3.1.4- Proteins

Question 1

Proteins

Answer 1

For growth, repair & transport as well as being used for cell structures and blood enzymes

Question 2

features of amino acids

Answer 2

Monomers that form polypeptides
20 naturally occurring amino acids
Each has a different R group

Question 3

What do all amino acids have?

Answer 3

Central Carbon Atom

Amino Group

Carboxyl group

Hydrogen atom

R group

Question 4

How are dipeptides formed?

Answer 4

condensation reaction between 2 amino acids

Question 5

Where would the amino and carboxyl groups be placed?

Answer 5

Opposite one another

Question 6

What bond is formed between amino acids?

Answer 6

peptide bond

Question 7

Protein test

Answer 7

Biuret test- purple if protein is present

Question 8

functions of proteins

Answer 8

structure, hormones, movement of cells, transport molecules, enzymes, antibodies

Question 9

Primary Protein Structure

Answer 9

sequence of a chain of amino acids. They are joined through polymerisation.

Question 10

Secondary protein structure

Answer 10

coiling or folding of a polypeptide due to H-bonding between amino acids. Hydrogen bond caused by NH positive charge and C=O negative charge

Question 11

tertiary protein structure

Answer 11

three-dimensional folding pattern of a protein due to side chain interactions. Bonds maintain the structure: disulphide bonds, ionic bonds and hydrogen bonds

Question 12

disulfide bonds

Answer 12

Strong chemical side bonds that can only be broken by chemical solutions

Question 13

Ionic bonds

Answer 13

Formed between carboxyl and amino groups. Broken by pH changes

Question 14

Hydrogen bonds

Answer 14

Very weak but many of them

Question 15

quartenary protein structure

Answer 15

protein consisting of more than one amino acid chain. Very complex and may contain non-protein groups

Question 16

Enzyme structure

Answer 16

Globular proteins (long polypeptide chain) that have a functional region known as an active site

Question 17

Enzyme function

Answer 17

speed up chemical reactions by lowering activation energy

Question 18

Limitations of the lock and key hypothesis

Answer 18

Doesn’t explain how products are released

Doesn’t explain why some enzymes can act on a small number of similar substrates

Question 19

induced fit model of enzyme action

Answer 19

Explains how activation energy is lowered & products are released. Active site flexibility shows how an enzyme may act on 2 similar substrates

Question 20

Ways to measure rate of enzyme reaction

Answer 20

Measure time course

Measure product

Measure substance disappearance

Question 21

Factors affecting enzyme activity

Answer 21

Temperature, pH, enzyme concentration, substrate concentration, concentration of inhibitors

Question 22

Temperature in enzyme controlled reactions

Answer 22

Temp increase= rate of reaction increase up until optimum temperature
High temp= kinetic energy gain= more collisions
After optimum temp, increase in temperature leads to the breaking of hydrogen bonds. Active site changes shape and the enzyme becomes denatured

Question 23

pH in enzyme controlled reactions

Answer 23

ph= hydrogen ion concentration

Altering ph changes charges on the active site so may prevent a substrate from binding.

Breaks bonds in the tertiary structure.

Question 24

Substrate concentration in enzyme controlled reactions

Answer 24

Low sub conc- low rate of reaction as there are too few substrate molecules to fill active sites

Conc increase then increase rate of reaction up to a point

More molecules= more collisions= more enzyme substrate complexes

Question 25

V max

Answer 25

Maximum rate of reaction- point where all available active sites are occupied

Question 26

Enzyme inhibitors

Answer 26

Substances that directly or indirectly interfere with the active site of an enzyme

May bind strongly and permanently prevent enzyme from working but most inhibitors are temporary

Question 27

2 types of inhibitors

Answer 27

competitive and non-competitive

Question 28

Competitive inhibitors

Answer 28

Competes with substrate to reach the active site first. They are a similar shape to substrate so they fit into the active site and prevent substrate binding.

This slows down rate of reaction

Question 29

low substrate concentration compared to inhibitor

Answer 29

Easy to inhibit because less substrates fight with the inhibitor.

Rate of reaction decreases.

Question 30

High substrate concentration compared to inhibitor

Answer 30

More competition for binding so less easy to inhibit.

Rate of reaction increases as there is higher chance of substrate collision

Question 31

Amount of inhibition depends on

Answer 31

Concentration of substrate

Concentration of inhibitor

Question 32

non-competitive inhibitor

Answer 32

Attaches to allosteric site (anywhere else on the enzyme) in order to change the shape of the active site and prevent binding. Doesn’t directly compete with substrate.

Question 33

Why is rate of reaction always low with a non-competitive inhibitor?

Answer 33

The active site denatures meaning substrates can’t bind to active site. Substrate and inhibitor aren’t competing for the same thing so the concentration of substrate won’t impact the actions of non-comp inhibitor. Regardless of how much substrate there is, none of it can bind= low reaction rate.

Question 34

Allosteric site

Answer 34

The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active. Not the active site.