Topic 1 - Biological Molecules Flashcards
What is a condensation reaction?
This is a reaction joining two molecules together to form a larger molecule through the formation of a glycosidic bond and involving the elimination of a water molecule.
What is a hydrolysis reaction?
This is a reaction that breaks a chemical bond between two molecules through the use of a water molecule
Which monosaccharides make up maltose?
Glucose + Glucose
Which monosaccharides make up sucrose?
Glucose + Fructose
Which monosaccharides make up lactose?
Glucose + Galactose
What type of bonds make up the disaccharides: maltose, sucrose and lactose?
1-4 glycosidic bonds
Describe the structure and function of cellulose.
- Makes up plant cell walls
- Made up of beta-glucose
- Made of glycosidic bonds
- Unbranched/straight chain structure
- Every other beta glucose flips 180º so that the OH molecules are next to each other
How is cellulose adapted to its function in the plant cell wall?
Cellulose is very strong to prevent cells from bursting when they take in excess water - they’re strong because glucose chains form rope-like microfibrils, layered to form a network with hydrogen bonds between these layers
What two units is starch arranged into?
Amylose and amylopectin
Describe the structure of amylose.
- 1-4 glycosidic bonds of alpha glucose in an unbranched and coiled shape
- It’s insoluble so it doesn’t affect water potential so no effect on osmosis
Describe the structure of amylopectin.
- 1-4 + 1-6 glycosidic bonds of alpha glucose in highly branched chains to increase the SA so it can be hydrolysed more quickly
- Insoluble so no effect on water potential or on osmosis
Describe the structure and function of glycogen.
- Stored as energy in animals in the form of small granules in muscles/liver
- Made up of many 1-6 glycosidic bonds producing a really branched structure to increase the SA
- Insoluble so has no effect on water potential or on osmosis
What’s the test for reducing sugars?
1) Add Benedict’s solution (blue)
2) Heat sample in water bath to 100°
3) If sugar present - turns red
What’s the test for non-reducing sugars?
1) Add some HCl
2) Boil in water bath
3) Test again for reducing sugars :
- If it turns red - non-reducing sugar
- If it stays same (blue) - no sugar/carbohydrate
What are the two types of lipids?
Triglycerides and phospholipids
Definitions of:
- Saturated
- Mono-unsaturated
- Polyunsaturated
Saturated - No double bonds between carbons
Mono-unsaturated - One double bond between carbon atoms
Polyunsaturated - More than one double bond between carbon atoms
What are triglycerides made up of?
Glycerol and fatty acids
Describe the structure of triglycerides.
Glycerol and 3 fatty acids joined together by and ester bond via a condensation reaction
Describe some features of triglycerides.
- Their main function is energy storage
- They’re long polymers with lots of bonds
- Insoluble so have no effect on water potential or osmosis
- Form insoluble droplets - have hydrophobic tails on the inside
Describe the structure of phospholipids.
- 1 glycerol molecule and 2 fatty acids
- Polar phosphate group is attached to the third hydroxyl group on the glycerol molecule
- Fatty acid ‘tails’ are hydrophobic
- Phosphate ‘head’ is hydrophilic
- Has amphipathic nature
What is the function of phospholipids?
They have a vital role in the cell membrane controlling what goes in or out of a cell
It’s called the phospholipid bilayer
Why is it difficult for water to diffuse in and out of cells?
The middle is hydrophobic due to the fatty acid tails and since water is polar it makes diffusion difficult due to repulsion
What are glycolipids and how are they formed?
Glycolipids are important in the cell membrane for cell recognition and are formed by combining phospholipids with carbohydrates
What does amphipathic mean?
It’s a molecule that has both hydrophilic and hydrophobic sections
What are the main roles of lipids (adipose tissue) ?
They’re stored in adipose tissue
⭐︎Heat insulation - in mammals, adipose tissue underneath the skin helps to reduce heat loss
⭐︎Protection - Adipose tissue around delicate organs such as kidneys act as a cushion against impacts
⭐︎Source of energy
Why do lipids dissolve in ethanol but not water?
Ethanol is also a non-polar molecule whereas water is polar
What is the test for lipids known as?
The emulsion test
Describe the emulsion test.
1) Mix 2cm³ of test sample to 5cm³ of ethanol and shake in order to dissolve any lipid in the sample
2) Add 5cm³ of water and shake gently
3) Observe - Milky layer if lipid is present
- No milky layer = no lipids
What is a protein?
A polymer built up of one or more amino acids with specific shapes essential to their function
What’s an amino acid?
The monomer that makes up proteins (polypeptides)
What makes up an amino acid chemically?
○Amino group (-NH2) - a basic group form which the amino part of the name amino acid is derived
○Carboxyl group (-COOH) - an acidic group which makes up the acid part of the name amino acid
○Hydrogen atom (-H)
○R (side) group - a variety of different chemical groups. Each amino acid has a different R group which means the R group is the only difference in the 20 naturally occurring animo acids
What bond joins amino acids together?
Peptide bonds
What are the main biological roles of proteins?
⭐︎Structural - main component of body tissues e.g. muscle, skin, ligaments, hair
⭐︎Catalytic - all enzymes are proteins, catalysing biochemical reactions
⭐︎Signalling - many hormones and receptors are proteins
⭐︎Immunological - all antibodies are proteins
Describe the primary structure of proteins
A sequence of amino acids in a polypeptide chain
Describe the secondary structure of a protein
Weak hydrogen bonds are formed between amino acids which caused the long polypeptide chain to be twisted into a 3D shape such as the coil known as an alpha-helix
Describe the structure of a tertiary protein
The alpha helixes can be twisted or folded to make the structure more complex and specific. This structure is maintained by a number of different bonds. Where these bonds occur is down to the primary structure of the protein
Name and describe the bonds in a tertiary protein
- Disulfide bridges - fairly strong and nit easily broken
- Ionic bonds - are formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They are weaker than disulfide bridges and are easily broken by changes in pH
- Hydrogen bonds - numerous but easily broken
Describe the structure of a quarternary protein
Large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. There also may be prosthetic groups associated with the molecules such as the iron-containing haem group in haemoglobin.
What’s a prosthetic group
Non-protein group
Name and describe the test for proteins
Biuret test to detect peptide bonds
- Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
- Add a few drops of very dilute (0.05%) copper (ll) sulfate solution and mix gently
- A purple coloration indicates the presence of peptide bonds and hence a protein. If solution remains blue there is no presence
