Proteins - Class notes 2

Question 1

what are the roles/uses of protein in an organism?

Answer 1

keratin
ENZYMES
muscle tissue
transport across membranes
receptor sites on membranes
anti bodies
haemoglobin
some hormones - insulin and glucagon
melanin
collagen

Question 2

what are proteins made up of?

Answer 2

proteins are made up of smaller units called amino acids and peptide bonds

Question 3

what is the different between a polypeptide and a protein?

Answer 3

polypeptides are classed when there are less than 50 amino acids. more than 50 is classed as a protein

Question 4

what is the structure of an amino acid? (refer to notes)

Answer 4

contains one central carbon with an acid (e.g., carboxylic acid = -COOH) group attached to the right.
Has an amine group attached to the left. (nitrogen with two hydrogens attached.
also has a hydrogen attached above the structure and a the rest of the hydrocarbon is attached to the bottom, represented by an R

Question 5

draw a condensation reaction involving amino acids

Answer 5

SEE NOTES

Question 6

draw a dipeptide

Answer 6

SEE NOTES

Question 7

what is an example of a condensation reaction?

Answer 7

protein synthesis - bringing two or more amino acids together and producing water plus a peptide/protein.

Question 8

what is an example of a hydrolysis reaction?

Answer 8

digestion via enzymes - braking up the bonds between proteins/peptides.

Question 9

what are the four types of protein structure?

Answer 9

primary structure, secondary structure, teriary structure, quarternary structure

Question 10

describe a primary structure

Answer 10

this structure relates to the sequence of amino acids only, I.e., the amino acids chain (I.e., polypeptide) just formed by the ribosome during translation (second stage of proteins synthesis) proteins are not functional at this level.
(see diagram)

Question 11

describe a secondary structure

Answer 11

this is the first level of folding that a protein undertakes. there are two forms of secondary structures
-helix
-pleated sheets
proteins with a secondary structure are reffered to as ‘structural proteins’. structural proteins arer important for support and strength in connective tissue.

Question 12

what are two examples of secondary structures?

Answer 12

KERATIN (found in hair and nails) and COLLAGEN (found in cartilage, bone and ligaments) are examples of these types of proteins

Question 13

describe a tertiary structure.

Answer 13

the tertiary structure is a folding upon secondry structure.

Question 14

what is the name given to proteins that have a tertiary structure? give an example

Answer 14

Globular proteins - enzymes.

Question 15

what are the four types of bonds that maintain tertiary structures? (see diagram)

Answer 15

covalent bonds (in the form of disulphide bridges)
ionic bonds
hydrogen bonds
Van der Wall forces

Question 16

describe a quarternary structure and give an example

Answer 16

the quarternary structure is when you have two or more tertiary structures linked together. Haemoglobin is an example.

Question 17

what factors affect protein structure (and hence effect ENZYME function) ?

Answer 17

temperature

pH

Question 18

how does temperature effect protein structure?

Answer 18

proteins require a stable temperature in their environment. a change in temperature can affect protein function

Question 19

What is happening in section A of temperature graph? (see diagram)

Answer 19

the rate of protein activity increases as temperature increases. the increase in activity is proportional (cite specific values, e.g., rate doubles from 10 to 20 degrees etc.).

as temperature increases, there is an increase in kinetic energy of the system. this increase in energy increases protein activity (movement)

Question 20

What is happening in section B of temperature graph? (see diagram)

Answer 20

the increase in the rate of protein activity still increase, but at a decreasing rate. the rate is approching an optimal value.

as temperature increases, more proteins are DENATURING, thus reducing the number of proteins available to take part in the reaction

Question 21

What is happening in section C of temperature graph? (see diagram)

Answer 21

the rate of protein activity has peaked. in other words the optimum rate of activity has been reached, i.e., the rate of activity equals the rate at which proteins denature

Question 22

What is happening in section D of temperature graph? (see diagram)

Answer 22

the rate of protein activity decreases, rapidly, beyond 40 degrees. the rate drops to zero by 60 degrees.

beyond optimum temperatures (e.g., 40 degrees) the rate of denaturing (of the protein) is greater than the rate of protein activity. Proteins denature due to the kinetic energy disrupting bonds that maintain the tertiary structure, i.e., bonds are broken and the precise three dimensional structure is lost - hence protein function ceases. ‘denature’ is a term used to describe this loss of structure.

Question 23

Learn Diagrams of proteins denaturing due to temperature.

Answer 23

See Diagram

Question 24

Learn diagrams for proteins denaturing due to pH

Answer 24

see diagram

Question 25

what factor causes irreversible denaturing?

Answer 25

high temperature.

Question 26

what is special about pH denaturation?

Answer 26

the protein may reform its original structure if the original/normal pH is re-established.

Question 27

What happens to proteins when the temperature is increased? Refer to diagrams

Answer 27

1) some, or all, bonds are broken
2) protein is denatured due to increased temperatures
3) precise three dimensional shape is lost.