeptides (>50 amino acids). (There are also peptides = 3-20 amino acids)

Question 5

What is the R group in an amino acid?

Answer 5

A variable side group, this is different for each amino acid. They decide if the molecule is hydrophobic, hydrophilic, positively or negatively charged.

Question 6

How many amino acids are there?

Answer 6

20, so there are 20 different R groups.

Question 7

What reaction occurs to bond amino acids?

Answer 7

A condensation reaction to produce a dipeptide/polypeptide and water.

Question 8

What bond is formed between two amino acids?

Answer 8

A peptide bond.

Question 9

What atoms make up an amino acid?

Answer 9

Carbon, hydrogen, oxygen, nitrogen and sometimes sulfur.

Question 10

What are the properties of a protein determined by?

Answer 10

The sequence of amino acids.

Question 11

In a polypeptide chain what always is there at the start and end of the chain?

Answer 11

There is always an amine group at one end and a carboxylic acid group at the other.

Question 12

What is the reverse reaction when dipeptides and polypeptides break down?

Answer 12

A hydrolysis reaction, water is taken in.

Question 13

Are amino acids found in plants?

Answer 13

Yes, nitrates from the soil are used to convert amino groups and bonded to products of photosynthesis. Animals can then take in these plants and digest the plant amino acids and then make proteins of their own.

Question 14

Where are amino acids found (generally)?

Answer 14

Meat and soya and eggs, cant be built - has to be taken in from food.

Question 15

What is done with excess amino acids?

Answer 15

Cant be stored because of toxicity. Deamination is the removal of amino acids, takes place in the liver, amino acid groups are converted to urea and removed in the urine.

Question 16

Give info about the primary structure of a protein.

Answer 16

Protein sequencing - a specific sequence of amino acids that make up a polypeptide chain, it is determined by the gene that codes for a polypeptide, sequence determined by dna

Question 17

Give info about the secondary structure of a protein.

Answer 17

Hydrogen bonds form between the carboxyl and the amine groups in the backbone of the polypeptide making it automatically coil into an alpha (α) helix or fold into a beta (β) pleated sheet.

Question 18

Give info about a right-handed alpha-helix.

Answer 18

Polypeptide wound to form a coil, hydrogen bonds run parallel with long helical axis, strong stable structure due to many hydrogen bonds.

Question 19

Give info about a beta pleated sheet.

Answer 19

(Consists of two or more amino acid chains running parallel to each other) The polypeptide chain folds back on itself forming a zigzag sheet, held by hydrogen bonds, is a flat structure.

Question 20

Give info about the tertiary structure of a protein.

Answer 20

The final 3D shape, specific shape means specific function and properties, the coiled or folded chain is often coiled and folded further as more bonds are formed.

Question 21

Tertiary structure - what bonds are formed?

Answer 21

Disulphide bonds, ionic bonds, hydrogen bonds, hydrophilic and hydrophobic interactions, Van der Waals forces (weak, non-specific)

Question 22

Tertiary structure - what are disulphide bonds?

Answer 22

Disulphide bridges form whenever two molecules of the amino acid cysteine come close together. It is a covalent S-S bond and is very strong.

Question 23

Tertiary structure - Where do the ionic bonds occur?

Answer 23

Between oppositely charged R groups (strong)

Question 24

Tertiary structure - Where do hydrogen bonds occur?

Answer 24

Between slightly oppositely charged groups (between the carboxyl and amino acid groups)

Question 25

Tertiary structure - What are hydrophilic and hydrophobic interactions?

Answer 25

In a water based environment, a globular protein will be found as: hydrophilic (attracts water) amino acids on the outside and hydrophobic (naturally repels water) amino acids in the centre.

Question 26

Explain how a protein can denature.

Answer 26

By heat. An increased kinetic energy means molecules vibrate which breaks some bonds holding the structure in place so the protein unravels meaning its function cannot be performed. Most bonds are not covalent so are weak and easily broken. It is not a reversible process.

Question 27

Tertiary structure - Give info about globular proteins.

Answer 27

Roll up into a compact globe/ball shape structure, hydrophobic turn inwards to the centre of the structure and hydrophilic are outwards making the protein water soluble, have metabolic roles, are enzymes, plasma proteins and antibodies in mammals.

Question 28

Tertiary structure - Give info about fibrous proteins.

Answer 28

Form fibres, have a regular/repetitive sequence of amino acids, usually insoluble to water, have structural roles. Eg. collagen found in bones and cartilage and keratin found in fingernails and hair.

Question 29

Tertiary structure - are there any examples of proteins that are both fibrous and globular?

Answer 29

Myosin - the muscle protein, a long fibrous tail with a globular head (is not two different polypeptides but the same one with two different shapes).

Question 30

Give info about the quaternary structure of a protein.

Answer 30

Some proteins are made up of several polypeptide chains held together by bonds, the quaternary structure is the way these polypeptide chains are assembled together. Only some proteins have a quaternary structure but for those proteins it is their final 3D structure.

Question 31

Give examples of proteins with quaternary structures.

Answer 31

Haemoglobin, insulin and collagen.

Question 32

Quaternary structure - give info about haemoglobin.

Answer 32

Have a prosthetic group -haem (Fe^2), water soluble, primary structure:lots of amino acid constituents, tertiary structure - globular protein (mostly wound up into an alpha helix structure), made up of 4 polypeptide chains (2 alpha and 2 beta).

Question 33

Quaternary structure - What is the function of haemoglobin?

Answer 33

To carry oxygen from the lungs to tissues.

Question 34

Quaternary structure - Give info about collagen.

Answer 34

Doesnt have a prosthetic group, insoluble in water, primary structure: little amino acid constituents, tertiary structure - fibrous protein, mostly a left-handed helix structure, is made up of three polypeptide chains tightly coiled together, between collagen molecules there are covalent bonds called cross-links providing strength called collagen fibril (lots of fibrils make a fibre).

Question 35

Quaternary structure - what is the function of collagen?

Answer 35

To provide mechanical strength in: cartilage made of collagen, tendons (mostly collagen), bones made from collagen - calcium phosphate makes them hard, in artery walls collagen prevent bursting at high pressures, used in cosmetic surgery as an anti-age agent, great supportive tissue in animals.

Question 36

How do you work out how many different sorts of proteins molecules can be made when given the number of amino acids in the chain?

Answer 36

Do 20 to the power of the number of amino acids in the chain, if the number is too big for your calculator then leave it as a power. This works because there are 20 possible amino acids.

Question 37

Give info about antibodies.

Answer 37

Involved in the immune system response, found in the blood. Made up of two light (short) and two heavy (long) amino acid polypeptide chains bonded together. Have regions which are variable (amino acid sequence changes greatly).

Question 38

Give info about transport proteins.

Answer 38

Eg. the channel proteins present in cell membranes. They contain hydrophobic and hydrophilic amino acids which cause the proteins to fold up and cause a channel. These proteins transport molecules and ions across membranes.

Question 39

Give info about structural proteins.

Answer 39

Physically strong, consist of polypeptide chains which lie parallel to each other with cross-links between them eg. keratin and collagen.

Question 40

Name everything that would be labelled on you paper when carrying out chromatography.

Answer 40

The solvent point (the line drawn in pencil at the bottom of the chromatography paper - where the solvent started), the pigments, the solvent front (where the solvent reaches, needs to be drawn on otherwise you can’t see it when its dry)

Question 41

Why can’t pen be used to draw the solvent point?

Answer 41

Pen is made up of ink so dissolves in the solvent and moves up the paper merging with you sample making it inaccurate.

Question 42

Does it matter which solvent is used in chromatography?

Answer 42

Yes, the solvent needs to be able to dissolve you sample in order for it to move up the paper.

Question 43

How do you work out an Rf value?

Answer 43

Distance moved by the chemical component/distance travelled by the solvent front.

Question 44

Use of chromatography?

Answer 44

To decipher what dyes are present in an ink, to find out what amino acids are present in an solution by comparing Rf values to known Rf values.

Question 45

What is an essential amino acid?

Answer 45

Amino acids that our body can’t make but are essential to building proteins.