Enzymes-biological molecules

Question 1

Describe how an enzyme, such as pepsin, breaks down a substrate

Answer 1

substrate / protein , shape is (nearly) complementary to
active site ; ora
substrate / protein , enters / fits into , active site (on
enzyme) ;
induced fit / description of induced fit ;
(forms) enzyme-substrate complex / ESC ;
destabilising / straining / AW , of bonds (in substrate) ;
then (forms) enzyme-product complex ;
product(s) / amino acids , leave (active site)

Question 2

Differences in structure between amylose and cellulose

Answer 2

• Amylose, alpha glucose + alpha 1-4 glycosidic bonds
• cellulose, beta glucose+ beta 1-4 glycosidic bonds
• amylose, same monomers
• cellulose, monomers flipped every 1
• amylose, granular protein
• cellulose, fibrous protein
• amylose, H bonds within molecule
• cellulose, H bonds between adjacent molecules

Question 3

Which properties of cellulose make it suitable for forming cell walls

Answer 3

(tensile) strength / strong ;
(H) bonds / links , can form (between adjacent fibrils) ;
insoluble ;

Question 4

The mechanism of enzyme action was originally explained in terms of the ‘lock-and-key
model’. It is now more often explained in terms of the ‘induced-fit’ model.
Suggest why the lock-and-key and induced-fit explanations are termed models

Answer 4

-idea of simple representation of the , process / structure
or
idea of showing people how it works

Question 5

Suggest why most scientists now accept the induced-fit model rather than the
lock-and-key model.

Answer 5

supported by , more evidence / new research /
more work ;
idea of fitting evidence more closely (than lock & key

Question 6

Suggest how a more flexible structure might help an enzyme work faster

Answer 6

easier for / increased chance of , substrate, entering active site ;
more bonds can form / greater surface area for contact
(between active site and substrate) ;
easier for active site to change shape (as part of induced fit) ;
-the induced fit , will be easier

Question 7

Enzymes are proteins. The enzymes in Antarctic fish have a different structure from those
found in non-Antarctic fish.
(i) Suggest how the structure of the enzymes may differ in Antarctic and non-Antarctic fish

Answer 7

different, amino acids / amino acid sequence / primary
structure
-different prosthetic group/ more a helices etc

Question 8

Enzymes are biological catalysts.

Explain the term biological catalyst.

Answer 8

speeds up metabolic/chemical reactions

Question 9

Identify one potential problem with using samples of (liquidised celery) - note could be other samples similar !!!! as a source of catalase in this investigation and suggest a way to minimise this problem

Answer 9

• samples have different concentrations of enzyme

- use a known concentration of enzyme

Question 10

State the colour of iodine solution in the presence of starch

Answer 10

-blue/black

Question 11

A student investigated the action of amylase on amylose. She mixed amylase with amylose
and placed the mixture in a water bath.
Describe how she could measure the change in concentration of maltose (reducing sugar) as
the reaction proceeds

Answer 11

take samples at a range of times / AW ;
same volumes (of solutions) added / removed (each time) ;
heat with, Benedict’s (solution) / CuSO4 and NaOH ;
(use of ) excess Benedict’s ;
changes to, green / yellow / orange / brown / (brick) red ;
remove precipitate / obtain filtrate ;
colorimeter ;
calibrate / zero, using, a blank / water / (unreacted)
Benedict’s ;
use (red / orange) filter ;
reading of, transmission / absorbance
OR
mass of precipitate ;
more transmission / less absorbance, of filtrate,
OR
greater mass ppt, = more maltose present ; ora
using, standard / known, concentrations (of maltose) ;
(obtain) calibration curve ;
plot, transmission / absorbance / mass of ppt, against
(reducing sugar) concentration ;
use graph to read off concentration of maltose