Biological molecules

Question 1

What’s the difference between starch and cellulose molecules?

Answer 1

Cellulose is B glucose and starch is A glucose

Question 2

Explain one way in which starch is adapted for their function in plant cells.

Answer 2

•insoluble
OR
•long helix shaped chains that are formed by hydrogen bonds

Question 3

The enzyme sucrase catalyses the breakdown of sucrose into monosaccharides. What type of reaction is this breakdown?

Answer 3

Hydrolysis

Question 4

Explain how cellulose molecules are adapted for their function in plant cells.

Answer 4

• cellulose chains are long and straight

* create strong cell walls in plants

Question 5

Describe a biochemical test to find out if the solution collected from an experiment contains glucose and fructose.

Answer 5

Benedicts test and heating the solution.

Question 6

Describe a sample test you would carry out to show that lactose is a reducing sugar.

Answer 6

Add benedicts solution and place in a 90 degree water bath for 10 mins, if the solution turns orange/red a reducing sugar is present

Question 7

Describe how the structure of a phospholipid differs from the structure of a triglyceride.

Answer 7

•phospholipids have phosphate and 2 fatty acids

Question 8

What does the term “unsaturated” mean?

Answer 8

Contains a carbon carbon double bond (C=C)

Question 9

What’s the advantage of writing data sets as percentages?

Answer 9

Data can be compared to other data sets

Question 10

Out of A and B glucose, which can’t be digested? And why?

Answer 10

A because the OH’s are both on the bottom side of the molecule at each end meaning the H bond that forms during a condensation reaction isn’t under any strain and is very strong.

Question 11

Complete these formations:

A) …………. + Glucose —> Maltose
B) Glucose + ………….. —> Sucrose
C) Glucose + Galactose —> ……….

Answer 11

A) Glucose
B) Fructose
C) Lactose

Question 12

What’s the test for non-reducing sugars?

Answer 12

• if sample is not liquid (must be ground up in water)
• add benedicts and place tube into gently boiling water - if it doesn’t change, reducing sugar is NOT present
• start with a new sample and add same vol of dil. HCl and place into gently boiling water (for 5 mins)
• slowly add NaHCO3 (check not alkaline)
• do benedicts year again on this sample
• if a non reducing sugar is present the sample will turn orange/brown.

Question 13

What are the properties of starch?

Answer 13

• insoluble (dosent affect water potential so no osmosis)
• large and insoluble (can’t diffuse out of cells)
• compact (for storage)
• made out of A Glucose (which when hydrolysed can be easily transported and ready for respiration)
• Many branches (so enzymes can attack with ease meaning glucose monomers are released rapidly)
• A Glucose

Question 14

What are the properties of Glycogen?

Answer 14

• insoluble (therefore no osmosis)
• insoluble (so it dosent diffuse out of cells)
• Compact (can be stored in small places)
• Very branched (more than starch) therefore more ends can be acted on simultaneously by enzymes therefore bore rapidly broken down to form glucose monomers which are used in resp. — this is important for animals that have a high metabolic rate so they need more energy quicker •A glucose

Question 15

What Properties of cellulose?

Answer 15

• B glucose
• straight
• unbranched (allowing links between chains)
• every other molecule flips in the chain
• run in parallel chains
• these chains are grouped to form microfibrils which turns into fibre

Question 16

What’s fibre made out of? Why can’t it be digested?

Answer 16

• made out of Cellulose (A Glucose) bunched together to form microfibrils
• cant be digested bc A glucose’s structure doesn’t allow enzymes to access the bonds very easily and the bonds aren’t under any stress (due to the structure again)
• no branches therefore less access point to the bonds for the enzymes to hydrolyse

Question 17

What are the roles of lipids?

Answer 17

• source of energy
• waterproofing
• insulation
• protection

Question 18

Explain the structure of Triglycerides.

Answer 18

Glycerol + 3 fatty acids

Question 19

How’s the structure of triglycerides related to their properties?

Answer 19

• they have a high ratio of energy stirring C-H bonds therefore excellent at STORING ENERGY
• low mass to energy ratio, therefore they’re GOOD STORAGE MOLECULES
• Large and non polar therefore INSOLUBLE
• their storage dosent effect the water potential in the cell

Question 20

Describe the structure of phospholipids.

Answer 20

• Hydrophilic phosphate head

* Hydrophobic fatty avid tail

Question 21

What’s the test for lipids?

Answer 21

1. Take completely dry and grease free test tube and add 2cm^3 of sample to test tube
2. Add 5sm^3 ethanol
3. Shake to dissolve any lipids in sample
4. Add 5cm^3 of water and shake gently
5. Cloudy white = lipids present

Question 22

What are the 4 chemical groups attached to the central carbon to form amino acids?

And describe the structure of the molecule.

Answer 22

•amino group
•carboxyl group
•R group H H
•hydrogen atom \ /
N
|
R—C—H
|
C
// \
O OH

Question 23

How does a peptide bond form?

Answer 23

Through a condensation reaction:
•the carboxyl group at the bottom of the molecule lines up with the amino group on the top of the second
•a bond between the C and N on opposing molecules forms
•This is called a peptide home

Question 24

Describe the structure of primary protein.

Answer 24

• Sequence of amino acids

* determines the ultimate shape of the protein

Question 25

Describe the structure of a tertiary protein.

Answer 25

* disulphide bridges * ionic bonds * hydrogen bonds

Question 26

What’s the difference between quaternary and tertiary structure?

Answer 26

•quaternary has many chains and prosthetic groups attached

Question 27

Describe secondary structure.

Answer 27

* A helix | * peptide chains

Question 28

What’s the test for proteins and describe it.

Answer 28

* place sample into test tube and add an equal amount of NaOH at RTP * add a few drops of very dilute Cu(ll)SO4 solution and mix gently * purple means presence of peptide bonds therefore protein

Question 29

``` Lols enzyme graph | _____________ | ／ | ／ | / | / |/_____________________ ``` Explain why the rate of the reaction decreases as the reaction progresses.

Answer 29

* bc the substrate runs out | * therefore no enzyme substrate complexes can be formed

Question 30

Why is there a use for an enzyme buffer during reactions?

Answer 30

To control the pH

Question 31

Explain how enzyme inhibitors affect the rate of reaction. | [6 marks]

Answer 31

Competitive inhibitors •similar molecular shape to substrate therefore bind to the active site and preventing ESC’s to be formed. Non competitive inhibitors •attach to a binding site that’s not the active site therefore altering the tertiary stricture of the enzyme and thus it’s active site meaning the substrate no longer fits, preventing ESC’s to be formed.

Question 32

In humans, the enzyme Maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why: • only breaks down maltase • allows this reaction to take place at normal body temp.

Answer 32

* maltose has tertiary structure * complimentary active site shape * forms an enzyme substrate complex * (description of enduced fit) * enzyme binds * enzyme changed shape * stress on bonds * enzymes lower activation energy (act as a catalyst)