1.4.1 General properties of proteins

Question 1

Are amino acids soluble or insoluble in water?

Answer 1

Soluble

Question 2

What do amino acids contain?

Answer 2

• An amino group (NH2)
• A carboxyl group (COOH)
• An R group

Question 3

What do R groups do?

Answer 3

• They affect the way the amino acid groups bond to each other.
• They affect the 3D shape of a protein.

Question 4

Definition of the primary structure?

Answer 4

The order and sequence of amino acids, held together by peptide bonds.

Question 5

What will the primary structure determine?

Answer 5

How the polypeptide chain will later fold, and therefore the 3D shape.

Question 6

What is the secondary structure formed as a result of?

Answer 6

The hydrogen bonds between amino acids (R groups).

Question 7

What can the secondary structure of a protein be?

Answer 7

Alpha helix or beta pleated sheet.

Question 8

Why will different R groups form more hydrogen bonds than others?

Answer 8

As they will contain more hydrogen.

Question 9

What are the 4 main types of bonds that form in the tertiary structure?

Answer 9

• Hydrogen bonds.
• Disulphide bonds.
• Ionic bonds.
• Hydrophobic and hydrophilic interactions.

Question 10

Hydrogen bonds in the tertiary structure?

Answer 10

• Weakest bond ON ITS OWN.
• Most common bond -> formed between a wide variety of R groups.
• When there are many H bonds = strong overall bond.
• Formed between strongly polar R groups.

Question 11

Disulphide bonds in the tertiary structure?

Answer 11

• Disulphide bridges can only form between R groups that contain sulphur.

Question 12

Ionic bonds in the tertiary structure?

Answer 12

• The electrostatic interaction between POSITIVE amino groups and NEGATIVE carboxyl groups.
• Less common.
• Stronger than individual hydrogen bonds.

Question 13

What does the tertiary structure determine?

Answer 13

• The shape of the active site of enzymes.
• The function of proteins.

Question 14

What are conjugated proteins?

Answer 14

Proteins that derive part of their function from prosthetic groups.

Question 15

What is a prosthetic group?

Answer 15

A non-protein group.

Question 16

Give 2 examples of conjugated proteins?

Answer 16

Haemoglobin and collagen.

Question 17

Condensation reactions of proteins?

Answer 17

• Join together 2 amino acids.
• A molecule of water is lost.
• A peptide bond is formed.

Question 18

Structure of haemoglobin?

Answer 18

4 polypeptide chains
with 1 haem group

Question 19

Where does oxygen attach to in haemoglobin?

Answer 19

The iron in the haem group.

Question 20

What is haem?

Answer 20

A pigment containing iron.

Question 21

Is haemoglobin soluble or insoluble in water?

Answer 21

Soluble

Question 22

Where is collagen present?

Answer 22

In bones and tendons.

Question 23

Structure of collagen?

Answer 23

• 3 polypeptide chains.
• Coiled around each other.
• With hydrogen bonds between the chains.

Question 24

Is collagen a strong molecule?

Answer 24

Yes.

Question 25

What are the 2 types of protein structures?

Answer 25

Fibrous and globular.

Question 26

Shape of fibrous proteins?

Answer 26

- Parallel chains that cross at regular intervals.

Question 27

Shape of globular proteins?

Answer 27

Roughly circular.

Question 28

Amino acid sequencing in fibrous proteins?

Answer 28

Repetitive.

Question 29

Amino acid sequencing in globular proteins?

Answer 29

Irregular.

Question 30

Are fibrous proteins generally soluble or insoluble in water?

Answer 30

Insoluble.

Question 31

Are globular proteins generally soluble or insoluble in water?

Answer 31

Soluble.

Question 32

Describe how the structure of a protein depends on the amino acids it contains.

Answer 32

1. Primary structure is determined by the order and sequence of amino acids. 2. Secondary structure is formed by hydrogen bonding between amino acids. 3. Tertiary structure is formed by interactions between R groups. 4. Which creates the shape of active sites in enzymes. 5. Quaternary structure contains more than 2 polypeptide chains.

Question 33

What is a dipeptide?

Answer 33

A dipeptide consists of two amino acids joined by a peptide bond. condensation of

Question 34

what is a polypeptide

Answer 34

formed by the condensation of many AA

Question 35

Describe two other ways in which all dipeptides are similar and one way in which they might differ.

Answer 35

S = Both contain an amine group. S = Both contain a carboxyl group. D = Different R groups.

Question 36

Describe how a peptide bond is formed between two amino acids to form a dipeptide.

Answer 36

- Condensation reaction. - Between amino and carboxyl group.

Question 37

Describe how the secondary structure of a polypeptide is produced by bonds between amino acids.

Answer 37

- Hydrogen bonds form. - Between NH group and C=O group. - Forming either an alpha helix or a beta-pleated sheet.

Question 38

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.

Answer 38

- Different sequence of amino acids. - Different primary structure. - Forms ionic, hydrogen, disulfide bonds in different places.

Question 39

Aspartic acid and pralinee are both amino acids. Describe how two amino acids differ from one another.

Answer 39

different R groups

Question 40

At what level of protein structure do hydrophobic interaction occurs?

Answer 40

Tertiary, Quaternary

Question 41

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

Answer 41

amino group and carboxylic group Condensation reaction Water removed

Question 42

Describe how A quaternary protein is formed from its monomers

Answer 42

Amino acid joined by peptide bonds - condensation reactions - secondary structure formed by hydrogen bonding - teritary structure is formed by interactions between R groups - quaternary strcutre contains more than 1 polypeptide - Quaternary strcutre is formed by interactions/ bonds between polypeptides

Question 43

describe how Monomers join to form the primary structure of protein

Answer 43

1-Condensation reaction between 2 AA 2- creating specific Sequence of AA 3- Joined by peptide bonds

Question 44

Describe how the structure of a protein depends on the amino acids it contains.

Answer 44

1. Structure is determined by position of amino acid/ 2. Primary structure is sequence of amino acids; 3. Secondary structure formed by hydrogen bonding 4. Tertiary structure formed by interactions between R groups 5. Creates active site in enzymes

Question 45

Describe the structure of proteins.

Answer 45

1. Polymer of amino acids; 2. Joined by peptide bonds; 3. Formed by condensation; 4. Primary structure is order of amino acids; 5. Secondary structure is folding of polypeptide chain due to hydrogen bonding; Accept alpha helix / pleated sheet 6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds; 7. Quaternary structure is two or more polypeptide chains.

Question 46

Different r group

Answer 46

different bonds form different tertiary structure

Question 47

Explain the tertiary structure of proteins and the forces involved in its formation + def

Answer 47

Folding of polypeptide into specific complex shape due to IMFs between R group e.g. Hydrogen bonds, ionic bonds, disulfide bridge and London forces

Question 48

Genes - how does it code for production of a polypeptide:

Answer 48

1- Triplet 2- Base/ nucleotide sequence 3- determines order/ Sequences of AA 4- Primary structure in polypeptide determined

Question 49

Give an example of a globular and a fibrous protein.

Answer 49

Globular- haemoglobin Fibrous - collagen

Question 50

How do amino acids provide indirect evidence for evolution?

Answer 50

The same 20 amino acids occur in all living organisms.

Question 51

How is the presence of proteins tested using buret test, and what constitutes a positive result (Shows what??)

Answer 51

add copper sulphate and sodium hydroxide to a solution +ve - blue - purple shows presence of peptide bond

Question 52

The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how

Answer 52

hydrogen bonds Between amino group and carboxylic group Forming alpha helix or beta pleated sheets

Question 53

two proteins have the same number and type of amino acids but different tertiary structures. Explain why

Answer 53

different primary sequence of AA R group bond form in different places Form ionic/ hydrogen/ disulphide bonds in different places

Question 54

What elements do all proteins/amino acids contain?

Answer 54

carbon hydrogen oxygen nitrogen

Question 55

what is the primary structure of a protein and what role does it play in protein shape?

Answer 55

refers to sequence of amino acids in a protein joined by peptide bonds controls the overall protein shape and function

Question 56

what is the significance of quaternary structure in proteins?

Answer 56

holds together multiple polypeptide chains and other molecules necessary for protein function therefore contributing to the overall structure and function of proteins

Question 57

what type of bond is formed in condensation reaction to create a polypeptide

Answer 57

peptide bond between amine group of one AA and carboxyl group releasing water

Question 58

Figure 2 shows the SGLT1 polypeptide with NH2 at one end and COOH at the other end. Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end. You may use a diagram in your answer.

Answer 58

1-   One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond; 2.      (So in chain) there is a free amine/NH2 group at one end and a free carboxyl/COOH group at the other OR Each amino acid is orientated in the same direction in the chain;