Proteins

Question 1

Name the parts of amino acids

Answer 1

Amine, hydrogen, carboxyl, R-group (variant). Carbon centre

Question 2

What is a:

a) Condensation reaction
b) Hydrolysis reaction

Answer 2

a) When 2 biological molecules join together to lose water

b) When 2 biological molecules spit apart by adding water

Question 3

What does proteinogenic mean?

Answer 3

The 20 amino acids which in different combinations make up all proteins in humans

Question 4

How many different amino acids are there in humans?

Answer 4

20 - the different combinations form the different proteins

Question 5

Where are proteins found in the body?

Answer 5

DNA (protein around it), digested in the small intestine & stomach, amino acids making them in the ribosomes, enzymes, anitbodies, antigens - surface of cells, haemoglobin, cologen (in skin)

Question 6

What are the base elements for amino acids?

Answer 6

Carbon, Hydrogen, Oxygen, Nitrogen

Question 7

Why is the shape of a enzyme important for its function?

Answer 7

Only the appropriate substrate will fit in the enzyme’s active site & and be broken down into its products

Question 8

What is an amino acid residue?

Answer 8

(Primary stage) when 2 amino acids join in a condenstaion reaction, a water molecule is lost. The 2 separate parts of the amino acid left before the peptide bond is formed are amino acid residues

Question 9

What bond is formed in proteins?

Answer 9

Peptide bonds

Question 10

Describe the process of a condensation reaction between 2 amino acids (primary stage)

Answer 10

2 amino acids (monomers) come together. The hydroxyl from the carboxyl section joins to a hydrogen from the amine section of the other amino acid. They break off from the amino acids to form a water molecule. The amino acid residues left form a peptide bond to the exposed carbon in the carboxyl section, and the exposed nitrogen from the amine section. This is now a dipeptide formed from the condensation reaction

Question 11

We eat food to get proteins, to break into amino acids and be reused. How do plants make proteins?

Answer 11

They absorb nitrogen from the soil, so can make their own amino acids from scratch

Question 12

What is the R group?

Answer 12

The varying group between all amino acids (below the centre carbon)

Question 13

What is the (briefly):

1) Primary structure
2) Secondary structure
3) Tertiary structure
4) Quaternary structure

Answer 13

1) Condensation reaction - 2 amino acids join (peptide bond) to form a dipeptide
2) H bonds form between remains of carboxyl & hydroxyl groups of the polypeptides, forming an alpha helix or beta pleated sheet
3) Disulfide bridges, H bonds & ionic bonds form between R groups, so the protein is twisted and folded & 3D
4) Not essential! When a protein is made from more than one type of polypeptide chain e.g. prosthetic group. Same as tertiary stricture bonds

Question 14

What happens in the secondary structure?

Answer 14

Either alpha helix or beta pleated sheet shapes form from hydrogen bonds made from the remains of the carboxyl and hydroxyl groups

Question 15

What happens if the secondary structure fails - the hydrogen bonds break (which can happen as they’re weak)?

Answer 15

Any change n the environment could cause this. The protein would unfold completely, becoming flat again

Question 16

Where are the hydrogen bonds formed in secondary structure?

Answer 16

Between the remains of the carboxyl and hydroxyl groups

Question 17

What happens in the tertiary structure?

Answer 17

Disulfide bridges, hydrogen bonds and ionic bonds form between R groups of amino acids, causing the structure to twist and fold, becoming more 3D

Question 18

Talk about these types of bonds:

a) Hydrogen bonds
b) Ionic bonds:
c) Disulfide bridges

Answer 18

All formed in tertiary structure (H bonds also 2ndary)

a) Numerous, but VERY easily broken. The more, the harder to break
b) Stronger, but VERY easily broken with any pH change
c) STRONGEST! Only formed when sulfur in R group. Only 2/20 human amino acids have sulfur though

Question 19

What does the tertiary structure depend on?

Answer 19

The R groups - both the combination and elements. Very specific

Question 20

If polypeptide has CHOCO in its R group, and another has COCO, why do they form different structures?

Answer 20

Because in the tertiary structure, bonds such as hydrogen bonds are formed between R groups. This is very specific, so altering the combination or - in this case - elements will completely change the outcome of the 3D protein it forms

Question 21

What is quaternary structure?

Answer 21

When a protein is made from more than 1 type of polypeptide chain, e.g. having a prosthetic group. The same bonds as tertiary structure hold it together (H bonds, ionic bonds, disulfide bridges)

Question 22

What is a prosthetic group? Give an example

Answer 22

A non-protein group. Haemoglobin contains iron, so has to go through quaternary structure

Question 23

Describe how a peptide bond is formed between 2 amino acids to form a dipeptide. (2)

Answer 23

A hydrogen from the amine section of one amino acid will combine with the hydroxide of another amino acid’s carboxyl section. These form the water molecule lost during this condensation reaction. The amino acid residues left form a peptide bond, forming a dipeptide

Question 24

What are primary peptides?

Answer 24

Polypeptides

Question 25

How would a mutation causing a change in the DNA sequence change the protein formed?

Answer 25

DNA sequences put amino acids in a specific order to create a specific protein. Mutating and altering this sequence means that the amino acids are in a different order, therefore the tertiary structure will be different as the hydrogen, ionic bonds and disulfide bridges will form in different places between the newly placed R groups. So, the resultant protein will form an entirely different 3D shape, making a different protein.

Question 26

What is the test for proteins?

Answer 26

Biuret reagent - made from equal amounts of sodium hydroxide & copper sulphate

1) Add biuret reagent to the suspect food
2) If the food contains protein, it will turn lilac. If not, it will stay blue.