1: Biological Molecules Flashcards
What is a monomer?
A monomer is a small identical / similar repeating unit / molecule from which larger molecules / polymers are made;
What is a Polymer?
Molecule made up of THREE or MORE / many identical/similar molecules/monomers.
What term is used to describe the different structures of α-glucose and β-glucose?
Isomer(ism)
A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
- Compact
- occupies small space
- tightly packed;
The structure of cellulose is related to its role in plant cell walls. Explain how. (3)
- Long, straight, unbranched chains of Beta glucose;
- (Joined by) many WEAK hydrogen bonds;
- Form microfibrils / macrofibrils;
- Provide rigidity/strength/support;
Reject reference to strong
Compare and contrast the structure of starch and the structure of cellulose. [6 marks]
- Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
- Both contain glycosidic bonds (between monomers);
- Both contain carbon, hydrogen and oxygen/C, H and O;
- Starch has α-glucose and cellulose has β-glucose;
- Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
- Both contain glycosidic bonds (between monomers);
- Both contain carbon, hydrogen and oxygen/C, H and O;
- Starch has α-glucose and cellulose has βglucose;
- Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
- Starch (molecule) is branched and cellulose is not/unbranched;
7.Cellulose has (micro/macro) fibrils and starch does not; - Starch has 1–6 glycosidic bonds and cellulose does not
OR Starch contains two types of molecule and cellulose contains one type of molecule
OR Starch is amylose and amylopectin and cellulose is one type of molecule;
cellulose has β-glucose; - Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
- Starch (molecule) is branched and cellulose is not/unbranched;
7.Cellulose has (micro/macro) fibrils and starch does not; - Starch has 1–6 glycosidic bonds and cellulose does not
OR Starch contains two types of molecule and cellulose contains one type of molecule
OR Starch is amylose and amylopectin and cellulose is one type of molecule;
Give one feature of starch and explain how this feature enables it to act as a storage
substance.
- Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
- Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
- Large molecule / long chain So does not leave cell / contains large number of glucose units;
- Branched chains So rapid hydrolysis to remove glucose for respiration;
Hydrogen bonds are important in cellulose molecules. Explain why.
- Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
- Providing strength/rigidity (to cellulose/cell wall);
- Weak Hydrogen bonds provide strength in large numbers;
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.
- Glucose and galactose
- Joined by condensation
- Joined by glycosidic bond
- Added to polypeptide in Golgi
Describe how the student would show that reducing sugars were present in a solution. [3]
- Add Benedict’s;
- Heat to 95°C;
- Red/orange/yellow/green precipitate (shows reducing sugar present);
Describe how you would test a sample of food for the presence of starch. [2]
- Add potassium iodide (KI) solution to the food sample;
- Blue/black/purple indicates starch is present;
Describe how you would test a liquid sample for the presence of a lipid and how you would recognise a positive result. [2]
- (Mix / shake sample) with ethanol, then water and shake;
- Cloudy White / milky (emulsion);
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?
- Double bond(s);
- (Bonds) between carbon atoms within the hydrocarbon chain;
Describe how an ester bond is formed in a phospholipid molecule. [2]
- Condensation (reaction) OR Loss of water;
- Between of glycerol and fatty acid;
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
- Crush/grind;
- With ethanol/ alcohol, to dissolve the lipid;
- Then add water then shake;
- Forms a white emulsion / goes white;
What are the differences between a triglyceride and a phospholipid? [2]
- Fatty acid removed;
- Replaced with a phosphate group;
Compare and contrast the structure and properties of triglycerides and phospholipids [5]
- 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 are also contain P
- Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
- Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
- Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. [6]
Lipid
1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion OR emulsion test turns white/milky;
Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. [2]
- Filter and dry (the precipitate);
- Find mass/weight;
Describe the structure of proteins. [5]
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation reactions;
- Primary structure is number AND order/sequence of amino acids;
- Secondary structure is folding of polypeptide chain into Alpha-helix and Beta-pleated sheets **due to hydrogen bonding; **
- Tertiary structure is 3-D folding due to hydrogen bonding and ionic bonding and disulfide bridges;
- Quaternary structure is two or more polypeptide chains joined together;
Describe how the structure of a protein depends on the amino acids it contains. [5]
- Structure is determined by (relative) position of amino acid/R group/interactions;
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions - Primary structure is sequence/order of amino acids;
- Secondary structure formed by hydrogen bonding (between amino acids);
Accept alpha helix/β-pleated sheet for ‘secondary structure’ - Tertiary structure formed by interactions (between R groups);
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions - Creates active site in enzymes OR Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);
- Quaternary structure contains >1 polypeptide chain OR Quaternary structure formed by interactions/bonds between polypeptides; Accept prosthetic (group)
Describe how a peptide bond is formed between two amino acids to form a dipeptide [2]
- Condensation (reaction) / loss of water;
- Between amine / NH2 and carboxyl / COOH;
Describe how monomers join to form the primary structure of a protein. [3]
- Condensation reaction between amino acids;
- (Forming) peptide bonds;
- Creating (specific) sequence/order of amino acids;
Describe how an enzyme-substrate complex increases the rate of reaction [2]
- Reduces activation energy
- Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein. [4]
- Change in primary structure changes
sequence of amino acids; - Hydrogen bonds and Ionic bonds and Disulphide bonds form in different positions;
- Alters the tertiary structure of the enzyme / alters shape of active site;
- No Enzyme-Substrate complexes can be formed;
What is the proteome of a cell?
(The proteome is the full) range of /** number of different** proteins that a cell is able to produce (at a given time);
OR
(The proteome is the full) range of / number of different proteins the genome / DNA is able to code for;
How often should you use Brainscape?
A minimum of 3 times per week
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.(2)
- Lactose has a different shape/structure;
- Does not fit/bind to active site of enzyme/sucrase;
OR - Active site of enzyme/sucrase has a specific shape/structure;
- Does not fit/bind to lactose so no Enzyme-Substrate Complexes formed.