Biological Molecules - Carbs And Lipids

Question 1

What is a monomer?

Answer 1

small identical/similar molecules condensed to make larger molecules called polymers
eg: alpha glucose, aa, nucleotides

Question 2

What is a polymer?

Answer 2

Large molecules made by joining 3 or more identical or similar monomers together
eg: proteins, polysaccharides, polynucleotides

Question 3

define condensation reactions

Answer 3

• joins two monomers together to form a - chemical bond
• removal of one water molecule
  eg: alpha glucose -> starch

Question 4

define hydrolysis reaction

Answer 4

• breaks a chemical bond between two monomers
• via addition of water molecule
  eg: cellulose -> beta glucose
  DNA -> DNA nucleotides

Question 5

disaccharide/dimer equation

Answer 5

C6H12O6 + C6H12O6 -> C12H22O11 + H2O

Question 6

Where do condensation reactions occur in monomers?

Answer 6

0H group of C4 and C1 H of other group

Question 7

maltose

Answer 7

alpha glucose + alpha glucose
maltase enzyme

Question 8

lactose

Answer 8

galactose + glucose
lactase enzyme

Question 9

sucrose

Answer 9

glucose + fructose
sucrase enzyme

Question 10

differences between monosaccharides

Answer 10

a-glucose: both OH (hydroxyl groups) down
galactose: both OH up
B-glucose: one OH down, one OH up
fructose: pointy top

Question 11

starch

Answer 11

• insoluble, doesn’t affect water potential
• helical, so compact
• large so doesnt diffuse out of cells
• branched so high surface area for rapid hydrolysis to release glucose for respiration

Question 12

amylose

Answer 12

a (1-4) glycosidic bonds
- linear chains of a glucose
- compact and helical, so good for storage
- insoluble, doesnt affect water potential

Question 13

amylopectin

Answer 13

branched
a(1-4) and a(1-6) glycosidic bonds
large SA for rapid hydrolysis
isnoluble doesnt affect water potential
large so doesnt diffuse out of cells

Question 14

glycogen

Answer 14

• shorter chains
• more branched
  -larger SA
  -humans/animal cells
  -short chains so more rapidly hydrolysed into glucose for RP
  -insoluble, doesnt affect water potential
• large, so doesnt diffuse out of cells

Question 15

a strach molecule has a spiral shape. explain why this shape is important to its function in cells.

Answer 15

helical so compact
insoluble, no effect in WP
large molecule so cant leave out of cell

Question 16

structure of cellulose is related to its role in plant cell walls. explain how.

Answer 16

• long straight unbranched chains of beta glucose
• joined by many weak hydrogen bonds
• form microfibrils
• provides strength

Question 17

cellulose structure

Answer 17

• long straight unbranched chains
• every other b glucose inverted 180 degrees
• b (1-4) glycosidic bonds
• weak Hydrogen bonds form cross links between chains
• forms microfibrils (that form cellulose fibres, stregnth and support in plant cell walls)

Question 18

hydrogen bonds are important in cellulose molecules. explain why.

Answer 18

hydrogen bonds forms cross links between chains
-form microfibrils
- provides strength and rigidity
-weak hydrogen bonds provide strength in large numbers

Question 19

reducing sugars

Answer 19

galactose
glucose
lactose
maltose
fructose

Question 20

non reducing sugars

Answer 20

sucrose

Question 21

describe how the student would show that a reducing sugar was present in a solution

Answer 21

• add equal volumes of benedicts solution
• and heat to 95 degrees celsius
• red/orange PPT is a positive result

Question 22

2 different reducing sugar solutions (A+B) of same concentration have an enzyme added before benedicts. They both produced red PPT.
After 20 minutes, B had twice as much PPT as A. Suggest why.

Answer 22

A is a monosaccharide and B is a disaccharide
- enzyme hydrolysed glycosidic bonds in disaccharide, releasing 2 monosaccharides
- both monosaccharides are reducing sugar, PPT doubled in B

Question 23

describe how the student would show a non-reducing sugar was present in a solution

Answer 23

• complete benedicts test and observe a negative result (blue solution)
• add acid (HCl) and heat to 95 degrees
• then neutralise with alkali
• add benedicts solution again and then heat to 95
• red/orange PPT is positive result

Question 24

describe how you would produce a calibration curve for a reducing sugar of unknown concentration and use it to obtain results

Answer 24

• make up several known concentrations of [R sugar]
• carry out benedicts test
• use a colourimeter to measure the colour absorbance of each solution
• and plot a calibration curve:
  X: known conc
  Y: absorbance/transmission
• find conc of unknown sample using calibration curve

Question 25

standardising colourimeter method

Answer 25

- samples shaken before testing - zero colourimeter before use with a control - use same filter - use same volume for each reading

Question 26

describe how you would test a sample of food for the presence of starch

Answer 26

- add potassium iodide (KI) solution - blue/black indicates starch is present

Question 27

The structure of cellulose is related to its role in a plant cell wall. Explain how.

Answer 27

- Long, straight unbranched chains of beta glucose - joined by many weak hydrogen bonds - form microfibrils - provide strength/rigidity

Question 28

Give one feature of starch and explain how it enables it to act as a storage substance

Answer 28

- helical so compact - insoluble so doesnt affect water potential - large molecule so doesnt leave cell - branched chains so rapid hydrolysis to remove glucose for respiration

Question 29

Hydrogen bonds are important in cellulose. Explain why.

Answer 29

Holds chain together/form microfibrils Providing strength and rigidity Weak Hydrogen bonds provide strength in large numbers

Question 30

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 30

Glucose and galactose Joined by condensation reaction Jojned by glycosidic bond Added to polypeptide in golgi

Question 31

Describe how you would test a liquid sample for the presence of a lipid vox and how you would recognise a positive result

Answer 31

Mix with ethanol then water And shake Cloudy white emulsion

Question 32

Omega 3 fatty acids are unsaturated. What is an unsaturated fatty acid?

Answer 32

Double bond Between carbon atoms within the hydrocarbon chain

Question 33

Describe how a ester bond is formed in a phospholipid molecule

Answer 33

Condensation Between a glycerol and fatty acid

Question 34

What are the differences between a triglyceride and a phospholipid

Answer 34

Fatty acid removed Replaced with a phosphate group

Question 35

Compare and contrast the structure and properties of triglycerides and phospholipids

Answer 35

- both contain ester bonds - both contain glycerol -fatty acids on both may be saturated or unsaturated - both are insoluble in water - both contain C, H and O but phospholipids also contain P - triglycerides have 3 fatty acids and phospholipids have 2 fatty acids plus a phosphate group - triglycerides are hydrophobic and phospholipids have a hydrophilic and hydrophobic region - phospholipids form bilayer but triglycerides do not

Question 36

Desctibe the biochemical tests you would use to confirm the presence of lipid, non reducing sugar and amylase in a sample

Answer 36

Lipid - add ethanol then water and shake - white milky emulsion Non reducing sugar - Do benedicts and get a negative result - boil with acid and immedicately neutralise with an alkali - heat with benedicts and red/orange precipitate Amylase - add bieuret reagenr and purple - add starch - test for reducing sugar

Question 37

A student carried out the benedicts test. Suggest a method, other than usinf a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution

Answer 37

- filter and dry the precipitate - find mass/weight