B1- Biological Molecules

Question 1

Monomers

Answer 1

Monomers are the smaller units from which larger molecules are made

Question 2

Polymers

Answer 2

are molecules made from a large number of monomers joined together in a chain

Question 3

Hydrolysis

Answer 3

polymers, covalent bonds are broken when water is added

Question 4

Condensation reaction

Answer 4

Monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed

Question 5

What are the two types of lipids?

Answer 5

Triglycerides - the main component of fats & oils
Phospholipids

Question 6

Describe the formation of triglycerides?

Answer 6

Glycerol is an alcohol (C - OH)

Fatty acids contain a methyl group (-CH3) at one end of the chain, and a carboxyl group at the other end (-RCOOH)

Fatty acids can vary in length and saturation

By esterification - an ester bond forms when a hydroxyl (-OH) group on glycerol bonds with the carboxyl (-COOH) group of the fatty acid

Three fatty acids join to one glycerol molecule to form a triglyceride

Question 7

What are triglycerides function?

Answer 7

Protection - triglycerides within adipose tissue protects organs from the risk of damage

Insulation - triglycerides are used to insulate nerve fibres & within adipose tissue below the skin

Buoyancy - the low density of fat tissue helps animals to float more easily

Energy storage - the many C-H bonds can be oxidised in cellular respiration to release lots of energy → used to produce ATP
Plants store triglycerides in the form of oils (within seeds & fruit)
Mammals store triglycerides as oil droplets in adipose tissue (a reserve energy source)

Question 8

Describe the structure of phospholipids?

Answer 8

Phospholipids have only two fatty acids

The third has been replaced by a phosphate ion (PO4 3-)

Question 9

How do you test for lipids?

Answer 9

Add ethanol and distilled water
If lipids are present, a milky emulsion will form (the solution appears ‘cloudy’); the more lipid present, the more obvious the milky colour of the solution

Question 9

What are the functions of phospholipid bilayer?

Answer 9

Phospholipids are the building block of cell membranes
They act as a barrier to water-soluble molecules & can control what substances enter and leave the cell

Different compositions of phospholipids helps to change the fluidity of the cell membrane
Mainly saturated fatty acids - membrane will be less fluid
Mainly unsaturated fatty acids - membrane will be more fluid

Phospholipids also control the orientation of proteins present in the cell membrane
Weak hydrophobic interactions hold proteins in place, but still allow them to move

Question 10

What are the structures of glucose and why are they different?

Answer 10

alpha (α) glucose and beta (β) glucose and is therefore known as an isomer
structural variety results in different functions between carbohydrates

Question 11

What bonds do carbohydrates form?

Answer 11

When two hydroxyl (-OH) groups (on different saccharides) interact to form a strong covalent bond called the glycosidic bond

Question 12

How do you form Maltose?

Answer 12

Two molecules of glucose form a glycosidic bond by condensation to form maltose (a reducing sugar)

Question 13

How do form lactose?

Answer 13

One molecule of glucose and one molecule of galactose form a glycosidic bond by condensation to form lactose (a reducing sugar)

Question 14

What are polysaccharides?

Answer 14

Polysaccharides are macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains

Question 15

Explain the structure and the benefits of glycogen?

Answer 15

-Glycogen is the storage polysaccharide of animals & fungi

-It is branched & not coiled - more compact
Often stored as granules in liver and muscle cells

-Branching allows glucose molecules to be easily added or removed

Question 16

What are the structural difference between starch and glycogen?

Answer 16

Both made of the same monomer
both are branched molecules
Both contain 1,4 and 1,6 glycosidic bonds

Starch is made of amylose and amylopectin
Glycogen is more highly branched

Question 17

What is the structure of cellulose?

Answer 17

Cellulose is a structural polysaccharide

It’s structure: long chains of β-glucose joined together by 1,4 glycosidic bonds

Consecutive β-glucose molecules are inverted forming myofibrils that give cellulose its strength

Question 18

What is the function of cellulose?

Answer 18

-The main structural component of cell walls

-Very strong & insoluble (due to the many H bonds between cellulose fibres)

-Cell walls are able to withstand turgor pressure

-Lignin further increases the strength & support to the plant

-Cellulose fibres are freely permeable

Question 19

What is the structure of amylopectin?

Answer 19

Branched - easily broken down for use in respiration

Question 20

What is the structure of amylose?

Answer 20

Unbranched & helix-shaped - more compact

Question 21

What is the benedict’s test for reducing and non-reducing sugars?

Answer 21

1)Add dilute hydrochloric acid to the sample and heat in a water bath that has been brought to the boil

2)addition of acid will hydrolyse any glycosidic bonds present in any carbohydrate molecules

3)Neutralise with sodium hydrogencarbonate

4) Carry out the Benedict’s test as normal

Question 22

How do you test for iodine?

Answer 22

1)add a few drops of orange/brown iodine in potassium iodide solution to the sample

2) Starch is present? - iodine ions in the solution interact with starch molecules → form a blue-black colour

Question 23

What is the structure of an amino acid?

Answer 23

General structure: a central carbon atom, an amine group (-NH2), a carboxylic acid group (-COOH), a hydrogen atom & an R group (differs depending on the amino acid)

Question 24

How do amino acids turn into polypeptide chains?

Answer 24

Peptide bonds form between an amine group of one amino acid and a carboxylic acid group of another → water is released (a condensation reaction)

Question 25

What function do proteins have from primary to quaternary?

Answer 25

Primary structure: the sequence of amino acids bonded by covalent peptide bonds Secondary structure: hydrogen* bonding between amino acids enable two shapes to form:Α-helix - H bonds between every 4th peptide bond and β-pleated sheet - H bonds between parallel parts of a polypeptide chain Tertiary structure: more conformational changes & additional bonds form between R-groups -Hydrogen bonds -Disulphide -Ionic -Weak hydrophobic interactions Quaternary structure: Occurs in proteins that have more than one polypeptide chain working together as a functional macromolecule

Question 25

What is the biochemical test for proteins?

Answer 25

Biuret solution Positive= purple Negative = Blue

Question 26

What is an example of globular proteins?

Answer 26

Quaternary structure (4 polypeptide chains) 4 subunits (two α–globins and two β–globins) held together by disulphide bonds Each subunit contains a haem prosthetic group: these contains Fe2+ which reversibly combine with oxygen molecules → forms oxyhaemoglobin (+ what makes blood red!)

Question 27

What is an example of a fibrous protein?

Answer 27

Three polypeptide chains held together by H bonds → form a triple helix - tropocollagen Each polypeptide chain is a helix shape & contains lots of glycine, proline & hydroxyproline amino acid monomers Covalent cross links also form between multiple triple helices → form collagen fibrils Many fibrils are then arranged together to form collagen fibres

Question 28

What are enzymes?

Answer 28

Are biological catalysts - they speed up the rate of chemical reactions without being used up →lower the activation energy required

Question 29

What is an enzyme-substrate complex?

Answer 29

- forms when an enzyme and its substrate join together -The enzyme-substrate complex is only formed temporarily, before the enzyme catalyses the reaction and the product(s) are released

Question 30

How do enzymes lower the activation energy?

Answer 30

Enzymes speed up this process by making bond-breaking & bond-forming occur more readily → lowers the activation energy

Question 31

What is the induced fit hypothesis?

Answer 31

The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme - these are called conformational changes

Question 32

How is temperature a limiting factor?

Answer 32

Bonds (e.g., hydrogen bonds) holding the enzyme molecules together start to break Tertiary structure of the protein (enzyme) changes Active site becomes damaged → substrate cannot bind → enzyme becomes denatured

Question 33

How does pH limit reactions?

Answer 33

Too acidic solutions (H+ ions) or alkaline solutions (OH- ions) can cause hydrogen & ionic bonds to break Shape of the active site changes → enzyme-substrate complexes form less easily - enzyme denatures

Question 34

How does enzyme concentration limit reactions?

Answer 34

Higher the enzyme conc. → greater number of active sites available → greater likelihood of enzyme-substrate complex formation This relationship is linear until the amount of substrate becomes limited … … any further increase in enzyme concentration will not increase the rate of reaction - substrate becomes the limiting factor

Question 35

How does substrate concentration increase?

Answer 35

Greater the substrate concentration → greater likelihood of enzyme-substrate complex formation → higher the rate of reaction When all active sites are saturated (full), no more enzyme-substrate complexes can form → rate of reaction plateaus

Question 36

What are competitive inhibitors?

Answer 36

Have a similar shape to substrate molecules → compete with the substrate for the active site

Question 37

What are non-competitive inibitors?

Answer 37

Bind to the enzyme at an alternative site → alters the shape of the active site → prevents the substrate from binding to it