Biological Molecules

Question 1

What does organic mean?

Answer 1

Contains the element carbon, organic compounds always contain carbon-carbon bonds

Question 2

What are the 4 types of organic compounds found in organisms?

Answer 2

Carbohydrates, amino acids, lipids and nucleic acid

Question 3

What conditions are needed for hydrogen bonds to form?

Answer 3

Between a d+ hydrogen and d- Nitrogen, Oxygen or Fluorine with an electron pair

Question 4

Why do hydrogen bonds form between water molecules?

Answer 4

• water molecules are polar, hydrogen is d+ while Oxygen is d-
• opposite partial charges of different water molecules causes these hydrogen bond (intermolecular forces)

Question 5

How do polar molecules interact with water?

Answer 5

Polar molecules dissolve readily in water being hydrophilic, eg salts, sugars and amino acids

Question 6

How do uncharged molecules interact with water?

Answer 6

Non-polar molecules do not dissolve in water and are called hydrophobic, eg lipids

Question 7

Why is it important for life that water molecules have high cohesive properties?

Answer 7

For long water columns in Transpiration and so insects can walk on water

Question 8

Give 3 examples of monosaccharides, disaccharides and polysaccharides:

Answer 8

Mono: glucose, fructose, galactose
Di: sucrose, maltose, lactose
Poly: starch, glycogen, cellulose

Question 9

What is the monosaccharide formula? And what type of sugar is glucose?

Answer 9

(CH2O)n when n is 3-7

Glucose is a hexose sugar

Question 10

What is an isomer? Give 2 isomers of glucose

Answer 10

Same chemical formula, different structural formulae

-galactose and fructose

Question 11

Name 3 pentose sugars:

Answer 11

Ribose, deoxyribose and ribulose (occurs in photosynthesis)

Question 12

How are disaccharides formed?

Answer 12

2 monosaccharides join together forming a glycosidic bond (C-O-C) in a condensation reaction releasing a water molecule

Question 13

Structure of sucrose, lactose and maltose:

Answer 13

Sucrose- glucose and fructose
Maltose- glucose and glucose
Lactose- glucose and galactose

Question 14

Describe a glucose molecule:

Answer 14

• Hexagonal shape
• 5 OH groups
• 1 (c-o-c) bond in top right
• carbon methyl group on top left with OH

Question 15

Describe a glycerol: or draw

Answer 15

• 3 carbon molecule
• each carbon contain OH group
• C3H803

Question 16

Describe or draw the structure of a fatty acid:

Answer 16

• Polar carboxylic acid group at one end
• non-polar hydrocarbon chain which varies in length (14-22)
• written as R-COOH

Question 17

How does the bond form between glycerol and fatty acid to form triglyceride?

Answer 17

• Glycerol loses OH group
• Carboxyl group of fatty acid loses H
• Ester bond forms (C-O-C)
• Therefore, polymerisation reaction=condensation reaction

Question 18

What are triglycerides used for and why cant they be mobilised easily?

Answer 18

• protection, insulation and energy storage in fatty tissues

- They are insoluble so cant be mobilised to respiring tissues easily

Question 19

Properties of saturated fatty acids:

Answer 19

• contain no C=C in hydrocarbon chain
• higher melting point, and solid at room temp (fats) eg butter, lard
• found in warm blooded animals

Question 20

Properties of unsaturated fatty acids (Poly-unsaturated, mono-unsaturated):

Answer 20

• contain C=C
• more than one C=C is poly unsaturated
• found in cold blooded animals and plants
• lower melting point (oils at room temp)

Question 21

Describe of draw a phospholipid:

Answer 21

• contains a phosphate group replacing a fatty acid
• phosphate group produces a polar hydrophilic head (negatively charged phosphate group)
• 2 non polar hydrophobic tails

Question 22

What is a liposome?

Answer 22

• when phospholipids interact with water they form droplet spheres
• a phospholipid bilayer creates a sphere trapping water in the center (aqueous compartment) from the outside

Question 23

Describe the structure of an amino acid:

Answer 23

• central carbon (alpha carbon) with 4 different chemical groups
• basic amino group (NH2)
• acidic carboxyl group (COOH)
• hydrogen
• variable R group (which determines the type of amino acid)

Question 24

How is a peptide bond formed?

Answer 24

• OH from carboxyl group and H from amino group form a water molecule
• this forms a dipeptide and peptide bond (C-N)
• polymerisation reaction = condensation reaction

Question 25

What is the free COOH group and NH2 group at either end of a polypeptide chain called?

Answer 25

``` COOH = C-terminus NH2 = N-terminus ```

Question 26

Where does polymerisation of amino acids occur?

Answer 26

In the ribosomes, this is also called protein synthesis

Question 27

What is the primary structure?

Answer 27

The sequence of amino acids in a polypeptide chain which determines the rest of the protein structure

Question 28

What is the secondary structure?

Answer 28

A basic level of protein folding occurs due to the hydrogen bonds between carboxyl groups and amino groups, forming either a: Alpha helix or beta pleated sheet

Question 29

What is the tertiary structure?

Answer 29

This is the compact globular structure due to the folding of a whole polypeptide chain Includes hydrogen bonds and disulphides bridges between 2 cysteine amino acids

Question 30

Why are the tertiary structures of protein different?

Answer 30

The tertiary structure is held together by bonds between R groups of the amino acids, and so depends on the sequence of amino acids (primary structure)

Question 31

What is the quaternary structure?

Answer 31

The arrangement of the different chains

Question 32

Give 3 examples of a quaternary structure protein:

Answer 32

1) haemoglobin- 4 chains in a tetrahedral shape each with an Fe group 2) Antibodies- 4 chains arranged in a Y shape 3) Enzymes 4) collagen- 3 chains in a triple helix structure 5) Actin- hundreds of glubular chains arranged in double helix

Question 33

Globular and fibrous proteins, what’s the difference?

Answer 33

Globular- compact ball shaped, usually enzymes, membrane proteins, receptors and storage proteins Fibrous proteins- long thin rope-like, usually structural roles like collagen (bone), keratin (hair), actin (muscle)

Question 34

What happens when a protein is denatured?

Answer 34

Under high temps or pH changes the hydrogen bonds break, since the the secondary, tertiary and quaternary structures are large sly held together by them, the polypeptide chains just fold up into a random coil and lose their function and shape

Question 35

Test for starch?

Answer 35

Add a few drops of potassium iodide solution into the sample. Blue/black colour change from yellow = positive -Black starch-polyiodide complex is formed

Question 36

Reducing sugars test?

Answer 36

Add a few mL of Benedictus reagent to sample, shake and heat at 95 degrees C in a water bath - the colour and density of precipitate indicates amount of reducing sugar present - Blue solution-> green precipitate->brick red precipitate (lots of reducing sugar) - this test is semi-quantitive

Question 37

Test for non reducing sugars?

Answer 37

- test sample for reducing sugars - using a separate sample add dilute hydrochloride acid for a few mins to hydrolyse the glycosidic bond - neutralise the solution by gently adding solid sodium hydrogen carbonate until stops fizzing - repeat test for reducing sugars

Question 38

How does the test for non reducing sugars work?

Answer 38

There is no direct test for non-reducing sugars eg sucrose so: Hydrolyse the di/polysaccharide into its constituent monosaccharides then test for reducing sugars

Question 39

Test for lipids?

Answer 39

Emulsion test- lipids are insoluble in water but dissolve in ethanol - add a sample to 4mL of ethanol and shake vigorously - decant the liquid into a second test tube of water leaving undissolved substances behind - a precipitate of lipids will form in the water forming white cloudy emulsion

Question 40

Test for proteins?

Answer 40

Biuret test: add a few mL of biuret solution to the sample, shake and if solution turns lilac/purple proteins are present