3.1.1 Biological Molecules Flashcards
Describe the structure of cellulose
cellulose is made of long unbranded chains of B glucose joined by 1-4 glycosidic bonds. Each monomer of B glucose is rotate by 180 degrees so that the cellulose molecule is perfectly straight
Link the structure of cellulose to its function
As each cellulose molecule is perfectly straight many molecules can line up in parallel and hyrdogen bonds between the molecules can form. In this way molecules aggregate into microfibrils and these aggregate into macrofibrils. The macrofibrils criss cross in the cell wall and have a high tensile strength that resists forces generated by the high hydrostatic pressure in plant cells
Describe the structure of starch. Explain how this structure makes it adapted for it’s role
A long branched chain (polysaccharide) of alpha glucose. Starch has coiled structure which makes it compact so good for storage. It’s side branches allow enzymes to get at the glycosidic bonds easily so glucose can be released quickly. it is insoluble in water and hence does not affect the water potential of the cell
Why are different enzymes needed to digest starch and cellulose?
A different shape molecule requires a different enzyme as the tertiary structure of the active site is different. Each enzyme is only complementary to a specific substrate
Describe the test for a reducing sugar and state the positive result
Add benedicts reagent, heat, positive result = turns from blue to orange-brown
Why is the benedicts test known as a semi-quantitive test
Because it tells you how much sugar there is, but not exactly how much (i.e. it’s not quantitative)
What’s the difference between quantitatve and qualitative results
Quantitative results are numbers - they tell you exactly how much. Qualitative results are words
What is a disaccharide? What type of bond is involved?
Two monosaccharides joined together by a glycosidic bond
What type of reaction joins monosaccharides together?
Condensation
What type of reaction breaks polysaccharides apart
Hydrolysis
Name 2 pentose sugars and in what macromolecules you would find them
Ribose (in RNA) and Deoxyribose (in DNA)
What disaccharide is made by joining glucose and glucose?
Maltose
What disaccharide is made by joining fructose and glucose?
Sucrose
What disaccharide is made by joining glucose and galactose?
Lactose
Describe the test (and result) for starch
add iodine solution. If starch is present it will change from orange/brown to blue/black
Describe the structure of glycogen
Polymer of alpha glucose - highly branched. Contains alpha 1-4 and alpha 1-6 glycosidic bonds. Has many ends for enzymatic hydrolysis to produce glucose molecules quickly. Enables rapid release of glucose stores in animals
What’s the differences and similarities between starch and glycogen?
Both are polysaccharides formed by condensation reactions joining alpha glucose monomers. Glycogen is more branched than starch (more 1-6 glycosidic bonds). Starch found in plants, glycogen in animals. Both are energy stores, both made of alpha glucose
State 4 roles of lipids
source of energy, waterproofing, insulation, protection
What does a tryglyceride consist of? Which type of bonds hold it together?
Glycerol and 3 fatty acids - ester bonds
How is a phospholipid different to a tryglyceride? And how are they similar?
Only 2 fatty acids (Tryglyceride has three). Phosphate head (tryglyceride has no phosphate). Both have fatty acids.
What are the monomers that make up a) proteins b) cellulose c) starch
amino acids, beta glucose, alpha glucose
What type of bond joins amino acids together and how is it formed
peptide bond, via condensation
Draw the structure of an amino acid
diagram
Which part of the amino acid is variable? Approx. how many different types are there
The r group - approx 20 amino acids
What amino acid forms disulphide bonds
cysteine
What’s the difference between primary and secondary structure of polypeptides?
Primary = sequence of amino acids. Secondary - the shape in which the chain forms due to hydrogen bonds in the main peptide backbone
Give two examples of secondary structure motifs found in protines
alpha helix and beta pleated sheet
Describe the test (and result) for proteins
The biuret test - add sodium hydroxide, then copper sulfate. If the blue solution turns purple then it’s a postive result
How do enzymes speed up reactions?
They lower the activation energy. This often occurs as when the substrate is in the active site it interacts with amino acid R groups that stabilise a transition state or directly catalyse a reaction
Describe the action of enzymes - how do they work?
The substrate binds to the active site making an enzyme-substrate complex. The shape of the active site changes slightly as it binds (induced fit), as it changes shape, the enzyme puts a strain on the substrate, causing it to distort slightly so this lowers the activation energy
What’s the difference between a competitive and non-competitive inhibitor?
Competitive inhibitors bind to the active site, blocking it so the substrate can’t bind. Non-competitive inhibitors bind elsewhere, causing the active site to change shape so the substrate can’t bind
How can you find out if an inhibitor is competitive or non-competitive?
Increase the substrate concentration, if it is non-competitive, it will make no difference, if it is competitive, then more substrates should increase the rate of reaction
Describe (draw) how a disaccharide is formed
Condensation reaction between two glucose monomers, 1-4 glycosidic bond
What type of reaction breaks a 1-4 glycosidic bond?
Hydrolysis reaction
What is a globular protein? Give an example
A roughly spherical (blob shaped) protein that tends to be soluble in water (it tends to have hydrophilic amino acids on the outside of its tertiary structure). Haemoglobin is an example
What is a fibrous protein? Give an example
Fibrous proteins are made up of elongated or fibrous polypeptide chains which form filamentous and sheet-like structures. These kind of protein can be distinguished from globular protein by its low solubility in water
