1.1-1.3 : biological molecules Flashcards
What is a monomer?
A monomer is a small identical repeating unit from which larger molecules(polymers) are made;
What is a Polymer?
Molecule made up of THREE or MORE identical molecules(monomers)
What term is used to describe the different structures of α-glucose and β-glucose?
Isomer(ism)
what is a condensation reaction?
joining two monomer units together with the removal of one water molecule which forms a bond
what is a hydrolysis reaction?
addition of one molcule of water to break the bond between two monomer
what is a disaccharide(DIMER) ?
TWO monosaccharides joined together in a condensation reaction
A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
-Compact
-occupies small space
-tightly packed
starch is a mixture of which two plysaccharides?
amylopectin and amylose
structure and function of amylose
-long unbranched chain of α-glucose
-carbon 1:4 glycosidic bonds provide a coiled structure
-compact so is good for storage
-insoluble so doesn’t affect water potential
-large so doesn’t diffuse out of cells
structure and function of amylopectin
-branched chain of α-glucose
-carbon 1:4 and 1:6 glycosidic bonds
-provides LSA for for rapid hydrolysis by
enzymes to release glucose for respiration
-insoluble so doesn’t affect water potential
-large so doesn’t diffuse out of cell
give three examples of monosaccharides
glucose
fructose
galactose
three examples of disaccharides
sucrose
maltose
lactose
give two types of polysaccharides
storage (glycogen and starch)
structural (cellulose)
give the structure and function of glycogen?
ONLY FOUND IN ANIMAL CELLS
-short chains so is more rapidly hydrolysed into glucose used in RESPIRATION
-more highly branched
-larger SA
-insoluble so does not affect water potential
Where is glycogen stored?
muscles and liver
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
Compare and contrast the structure of starch and the structure of cellulose. [6 marks]
-Both polysaccharides / 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;
-Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
-Starch (molecule) is branched and cellulose is not/unbranched;
-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
Give one feature of starch and explain how this feature enables it to act as a storage
substance.
-Helical So compact / tightly packed
-Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
-Large molecule So does not leave cell
-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/forms microfibrils;
-Providing strength/rigidity
-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 sucrose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.
Glucose and fructose
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;
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;
Describe how an ester bond is formed in a phospholipid molecule. [2]
Condensation (reaction) OR Loss of water;
Between of glycerol and fatty acid;
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 non-reducing sugar
-Do Benedict’s test and stays blue/negative;
-Boil with acid then neutralise with alkali;
-Heat with Benedict’s and becomes red/orange (precipitate);
describe how you would produce a calibration curve for a reducing sugar of unknown concentration and use it to obtain results.
-make up several known concentrations of maltose/glucose/lactose/galactose/fructose
-carry out the benedict’s test on each sample
-use a colorimeter to measure the colour intensity of each solution and plot a calibration curve
-known conc.on X axis and transmission on Y
-find the conc of the known sample using the calibration curve
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
-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);
-Creates active site in enzymes
-Quaternary structure contains >1 polypeptide chain OR Quaternary structure formed by interactions/bonds between polypeptides;
name and explain the 3 different types of bonds between R groups
1- WEAK hydrogen bonds between C=O and NH of the adjacent amino acid
2-IONIC BONDs between oppositely charged R groups
-DISULPHIDE BRIDGES between cysteine amino acids( has sulfur)
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;
Describe & explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose (2)
-Add Biuret reagent to both solutions
-Lactase / enzyme will give purple OR
-Lactose / reducing sugar will remain blue;
-Because Lactase is a protein;
What is the proteome of a cell?
number of different proteins the genome / DNA is able to code for;
what is activation energy?
the minimum energy required for a successful chemical reaction
Describe the induced fit model of enzyme action.(2)
-Active site not complementary;
-Active site changes (shape) / is flexible;
-(Change in enzyme allows) substrate to able to fit / Enzyme-Substrate complex to form;
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)
-Substrate binds to the active site
-Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
-Reduces activation energy;
Describe one way that the lock and key model is different from the induced fit model.(2)
-Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
-substrate / (already) fits the substrate / is
-complementary (before binding);
An enzyme catalyses only one reaction. Explain why. [2]
-(Enzyme has) active site is a specific shape;
-Only one substrate fits / binds (the active site);
Insulin is a protein so it cannot be taken orally. Suggest why insulin cannot be taken orally.(2)
-Broken down by enzymes / digested / denatured (by pH) /too large to be absorbed;
-Insulin no longer functional
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.
What is the effect of substrate concentration on the rate of an enzyme controlled reaction(3)
-Increases then plateaus / constant / steady / rate does not change;
-It plateaus as all active sites occupied / Saturated;
-(rate of reaction) / maximum number of Enzyme-Substrate complexes per second;
Explain how a competitive inhibitor works (3)
-Inhibitor is a similar shape to substrate;
-Inhibitor enters active site / competes with substrate;
-Less substrate binds/fewer enzyme-substrate complexes form per second.
Describe how a non-competitive inhibitor works [3]
-Attaches to the enzyme at a site other than the active site (allosteric site);
-Changes (shape of) the active site OR Changes tertiary structure (of enzyme);
-(So active site and substrate) no longer complementary so less/no enzyme-substrate complexes form
Describe the effect of temperature on enzyme action
-increasing the temperature increases the KE of molecules
-so more likely to sucessfully collide and react
-more enzyme-substrate complexes from per second
-beyond optimum: atoms vibrate faster
-this causes weak hydrogen and ionic bonds to break which causes a change in the tertiary structure
-active site is no longer complementary to the substrate
-enzyme is DENATURED( no ES complexes can form)
Describe the effect of pH on enzyme action
pH is the measure of H+ concentration so if pH is changed from optimum then
- the charg eon the R groups of the amino acids is altered
-ionic bonds in the tertiary structure are broken
-active site changes shape
-less E-S complexes form so enzyme denatures
Describe how the structure of DNA relates to its function. [6]
- Sugar-phosphate (backbone) so provides strength
-Long/large molecule so can store lots of information;
-Helix/coiled so compact;
-Base sequence codes for amino acids/protein;
-Double stranded so replication can occur semi-conservatively
-Complementary base pairing so accurate replication
-(Weak) hydrogen bonds for replication/ unzipping
-Many weak hydrogen bonds so stable/strong molecule;
Describe the structure of DNA. [5]
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate (group) and an nitrogenous base;
- Phosphodiester bonds (between nucleotides);
- Double helix held by hydrogen bonds;
- (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
Describe Semi-conservative replication. [5]
- Strands separate / H-bonds break;
- DNA helicase (involved);
- Both strands act(s) as (a) template(s);
- (Free) nucleotides attach;
- Complementary base pairing due to H bonds forming between bases
- DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
- new DNA molecules contain one old strand and one new strand;
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. [3]
-Condensation (reaction)/loss of water;
-(Between) phosphate and deoxyribose;
-(Catalysed by) DNA polymerase;
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.
Crick and Watson
Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. [2]
-Weak hydrogen bonds between bases allow two strands to separate
- two strands so both act as templates;
-Complementary base pairing allows accurate replication;
State four structural differences between a DNA molecule and an mRNA molecule [4]
1- DNA has deoxyribose, mRNA has ribose;
2- DNA has thymine, mRNA has uracil;
3- DNA longer, mRNA shorter;
4- DNA is double stranded, mRNA is single stranded;
5- DNA has hydrogen bonds, mRNA has no hydrogen bonds
Give two ways in which ATP is a suitable energy source for cells to use. [2]
1- Releases relatively small amount of energy/ little energy is lost as heat;
2- Releases energy instantaneously;
3- Phosphorylates other compounds, making them more reactive;
4- Can be rapidly re-synthesised;
5- Is not lost from/ does not leave cells;
give 2 ways in which the hydrolysis of ATP is used in cells(2)
1- PROVIDES ENERGY FOR:
active transport
muscle contraction
protein synthesis
2- PHOSPHOYLATION:
of molecules to lover Ea
make substrate more reactive
Describe how an enzyme can be phosphorylated.
- Attachment/association of (inorganic) phosphate (to the enzyme);
- (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;
Explain five properties that make water important for organisms. [5]
1- A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
2- A solvent so (metabolic) reactions can occur
3- High heat capacity so buffers changes in temperature;
4- Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5- Cohesion (between water molecules) so supports columns of water (in plants);
6- Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm.
[4]
- Polar molecule;
- Acts as a (universal) solvent;
- (Metabolic) reactions occur faster in solution;
- Reactive;
Takes place in hydrolysis / condensation reaction;
Describe the roles of iron ions, sodium ions, and phosphate ions in cells. [5]
Iron ions
1. Haemoglobin binds/associates with oxygen
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane
describe how ATP is resynthesised in cells(2)
1- ADP + Pi
2- by ATP synthase
3- in respiration
contrast the structures of ATP and a nucleotide found in DNA to give TWO differences(2)
- ATP has ribose and DNA has deoxyribose
- ATP has 3 phosphate groups and DNA has 1
- ATP base is always adenine and in DNA it can be different
suggest why water becomes lighter as it expands(2)
- density=mass/volume
- ice has same mass of water but greater volume
suggest one biological advantage of water becoming lighter (2)
- ice is colder than water
- is lighter so ice floats on water
-reduces freezing of water below ice
Explain why water is considered so important for life to ocuur (6)
- life evolved in water
- water provides support for bodies of oragnisms
- water is a major component of cytoplasm
- water is a universal solvent
- water is a metabolite
- water stabilises external temperatures
